1. Biomass Fuel Cells Sergey Kalyuzhnyi
Department of Chemical Enzymology, Chemistry Faculty
Moscow State University, , Moscow, Russia

2. Content Basic principles of fuel cell
Limitations of chemical fuel cell
Enzymatic fuel cell
Biomass fuel cell:
how it works?
performance
problems
perspectives

3. Basic principles of fuel cell (FC)
Related to battery: both convert chemical energy into electricity
Battery: the chemical energy has to be stored beforehand
FC only operates when it is supplied from external sources
Fundamental mechanism: inverse water hydrolysis reaction
Anode: 2H 2 4H +
+ 4e -
Cathode: 4e -
+ 4H +
+ O 2 2H O
Net reaction:
2H2 + O2  2H2O

4. Fuel cell technologies
Operating temp., °C
Specific power, kW/l
Alkaline (AFC)
60-100
<0.3
Polymer electrolyte (PEPC, PEMFC, SPFC)
80-100
0.2-1
Phosphoric Acid (PAFC)
<0.1
Direct methanol (DMFC)
60-120
Molted carbonate (MCFC)
Solid Oxide (SOFC)

5. Hydrogen-oxygen PEFC (data of US Department of Energy )
Parameters
Modern state
Goal for 2008
Specific power, W/kg
200
550
Efficiency, % 45 55
Work time, months
1.4 7
СО inhibition, ppm
100
1000
Capital cost, $/kW 35
Pt expense, g/kW 20
less
Temperature, oC
~80
same

6. Limitations of large chemical FC
Cost is the major hurdle
The most widely marketed FC - 4,500 $/kW
Diesel generators – 800-1,500 $/kW
Natural gas turbines - even less!
The goal of US DOE – to cut costs for FC to 400 $/kW by 2010

7. Limitations of small chemical FC
50 kW (<$ )
Cost as well
$10,000 – only engine!
Pt-based:
poisoning with CO, H2S etc.
low fuel versatility (H2, CH3OH)
cost & shortage of Pt

8. Dynamic of Pt cost & its availability
Annual production:
180 tons
In 2000: 57.5 mln. cars
5750 tons Pt
50 kW engines

9. Poisoning by fuel impurities
Reforming gas (H2):
12.5 % of CO
Pt electrodes:
under 0.1% CO activity irreversibly decreases 100 times after 10 min
Hydrogenase el-ds:
-not sensitive up to 1% of CO;
-reversibly restore activity after inhibition;
- catalyst is renewable

10. Enzymatic fuel cell (indirect bioFC)
Electric current
Solid polymer electrolyte
Power density – till 40 W/m2 O2 Н2
Immobilised hydrogenase
Immobilised oxydase (laccase)
Specific power - till 6 kW/l
Theoretical specific power - till 20 kW/l

11. Problems of enzymatic fuel cells
No any full scale implementation
Cost (pure enzymes are expensive)
Stability of enzymes (inactivation, inhibition)
Low fuel versatility (enzymes are too specific)
Strong need in further R&D:
Genetic engineering for improvement of enzyme properties & development of stable large-scale source of enzymes
Improvement of electrode compartments (mass-transfer, new methods of enzyme immobilization)

12. Microbial fuel cell (MFC)
Mox
Mred
Anode
Solid electrolyte
Cathode V O2
H2O H+
Organics
Electron
chain of cell
Electron transport
CO2
MFC – mimic of biological system in which bacteria do not directly transfer their produced electrons to their characteristic acceptors
MFC could be mediator–less (e.g., external cytochromes like in Shewanella putrefaciens or Geobacter sulfurreducens)

13. History & current developments of MFC
Pioneering research: Potter (1912), Cohen (1931), Allen (1972) - inefficient
The first viable MFC – Bennetto et al., 1984
Yeast-driven MFC (Reed & Nagodawithana, 1991)
Current interest on the following types of prokaryotes:
Heterotrophs (Delaney et al., 1984)
Photoheterotrophs (Tsujimura et al., 2001)
Sediment (Tender et al., 2002)

14. Electricity from anaerobic digestion
Indirect (via biogas)
Gas-generators (additionally - heat production)
Reforming (conversion to H2) + H2-O2 fuel cell
Direct (without biogas)
Mediator MFC
Sulphate reducing fuel cell (sulphide is mediator)
Mediator-less MFC (direct transfer of electrons from cells)

15. Sulphate reducing fuel cell
SRB cells
Organics
CO2
SO42-
S2-
Anode
Solid electrolyte
Cathode V O2
H2O H+
Electron
Biological reaction: SO CH2O S2- + 2CO2 + 2H2O
Anode reaction: S2- + 4H2O SO H+ + 8e
Cathode reaction: 2O2 + 8H+ + 8e H2O

16. Coulombic efficiency, %
Performance of MFC
Microbe (fuel)
Power density, W/m2
Coulombic efficiency, %
Reference
Sediment (Pt or graphite)
Mixed population (decay organics)
0.01 ND
Reimers et al., 2001
Mediator-less (graphite felt)
Shewanella putre-faciens (starch WW)
0.012
Gil et al., 2003
Mediator-less (graphite)
Geobacter sulpfur-reducens (acetate)
0.016
96.8
Bond & Lovley, 2003
Mediator, photo (felt carbon)
Synechococcus sp. (light)
(light yield)
Tsujimura et al., 2001
Mediator-less (graphite + MnO2)
Activated sludge (glucose)
0.7
Park & Zeikus, 2003
Mixed population (glucose)
3.6 89
Rabaey et al., 2003
Sulphate reducing (graphite+Co(OH)2
Mixed population (sugar WW)
150 (short-term)
Habermann & Pommer, 1991

17. Problems of Microbial FC
Anode efficiency (harmonization of biological & anode reactions)
Inhibition of biological activity (pH, products)
Biofilm formation on electrode (hardly controlled)
Mass transfer limitations
Good mediators are toxic, stable binding to the electrode surface is difficult to achieve
Cathode efficiency: overpotential, H2O2 production (the same as for chemical FC), biocathodes are possible
Proton transport (membranes are costly – 100$/m2)

18. Perspectives of MFC No any full scale implementation
Due broad fuel versatility - not only energy production but waste(water) treatment too!
Load,
kg COD/m3/d
Efficiency
Power density, kW/m3
UASB-reactor 10
0.85*0.38=0.32
0.5
Best lab MFC 3
0.65
0.54
Monolayer porous electrode*
0.7
1.5
Mediated MFC* 32
4.7
*Calculations of Bert Hamelers (Wageningen University)

19. Gastrorobot Literally: robot with a stomach (food powered machine)
Goal – to create bioelectrochemical machine that derives all the operational power by tapping the energy of real food digestion, using microorganisms as biocatalysts
The challenges of gastrorobotics:
Foraging (food location & identification)
Harvesting (food gathering)
Mastication (chewing)
Ingestion (swallowing)
Digestion (energy extraction) - MFC
Defecation (waste removal)

20. “Gastronome”: a prototype MFC powered robot
Wilkinson (2000), University of South Florida

21. Thank you!