Mechanical suppression of proton-coupled electron transfer in MXene nanoconfinement

Ion adsorption and electron transfer govern electrochemical charge storage in porous electrodes 1,2 . When ions enter subnanometer pores, ionic desolvation and solvation can strongly shift this balance 2,3 . In two-dimensional (2D) materials like MXenes and graphene, insertion and removal of solvated ions induce significant interlayer expansions 4,5,6 . The transport mechanisms of protons and other ions behave differently under nanoconfinement. In extreme cases, electrolyte ions are sterically blocked by a trapped water monolayer, while water and protons remain mobile 7 . However, how externally applied pressure affects electrochemical processes under nanoconfinement is still unclear. Here, we show how various ions insert and react electrochemically within Ti₃C₂T ₓ MXene (T x : mixed terminations) layers under in situ mechanical constraint. We find that such nanoconfinement significantly suppresses redox reactions, including Ti–OH formation and water splitting. Using multiscale modeling — ab initio molecular dynamics, metadynamics, and a continuum kinetic model — we show that mechanical constraint disrupts the hydrogen-bond network of confined water, stabilizing surface-bound protons, and limiting their exchange with water. This coupling between mechanical and chemical effects enables micrometer-thin electrochemical pressure sensors that function under high loads and offers a route to suppress unwanted redox reactions, extending the safe voltage window for devices. These insights contribute to the advancement of pseudocapacitive energy storage, capacitive deionization, electrocatalysis, and electrochemical actuator technologies.