Material development of cost-effective electrocatalysts for water oxidation reactions

Belami, Debora (2024) Material development of cost-effective electrocatalysts for water oxidation reactions. Doctoral thesis (PhD), Manchester Metropolitan University.

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Abstract

Proton exchange membrane (PEM) electrolysis is a promising technology that can produce high purity, desirable products such as hydrogen and hydrogen peroxide via electrolysis. However, the large-scale commercialisation of PEM electrolysers is hindered due to the expensive and non-selective catalysts necessary for 2-electron (2e-WOR) and 4-electron (4e-WOR) water oxidation reactions. This work aims to develop supported electrocatalysts to address the need for cost-effective and high performing electrocatalysts for the WORs. The use of high surface area catalyst supports can enhance the intrinsic activity of Ir at low loadings (< 75 wt%). Sn and Ti oxides have been widely used as catalyst-supports due to their abundance and stability in corrosive WOR environments. However, Sn and Ti oxides suffer from low conductivity, hindering electrocatalytic activity. In this work, M-doped-SnO2 (where M = Sb, Ta, Mo and Nb) and AuPd coated TiO2 were synthesised and characterised to investigate the influence of their physical properties on the 4e-WOR. Additionally, Ir deposition syntheses (polyol and acid modified polyol) were investigated and found that the surface charge on the support has significant influence on the Ir loading. Furthermore, the presence of dopants in the supports rendered them unstable while the addition of AuPd to TiO2 supports enhances the electrochemical activity and stability. These trends were consistent across the three-electrode rotating disk electrode and in a 5 cm2 membrane electrode assembly testing for activity and durability. The second part of this work focused on the development of electrocatalysts with a selectivity towards hydrogen peroxide (H2O2). Thin films and nanopowders of metal stannates (Ca-SnO3, Ba-SnO3 and Au-CaSnO3) were synthesised to generate H2O2 through the electrochemical pathway. The activity and selectivity for H2O2 are encouraging despite being relatively low due to lack of conductivity and rapid catalyst degradation. This work will continue in the future to optimise the electrocatalytic activities and selectivities and dissolved catalyst quantification techniques.