(Invited) Advances in Proton Ceramic Fuel Cells, Steam Electrolyzers, and Dehydrogenation Reactors Based on Materials and Process Optimizations

Abstract

Proton-conducting ceramics such as Y-doped BaZrO3-based perovskites form basis for hydrogen-fueled proton ceramic fuel cells (PCFCs) and proton ceramic electrolyzers (PCEs) for steam. Like the PCFC benefits from running undiluted hydrogen with superior fuel utilization without circulation, the PCEs produce directly dry hydrogen at the balanced total pressure of the electrolyzer while oxygen is diluted to lower pressure with the feed of steam, lowering the hazard of pressurized oxygen. The use of waste or renewable heat to generate and superheat the steam allows operation at high electrical efficiencies.Operation at high steam pressures reduces p-type electronic conduction at the steam+oxygen electrode and the use of novel mixed proton-electron conducting double perovskites lowers the overpotential and hence p-type electronic conductivity further, altogether yielding acceptable faradayic efficiencies of the electrolyzer. The presence of protons and significant protonic conduction in certain double perovskites in combination with their high electronic conductivity can be rationalized by recent results of studies of their structure and defect chemistry. Proton-conducting ceramics also offer unique opportunities for dehydrogenation of hydrocarbons including natural gas along different schemes and for different products, as suggested by Iwahara three decades ago. With materials and reactor design optimizations as well as process adaptions we now see emerging demonstrations of such use of proton-conducting ceramics.