Novel formulation of self-oriented ZnSe/rGO/Ag₂CO₃ Z-scheme towards augmented methanol photoreforming for simultaneous productions of hydrogen and value-added by-product

As a green and sustainable approach, photoreforming of organic feedstocks has been extensively scrutinized for its potential to simultaneously produce hydrogen (H₂) and by-products under solar irradiation. Methanol is a compelling photoreforming substrate owing to low Gibbs free energy demand and generation of value-added by-products, for instance, formaldehyde (HCHO). In this work, a novel all-solid-state Z-scheme (ZGA) consisting of zinc selenide (ZnSe) coupled with silver carbonate (Ag₂CO₃) bridged by reduced graphene oxide (rGO) as an electron mediator was successfully synthesized as authenticated using XPS and FTIR. Intimate integration of nanosized ZnSe and Ag₂CO₃ enwrapped by rGO was disclosed by HRTEM, which was beneficial for efficient charge transfer. The optical absorption profile of ZGA was elevated in the visible light regime. The Nyquist plot of ZGA exhibited the smallest arc radius, accompanied by the highest transient photocurrent response as well as the shortest average carrier lifetime measured using TRPL. These outcomes collectively corroborated the superior photogeneration and transportation of charge carriers in ZGA. The overall production rate of H₂ achieved by ZGA was 77.7 µmol/g hr, which was 53% and 74% more superior than pristine ZnSe and Ag₂CO₃, respectively. Besides, a remarkable HCHO yield of 248 µmol/g hr was produced from ZGA, signifying the lucrativeness of methanol photoreforming compared to pure water splitting. The boosted performance in ZGA was attributed to the efficient Z-schematic charge transfer pathway endowed by the rGO mediator, which has been substantiated by DFT theoretical calculations. Succinctly, this work established the significance of the charge mediator in facilitating the photocatalytic performance of Z-scheme composites.