The Ni─Cl─Ni Sites Bridged by Chlorine to Stabilize Short-Range Order in Nickel Complex for Amorphous Electrocatalysts

Abstract

Amorphous catalysts have shown great promise for electrocatalysis due to their unique short-range ordered structures, which allow performance optimization through structural engineering. However, inadequate structural collapse during crystalline-amorphous transformations compromises coordination environment retention and impedes understanding of structure-property/performance correlations in disordered amorphous catalysts/materials. In this study, we ingeniously introduced a chloro-bridging structure, which successfully preserves the µ₂─Cl bridging motif in the nickel complex precursor (Ni₂(µ₂─Cl)(HL)₂(CH₃OH)(H₂O)Cl). This achievement enables the synthesis of a highly stable amorphous catalyst, a-250-I, featuring an enhanced short-range order. Through comprehensive experimental and computational investigations, it is discovered that the remarkable activity enhancement can be ascribed to the dynamic transition from μ₂─Cl to μ₂─O bridging at the nickel site. This transformation elegantly tunes the d-orbital energy levels to lower values, unleashing a cascade of effects that accelerate the reaction kinetics and catapult the electrocatalytic performance to new heights. At 10 mA·cm⁻² current density, the optimized a-250-I catalyst achieves low overpotentials of 1.47 V (OER) and 1.36 V (UOR), showcasing robust stability with dual-functional catalytic capability. This strategy offers a controllable way to stabilize the short-range ordering of amorphous catalysts for enhancing catalytic activity by modulating the electronic structure through local bridge coordination.