The development of high-activity, low-cost non-noble metal oxygen reduction/oxygenation catalysts is crucial for improving the electrical performance of fuel cells and metal air batteries and their large-scale application. Among the many alternatives studied, transition metal oxides (such as Co3O4) catch our attention because of their low cost, abundant sources, and potential oxygen catalysis. However, the poor electron conductivity of Co3O4 has not yet been fully exploited, and its oxygen reduction activity is significantly lower than that of noble metal platinum. In addition, there is still a lack of controllable synthesis of Co3O4 nanostructures, especially a simple and rapid synthesis strategy for controlling the exposed crystal planes on the surface. This has given rise to the challenge of investigating the structure-activity relationship between the microscopic crystal orientation and its macroscopic electrocatalytic properties, thereby further clarifying the active sites on the surface of the transition metal catalysts and further improving the performance to rival the precious metals.
Figure 1. Schematic illustration of the controllable fabrication of Co3O4-NC/N-rGO, Co3O4-NTO/N-rGO, and Co3O4-NP/N-rGO nanocomposites via a facile and template-free hydrothermal strategy.
Recently, Prof. Deng Yida and Prof. Hu Wenbin of Tianjin University proposed a simple, rapid, and controllable synthesis of nitrogen-doped graphene loaded on Co3O4 nanostructures with different crystal planes to encapsulate the Co3O4 nanostructures, by optimizing the proportion of Co2+ and Co3+ active sites on the Co3O4 surface and the adsorption and desorption behavior of oxygen, obtained excellent bifunctional catalytic activity and zinc-air battery performance, and carried out in-depth analysis of the catalytic mechanism. The team proposed that the relative molar ratio of ammonia molecules to cobalt ions is the key parameter affecting Co3O4 nucleation and preferential growth along different crystal planes. With the increasing amount of ammonia added, the Co3O4 cubes, truncated octahedrons and polyhedron nanoframes constructed by {001}, {001}+{111} and {112} crystal planes were obtained on the nitrogen-doped graphene substrates, respectively. The experimental results and density functional theory respectively illustrate that the Co3+ active sites on Co3O4 surface octahedral gap and the electronic coupling between Co3O4 and nitrogen-doped graphene can optimize the adsorption, activation, and desorption features of oxygen species on the surface of the material, which is the intrinsic reasons for exhibiting high electrocatalytic activity. The results provide a new way to advance the activity of nano-catalysts by regulating surface catalytic sites at the atomic scale. (Correspondent: Prof. Deng Yida)
The related article was published in Advanced Energy Materials (DOI: 10.1002/aenm.201702222). The first author of the article is Dr. Han Xiaopeng, a faculty member at the School of Materials Science and Engineering, Tianjin University.
By: the School of Materials Science and Engineering
Editors: Qin Mian and Keith Harrington
