Performance Analysis of Molten Carbonate Fuel Cell VII. Behavior of Molten Carbonate Fuel Cell under Shutdown of Reactive Gas Supply

Abstract

The main electrode reaction of Molten Carbonate Fuel Cell (MCFC) is oxidation of hydrogen at anode and reduction of oxygen and CO₂ at cathode. These gas would be supplied to MCFC through LNG reformer, compressor combined gas-turbine unit or CO₂ recirculation by burning the H₂ and CO of anode exhaust gas in a catalytic burner on MCFC power plant’s level. In case a unit for supplying gas to MCFC stack is in some trouble, it is perhaps possible to force the MCFC stack to generate electricity in spite of short reactive gas through inverter. In order to clarify the behavior of MCFC under such a situation, we carried out durability tests in keeping MCFC generating under no supply of respective gases (anode hydrogen, cathode oxygen or CO₂) with bench-scale cells. As a result of the tests, 1) the reduction of cathode NiO to Ni (NiO + 2e⁻ → Ni + O²⁻) and subsequent CO product by reduction of carbonate ion (CO₃²⁻ + 2e⁻ → CO + 2O²⁻) occur under no supply of cathode oxygen, 2) the reduction of oxygen and CO₂ by dissociation of carbonate ion (CO₃²⁻ → CO₂ + O²⁻ and 1/2O₂ + CO₂ + 2e⁻ → CO₃²⁻) occurs under no supply of cathode CO₂ and 3) the oxidation of anode Ni to NiO (Ni + O²⁻ → NiO + 2e⁻) and subsequent oxygen and CO₂ product by oxidation of carbonate ion (CO₃²⁻ → 1/2 O₂ + CO₂ + 2e⁻) occur under no supply of anode hydrogen.