Energy storage is required in scale, to enable the transition from the current carbon-based to a renewable-energy driven economy. In fact, this is one of the most important challenges to the movement towards a sustainable future. Hence utilization of earth abundant materials for developing energy storage technologies is essential. Ceria is among the rare earth oxides that are well distributed and it exhibits promising redox behaviour (Ce4+/Ce3+). Even though this property of ceria is favourable for supercapacitor-electrode, ceria provides only moderate specific capacitance and hence offers scope for significant improvement.

Here, we have explored two possible approaches to enhance the supercapacitive performance of ceria: (i) the role of substitutional doping, and (ii) use of redox-additives in the traditional alkaline aqueous electrolyte. For substitutional doping, different dopants are used with primary oxidation states as 4+, and 3+. Dopant is found to aid in enhancement of (i) the oxygen-vacancy concentration, and (ii) lattice oxygen mobility, compared to pristine ceria. Increasing oxygen vacancy facilitates fast redox-reaction associated with Ce4+/Ce3+ in-situ redox-reaction, which is advantageous for supercapacitors.

We show that doping *standalone* can be used to obtain a significant improvement of specific capacitance over pristine ceria. There after we used the Mott-Littleton method to predict the more useful dopant and validated performance in a device. An important outcome of this work is that a single predictor – namely the enthalpy of point defects – as elucidated by the Mott-Littleton method is found to be a good measure of suitability of the material for supercapacitive behaviour.

A redox-additive [K3Fe(CN)6] is used to enhance the specific capacitance of the supercapacitor. Redox-additives are often seen as a cost-effective means to improve low-temperature charge-storage capacity for supercapacitors with aqueous electrolyte. However, from a technology-development standpoint, there are challenges associated with a lack of standard techniques to measure the redox-additive based device-parameters. This challenge and corresponding technological gap, results in a relatively poor understanding of the charge storage processes of the relevant charge-storage device. To address this concern, we have developed a method that enables the delineation of the contribution of the effective-mass of the redox-additive on the electrode-surface.

In this doctoral research proposal seminar, a way forward in terms of material prediction, performance analysis, and environmental study will be laid out.