2D Cocrystallized Metal–Organic Nanosheet Array as an Efficient and Stable Bifunctional Electrocatalyst for Overall Water Splitting

Abstract

Electrochemical water splitting to produce hydrogen can meet growing energy needs while balancing the impact of severe fossil fuel consumption. To date, it is still greatly desirable to obtain bifunctional and precious metal-free electrocatalysts for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) simultaneously during overall water splitting toward actual applications. Herein, we develop a cocrystallized strategy to obtain a Co/Ni-based mixed metal–organic nanosheet array (NiCo-9AC-AD) on a nickel foam (NF) substrate with controlled composition and morphology as a bifunctional electrocatalyst. The optimized Ni0.3Co0.7-9AC-AD/NF reveals efficient electrocatalytical activity and very low overpotentials of 350 mV for OER to attain a current density value of 100 mA cm–2 and 143 mV for HER at 10 mA cm–2. This is due to the synergistic effect of Ni/Co double catalytical active sites and ultrathin 2D nanosheet topology. More importantly, as an exceptionally active and stable electrocatalyst, the NiCo-9AC-AD nanosheet array requires merely 1.56 V to deliver a current density value of 10 mA cm–2 in an overall water-splitting application. This work thus develops a simple approach to obtain a highly active cocrystallized metal–organic hybrid for both OER and HER, which may open the way to rational design of similar Ni/Co-based supramolecular systems toward electrochemical and energy storage applications.