The role of elevated temperatures in electrolysis has generally been regarded as accelerations of electron transport, mass transport, and adsorption/desorption processes. In the present work, with first-principles calculations, we demonstrate that thermally activated on-surface reactions can significantly increase the efficiency of energy conversions in electrolysis via a thermally and electrically cascaded mechanism. In the oxygen evolution reaction (OER), to be specific, the formation of high-energy *OOH on Fe can be assisted by thermally activated combination of *O and *OH on the surface of ironbenzenehexathiol coordination polymer (Fe-BHT). Such theoretical predictions are then confirmed by our experimental measurements. The OER efficiency on Fe-BHT increases with increasing temperature and outperforms the state-of-the-art IrO 2 catalyst at around 80 °C. This research may shed light on an avenue for designing and preparing electrocatalysts with enhanced catalytic performance.