Development and Characterization of Organic Electrocatalysts for use in Zinc-Air Batteries

The global deployment of solar photovoltaic and wind power is projected by the International Energy Agency as the primary pathway to reduce dependence on fossil fuels. However, these technologies face a critical bottleneck: their inherently intermittent power generation. For “intermittent renewables” to become the dominant source of electrical energy, efficient energy storage systems are essential. Current storage solutions are not viable on a global scale due to material scarcity, safety concerns, and high capital costs. Among emerging technologies, zinc-air batteries (ZABs) have garnered significant interest. ZABs offer a theoretical energy density five times greater than traditional lithium-ion batteries, utilize safe aqueous alkaline electrolytes, and are composed primarily of abundant materials. Despite these advantages, ZABs suffer from sluggish reaction kinetics due to the high cathodic potentials required for oxygen reduction at the cathode. Traditional catalysts, made from noble metals, lower this cathodic potential but are hindered by cost and scarcity, limiting large-scale deployment. This study investigates the use of an organic electrocatalyst, 5,10,15,20-tetrakis(4-aminophenyl)porphyrin (TAPP), as a sustainable alternative. TAPP was synthesized using a bottom-up approach, and polymerized TAPP (pTAPP) was produced through electrochemical and oxidative chemical vapor deposition methods. Catalytic activity for oxygen reduction in aqueous alkaline solutions, mimicking ZAB environments, was analyzed. A minimum overpotential of 0.37 V vs. RHE was achieved for oxygen reduction using vapor-phase-deposited pTAPP, with maximum current densities of 0.4 mA/cm² at an overpotential of 0.58 V vs. RHE in diffusion-limited conditions. In kinetically-limited conditions a maximum current density of 1.78 mA/cm2 at an over potential of 0.965 V vs. RHE was achieved. The results demonstrate that vapor-phase-deposited pTAPP catalysts have the potential to enhance the feasibility of ZABs for large-scale energy storage, owing to their low precursor requirements and tunable surface morphology. Advisor: Siamak Nejati