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 employ 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, proton redox rate in the dissimilar interface of graphene-Ti3C2O2 is much higher, owning 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 of proton mobility with proton concentration in the graphene-Ti3C2O2 interface. As the proton concentration further increases, proton mobility deceases, 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.