The burgeoning field of photocatalytic reduction of CO₂ has emerged as a remarkable promising solution to address some of the most pressing global energy and environmental issues which we face today. Researchers around the global have been striving to augment the efficiency of CO₂ photocatalytic reduction, employing strategies that range from modifying the fundamental properties of photocatalysts to suppress the electron-hole recombination, optimizing reaction conditions to achieve the highest yield, and conceptualizing and constructing photoreactors to improve the adsorption process. Among these factors, the photoreactor plays a critical role in enhancing the overall photocatalytic efficiency. Understanding the various types of photoreactors and their operational dynamic can significantly influence the experimental design, thus guiding the data collecting and analysis. Compared to the solid-liquid phase, gas-solid phase photocatalytic reduction of CO₂ is gaining recognition for its potential advantages, such as rapid molecular diffusion rates, adjustable CO₂ concentrations, and uniform and sufficient light exposure. Nonetheless, the currently reported gas-solid phase photoreactors are still in their infancy. In this review, we dissect the underlying mechanism of photocatalytic CO₂ reduction and the performance evaluation criteria of photoreactors, and review the development process of gas-solid phase photoreactors. Furthermore, we explore the evolution of gas-solid phase photoreactors, elucidating their growth trajectory and future possibilities. We present a comprehensive classification of gas-solid phase photoreactors, offering a new insight into their design and functionality, summarizing their strengths and inevitable limitations. Finally, we provide a forward-looking perspective on the future developmental prospects of carbon neutrality.

Metal-free catalyst for photocatalytic production of H₂O₂ is highly desirable with the long-term vision of artificial photosynthesis of solar fuel. In particular, the specific chemical bonds for selective H₂O₂ photosynthesis via 2e^– oxygen reduction reactions (ORR) remain to be explored for understanding the forming mechanism of active sites. Herein, we report a facile doping method to introduce boron-nitrogen (B–N) bonds into the structure of graphitic carbon nitride (g-C₃N₄) nanosheets (denoted as BCNNS) to provide significant photocatalytic activity, selectivity and stability. The theoretical calculation and experimental results reveal that the electron-deficient B–N units serving as electron acceptors improve photogenerated charge separation and transfer. The units are also proved to be superior active sites for selective O₂ adsorption and activation, reducing the energy barrier for *OOH formation, and thereby enabling an efficient 2e^– ORR pathway to H₂O₂. Consequently, with only bare loss of activity during repeated cycles, the optimal H₂O₂ production rate by BCNNS photocatalysts reaches 1.16 mmol·L^–1·h^–1 under 365 nm-monochrome light emitting diode (LED_365nm) irradiation, increasing nearly 2–5 times as against the state-of-art metal-free photocatalysts. This work gives the first example of applying B–N bonds to enhance the photocatalytic H₂O₂ production as well as unveiling the underlying reaction pathway for efficient solar-energy transformations.