Shape‑Dependent Co3O4/Zn2InS4 p-n Facet Heterojunctions: Modulating Built‑In Electric Field Toward Long‑Lived Charge Separation for Boosted Photocatalytic Hydrogen Evolution.

Abstract

Photocatalytic water splitting for H2 generation represents a promising pathway for converting solar energy into clean chemical fuels, yet the efficiency is often limited by sluggish charge separation and inadequate utilization of photogenerated carriers. Here, we rationally design a novel p-n heterojunction photocatalyst composed of shape-controlled Co3O4 nanocrystals (nanocubes, nanoplatelets, and nanorods) coupled with Zn2InS4 nanosheets for enhanced photocatalytic H2 evolution. Among these, Co3O4 nanocubes exhibit the highest H2 evolution activity when integrated with Zn2InS4. Systematic characterization reveals that the heterojunction interface generates a robust built-in internal electric field (IEF) through via controlled engineering of facet heterojunctions, which strongly drives the separation and migration of electron-hole pairs. In situ X-ray photoelectron spectroscopy, femtosecond-to-microsecond transient spectroscopy, and theoretical calculations provide the direct evidence for a new Type‑I charge-transfer pathway with significantly prolonged carrier lifetimes. The optimal Co3O4/Zn2InS4 heterojunction achieves a remarkable H2 evolution rate of 8570 µmol h-1 g-1 and excellent stability under visible-light irradiation-an 11‑fold improvement over pristine Zn2InS4-with an apparent quantum yield of 9.5% at 420 nm. This work underscores the pivotal role of Co3O4 morphology in tuning interfacial properties and offers a generalizable, noble-metal-free strategy for developing high-performance p-n heterojunction photocatalysts for sustainable H2 production and beyond.