N self‐doped multifunctional chitosan biochar-based microsphere with heterogeneous interfaces for self-powered supercapacitors to drive overall water splitting

Abstract Due to the rising need for clean and renewable energy, green materials including biochar are becoming increasingly popular in the field of energy storage and conversion. However, the lack of highly active and stable electrode materials hinders the development of stable energy supplies and efficient hydrogen production devices. Herein, we fabricated stable, conductive, and multifunctional chitosan microspheres by a facile emulsion crosslinking solution growth and hydrothermal sulphuration methods as multifunctional electrodes for overall water splitting driven by supercapacitors. This material possessed three-dimensional layered conductors with favorable heterojunction interface, ample hollow and porous structures. It presented remarkably enhanced electrochemical and catalytic activity for both supercapacitors and overall water electrolysis. The asymmetric supercapacitors based on chitosan biochar microsphere achieved high specific capacitance (260.9 F g −1 at 1 A g −1 ) and high energy density (81.5W h kg −1 ) at a power density of 978.4 W kg −1 . The chitosan biochar microsphere as an electrode for electrolyze only required a low cell voltage of 1.49 V to reach a current density of 10 mA cm −2 , and achieved excellent stability with 30 h continuous test at 20 mA cm −2 . Then, we assembled a coupled energy storage device and hydrogen production system, the SCs as a backup power source availably guaranteed the continuous operation of overall water electrolysis. Our study provides valuable perspectives into the practical design of both integrated biochar-based electrode materials and coupled energy storage devices with energy conversion and storage in practical. Graphical Abstract