Progress of elevated-temperature alkaline electrolysis hydrogen production and alkaline fuel cells power generation

Progress of elevated-temperature alkaline electrolysis for hydrogen production and alkaline fuel cells for power generation are presented. Using platinum group metals and Ni-based alloys, such as Raney Ni and stainless steel, as electrocatalysts, alkaline water electrolysis adopts aqueous KOH solutions or molten KOH-NaOH-LiOH as liquid electrolytes, and combining with metal oxide diaphragms fabricated by tape casting sintering or electrode-supported powder sintering for product separation. Electrolysis longer than 400 hours at 100−400 ℃ and degradation rate of <0.1 V/kh have been realized. In system level, 20 kW stable water electrolysis at 130 ℃ has been realized, and flexible transition of endo/exothermic mode allowing multi-thermal-source thermo-hydrogen energy conversion and high value electric-hydrogen-heat coordination has been proposed. Relying on similar platinum group metals, Ni as well as its oxides as electrocatalysts, elevated-temperature alkaline fuel cells widen applicable electrolytes from aqueous KOH solutions and molten hydroxides to solid materials with adequate ionic conductivity, including high-valence metal doped phosphates. Equipment with liquid electrolyte have accomplished kW-level ground and space applications, while recently developed solid electrolyte cells have realized over 160 hours of continuous operation, while elevated-temperature alkaline membrane fuel cells have made significant progress in recent years, achieving stable operation for over 195 hours.