A self-generated and degradation-resistive cratered stainless steel electrocatalyst for efficient water oxidation in a neutral electrolyte

An electron-mediated CO₂-to-chemical conversion system is regarded as one of the effective solutions for the depletion of fossil fuels and the accumulation of atmospheric CO₂. In this process, the protons and electrons generated from the water-oxidation reaction at an anode are used during the reduction of CO₂ at a cathode, in order to produce high-value hydrocarbon chemicals. Therefore, water oxidation is also a key reaction for the overall electron-mediated CO₂-to-chemical conversion. In this work, a facile preparation method is developed for a highly efficient water oxidation electrocatalyst which stably operates in a neutral bicarbonate electrolyte optimized for CO₂-reduction conditions. Ni-rich cratered structures were spontaneously formed on the stainless steel surface by harsh electro-oxidation, and the chemical composition changes of Fe and Ni on the catalyst surface dramatically enhance water-oxidation activity showing an overpotential value of 504 mV at 10 mA cm^-2 in a CO₂-saturated bicarbonate electrolyte. In contrast to a severe degradation in the phosphate electrolyte, the cratered stainless-steel (CSS) catalyst is very stable for an 18 h reaction in the bicarbonate electrolyte. Surface spectroscopic analyses of CSS consistently revealed that the active-surface structure of the NiOOH and adsorbed water molecules is remarkably stable throughout water-oxidation in the neutral bicarbonate electrolyte, while the destruction of Ni structures by the phosphate electrolyte is proposed to cause concomitant activity loss for water oxidation.