Tuning the photoelectrochemical activity of few-layer WS2 through phosphorus doping for efficient water splitting

Photoelectrochemical (PEC) water splitting has emerged as a promising strategy for sustainable hydrogen production. In this study, few-layer WS 2 and phosphorus-doped WS 2 (WS 2 /P) thin films are synthesized by a one-step chemical vapor deposition (CVD) method and evaluated as photocathodes for hydrogen evolution. Structural and optical characterizations confirm the formation of predominantly few-layer WS 2 -based films and phosphorus-induced structural and electronic modifications while preserving the fundamental optical characteristics of WS 2 . Photoluminescence measurements reveal thickness-dependent emission and reduced PL intensity following phosphorus incorporation, indicating modified carrier relaxation and recombination pathways. The electrical and PEC responses of WS 2 and WS 2 /P are systematically investigated under blue (405 nm), green (532 nm), and broadband halogen illumination at different power densities. WS 2 /P exhibits a pronounced wavelength- and intensity-dependent photocathodic response, particularly under blue-light excitation, where its photocurrent increases continuously with increasing illumination intensity, in contrast to the partial saturation observed for pristine WS 2 . The applied bias photon-to-current efficiency (ABPE) of WS 2 /P increases monotonically with blue-light intensity, reaching a maximum of 19.9% at approximately −0.78 V vs. RHE under 20 mW cm −2 blue-light irradiation, while the net photocurrent density reaches −21.37 mA cm −2 at −0.4 V vs. RHE under the same illumination condition. Electrochemical impedance spectroscopy further reveals that phosphorus incorporation facilitates interfacial charge transfer, as evidenced by the decrease in charge-transfer resistance from 27.81 kΩ for WS 2 to 15.89 kΩ for WS 2 /P. For WS 2 /P, blue-light illumination at 10 mW cm −2 further decreases the charge-transfer resistance from 46.59 kΩ under dark conditions to 33.00 kΩ, indicating photo-assisted enhancement of interfacial charge transfer. Transient photocurrent measurements further support enhanced photogenerated charge-carrier extraction in WS 2 /P under blue-light illumination, while chronoamperometric measurements demonstrate a stable photocathodic response after an initial transient decay under continuous blue-light irradiation. Overall, the combined structural, optical, electrical, PEC, and electrochemical results demonstrate that phosphorus incorporation improves charge transport and interfacial charge transfer in few-layer WS 2 , particularly under blue-light excitation, highlighting its potential for PEC hydrogen evolution.