(Invited) High-Temperature Alkaline Water Electrolysis Using Composite Ceramic-Molten Hydroxide Membrane

Hydrogen production from water electrolysis for mobile and energy storage applications is attractive due to its high efficiency, fast ramp rates, and potential for the clean energy economy. However, current hydrogen production from electrolysis comprises only a small fraction of the global hydrogen market due to the high cost associated with expensive stack materials (membrane, catalyst, and bipolar plates) and electricity consumption of the commercial electrolysis systems. We have developed a high temperature alkaline electrolyte-based water electrolyzer (HTAWE) that operates at 350-550 °C, enabling high reaction rates while limiting thermal degradation compared to solid oxide cells operating above 700 °C. This water electrolyzer is based on our innovative molten hydroxide electrolyte impregnated in a porous ceramic matrix, which has conductivity as high as 0.4 S/cm at 350 °C, enabling rapid hydroxide transport. This HTAWE can simultaneously reduce the electrolyzer cost (by adopting cheap material) and improve energy efficiency (by enabling high-temperature operation). Using an innovative new SrZrO3-based matrix, we have demonstrated exceptional water electrolysis performance using both single and binary hydroxide mixtures. We successfully achieved sustained cell performance of 1.35 V at a current density of 1,000 mA/cm2 with area specific resistance (ASR) 0.1 Ohm-cm2 across the cell at furnace temperature 500 °C. We were also able to demonstrate cell performance of 1.45 V at a current density of 1,000 mA/cm2 with ASR of <0.2 Ohm-cm2 across the cell at a furnace temperature 400 °C. Furthermore, we have demonstrated stable cell performance for >1000 h of continuous operation at 1 A/cm2 with ASR of 0.2 Ohm∙cm2 across the cell.