Effect of surface functional groups on MXene conductivity

We report the in-plane electron transport in the MXenes (i.e., within the MXene layers) as a function of composition using the density-functional tight-binding method, in conjunction with the non-equilibrium Green's functions technique. Our study reveals that all MXene compositions have a linear relationship between current and voltage at lower potentials, indicating their metallic character. However, the magnitude of the current at a given voltage (conductivity) has different trends among different compositions. For example, MXenes without any surface terminations (Ti3C2) exhibit higher conductivity compared to MXenes with surface functionalization. Among the MXenes with -O and -OH termination, those with -O surface termination have lower conductivity than the ones with -OH surface terminations. Interestingly, conductivity changes with the ratio of -O and -OH on the MXene surface. Our calculated I-V curves and their conductivities correlate well with transmission functions and the electronic density of states around the Fermi level. The surface composition-dependent conductivity of the MXenes provides a path to tune the in-plane conductivity for enhanced pseudocapacitive performance.

Automated summary

We studied the electron transport within the MXene layers as a function of composition and found a linear relationship between current and voltage at lower potentials in all MXene compositions, indicating their metallic character. However, the conductivity varies among different compositions, with MXenes without surface terminations exhibiting higher conductivity compared to MXenes with surface functionalization. The conductivity also changes with the ratio of -O and -OH on the MXene surface. The surface composition-dependent conductivity of MXenes provides a way to enhance the pseudocapacitive performance.