The electrooxidation of CO: a test reaction in electrocatalysis

This review paper aims to show how the electrochemical behaviour of CO plays a key role in the understanding of the reaction mechanism of many electrocatalytic oxidations of small organic molecules. For that purpose, the adsorption of CO on noble metal electrodes, eventually modified by foreign metal adatoms, is reviewed, taking into account both experimental (electrochemical and spectroscopic techniques) and theoretical (Extended Hückel Model) approaches. Data from the gas phase-solid metal interface are also considered.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas (INIFTA)Facultad de Ciencias Exacta

The electrooxidation of CO: a test reaction in electrocatalysis

This review paper aims to show how the electrochemical behaviour of CO plays a key role in the understanding of the reaction mechanism of many electrocatalytic oxidations of small organic molecules. For that purpose, the adsorption of CO on noble metal electrodes, eventually modified by foreign metal adatoms, is reviewed, taking into account both experimental (electrochemical and spectroscopic techniques) and theoretical (Extended Hückel Model) approaches. Data from the gas phase-solid metal interface are also considered.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas (INIFTA)Facultad de Ciencias Exacta

The electrooxidation of CO: a test reaction in electrocatalysis

This review paper aims to show how the electrochemical behaviour of CO plays a key role in the understanding of the reaction mechanism of many electrocatalytic oxidations of small organic molecules. For that purpose, the adsorption of CO on noble metal electrodes, eventually modified by foreign metal adatoms, is reviewed, taking into account both experimental (electrochemical and spectroscopic techniques) and theoretical (Extended Hückel Model) approaches. Data from the gas phase-solid metal interface are also considered.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas (INIFTA)Facultad de Ciencias Exacta

A contribution to the mechanism of “reduced” CO₂ adsorbates electro-oxidation from combined spectroelectrochemical and voltammetric data

The nature of reduced CO2 adsorbates, as well as the mechanisms for their electro-oxidation on platinum, have been reviewed through the light of new experimental data obtained by cyclic voltammetry and by Fourier transform infrared reflectance spectroscopy. Three different “reduced” CO2 adsorbates are described as “‘ensembles”. It is suggested that they involve different extents of adsorbed entities, among which weakly bound and strongly bound hydrogen atoms play the most important role.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicada

EMIRS studies of formic acid electrooxidation on Pd, Au and Pd + Au alloys : Part 1. Investigation of the adsorbates derived from HCOOH and NACOOH chemisorption at Pd in acid and alkaline solutions

An electromodulated IR reflectance spectroscopy (EMIRS) study of the adsorbed species resulting from HCOOH and NaCOOH chemisorption at a smooth Pd electrode is presented. In acid solution, large amounts of multibonded CO species are detected, in contrast with the absence of any type of CO adsorbate in alkaline solutions. For the latter, the appearance of adsorbed formate species can be concluded from the increase in the intensity of two bands at 1060 and 2960 cm−1. These results suggest that the adsorbate is bound to Pd via two O atoms. In acid solution, however, the contribution of a formate species bound to the metal through a single O atom is discussed as the result of competitive adsorption with the multibonded CO species.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicada

Chemisorption of methanol on different platinum electrodes (smooth and rough polycrystalline, monocrystalline, and preferentially oriented), as studied by EMIRS

EMIR spectra of methanol electroadsorbates on smooth and rough polycrystalline, monocrystalline and preferentially oriented platinum electrodes are reported. The (100)-type preferred oriented platinum behaves approximately as Pt (100) single crystals. On electrodispersed platinum electrodes the poisoning phenomena due to CO adsorbates appear to be reduced as compared to smooth platinum electrodes. EMIRS results correlate well with the electrochemical behaviour of the different platinum electrodes for methanol electrooxidation.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicada

Pt-decorated nanoporous gold for glucose electrooxidation in neutral and alkaline solutions

Exploiting electrocatalysts with high activity for glucose oxidation is of central importance for practical applications such as glucose fuel cell. Pt-decorated nanoporous gold (NPG-Pt), created by depositing a thin layer of Pt on NPG surface, was proposed as an active electrode for glucose electrooxidation in neutral and alkaline solutions. The structure and surface properties of NPG-Pt were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray powder diffraction (XRD), and cyclic voltammetry (CV). The electrocatalytic activity toward glucose oxidation in neutral and alkaline solutions was evaluated, which was found to depend strongly on the surface structure of NPG-Pt. A direct glucose fuel cell (DGFC) was performed based on the novel membrane electrode materials. With a low precious metal load of less than 0.3 mg cm-2 Au and 60 μg cm-2 Pt in anode and commercial Pt/C in cathode, the performance of DGFC in alkaline is much better than that in neutral condition

Characterization of different FAD-dependent glucose dehydrogenases for possible use in glucose-based biosensors and biofuel cells

In this study, different flavin adenine dinucleotide (FAD)-dependent glucose dehydrogenases (FADGDHs) were characterized electrochemically after “wiring” them with an osmium redox polymer [Os(4,4′-dimethyl-2,2′-bipyridine)2(PVI)10Cl]+ on graphite electrodes. One tested FADGDH was that recently discovered in Glomerella cingulata (GcGDH), another was the recombinant form expressed in Pichia pastoris (rGcGDH), and the third was a commercially available glycosylated enzyme from Aspergillus sp. (AspGDH). The performance of the Os-polymer “wired” GDHs on graphite electrodes was tested with glucose as the substrate. Optimal operational conditions and analytical characteristics like sensitivity, linear ranges and current density of the different FADGDHs were determined. The performance of all three types of FADGDHs was studied at physiological conditions (pH 7.4). The current densities measured at a 20 mM glucose concentration were 494 ± 17, 370 ± 24, and 389 ± 19 μA cm−2 for GcGDH, rGcGDH, and AspGDH, respectively. The sensitivities towards glucose were 2.16, 1.90, and 1.42 μA mM−1 for GcGDH, rGcGDH, and AspGDH, respectively. Additionally, deglycosylated rGcGDH (dgrGcGDH) was investigated to see whether the reduced glycosylation would have an effect, e.g., a higher current density, which was indeed found. GcGDH/Os-polymer modified electrodes were also used and investigated for their selectivity for a number of different sugars

Determination of Specific Electrocatalytic Sites in the Oxidation of Small Molecules on Crystalline Metal Surfaces

The identification of active sites in electrocatalytic reactions is part of the elucidation of mechanisms of catalyzed reactions on solid surfaces. However, this is not an easy task, even for apparently simple reactions, as we sometimes think the oxidation of adsorbed CO is. For surfaces consisting of non-equivalent sites, the recognition of specific active sites must consider the influence that facets, as is the steps/defect on the surface of the catalyst, cause in its neighbors; one has to consider the electrochemical environment under which the “active sites” lie on the surface, meaning that defects/steps on the surface do not partake in chemistry by themselves. In this paper, we outline the recent efforts in understanding the close relationships between site-specific and the overall rate and/or selectivity of electrocatalytic reactions. We analyze hydrogen adsorption/desorption, and electro-oxidation of CO, methanol, and ammonia. The classical topic of asymmetric electrocatalysis on kinked surfaces is also addressed for glucose electro-oxidation. The article takes into account selected existing data combined with our original works.M.J.S.F. is grateful to PNPD/CAPES (Brazil). J.M.F. thanks the MCINN (FEDER, Spain) project-CTQ-2016-76221-P