As environmental protection and energy shortage become the top priorities for the current world. More and more scientific research effort has been put into the investigation and development of clean and alternative energy, as well as renewable energy conversion systems including fuel cells and water electrolyser. The continuous development of these systems also means the ever-increasing demand for highly efficient catalysts day by day. However, the commercialization of these devices has always been hindered by their heavy reliance on scarce noble metal catalysts.
Alternatively, 3d transition metal cobalt, as its unique electronic configuration and lower cost, could potentially replace the expensive precious metal catalysts. Therefore, the research presented in this thesis tried to use the strategy of regulating the microstructure and chemical local environment of cobalt to design and synthesize different cobalt-based carbon supported electrocatalysts by high-temperature pyrolysis.
Firstly, carbon black-supported cobalt phosphide nanoparticles were prepared and their catalytical activities toward alkaline HER and OER were evaluated. Besides, chromium dopant was successfully introduced into the cobalt phosphide lattice and the performance of the catalyst was further enhanced by more facile kinetics obtained through chromium doping.
Secondly, Co nanoparticles supported on N-doped carbon matrix were prepared and their performance toward electrosynthesis of H2O2 via a 2e- oxygen reduction in alkaline solution were evaluated. The catalyst shows high selectivity and reactivity toward ORR. The high performance of the catalyst was caused by the synergy of Co nanoparticles and the N-doped carbon support, as well as the reduced activity on cobalt nanoparticles toward H2O2 decomposition compared with Co single atoms. Furthermore, high pH also appears to affect the catalyst surface composition (i.e., more OH covered catalysts surface formed) and hence favor the production of H2O2 from 2e- oxygen reduction.
Finally, atomically dispersed Co and N-doped carbon were prepared. Its catalytical activity toward the ORR in acidic solution and practicability in PEMFC were evaluated. The best performing Co-Nx/C catalyst shows low H2O2 selectivity (~3%) with high half-wave potential (E1/2) of ~0.78 VRHE in 0.5 M H2SO4. The intrinsic activity of the catalyst was further investigated by enhanced physical characterization and the active sites of the catalyst were quantified by a nitrite stripping method. Finally, the catalyst was assembled into the MEA for evaluating its performance under a more practical conditions in PEMFC system.