Definition of photocatalysis: Current understanding and perspectives

Photocatalysis is a prospective way to efficiently convert and store solar energy, which is beneficial for achieving the Sustainable Development Goals (SDGs) proposed by the United Nations. However, with almost one century research on this topic, there are still controversies about the definition of photocatalysis. Wherein, the difference between photocatalytic and photosynthetic processes is especially argued. In this brief review, the timeline for major discovery about photocatalysis is combed and the current understanding of photocatalysis is summarized. Through analogy with the electrocatalysis, a revisiting definition towards photocatalysis is presented. The term "photochemical potential" is proposed based on regarding photons as reactants. Accordingly, the so-called "photo catalytic" and "photosynthetic" processes are both spontaneous reactions in the corresponding physical fields, which reveals that all light-induced catalytic processes can be generally defined as photocatalysis.