Electrooxidation electrochemical measurements

It can also be observed from this figure that Sn-containing catalyst is a more effective catalyst for the oxidation of CO than that containing Ru, as a lower onset potential of the oxidation wave is obtained with the former catalyst. It has also to be noted that PtSn catalysts are less active towards methanol electrooxidation than PtRu catalysts (see Section IV. 1). ° However, adsorbed CO species are proposed as reaction intermediates of methanol electro-oxidation, which seems to lead to a paradoxical behavior of PtSn based catalysts. In CO stripping experiments, a negative shift of the onset potential for the oxidation of adsorbed CO on PtSn also occurs. " On the basis of in situ infrared spectroscopy studies coupled with electrochemical measurements, Mo-... 

Electrolytes were prepared with water of 18 cm conductivity purified by a Bamstead Nanopure system and doubly distilled perchloric acid (70 wt%, G. F. Smith Chemicals). Carbon monoxide was dosed from solution by a 1 min exposure of the sample to 0.1 mol/dm perchloric acid saturated with carbon monoxide at 1 atm while maintaining the potentid at 0.3 V. The carbon monoxide solution was then removed and the sample rinsed once with blank electrolyte prior to electrochemical measurements. Electrode potentials were measured with respect to a gold/gold oxide reference electrode and converted to the reversible hydrogen electrode (RHE) scale. All cyclic voltammograms were recorded at room temperature with a sweep rate of 50 mV/s. To avoid electrooxidation of the carbon adlayers the sample potential was not allowed to exceed 0.95 V. 

The electrosynthesis of metalloporphyrins which contain a metal-carbon a-bond is reviewed in this paper. The electron transfer mechanisms of a-bonded rhodium, cobalt, germanium, and silicon porphyrin complexes were also determined on the basis of voltammetric measurements and controlled-potential electrooxidation/reduction. The four described electrochemical systems demonstrate the versatility and selectivity of electrochemical methods for the synthesis and characterization of metal-carbon o-bonded metalloporphyrins. The reactions between rhodium and cobalt metalloporphyrins and the commonly used CH2CI2 is also discussed. 

From the above experimental results, it can be seen that the both PtSn catalysts have a similar particle size leading to the same physical surface area. However, the ESAs of these catalysts are significantly different, as indicated by the CV curves. The large difference between ESA values for the two catalysts could only be explained by differences in detailed nanostructure as a consequence of differences in the preparation of the respective catalyst. On the basis of the preparation process and the CV measurement results, a model has been developed for the structures of these PtSn catalysts as shown in Fig. 15.10. The PtSn-1 catalyst is believed to have a Sn core/Pt shell nanostructure while PtSn-2 is believed to have a Pt core/Sn shell structure. Both electrochemical results and fuel cell performance indicate that PtSn-1 catalyst significantly enhances ethanol electrooxidation. Our previous research found that an important difference between PtRu and PtSn catalysts is that the addition of Ru reduces the lattice parameter of Pt, while Sn dilates the lattice parameter. The reduced Pt lattice parameter resulting from Ru addition seems to be unfavorable for ethanol adsorption and degrades the DEFC performance. In this new work on PtSn catalysts with more... 

The chemisorption of sulfur from mixtures of H,S and H2 has been widely studied we have discussed some of the results. Nevertheless, introduction of irreversible and reversible adsorbed sulfur, which is in line with adsorption stoichiometries varying from more than 1 to 0.4 sulfur atom by accessible platinum atom, shows that different adsorbed species are involved in sulfur chemisorption. In fact, electrooxidation of adsorbed sulfur on platinum catalysts occurs at two different electrochemical potentials (42) in the same way, two different species of adsorbed sulfur were identified on gold by electrochemical techniques and XPS measurements (43,44). By use of 35S (45) it was pointed out that, according to the experimental conditions, reducible PtS2 or nonreducible PtS mono-layers can be created. 

It is worth noting that the remarkable effect described for the carbon support porosity on the metal utilization factor and hence on the specific electrocat-alytic activity in methanol electrooxidation was only observed when the catalysts were incorporated in ME As and measured in a single cell. The measurements performed for thin catalytic layers in a conventional electrochemical cell with liquid electrolyte provided similar specific catalytic activities for Pt-Ru/C samples with similar metal dispersions but different BET surface areas of carbon supports [223]. The conclusions drawn from measurements performed in liquid electrolytes are thus not always directly transferable to PEM fuel cells, where catalytic particles are in contact with a solid electrolyte. Discrepancies between the measurements performed with liquid and solid electrolytes may arise from (1) different utilization factors (higher utilization factors are usually expected in the former case), (2) different solubilities and diffusion coefficients, and (3) different electrode structures. Thus, to access the influence of carbon support porosity... 

Instrumentation. A cell design employing reticulated vitreous carbon as the working electrode material that enables both UV-Vis absorption and luminescence measurements has been described [47]. A thin-layer cell with a platinum working electrode has been developed [69]. The luminescence of the electrooxidation products of o-tolidine as a function of electrode potential was studied. A simplified flow cell design has been reported [70]. Luminescence spectra and fluorescence intensity for various aromatic compounds and their electrochemical and photochemical reaction products were observed as a function of flow rate, current and time after the potential step. In the latter study the electrooxidation of p-phenylenediamine (PPD) was examined. The cyclic voltammogram showed two oxidation peaks the first one is assumed to be caused by the formation of the radical cation according to... 

An optimized design employing a tubular electrode in a cylindrical cavity has been described [638]. The mechanism and kinetics of the electrooxidation of several para-haloanilines and the follow-up reactions in acetonitrile have been investigated with this cell [639]. A similar design that is suitable for low temperature measurements (233 K) has been reported [640]. It has been employed in a study of the temperature dependence of the reduction of bromonitrobenzene in acetonitrile solution. The electroreduction of perinaphthenone in a single electron process has been investigated with this cell [641]. The lifetime of the neutral radical formed by deprotonation of the radical anion has been estimated to be around 1 min. A similar electrochemical behavior of benzanthrone was observed. 

Electrochemical quartz crystal microbalance. To monitor adsorbate accumulation on catalyst surfaces from formic acid electrooxidation and advance mechanistic understanding, an electrochemical quartz crystal microbalance (EQCM) can be used to simultaneously measure current and mass [22, 66, 81-83]. The dampening of the vibration frequency (A/) of an AT-cut 9 MHz piezoelectric crystal is directly proportional to mass accumulation (Am) on the catalyst surface through the Sauerbrey equation (A/ = —/o 2(jUqPq) Am/A) [84], where /o is the base... 

Frelink T, Visscher W, van Veen JAR. Measurement of the Ru surface content of electrocodeposited PtRu electrodes with the electrochemical quartz crystal microbalance implications for methanol and CO electrooxidation. Langmuir 1996 12 3702-8. 

Kanazawa, A., T. Daisaku, T. Okajima, S. Uchiyama, S. Kawauchi, and T. Ohsaka. Characterization by electrochemical and X-ray photoelectron spectroscopic measurements and quantum chemical calculations of N-containing functional groups introduced onto glassy carbon electrode surfaces by electrooxidation of a carbamate salt in aqueous solutions. Langmuir 30, 2014 5297-530. 

Simple calculations show that when three electrons are transferred during the slow electrochemical step and the transfer number is 0.5, a slope of the Tafel correlation between p and Ig i must equal 2.3RT/(anF) = 39 mV. However, completely different slopes can be measured experimentally. Data for the same electrochemical system can heavily depend on the electrolyte composition. This leads to a conclusion that electrooxidation or electroreduction of charged particles can proceed through a stepwise electron transfer mechanism. 

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