Fuel cell in the energy production Fuel cell

Fuel cell in the energy production

Fuel cell • A Fuel is a device that converts directly the chemical energy of reactants (fuel and oxidant) into electricity. • high efficiency (el, el+ heat) • flexibility in the source of fuel (Hx. Cy, biomass, H 2 O) • efficiency independent of plant size • installation of big and small modules • application in stationary, transport and small • electronic devices and systems • non-pollutant and noiseless

Fuel cell fundamentals Electrochemistry H 2=2 H++2 e-(anode) 1/2 O 2+ 2 H++2 e-=H 2 O(cathode) Overall cell reaction 1/2 O 2+ H 2=H 2 O

Power supply and stacks

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Fuel cells types Type AFC Electrolyte KOH T (C) 50 -100 Electrode C/metal Anode Pt/ Ra-Ni Cathode Ag/Pt/oxides/TPP Fuel H 2 Oxidant O 2/air PEFC Membr. 50 -100 C Pt Pt PAFC H 3 PO 4 200 C Pt Pt MCFC K/Li-CO 3 650 metal Ni Ni. O SOFC Zr/Y 2 -O 3 <1000 cermets Ni. Zr. O 2 Perovskite H 2 O 2/air H 2 -CO O 2/air AF C-Alkaline fuel cells, PEFC-Po lymer elec trolyte mem brane fuel ce lls, PAFCPhosphoric acid fuel cells, MCFC-Molten carbonate fuel cells, SOFC-Solid oxide fuel cells, DMFC-Direct methanol fuel cell, DBFC-borohydride Bio. FC-Biological fuel cell, DHFC- hydrazine BOFC-bioorganic fuel cell, DFAFC-formic acid

Electrocatalyst An electrocatalyst is a substance which increases the rate of the reaction by providing an alternative reaction path with a lower activation energy barrier (Appelby, Foulkes) • • Electronic conductivity Stability in the electrolyte Selective for the oxidation/reduction reactions Suitable adsorption characteristics

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Irreversible cell reaction

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Electrode reactions for selected fuel cells Type Anode Ion Cathode AFC H 2+2 OH-=2 H 2 O+2 e- <-OH- 1/2 O 2+H 2 O+2 e-=2 OH- PEFC H 2=2 H++2 e- H+-> 1/2 O 2+2 H++2 e-=H 2 O DMFC CH 3 OH+H 2 O=CO 2+6 H++6 e- H+-> <-OH- 3/2 O 2+6 H++6 e-=3 H 2 O 3/2 O 2+ 3 H 2 O +6 e-=6 OH- <-OH- 2 O 2+4 H 2 O+8 e-=8 OH- H+-> <-OH- O 2+4 H-+4 e-=2 H 2 O O 2+2 H 2 O+4 e-=4 OH- CH 3 OH+6 OH-=CO 2+5 H 2 O+6 e- - DBFC BH 4 +8 OH =8 BO 2 +H 2 O+8 e DHFC N 2 H 4=N 2+4 H-+4 e. N 2 H 4+4 OH-=N 2+4 H 2 O -

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• NASA Fuel cell R &D -High power density (k. W/kg) 1. 6 k. Wh/kg vs. 0. 2 k. Wh/kg -lightweight -length of operation Contracts to Universities and industries for fuel cell characterizations *Apollo (UTC, alkaline fuel cell) *Gemini (GE, ion-exchange membrane)