Mesoporous non-noble mixed metal oxide catalysts for electrochemical oxygen evolution and reduction reactions

Developing efficient, low-cost earth-abundant electrocatalysts to replace the expensive and scarce state-of-the-art noble metal-based catalysts, such as Pt and IrO2, is a significant challenge to implementing a sustainable energy-based economy. Recent studies have shown that porous non-noble transition metal-based catalysts, such as oxides, alloys, perovskites, sulfides, and phosphides, can efficiently catalyze oxygen evolution and reduction reactions (OER and ORR, respectively). Transition metal oxides are cheap, easy to synthesize, non-toxic, and thus appealing as potential catalysts. Mesoporous cobalt-based oxides have demonstrated good electrocatalytic activity and excellent stability in alkaline media. Introducing other transition metals or (and) structural defects is a popular way to enhance the activity of these catalysts. However, there is a lack of systematic experimental and theoretical studies on mixed metal oxides for predicting or explaining the increase or decrease in the activity and stability upon incorporating other metals into the catalysts. Moreover, the effect of synthesis conditions on the properties of the materials is not fully explored, which is crucial for accurately producing complex oxides of desired compositions. In this thesis, I try to address these issues. Ordered mesoporous mixed metal oxides were synthesized under various conditions and thoroughly characterized to establish the optimal calcination procedures to prepare phase-pure oxides. Cu, Ni, Zn, Mn, and Fe were systematically introduced in the spinel Co3O4 through partial cation substitution to investigate the impact of each metal alone and in combination with other metals on the physicochemical electrocatalytic properties of these materials. Furthermore, an in-depth study of the (mixed) metal oxides with engineered structural defects was performed to analyze their role in the electrocatalytic properties of these oxides. (author)