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

Nb2C–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 Nb2C–X MXenes and graphene was explored using density functional theory. We found that Nb2C–X/graphene heterostructures are less prone to oxidation compared to pristine Nb2C–X MXene. Especially, Nb2C–F/graphene was found to possess higher oxidative resistance compared to those of Nb2C–S/graphene and Nb2C–Cl/graphene. An analysis of the electronic properties of the Nb2C–X/graphene heterostructures indicated improved conductivity compared to that of pristine Nb2C–X structures and gave insight into the influence of graphene on the MXene's electronic structure. In addition, the resistance to hydrolysis of pristine Nb2C–S and the Nb2C–S/graphene heterostructures was compared. Nudged elastic band calculations indicated significantly higher activation energies for water adsorption and dissociation on the Nb2C–S/graphene heterostructure as compared to that on pristine Nb2C–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 Nb2C–S/graphene compared to that of pristine Nb2C–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.