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/cm(2). 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/cm(2). 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.

Automated summary

This study investigated the self-photorechargeability of a Pt/MoO3 photoanode-driven photoelectrochemical system and found that the presence of H+, Na+, and K+ cations had different effects on the charge density of the system. It was observed that the Pt/MoO3 system exhibited higher charge density in H+ electrolyte, while a low concentration of K+ electrolyte resulted in the highest charge density. Additionally, FE-SEM and HR-TEM analysis revealed the importance of the surface structure of the Pt/MoO3 photoanode and the formation of an interfacial heterojunction between Pt co-catalyst and MoO3 in improving the system's performance.