The unique properties of aqueous polyoxometalate (POM) mixtures and their role in the design of molecular coatings for electrochemical energy storage

A facile method to combine Keggin polyoxometalates (POMs) e.g. PMo12O403− (PMo12) and PW12O403− (PW12) in aqueous solutions has led to a unique electrochemical phenomenon, in which the POM mixtures demonstrate their own tunable redox activity, far different from the pure components. Through electrochemical and NMR analyses we have confirmed that this interesting behaviour arises from the spontaneous hydrolysis and recombination of PMo12 and PW12 ions forming complex blends of PMo12-xWx mixed addenda chemistries. While this process occurs spontaneously for the PMo12-PW12 system due to the ready hydrolysis, it can be induced in other POM mixtures such as SiMo12-SiW12 by adjusting the pH to stimulate hydrolysis. The highly tunable redox properties of the mixtures can be leveraged to design molecular coatings for a variety of applications. When deposited on nanocarbon, the overlapping redox features of the POM mixtures result in cyclic voltammograms with substantial pseudocapacitive currents which maintain relatively smooth charge/discharge profiles, ideal for supercapacitor electrodes.