A self-circulating pathway for the oxygen evolution reaction

The oxygen evolution reaction (OER) suffers from the sluggish kinetics of traditional four-electron-transfer pathways (4e--OER). Herein, we propose a self-circulating electrochemical-thermal OER mechanism (SET-OER) as a new pathway for high-efficiency water oxidation. The SET-OER couples two consecutive reactions in the anode: (i) one-electron electrochemical oxidation of Ni(OH)2 to generate NiOOH and (ii) in situ thermal decomposition of NiOOH to release O2 and recover Ni(OH)2. Compared with the traditional 4e--OER, the SET-OER significantly reduces the potential for water oxidation to only 1.25 V vs. RHE at 10 mA cm-2 at 120 degrees C. The different dominant mechanisms as the temperature changes are discussed based on our experimental results and density functional theory calculations. This work provides new insights for the understanding of the OER process at high temperatures. The self-circulation between Ni(OH)2 and NiOOH during water oxidation significantly lowers the overpotential of the oxygen evolution reaction (OER).