Schottky Heterojunction Photocatalysts for Efficient CO₂ Reduction: Mechanisms, Advances, and Future Prospectives

The increasing concentration of atmospheric CO₂ has accelerated the global demand for sustainable carbon mitigation technologies. The solar-energy-driven photocatalytic CO₂ reduction provides an eco-friendly and effective method to transform CO₂ to useful fuels and chemicals. However, conventional semiconductor photocatalysts often exhibit low efficiency owing to fast recombination of photogenerated electron and hole pairs along with its limited light absorption capability. In this context, Schottky heterojunctions formed by coupling metals with semiconductors have been recognized as an efficient solution to improve charge separation, light harvesting, and catalytic stability. This review comprehensively summarizes the fundamentals of Schottky heterojunctions, its synthesis strategies, and the charge transfer processes that facilitates effective photocatalytic CO₂ reduction. Unlike previous reviews primarily focused on conventional semiconductor heterojunctions or generalized photocatalytic CO₂ conversion systems, this review critically correlates Schottky barrier engineering, interfacial charge transfer, and product selectivity in metal-semiconductor photocatalysts. Particular emphasis is placed on structure-activity relationships, plasmonic enhancement, defect engineering, and mechanistic pathways governing formation of selective carbon-based products. Various metal-semiconductor systems including noble metal-based (Au, Ag, Pt) and earth-abundant metal-based (Cu, Ni, Co) heterostructures, are discussed with emphasis on its synthesis strategies, structural configurations, and performance enhancement factors. Furthermore, the role of plasmonic effects, barrier height modulation, and interfacial engineering in optimizing photocatalytic activity is elucidated. Finally, the article outlines the existing limitations and future perspectives in the design of cost-effective, stable, and scalable Schottky heterojunction photocatalysts, aiming to establish a robust foundation for next-generation solar-driven CO₂ reduction technologies.