High barriers of water oxidation mediated by redox couple continuously challenge to maximizing efficiency from renewables to hydrogen energy. Here, an electricity-heat complementary strategy was achieved by a heat-electricity-sensitive interconversion of the α-Ni(OH)2/γ-NiOOH redox couple. In our strategy, the thermo-activated effects significantly lower the barrier energies of initial electroxidation of Ni2+/Ni3+ and subsequent chemical water oxidation to the nearly equal value via coupling a low-grade heat field (<100 °C), thereby achieving a consecutive two-step cascade reaction without kinetic delay. As a result, the cascaded water splitting reaction can happen at an extremely low overpotential of 130 mV and affords a low cell voltage of 1.73 V at 100 mA cm-2 at 90 °C in alkaline electrolyte. Our findings open a new avenue to produce hydrogen by complementation and gain effects of different-grade energies.