Identification of bimetallic electrocatalysts for ethanol and acetaldehyde oxidation: Probing C2-pathway and activity for hydrogen oxidation for indirect hydrogen fuel cells

Abstract

Hydrogen, in the ethanol molecule, can be utilized in indirect hydrogen fuel cells. In this device, ethanol can be dehydrogenated producing H2 and acetaldehyde in an external fuel processor, and the H2 molecules are electro-oxidized in the anode. The anode electrocatalyst can, additionally, be active for the electro-oxidation of residual ethanol or acetaldehyde, but must catalyze the reaction via the C2-pathway (intact CC bond), in order to avoid the formation poisoning species. This work investigated potential materials that are active for H2 and catalyze the selective electro-oxidation of ethanol and acetaldehyde via the C2-pathway. The bimetallic electrocatalysts were formed by W, Ru and Sn-modified Pt nanoparticles. The reaction products were followed by on-line differential electrochemical mass spectrometry (DEMS) experiments. The results showed that Ru/Pt/C and Sn/Pt/C presented higher overall reaction rate when compared to the other studied materials. However, they were non-selective, even at different atomic proportions, and catalyzed the reaction in parallel pathways producing CO2 and acetaldehyde, with Ru/Pt/C presenting the highest average current efficiency for CO2 formation (16.6%). On the other hand, W/Pt/C with high W content was more selective to the C2 route, evidenced by the absence of the DEMS signals for molecules with one carbon atom such as CH4 and CO2. Additionally, this material was active and stable for H2 electro-oxidation, even in the presence of acetaldehyde in solution, contrarily to what was observed for Pt/C, and this was associated to its activity for H2 oxidation and its inability for the CC dissociation, as evidenced by the DEMS measurements. The high selectivity obtained for the W/Pt/C material to the C2-pathway, and its capability for hydrogen electro-oxidation, is an important novelty in this work, as it turns into a potential electrocatalyst for application in the anode of indirect hydrogen fuel cells powered by ethanol, mainly for those that operates as auxiliary power units of internal combustion engine cars.