S-Scheme MnCo2S4/g-C3N4 Heterojunction Photocatalyst for H2 Production

The increased global demand for energy and the enhanced deterioration of the environment are the two urgent challenges of the 21st century on the way to sustainable development for human society. Currently, green and renewable energy conversion technology has received much attention as a substitute for limited and non-renewable fossil fuels. Hydrogen energy is advantageous because of its high energy capacity (142 MJ center dot kg-1) and its production by green conversion technology, consisting of H2 reacting with O2 to generate H2O. It can establish a clean and sustainable hydrogen economic system, as well as reduce the utilization of fossil fuels and carbon dioxide emissions. Water splitting technology is an efficient approach to acquire the featured H2 energy of the green reaction (2H2O -> 2H2 + O2) through electrocatalytic and photocatalytic reactions. Photocatalysis technology, with the advantage of huge solar energy utilization, has been widely regarded as a promising method for the realization of this chemical synthesis. Among photocatalysis technologies, photocatalytic H2 production from water is considered a promising approach to obtain H2 energy due to its environmentally friendly energy conversion. However, the effectiveness of acquiring H2 energy through photocatalytic water splitting is intimately related with photocatalysts. In general, photocatalysts still face the big challenge of their low solar energy utilization efficiency, which restricts the large-scale application of photocatalytic technology to obtain H2 energy. Thus, developing highly efficient photocatalysts for H2 production is critical in promoting this technology moving forward, and obtaining renewable energy. Herein, we successfully construct the S-scheme MnCo2S4/g-C3N4 heterojunction through an expedient physical mixing process at a low temperature, which can be separately obtained via the pyrolysis process and hydrothermal method. The H2 production rate of MnCo2S4/g-C3N4 heterojunction can achieve up to 2979 mu mol center dot g-1 center dot h-1, which is 26.4 and 8.7 times higher than those of g-C3N4 (113 mu mol center dot g-1 center dot h-1) and MnCo2S4 (341 mu mol center dot g-1 center dot h-1), respectively, and presents a superior stability in three continuous cycles during H2 production tests. The high H2 production of MnCo2S4/g-C3N4 heterojunction is mainly ascribed to the following three reasons: i) The light absorption region of the heterojunction is extended to visible light. ii) MnCo2S4/g-C3N4 possesses low impedance during the reaction, high photocurrent density, and more exposed sites in solution. iii) The efficient reservation of active electron-hole pairs greatly enhances the ratio of electrons reacting with H* species to generate H2 over MnCo2S4/g-C3N4 heterojunction. This work provides an efficient approach to constructing advanced g-C3N4-based photocatalysts through hybridization with metal sulfides to form S-scheme heterojunctions.