Electrocatalytic and Optoelectronic Characteristics of Exfoliated Two-Dimensional Titanium Nitride Ti4N3Tx mxene

Abstract

A relatively new class of two-dimensional (2D) materials called MXenes have garnered tremendous interest in the field of energy storage and conversion. Thus far nearly all MXenes reported experimentally have been described as metals, with a lone report of a mixed-metal carbide phase exhibiting semiconducting character. Here, we report the optical, electrocatalytic and electrical properties of the 2D Ti4N3TxMXene (Tx= basal plane surface terminating groups) and show this material exhibits both metallic and semiconducting behavior. We provide complete structural characterization of exfoliated Ti4N3TxMXene and assign Tx= O and/or OH and find that this material is susceptible to surface oxidation. Optical experiments indicate that the exfoliated Ti4N3TxMXene forms a hybrid with a thin surface oxide layer resulting in visible light absorption at energies greater than ~2.0 eV and an excitation wavelength-dependent defect-state emission over a broad range centered at ~2.9 eV. As an electrocatalyst for the hydrogen evolution reaction, the exfoliated Ti4N3Txshows an overpotential of ~300 mV at –10 mA cm–2and a Tafel slope of ~190 mV/decade. Finally, we observe a clear semiconductor-to-metal transition at ~90 K from temperature-dependent transport measurements under 5 T magnetic field likely resulting from the thin oxide layer. These results unveil the intriguing optical, electrocatalytic, and electrical properties of this 2D Ti4N3TxMXene that expands the potential of these new 2D materials into electrocatalysis and (opto)electronic applications.