Photocatalytic CO2 reduction through heterojunction engineering: environmental and energy perspectives

Photocatalytic CO 2 reduction is an appealing approach for producing value-added chemicals and fuels from greenhouse gases. However, it faces challenges because of low activity, poor selectivity, and catalyst instability. Heterojunction engineering is a viable approach to improve charge-carrier separation and transfer and enhance light absorption in CO 2 -reduction photocatalysts; however, incomplete mechanistic understanding and inconsistent evaluation often hinder this strategy. This review covers research progress on CO 2 reduction from a heterojunction perspective. First, it reviews thermodynamic and kinetic challenges, including limited CO 2 activation, the multielectron nature of the reduction reactions, and competition from the hydrogen evolution reaction. Subsequently, the review discusses different heterojunction structures, including Type II, Z-scheme, S-scheme, and Schottky or p–n junctions, in the context of charge transfer and separation, emphasizing the internal electric fields induced at the heterojunction interface and charge transfer through junction defects after Fermi-level alignment. The review also compares structure–activity relationships across major material systems and practical challenges related to stability, scalability, and environmental impact. It also reviews issues and inconsistencies in benchmarking and reports as current challenges in heterojunction engineering for photocatalytic CO 2 reduction.