The EPOC effect can be observed in a wide range of catalytic reactions with several kinds of metal or metal oxide catalysts mostly coupled with solid electrolytes. Versatile catalytic reactions including hydrogenations, dehydrogenations, oxidations, reductions, isomerizations, and chemical decompositions have been known to be promoted electrochemically on various transition metal and oxide catalysts (e.g., Pt, Pd, Rh, Ag, Au, Ni, Cu, Fe, IrO, RuO) deposited on O (YSZ), Na or K, H, F, aqueous, CeO conductors, and molten salts. The main focus and purpose of numerous studies regarding the EPOC effect have been reported so far can be classified as follows: 1) the elucidation of examples for the EPOC effects on specific catalytic reactions with environmental or industrial interest (ex. NOx reduction and hydrocarbons oxidations), 2) the mechanistic investigation of the origin of the EPOC effects (mainly focusing on the system with oxygen-ion conducting electrolytes), 3) the large-scale application and commercialization of the chemical reactions promoted by the EPOC effects along with development of novel compact monolithic reactors and 4) the utilization and incorporation of the EPOC effect in high or low-temperature fuel cell systems.