Hybrid PEDOT Conductive Polymer-Powdered Metal Sulfide Photocathodes for Photoelectrochemical Green H₂ Production

Hybrid photocathodes combining metal sulfide powders with poly-3,4-ethylenedioxythiophene (PEDOT) as an effective hole transporting polymer were prepared through a facile drop-casting method and electrochemically oxidative polymerization of 3,4-ethylenedioxythiophene (EDOT). The PEDOT modification remarkably enhanced a photocurrent density of a powder-based (CuGa)_0.5ZnS₂ photocathode (bandgap (BG): 2.3 eV) for hydrogen evolution under visible light irradiation at 0 V vs RHE, 60-times higher compared with an unmodified photocathode. The improvement was advantageously effective when using small metal sulfide particles prepared by a flux method compared to large particles synthesized by a solid-state reaction due to improved necking and interfacial contact facilitated by PEDOT in the fine physical structure. The optimized PEDOT/(CuGa)_0.5ZnS₂-composited photocathode (PEDOT-(CuGa)_0.5ZnS₂) achieved an incident photon-to-current conversion efficiency (IPCE) of 30% at 420 nm and 0 V vs RHE for the H₂ evolution. PEDOT modification was also effective for Cu₂ZnSnS₄ (BG: 1.4 eV) and Cu₃VS₄ (BG: 1.5 eV) black metal sulfide photocathodes. Furthermore, solar water splitting proceeded in a two-electrode photoelectrochemical cell consisting of a PEDOT-(CuGa)_0.5ZnS₂ photocathode and a BiVO₄-based photoanode, even without applying an external bias. The photoelectrochemical cell gave 0.08% for nonbias and 0.21% for 0.4 V of an external bias of a solar-to-hydrogen energy conversion efficiency (STH), even though both photoelectrodes were fabricated without any vacuum process and using just two ingredients. Our findings will offer a viable strategy for developing photocathodes that unite simplicity and high performance by using powder materials for the scalable application of photoelectrochemical green H₂ production.