Two-dimensional carbonitride MXenes as an efficient electrocatalyst for hydrogen evolution

Abstract

Owing to their excellent thermostability, superior electrical conductivity, and tunable surface chemistry, two-dimensional transition-metal carbides, nitrides, and carbonitrides (MXenes) are highly desirable as potential electrocatalysts for the hydrogen evolution reaction (HER). However, while nearly 30 MXenes have already been synthesized, less carbonitride MXenes were experimentally reported so far, yet their potential promising electrochemical properties are greatly expected. Here, we explored the thermodynamically favorable configurations of Mo-2(CN)T-x (T = F, OH, and O) with a mixture of functional groups under various electrochemical environments. It is revealed that the O*/OH*-terminated Mo-based carbonitride MXenes exhibit the most stable state under ambient conditions. By exploring the catalytic performance of HER for various Mo-2(CxN1-x)T-2 at different ratios of C and N atoms, we found that three optimal C/N ratios with 0.5 ML O* and 0.5 ML OH* showed good catalytic activity of HER, comparable to Pt metals. Further investigations of strain-tunable HER of the cofunctionalized Mo-2(CxN1-x)OOH suggest that the biaxial strain may effectively modify the Delta G(H*) of HER, which can be ascribed to the asymmetrical surface topology and charge polarization. These results provide not only a strategy to synthesize carbonitride MXenes with various surface functionalizations but also a feasible solution to design by chemical doping and strain engineering.