Characterisation of novel electrode materials for renewable energy storage application

Shaymaa Albohani

Increasing requirements for renewable energy supply have pushed forward the development of low-cost, high-performance energy storage systems. Supercapacitors are a promising alternative to traditional electrochemical battery power storage devices as they have high power and energy densities and long cycle lives. Binary transition metal oxides (BTMOs) have been investigated as promising materials to improve supercapacitors as they can harness both faradaic and non-faradaic mechanism for energy storage and may exhibit improved conductance compared to simple metal oxides. The combination of these parameters leads to materials that can deliver superior capacitance, long cycling life, and good rate performance. Energy storage mechanisms in electrochemical devices are primarily surface reactions and maximising the available surface area for electrode/electrolyte interaction should improve storage capacity. As such, being able to create a porous electrode material with a suitable pore size distribution should improve the electrochemical performance of supercapacitors. The main aim of this work was to use polymeric templates to synthesise porous binary transition metal oxides (BTMOs) as a way of improving the specific capacitance of materials that could be used to construct supercapacitor electrodes. Novel, porous BTMO materials (NiMoO4, NiCo2O4, CoMoO4 and NaNiVO4) were synthesised using Egg-Shell Membrane (ESM) and poly(methylmethacrylate) (PMMA) using simple, one-pot hydrothermal combustion techniques. The synthesised materials were physically and electrochemically characterized. Addition of a template to the synthesis procedure resulted in improved performance compared to non-templated material for NiMoO4, NiCo2O4, and CoMoO4. In particular, use of the ESM template resulted in significant improvements in performance of the molybdates. The ESM templated NiMoO4 had the best performance with a measured specific capacitance 259 F.g-1 (2-electrode system) with an energy density of 252.2 Whkg-1. The ESM template seemed to promote the formation of β-NiMoO4, a crystal structure that has superior electrochemical storage properties compared to other isomorphs. This was achieved with relatively mild synthesis conditions and resulted in a material that had a porous structure consisting of nanowire like particles. This open, fibrous structure increased available surface area and accessibility to the interior of the bulk material. Optimal choice of polymeric template may need to be tuned to the final product as the best specific capacitances for CoMoO4 (74.45 F.g-1) and NiCo2O4 (38.03 F.g-1) were achieved using different templates; ESM for the former and PMMA for the latter. Synthesis of a novel material, NaNiVO4, was attempted but the resulting material was not fully characterised due to poor performance during initial electrochemical testing.

Characterisation of novel electrode materials for renewable energy storage application

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