Dual-functional photocatalysts for in-situ generation of proton (H⁺) and photoreduction of carbon dioxide (CO₂): A review

To date, the question of how to address the challenges associated with urgent global carbon emissions while harnessing renewable energy remains unanswered, a challenge that our world has so far failed to solve. Among many strategies, artificial photosynthesis systems that mimic natural processes to enable the in-situ generation of protons (H⁺) for hydrogenation of CO₂ into value-added carbonaceous fuels represent a promising route. Herein, this review highlights recent advancements in solar-driven photoreduction of CO₂ in the presence of H⁺. Emphasis is placed on photocatalysts and their fundamental mechanisms governing the photoreduction of CO₂, including light absorption, charge-carrier dynamics, surface adsorption, and photocatalytic efficiency. The concept of dual-functional photocatalytic active CO₂ via in-situ generation of H⁺ provides a sustainable and carbon-neutral pathway to produce renewable energy. Although many efforts have been made, the overall energy conversion efficiency remains limited by the complexity of multistep reactions, rapid electron-hole recombination rates, and low quantum efficiencies. This review critically examines the key technical challenges and current strategies for further improving solar-to-fuel efficiency, with a focus on developing novel photocatalysts. Additionally, combining photocatalysis with biocatalysis, electrocatalysis, photoelectrochemical architectures, or membrane-assisted processes may enable the practical applications of artificial photosynthesis and help bridge the efficiency gap between lab-scale to industrial-scale.