Chemistry · Ch 9 — Electrochemistry
Fuel Cells
Fuel Cells
A fuel cell is a special type of galvanic cell in which the energy released by the combustion of a fuel is converted directly into electrical energy, rather than being released as heat the way ordinary combustion would release it. Unlike an ordinary battery, which stores a fixed quantity of reactant sealed inside it and eventually runs down, a fuel cell needs a continuous external supply of both fuel and oxidant to keep functioning — it is written in general form as
The hydrogen–oxygen fuel cell is the representative example. Hydrogen serves as the fuel and oxygen as the oxidant, with aqueous KOH as the electrolyte, maintained at around 200°C and 20–40 atm; porous graphite electrodes containing nickel and nickel oxide serve as the inert catalytic surfaces. Hydrogen and oxygen gases are bubbled continuously through the anode and cathode chambers respectively. …
What this figure shows. Hydrogen gas is bubbled continuously over a porous anode and oxygen gas over a porous cathode, both made of graphite embedded with nickel and nickel oxide as inert catalytic surfaces, with aqueous KOH as the electrolyte maintained at around 200°C and 20–40 atm. The cell has a flow field to distribute gas evenly, a catalyst layer at each electrode, a central membrane, and a porous gas-diffusion layer on each side. At the anode, hydrogen is oxidised in the presence of hydroxide ions to give water and release electrons; at the cathode, oxygen is reduced using those electrons and water to regenerate hydroxide ions — the two half-reactions never let hydrogen and oxygen react directly, which is exactly what allows their combined ch …