Correlative nanoscale chemical imaging reveals delocalized Faradaic processes at isolated MXene flakes

Abstract Two-dimensional transition metal carbides and nitrides (MXenes) combine an electrochemically active surface with high conductivity and hydrophilicity, which makes them a unique class of materials for electrochemical applications. While the pseudocapacitive behaviour of MXenes in acidic environments is relatively well understood on macroscale electrodes, intrinsic electrochemical phenomena occurring on single MXene flakes remain unclear. Here, we use scanning X-ray microscopy (SXM) to correlate the electronic structure of Ti 3 C 2 T x MXene flakes at the nanoscale with local electrochemical reactions triggered at the sub-flake level by scanning electrochemical cell microscopy (SECCM). For several proton-coupled electron transfer reactions, including electrochemical oxidation and the hydrogen evolution reaction, we demonstrate a delocalization of the reactions well beyond the MXene flake area in contact with the droplet cell. Furthermore, we show evidence of hydrogen storage on monolayer MXene flakes. This work highlights fundamental insights into the role of interfacial water on surface redox reactions.