Recent advances in the use of MXenes for photoelectrochemical sensors

MXene is a newly discovered family of 2D transition metal carbides, nitrides, or carbonitrides that is predominantly conductive. The most common MXene, titanium carbide (Ti3C2), can be used as a conductive material to enhance the photocurrent generated by photoelectrochemical (PEC) sensors. In order to produce MXene sheets that are of high quality for PEC sensors and other light-based applications, it is imperative that the synthesis methods for MXene production continue to be improved and that an extensive understanding of its properties is gained. Several fluorinated and non-fluorinated MXene synthesis methods from MAX are discussed in this review. Detailed description of the mechanical, optical, topological, electronic, and electrochemical properties of the resultant MXenes are also presented. A critical analysis of the density functional theory (DFT) data for pure MXene, as well as the changes in the optical bandgap of MXene when doped with other heteroatoms to form heterojunctions or ternary nanocomposites, are extensively described. Additionally, a systematic exposition is done on the current MXene-based PEC sensors, highlighting the critical parameters that yield a high performing sensor. The review concludes with an opinion on the future direction of MXenes in PEC sensing and the electrochemical field.