Hydrogen Oxygen Fuel Cell — the NEET Chemistry reaction: mechanism, reagents, conditions, structures and exam traps.
Hydrogen-Oxygen Fuel Cell An alkaline hydrogen–oxygen fuel cell continuously converts the chemical energy of H2 and O2 directly into electrical energy using an aqueous KOH electrolyte and porous Pt-catalyzed electrodes. Hydrogen is oxidized at the anode and oxygen is reduced at the cathode to form water; the overall cell has E° ≈ 1.23 V at 298 K. No flame; silent operation. A steady voltage near 1.23 V open-circuit at 298 K; under load typically ~0.9–1.0 V per cell. Consumption of H2 and O2 gases with formation of liquid water and noticeable heat release; electrodes remain solid and porous. Highly exothermic; for 2H2(g) + O2(g) 2H2O(l), H -571.6 , kJ at 298 K. E cell 1.23 , V at 298 K (activity of H2O = 1); actual cell voltage under load is lower due to overpotentials and mass-transport losses. 1. Diffusion and adsorption: H2(g) diffuses to the porous Pt anode and dissociatively adsorbs as H on Pt. 2. Anodic oxidation (alkaline): Adsorbed H reacts with hydroxide to release electrons: H 2(g) + 2OH - (aq) 2H 2O(l) + 2e -. 3. Electron transport: Electrons flow through the external circuit from anode (−) to cathode (+), delivering electrical work. 4. Oxygen adsorption and reduction: O2(g) is reduced on the Pt cathode in alkaline medium: O 2(g) + 2H 2O(l) + 4e - 4OH - (aq). 5. Ionic migration/closure: OH - produced at the cathode migrates through the KOH electrolyte toward the anode, where it is consumed in the anodic process. 6. Net reaction and product removal: Adding the half-reactions gives 2H 2(g) + O 2(g) 2H 2O(l); water and heat are removed while fresh H2 and O2 are continuously supplied. Writing acidic half-reactions (H+ based) for the alkaline cell—remember OH− migrates in AFCs. Placing water on the wrong side: in alkaline medium, water is produced at the anode and consumed at the cathode in the half-steps. Confusing electrodes: H2 is oxidized at the anode (−), O2 is reduced at the cathode (+). Quoting E° as 1.5 V or 1.0 V—NCERT uses ~1.23 V at 298 K under standard conditions. Stating that CO2 is formed—only water is the product (clean energy device).