RESUMO
In an effort to develop durable, corrosion-resistant catalyst support materials for polymer electrolyte fuel cells, modified polymer-assisted deposition method was used to synthesize tungsten carbide (WC, WC1-x), which was later used as a support material for Pt-based oxygen reduction reaction catalyst, as an alternative for the corrosion-susceptible, carbon supports. The Pt-deposited tungsten carbide's corrosion-resistance, oxygen reduction reaction electrocatalysis, and durability were studied and compared to that of Pt/C. Bulk free carbon was found to be absent from the ceramic matrix which had particle size in the range of 2-25 nm. Tungsten carbide support appears to enhance the oxygen reduction activity on Pt, showing an increase in mass activity (nearly 2-fold at 0.85 V vs RHE) and specific activity (more than 7 times higher), alongside decrease in overpotential, in comparison to Pt/C. A significant increase in durability was also observed with the tungsten carbide-based system.
RESUMO
We use first-principles calculations to study the formation of Pt nanorafts and their oxygen reduction reaction (ORR) catalytic activity on Mo2C. Due to the high Pt binding energy on C atoms, Pt forms sheet-like structures on the Mo2C surface instead of agglomerating into particles. We find that the disordered Mo2C surface carbon arrangement limits the Pt sheet growth, leading to the formation of 4-6 atom Pt nanorafts. The O-O repulsion between the O atoms on the Mo2C and O adsorbate enhances the ORR activity by weakening the O adsorption energy. We find a significant change from the usual scaling of the energies of the intermediates in the ORR pathway and a strong interaction between the nanoraft and water that lead to a high activity of the Pt nanorafts. Fundamentally, our work demonstrates that the activity of metal catalysts can be strongly affected by manipulation of the atomic arrangement of the supporting carbide surface.