Polyoxometalate intercalated MXene with enhanced electrochemical stability

Nanoscale. 2022 Oct 21;14(40):14921-14934. doi: 10.1039/d2nr01410f.

Abstract

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 Ti3C2Tx MXene through the interaction between POM anions and pre-intercalated surfactant cations. A variety of quaternary ammonium cations have been used to expand Ti3C2Tx 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 Ti3C2Tx. The CTA+-delaminated Ti3C2Tx 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 Ti3C2Tx layers. The redox reactions in CTA+-delaminated Ti3C2Tx/PW12 are diffusion-controlled, which proves the well-dispersed PW12 clusters are not adsorbed on the surface of Ti3C2Tx particles but within Ti3C2Tx layers. The CTA+- delaminated Ti3C2Tx/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 Ti3C2Tx 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.