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-C3 N4 ) and g-C3 N4 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.
Keywords: CO2 reduction; cocatalysts; light congestion; light intensity; photocatalysis.
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