Abstract: Oxygen reduction reaction (ORR) and conversion of bicarbonate into value-added chemicals are two significant electrochemical processes for energy storage and conversion. ORR is an important electrochemical reaction in fuel cells and metal air batteries that provides power conversion and storage capacity, respectively, for portable electronics and electric vehicles. However, the performance of catalysts (e.g., platinum-based) is critically limited by slow kinetics, inefficient four-electron pathway and surface deactivation. This limited performance of platinum-based catalysts, the scarcity of platinum, and vulnerable supply chains for critical minerals require the development of alternative electrocatalysts now more than ever.
Carbon-based materials possess several key properties that are beneficial for catalytic applications such as high electric conductivity, large surface area, inert electrode surface and low cost. Catalytic activity of carbon-based electrode can be promoted by tailoring surface and structure through the incorporation of heteroatom dopants. This work focus on synthesis of electrocatalysts and their surface modification to achieve effective ORR performance in alkaline media. The ORR performance of nitrogen (N) and boron (B) co-doped carbon nano onions (CNOs). In this work annealing temperature was found a crucial factor in the synergistic benefit of N and B towards ORR. Furthermore, this research was extended to discuss the impacts of nitrogen heteroatom and copper nanoparticles on ORR performance.
Moreover, electrocatalytic carbon dioxide (CO2) reduction (CO2RR) in a membrane electrode assembly was investigated. Atmospheric CO2 has significantly increased in last two decades. Since CO2 is a primary greenhouse gas emitted on earth, it is imperative to suppress the concentration of emitted CO2. While the regulation of CO2 emissions is critical, CO2 capture and storage (CCS), and biological, chemical, and electrochemical conversions are promising approaches to reduce atmospheric CO2 concentration. In electrochemical conversion, a common method employs the feed of high-purity compressed CO2 gas into an electrolyzer. This method, however, is not economically viable because it requires the release and/or pressurization of CO2 from captured CO2 solution, which are energy-intensive. To resolve this issue, aqueous carbonate/bicarbonate (CO32-/HCO3-) transported from upstream carbon capture process can be directly fed into an electrolyzer. We demonstrate that a cationic exchange membrane coated with a thin copper film can efficiently convert bicarbonate to C1-C2 products such as formic acid and acetic acid. Both liquid and gas products were quantified by using proton nuclear magnetic resonance (H1 NMR) and gas chromatography, respectively.
The studies herein highlight the importance of structure modification of catalysts, surface chemistry, and membrane-electrode interface to improve the efficiency and selectivity of ORR and CO2RR processes.
