Metal vacancies and self-reconstruction of high entropy metal borates to boost the oxygen evolution reaction

Exploring highly efficient oxygen evolution reaction (OER) electrocatalysts is important for industrial water electrolysis. Herein, a new high entropy material was reported, i.e., an amorphous high entropy metal borate (CrMnCoNiFe)_0.2BO_x was synthesized by a new simple solvothermal method. The key of this new synthesis method was to obtain (CrMnCoNiFe)_0.2BO_x with a high specific surface area (446 m²/g) and porous structure, being expected to promote OER reaction. (CrMnCoNiFe)_0.2BO_x provided a low overpotential of 236 mV at 10 mA cm⁻², a reduced Tafel slope of 64 mV dec^–1, and good stability. The outstanding OER performance of (CrMnCoNiFe)_0.2BO_x was attributed to the high entropy structure, generation of metal vacancies, and self-reconstruction during OER. The Cr vacancies generated during the OER process have been demonstrated by Cr 2P XPS and EPR experiments. Various in situ and Ex-situ analyses such as In situ Raman, XPS, and TEM were used to investigate the self-reconstruction of the (CrMnCoNiFe)_0.2BO_x during the OER. The resulting metal (oxy)hydroxide was believed to be the true active center for OER. The DFT calculation showed the high entropy structure can reduce the adsorption and conversion energy barriers of oxygen-containing intermediates, matching well with the catalytic performance results. This study provided a new simple strategy to construct high entropy metal borate (CrMnCoNiFe)_0.2BO_x and would inspire the design of high-performance OER catalysts.