Proton dynamics in water confined at the interface of the graphene-MXene heterostructure

Heterostructures of 2D materials offer a fertile ground to study ion transport and charge storage. Here, we use ab initio molecular dynamics to examine the proton-transfer/diffusion and redox behavior in a water layer confined in the graphene-Ti₃C₂O₂ heterostructure. We find that in comparison with the similar interface of water confined between Ti₃C₂O₂ layers, the proton redox rate in the dissimilar interface of graphene-Ti₃C₂O₂ is much higher, owing to the very different interfacial structure as well as the interfacial electric field induced by an electron transfer in the latter. Water molecules in the dissimilar interface of the graphene-Ti₃C₂O₂ heterostructure form a denser hydrogen-bond network with a preferred orientation of water molecules, leading to an increase in proton mobility with proton concentration in the graphene-Ti₃C₂O₂ interface. As the proton concentration further increases, proton mobility decreases due to increasingly more frequent surface redox events that slow down proton mobility due to binding with surface O atoms. Our work provides important insights into how the dissimilar interface and their associated interfacial structure and properties impact proton transfer and redox in the confined space.