Magnetic Stimuli-Guided Multiple Charge Transfer Pathways for Boosted Overall Water Splitting

Abstract

Stimuli-driven electrochemical water splitting has emerged as a promising strategy to enhance the electrocatalytic efficiency for overall water splitting. In this context, a series of electrocatalysts─cobalt borophosphate (CoBP), Ni-doped cobalt borophosphate (NCBP), and Ag₂S-decorated NCBP (Ag₂S@NCBP)─have been rationally designed and synthesized via a sequential solvothermal and wet-chemical approach. The influence of an external magnetic field on borophosphate-based bifunctional electrocatalysts has been sparsely investigated, concentrating on reaction kinetics such as relaxation times and directional motion of electrolyte. The composite Ag₂S@NCBP demonstrates remarkable electrocatalytic performance, achieving overpotentials of 253 mV for the oxygen evolution reaction (OER) and 73 mV for the hydrogen evolution reaction (HER) under the influence of an external magnetic field. These results are attributed to the faster relaxation for processes involving interfacial charge transfer and a dynamically favorable flow pattern of electrolyte ions causing the easy accessibility of active sites at the electrode, quantified by the improved double-layer capacitance (C_dl) from 0.045 to 0.15 mF cm^–2. As a result, the reaction kinetics of electrodes for HER and the OER are enhanced as evidenced by low Tafel slopes of 74 mVdec^–1 (OER) and 72 mVdec^–1 (HER). Additionally, the bifunctional activity of Ag₂S@NCBP enables efficient overall water splitting with a low cell voltage of 1.54 V at 10 mA cm^–2, accompanied by excellent stability for up to 40 h. Therefore, controlling multiple charge transfer pathways by charge carrier relaxation times using an external magnetic field offers an alternate approach to optimizing water-splitting technologies for sustainable energy applications.