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New in ethanol oxidation

12 June 2019 - Catalysis

Liang et al. report a direct 12-electron ethanol oxidation with a new type of catalyst system. Ethanol fuel cells have a lot of advantages: high energy content, non-toxic, fuel readily available, light-weight but are not exactly commerce-ready: the only cell found available in a shop is a fuel cell science kit. The Nissan car ethanol fuel cell reforms ethanol to hydrogen first. Other cars with fuel cells use methanol or hydrogen.
Back to the science report: direct 12e oxidation means CH3CH2OH + 3H2O => 2CO2 + 12H+ + 12e-. The catalyst is core/shell Au@PtIr/C which means the core is made up of a gold supported by carbon nanoparticle with the shell a monolayer of platinum and iridium. Because Pt and Ir are sitting directly on the gold lattice, their mutual orientation is not ideal and hence the reactivity. The analytic toolbox has the following: energy-dispersive X-ray spectroscopy exposes the individual Pt and Ir atoms in a 2D map and cyclic voltammetry gives a peak current of 58 Ampere per mg, a lot more than that measured for for Au@Pt/C (no Ir) and Au@Ir/C (no Pt). A 2017 record by another team for Pd40Ni43P17 with almost 5 A/mg was smashed.(Chen et al. DOI). Infrared reflection absorption spectroscopy (IRRAS, alkaline, in-situ) allowed the team to look around for reaction intermediates. As they did find carbon dioxide (and as secondary reaction product carbonate) but not carbon monoxide - a catalyst poison - they conclude the reaction path is truly a 12 electron one with the carbon carbon bond broken in step 1.