CoP Decorated on Ti<sub>3</sub>C<sub>2</sub>T<sub>x</sub> MXene Nanocomposites as Robust Electrocatalyst for Hydrogen Evolution Reaction

Abstract: Electrocatalysts play a pivotal role in the electrochemical water splitting process to produce hydrogen fuel. The advancement of this technology relies on the development of efficient, cost-effective, and readily available electrocatalysts. Two-dimensional (2D) MXene materials have garnered significant attention due to their unique physicochemical properties, rendering them promising candidates for electrocatalytic applications. While there are numerous types of MXene materials available, only a few possess intrinsic hydrogen evolution reaction (HER) catalytic activity. However, MXene materials can serve as excellent platforms for enhancing catalytic HER activity by combining them with other substances, owing to their large specific surface area, high conductivity, and abundant surface functional groups. In this study, we initially conducted a predictive analysis using density functional theory (DFT) to assess the potential of combining CoP with Ti3C2Tx MXene materials (where Tx represents ―F and ―OH functional groups) in reducing the adsorption free energy of hydrogen (ΔGH*). The results indicated that the CoP-Ti3C2Tx nanocomposites exhibited a ΔGH* value approaching 0, suggesting promising HER performance. Following this theoretical prediction, we synthesized the CoP-Ti3C2Tx MXene nanocomposites. Comprehensive characterization of the synthesized nanocomposites was performed using various techniques, including scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). These analyses confirmed the successful decoration of CoP on the MXene nanosheets and provided insights into the structural and compositional properties of the nanocomposites. Furthermore, we evaluated the electrochemical performance of the CoP-Ti3C2Tx nanocomposites through linear sweep voltammetry and chronoamperometry measurements. The results demonstrated superior catalytic activity and stability for the HER compared to pure Ti3C2Tx and CoP catalysts. Specifically, the as-synthesized CoP-Ti3C2Tx MXene nanocomposites exhibited remarkable electrocatalytic HER kinetics, featuring a low overpotential of 135 mV at a current density of 10 mA∙cm−2 and a small Tafel slope of 48 mV∙dec−1 in a 0.5 mol∙L−1 H2SO4 solution, with the electrocatalyst maintaining stability for up to 50 h. Subsequent theoretical calculations were conducted to elucidate the factors contributing to the exceptional electrocatalytic performance of the CoP-Ti3C2Tx MXene nanocomposites. It was determined that the metallic conductivity of Ti3C2Tx MXene materials, well-structured interface charge transfer, and optimized electronic structure of CoP played significant roles in enhancing catalytic activity. In conclusion, this study underscores the potential of CoP-decorated Ti3C2Tx MXene nanocomposites as promising electrocatalysts for efficient HER in various energy conversion and storage devices. These findings represent a significant contribution to the development of robust and efficient catalysts for hydrogen generation, a critical component of renewable energy applications and sustainable development.