Fig. 4: Origin of the enhanced transient performance attributed by the WO₃ layer.

a An equivalent circuit model for the control cell and hybrid cell. The values of CRR for the control cell (black) and hybrid cell (red) at time zero are listed in Supplementary Table 1. b, c Voltage–time profiles measured and fitted profiles of the hybrid cell and control cell upon switching the current density from 0.2 to 2 A cm⁻², 3, and 4 A cm⁻² at 30 °C (b) and 50 °C (c), respectively. d, e Anode overpotential of a hybrid cell (solid lines) and a control cell (dashed lines) vs. current density and H₂ utilization rate (d) and time (e) at different scan rates. 10 mL min⁻¹ H₂ (100% humidified) was fed to both the anodes and cathodes. f Voltage profiles of a hybrid cell and control cell in response to a current switching from 0.2 to 2 A cm⁻² at 30 °C. 50 mL min⁻¹ of H₂ (100% humidified) was fed to both the anodes and cathodes.