Photovoltaic-powered supercapacitors for driving overall water splitting: a dual-modulated 3D architecture

Abstract

Due to the growing demand for clean and renewable hydrogen fuel, there has been a surge of interest in electrocatalytic water-splitting devices driven by renewable energy sources. However, the feasibility of self-driven water splitting is limited by inefficient connections between functional modules, lack of highly active and stable electrocatalysts, and intermittent and unpredictable renewable energy supply. Herein, we construct a dual-modulated three-dimensional (3D) NiCo2O4@NiCo2S4 (denoted as NCONCS) heterostructure deposited on nickel foam as a multifunctional electrode for electrocatalytic water splitting driven by photovoltaic-powered supercapacitors. Due to a stable 3D architecture configuration, abundant active sites, efficient charge transfer, and tuned interface properties, the NCONCS delivers a high specific capacity and rate performance for supercapacitors. A two-electrode electrolyzer assembled with the NCONCS as both the anode and the cathode only requires a low cell voltage of 1.47 V to achieve a current density of 10 mA cm−2 in alkaline electrolyte, which outperforms the state-of-the-art bifunctional electrocatalysts. Theoretical calculations suggest that the generated heterointerfaces in NCONCS improve the surface binding capability of reaction intermediates while regulating the local electronic structures, which thus accelerates the reaction kinetics of water electrolysis. As a proof of concept, an integrated configuration comprising a two-electrode electrolyzer driven by two series-connected supercapacitors charged by a solar cell delivers a high product yield with superior durability.