Selenic Acid Etching Assisted Vacancy Engineering for Designing Highly Active Electrocatalysts toward the Oxygen Evolution Reaction

Oxygen evolution electrocatalysts are central to overall water splitting, and they should meet the requirements of low cost, high activity, high conductivity, and stable performance. Herein, a general, selenic-acid-assisted etching strategy is designed from a metal-organic framework as a precursor to realize carbon-coated 3d metal selenides Mm Sen (Co0.85 Se1- x , NiSe2- x , FeSe2- x ) with rich Se vacancies as high-performance precious metal-free oxygen evolution reaction (OER) electrocatalysts. Specifically, the as-prepared Co0.85 Se1- x @C nanocages deliver an overpotential of only 231 mV at a current density of 10 mA cm-2 for the OER and the corresponding full water-splitting electrolyzer requires only a cell voltage of 1.49 V at 10 mA cm-2 in alkaline media. Density functional theory calculation reveals the important role of abundant Se vacancies for improving the catalytic activity through improving the conductivity and reducing reaction barriers for the formation of intermediates. Although phase change after long-term operation is observed with the formation of metal hydroxides, catalytic activity is not obviously affected, which strengthens the important role of the carbon network in the operating stability. This study provides a new opportunity to realize high-performance OER electrocatalysts by a general strategy on selenic acid etching assisted vacancy engineering.