Defect-engineered semiconductor nanomaterials for photocatalytic hydrogen evolution: mechanistic insights, design strategies, and future perspectives

Photocatalytic hydrogen production is an insistent route to solar fuel generation, yet its practical efficiency remains limited by charge recombination, photocorrosion, sluggish interfacial kinetics, and inadequate visible-light harvesting. Defect engineering offers a powerful solution by precisely reshaping semiconductor electronic structures, carrier dynamics, surface reactivity, and reaction pathways. Anion vacancies, cation deficiencies, dopant-induced distortions, and surface disorder can create active states, regulate charge separation, and optimise adsorption energetics across oxides, sulphides, nitrides, and carbon-based photocatalysts. Advances in defect-controlled synthesis and operando characterisation are enabling increasingly rational structure–activity relationships. However, defect instability, synthetic reproducibility, ambiguous defect quantification, inconsistent performance benchmarking, and scale-up remain critical barriers. Future progress demands an integrated paradigm coupling defect engineering with morphology control, heterointerface design, and device-level architectures. Such convergence can transform defect-rich photocatalysts from laboratory-scale materials into durable, high-efficiency platforms for economically viable solar hydrogen production.