An understanding of the oxidation of chemisorbed CO (CO(chem)) on Pt nanoparticle surfaces is of major importance to fuel cell technology. Here, we report on the relation between Pt nanoparticle surface structure and CO(chem) oxidative stripping behavior. Oxidative stripping voltammograms are obtained for CO(chem) preadsorbed on cubic, octahedral, and cuboctahedral Pt nanoparticles that possess preferentially oriented and atomically flat domains. They are compared to those obtained for etched and thermally treated Pt(poly) electrodes that possess atomically flat, ordered surface domains separated by grain boundaries as well as those obtained for spherical Pt nanoparticles. A detailed analysis of the results reveals for the first time the presence of up to four voltammetric features in CO(chem) oxidative stripping transients, a prepeak and three peaks, that are assigned to the presence of surface domains that are either preferentially oriented or disordered. The interpretation reported in this article allows one to explain all features within the voltammograms for CO(chem) oxidative stripping unambiguously.

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The oxidative stripping of a saturation layer of CO(chem) was studied on platinum nanoparticles of high shape selectivity and narrow size distribution. Nanospheres, nanocubes, and nano-octahedrons were synthesized using the water-in-oil microemulsion or polyacrylate methods. The three shapes allowed examination of the CO(chem) stripping in relation to the geometry of the nanoparticles and presence of specific nanoscopic surface domains. Electrochemical quartz crystal nanobalance (EQCN) measurements provided evidence for the existence of more than one mechanism in the CO(chem) stripping. This was corroborated by chronoamperometry transient for a CO(chem) saturation layer at stripping potentials of E(strip) = 0.40, 0.50, 0.60, and 0.70 V. The first mechanism is operational in the case of CO(chem) stripping at lower E(strip) values; it proceeds without adsorption of anions or H(2)O molecules and corresponds to desorption of a fraction of CO(chem) in the form of a prepeak in voltammograms or in the form of an exponential decay in chrono-amperometry (CA) transients. The second mechanism is operational in the desorption of the remaining CO(chem) at higher E(strip) values and gives rise to at least two voltammetric peaks or two CA peaks. Analysis of the experimental data and modeling of the CA transients lead to the conclusion that the stripping of a saturation layer of CO(chem) first follows an Eley-Rideal mechanism in the early stage of the process and then a Langmuir-Hinshelwood mechanism.

The effect of thiophenol layer grafted on carbon for platinum catalyst stabilization was studied. The grafted layer was prepared by reduction of 4-thiophenoldiazonium ions in the presence of Vulcan XC72 substrate. The grafted layer was characterized by elemental analysis, thermogravimetric analysis coupled with mass spectrometry, and X-ray photoelectron spectroscopy. Platinum nanoparticles prepared by the "water in oil" microemulsion method were then deposited on modified substrates and bare Vulcan XC72. The platinum stability improvement was characterized by in situ X-ray diffraction and electrochemical aging. These experiments enabled to evidence a lower crystallite growth during heat treatment under hydrogen atmosphere and a lower active surface area loss for platinum particles deposited on modified substrates compared to those deposited on bare Vulcan XC72. This stability improvement can be attributed to a better interaction between platinum particles and carbon substrate due to the thiophenol molecular bridge.

Automotive fuel cells are plagued by high platinum-based cathode catalyst costs exacerbated by high catalyst loadings to circumvent performance losses induced by typical urban drive cycles. Accelerated durability tests are commonly used to evaluate the impact of nano-structure and/or operating conditions on cathode catalyst loss rates. To map out loss rates the electrochemical surface area (ECSA) of the catalyst is periodically monitored. Herein the accelerated stress testing was performed 25,000 times by imposing perturbations from 0.9 V to 0.6 V in a triangular wave profile while the ECSA was measured by assessing the hydrogen adsorption/desorption region with a lower potential limit of 0.025 V at intermittent points during the triangular wave perturbations. The ECSA loss observed during the 25,000 triangle wave cycles is 7% when measured only 2 times, but 26.3% when measured 250 times. The exacerbated losses during frequent low potential ECSA measurements suggest a restructuring of the catalyst surface due to the formation of a protective β-oxide, as seen by alterations in the cyclic voltammtric profile and particle size distribution. The increasing price of fossil fuel stimulated by an impending near future accessible supply depletion combined with the increased awareness of the adverse contributions of the Internal Combustion Engines (ICEs) on global warming has driven an international research thrust toward alternative energy production for personal automotive transportation from alternative energy technologies. Proton Exchange Membrane Fuel Cells (PEMFCs) currently appear as one of the potential alternatives to ICEs for automotive applications due to their higher efficiency and the fact that they use hydrogen and air (21% oxygen) as fuel and oxidant, respectively, with water as the only by-product. Furthermore, depending on the production method, hydrogen can be considered as a renewable source of energy if generated in ways such as electrolysis from either wind turbines or solar energy.The commercialization and massive production of automotive PEMFC technologies is still a challenge due to durability and cost limitations.1 The PEMFC type is the most suitable fuel cell technology to replace ICEs for vehicle propulsion because of the solid electrolyte permitting comparable travel distances, available power for frequent fast idle-to-peak transients to support typically sized personal vehicles and fast startup/shutdown. However, the relatively low working temperature of PEMFCs (typically below 100• C, due to membrane limitations) requires the use of Pt based catalysts for both the anode and the cathode catalyst layers thereby significantly increasing their price. Utilization of finely dispersed catalyst nanoparticles onto a high surface electrically conducting substrates (typically high surface carbon supports) and optimization of catalytic layers have yet allowed a drastic decrease of the catalytic layer cost by lowering the Pt loading by a factor of 10 (reaching 0.4 mg. cm −2 total loading) in the past 30 ...

Platinum nanocubes and tetrahedrons/octahedrons were synthesized by different methods using different surfactants (tetradecyltrimethylammonium bromide (TTAB) and sodium polyacrylate). Transmission electron microscopy (TEM) investigations show high selectivity in shape and low size dispersion. However, the small nuclei observed at the surface of some nanocubes synthesized using the TTAB method is not yet clarified. The presence of such small particles could be explained by a double nucleation or different growth processes which might occur during synthesis. Electrochemical characterizations indicated that particles exhibited ca. 60% of oriented surface domains. Cyclic voltammetry and adatom adsorption displayed a very good agreement with TEM results.

In polymer electrolyte fuel cells a decrease in catalytic surface-area within the cathode catalyst layer is a critical barrier to commercialization. This loss in catalytic surface-area manifests as a loss in cell voltage and thus power density of the cell. It has been established that potential cycling accelerates the loss in catalytic surface-area yet isolating the contributing mechanisms as well as relating mechanisms to operating conditions is not as straightforward. We approach the issue of surface-area loss deconvolution with a combined experimental, modelling and theoretical framework. The methodology is based on the Lifshitz-Slyozov-Wagner and Smoluchowski theories of particle size distribution evolution. Electrochemical surface-area loss experiments probing upper potential limits of 0.9 and 1.2 V as well as temperatures from 298 to 343 K were analyzed with the model. A dissolution and redeposition mechanism was correlated with the measurements for both upper potential limits; however, at the upper potential limit of 1.2 V, ambiguity between the coagulation and the dissolution and redeposition mechanisms was found. Notwithstanding, the extracted dissolution and redeposition parameters aligned with independent studies on Pt dissolution whereas similar positive comparisons with independent results were unable to be made for the coagulation mechanism.