Unravelling the roles of H⁺, Na⁺ and K⁺ cations over the self-photorechargeability of a Pt-mediated MoO₃ photoanode-driven photoelectrochemical system: Experimental and DFT study

Renewable energy systems are a critical game changer of the 21st century, where various fundamental and applied researches are realised for advancing the practicality of energy provision at a multitude of scales. This study aimed to unravel the roles of H⁺, Na⁺ and K⁺ cations over the self-photorechargeability of a novel Pt/MoO₃ photoanode-driven photoelectrochemical (PEC) system with dual-functionalities of solar photon-to-electron conversion and storage of electrons. FE-SEM analysis showed that the Pt/MoO₃ photoanode consists of a 3D plate-like surface structure with favourable void spaces and internal channels for promoting the photo-intercalation and de-intercalation reactions. HR-TEM analysis validated the formation of interfacial heterojunction between Pt co-catalyst and MoO₃ in Pt/MoO₃ photoanode for improving the overall work function as well as synergising the self-photorechargeability properties. Further current and charge density profiling for the Pt/MoO₃-driven self photorechargeable system over three consecutive charging-discharging cycles demonstrated a slow charge decay kinetics in H⁺ electrolyte resulted in a relatively high charge density of 5.53 mC/cm². EIS Nyquist analysis depicted a smaller arc radius in the Nyquist plot of the Pt/MoO₃-driven self photorechargeable system which indicates a lower charge transfer impedance and thus, facilitating a better separation efficiency of electron-hole pairs than bare MoO₃. From the systematic study on H⁺, Na⁺ and K⁺ cations with varying concentrations over the self-photorechargeability of Pt/MoO₃-driven system, it was revealed that the K⁺ electrolyte at a low concentration of 0.01 M resulted in the highest charge density of 22.89 mC/cm². Other H⁺ and Na⁺ cations and concentrations are unfavourable due to the potentiality in inducing structural distortment as well unparallel rates of charging and discharging in the Pt/MoO₃-driven system. Finally, DFT was simulated and the calculated binding energies (E_ads) between the studied cations with the Pt/MoO₃ crystalline framework validated the experimental finding.