Hematite has a great potential as a photoanode for photoelectrochemical (PEC) water splitting by converting solar energy into hydrogen fuels, but the solar-to-hydrogen conversion efficiency of state-of-the-art hematite photoelectrodes are still far below the values required for practical hydrogen production. Here, we report a core-shell formation of gradient tantalum-doped hematite homojunction nanorods by combination of hydrothermal regrowth strategy and hybrid microwave annealing, which enhances the photocurrent density and reduces the turn-on voltage simultaneously. The unusual bi-functional effects originate from the passivation of the surface states and intrinsic built-in electric field by the homojunction formation. The additional driving force provided by the field can effectively suppress charge–carrier recombination both in the bulk and on the surface of hematite, especially at lower potentials. Moreover, the synthesized homojunction shows a remarkable synergy with NiFe(OH)_x cocatalyst with significant additional improvements of photocurrent density and cathodic shift of turn-on voltage. The work has nicely demonstrated multiple collaborative strategies of gradient doping, homojunction formation, and cocatalyst modification, and the concept could shed light on designing and constructing the efficient nanostructures of semiconductor photoelectrodes in the field of solar energy conversion.

The continuing increase in atmospheric carbon dioxide (CO ₂ ), a major greenhouse gas and accelerating climate change are driving demand for innovative mitigation strategies. The photocatalytic CO ₂ reduction reaction (PCO ₂ RR) presents a promising and sustainable route to convert CO ₂ into useful hydrocarbons and fuels utilizing sunlight, thereby mitigating CO ₂ emissions. This review examines the developmental aspects of light‐driven CO ₂ conversion using organic polymeric photocatalysts, focusing on carbon nitrides (CNs), covalent triazine frameworks (CTFs), and covalent organic frameworks (COFs). These materials are verified to possess great potential for PCO ₂ RR, because they offer tunable band gaps, large surface areas, efficient light absorption, and remarkable activity and selectivity in photocatalysis. In this review, the comprehensive analysis of photocatalytic materials (e.g., CNs, CTFs, and COFs) are thoroughly discussed, along with their mechanisms, historical advancements, and urgent roles in PCO ₂ RR. Strategies for enhancing the CO ₂ photoreduction efficiency of CNs, CTFs, and COFs are also highlighted. Each organic material brings distinct advantages. The review also addresses critical challenges, such as improving efficiency and managing charge transport dynamics for PCO ₂ RR. Finally, the review underscores the need to develop scalable CO ₂ conversion applications, advance organic photocatalyst material science, and support sustainable energy conversion technologies.

In the realm of photoconversion of CO ₂ into high-value chemicals, the importance of near-infrared (NIR) light is gradually gaining recognition.