2D Rhenium- and Niobium-Doped WSe 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 WSe, Re- or Nb-doped WSe 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 WSe 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 WSe (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. The cell also provided a specific energy density of 574.21 mWh kg and a power density of 5906 mW kg at 15 mA g. Under otherwise similar conditions, the pristine WSe and Nb-doped WSe showed photoenhanced induced capacitance of 43% and 27% at 15 mA g and supplied an energy density of 436.4 mWh kg and 202 mWh kg, respectively. As a result, a reasonable capacitance improvement obtained by the Re-WSe photoenhanced zinc-ion capacitor could provide a facile and constructive way to achieve a highly efficient and low-cost solar-electrochemical capacitor system.