Synthesis and physical-chemical characterization of nanocrystalline Ta modified TiO2 as potential support of electrocatalysts for fuel cells and electrolyzers

This work was focused on the synthesis of tantalum (Ta) modified TiO2 mixed oxides and their structural and surface properties characterization using XRD, XPS, BET and H2-TPR techniques. Ta-modified TiO2 samples were synthesized using a sol-gel procedure and evaluated for potential application as electrocatalysts support. The tantalum (Ta) modified TiO2 mixed oxides showed a unimodal nanoporous structure with pore sizes ranging from 3 nm to 5 nm. Concomitant with their higher surface area and pore volume, the mixed oxides were nanocrystalline and significantly smaller than Ti and Ta single oxides prepared by the same method (7-8 nm). A dominant anatase phase was detected by XRD at low calcination temperature, while the crystallographic structure becomes rutile when the sample was treated at 850 °C. By incorporating Ta into TiO2, the lattice parameters were changed, the reducibility of mixed oxides was increased and the surface oxygen deficiency was significantly enhanced as well. The present study clearly established that the structural (crystal phase, crystal size, nanoporosity, pore size) and surface properties (reducibility, oxygen deficiency, acidity, oxidation activity) of the Ta-modified TiO2 mixed oxides can be tailored by modifying the sol-gel procedure and the thermal treatment. A palladium catalyst supported on this oxide (30% Pd/TaTiOx) was prepared by the sulphite complex route. The catalyst was ex-situ characterized by physico-chemical analysis and investigated for the ORR to evaluate its activity, stability and durability. The Pd/TaTiOx catalyst, compared with catalysts from literature, showed a very promising stability, figuring good perspectives for application in fuel cells and/or electrolyzers.