Zn²⁺ Ion-assisted growth of cobalt phosphate towards water oxidation reaction

Kumar, Rahul (2019) Zn²⁺ Ion-assisted growth of cobalt phosphate towards water oxidation reaction. Masters thesis, Indian Institute of Science Education and Research Kolkata.

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Abstract

Water splitting is a two electrode process in which at cathode reduction of proton takes place giving hydrogen molecule called as Hydrogen evolution reaction (HER) process while at anode oxidation of water molecule takes place giving oxygen molecule called as oxygen evolution reaction (OER) process. The well-known catalysts having high activity for these reactions are Pt, Ru and Ir, however, they suffer from limitations of being expensive and not stable for longer duration. Catalysts from earth abundant materials giving higher activity and stable for long period of time need to be developed. In this research Zinc Cobalt phosphate hydrate is being prepared by simple hydrothermal technique. Although Zinc ion (Zn²⁺) is redox inactive and not a promising catalyst towards OER our results suggest it is bolstering the OER catalytic activity of Cobalt phosphate sample by reducing the overpotentials. The required overpotential for Cobalt hydroxide hydrogen phosphate is 480 mV to reach the current density of 100 mA/cm². After the incorporation of Zn²⁺ ion into the cobalt system the over potential is reduced to 410 mV to reach the same current density. The superior catalytic activity of Zinc cobalt phosphate may be originating from the leaching of Zinc ions from the catalyst surface during OER measurement in 1M KOH. This could in turn helps in the exposure of more Co³⁺/Co⁴⁺ (catalytic active sites) to the electrolyte. Furthermore, Zinc being Lewis acidic in nature also helping in the adsorption of water molecule on to catalyst surface resulting in improving the sluggish kinetics of OER. This could be an interesting strategy to develop numerous electro catalysts which work in the alkaline medium.

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