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Solar driven carbon dioxide (CO2) recycling into hydrocarbon fuels using semiconductor photocatalysts offers an ideal energy conversion pathway to solve both the energy crisis and environmental degradation problems. However, the ubiquitous presence of carbonaceous contaminants in photocatalytic CO2 reduction system and the inferior yields of hydrocarbon fuels raise serious concerns about the reliability of the reported experimental results. Here in this perspective, we focus on the accurate assessment of the CO2 reduction products, systemically discuss the possible sources of errors in the product quantification, elaborate the common mistakes spread in the analysis of reaction products obtained in 13CO2 labelling experiments, and further propose reliable protocols for reporting the results of these isotopic tracing experiments. Moreover, the challenges and cautions in the precise measurement of O2 evolution rate are also depicted, and the amplification of the concentration of O2 in photoreactors well above the limit of detection is still demonstrated to be the most effective solution to this troublesome issue. We hope the viewpoints raised in this paper will help to assessment the reliability of the reported data in future, and also benefit the beginners that intend to dive in the photocatalytic CO2 reduction area. Graphical abstract

Artificial photoreduction of CO2 is vital for the sustainable development of human beings via solar energy storage in stable chemicals. This process involves intricate light‐matter interactions, but the role of incident light intensity in photocatalysis remains obscure. Herein, the influence of excitation intensity on charge kinetics and photocatalytic activity is investigated. Model photocatalysts include the pure graphitic carbon nitride (g‐C3N4) and g‐C3N4 loaded with noble/non‐noble‐metal cocatalysts (Ag, TiN, and CuO). It is found that the increase of light intensity does not always improve the electron utilization. Overly high excitation intensities cause charge carrier congestion and changes the recombination mechanism, which is called the light congestion effect. The electron transport channels can be established to mitigate the light‐induced effect via the addition of cocatalyst, leading to a nonlinear growth in the reaction rate with increasing light intensity. From experiments and simulations, it is found that the light intensity and active site density should be collectively optimized for increasing the energy conversion efficiency. This work elucidates the effect of light intensity on photocatalytic CO2 reduction and emphasizes the synergistic relationship of matching the light intensity and the photocatalyst category. The study provides guidance for the design of efficient photocatalysts and the operation of photocatalytic systems.

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