Tuning the Electronic Spin State of Catalysts by Strain Control for Highly Efficient Water Electrolysis

The electronic configuration is crucial in governing the binding strength of intermediates with catalysts, yet it is still challenging to control the catalysts’ surface electronic spin state. Here, it is demonstrated that through surface metal–organic framework transformation followed by acid etching, the electronic spin state of surface Co³⁺ ions on spinel Co₃O₄ can be transformed from t_2g 6 to the high electronic spin state of t_2g⁴e_g 2 by expanding the surface lattice constant, which significantly enhances the overlap of the e_g orbital of cobalt with the oxygen adsorbates, and greatly improves the intermediates adsorption and thus the oxygen evolution reaction activity. The high electronic spin rich Co₃O₄ electrode exhibits an anodic current density of 10 mA cm⁻² at an overpotential of 280 mV. The finding offers a rational design strategy to manipulate the electronic spin state of catalyst and the hybridization of molecular orbitals in water electrolysis.