UC Merced

The studies presented in this thesis focus on developing non-precious metal electrodes for oxygen reduction reactions (ORR), oxygen evolution reactions (OER), and hydrogen evolution reaction (HER), the core catalysis of fuel cells and electrolyzers. Metal oxides on carbon support are mainly considered as the catalytically active materials in this study. Two approaches of fabrication are presented: one based upon atomic layer deposition (ALD) and one by a wet synthesis process known as the solvothermal method. The resulting catalysts are characterized to reveal the process-performance relationship for ORR, OER, and HER. In the first study (Chapter 4), we demonstrate a bimetallic Co/Cu-embedded N-doped carbon structure for trifunctional catalysis of ORR, OER, and HER in alkaline media. A hybrid catalyst synthesized through a metal-organic framework-based process (M-NC-CoCu) enables active trifunctional catalysis due to its multi-faceted favorable characteristics. It is believed that a range of catalytically active sites are formed through the approach including well-dispersed tiny CuCo2O4 phases, a high concentration of pyridinic and graphitic N, and Cu-Ox, Cu-Nx, and Co-Nx moieties. In addition, a high-surface-area morphology with a high concentration of sp2 bonding, which is beneficial for facilitated electron conduction, further contributes to the performance as an electrocatalyst. The second study (Chapter 5) investigates the catalytic activities of titanium dioxide (TiO2) incorporated onto graphene oxygen (GO) by atomic layer deposition (ALD). The catalytic activity was systematically measured by cyclic voltammetry (CV). Evidence shows that TiO2 bonded on the surface of GO is catalytic active. An ALD treatment of TiO2 shows improvement in the catalytic activity compared to non-treated graphene. The ALD temperature also affects the catalytic performance. A higher temperature results in a higher catalytic activity, which is ascribed to the simultaneous reduction of GO and the addition of catalytically active TiO2/GO interfaces by ALD. In addition, there is also an optimal number of ALD cycles for enhanced catalytic activity. In the third study (Chapter 6), a zinc-based zeolitic imidazole framework (ZIF-8) is carbonized to form organized N-doped carbon nanostructures. The carbonized ZIF-8 (C-ZIF-8) was then used as a substrate (support) for ALD. Titanium (Ti) and/or cerium (Ce) precursors were introduced to the ALD chamber to form bimetallic (Ti and Ce) or monometallic (Ti or Ce) hybrids with C-ZIF-8. I investigated the effects of bimetal incorporation in the electrocatalytic properties of the resulting hybrid systems toward OER and HER. The optimization of ALD parameters, such as the number of cycles, temperature, and pressure for catalytic performance are also discussed.