Z‐Scheme Heterojunction Photocatalysts: Principles, Engineering Strategies, and Applications in Solar‐Driven Energy Conversion and Environmental Remediation

ABSTRACT Heterogeneous photocatalysis has emerged as a pivotal sustainable technology for addressing the dual global challenges of energy scarcity and environmental pollution. Among the diverse heterojunction architectures developed to date, Z‐scheme configurations hold a uniquely advantageous position by emulating the two‐photosystem electron‐transfer cascade of natural photosynthesis. Unlike type‐II heterojunctions, which compromise redox driving force through charge accumulation at energetically intermediate band positions, Z‐scheme systems enable selective interfacial recombination of low‐energy carriers while simultaneously preserving highly reductive electrons and strongly oxidative holes at the outer band edges of the respective photosystems. This review provides a systematic and critical analysis of Z‐scheme heterojunction photocatalysts, spanning mechanistic principles, materials engineering strategies, and solar‐driven applications. Six performance‐enhancement strategies are comprehensively examined: morphological and dimensionality control, elemental doping, oxygen and nitrogen vacancy engineering, co‐catalyst loading, interface engineering, and reactive crystal facet optimization. The review then systematically covers five principal application domains: photocatalytic hydrogen evolution, oxygen evolution, overall water splitting, CO 2 photoreduction to solar fuels, photocatalytic nitrogen fixation, and selective hydrogen peroxide production, analyzing representative high‐performance systems with respect to their design logic and benchmark metrics. The review concludes with a forward‐looking discussion of 10 emerging research frontiers, including machine learning‐accelerated materials discovery, single‐atom catalysts, two‐dimensional van der Waals heterostructures, and techno‐economic assessment toward practical solar‐to‐chemical energy conversion.