Fig. 5: Mechanism of releasing hydrogen atoms.

a Release rate of stored H(D) atoms for Cu/HxWO3 and Cu/DxWO3. b Calculated free energy diagram for transfer of H to catalyst surface over WO3 and Cu/WO3. The inserted figure shows the optimized H atom adsorption structure at various sites. c Electron density difference plot of Cu/WO3 surface. Electron accumulation and depletion are indicated in yellow and blue, respectively. The structural models in (b) and the differential charge density plot in (c) were visualized using VESTA47.