A novel method for the preparation of bi-metallic (Pt-Au) nanoparticles on boron doped diamond (BDD) substrate: application to the oxygen reduction reaction

A novel method was developed to synthesize bi-metallic nanoparticles (Au-Pt) on boron-doped diamond (BDD) substrate. This method consisted of (a) deposition of a small amount of gold (equivalent to a few monolayers) by sputtering on the BDD surface, (b) heat treatment of the obtained sample at 600°C in air, resulting in the formation of stable nanoparticles on BDD (Au/BDD electrode), (c) electrodeposition of Pt on the Au/BDD surface occurring preferentially on the Au nanoparticles, and finally (d) heat treatment at 400°C to enhance the interaction between Au and Pt. The ratio between Au and Pt nanoparticles can be modified by modifying the amount of electrodeposited Pt and was estimated using cyclic voltammetry. These Pt-Au/BDD composite electrodes were used to study oxygen reduction using both potential sweep (cyclic voltammetry) and hydrodynamic (turbine electrochemical cell) method

Impedance spectroscopic investigation of a Rh/YSZ catalyst under polarization

Electrochemical impedance spectra at 450-600 °C and $${P_{{\rm{O}}_{\rm{2}} } = 0.5}$$ kPa of a rhodium catalyst interfaced with yttria-stabilized-zirconia (Rh/YSZ) were compared with a model based on the mechanism of electrochemical promotion. In the proposed equivalent electric circuit, existence of an "effective” double layer at the gas-exposed catalyst surface and its potential-controlled modification via diffusion of oxygen ions between the O2− conducting solid electrolyte support (YSZ) and the catalyst are represented by two additional elements: adsorption capacitance and Warburg impedance. Under positive polarization, the adsorption capacitance increases dramatically indicating reinforcement of the "effective” double layer at the catalyst/gas interface, in agreement with the observation known from electrochemical promotion practice that positive polarization of a rhodium electrode leads to rhodium oxide reduction, hence, to dramatic increase in catalytic reaction rat

Relation between potential and catalytic activity of rhodium in propylene combustion

The relation between the catalyst potential and the catalytic performance has been investigated in the gas-phase combustion of propylene with oxygen over rhodium catalysts at 375 °C. The rhodium catalyst, deposited on yttria-stabilized zirconia (YSZ) solid electrolyte, also served as working electrode in the electrochemical cell. Under open-circuit conditions, the measured catalyst potential was found to be a sensitive indicator of the oxidation state of the rhodium catalyst, which influences the catalytic reaction rate dramatically and depends strongly both on the method of catalyst film preparation and on the composition of the reacting gas mixture. In turn, under closed-circuit conditions, the applied catalyst potential is a convenient tool to maintain the catalyst in its more active, reduced form and to control its catalytic performance. The activity of atomic oxygen at the three-phase boundary (tpb) during open-circuit catalytic reaction was estimated from solid electrolyte potentiometric (SEP) measurements, in good agreement with the average surface oxidation state obtained from XRD and XPS analyses. O/Rh atomic ratios higher than stoichiometric were found by XPS at the outer surface of the catalysts suggesting a strong open circuit O2− spillover due to strong metal support interactions (SMSI) and a concomitant extension of the electric double layer to the gas-exposed catalyst surface, similarly to emersed electrodes in aqueous electrochemistry. Applying potentials up to several hundreds of mV, highly nonfaradaic promotion of propylene combustion was achieved. Electrochemical promotion of catalysis (EPOC) was most efficient at stoichiometric gas composition, that is, close to the limit of surface reduction, and with the catalyst exhibiting the smallest O2− spillover population at open-circuit condition

Deposition of clusters and nanoparticles onto boron-doped diamond electrodes for electrocatalysis

Metal and metal oxide particles and nanoparticles, differing from each other by their nature and synthesis technique, were deposited onto boron-doped diamond (BDD) thin film electrodes. The applicability in electrocatalysis of thermally decomposed IrO2 and Au nanoparticles, electrodeposited Pt particles, dendrimer-encapsulated Pt nanoparticles (Pt DENs) and microemulsion-synthesized Pt/Ru nanoparticles was studied, once deposited on BDD substrate. In all cases, the electrochemical response of the composite electrodes could be solely attributed to the supported particles. All the particles, with the exception of Pt DENs, exhibited electrocatalytic activity. Pt DENs inactivity has been attributed to insufficient removal of the dendrimer polymer matrix. It was concluded that the BDD electrode is a suitable substrate for the electrochemical investigation of supported catalytic nanoparticle

Electrochemical modification of the catalytic activity of TiO2/YSZ supported rhodium films

The electrochemical activation of ethylene oxidation was studied over rhodium catalysts of different thickness (40, 100 and 160 nm) sputtered on top of a thin layer of TiO2 deposited on YSZ. The strong relationship between catalytic activity and oxidation state of rhodium was confirmed. Under open-circuit operation the catalyst potential appears as a suitable indicator of the surface oxidation state of rhodium allowing a prediction of the catalytic behavior from solid electrolyte potentiometric measurements. Under closed-circuit conditions the catalyst potential was used as a tool to tune the catalytic activity of rhodium which showed increasing promotional efficiency with decreasing catalyst film thicknes

Effect of microstructure on the electrochemical behavior of Pt/YSZ electrodes

Two types of O2,Pt/YSZ electrode preparation (Pt/YSZ cermet and sputtered platinum film) have been characterized by SEM and by cyclic voltammetry and chronoamperometry at 450 °C in 20 kPa oxygen. Cyclic voltammetry on the cermet and on the as-sputtered non-porous film electrode evidenced the characteristics of the PtO x /Pt couple. The corresponding redox reaction occurs at the metal/electrolyte interface and it manifests itself by an anodic wave and one of more cathodic peaks in the voltammogram. Heat treatment of the sputtered electrode at 700 °C in oxygen atmosphere resulted in a porous structure by coalescence of the film. Cyclic voltammetry of the porous film electrode featured the characteristics of the O2/O2− couple, i.e. the redox reaction of gaseous oxygen occurring at the tpb. Chronoamperometry at anodic potentials showed similar features for both electrode preparations: an initial inhibition, a current peak and a slow activation, the latter being related to the phenomenon of electrochemical promotion of catalysi

Electrochemical behaviour of DSA type electrodes prepared by induction heating

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