Mechanistic Understanding of the Interactions and Pseudocapacitance of Multi-Electron Redox Organic Molecules Sandwiched between MXene Layers

Using a combined theoretical and experimental approach, a mechanisticunderstanding of the interactions and pseudocapacitance of different quinone-coupled viologen and pyridiniumium molecules sandwiched betweentitanium carbide (Ti3C2Tx) MXene layers has been provided. Three differentderivatives of quinone-coupled viologen and pyridiniumium are synthesizedusing nucleophilic substitution reaction and subsequently hybridized withTi3C2Tx MXene (organic@Ti3C2Tx) using self-assembly approach. The atomicstructure of pristine Ti3C2Tx and organic@Ti3C2Tx hybrid films is investigatedusing grazing incidence X-ray diffraction and X-ray pair distribution functionanalysis using synchrotron radiation. Spectroscopic results confirm thecoupling of quinones with viologen and pyridiniumium molecules and theirnon-covalent functionalization to the MXene without their catalytic decomposition.First-principles calculations confirm that the preferred orientation oforganic molecules upon intercalation/adsorption is horizontal to the Ti3C2Txsurface. The authors reveal that these molecules attach to the Ti3C2Tx surfacewith a significantly high binding energy (up to -2.77 eV) via a charge transfermechanism. The electronic structure calculations show that all organic@Ti3C2Tx hybrids preserved their metallic behavior. Free-standing organic@Ti3C2Tx hybrid films show a more than three times higher capacitance at ultrahighscan rates (up to 20 V s-1) compared to their pristine counterpart dueto molecular pillaring of organic molecules between Ti3C2Tx layers via strongbinding energies and charge transfer.