Special attention has being directed at improving the efficiency of energy conversion, which plays a pivotal role in slowing global warming and addressing energy-related challenges such as biomass power generation. Among them, the redox system of bioactive quinone as an electron carrier in organisms is promising for realizing truly efficient energy conversion in industrial use. In particular, aerobic organisms efficiently convert energy using dioxygen (O2) and quinones. In the photosystem II protein complex, plastoquinone exhibits two distinct electron-carrying modes depending on their proton environment: quinonehydroquinone (Q-H2Q, electron acceptor and electron donor) πconjugation. In the Q-H2Q redox system, the cyclohexa-2,5diene-1,4-dione (benzoquinone, Q) moiety accepts two electrons and two protons from reducing and acidic substrates, forming the reduced form, benzene-1,4-diol (hydroquinone, H2Q) moiety. The reverse conversion from H2Q to Q also occurs, thereby making reversible redox possible. Plastoquinone can transmit electrons to the next reaction system, such as the redox of O2 generating hydroperoxide (H2O2) that is expected as one of the nextgeneration energy materials. Thus, the research and development of a redox mechanism between biomimetic quinones and oxygen species are important. These species can be used in the energy industry as artificial electron carriers, in catalysis for energy conversion, and as fuel storage (H2O2). In decades, Meyer et al. and Hammes-Schiffer et al. investigated the relationship between electron transfer (ET) and proton transfer (PT), i.e., proton-coupled electron transfer (PCET), clarifying that the PCET mechanism embodies efficient ET in natural environments. PCET is distinguished from classical hydrogen-atom transfer as it involves concerted PT and ET in one-kinetic process. Referring to their pioneering works, we investigated electrochemical studies of PCET between H2Q and superoxide radical anion (O2 •-) using cyclic voltammetry of O2. In these studies, a quasireversible cyclic voltammogram (CV) of O2 forming O2 •-(Equation ( )) in the presence of H2Q isomers was obtained in N,N-dimethylformamide (DMF) solutions. Based on the CV of O2/O2 •-, we clarified the PCET mechanism between electrogenerated O2 •-and H2Q forming H2O2 and quinone radical anion (Q •-) (Equation ( )), and the electronic inductive and resonance effects of substituents on PCET that control and improve its efficiency. O2 + e -↔ O2 •-E°O2 = -1.284 V vs. Fc + /Fc (1)