Polyoxometalate intercalated MXene with enhanced electrochemical stability

Abstract

Altres ajuts: ICN2 is funded by the CERCA programme/Generalitat de Catalunya. This work has been carried out within the framework of the doctoral program (PhD) of Material Science (Department of Physics) of Universitat Autonoma de Barcelona (UAB).

MXene/polyoxometalate (POM) hybrids are useful target materials for a variety of applications. Yet, the goal of preparing simple binary hybrids by intercalation of POMs into MXene has not been achieved. We propose and demonstrate here a method to intercalate POMs (phosphotungstate, PW12) into TiCT MXene through the interaction between POM anions and pre-intercalated surfactant cations. A variety of quaternary ammonium cations have been used to expand TiCT interlayer spacing. Cetyltrimethylammonium cations (CTA) lead to an expansion of 2 nm while allowing intercalation of a considerable load (10 wt%) thanks to their tadpole-like shape and size. CTAPW12 has a layered structure compatible with TiCT. The CTA-delaminated TiCT keeps the large interlayer spacing after being coupled with PW12. The PW12 clusters are dispersed and kept isolated thanks to CTA surfactant and the confinement into TiCT layers. The redox reactions in CTA-delaminated TiCT/PW12 are diffusion-controlled, which proves the well-dispersed PW12 clusters are not adsorbed on the surface of TiCT particles but within TiCT layers. The CTA- delaminated TiCT/PW12 shows superior electrochemical stability (remaining redox active after 5000 cycles) over the other MXene/POM hybrids prepared in this work (inactive after 500 cycles). We associate this improved stability to the effective intercalation of PW12 within TiCT layers helped by the CTA cations, as opposed to the external aggregation of PW12 clusters into micro or nanocrystals taking place for the other cations. The results provide a solid guide to help develop high-performance MXene/POM hybrid materials for a variety of applications.