A brief review on the progress of MXene-based catalysts for electro- and photochemical water splitting for hydrogen generation.

The development and generation of affordable and highly efficient energy, particularly hydrogen, are one of the best approaches to address the challenges posed by the depletion of non-renewable energy sources. Hydrogen energy, as a green and ecosystem-friendly source with zero carbon emission, can be generated through various methods, including water splitting (HER/OER) via either photo- or electrocatalytic reactions. To implement these reactions effectively in practical applications, it is highly desirable to develop extremely efficient and cost-effective catalytic materials that are comparable to contemporary catalysts. MXenes, a family of newly discovered 2D transition metal carbides, nitrides, or carbonitrides with surface termination groups, such as -OH, -O, and -F, have emerged as promising materials and substrates for photo- and electrocatalytic applications due to their unique characteristics. These include excellent conductivity provided by the transition metals, hydrophilic nature imparted by the surface termination groups, high mechanical stability, fast electronic transmission and extremely high surface area-to-volume ratios. In this review, we provide detailed insights into the synthesis, properties, and catalytic applications of MXenes. We systematically outline the photo- and electrocatalytic water splitting reactions carried out by various MXene-based heterostructures, supported by experimental data. A thorough deliberation on the structure-activity associations of reported catalysts and a basic understanding of the electrocatalytic applications of MXenes are also included. Furthermore, we offer an insight into the upcoming tasks, challenges, prospects and new research strategies for MXenes in water splitting applications. A noteworthy recognition of the design and optimization of extremely efficient MXene-based catalysts in water splitting applications is therefore offered in this review.