Shape‑Dependent Co 3 O 4 /Zn 2 InS 4 p–n Facet Heterojunctions: Modulating Built‑In Electric Field Toward Long‑Lived Charge Separation for Boosted Photocatalytic Hydrogen Evolution

ABSTRACT Photocatalytic water splitting for H 2 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 Co 3 O 4 nanocrystals (nanocubes, nanoplatelets, and nanorods) coupled with Zn 2 InS 4 nanosheets for enhanced photocatalytic H 2 evolution. Among these, Co 3 O 4 nanocubes exhibit the highest H 2 evolution activity when integrated with Zn 2 InS 4 . 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 Co 3 O 4 /Zn 2 InS 4 heterojunction achieves a remarkable H 2 evolution rate of 8570 µmol h −1 g −1 and excellent stability under visible‐light irradiation—an 11‑fold improvement over pristine Zn 2 InS 4 —with an apparent quantum yield of 9.5% at 420 nm. This work underscores the pivotal role of Co 3 O 4 morphology in tuning interfacial properties and offers a generalizable, noble‐metal‐free strategy for developing high‐performance p−n heterojunction photocatalysts for sustainable H 2 production and beyond.