Microbial fuel cells

Microbial Fuel CellsPaul BentzKevin Cao

ConceptBacteria convert substrate into electrons.The electrons run through the circuit and to

power the load.The byproducts include carbon dioxide,

water, and energy.

ComponentsAnodeCathodeExchange membraneElectrical circuit

AnodeThe bacteria live in the anode

and convert substrate to carbon dioxide, water, and energy.

Various things like glucose and acetate can be used.

The bacteria are kept in an oxygen-less environment to promote the flow of electrons through the anode.

Electrical CircuitAfter leaving the anode, the electrons travel

through the circuit.These electrons power the load.The voltage multiplied by the current shows

the power.

Exchange MembraneThe protons that the bacteria

separated from the electrons flows through the exchange membrane.

They recombine on the other side.Can be a proton or cation exchange

membrane.

CathodeThe electrons and protons

recombine at the cathode.Oxygen is reduced to water.A platinum catalyst is used so

the oxygen is sufficiently reduced.

Video

ReactionsBEAMRHydrogen evolution reaction

BEAMRUtilizes electrohydrogenesis, which uses an

anaerobic environment to produce pure hydrogen.

It uses about one ninth of the energy required by normal electrolysis.

It has many different names:Bioelectrochemically assisted microbial reactorBiocatalyzed electrolysis cellsMicrobial electrolysis cells

Hydrogen Evolution ReactionThe bacteria in the anode separate the

protons and electrons.This reaction occurs at the cathode, where

they recombine to form hydrogen gas.

HistoryM.C. Potter first performed work on the

concept in 1911 with E. coli at the University of Durham

In 1976 the current design was came into existence by the work of Suzuki

Operating ConditionsFunction well in mild conditionsOperate at 70-100°F

UsesBeer breweries produce biodegradable

wastewater, which MFCs clean.Desalinating waterCreating fertilizer

Environmental ImpactIf the variety of substrates is increased,

waste can be used to create more energy.Instead of big factory manufacturing,

fertilizer for farmers can be created with MFCs and common materials.

MFCs can be used to desalinate seawater without burning fossil fuels, although not very efficiently yet.

EfficiencyThe efficiency varies based on the substrate

used, but it can reach very high efficiencies.91% efficiency has been reached.

CostPower density = 150 mW/m2

Volume (MFC): 28 x 10^-6 m3

A/V-ratio: 25 m2/m3 Anode surface area (single chamber) = 7 x 10^-4 m2 Power = 0.165 mW 

Cost of single-chamber fuel cell: (lab-scale) Toray paper (10x10 cm): $ 11 XC-72 (10x10 cm): $65 Others (perspex, glue, wire): $ 25 Total = $ 100 

Cost per Watt = $ 600/mW

FutureMore types of substrateAmmonia-treated anodes

SubstrateCurrently there is a limit to what can be used

as a substrate for the bacteria.Scientists hope to increase these fuel types to

include things like sewage and manure.

Ammonia-Treated AnodesAnodes of MFCs are naturally

negative in charge.The anodes can be changed to

a positive charge by being treated with ammonia.

This will make the anode more receptive to the electron transfer from the bacteria.

The energy trade-off to produce this might not be worth the increase in production.

Bibliographyhttp://www.microbialfuelcell.org/http://www.engr.psu.eduhttp://microbialfuelcell.wordpress.com/http://www.sciencedaily.com/releases/

2008/01/080103101137.htmhttp://peswiki.com/index.php/

Directory:Penn_State_Microbial_Fuel_Cells_Produce_Hydrogen_from_Waste_Water

www.popsci.com/scitech/article/2009-08/microbial-fuel-cell-cleans-wastewater-desalinates-seawater-and-generates-power

http://www.fuelcells.org/info/summer2007.pdf