Journal of The ElectrochemicalSociety

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Production of Hydrogen Peroxide for Drinking Water Treatment in aProton Exchange Membrane Electrolyzer at Near-Neutral pHTo cite this article Winton Li et al 2020 J Electrochem Soc 167 044502

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Production of Hydrogen Peroxide for Drinking Water Treatmentin a Proton Exchange Membrane Electrolyzer at Near-Neutral pHWinton Li Arman Bonakdarpour Előd Gyengez and David P Wilkinsonz

Department of Chemical and Biological Engineering and the Clean Energy Research Center University of British ColumbiaVancouver BC V6T 1Z3 Canada

We provide a detailed report on the electrosynthesis of H2O2 for drinking water treatment under near-neutral conditions using aproton exchange membrane (PEM) electrolyzer Two novel cathode catalysts for O2 electroreduction to H2O2 were investigated inthe PEM electrolyzer an inorganic cobalt-carbon (CondashC) composite and an organic redox catalyst anthraquinone-riboflavinylmixed with carbon (AQndashC) respectively The impact of operational variables such as temperature cathode carrier water flow rateand anode configurations (aimed at mitigating carbon corrosion at the anode) were examined in single-pass and full recycleoperation Using a superficial current density of 245 mA cmminus2 and an operating temperature of 40 degC H2O2 molar fluxes of360 μmol hrminus1 cmminus2 and 580 μmol hrminus1 cmminus2 were generated at near-neutral pH with the CondashC and RF-AQ catalystsrespectively Seventy-two hour experiments with closed loop recirculation produced H2O2 concentrations of 1300 and 3000 ppmfor the CondashC and AQndashC catalysts respectively These concentrations are adequate for advanced oxidation (UVH2O2) treatment ofdrinking water rendering the PEM electrolysis approach particularly suitable for on-site and on-demand production of H2O2copy 2020 The Author(s) Published on behalf of The Electrochemical Society by IOP Publishing Limited This is an open accessarticle distributed under the terms of the Creative Commons Attribution 40 License (CC BY httpcreativecommonsorglicensesby40) which permits unrestricted reuse of the work in any medium provided the original work is properly cited [DOI 1011491945-7111ab6fee]

Manuscript submitted September 30 2019 revised manuscript received December 16 2019 Published February 11 2020

Supplementary material for this article is available online

Hydrogen peroxide is an excellent oxidizer and is widely used ina number of applications such as waste or drinking water treatmenttextile industry pulp and paper bleaching and a number of otherchemical oxidation processes Furthermore it is considered anenvironmentally-friendly oxidizer because oxygen and water arethe only products of H2O2 decomposition For these reasonshydrogen peroxide with a global market of about $244 billion(USD) per year has a steady market growth trajectory for the nextdecade1 At present economic and high-volume production ofhydrogen peroxide is only achieved by the anthraquinone auto-oxidation (AQAO) process (also known as the Riedl-Pfleidererprocess) involving cyclic hydrogenation and oxidation of analkylanthraquinone precursor Pd-catalysts organic solvents andliquid-liquid extraction The Riedl-Pfleiderer process requires sig-nificant energy input and in addition produces waste chemicals thatrequire proper disposal andor recycling Because of these difficul-ties and also the great importance of H2O2 in the chemical industryand water treatment sectors research on sustainable and greenmethods of H2O2 production remains quite active One suchapproach is the reduction of O2 to H2O2 through an electrochemicalprocess Campos et al provide a review of AQAO and alternativemethods of H2O2 production

2

In alkaline media various forms of carbon can produce sig-nificant amounts of hydrogen peroxide Alkaline peroxide synthesishas been demonstrated in a number of different reactor designs suchas trickle bed fluidized bed and gas diffusion electrode designs3 Inacidic to neutral media however modified forms of carbon (egwith added metals such as cobalt) leads to lower oxygen reductionoverpotentials4ndash6 More recent research in this area include the workof Zhao et al who reported high production rates and efficiency forthe 2e- reduction of O2 to H2O2 on fluorine-doped hierarchicallyporous carbons at low pH (sim1) As a result of fluorine doping theelectronic properties of porous carbon was tuned to facilitate thedesorption of the HOO radical intermediate7 Other recent reportsof electrocatalysts for the electroreduction of oxygen to hydrogenperoxide include highly ordered mesoporous nitrogen-dopedcarbon89 and hierarchically-structured porous carbons10 On theapplication side Drogui and co-workers have used a RuO2-coated

titanium anode for generation of oxygen and a carbon felt cathodefor reduction of the generated O2 to produce H2O2 in order toremove dissolved organic carbonaceous compounds from municipalsewage plant effluents11 In another application Ridruejo et alreported on the activity of pyrite-structured nanoparticles ofsupported-CoS2 towards production of H2O2 and demonstrated theireffectiveness on the removal of pharmaceutical tetracaine from anacidic solution12 Besides experimental activities theoretical calcu-lations are also gaining significant attention in catalyst design andidentification of catalytic trends The propensity of an electrocatalystfor reduction of O2 to H2O2 can be largely gauged by the adsorptionenergy of the HOO intermediate in the overall reaction pathwaythe strength of which should ideally be thermoneutral at theequilibrium potential (O2H2O2 = 07 V vs SHE) in order to yielda theoretically zero-overpotential active surface Recently densityfunctional theory (DFT) techniques have been successfully used todetermine and even predict the trends in activity and selectivity ofcatalysts for the direct reduction of O2 to H2O2 by locating theoptimum values of HOO binding energy For example Verdaguer-Casadevall and co-workers have identified Pt-Hg and Ag-Hgelectrocatalysts with enhanced activity for the reduction of O2 toH2O2

1314 However the practical applicability of Hg containing Ptand Ag catalysts is very limited DFT calculations have also beenused to identify electrocatalysts such as SnO2 which can selectivelyoxidize water to H2O2 (as opposed to O2) by tuning the OH bindingenergy in order to suppress the four electron process of oxygenevolution15

In our earlier studies we reported on the synthesis and electro-chemical characterization of novel catalysts for the 2-electronreduction of O2 to H2O2 including low-cost inorganic CondashCcomposites and also organic redox mediators (riboflavin anthraqui-none derivatives and riboflavinylndashanthraquinone 2-carboxylateester)1617 The CondashC composite was successfully demonstrated in aH2O2 PEM fuel cell with simultaneous production of electric powerand H2O2 at neutral pH18 Furthermore a number of differentbifunctional cathode structures were examined to optimize the H2O2

production and power output19 Although in the H2O2 fuel cell modeonly the CondashC composite can operate both CondashC and the organic-based redox mediator catalysts are functional in a PEM electrolyzer

The work presented here is part of a large research initiative theREASrsquoEAU WaterNet Program a federally funded research pro-gram aimed at studying drinking water issues currently affectingzE-mail egyengechbeubcca dwilkinsonchbeubcca

Electrochemical Society Member

Journal of The Electrochemical Society 2020 167 044502

small rural communities across Canada The intent has been todevelop cost-effective portable water treatment using H2O2UVadvanced oxidation and producing the hydrogen peroxide on-siteand on-demand for small communities Based on 500 liters of waterrequired per day for each resident in a community of 500 residentsthe H2O2UV treatment unit would require 10 ppm (or 03 mM) ofH2O2 in order to provide sufficient treatment for 250000 liters ofwater supplied at a flow rate of 100ndash300 l minminus1 Both the inorganic(cobalt-carbon composite) and the organic redox catalyst (anthra-quinone-riboflavinyl) were evaluated using a PEM electrolyzer with49 cm2 geometric electrode area Specifically cell polarization andalso steady-state long-term experiments were performed to study theimpact of cathode water flow rate temperature and cathode catalystand anode configuration on the production and stability of hydrogenperoxide To the best of the knowledge of the authors this is the firstreport on the use of an organic redox catalyst for hydrogen peroxideproduction in a PEM electrolyzer and moreover the first compar-ison with an inorganic composite catalyst

Experimental Methods

Cathode and anode electrode preparationmdashThe cathode cata-lyst synthesis methods for the inorganic CondashC composite and theorganic 10 wt anthraquinone-riboflavinyl on carbon (AQndashC)catalysts were previously reported by our group1617 The catalystinks were prepared by mixing pre-weighed amounts of CondashC (orAQndashC) powders with deionized (DI) water (182 MΩ cm BarnsteadE-Pure System Thermo-Fisher) 10 wt Nafion solution (Sigma-Aldrich) and 2-propanol (Fischer-Scientific) then sonicating themixture for 60 min The catalyst inks were sprayed by a hand-heldspray gun pressurized with compressed air (Mastercraft HVLP AirSpray Gun Set Canadian Tire) onto a gas diffusion layer (GDL)(TGPH-060 Toray paper with 10 wt teflon Fuel Cell Earth LLC)while maintaining the temperature at about 80 degC using a hotplate(Corning PC-620D Cole-Parmer Canada Company) Similarcathode loadings of about 36 mg cmminus2 were used for both catalysts

Two types of anode configurations were investigated using Ptblack catalyst (Platinum black standard Johnson MattheyCompany) i) (Type I) Pt-black catalyst ink sprayed onto TGP-H060 unteflonated Toray carbon paper with a catalyst loading of02 mgPt cm

minus2 and ii) (Type II) Pt-black catalyst ink sprayed on oneside of a polymer exchange membrane (Nafionreg PFSA membrane

NR-112 Dupont Nafionreg Products) with a catalyst loading of04 mgPt-black cm

minus2 (identified as a half-CCM) Figure 1 shows theschematic diagram of anode types I and II The Ti-mesh was chosenbecause of its superior corrosion resistance at higher potentials withrespect to the carbon support

The half-CCM was prepared by first drying a cleaned protonatedNafion 112 membrane using a hotpress (Dake Model 44226) at135 degC for two minutes After cooling the dried membrane wassecured on a hotplate (at 70 degC) using a vacuum table and Pt blackanode catalyst inks were then sprayed on the membrane using a spraygun Catalyst loading was determined by weighing the membranebefore and after the spraying Membrane electrode assemblies(MEA) were produced by hot pressing (Dake Model 44226) asandwich of membrane with the catalyst coated GDEs at 135 degC and7584 kPa for a period of 25 min

Electrolysis cell hardware and testing equipmentmdashA commer-cially-available fuel cell hardware with an active area of 49 cm2

(TP50 Tandem Technologies Ltd) was modified in-house and wasused for all the electrolysis experiments Six K-type thermocouples(Omega Engineering Canada) were inserted into the cell hardwarethrough the bottom endplate to the test station and were used tomonitor the temperature of the cooling water loop the anode andcathode streams (both inlet and outlet) and the cell temperature Thishardware enabled us to readily replace the cell components withoutany disruption of the input feed A standard single pass serpentineflow field design was used for both the anode and the cathode flowfield plates and the assembled plates were in a cross-flow config-uration The cathode plate used was the original graphite plateprovided by Tandem Technologies The anode plate was howevermachined in-house from brass (McMaster Carr Supply Company)and was coated with 4 μm nickel and 1 μm gold (ACME Plating andSilver Shop Ltd Vancouver Canada) in order to provide adequatecorrosion resistance at the high electrolysis potentials

Sealing of the MEA between the flow field plates was achievedwith Silicone JRTV gaskets (Dow Corning Corporation) Figure S1and Table SI (available online at stacksioporgJES167044502mmedia) show the cell hardware and details of the cell componentsused (see the Supplementary Electronic Information) Figure 2 showsthe schematics of the experimental setup used for the experimentsreported here A 2-kW fuel cell test station (G100 Test Station withHYWARE II software Green Light Innovation) was used to control

Figure 1 Comparison of MEA configurations with two anode types using Ti mesh (a) Type I Pt-black catalyst ink sprayed onto TGP-H060 unteflonated Toraycarbon paper with a catalyst loading of 02 mgPt cm

minus2 and (b) Type II Pt catalyst layer sprayed on the anode side of the membrane (half-CCM) and brought intocontact with the Ti-mesh

Journal of The Electrochemical Society 2020 167 044502

the flows of cathode gas and coolant loop to the electrolysis cell Thecarrier water feed (neutral DI water) to the cathode was controlled by aperistaltic pump (model 7553ndash80 Masterflex) The water flow rate inthe anode compartment was 15 ml minminus1 and was provided by asimilar peristaltic pump An external power supply (Xantrex XHR20ndash50 AMETEK Programmable Power Inc) was used to provide therequired electrical power for the electrolysis experiments

MEA conditioning and polarization measurementsmdashDuringthe electrolysis experiments the modified TP50 cell was compressedto a pressure of 827 kPa Table I presents the employed experimentalconditions controlled and monitored by the Greenlight test stationAt the beginning of the experiments first the cathode and anode DIwater streams were turned on and then an initial current density(asymp 29 mA cmminus2) was applied to initiate the MEA conditioning at60 oC The current density was slowly increased every 10ndash15 min upto asymp 143 mA cmminus2 while monitoring the cell potential The MEAwas conditioned at this higher current density for one hour

All polarization measurements were carried out galvanostaticallyusing eighteen different superficial current densities between 30 to300 mA cmminus2 Each polarization current density point was held fortwo minutes during which time the voltage was approximatelyconstant throughout and its value was recorded at the end of thetwo-minute period

Full recycle loop experimentsmdashThe operating conditions for thelong-term recycle tests were the same as those listed in Table IThese experiments started with the cell operating in a single passmode for 25 min with the cathode carrier water flow at 15 ml minminus1

at a current density of 61 mA cmminus2 Once sufficient product solutionwas accumulated in the collection reservoir in order to allow forsampling the recycle pump was turned on with the recycle cathode

carrier flow rate fixed at 15 ml minminus1 The anode water was notrecycled during the experiments and was operated in a single passmode with a fixed flow rate of 15 ml minminus1 The recycle experimentswere conducted up to 72 h of continuous operation with samplestaken periodically for analysis

Chemical analysismdashBoth the anode and the cathode outlet waterstreams were sampled On the anode side the outlet water samplewas tested for trace metal ions from possible anode corrosion On thecathode side samples were analyzed for H2O2 concentration as wellas trace metal ions

Quantitative analysis of H2O2 concentration was performed by amodified tri-iodideUVndashVIS spectroscopy method described byKlassen et al20 This method is suitable for H2O2 concentrations ofup to 10 ppm Samples with greater H2O2 concentrations werediluted prior to analysis All the measurements were carried outunder neutral conditions The UVndashVIS measurements were con-ducted with a UVndashVIS spectrophotometer (UVmini-1240 ShimadzuCorp) and were performed at least twice to ensure repeatabilityErrors were within plusmn 05

Inductively coupled plasmamdashoptical emission spectrometry(ICP-OES) measurements were performed using an Agilent 725ICP-OES equipped with an auto-sampler and radial view Thesamples were prepared by mixing a 1 ml solution of the cathode (oranode) in a 2 HNO3 solution to a final volume of 10 ml

Results and Discussion

The fundamental mechanisms for the two-electron O2 reductionon either CondashC or the organic redox catalyst anthraquinone-riboflavynil (AQndashC) were discussed by us previously1617 Herethe focus is exclusively on the results obtained in the PEMelectrolyzer

Figure 2 Process flow diagram of the experimental setup for hydrogen peroxide production in a PEM electrolyzer

Journal of The Electrochemical Society 2020 167 044502

Table I Standard operating conditions and the experimental variables investigated for the electrolytic generation of H2O2

Operating Variable Value

PEM Electrolyzer Compression [kPa(g)] 827Anode DI Water Flow Rate [ml minminus1] 15Cathode Relative Humidity [] 100Cathode Gas Flow [ml minminus1 O2] 1000

Stoichiometric factor 586 100 mA cmminus2

Cathode Pressure [kPa] 150Operating Temperature [degC] 20 40 60 80Cathode DI Water Flow Rate [ml minminus1] 5 15

Figure 3 Impact of temperature on the electrolyzer performance for H2O2 production with (a)ndash(c) CondashC and (d)ndash(f) AQndashC cathode catalysts (a) (d) currentefficiency for H2O2 production (b) (e) electrolysis cell polarizations and (c) (f) H2O2 production rates Anode DI water flow rate 15 ml minminus1 catalyst loading02 mgPt cm

minus2 on TGP-H060 with 0 wt PTFE Toray paper (Type I) Cathode O2 flow rate 1000 ml minminus1 pressure 150 kPa(g) DI water flow rate 15 mlminminus1 (a)ndash(c) CondashC catalyst loading 36 mgCondashC cmminus2 on TGP-H060 10 wt PTFE and (d)ndash(f) AQndashC catalyst loading 36 mgAQndashC cmminus2 on TGP-H060 10 wtPTFE

Journal of The Electrochemical Society 2020 167 044502

Effect of temperature on H2O2 productionmdashFigure 3 shows theimpact of temperature on current efficiency cell potential and H2O2

production for the CondashC catalyst (andashc) and the AQndashC cathodecatalysts (dndashf) respectively The type I anode (ie PtC) was usedin these experiments With CondashC catalyst at current densities⩽ 100 mA cmminus2 the H2O2 production rate is almost identical forall temperatures examined As the current density increases above100 mA cmminus2 however differences among the four temperaturesstudied appear (Fig 3c) The highest H2O2 production rate isobtained at 40 degC as well as a corresponding increase in currentefficiency (Figs 3a and 3c) Further increase of the temperature to60 degC and 80 degC is not beneficial in terms of H2O2 production andcurrent efficiency At elevated operating temperatures the H2O2

decomposition rate increases more significantly with current densityThe AQndashC catalyst shows generally similar trends to the CondashC

with respect to the temperature effect (Figs 3dndash3f) At either 40 degCor 60 degC the H2O2 production rate on AQndashC reaches a maximum of

approximately 580 μmol hrminus1 cmminus2 (at 245 mA cmminus2) exceeding byabout 21 the maximum production rate obtained using CondashC(Figs 3f and 3c) At 40 degC and 100 mA cmminus2 the organic redoxcatalyst AQndashC generated a 19 current efficiency whereas withCondashC the current efficiency was only 10 (Figs 3d and 3a)However the current efficiency on AQndashC decreases at currentdensities higher than 100 mA cmminus2 This indicates that the rates ofthe secondary reactions H2O2 reduction and H2 evolution becomemore significant In terms of temperature similar to the CondashCcatalyst 40 degC is optimal favoring higher production rate whilekeeping the H2O2 decomposition rate low

Effect of cathode carrier water flow rate on H2O2 productionmdashFigure 4 shows the results of experiments performed with both typesof catalysts at 40 degC and water flow rates of 5 and 15 ml minminus1respectively In case of the AQndashC cathode catalyst the cellperformance was similar for both cathode water flow rates ForCondashC however the higher water flow rate (ie shorter residencetime) had a significant beneficial effect on all figures of merit H2O2

production rate cell voltage and current efficiency This may

Figure 4 Effect of cathode water flow rate on the electrolyzer performanceat 40 degC for H2O2 production and comparison between CondashC and AQndashCcathode catalysts Cathode carrier water flow rate 5 ml minminus1 and 15 mlminminus1 respectively Anode DI water flow rate 15 ml minminus1 catalyst loading02 mgPt cm

minus2 on TGP-H060 (0 wt PTFE) Toray paper (Type I anode)Cathode O2 flow rate 1000 ml minminus1 pressure 150 kPa(g) Cathodecatalyst either AQndashC 36 mgAQndashC cmminus2 on TGP-H060 (10 wt PTFE) orCondashC 36 mgCondashC cmminus2 on TGP-H060 (10 wt PTFE)

Figure 5 Comparison of the two anode types using AQndashC cathode catalystat 40 degC Type I C-Pt and Type II Ti-Pt half-CCM Cathode carrier waterflow rate 15 ml minminus1 O2 flow rate 1000 ml minminus1 pressure 150 kPa(g)AQndashC catalyst loading 36 mgAQndashC cmminus2 on TGP-H060 (10 wt PTFE)Anode water flow rate 15 ml minminus1

Journal of The Electrochemical Society 2020 167 044502

indicate that CondashC is catalytically more active for the secondaryreactions of H2O2 electroreduction andor thermocatalytic decom-position of H2O2 Therefore a shorter residence time is beneficial

Effect of the anode configurationmdashThe durability of the PEMelectrolyzer for H2O2 production can be compromised by carboncorrosion at the anode (ie carbon paper GDL Type I anodeFig 1) To address this issue an anode configuration composed of Ptcatalyst coated half-membrane (half-CCM) was also used in con-junction with Ti mesh (Type II anode Fig 1) Figure 5 shows acomparison of the two anode types tested Ti-CCM and C-Pt anodeswith AQndashC cathode catalyst The cell potential using the half-CCManode with Ti mesh is similar to that of the carbon paper GDL-Ptanode (Fig 6b) however the H2O2 production is lower (Fig 6c)The reason for lower H2O2 production with Type II anode could beattributed to the different preparation of the MEAs The MEA withthe Type I anode (ie containing the carbon paper GDL) wasprepared using a hot press method whereas the MEA with a half-CCM and Ti mesh anode (Type II) was not hot pressed Therefore

the interaction and bonding between the ionomer and the cathodecatalyst layer is superior in the case of the hot pressed MEA (iewith Type I anode) improving the cathode catalyst layer utilizationand therefore the H2O2 production rate It should be also mentionedthat further reduction of the over cell potential can be achieved usingiridium oxide-based anodes In the present work Pt-based anodeswere used for direct comparison of the same cell in eitherelectrolysis or fuel cell mode operation for peroxide generation1819

Full recycle operation modemdashThe capability to produce H2O2

over a longer period of time is crucial to assess the applicability ofthe proposed PEM electrolyzer approach for commercial operationIn order to simulate on a laboratory scale such a scenarioexperiments with full recycle of the cathode product solution wereperformed for 72 h For the continuous recycle operation experi-ments the AQndashC (half CCM) cathode with the Ti mesh-based anodeconfigurations (Type II Fig 1) was employed to mitigate the carboncorrosion on the anode side (Fig 6) Results show that the AQndashCcatalyst produced 3000 ppm (03 wt ) of H2O2 by the end of the72-hour experiment (Fig 6b) The H2O2 production rate peaked afterapproximately 20 h (Fig 6a) Beyond 20 h the production ratedecreased and the net accumulated H2O2 concentration virtuallylevelled off (Fig 6b) This is due to the competition between H2O2

generation and losses through pathways such as secondary electro-reduction and thermocatalytic decomposition (see next section)

Effect of catalyst and temperature on H2O2 degradationmdashTheH2O2 stability was investigated at three different temperatures (4060 80 degC) using a fully assembled electrolysis cell consisting ofAQndashC cathode catalyst and a half-CCM Pt anode with a Ti meshcurrent collector The goal was to determine the H2O2 loss underopen circuit conditions due to thermocatalytic (ie non-electroche-mical) degradation Figures 7a and 7b show clear evidence forthermal decomposition of H2O2 with higher temperatures leading toincreased decomposition of H2O2 Figures 7c and 7d display the dataon a semi logarithmic plot where dashed lines show the linearregression Clearly full recycle operation of the electrolyzer at 80 degCfor over two hours is not beneficial Furthermore the presence of O2

gas enhanced the H2O2 decomposition in a positive synergisticinteraction effect with temperature (ie the higher the temperaturethe higher was the interaction effect between gas presence andtemperature regarding H2O2 decomposition compare Figs 7c and7d 80 degC data) Similar behavior was reported before as well18

In addition the membrane degradation was also evaluated byanalyzing the fluoride released The median fluoride release rate wassim003 ng hrminus1 cmminus2 for the sixteen samples analyzed Drinkingwater guidelines from the Government of BC in Canada suggests afluoride limit of 10ndash15 mg lminus121 The long-term recycle experi-ments showed the cumulative fluoride concentration over the threeday runs was well below the limit set out by the guidelines at about22 μg lminus1

Conclusions

The electroreduction of O2 to H2O2 was investigated in a PEMelectrolyzer under near-neutral pH operation using deionized waterTwo novel cathode catalysts a cobalt-carbon composite (CondashC) andan organic redox catalyst anthraquinone-riboflavinyl supported oncarbon (AQndashC) were investigated Using a superficial currentdensity of 245 mA cmminus2 and an operating temperature of 40 degCH2O2 molar fluxes of 360 μmol hrminus1 cmminus2 and 580 μmol hrminus1 cmminus2

were obtained in single pass mode with the CondashC and RF-AQcatalysts respectively To the best of our knowledge this is the firsttime that H2O2 production in a PEM electrolyzer with an organicredox catalyst has been reported

Longer term (72 h) experiments conducted at a constant super-ficial current density of 61 mA cmminus2 with complete recycle of thecathode carrier water solution showed a maximum steady-state

Figure 6 Continuous recycle operation (for up to 72 h) of the PEMelectrolyzer for H2O2 production AQndashC cathode catalyst with Pt on Ti-meshanode (a) H2O2 production rate (b) total accumulated H2O2 concentrationand (c) cell voltage Current density 61 mA cmminus2 temperature 40 degC and restof the conditions identical to Fig 5

Journal of The Electrochemical Society 2020 167 044502

H2O2 concentration of 3000 ppm for the AQndashC catalyst Theelectrolytic production of H2O2 using the AQndashC composite catalystin a PEM electrolyzer can provide an adequate supply of H2O2 foradvanced oxidation drinking water treatment applications on-siteand on-demand

Acknowledgments

Funding for this work has been provided by the Natural Sciencesand Engineering Research Council of Canada (NSERC) through theStrategic ResrsquoEau WaterNet program and the NSERC DiscoveryGrant program

References

1 httpstransparencymarketresearchcompressreleasehydrogen-peroxide-markethtm (accessed February 2 2020)

2 J M Campos-Martin G Blanco-Brieva and J L G Fierro ldquoHydrogen peroxidesynthesis an outlook beyond the anthraquinone processrdquo Angew ChemiemdashInt Ed45 6962 (2006)

3 C W Oloman in Electrochemical Processing for the Pulp amp Paper Industry (TheElectrochemical Consultancy New York) (1996)

4 I Yamanaka S Tazawa T Murayama T Iwasaki and S Takenaka ldquoCatalyticsynthesis of neutral hydrogen peroxide at a CoN2Cx cathode of a polymerelectrolyte membrane fuel cell (PEMFC)rdquo Chem Sus Chem 3 59 (2010)

5 W Zhang A U Shaikh E Y Tsui and T M Swager ldquoCobalt porphyrinfunctionalized carbon nanotubes for oxygen reductionrdquo Chem Mater 21 3234 (2009)

6 H J Zhang X Yuan W Wen D Y Zhang L Sun Q Z Jiang and Z F MaldquoElectrochemical performance of a novel CoTETAC catalyst for the oxygenreduction reactionrdquo Electrochem Commun 11 206 (2009)

7 K Zhao Y Su X Quan Y Liu S Chen and H Yu ldquoEnhanced H2O2 productionby selective electrochemical reduction of O2on fluorine-doped hierarchicallyporous carbonrdquo J Catal 357 118 (2018)

8 J Park Y Nabae T Hayakawa and M A Kakimoto ldquoHighly selective two-electron oxygen reduction catalyzed by mesoporous nitrogen-doped carbonrdquo ACSCatal 4 3749 (2014)

9 T P Fellinger F Hascheacute P Strasser and M Antonietti ldquoMesoporous nitrogen-doped carbon for the electrocatalytic synthesis of hydrogen peroxiderdquo J Am ChemSoc 134 4072 (2012)

10 Y Liu X Quan X Fan H Wang and S Chen ldquoHigh-yield electrosynthesis ofhydrogen peroxide from oxygen reduction by hierarchically porous carbonrdquoAngew ChemiemdashInt Ed 54 6837 (2015)

11 P Drogui S Elmaleh M Rumeau C Bernard and A Rambaud ldquoHydrogenperoxide production by water electrolysis application to disinfectionrdquo J ApplElectrochem 31 877 (2001)

12 C Ridruejo F Alcaide G Aacutelvarez E Brillas and I Sireacutes ldquoOn-site H2O2

electrogeneration at a CoS2-based air-diffusion cathode for the electrochemicaldegradation of organic pollutantsrdquo J Electroanal Chem 808 364 (2018)

13 A Verdaguer-Casadevall D Deiana M Karamad S Siahrostami P MalacridaT W Hansen J Rossmeisl I Chorkendorff and I E L Stephens ldquoTrends in theelectrochemical synthesis of H2O2 enhancing activity and selectivity by electro-catalytic site engineeringrdquo Nano Lett 14 1603 (2014)

14 S Siahrostami et al ldquoEnabling direct H2O2 production through rational electro-catalyst designrdquo Nat Mater 12 1137 (2013)

15 V Viswanathan H A Hansen and J K Noslashrskov ldquoSelective electrochemicalgeneration of hydrogen peroxide from water oxidationrdquo J Phys Chem Lett 64224 (2015)

16 A Bonakdarpour D Esau H Cheng A Wang E Gyenge and D P WilkinsonldquoPreparation and electrochemical studies of metal-carbon composite catalysts forsmall-scale electrosynthesis of H2O2rdquo Electrochim Acta 56 9074 (2011)

17 A Wang A Bonakdarpour D P Wilkinson and E Gyenge ldquoNovel organic redoxcatalyst for the electroreduction of oxygen to hydrogen peroxiderdquo ElectrochimActa 66 222 (2012)

18 W Li A Bonakdarpour E Gyenge and D P Wilkinson ldquoDrinking waterpurification by electrosynthesis of hydrogen peroxide in a power-producing PEMfuel cellrdquo Chem Sus Chem 6 2137 (2013)

19 W Li A Bonakdarpour E Gyenge and D P Wilkinson ldquoDesign of bifunctionalelectrodes for co-generation of electrical power and hydrogen peroxiderdquo J ApplElectrochem 48 985 (2018)

20 N V Klassen D Marchington and H C E McGowan ldquoH2O2 Determination bythe I3minus method and by KMnO4 titrationrdquo Anal Chem 66 2921 (1994)

21 BC Ministry of Environment and Climate Change Strategy ldquoBC Source DrinkingWater Quality Guidelines Guideline Summaryrdquo Water Quality Guideline SeriesWQG-01 (2017)

Figure 7 H2O2 stability in the electrolysis cell at open circuit as a function of temperature and oxygen gas flow (a) (c) no oxygen gas (b) (d) with oxygen gasflow Cathode catalyst AQndashC 36 mgAQndashC cmminus2 on TGP-H060 (10 wt PTFE) Continuous recycle of the cathode water carrier flow at 15 ml minminus1 O2 flowrate 1000 ml minminus1 pressure 150 kPa(g) Anode conditions water flow 15 ml minminus1 Ti-Pt anode

Journal of The Electrochemical Society 2020 167 044502

Table I Standard operating conditions and the experimental variables investigated for the electrolytic generation of H2O2

Operating Variable Value

PEM Electrolyzer Compression [kPa(g)] 827Anode DI Water Flow Rate [ml minminus1] 15Cathode Relative Humidity [] 100Cathode Gas Flow [ml minminus1 O2] 1000

Stoichiometric factor 586 100 mA cmminus2

Cathode Pressure [kPa] 150Operating Temperature [degC] 20 40 60 80Cathode DI Water Flow Rate [ml minminus1] 5 15

Figure 3 Impact of temperature on the electrolyzer performance for H2O2 production with (a)ndash(c) CondashC and (d)ndash(f) AQndashC cathode catalysts (a) (d) currentefficiency for H2O2 production (b) (e) electrolysis cell polarizations and (c) (f) H2O2 production rates Anode DI water flow rate 15 ml minminus1 catalyst loading02 mgPt cm

minus2 on TGP-H060 with 0 wt PTFE Toray paper (Type I) Cathode O2 flow rate 1000 ml minminus1 pressure 150 kPa(g) DI water flow rate 15 mlminminus1 (a)ndash(c) CondashC catalyst loading 36 mgCondashC cmminus2 on TGP-H060 10 wt PTFE and (d)ndash(f) AQndashC catalyst loading 36 mgAQndashC cmminus2 on TGP-H060 10 wtPTFE

Journal of The Electrochemical Society 2020 167 044502

Effect of temperature on H2O2 productionmdashFigure 3 shows theimpact of temperature on current efficiency cell potential and H2O2

production for the CondashC catalyst (andashc) and the AQndashC cathodecatalysts (dndashf) respectively The type I anode (ie PtC) was usedin these experiments With CondashC catalyst at current densities⩽ 100 mA cmminus2 the H2O2 production rate is almost identical forall temperatures examined As the current density increases above100 mA cmminus2 however differences among the four temperaturesstudied appear (Fig 3c) The highest H2O2 production rate isobtained at 40 degC as well as a corresponding increase in currentefficiency (Figs 3a and 3c) Further increase of the temperature to60 degC and 80 degC is not beneficial in terms of H2O2 production andcurrent efficiency At elevated operating temperatures the H2O2

decomposition rate increases more significantly with current densityThe AQndashC catalyst shows generally similar trends to the CondashC

with respect to the temperature effect (Figs 3dndash3f) At either 40 degCor 60 degC the H2O2 production rate on AQndashC reaches a maximum of

approximately 580 μmol hrminus1 cmminus2 (at 245 mA cmminus2) exceeding byabout 21 the maximum production rate obtained using CondashC(Figs 3f and 3c) At 40 degC and 100 mA cmminus2 the organic redoxcatalyst AQndashC generated a 19 current efficiency whereas withCondashC the current efficiency was only 10 (Figs 3d and 3a)However the current efficiency on AQndashC decreases at currentdensities higher than 100 mA cmminus2 This indicates that the rates ofthe secondary reactions H2O2 reduction and H2 evolution becomemore significant In terms of temperature similar to the CondashCcatalyst 40 degC is optimal favoring higher production rate whilekeeping the H2O2 decomposition rate low

Effect of cathode carrier water flow rate on H2O2 productionmdashFigure 4 shows the results of experiments performed with both typesof catalysts at 40 degC and water flow rates of 5 and 15 ml minminus1respectively In case of the AQndashC cathode catalyst the cellperformance was similar for both cathode water flow rates ForCondashC however the higher water flow rate (ie shorter residencetime) had a significant beneficial effect on all figures of merit H2O2

production rate cell voltage and current efficiency This may

Figure 4 Effect of cathode water flow rate on the electrolyzer performanceat 40 degC for H2O2 production and comparison between CondashC and AQndashCcathode catalysts Cathode carrier water flow rate 5 ml minminus1 and 15 mlminminus1 respectively Anode DI water flow rate 15 ml minminus1 catalyst loading02 mgPt cm

minus2 on TGP-H060 (0 wt PTFE) Toray paper (Type I anode)Cathode O2 flow rate 1000 ml minminus1 pressure 150 kPa(g) Cathodecatalyst either AQndashC 36 mgAQndashC cmminus2 on TGP-H060 (10 wt PTFE) orCondashC 36 mgCondashC cmminus2 on TGP-H060 (10 wt PTFE)

Figure 5 Comparison of the two anode types using AQndashC cathode catalystat 40 degC Type I C-Pt and Type II Ti-Pt half-CCM Cathode carrier waterflow rate 15 ml minminus1 O2 flow rate 1000 ml minminus1 pressure 150 kPa(g)AQndashC catalyst loading 36 mgAQndashC cmminus2 on TGP-H060 (10 wt PTFE)Anode water flow rate 15 ml minminus1

Journal of The Electrochemical Society 2020 167 044502

indicate that CondashC is catalytically more active for the secondaryreactions of H2O2 electroreduction andor thermocatalytic decom-position of H2O2 Therefore a shorter residence time is beneficial

Effect of the anode configurationmdashThe durability of the PEMelectrolyzer for H2O2 production can be compromised by carboncorrosion at the anode (ie carbon paper GDL Type I anodeFig 1) To address this issue an anode configuration composed of Ptcatalyst coated half-membrane (half-CCM) was also used in con-junction with Ti mesh (Type II anode Fig 1) Figure 5 shows acomparison of the two anode types tested Ti-CCM and C-Pt anodeswith AQndashC cathode catalyst The cell potential using the half-CCManode with Ti mesh is similar to that of the carbon paper GDL-Ptanode (Fig 6b) however the H2O2 production is lower (Fig 6c)The reason for lower H2O2 production with Type II anode could beattributed to the different preparation of the MEAs The MEA withthe Type I anode (ie containing the carbon paper GDL) wasprepared using a hot press method whereas the MEA with a half-CCM and Ti mesh anode (Type II) was not hot pressed Therefore

the interaction and bonding between the ionomer and the cathodecatalyst layer is superior in the case of the hot pressed MEA (iewith Type I anode) improving the cathode catalyst layer utilizationand therefore the H2O2 production rate It should be also mentionedthat further reduction of the over cell potential can be achieved usingiridium oxide-based anodes In the present work Pt-based anodeswere used for direct comparison of the same cell in eitherelectrolysis or fuel cell mode operation for peroxide generation1819

Full recycle operation modemdashThe capability to produce H2O2

over a longer period of time is crucial to assess the applicability ofthe proposed PEM electrolyzer approach for commercial operationIn order to simulate on a laboratory scale such a scenarioexperiments with full recycle of the cathode product solution wereperformed for 72 h For the continuous recycle operation experi-ments the AQndashC (half CCM) cathode with the Ti mesh-based anodeconfigurations (Type II Fig 1) was employed to mitigate the carboncorrosion on the anode side (Fig 6) Results show that the AQndashCcatalyst produced 3000 ppm (03 wt ) of H2O2 by the end of the72-hour experiment (Fig 6b) The H2O2 production rate peaked afterapproximately 20 h (Fig 6a) Beyond 20 h the production ratedecreased and the net accumulated H2O2 concentration virtuallylevelled off (Fig 6b) This is due to the competition between H2O2

generation and losses through pathways such as secondary electro-reduction and thermocatalytic decomposition (see next section)

Effect of catalyst and temperature on H2O2 degradationmdashTheH2O2 stability was investigated at three different temperatures (4060 80 degC) using a fully assembled electrolysis cell consisting ofAQndashC cathode catalyst and a half-CCM Pt anode with a Ti meshcurrent collector The goal was to determine the H2O2 loss underopen circuit conditions due to thermocatalytic (ie non-electroche-mical) degradation Figures 7a and 7b show clear evidence forthermal decomposition of H2O2 with higher temperatures leading toincreased decomposition of H2O2 Figures 7c and 7d display the dataon a semi logarithmic plot where dashed lines show the linearregression Clearly full recycle operation of the electrolyzer at 80 degCfor over two hours is not beneficial Furthermore the presence of O2

gas enhanced the H2O2 decomposition in a positive synergisticinteraction effect with temperature (ie the higher the temperaturethe higher was the interaction effect between gas presence andtemperature regarding H2O2 decomposition compare Figs 7c and7d 80 degC data) Similar behavior was reported before as well18

In addition the membrane degradation was also evaluated byanalyzing the fluoride released The median fluoride release rate wassim003 ng hrminus1 cmminus2 for the sixteen samples analyzed Drinkingwater guidelines from the Government of BC in Canada suggests afluoride limit of 10ndash15 mg lminus121 The long-term recycle experi-ments showed the cumulative fluoride concentration over the threeday runs was well below the limit set out by the guidelines at about22 μg lminus1

Conclusions

The electroreduction of O2 to H2O2 was investigated in a PEMelectrolyzer under near-neutral pH operation using deionized waterTwo novel cathode catalysts a cobalt-carbon composite (CondashC) andan organic redox catalyst anthraquinone-riboflavinyl supported oncarbon (AQndashC) were investigated Using a superficial currentdensity of 245 mA cmminus2 and an operating temperature of 40 degCH2O2 molar fluxes of 360 μmol hrminus1 cmminus2 and 580 μmol hrminus1 cmminus2

were obtained in single pass mode with the CondashC and RF-AQcatalysts respectively To the best of our knowledge this is the firsttime that H2O2 production in a PEM electrolyzer with an organicredox catalyst has been reported

Longer term (72 h) experiments conducted at a constant super-ficial current density of 61 mA cmminus2 with complete recycle of thecathode carrier water solution showed a maximum steady-state

Figure 6 Continuous recycle operation (for up to 72 h) of the PEMelectrolyzer for H2O2 production AQndashC cathode catalyst with Pt on Ti-meshanode (a) H2O2 production rate (b) total accumulated H2O2 concentrationand (c) cell voltage Current density 61 mA cmminus2 temperature 40 degC and restof the conditions identical to Fig 5

Journal of The Electrochemical Society 2020 167 044502

H2O2 concentration of 3000 ppm for the AQndashC catalyst Theelectrolytic production of H2O2 using the AQndashC composite catalystin a PEM electrolyzer can provide an adequate supply of H2O2 foradvanced oxidation drinking water treatment applications on-siteand on-demand

Acknowledgments

Funding for this work has been provided by the Natural Sciencesand Engineering Research Council of Canada (NSERC) through theStrategic ResrsquoEau WaterNet program and the NSERC DiscoveryGrant program

References

1 httpstransparencymarketresearchcompressreleasehydrogen-peroxide-markethtm (accessed February 2 2020)

2 J M Campos-Martin G Blanco-Brieva and J L G Fierro ldquoHydrogen peroxidesynthesis an outlook beyond the anthraquinone processrdquo Angew ChemiemdashInt Ed45 6962 (2006)

3 C W Oloman in Electrochemical Processing for the Pulp amp Paper Industry (TheElectrochemical Consultancy New York) (1996)

4 I Yamanaka S Tazawa T Murayama T Iwasaki and S Takenaka ldquoCatalyticsynthesis of neutral hydrogen peroxide at a CoN2Cx cathode of a polymerelectrolyte membrane fuel cell (PEMFC)rdquo Chem Sus Chem 3 59 (2010)

5 W Zhang A U Shaikh E Y Tsui and T M Swager ldquoCobalt porphyrinfunctionalized carbon nanotubes for oxygen reductionrdquo Chem Mater 21 3234 (2009)

6 H J Zhang X Yuan W Wen D Y Zhang L Sun Q Z Jiang and Z F MaldquoElectrochemical performance of a novel CoTETAC catalyst for the oxygenreduction reactionrdquo Electrochem Commun 11 206 (2009)

7 K Zhao Y Su X Quan Y Liu S Chen and H Yu ldquoEnhanced H2O2 productionby selective electrochemical reduction of O2on fluorine-doped hierarchicallyporous carbonrdquo J Catal 357 118 (2018)

8 J Park Y Nabae T Hayakawa and M A Kakimoto ldquoHighly selective two-electron oxygen reduction catalyzed by mesoporous nitrogen-doped carbonrdquo ACSCatal 4 3749 (2014)

9 T P Fellinger F Hascheacute P Strasser and M Antonietti ldquoMesoporous nitrogen-doped carbon for the electrocatalytic synthesis of hydrogen peroxiderdquo J Am ChemSoc 134 4072 (2012)

10 Y Liu X Quan X Fan H Wang and S Chen ldquoHigh-yield electrosynthesis ofhydrogen peroxide from oxygen reduction by hierarchically porous carbonrdquoAngew ChemiemdashInt Ed 54 6837 (2015)

11 P Drogui S Elmaleh M Rumeau C Bernard and A Rambaud ldquoHydrogenperoxide production by water electrolysis application to disinfectionrdquo J ApplElectrochem 31 877 (2001)

12 C Ridruejo F Alcaide G Aacutelvarez E Brillas and I Sireacutes ldquoOn-site H2O2

electrogeneration at a CoS2-based air-diffusion cathode for the electrochemicaldegradation of organic pollutantsrdquo J Electroanal Chem 808 364 (2018)

13 A Verdaguer-Casadevall D Deiana M Karamad S Siahrostami P MalacridaT W Hansen J Rossmeisl I Chorkendorff and I E L Stephens ldquoTrends in theelectrochemical synthesis of H2O2 enhancing activity and selectivity by electro-catalytic site engineeringrdquo Nano Lett 14 1603 (2014)

14 S Siahrostami et al ldquoEnabling direct H2O2 production through rational electro-catalyst designrdquo Nat Mater 12 1137 (2013)

15 V Viswanathan H A Hansen and J K Noslashrskov ldquoSelective electrochemicalgeneration of hydrogen peroxide from water oxidationrdquo J Phys Chem Lett 64224 (2015)

16 A Bonakdarpour D Esau H Cheng A Wang E Gyenge and D P WilkinsonldquoPreparation and electrochemical studies of metal-carbon composite catalysts forsmall-scale electrosynthesis of H2O2rdquo Electrochim Acta 56 9074 (2011)

17 A Wang A Bonakdarpour D P Wilkinson and E Gyenge ldquoNovel organic redoxcatalyst for the electroreduction of oxygen to hydrogen peroxiderdquo ElectrochimActa 66 222 (2012)

18 W Li A Bonakdarpour E Gyenge and D P Wilkinson ldquoDrinking waterpurification by electrosynthesis of hydrogen peroxide in a power-producing PEMfuel cellrdquo Chem Sus Chem 6 2137 (2013)

19 W Li A Bonakdarpour E Gyenge and D P Wilkinson ldquoDesign of bifunctionalelectrodes for co-generation of electrical power and hydrogen peroxiderdquo J ApplElectrochem 48 985 (2018)

20 N V Klassen D Marchington and H C E McGowan ldquoH2O2 Determination bythe I3minus method and by KMnO4 titrationrdquo Anal Chem 66 2921 (1994)

21 BC Ministry of Environment and Climate Change Strategy ldquoBC Source DrinkingWater Quality Guidelines Guideline Summaryrdquo Water Quality Guideline SeriesWQG-01 (2017)

Figure 7 H2O2 stability in the electrolysis cell at open circuit as a function of temperature and oxygen gas flow (a) (c) no oxygen gas (b) (d) with oxygen gasflow Cathode catalyst AQndashC 36 mgAQndashC cmminus2 on TGP-H060 (10 wt PTFE) Continuous recycle of the cathode water carrier flow at 15 ml minminus1 O2 flowrate 1000 ml minminus1 pressure 150 kPa(g) Anode conditions water flow 15 ml minminus1 Ti-Pt anode

Journal of The Electrochemical Society 2020 167 044502

Effect of temperature on H2O2 productionmdashFigure 3 shows theimpact of temperature on current efficiency cell potential and H2O2

production for the CondashC catalyst (andashc) and the AQndashC cathodecatalysts (dndashf) respectively The type I anode (ie PtC) was usedin these experiments With CondashC catalyst at current densities⩽ 100 mA cmminus2 the H2O2 production rate is almost identical forall temperatures examined As the current density increases above100 mA cmminus2 however differences among the four temperaturesstudied appear (Fig 3c) The highest H2O2 production rate isobtained at 40 degC as well as a corresponding increase in currentefficiency (Figs 3a and 3c) Further increase of the temperature to60 degC and 80 degC is not beneficial in terms of H2O2 production andcurrent efficiency At elevated operating temperatures the H2O2

decomposition rate increases more significantly with current densityThe AQndashC catalyst shows generally similar trends to the CondashC

with respect to the temperature effect (Figs 3dndash3f) At either 40 degCor 60 degC the H2O2 production rate on AQndashC reaches a maximum of

approximately 580 μmol hrminus1 cmminus2 (at 245 mA cmminus2) exceeding byabout 21 the maximum production rate obtained using CondashC(Figs 3f and 3c) At 40 degC and 100 mA cmminus2 the organic redoxcatalyst AQndashC generated a 19 current efficiency whereas withCondashC the current efficiency was only 10 (Figs 3d and 3a)However the current efficiency on AQndashC decreases at currentdensities higher than 100 mA cmminus2 This indicates that the rates ofthe secondary reactions H2O2 reduction and H2 evolution becomemore significant In terms of temperature similar to the CondashCcatalyst 40 degC is optimal favoring higher production rate whilekeeping the H2O2 decomposition rate low

Effect of cathode carrier water flow rate on H2O2 productionmdashFigure 4 shows the results of experiments performed with both typesof catalysts at 40 degC and water flow rates of 5 and 15 ml minminus1respectively In case of the AQndashC cathode catalyst the cellperformance was similar for both cathode water flow rates ForCondashC however the higher water flow rate (ie shorter residencetime) had a significant beneficial effect on all figures of merit H2O2

production rate cell voltage and current efficiency This may

Figure 4 Effect of cathode water flow rate on the electrolyzer performanceat 40 degC for H2O2 production and comparison between CondashC and AQndashCcathode catalysts Cathode carrier water flow rate 5 ml minminus1 and 15 mlminminus1 respectively Anode DI water flow rate 15 ml minminus1 catalyst loading02 mgPt cm

minus2 on TGP-H060 (0 wt PTFE) Toray paper (Type I anode)Cathode O2 flow rate 1000 ml minminus1 pressure 150 kPa(g) Cathodecatalyst either AQndashC 36 mgAQndashC cmminus2 on TGP-H060 (10 wt PTFE) orCondashC 36 mgCondashC cmminus2 on TGP-H060 (10 wt PTFE)

Figure 5 Comparison of the two anode types using AQndashC cathode catalystat 40 degC Type I C-Pt and Type II Ti-Pt half-CCM Cathode carrier waterflow rate 15 ml minminus1 O2 flow rate 1000 ml minminus1 pressure 150 kPa(g)AQndashC catalyst loading 36 mgAQndashC cmminus2 on TGP-H060 (10 wt PTFE)Anode water flow rate 15 ml minminus1

Journal of The Electrochemical Society 2020 167 044502

indicate that CondashC is catalytically more active for the secondaryreactions of H2O2 electroreduction andor thermocatalytic decom-position of H2O2 Therefore a shorter residence time is beneficial

Effect of the anode configurationmdashThe durability of the PEMelectrolyzer for H2O2 production can be compromised by carboncorrosion at the anode (ie carbon paper GDL Type I anodeFig 1) To address this issue an anode configuration composed of Ptcatalyst coated half-membrane (half-CCM) was also used in con-junction with Ti mesh (Type II anode Fig 1) Figure 5 shows acomparison of the two anode types tested Ti-CCM and C-Pt anodeswith AQndashC cathode catalyst The cell potential using the half-CCManode with Ti mesh is similar to that of the carbon paper GDL-Ptanode (Fig 6b) however the H2O2 production is lower (Fig 6c)The reason for lower H2O2 production with Type II anode could beattributed to the different preparation of the MEAs The MEA withthe Type I anode (ie containing the carbon paper GDL) wasprepared using a hot press method whereas the MEA with a half-CCM and Ti mesh anode (Type II) was not hot pressed Therefore

the interaction and bonding between the ionomer and the cathodecatalyst layer is superior in the case of the hot pressed MEA (iewith Type I anode) improving the cathode catalyst layer utilizationand therefore the H2O2 production rate It should be also mentionedthat further reduction of the over cell potential can be achieved usingiridium oxide-based anodes In the present work Pt-based anodeswere used for direct comparison of the same cell in eitherelectrolysis or fuel cell mode operation for peroxide generation1819

Full recycle operation modemdashThe capability to produce H2O2

over a longer period of time is crucial to assess the applicability ofthe proposed PEM electrolyzer approach for commercial operationIn order to simulate on a laboratory scale such a scenarioexperiments with full recycle of the cathode product solution wereperformed for 72 h For the continuous recycle operation experi-ments the AQndashC (half CCM) cathode with the Ti mesh-based anodeconfigurations (Type II Fig 1) was employed to mitigate the carboncorrosion on the anode side (Fig 6) Results show that the AQndashCcatalyst produced 3000 ppm (03 wt ) of H2O2 by the end of the72-hour experiment (Fig 6b) The H2O2 production rate peaked afterapproximately 20 h (Fig 6a) Beyond 20 h the production ratedecreased and the net accumulated H2O2 concentration virtuallylevelled off (Fig 6b) This is due to the competition between H2O2

generation and losses through pathways such as secondary electro-reduction and thermocatalytic decomposition (see next section)

Effect of catalyst and temperature on H2O2 degradationmdashTheH2O2 stability was investigated at three different temperatures (4060 80 degC) using a fully assembled electrolysis cell consisting ofAQndashC cathode catalyst and a half-CCM Pt anode with a Ti meshcurrent collector The goal was to determine the H2O2 loss underopen circuit conditions due to thermocatalytic (ie non-electroche-mical) degradation Figures 7a and 7b show clear evidence forthermal decomposition of H2O2 with higher temperatures leading toincreased decomposition of H2O2 Figures 7c and 7d display the dataon a semi logarithmic plot where dashed lines show the linearregression Clearly full recycle operation of the electrolyzer at 80 degCfor over two hours is not beneficial Furthermore the presence of O2

gas enhanced the H2O2 decomposition in a positive synergisticinteraction effect with temperature (ie the higher the temperaturethe higher was the interaction effect between gas presence andtemperature regarding H2O2 decomposition compare Figs 7c and7d 80 degC data) Similar behavior was reported before as well18

In addition the membrane degradation was also evaluated byanalyzing the fluoride released The median fluoride release rate wassim003 ng hrminus1 cmminus2 for the sixteen samples analyzed Drinkingwater guidelines from the Government of BC in Canada suggests afluoride limit of 10ndash15 mg lminus121 The long-term recycle experi-ments showed the cumulative fluoride concentration over the threeday runs was well below the limit set out by the guidelines at about22 μg lminus1

Conclusions

The electroreduction of O2 to H2O2 was investigated in a PEMelectrolyzer under near-neutral pH operation using deionized waterTwo novel cathode catalysts a cobalt-carbon composite (CondashC) andan organic redox catalyst anthraquinone-riboflavinyl supported oncarbon (AQndashC) were investigated Using a superficial currentdensity of 245 mA cmminus2 and an operating temperature of 40 degCH2O2 molar fluxes of 360 μmol hrminus1 cmminus2 and 580 μmol hrminus1 cmminus2

were obtained in single pass mode with the CondashC and RF-AQcatalysts respectively To the best of our knowledge this is the firsttime that H2O2 production in a PEM electrolyzer with an organicredox catalyst has been reported

Longer term (72 h) experiments conducted at a constant super-ficial current density of 61 mA cmminus2 with complete recycle of thecathode carrier water solution showed a maximum steady-state

Figure 6 Continuous recycle operation (for up to 72 h) of the PEMelectrolyzer for H2O2 production AQndashC cathode catalyst with Pt on Ti-meshanode (a) H2O2 production rate (b) total accumulated H2O2 concentrationand (c) cell voltage Current density 61 mA cmminus2 temperature 40 degC and restof the conditions identical to Fig 5

Journal of The Electrochemical Society 2020 167 044502

H2O2 concentration of 3000 ppm for the AQndashC catalyst Theelectrolytic production of H2O2 using the AQndashC composite catalystin a PEM electrolyzer can provide an adequate supply of H2O2 foradvanced oxidation drinking water treatment applications on-siteand on-demand

Acknowledgments

Funding for this work has been provided by the Natural Sciencesand Engineering Research Council of Canada (NSERC) through theStrategic ResrsquoEau WaterNet program and the NSERC DiscoveryGrant program

References

1 httpstransparencymarketresearchcompressreleasehydrogen-peroxide-markethtm (accessed February 2 2020)

2 J M Campos-Martin G Blanco-Brieva and J L G Fierro ldquoHydrogen peroxidesynthesis an outlook beyond the anthraquinone processrdquo Angew ChemiemdashInt Ed45 6962 (2006)

3 C W Oloman in Electrochemical Processing for the Pulp amp Paper Industry (TheElectrochemical Consultancy New York) (1996)

4 I Yamanaka S Tazawa T Murayama T Iwasaki and S Takenaka ldquoCatalyticsynthesis of neutral hydrogen peroxide at a CoN2Cx cathode of a polymerelectrolyte membrane fuel cell (PEMFC)rdquo Chem Sus Chem 3 59 (2010)

5 W Zhang A U Shaikh E Y Tsui and T M Swager ldquoCobalt porphyrinfunctionalized carbon nanotubes for oxygen reductionrdquo Chem Mater 21 3234 (2009)

6 H J Zhang X Yuan W Wen D Y Zhang L Sun Q Z Jiang and Z F MaldquoElectrochemical performance of a novel CoTETAC catalyst for the oxygenreduction reactionrdquo Electrochem Commun 11 206 (2009)

7 K Zhao Y Su X Quan Y Liu S Chen and H Yu ldquoEnhanced H2O2 productionby selective electrochemical reduction of O2on fluorine-doped hierarchicallyporous carbonrdquo J Catal 357 118 (2018)

8 J Park Y Nabae T Hayakawa and M A Kakimoto ldquoHighly selective two-electron oxygen reduction catalyzed by mesoporous nitrogen-doped carbonrdquo ACSCatal 4 3749 (2014)

9 T P Fellinger F Hascheacute P Strasser and M Antonietti ldquoMesoporous nitrogen-doped carbon for the electrocatalytic synthesis of hydrogen peroxiderdquo J Am ChemSoc 134 4072 (2012)

10 Y Liu X Quan X Fan H Wang and S Chen ldquoHigh-yield electrosynthesis ofhydrogen peroxide from oxygen reduction by hierarchically porous carbonrdquoAngew ChemiemdashInt Ed 54 6837 (2015)

11 P Drogui S Elmaleh M Rumeau C Bernard and A Rambaud ldquoHydrogenperoxide production by water electrolysis application to disinfectionrdquo J ApplElectrochem 31 877 (2001)

12 C Ridruejo F Alcaide G Aacutelvarez E Brillas and I Sireacutes ldquoOn-site H2O2

electrogeneration at a CoS2-based air-diffusion cathode for the electrochemicaldegradation of organic pollutantsrdquo J Electroanal Chem 808 364 (2018)

13 A Verdaguer-Casadevall D Deiana M Karamad S Siahrostami P MalacridaT W Hansen J Rossmeisl I Chorkendorff and I E L Stephens ldquoTrends in theelectrochemical synthesis of H2O2 enhancing activity and selectivity by electro-catalytic site engineeringrdquo Nano Lett 14 1603 (2014)

14 S Siahrostami et al ldquoEnabling direct H2O2 production through rational electro-catalyst designrdquo Nat Mater 12 1137 (2013)

15 V Viswanathan H A Hansen and J K Noslashrskov ldquoSelective electrochemicalgeneration of hydrogen peroxide from water oxidationrdquo J Phys Chem Lett 64224 (2015)

16 A Bonakdarpour D Esau H Cheng A Wang E Gyenge and D P WilkinsonldquoPreparation and electrochemical studies of metal-carbon composite catalysts forsmall-scale electrosynthesis of H2O2rdquo Electrochim Acta 56 9074 (2011)

17 A Wang A Bonakdarpour D P Wilkinson and E Gyenge ldquoNovel organic redoxcatalyst for the electroreduction of oxygen to hydrogen peroxiderdquo ElectrochimActa 66 222 (2012)

18 W Li A Bonakdarpour E Gyenge and D P Wilkinson ldquoDrinking waterpurification by electrosynthesis of hydrogen peroxide in a power-producing PEMfuel cellrdquo Chem Sus Chem 6 2137 (2013)

19 W Li A Bonakdarpour E Gyenge and D P Wilkinson ldquoDesign of bifunctionalelectrodes for co-generation of electrical power and hydrogen peroxiderdquo J ApplElectrochem 48 985 (2018)

20 N V Klassen D Marchington and H C E McGowan ldquoH2O2 Determination bythe I3minus method and by KMnO4 titrationrdquo Anal Chem 66 2921 (1994)

21 BC Ministry of Environment and Climate Change Strategy ldquoBC Source DrinkingWater Quality Guidelines Guideline Summaryrdquo Water Quality Guideline SeriesWQG-01 (2017)

Figure 7 H2O2 stability in the electrolysis cell at open circuit as a function of temperature and oxygen gas flow (a) (c) no oxygen gas (b) (d) with oxygen gasflow Cathode catalyst AQndashC 36 mgAQndashC cmminus2 on TGP-H060 (10 wt PTFE) Continuous recycle of the cathode water carrier flow at 15 ml minminus1 O2 flowrate 1000 ml minminus1 pressure 150 kPa(g) Anode conditions water flow 15 ml minminus1 Ti-Pt anode

Journal of The Electrochemical Society 2020 167 044502

indicate that CondashC is catalytically more active for the secondaryreactions of H2O2 electroreduction andor thermocatalytic decom-position of H2O2 Therefore a shorter residence time is beneficial

Effect of the anode configurationmdashThe durability of the PEMelectrolyzer for H2O2 production can be compromised by carboncorrosion at the anode (ie carbon paper GDL Type I anodeFig 1) To address this issue an anode configuration composed of Ptcatalyst coated half-membrane (half-CCM) was also used in con-junction with Ti mesh (Type II anode Fig 1) Figure 5 shows acomparison of the two anode types tested Ti-CCM and C-Pt anodeswith AQndashC cathode catalyst The cell potential using the half-CCManode with Ti mesh is similar to that of the carbon paper GDL-Ptanode (Fig 6b) however the H2O2 production is lower (Fig 6c)The reason for lower H2O2 production with Type II anode could beattributed to the different preparation of the MEAs The MEA withthe Type I anode (ie containing the carbon paper GDL) wasprepared using a hot press method whereas the MEA with a half-CCM and Ti mesh anode (Type II) was not hot pressed Therefore

the interaction and bonding between the ionomer and the cathodecatalyst layer is superior in the case of the hot pressed MEA (iewith Type I anode) improving the cathode catalyst layer utilizationand therefore the H2O2 production rate It should be also mentionedthat further reduction of the over cell potential can be achieved usingiridium oxide-based anodes In the present work Pt-based anodeswere used for direct comparison of the same cell in eitherelectrolysis or fuel cell mode operation for peroxide generation1819

Full recycle operation modemdashThe capability to produce H2O2

over a longer period of time is crucial to assess the applicability ofthe proposed PEM electrolyzer approach for commercial operationIn order to simulate on a laboratory scale such a scenarioexperiments with full recycle of the cathode product solution wereperformed for 72 h For the continuous recycle operation experi-ments the AQndashC (half CCM) cathode with the Ti mesh-based anodeconfigurations (Type II Fig 1) was employed to mitigate the carboncorrosion on the anode side (Fig 6) Results show that the AQndashCcatalyst produced 3000 ppm (03 wt ) of H2O2 by the end of the72-hour experiment (Fig 6b) The H2O2 production rate peaked afterapproximately 20 h (Fig 6a) Beyond 20 h the production ratedecreased and the net accumulated H2O2 concentration virtuallylevelled off (Fig 6b) This is due to the competition between H2O2

generation and losses through pathways such as secondary electro-reduction and thermocatalytic decomposition (see next section)

Effect of catalyst and temperature on H2O2 degradationmdashTheH2O2 stability was investigated at three different temperatures (4060 80 degC) using a fully assembled electrolysis cell consisting ofAQndashC cathode catalyst and a half-CCM Pt anode with a Ti meshcurrent collector The goal was to determine the H2O2 loss underopen circuit conditions due to thermocatalytic (ie non-electroche-mical) degradation Figures 7a and 7b show clear evidence forthermal decomposition of H2O2 with higher temperatures leading toincreased decomposition of H2O2 Figures 7c and 7d display the dataon a semi logarithmic plot where dashed lines show the linearregression Clearly full recycle operation of the electrolyzer at 80 degCfor over two hours is not beneficial Furthermore the presence of O2

gas enhanced the H2O2 decomposition in a positive synergisticinteraction effect with temperature (ie the higher the temperaturethe higher was the interaction effect between gas presence andtemperature regarding H2O2 decomposition compare Figs 7c and7d 80 degC data) Similar behavior was reported before as well18

In addition the membrane degradation was also evaluated byanalyzing the fluoride released The median fluoride release rate wassim003 ng hrminus1 cmminus2 for the sixteen samples analyzed Drinkingwater guidelines from the Government of BC in Canada suggests afluoride limit of 10ndash15 mg lminus121 The long-term recycle experi-ments showed the cumulative fluoride concentration over the threeday runs was well below the limit set out by the guidelines at about22 μg lminus1

Conclusions

The electroreduction of O2 to H2O2 was investigated in a PEMelectrolyzer under near-neutral pH operation using deionized waterTwo novel cathode catalysts a cobalt-carbon composite (CondashC) andan organic redox catalyst anthraquinone-riboflavinyl supported oncarbon (AQndashC) were investigated Using a superficial currentdensity of 245 mA cmminus2 and an operating temperature of 40 degCH2O2 molar fluxes of 360 μmol hrminus1 cmminus2 and 580 μmol hrminus1 cmminus2

were obtained in single pass mode with the CondashC and RF-AQcatalysts respectively To the best of our knowledge this is the firsttime that H2O2 production in a PEM electrolyzer with an organicredox catalyst has been reported

Longer term (72 h) experiments conducted at a constant super-ficial current density of 61 mA cmminus2 with complete recycle of thecathode carrier water solution showed a maximum steady-state

Figure 6 Continuous recycle operation (for up to 72 h) of the PEMelectrolyzer for H2O2 production AQndashC cathode catalyst with Pt on Ti-meshanode (a) H2O2 production rate (b) total accumulated H2O2 concentrationand (c) cell voltage Current density 61 mA cmminus2 temperature 40 degC and restof the conditions identical to Fig 5

Journal of The Electrochemical Society 2020 167 044502

H2O2 concentration of 3000 ppm for the AQndashC catalyst Theelectrolytic production of H2O2 using the AQndashC composite catalystin a PEM electrolyzer can provide an adequate supply of H2O2 foradvanced oxidation drinking water treatment applications on-siteand on-demand

Acknowledgments

Funding for this work has been provided by the Natural Sciencesand Engineering Research Council of Canada (NSERC) through theStrategic ResrsquoEau WaterNet program and the NSERC DiscoveryGrant program

References

1 httpstransparencymarketresearchcompressreleasehydrogen-peroxide-markethtm (accessed February 2 2020)

2 J M Campos-Martin G Blanco-Brieva and J L G Fierro ldquoHydrogen peroxidesynthesis an outlook beyond the anthraquinone processrdquo Angew ChemiemdashInt Ed45 6962 (2006)

3 C W Oloman in Electrochemical Processing for the Pulp amp Paper Industry (TheElectrochemical Consultancy New York) (1996)

4 I Yamanaka S Tazawa T Murayama T Iwasaki and S Takenaka ldquoCatalyticsynthesis of neutral hydrogen peroxide at a CoN2Cx cathode of a polymerelectrolyte membrane fuel cell (PEMFC)rdquo Chem Sus Chem 3 59 (2010)

5 W Zhang A U Shaikh E Y Tsui and T M Swager ldquoCobalt porphyrinfunctionalized carbon nanotubes for oxygen reductionrdquo Chem Mater 21 3234 (2009)

6 H J Zhang X Yuan W Wen D Y Zhang L Sun Q Z Jiang and Z F MaldquoElectrochemical performance of a novel CoTETAC catalyst for the oxygenreduction reactionrdquo Electrochem Commun 11 206 (2009)

7 K Zhao Y Su X Quan Y Liu S Chen and H Yu ldquoEnhanced H2O2 productionby selective electrochemical reduction of O2on fluorine-doped hierarchicallyporous carbonrdquo J Catal 357 118 (2018)

8 J Park Y Nabae T Hayakawa and M A Kakimoto ldquoHighly selective two-electron oxygen reduction catalyzed by mesoporous nitrogen-doped carbonrdquo ACSCatal 4 3749 (2014)

9 T P Fellinger F Hascheacute P Strasser and M Antonietti ldquoMesoporous nitrogen-doped carbon for the electrocatalytic synthesis of hydrogen peroxiderdquo J Am ChemSoc 134 4072 (2012)

10 Y Liu X Quan X Fan H Wang and S Chen ldquoHigh-yield electrosynthesis ofhydrogen peroxide from oxygen reduction by hierarchically porous carbonrdquoAngew ChemiemdashInt Ed 54 6837 (2015)

11 P Drogui S Elmaleh M Rumeau C Bernard and A Rambaud ldquoHydrogenperoxide production by water electrolysis application to disinfectionrdquo J ApplElectrochem 31 877 (2001)

12 C Ridruejo F Alcaide G Aacutelvarez E Brillas and I Sireacutes ldquoOn-site H2O2

electrogeneration at a CoS2-based air-diffusion cathode for the electrochemicaldegradation of organic pollutantsrdquo J Electroanal Chem 808 364 (2018)

13 A Verdaguer-Casadevall D Deiana M Karamad S Siahrostami P MalacridaT W Hansen J Rossmeisl I Chorkendorff and I E L Stephens ldquoTrends in theelectrochemical synthesis of H2O2 enhancing activity and selectivity by electro-catalytic site engineeringrdquo Nano Lett 14 1603 (2014)

14 S Siahrostami et al ldquoEnabling direct H2O2 production through rational electro-catalyst designrdquo Nat Mater 12 1137 (2013)

15 V Viswanathan H A Hansen and J K Noslashrskov ldquoSelective electrochemicalgeneration of hydrogen peroxide from water oxidationrdquo J Phys Chem Lett 64224 (2015)

16 A Bonakdarpour D Esau H Cheng A Wang E Gyenge and D P WilkinsonldquoPreparation and electrochemical studies of metal-carbon composite catalysts forsmall-scale electrosynthesis of H2O2rdquo Electrochim Acta 56 9074 (2011)

17 A Wang A Bonakdarpour D P Wilkinson and E Gyenge ldquoNovel organic redoxcatalyst for the electroreduction of oxygen to hydrogen peroxiderdquo ElectrochimActa 66 222 (2012)

18 W Li A Bonakdarpour E Gyenge and D P Wilkinson ldquoDrinking waterpurification by electrosynthesis of hydrogen peroxide in a power-producing PEMfuel cellrdquo Chem Sus Chem 6 2137 (2013)

19 W Li A Bonakdarpour E Gyenge and D P Wilkinson ldquoDesign of bifunctionalelectrodes for co-generation of electrical power and hydrogen peroxiderdquo J ApplElectrochem 48 985 (2018)

20 N V Klassen D Marchington and H C E McGowan ldquoH2O2 Determination bythe I3minus method and by KMnO4 titrationrdquo Anal Chem 66 2921 (1994)

21 BC Ministry of Environment and Climate Change Strategy ldquoBC Source DrinkingWater Quality Guidelines Guideline Summaryrdquo Water Quality Guideline SeriesWQG-01 (2017)

Figure 7 H2O2 stability in the electrolysis cell at open circuit as a function of temperature and oxygen gas flow (a) (c) no oxygen gas (b) (d) with oxygen gasflow Cathode catalyst AQndashC 36 mgAQndashC cmminus2 on TGP-H060 (10 wt PTFE) Continuous recycle of the cathode water carrier flow at 15 ml minminus1 O2 flowrate 1000 ml minminus1 pressure 150 kPa(g) Anode conditions water flow 15 ml minminus1 Ti-Pt anode

Journal of The Electrochemical Society 2020 167 044502

H2O2 concentration of 3000 ppm for the AQndashC catalyst Theelectrolytic production of H2O2 using the AQndashC composite catalystin a PEM electrolyzer can provide an adequate supply of H2O2 foradvanced oxidation drinking water treatment applications on-siteand on-demand

Acknowledgments

Funding for this work has been provided by the Natural Sciencesand Engineering Research Council of Canada (NSERC) through theStrategic ResrsquoEau WaterNet program and the NSERC DiscoveryGrant program

References

1 httpstransparencymarketresearchcompressreleasehydrogen-peroxide-markethtm (accessed February 2 2020)

2 J M Campos-Martin G Blanco-Brieva and J L G Fierro ldquoHydrogen peroxidesynthesis an outlook beyond the anthraquinone processrdquo Angew ChemiemdashInt Ed45 6962 (2006)

3 C W Oloman in Electrochemical Processing for the Pulp amp Paper Industry (TheElectrochemical Consultancy New York) (1996)

4 I Yamanaka S Tazawa T Murayama T Iwasaki and S Takenaka ldquoCatalyticsynthesis of neutral hydrogen peroxide at a CoN2Cx cathode of a polymerelectrolyte membrane fuel cell (PEMFC)rdquo Chem Sus Chem 3 59 (2010)

5 W Zhang A U Shaikh E Y Tsui and T M Swager ldquoCobalt porphyrinfunctionalized carbon nanotubes for oxygen reductionrdquo Chem Mater 21 3234 (2009)

6 H J Zhang X Yuan W Wen D Y Zhang L Sun Q Z Jiang and Z F MaldquoElectrochemical performance of a novel CoTETAC catalyst for the oxygenreduction reactionrdquo Electrochem Commun 11 206 (2009)

7 K Zhao Y Su X Quan Y Liu S Chen and H Yu ldquoEnhanced H2O2 productionby selective electrochemical reduction of O2on fluorine-doped hierarchicallyporous carbonrdquo J Catal 357 118 (2018)

8 J Park Y Nabae T Hayakawa and M A Kakimoto ldquoHighly selective two-electron oxygen reduction catalyzed by mesoporous nitrogen-doped carbonrdquo ACSCatal 4 3749 (2014)

9 T P Fellinger F Hascheacute P Strasser and M Antonietti ldquoMesoporous nitrogen-doped carbon for the electrocatalytic synthesis of hydrogen peroxiderdquo J Am ChemSoc 134 4072 (2012)

10 Y Liu X Quan X Fan H Wang and S Chen ldquoHigh-yield electrosynthesis ofhydrogen peroxide from oxygen reduction by hierarchically porous carbonrdquoAngew ChemiemdashInt Ed 54 6837 (2015)

11 P Drogui S Elmaleh M Rumeau C Bernard and A Rambaud ldquoHydrogenperoxide production by water electrolysis application to disinfectionrdquo J ApplElectrochem 31 877 (2001)

12 C Ridruejo F Alcaide G Aacutelvarez E Brillas and I Sireacutes ldquoOn-site H2O2

electrogeneration at a CoS2-based air-diffusion cathode for the electrochemicaldegradation of organic pollutantsrdquo J Electroanal Chem 808 364 (2018)

13 A Verdaguer-Casadevall D Deiana M Karamad S Siahrostami P MalacridaT W Hansen J Rossmeisl I Chorkendorff and I E L Stephens ldquoTrends in theelectrochemical synthesis of H2O2 enhancing activity and selectivity by electro-catalytic site engineeringrdquo Nano Lett 14 1603 (2014)

14 S Siahrostami et al ldquoEnabling direct H2O2 production through rational electro-catalyst designrdquo Nat Mater 12 1137 (2013)

15 V Viswanathan H A Hansen and J K Noslashrskov ldquoSelective electrochemicalgeneration of hydrogen peroxide from water oxidationrdquo J Phys Chem Lett 64224 (2015)

16 A Bonakdarpour D Esau H Cheng A Wang E Gyenge and D P WilkinsonldquoPreparation and electrochemical studies of metal-carbon composite catalysts forsmall-scale electrosynthesis of H2O2rdquo Electrochim Acta 56 9074 (2011)

17 A Wang A Bonakdarpour D P Wilkinson and E Gyenge ldquoNovel organic redoxcatalyst for the electroreduction of oxygen to hydrogen peroxiderdquo ElectrochimActa 66 222 (2012)

18 W Li A Bonakdarpour E Gyenge and D P Wilkinson ldquoDrinking waterpurification by electrosynthesis of hydrogen peroxide in a power-producing PEMfuel cellrdquo Chem Sus Chem 6 2137 (2013)

19 W Li A Bonakdarpour E Gyenge and D P Wilkinson ldquoDesign of bifunctionalelectrodes for co-generation of electrical power and hydrogen peroxiderdquo J ApplElectrochem 48 985 (2018)

20 N V Klassen D Marchington and H C E McGowan ldquoH2O2 Determination bythe I3minus method and by KMnO4 titrationrdquo Anal Chem 66 2921 (1994)

21 BC Ministry of Environment and Climate Change Strategy ldquoBC Source DrinkingWater Quality Guidelines Guideline Summaryrdquo Water Quality Guideline SeriesWQG-01 (2017)

Figure 7 H2O2 stability in the electrolysis cell at open circuit as a function of temperature and oxygen gas flow (a) (c) no oxygen gas (b) (d) with oxygen gasflow Cathode catalyst AQndashC 36 mgAQndashC cmminus2 on TGP-H060 (10 wt PTFE) Continuous recycle of the cathode water carrier flow at 15 ml minminus1 O2 flowrate 1000 ml minminus1 pressure 150 kPa(g) Anode conditions water flow 15 ml minminus1 Ti-Pt anode

Journal of The Electrochemical Society 2020 167 044502