Vertically aligned Ni/NiO nanocomposites with abundant oxygen deficient hetero-interfaces for enhanced overall water splitting

The design of heterostructured transition metal-based electrocatalysts with controlled composition and interfaces is key to increasing the efficiency of the water electrolysis and the elucidation of reaction mechanisms. In this work, we report the synthesis of well-controlled vertically aligned Ni/NiO nanocomposites consisting of Ni nanoclusters embedded in NiO, which result in highly efficient electrocatalysts for overall water splitting. We show that such a high catalytic efficiency toward both the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) originates from a synergetic effect at Ni/NiO interfaces that significantly reduces the energy barrier for water dissociation, and favours the formation of reactive H* intermediates on the Ni side of the interface, and OHads on the NiO side of the interface. A study of water chemisorption based on near-ambient pressure photoelectron spectroscopy indicates that the abundant hetero-interfaces in Ni/NiO nanocomposite promote the dissociation of water with a three-fold increase in the surface concentration of OHads compared with pure NiO. Density functional theory calculations indicate that Ni/NiO interface leads to the reduction of the water dissociation energy barrier due to a high concentration of oxygen vacancies at NiO side of the interface, whereas the formation of highly active metallic Ni sites with an optimal value of Gibbs free energy of H* (Delta G(H*) = -0.16 eV) owes to a favourable adjustment of the electron energetics at the interface, thus accelerating the overall electrochemical water splitting.

Automated summary

This study reports the synthesis of vertically aligned Ni/NiO nanocomposites and their highly efficient catalytic activity for overall water splitting. The catalytic effect originates from the synergetic effect at the Ni/NiO interfaces, which reduces the energy barrier for water dissociation and favors the formation of reactive intermediates. The results suggest that the hetero-interfaces in the nanocomposites promote the dissociation of water, leading to improved efficiency for water electrolysis.