Improving the electrocatlytic activity of cobalt oxide for acidic oxygen evolution reaction with bismuth dopants
Creators: name: Peng, Bowen
Publisher: name: No Publisher Supplied
Year: 2024

description: The continued overuse of fossil fuels for energy purposes does not only exacerbate the environment pollution but also causes the depletion of these energy resources. This makes the development of sustainable energy sources, such as green hydrogen, urgent and essential. Currently hydrogen is produced through traditional fossil fuel reforming or dehydrogenation processes. These processes, however, produce greenhouse gases and deplete fossil fuels. In contrast to these processes, water splitting utilizes an abundant raw material (i.e., water) and generates less pollution, if any. As such, this method exhibits a significant potential for massive production of hydrogen and aligns well with the principles of green chemistry. The method is especially quite appealing to produce green hydrogen when coupled with sustainable energy sources such as solar and wind energy. However, the oxygen evolution reaction (OER), a key reaction required for water splitting, hinders the overall efficiency of water splitting due to its slow reaction kinetics and high overpotential resulting from its intricate four-electron transfer processes. Furthermore, in acidic electrolyte, where the abundance of protons results in an efficient hydrogen evolution reaction (HER), most catalysts are unfortunately inactive and highly unstable towards OER. Thus, constructing stable, highly active acidic OER catalysts is of vital importance.With this aim in mind, and to solve the issues mentioned above, a kind of high-performance acidic OER catalyst that is composed of bismuth-cobalt oxide annealed on fluorine-doped tin oxide (FTO) glass substrate is designed and synthesized. In the design of the catalyst, fundamental principles are considered. Co is included as it conforms with the so-called Sabatier principle well, which entails not only high catalytic activity, but also good stability in catalysts. Meanwhile, Bi is chosen as it is expected to work as a catalytically active center when it is with Co for OER. It is also expected to improve the density of active sites and oxygen vacancy in the catalysts, which are favorable for OER. Additionally, catalysts containing Co and Bi in different ratios are synthesized to investigate the effects of their compositions on their electrocatalytic properties. The results show that Co9BiOx, which has a Co:Bi ratio of 9:1, exhibits the best electrocatalytic activity with the lowest overpotential (540 mV) at a current density of 10 mA·cm-2 and the lowest Tafel slope (113 mV·dec-1) to drive the OER. Its electrocatalytic activity is also found to be higher than those of the pristine Co3O4 and the catalysts prepared with other Co:Bi ratios. The high activity of the Co9BiOx, catalyst is accounted by its high electrochemical active surface area and double-layer capacitance. The participation of Bi in the electrocatalytic activities of the catalysts is further confirmed by density-functional theory (DFT) calculations.This project’s findings not only highlight the potential of bismuth doping cobalt oxide to improve the acidic OER activity of this transition metal oxide, but also show the necessity of deeper investigations of p-block elements like bismuth for electrocatalytic applications. Furthermore, the research work leads to an eco-friendly catalyst for sustainable energy solutions.