Amorphization-induced abundant coordinatively unsaturated Ni active sites in NiCo(OH)2 for boosting catalytic OER and HER activities at high current densities for water-electrolysis.

With rich corner sites and edge sites, the amorphous-crystalline NiCo(OH) 2 catalyst exhibits superior catalytic OER and HER activities at high current densities since the amorphization can promote the partial electron transfer from Co to Ni species and result in the tensile Ni-O bonds. The coordinatively unsaturated Ni sites in up-shift d -band centers toward Fermi level can reduce the antibonding states, creating optimized adsorption and promoting both OER and HER. [Display omitted] • Successfully synthesized 2D NiCo(OH) 2 catalyst with amorphous-crystalline structure. • Achieved high catalytic OER and HER activities at high current densities in the application of anion exchange membrane electrolysers for water-electrolysis. • Fundamentally investigated the structural characteristics and catalytic mechanism of amorphous catalysts.. The large overpotential required for oxygen evolution reaction (OER) is one of the major factors limiting the efficiency of electrochemical water-electrolysis for hydrogen production. In this work, to decrease OER energy barrier and obtain low overpotential, amorphous-crystalline NiCo(OH) 2 nanoplates are in-situ grown on nickel foam surface to form a catalyst-based electrode (ac-NiCo(OH) 2 /NF) for water-electrolysis application. As the inner amorphization of NiCo(OH) 2 results in increased electron density of the metal sites, leading to the formation of tensile Ni-O bond, the coordinatively unsaturated Ni sites in the down-shift d -band centers toward Fermi level can lower the antibonding states. This can lead to optimized adsorption and desorption energies for oxygen-containing intermediates for OER. As expected, the prepared ac-NiCo(OH) 2 /NF electrode presents a low overpotential of 364 mV to deliver 1000 mA cm−2 toward OER with impressively high robust stability. When this electrocatalyst electrode serves as both the anode and cathode, the assembled anion exchange membrane (AEM) electrolyser only needs a cell voltage of 1.68 V to drive the overall water-electrolysis process at a current density of 10 mA cm−2. [ABSTRACT FROM AUTHOR]