Advancing Energy Materials: Exploring Catalysis, Energy Storage, and Synthetic Strategies with Keggin-type Polyoxotungstates

Abstract

The need for sustainable energy solutions to mitigate climate change is becoming increasingly urgent. Discovering efficient materials that are affordable and widely available is an ongoing issue. This PhD thesis focuses on developing polyoxometalate energy materials through synthesising novel compounds, investigating their catalytic properties, and exploring their potential for energy storage applications. The novel non-aqueous synthesis and characterisation of a series of post-transition metal substituted Keggin polyoxometalates (POMs), with the general formula (TBA)m[XPW11O39]m- , where X = Bi(III), Sb(III) and Pb(II) is reported. These compounds are characterised by multinuclear NMR, FTIR and electrochemistry to gain a comprehensive understanding of their structural and chemical properties, notably regarding the Bi-containing Keggin which forms both the 1:1 open and 2:1 sandwich structures. The substituted POMs are investigated as electrocatalysts for CO2 reduction. The catalytic performance is evaluated, focusing on activity, selectivity, and stability under a range of electrocatalytic conditions. The mechanism of action is evaluated with chemical reductant binding studies, systematic protonation studies, and spectroelectrochemistry. Key differences are found when the substituent and structure are varied, with {BiPW11O39] 4- showing the most promising activity. Furthermore, the Keggin POM anions {PMo12O40} 3- and {PW12O40} 3- with either H+ , Na+ , or TBA+ counter cations are combined with carbon ink to form carbon-POM hybrid electrodes which are implemented into symmetric supercapacitors. Energy storage technologies are crucial for the effective integration and utilisation of renewable energy sources. Their energy storage capacity, stability, and charging-discharging cyclability are assessed, in addition to the full characterisation of the electrode. Humidity and gas sensing applications are also explored with the substituted lacunary species. Through this research, the application of POMs as energy materials is shown to hold promise for addressing the challenges of climate change and transitioning to a cleaner and more sustainable future.