Rational construction of loosely packed nickel nanoparticulates with residual HCOO ligands derived from a Ni-MOF for high-efficiency electrocatalytic overall water splitting

Abstract

Introducing organic ligands into metals or metal oxides is an important approach to fabricating highly efficient, scalable and inexpensive electrocatalysts for widespread energy-related applications. Taking advantage of the uniqueness of MOFs, loosely packed nanoparticulate Ni-250-2@NF architecture with the existence of residual HCOO ligands is synthesized via using Ni-MOF@NF as a precursor followed by calcination in a H₂ atmosphere at a mild temperature (250 °C). The optimal Ni-250-2@NF exhibits a boosted HER activity and high electrocatalytic OER activity (overpotential of 56 mV @ 10 mA cm⁻² for the HER and 289 mV @ 10 mA cm⁻² for the OER). The remarkable catalytic performance is attributed to the unique presence of residual organic ligands, which not only accelerates electron transfer between the catalyst surface and electrolyte, but also optimizes the hydrophilicity and aerophobicity. Density functional theory (DFT) calculations also reveal that the existence of the HCOO organic ligand (Ni(111)–HCOO) can both accelerate water adsorption/dissociation and effectively adsorb the generated H, thus improving the alkaline HER activity of Ni-250-2@NF electrocatalyst. Additionally, the practical application of Ni-250-2@NF as a bifunctional catalyst for the overall water splitting reaction yields a low cell voltage of 1.58 V to reach a current density of 10 mA cm⁻². This study paves an attractive route to explore materials with ligand residue structures as highly efficient HER/OER bifunctional catalysts for the electrolysis of overall water splitting.