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Biomass Fuel Cells
Sergey Kalyuzhnyi
Department of Chemical Enzymology, Chemistry Faculty
Moscow State University, 119992, Moscow, Russia
Content
•Basic principles of fuel cell
•Limitations of chemical fuel cell
•Enzymatic fuel cell
•Biomass fuel cell:
– how it works?
– performance
– problems
– perspectives
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 2 O
Net reaction:
2H2 + O2  2H2O
Fuel cell technologies
Operating temp., °C
Specific power,
kW/l
Alkaline (AFC)
60-100
<0.3
Polymer electrolyte (PEPC,
PEMFC, SPFC)
Phosphoric Acid (PAFC)
Direct methanol (DMFC)
80-100
0.2-1
160-200
60-120
<0.1
<0.1
Molted carbonate (MCFC)
600-700
<0.1
Solid Oxide (SOFC)
900-1000
<0.1
Fuel cell
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
200
35
Pt expense, g/kW
20
less
Temperature, oC
~80
same
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
Limitations of small chemical FC
• Cost as well
$10,000 –
only engine!
50 kW (<$ 10 000)
•Pt-based:
– poisoning with CO, H2S etc.
– low fuel versatility (H2, CH3OH)
– cost & shortage of Pt
Dynamic of Pt cost & its availability
22
20
Cost of Pt / US$ g
-1
18
Annual production:
16
14
180 tons
12
10
8
6
4
2
0
1960
1970
1980
1990
2000
year
In 2000: 57.5 mln. cars
50 kW engines
5750 tons Pt
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
Enzymatic fuel cell (indirect bioFC)
Electric current
Solid polymer
electrolyte
Power density – till 40 W/m2
Н2
Immobilised
hydrogenase
O2
Immobilised oxydase
(laccase)
Specific power - till 6 kW/l
Theoretical specific power till 20 kW/l
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 (masstransfer, new methods of enzyme immobilization)
Microbial fuel cell (MFC)
V
Organics
H2 O
Cathode
Mox
Solid electrolyte
Anode
CO2
Electron
transport
chain of cell
Electron
Mred
O2
H+
• 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)
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)
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)
Sulphate reducing fuel cell
V
SO4
2-
H2O
Cathode
CO2
SRB cells
Electron
S2-
Solid electrolyte
Anode
Organics
O2
H+
Biological reaction: SO42- + 2CH2O
Anode reaction: S2- + 4H2O
S2- + 2CO2 + 2H2O
SO42- + 8H+ + 8e
Cathode reaction: 2O2 + 8H+ + 8e
4H2O
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 putrefaciens (starch WW)
0.012
ND
Gil et al., 2003
Mediator-less
(graphite)
Geobacter sulpfurreducens (acetate)
0.016
96.8
Bond &
Lovley, 2003
Mediator, photo
(felt carbon)
Synechococcus sp.
(light)
0.3-0.4
2.5-4.0 (light
yield)
Tsujimura et
al., 2001
Mediator-less
(graphite + MnO2)
Activated sludge
(glucose)
0.7
ND
Park & Zeikus,
2003
Mediator-less
(graphite)
Mixed population
(glucose)
3.6
89
Rabaey et al.,
2003
150 (shortterm)
ND
Habermann &
Pommer, 1991
Sulphate reducing Mixed population
(graphite+Co(OH)2 (sugar WW)
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)
Perspectives of MFC
• No any full scale implementation
• Due broad fuel versatility - not only energy
production but waste(water) treatment too!
UASB-reactor
Load,
Efficiency
kg COD/m3/d
10
0.85*0.38=0.32
Power density,
kW/m3
0.5
Best lab MFC
3
0.65
0.54
Monolayer porous
electrode*
10
0.7
1.5
Mediated MFC*
32
0.7
4.7
*Calculations of Bert Hamelers (Wageningen University)
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)
“Gastronome”: a prototype MFC
powered robot
Wilkinson (2000), University of South Florida
Thank you!