Abstract:

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·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 µmol·g⁻¹·h⁻¹, which is 26.4 and 8.7 times higher than those of g-C₃N₄ (113 µmol·g⁻¹·h⁻¹) and MnCo₂S₄ (341 µmol·g⁻¹·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.

Key words: MnCo₂S₄, Carbon nitride, S-scheme heterojunction, Photocatalytic H₂ production from water splitting