Effect of iron addition to the electrolyte on alkaline water electrolysis performance

Abstract

Improvement of alkaline water electrolysis is a key enabler for quickly scaling up green hydrogen production. Fe is omnipresent within most industrial alkaline water electrolyzers and its effect on electrolyzer performance needs to be assessed. We conducted three-electrode and flow cell experiments with electrolyte Fe and Ni electrodes. Three-electrode cell experiments show that Fe ([Fe]= 6-357μM; ICP-OES) promotes HER and OER by lowering both overpotentials by at least 100mV at high current densities (T= 35°C-91°C). The overpotential of a zero-gap flow cell was decreased by 200mV when increasing the Fe concentration ([Fe]= 13-549μM, T= 21°C-75°C). HER benefits from the formation of Fe dendrite layers (SEM/EDX, XPS), which prevent NiHx formation and increase the overall active area. The OER benefits from the formation of mixed Ni/Fe oxyhydroxides leading to better catalytic activity and Tafel slope reduction.