Z-Scheme Overall Water Splitting Using Zn_xCd_1–xSe Particles Coated with Metal Cyanoferrates as Hydrogen Evolution Photocatalysts

Abstract

Solid solutions of ZnSe and CdSe (Zn x Cd1–x Se) exhibit intense visible-light absorption in the wavelength region from 480 to 750 nm, which can be tuned by adjusting the Zn/Cd ratio. These materials generated hydrogen from water containing [Fe­(CN)6]4– as an electron donor after modification with a Pt cocatalyst. The surfaces of Pt/Zn x Cd1–x Se specimens were shown to be coated with zinc and/or cadmium cyanoferrates during the photocatalytic reaction, resulting in stable hydrogen evolution. This layer of metal cyanoferrates is expected to promote the oxidation of [Fe­(CN)6]4– and to protect the selenide photocatalysts against photocorrosion. A Z-scheme system consisting of the particulate Pt/Zn0.75Cd0.25Se and a CoO y /TaON photoanode combined with [Fe­(CN)6]3–/4– as a redox mediator promoted overall water splitting under visible light. This is the first-ever demonstration of redox-mediated Z-scheme overall water splitting using selenide photocatalyst particles. The present study suggests the feasibility of using metal cyanoferrates to inhibit photocorrosion of group II metal selenide photocatalysts during Z-scheme water splitting.

Synergistic Effect of the Surface Vacancy Defects for Promoting Photocatalytic Stability and Activity of ZnS Nanoparticles

“…Among them, because of a relatively negative conduction band position, relatively shallow valence band, and rapid photoelectric response ability, metal sulfides show great potential for photocatalytic applications. − However, the surface S ions of metal sulfides can be oxidized to S 0 or SO 4 2– by photogenerated holes (h + ) and thus be deactivated, , limiting further development and practical application. To improve the photocorrosion and stability, most studies adopted the strategies of a composite structure, controlling the morphology or doping, such as the heterojunction with other semiconductors, , hybridization with cocatalyst, , or the use of a template or surfactant to control the size and morphology, , noble-metal decorating, , and cation or anion doping. , However, the compactness of the composite interface, template, or surfactant and the introduction of high energy cause complicated synthesis processes, the harsh reaction conditions, and high cost, which impedes the large-scale application of photocatalysts. Therefore, it is badly in need of designing and developing a kind of metal sulfide photocatalyst with simple structures, high activity and stability.…”

A perspective on two pathways of photocatalytic water splitting and their practical application systems

“…40 H + ions are reduced by electrons in the conduction band of the HEP while mediators in the reduced state are oxidized by holes in the valence band to generate H 2 and oxidized mediators, respectively. 41 Conversely, the oxidized mediators are transitioned back to their reduced forms by photoexcited electrons on the OEP while H 2 O molecules are oxidized to O 2 molecules by holes. 42 Therefore, the OWS process depends on the circulation of redox mediators.…”

Boosted photocatalytic performance on molecule/semiconductor hybrid materials: conversion of sunlight energy into hydrogen fuel

“…To solve these issues, construction of an efficient photocatalytic system is of the utmost significance. Under these circumstances, ever more endeavors have contributed to the development of semiconductor materials through doping, 4,5 sensitization, 6,7 construction of heterojunctions, 8,9 Z-scheme systems, 10,11 establishment of microsize architectures, 12,13 annexing appropriate molecular catalyst [14][15][16] and other thermodynamic and kinetics methods. Among them, loading a suitable molecular catalyst is widely perceived to be a promising method to enhance catalytic application of a single semiconductor that can synchronously implement dissociation of the exciplex, accelerate surface reaction kinetics, and suppress counterreactions.…”