p-n junction-induced bipolar charge micro-regions driving enhanced redox kinetics for efficient overall water splitting

Abstract

Rational regulation of electrochemical reconfiguration and elucidation of activity sources constitute crucial yet challenging prerequisites for optimizing electrocatalyst activity. Herein, we report a novel p-n heterojunction catalyst comprising S-doped g-C3N4 (SCN) nanotubes coupled to NiFe LDH nanosheets (SCN@NiFe). This heterostructure fully leverages the semiconductor properties of SCN and the high catalytic activity of NiFe LDH, triggering a nanoscale built-in electric field (BIEF) and establishing space charge regions with dual charge separation characteristics. This charge environment facilitates the enrichment of H⁺ and OH- ions during the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) catalytic processes. Consequently, SCN@NiFe exhibits ultralow overpotentials of 82 mV for the HER and 227 mV for the OER at 10 mA cm-2 in alkaline electrolyte, along with a low cell voltage of 1.51 V for overall water splitting (OWS). Kelvin probe force microscopy (KPFM) and theoretical calculations collectively reveal the intensity and direction of BIEF within SCN@NiFe, demonstrating that this induced BIEF selectively optimizes the adsorption and desorption of key intermediates during both the HER and OER. This work elucidates the enhancement mechanism afforded by p-n junction in OWS, providing new insights into the electronic effects of asymmetric sites and their structure-activity relationships.