The ideal device for energy storage would provide high energy density, high power density and long lifespan. In other words, it would allow to storage a lot of energy in a small space, to deliver it back very quickly, and to be able to repeat the charge-discharge cycle an incredible number of times. Currently known technologies are able to offer, in general, either high energy or high power density. Among them, supercapacitors are outstanding devices for high power density and extended cyclability, but great efforts are still needed to increase their energy density.
One of the approaches that researchers are exploring is to develop new materials for the supercapacitor electrodes to increase storage capacity. This is the path taken by members of the ICN2 Novel Energy-Oriented Materials Group (NeoEnergy), who are seeking for a way to best combine the different and complementary properties of MXenes and polyoxometalates (POMs). The first are 2D materials that stand out for their remarkable volumetric capacitance, which allows for device compactness. The second are a family of nanometric metal-oxide clusters able to provide fast and reversible redox reactions, i.e. charge-discharge cycles. A few research groups working on this topic have already attempted to synthesise hybrid materials based on MXenes and POMs with the aim of enhancing the performance of energy storage devices by intercalating POMs into MXenes, but their results were not fully satisfactory.
In two recently published works, Jun-Jie Zhu and Prof. Pedro Gómez Romero, –a doctoral student and the leader of the NeoEnergy group, respectively– in collaboration with other colleagues from the ICN2 and the Catalan Institute for Energy Research (IREC, Barcelona), used two different strategies to address these problems. In particular, previous studies by other authors reported either failing to uniformly disperse POM nanoclusters or needing to anchor them to MXenes using linkers that limited the applicability of the resulting structure.
In the first paper, published in ‘Journal of Colloid and Interface Science’, they used activated carbon (AC) as a porous matrix for anchoring POM clusters to a MXene. The resulting MXene/AC/POM hybrid material showed increased capacitance as a result of synergic effects between the three constituents. In the second, released more recently in ‘Nanoscale’, they achieved for the first time the intercalation of POMs into a MXene scaffold –something that had proved to be very hard due to the structure and charge of these bidimensional materials. Specifically, during a process called delamination they introduced large cations into MXene, which are able to increase its interlayer distance. As a consequence, in the following step, POM nanoclusters can accomodate in-between the layers of the MXene, giving origin to a POM-intercalated MXene material. This stronger hybridization results in increased electrochemical stability and, ultimately, in better performance of the material for energy storage, catalysis and sensing applications. References Rational design of MXene/activated carbon/polyoxometalate triple hybrid electrodes with enhanced capacitance for organic-electrolyte supercapacitors
Jun-Jie Zhu, Avireddy Hemesh, Jordi Jacas Biendicho, Luis Martinez-Soria, Daniel Rueda-Garcia, Joan Ramon Morante, Belen Ballesteros, Pedro Gomez-Romero https://www.sciencedirect.com/science/article/pii/S0021979722007536?via%3Dihub
Polyoxometalate intercalated MXene with enhanced electrochemical stability Jun-Jie Zhu and Pedro Gomez-Romero