HF-free low-temperature synthesis of MXene for electrochemical hydrogen production

Abstract MXenes [two-dimensional (2D) transition-metal carbides, nitrides and carbonitrides] are gaining significant interest as alternative electrocatalysts for the hydrogen evolution reaction due to their excellent properties such as high electrical conductivity, large surface area and chemical stability. MXenes are traditionally synthesized using hydrofluoric acid (HF), which raises safety and environmental concerns due to its highly corrosive and toxic nature. HF introduces fluoride functional groups on the surface of MXenes, and these have been reported to have a detrimental effect on electrocatalysis. As a result, there is growing interest in developing MXenes through non-fluoride routes. Here, we report room-temperature, HF-free, wet-chemical synthesis of MXene using a mixture of hydrogen peroxide and chromium chloride. The newly prepared CH-MXenes possess hydrophilic functionalities (–Cl, –OH and =O). Key advantages of the CH route over HF-based synthesis include the elimination of an additional delamination step, the prevention of MXene restacking via chloride functionalities and the consistent production of high-quality 2D MXenes with a reproducible flake size (∼650 nm). These CH-MXenes exhibit a high surface area, excellent conductivity and enhanced chemical stability, making them suitable for various energy and other applications.