Heat-Electricity Coupling Driven Cascade Oxidation Reaction of Redox Couple and Water.

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 Ni ²⁺ /Ni ³⁺ 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.