2D Rhenium- and Niobium-Doped WSe₂ Photoactive Cathodes in Photo-Enhanced Hybrid Zn-Ion Capacitors

Designing a multifunctional device that combines solar energy conversion and energy storage is an appealing and promising approach for the next generation of green power and sustainable society. In this work, we fabricated a single-piece device incorporating undoped WSe₂, Re- or Nb-doped WSe₂ photocathode, and zinc foil anode system enabling a light-assisted rechargeable aqueous zinc metal cell. Comparison of structural, optical, and photoelectric characteristics of undoped and doped WSe₂ has further confirmed that ionic insertion of donor metal (rhenium and niobium) plays an important role in enhancing photoelectrochemical energy storage properties. The electrochemical energy storage cell consisting of Re-doped WSe₂ (as the photoactive cathode and zinc metal as anode) showed the best photodriven enhancement in the specific capacitance of around 45% due to efficient harvesting of visible light irradiation. The assembled device exhibited a loss of 20% of its initial specific capacitance after 1500 galvanostatic charge-discharge cycles at 50 mA g^-1. The cell also provided a specific energy density of 574.21 mWh kg^1- and a power density of 5906 mW kg^1- at 15 mA g^-1. Under otherwise similar conditions, the pristine WSe₂ and Nb-doped WSe₂ showed photoenhanced induced capacitance of 43% and 27% at 15 mA g^-1 and supplied an energy density of 436.4 mWh kg^1- and 202 mWh kg^1-, respectively. As a result, a reasonable capacitance improvement obtained by the Re-WSe₂ photoenhanced zinc-ion capacitor could provide a facile and constructive way to achieve a highly efficient and low-cost solar-electrochemical capacitor system.