Revisiting the Concept of Photocatalysis: An Analysis from the Chemical Potentials

A renewed criterion of photochemical free energy is proposed by introducing the concept of absorbed photon chemical potential. The so-called “photocatalytic” and “photosynthetic” processes are both spontaneous reactions in the corresponding physical fields. The misconception towards the classification method according to thermodynamic spontaneity of chemical reactions can be rectified. In this new vision, the photocatalysts in photochemical systems act as the “mediator” between the reactants and photons (a special reactant) to accelerate the kinetics process, which is exactly what the catalysts does.