First-Principles Study on Nb₂C–X (X = S, Cl, F)/Graphene Heterostructures: Assessing Aqueous Stability and Implications for Electrocatalysis

Nb 2 C–X MXenes (X = S, Cl, F) have the potential to be promising economical (electro)catalysts, but their degradation in oxidative and aqueous environments remains a major concern. In this work, the resistance to oxidation and hydrolysis of heterostructures made of Nb 2 C–X MXenes and graphene was explored using density functional theory. We found that Nb 2 C–X/graphene heterostructures are less prone to oxidation compared to pristine Nb 2 C–X MXene. Especially, Nb 2 C–F/graphene was found to possess higher oxidative resistance compared to those of Nb 2 C–S/graphene and Nb 2 C–Cl/graphene. An analysis of the electronic properties of the Nb 2 C–X/graphene heterostructures indicated improved conductivity compared to that of pristine Nb 2 C–X structures and gave insight into the influence of graphene on the MXene’s electronic structure. In addition, the resistance to hydrolysis of pristine Nb 2 C–S and the Nb 2 C–S/graphene heterostructures was compared. Nudged elastic band calculations indicated significantly higher activation energies for water adsorption and dissociation on the Nb 2 C–S/graphene heterostructure as compared to that on pristine Nb 2 C–S, which are the first steps in MXene decomposition in aqueous media. Moreover, an assessment of the oxygen evolution reaction (OER) performance showed a significantly lower overpotential for the OER on Nb 2 C–S/graphene compared to that of pristine Nb 2 C–S, indicating the improved electrocatalytic activity of the heterostructure. This work presents the critical role of graphene in improving the resistance to oxidation and stability in aqueous media of MXenes, which is a valuable insight for the synthesis of stable MXene-based (electro)catalysts.