Heavily Doped Trifunctional WS₂ Semiconductor Exhibiting Efficient Water Electrocatalysis and Supercapacitor Performance

The development of a bifunctional electrocatalyst capable of producing hydrogen and oxygen fuels simultaneously through electrochemical water splitting is crucial in electrochemical energy conversion technology. Two-dimensional transition metal dichalcogenide semiconductors, such as MoS₂ and WS₂, are known to exhibit excellent hydrogen evolution reaction (HER) activity and supercapacitor performance. However, these semiconductor catalysts show relatively poor oxygen evolution reaction (OER) activity due to slow kinetic reactions. Here, we report the trifunctional behavior of Fe and Co heavily (17 atomic %) doped WS₂ semiconductor electrodes with efficient hydrogen and oxygen evolution and supercapacitor performance in an alkaline electrolyte. It is observed that heavy doping improves the HER and OER activities of Fe (17% Fe-WS₂) and Co-doped (17% Co-WS₂) WS₂ electrodes. The best electrode, i.e., 17% Co-WS₂, delivered a cathode and anode current density of 10 mA cm^-2 at an overpotential of 130 and 418 mV vs reversible hydrogen electrode with a low Tafel slope of 70 and 74 mV dec^-1 in 1 M KOH electrolyte, respectively. Further, heavily doped WS₂ symmetric supercapacitor electrodes exhibit improved storage performance with a high specific capacitance of 257 F g^-1 (at 0.5 A g^-1) and a high energy density of 17.5 Wh kg^-1 (at a power density of 1000 W kg^-1) in a 17% Co-WS₂ electrode. The enhanced active sites and electrical conductivity of WS₂ after heavy doping are responsible for improving the catalytic and storage performance of the electrocatalyst and supercapacitor electrode. We demonstrate that heavy doping is beneficial for improving the electrochemical energy conversion and storage performance of WS₂-based electrodes.