Er-Doping Enhances\nthe Oxygen Evolution Performance\nof Cobalt Oxide in Acidic Medium

Exploring highly active and durable non-noble electrocatalysts\nfor acidic oxygen evolution reaction (OER) is critical for advancing\nH<sub>2</sub> production via water electrolysis using proton exchange\nmembrane electrolyzer. However, it remains an immense challenge. Herein,\nwe propose a strategy to synergistically enhance catalytic activity\nthrough Er doping, thereby enhancing both the intrinsic OER activity\nand stability of Co<sub>3</sub>O<sub>4</sub>. The cost-effective Er–Co<sub>3</sub>O<sub>4</sub> catalyst with 4% Er demonstrates significantly\nimproved performance with an overpotential of 321 ± 5 mV at 10\nmA cm<sup>–2</sup> and exceptional stability exceeding 250\nh. Additionally, doping Er into Co<sub>3</sub>O<sub>4</sub> induces\nstructure defects to generate oxygen vacancies, increasing the ratio\nof Co<sup>3+</sup>/Co<sup>2+</sup>. <i>In situ</i> Raman\nanalyses showed that during the OER process, there was an increase\nin Co–O active species at octahedral sites in 4% Er–Co<sub>3</sub>O<sub>4</sub>, indicating accelerated generation of the key\n*O intermediates for enhanced OER kinetics. Microkinetic modeling\nand density functional theory calculations further demonstrate an\noptimized G<sub>O</sub>-G<sub>HO</sub> value at Er–Co<sub>3</sub>O<sub>4</sub>, which is close to the theoretical optimal OER activity\nat the current density of interest. This study not only develops a\ncost-effective electrocatalyst for acidic OER but also provides fundamental\ninsights into manipulating the structure of Co<sub>3</sub>O<sub>4</sub> for water electrolysis.