Highly efficient twinned MnxCd1-xS homojunction photocatalyst modified by noble metal-free Ni12P5 for H2 evolution under visible light

Abstract

A series of twin-phase MnxCd1-xS solid solutions with zinc blende (ZB) and wurtzite (WZ) structures were prepared by an alkaline hydrothermal method in this work. When using 0.35 M Na2SO3/0.25 M Na2S solution as a sacrificial agent under visible light (λ ≥ 420 nm), the H2 production activity of T-Mn0.5Cd0.5S is 33.4 mmol h−1 g−1, significantly higher than that of ZB-Mn0.5Cd0.5S (15.4 mmol h−1 g−1) or WZ-Mn0.5Cd0.5S (18.2 mmol h−1 g−1). The photocatalytic activity of T-Mn0.5Cd0.5S is further enhanced by introducing Ni12P5 as a cocatalyst, in which the H2 evolution rate of 0.2% Ni12P5/T-Mn0.5Cd0.5S can reach 96.5 mmol h−1 g−1, 2.89 and 1.77 times than that of pure T-Mn0.5Cd0.5S and 0.5% Pt/T-Mn0.5Cd0.5S (54.6 mmol h−1 g−1), respectively. The crystalline phase, microstructure, elemental composition, optical and optoelectronic properties of the samples were characterized by XRD, SEM, TEM, HRTEM, XPS, UV–vis, PL and electrochemical workstation. The results show that the formation of a homojunction with interlaced energy band inhibits carrier recombination in the bulk phase of T-Mn0.5Cd0.5S. In addition, Ni12P5 can substitute for the noble metal as a cocatalyst to reduce the overpotential and improve the separation rate of electrons and holes to enhance H2 evolution. This work provides reference for building homojunction photocatalysts and loading inexpensive transition metal phosphides instead of noble metals.