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 Ti₃C₂Tₓ MXene (Tx: 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.