Amaël Caillard

Plasma sputtering deposition of platinum into porous fuel cell electrodes

Platinum is deposited into porous carbon materials relevant for fuel cell electrodes using plasma sputtering techniques. The resulting platinum concentration profile extends up to 2 µm into the porous carbon and is well fitted by a generalized stretched Gaussian function, which displays the non-thermal nature of the penetration process. Platinum deposits are observed to grow as clusters. On the outermost carbon particles, platinum nano-cluster sizes of 3.5 nm have been measured. In tests using actual PEM fuel cells, current densities as high as 1000 mA cm−2 have been obtained at 400 mV with 25 cm2 plasma electrodes. This compares favourably with commercially available electrodes but the present electrodes have a platinum density 4.5 times lower and hence can be considered to be significantly more efficient.

Anomalous diffusion mediated by atom deposition into a porous substrate.

Constant flux atom deposition into a porous medium is shown to generate a dense overlayer and a diffusion profile. Scaling analysis shows that the overlayer acts as a dynamic control for atomic diffusion in the porous substrate. This is modeled by generalizing the porous diffusion equation with a time-dependent diffusion coefficient equivalent to a nonlinear rescaling of time.

Effect of Nafion and platinum content in a catalyst layer processed in a radio frequency helicon plasma system

A helicon plasma sputtering system is used to deposit small amounts of platinum on microporous carbon support composed of Vulcan XC 72 carbon particles (known as gas diffusion layer) to form Pt catalyzed electrodes for proton exchange membrane fuel cells. Electrodes with low Pt loading are prepared, assembled in custom-made membrane electrode assemblies (MEAs) and tested for the hydrogen oxydation and the oxygen reduction. Initially, the Nafion ® loading spread on these plasma prepared electrodes is optimized by measuring the MEA performance. It is found that the optimum Nafion ® loading is 1 mg cm −2 for an electrode previously covered with 0.1 mgPt cm −2 using the helicon plasma system. For a commercial electrode prepared by ink processes with 0.5 mg Pt cm −2 , the optimized Nafion ® loading is 2m g cm −2 . Using the respective optimized Nafion ® loading, the electrical performance of the custom-made MEA with one plasma prepared electrode (either anode or cathode) is compared with that of a reference MEA from Electrochem Inc. (Pt loading per electrode of 0.5 mg cm −2 and maximum power density of 425 mW cm −2 ) without gas humidification. The custom-made MEA fitted with an anode covered with 0.005 mg Pt cm −2 leads to the same performance as that of the reference MEA at low current density (<500 mA cm −2 ) and high gas backpressure (3 bar). This result indicates that the catalyst utilization efficiency in the plasma prepared anode is 100 times higher than that in the commercial anode (85 kW g −1 Pt versus 0.85 kW g −1 Pt ). For plasma prepared cathodes with 0.1 mgPt cm −2 , the cathodic Pt utilization efficiency is 2.7 kW g −1 Pt , which is 3 times higher than that obtained in the commercial cathode. (Some figures in this article are in colour only in the electronic version)

One-step synthesis and chemical characterization of Pt-C nanowire composites by plasma sputtering.

Plasma increases activity: A one-step synthesis of Pt-C nanowire composites using a plasma co-deposition method is reported. Electrodes with a very low Pt loading can be obtained. Pt particles with sizes ranging from 1 to 2 nm are decorating the columnar carbon nanostructures because of strong interactions. The composite microstructure is responsible for a very high metal utilization rate as exemplified by reactions occurring in fuel cell electrodes.

PdPt catalyst synthesized using a gas aggregation source and magnetron sputtering for fuel cell electrodes

, +33 (0)2 3849 4352 KEYWORDS. gas aggregation source, magnetron sputtering, platinum, nanoclusters, catalyst. Abstract. PdPt catalysts with different morphologies and atomic ratios have been synthesized on native SiO2/Si and on proton exchange membrane. The combination of the gas-aggregation source and of the magnetron sputtering techniques allows the formation of quasi core-shell Pd0.97Pt0.03@Pt nanoclusters. Transmission electron microscopy and grazing incidence wide angle X-ray scattering measurements on Pd-rich core reveal a mean diameter of 4 nm and a fcc structure. The Pt shell around the half of the Pd-rich core is formed by magnetron sputtering which leads to the increase of nanocluster diameter (up to 10 nm) and of the overall Pt content (up to 85%). The membranes coated by PdPt core catalyst and PdPt@Pt catalyst (resulting in the formation of catalyst coated membrane) are incorporated into fuel cells and their electrical characteristics are measured. The association of the two deposition techniques resulting in the formation of quasi core-shell PdPt@Pt nanoclusters improves the startup step of the fuel cell.

Low energy plasma treatment of a proton exchange membrane used for low temperature fuel cells

A low energy (∼30 V) plasma treatment of Nafion, a commercial proton exchange membrane used for low temperature fuel cells, is performed in a helicon radiofrequency (13.56 MHz) plasma system. For argon densities in the 10 9 –10 10 cm −3 range, the water contact angle (hydrophobicity) of the membrane surface linearly decreases with an increase in the plasma energy dose, which is maintained below 5.1 J cm −2 , and which results from the combination of an ion energy dose (up to 3.8 J cm −2 ) and a photon (mostly UV) energy dose (up to 1.3 J cm −2 ). The decrease in water contact angle is essentially a result of the energy brought to the surface by ion bombardment. The measured effect of the energy brought to the surface by UV light is found to be negligible.

Deposition of platinum catalyst by plasma sputtering for fuel cells: 3D simulation and experiments

Plasma sputtering is one of the most promising methods for reducing the amount of platinum catalyst in porous electrodes for low temperature fuel cells. Here, a simulation of the platinum deposition by radio frequency plasma sputtering has been developed and compared with experimental results to allow optimization of the deposition process. In the simulation, the transport of sputtered atoms through the argon plasma is obtained using a 3D Monte Carlo model called SPaTinG (Sputtered Particles Transport in Gas). The Yamamura formula provides the Pt sputtering yield on the target, and the initial energy distribution of sputtered atoms is given by the Thompson distribution. A 1D hybrid model is used to estimate the mean energy of argon ions impinging onto the platinum target. Experimentally, platinum is deposited on silicon in two plasma sputtering chambers with different geometries. The deposition rate is measured by Rutherford backscattering spectroscopy. The angular distribution of the Pt atoms ejected from the target surface and the condensation coefficient of the Pt atoms on silicon are calculated by adjusting the simulated and experimental deposition rates at 0.5 Pa. A good agreement between the simulation and the experiment is observed as a function of the target–substrate distance for the two system geometries at low pressure (0.5 Pa). (Some figures in this article are in colour only in the electronic version)

Energy Transferred From a Hot Nickel Target During Magnetron Sputtering

The energy influx emanating from a sputtered Nickel target in a magnetron apparatus is studied using an energy flux diagnostic. An image of the Ni target before, during, and after the sputtering process is presented and correlated to the energy flux results. For an input power above 50 W (i.e., ≈10 W/cm2), an abrupt increase of the energy flux is observed. This phenomenon is associated to the emission of visible and IR lights by the target, and to an increase of the sputtering rate.

Synthesis of Carbon Nanofibers and Pt-Nanocluster-Based Electrochemical Microsystems by Combining Low-Pressure Helicon Plasma Techniques

Although carbon-nanofiber (CNFs) or nanotube growth and their applications are well documented, engineering their shape and their integration in a microsystem for successful applications is an important issue. We report on the synthesis of aligned CNFs (ACNFs) covered by metallic catalytic nanoclusters by a combination of different low-pressure deposition techniques based on high-density radio-frequency helicon plasmas. An image of a ldquobright-dress-shaperdquo helicon plasma and of a synthesized ACNF coated by Pt nanoclusters is presented.

An efficient way to evidence and to measure the metal ions fraction in high power impulse magnetron sputtering (HiPIMS) post- discharge with Pt, Au, Pd and mixed targets

The proportion of metal ions in a High Power Impulse Magnetron Sputtering discharge is a key information for the potential development of new materials and new layer architectures deposited by this technique. This paper aims to measure this proportion by using a homemade system consisting of a quartz crystal microbalance and a grid energy analyzer assembly. Such a system yields relevant results on the composition of the post-discharge depending on the nature of the gas (Ar, Kr, Xe) and the target materials (Pt, Pd, Au, Pt50Au50 and Pt5Pd95). In our conditions, the highest proportions of metal ions in the post-discharge are obtained by using Ar gas and reaches 10 %, 12 %, 50 %, 19 % and 88 % for respective Pt, Au, Pd, Pt50Au50 and Pt5Pd95 target, respectively.