Polyoxometalates (POMs): From electroactive clusters to energy materials

Polyoxometalates (POMs) represent a class of nanomaterials, which hold enormous promise for a range of energy-related applications. Their promise is owing to their "special"structure that gives POMs a truly unique ability to control redox reactions in energy conversion and storage. One such amazing capability is their large number of redox active sites that arises from the complex three-dimensional cluster of metal-oxide ions linked together by oxygen atoms. Here, a critical review on how POMs emerged from being molecular clusters for fundamental studies, to next-generation materials for energy applications is provided. We highlight how exploiting the versatility and activity of these molecules can lead to improved performance in energy devices such as supercapacitors and batteries, and in energy catalyst applications. The potential of POMs across numerous fields is systematically outlined by investigating structure-property-performance relationships and the determinant factors for energy systems. Finally, the challenges and opportunities for this class of materials with respect to addressing our pressing energy-related concerns are identified. This journal isD. P. D. acknowledges the Queensland University of Technology (start-up grant: 323000-0424/07) and Australian Research Council (ARC), Australia for the Future Fellowship (FT180100058). D. P. D. would also like to acknowledge the financial support from Centre for Materials Science, QUT, Australia. N. M. acknowledges funding from ARC (DP200102546). Sara Goberna-Ferrón has received funding from the postdoctoral fellowship programme Beatriu de Pinós, funded by the Secretary of Universities and Research (Government of Catalonia) and by the Horizon 2020 programme of research and innovation of the European Union under the Marie Skłodowska-Curie grant agreement No 801370. Partial funding from Ministry of Science, Innovation and Universities (MCIU), the State Research Agency (AEI) and the European Regional Development Fund (FEDER) (grant RTI2018-099826-B-I00) and AGAUR (2017 SGR 00870) are gratefully acknowledged. ICN2 is funded by the CERCA programme/Generalitat de Catalunya, and it is supported by the Severo Ochoa Centres of Excellence programme, funded by the Spanish Research Agency (AEI, grant no. SEV-2017-0706)