Lithium ion battery-assisted solar-driven water splitting

Abstract

Electrocatalytic water splitting is an efficient strategy to substitute traditional fossil fuels with renewable energy H2. However, its scalable implementation, especially outdoors, has been hindered due to the lack of highly efficient and stable electrocatalysts and high-cost external electricity from the power grid. Here, we develop a hybrid nanostructure comprising N-doped carbon nanotube (NCNT) covalent-linked cobalt disulfide nanoparticles (CoS2-NPs) confined in hollow carbon nanocages (h-CoS@NC). As a bifunctional electrocatalyst for overall water splitting, the multi-heterostructure exhibits superior catalytic activities towards both hydrogen and oxygen-containing intermediates. Inspiringly, a two-electrode electrolyzer combined with the multi-heterostructure realizes a current density of 10 mA cm−2 at a low cell voltage of 1.58 V. When employing an anode of lithium ion battery (LIB), the h-CoS@NC delivers a high specific capacity of 1040 mAh g−1 at 0.1 A g−1 and maintains a considerable capacity of 648 mAh g−1, especially at rate of 5 A g−1. Furthermore, a large capacity of 582 mAh g−1 is achieved at 0.1 A g−1 for sodium ion battery. Moreover, theoretical calculations interpret that the enhanced electrochemical activities of h-CoS@NC should be attributed to the interaction between the CoS2 and carbon matrix, which effectively regulates the local electronic structures and weakens water adsorption/dissociation energies. As a proof-of-concept, a self-powered water splitting system integrating solar-charged lithium-ion battery with a water splitting electrolyzer achieves a steady H2 evolution rate at 0.4 A.