High-entropy optimizing d-orbital electronic configuration of metal organic framework for high-current-density anion exchange membrane water electrolysis

Abstract

Water electrolysis provides a promising way for hydrogen production through renewable power sources. The exploration of non-precious metal-based electrocatalysts capable of sustaining high current densities for water electrocatalysis is of critical importance. Herein, we develop a high-entropy Mil53 metal organic framework (denoted as Mil53-HE) bifunctional electrocatalyst with improved performance for overall water splitting at large current densities. The improved activity and stability of Mil53-HE for water electrolysis stem from the optimized electronic configurations of d-orbitals in the metal centers, as the overall d-band center ($\bar{E}$_d) is upshifted and the total number of d-orbital electrons in the supercell (∑N_d) is decreased of Mil53-HE. Therefore, the reduced reaction energy barriers and enriched unpaired d-electrons promote both the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). As a result, the HER and OER activities of Mil53-HE surpass those of their benchmark Pt/C and RuO₂, respectively. Meanwhile, the HER and OER mechanisms on Mil53-HE are revealed by in-situ characterizations and theoretical calculations. Furthermore, the anion exchange membrane water electrolysis cell with Mil53-HE can stably operate at large current densities with small voltages (1.9 V at 0.52 A cm^-2 and 2.1 V at 1.48 A cm^-2), demonstrating good feasibility for practical application.