2D MXenes and their heterostructures for HER, OER and overall water splitting: A review

MXenes are a family of 2D transition metal carbides, nitrides, and carbonitrides that have surface termination groups such as –OH, –O, and –F. The presence of transition metal imparts conductivity, surface termination groups induce hydrophilicity and layered structure offers large surface area which makes MXenes a potential candidate to be utilized as an electro-catalyst with enhanced efficiency. The Water Electrolysis (WE) efficiency of an electro-catalysts is dependent on the performance of half-cell reactions i.e. Hydrogen Evolution Reaction (HER) and Oxygen Evolution Reaction (OER). The OER kinetics of most of the bi-functional electrocatalysts are considered sluggish due to which they are tested in alkaline media. However, due to the metallic nature and surface properties of MXenes, they as substrate not only improve HER performance of grown electro-catalyst but also facilitate OER kinetics which is considered sluggish for most bi-functional electrocatalysts. This review presents the significance of MXenes as HER, OER, and bi-functional electrocatalysts by discussing the electrocatalytic properties of a wide range of MXenes and how their hetero-structures affect HER, OER, and bi-functional electrocatalytic performance. In the end, the current challenges, and future perspectives of MXenes and their nanocomposites for water electrolysis have been discussed.