Milder solar thermochemical water splitting for hydrogen production: Coupling CH4-assisted reduction with Zr4+ doped CeO2

Solar-driven two-step thermochemical H 2 O splitting offers a viable pathway toward hydrogen production. CeO 2 has emerged as a leading material candidate. Nevertheless, the practical deployment of CeO 2 -based systems is constrained by the high temperatures required for reduction in the redox cycle. To overcome this limitation, a strategy combining CH 4 -assisted reduction with Zr 4+ doping was examined to enhance cycle performance under milder conditions. An integrated experimental and density functional theory (DFT) study reveals the mechanism at the atomic level. In a fixed-bed reactor, Ce 0.75 Zr 0.25 O 2 (25 mol% Zr 4+ doping) is found to be optimal, achieving a peak H 2 yield of 1.21 mmol g −1 at 900℃, attributed to improved oxygen exchange capacity and redox cycling stability. DFT calculations elucidate the complete H 2 O-splitting pathway on the doped surface, identifying OH* cleavage as the rate-determining step; the dopant lowers the energy barrier of this step and facilitates H 2 O adsorption, thereby enhancing overall efficiency. These results provide a mechanistic understanding of how doping modulates H 2 O splitting and offer guidance for the design of more efficient oxides for solar-fuel generation.