OPTIMIZATION OF SYNTHESIS PARAMETERS OF TRANSITION METALS DEPOSITED ON CARBON STRUCTURES FOR ENHANCING ELECTROCATALYTIC ACTIVITY

This study focuses on developing non-precious metal electrodes for oxygen reduction reactions (ORR) and oxygen evolution reactions (OER), the core catalysis of fuel cells and electrolyzers, respectively. Specifically, metal oxides on carbon support are considered as the catalytically active electrode 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 and OER. The first study 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. Comparing the CV before and after ALD of TiO2 shows improvement on the catalytic activity after deposition of TiO2. Temperature effects, during deposition, were also measured by CV. The trends show that at higher temperature there is an increase in catalytic activity, which is due to the simultaneous reduction and addition of TiO2 during ALD. In addition, there is also an optimal amount of TiO2 that can be deposited for enhanced catalytic activity, which is 25 cycles. In the second study, a bimetallic metal organic framework (MOF) was synthesized using cobalt and copper chloride, complexed with 2-aminoterephthalic acid and incorporated with graphene oxide (GO), which resulted in flower-like nanostructures. Effects of post-annealing on catalytic activity for this material were measured using CV and linear sweep voltammetry (LSV). This bimetallic MOF material showed both ORR and OER activity in an alkaline environment. In addition, as the annealing temperature was increased to 700°C, the ORR and OER catalytic capabilities improved for this material resulting in an ORR half-way potential at around 0.72 V and OER on-set potential of 1.57 V (at 10 mA/cm2). With the overall oxygen electrode performance gauged by the difference of ORR and OER metrics (E = EOER,j=10 – EORR,1/2 = 0.85 V), the bimetallic MOF material has a potential of serving as an excellent bifunctional electrocatalyst for regenerative fuel cells