Nanomaterials, Catalysis, Electrochemistry

Summary of the PhD thesis, entitled "Study of the anode of the Direct Borohydride Fuel Cell"

The thesis work focuses on direct borohydride fuel cell (DBFC) anodes. A first approach to develop a suitable anode design for the DBFC consists in the study of the anode within the real DBFC system. In that frame, carbon-supported platinum and palladium nanoparticles are characterized and compared as anode electrocatalyst in DBFC configuration. Other variables such as the morphology of the anode and the stability of the catalyst nanoparticles are considered.

The ideal DBFC anode catalyst should show a suitable electrocatalytic activity towards the borohydride oxidation reaction (BOR), without quantitative production/escape of gaseous hydrogen during the reaction. Studying these aspects is not straightforward using a real DBFC system, as the global behavior of the DBFC depends on numerous experimental variables external to the anode. In order to overcome this issue, a prospective anode catalyst can be isolated and specifically studied in half-cell configuration in a more controlled environment. The different methods possible for the evaluation of an electrocatalyst for the anode of the DBFC are discussed in this work, and benchmarks are proposed to compare a given material with the DBFC literature.

Another strategy to develop suitable DBFC anode catalysts is to further understand the BOR mechanism. In that frame, the BOR is studied on model platinum-based electrodes with different levels of complexity. Bulk polycrystalline and single-crystals Pt flat electrodes enable to study the structure sensitivity of the BOR. The poisoning of the Pt active surface is investigated using Pt nanoparticles supported on flat glassy carbon substrate. Three-dimensional electrodes are also surveyed: Pt nanoparticles supported on vertically-aligned carbon nanofiber electrodes. The deposition of various amounts of Pt nanoparticles on the VACNF substrate enables to study the influence of the density of Pt active sites towards the BOR. The findings obtained using these model electrodes are gathered with previous results from the literature in order to propose a BOR mechanism on Pt. This mechanism is used in a mean-field microkinetics model. The simulated curves of this mechanism reproduce the main experimental features.

The complete thesis can be downloaded here. The corresponding publications are