Understanding the electrochemical hydrogenation of acetone on Pt single crystal electrodes

The heterogeneous upgrading of biomass by means of electrocatalytic hydrogenation is an attractive way to refine products for industrial and pharmaceutical purposes. Also, the efficient electrochemical reduction of carbonyl compounds can act as hydrogen vectors, and therefore energy vectors. In this manuscript, we render further fundamental insights into the electrochemical reduction of acetone as a model molecule of carbonyl compounds. The structural sensitivity of the reaction is demonstrated by using platinum single crystal electrodes with low Miller indices and stepped electrodes with (110) terraces and either (111) or (100) monoatomic steps. Among the basal planes, Pt(110) is the only one active for the electroreduction of acetone. The inclusion of (111) steps on the (110) terraces does not significantly alter the behavior of Pt(110), but increasing the (100) step density has been observed to decrease the activity. We attribute this different performance to a geometrical effect of the active sites. By using different supporting electrolytes, we have found that sulfate competes with acetone for the surface sites, thus modifying the adlayer interfacial structure and hampering acetone reactivity.This research was funded by Ministerio de Ciencia e Innovación (Spain) grant number PID2019-105653GB-I00), Generalitat Valenciana (Spain) grant number PROMETEO/2020/063. RMAA. acknowledges the financial support from Generalitat Valenciana (CDEIGENT/2019/018)

On the oxidation of isopropanol on platinum single crystal electrodes. A detailed voltammetric and FTIR study

Isopropanol oxidation is studied on platinum single crystals using electrochemical techniques and FTIR spectroscopy at different isopropanol concentrations. Isopropanol oxidation is found to be facilitated by the presence of adsorbed OH on the electrode surface, which reacts with an isopropanol molecule to yield the adsorbed alkoxide. Thus, when sulfuric acid is used as the supporting electrolyte instead of perchloric acid, oxidation currents diminish drastically since sulfate hinders OH adsorption. Kinetic measurements reveal that the chemical reaction between adsorbed OH and isopropanol is the rate-determining step in the mechanism. Voltammetric and FTIR experiments show that acetone is the major product of the reaction. On the Pt(111) surface, acetone is produced exclusively, and oxidation currents are controlled by diffusion since, on this electrode, acetone is not adsorbed and the adsorbed OH mobility is high. The adsorption of acetone-related species on the Pt(110) surface, which partially block the surface, leads to slightly lower currents. On the other hand, the Pt(100) electrode is the one showing significant rates for the C–C bond cleavage, yielding adsorbed CO and other species. Although this route is a minor path, the surface blockage by these species leads to a significant diminution of the currents.This research was funded by Ministerio de Ciencia e Innovación (Spain) grant number PID2019-105653 GB-I00) and Generalitat Valenciana (Spain) grant number PROMETEO/2020/063. RMAA acknowledges the financial support from Generalitat Valenciana (CDEIGENT/2019/018). DSM thanks the Government of Argelia for the award of a doctoral fellowship to support her studies at the University of Alicante

Why Methanol Electro-oxidation on Platinum in Water Takes Place Only in the Presence of Adsorbed OH

Untangling the mechanism of the methanol electro-oxidation on platinum in water as a model reaction is essential to optimize fuel cells using alcohols as fuel. Recent experiments unexpectedly suggested that this electro-oxidation process would take place only in the presence of adsorbed OH. The here reported results, carefully obtained under low methanol concentrations on the three basal planes of platinum at different scan rates to discriminate between oxidation and adsorption processes, confirm such an unexpected preliminary observation. It is found that adsorbed CO from methanol is only formed when adsorbed OH is already present on the surface. This observation is a clear indication that adsorbed OH is involved in the mechanism beyond providing the oxygen group required to oxidize adsorbed CO, which has never been considered before. Supported by density functional theory calculations, the role played by adsorbed OH in the methanol electro-oxidation to CO on platinum in water and the reason why this reaction is not observed in the absence of adsorbed OH are also here both elucidated. A combination of kinetic and thermodynamic factors, such as the presence of multiple water molecules per methanol molecule, the high adsorbed OH mobility on the surface, the favorable coadsorption of methanol in the presence of adsorbed OH, and the favorable and virtually barrier-less hydrogen transference from the hydroxy group of methanol to adsorbed OH to yield water result in the immediate activation of methanol (as soon as the molecule approaches the surface) through the favorable substitution of adsorbed OH by adsorbed methoxy. This contribution represents a change of paradigm in the understanding of how alcohols are electro-oxidized in reference systems and have crucial implications in the search for better electrocatalysts.This research was funded by Ministerio de Ciencia e Innovación (Spain) Grant No. PID2019-105653GB-I00) and Generalitat Valenciana (Spain) Grant No. PROMETEO/2020/063. R.M.A.-A. acknowledges financial support from Generalitat Valenciana (Grant No. CDEIGENT/2019/018)