Platinum electrodeposition for polymer electrolyte membrane fuel cells

A novel electrodeposition technique for preparing the catalyst layer in polymer electrolyte membrane fuel cells has been designed, which may enable an increase in the level of platinum utilisation currently achieved in these systems. This method consists of a two-step procedure involving the impregnation of platinum ions into a preformed catalyst layer (via an ion-exchange into the Nafion polymer electrolyte), followed by a potentiostatic reduction. The concentration of Nafion within the catalyst layer was found to have a significant bearing on the size of the platinum deposits. The preparation of catalyst layers containing a desired platinum loading should also be possible using this method. Surface areas of the platinum deposits were determined using cyclic voltammetry. The prepared catalyst was compared with a conventional electrode made from E-TEK Pt/C. Scanning electron microscopy was used to investigate the dispersion of the platinum particles. Platinum loadings were determined quantitatively by atomic absorption spectroscopy.

Characterising nonuniform electrodeposition and electrodissolution using the novel wire beam electrode method

An electrochemically integrated multi-electrode system namely the wire beam electrode (WBE) has been applied as a new method of characterising nonuniform electrodeposition and electrodissolution, by measuring and identifying characteristic patterns in electrodeposition and electrodissolution current distribution maps. Various patterns of electrodeposition current distribution have been obtained from Watts nickel plating and bright acid copper plating baths with the effects of several affecting factors such as bath concentration, temperature, agitation and electrolyte flow. Typical patterns of electrodissolution current distribution have also been detected over a WBE surface under anodic dissolution. This work suggests that the WBE method can be used as a new tool for monitoring, characterising and optimising electrodeposition and electrodissolution processes in the laboratory, and can also be applied as an experimental method to verify the accuracy and completeness of mathematical models for electrodeposition and electrodissolution.

Studying non-uniform electrodeposition using the wire beam electrode method

Nonuniform electrodeposition is a major concern in almost every practical electrodeposition application. The ablility to control nonuniformity in electrodeposition is the key to successful plating for corrosion resistance, and more especially to meeting the very exacting requirements of electroforming, electrodeposition. This paper presents a novel technique namely the wire beam electrode (WBE) for characterizing and monitoring nonuniform electroplating processes. For the first time, the nonuniform distribution of electroplating currents (NDEC) has been mapped. Preliminary experimental results indicated that electrochemical heterogeneity was the key factor affecting NDEC. The secondary current distribution, rather than the primary current distribution, played a major role in determining the NDEC. This work suggests that the WBE is a practical tool for characterizing and optimizing electrodeposition processes and for verifying the accuracy and completeness of mathematic modelling of electrodeposition processes.

X-ray diffraction line broadening from gold and platinum thin films

X-ray diffraction line profile analysis has been used to study the microstructure of (Ill) oriented gold and platinum thin films deposited by thermal evaporation and DC magnetron sputtering. In addition to crystallite size broadening, the profiles from these films displayed broadening arising from dislocations. A parallel investigation, using transmission electron microscopy (TEM) was undertaken to study the nature of dislocations formed, and to provide information on the dimensions of the crystallite columns in the films. X-ray data were collected at room temperature to determine the anisotropy of the broadening with (hkl), using a Siemens D5000 powder diffractometer (CuKa radiation) and two high-resolution synchrotron instruments (BM 16 at the ESRF [A=0.35A] and station 2.3 at the Daresbury laboratory. Two approaches to instrument deconvolution were investigated; Fourier deconvolution and fundamental parameters profile fitting, using Lab6 as a reference material to determine the instrument profile function. After removal of the crystallite size broadening contribution from the measured integral breadths, the residual microstrain broadening was modelled assuming dislocations based on a FCC a/2<110>{ Ill} slip system. The results of the X-ray analysis agreed with dark field TEM micrographs, which showed that many of the crystallites contained dislocations of mixed character (screw- edge).

Recent developments in characterising electrodeposition of anti-corrosion coatings using the wire beam electrode method

New progresses have been made during recent years in the application of the wire beam electrode (WBE, a coupled multielectrode array) for studying electroplating of metallic coatings, for monitoring the electrodeposition of polymer coatings, and for evaluating the performance of anti-corrosion coatings. The WBE allows localized electrode processes to occur over different locations of its surface under external anodic or cathodic polarization and permits monitoring of nonuniform electrodeposition processes. Several typical experiments are presented in this paper. One sample experiment is the characterization of nonuniform electroplating of nickel coating, which was achieved by mapping the distributions of currents over a WBE surface that was under cathodic polarization. Various characteristic current distribution patterns, which indicate different electrodeposition mechanisms or low covering-power, have been observed. These patterns were found to correlate with the effects of several affecting factors such as electrolyte concentration, temperature and agitation flow. Another sample experiment is the investigation of nonuniform anodic electrodeposition of polyaniline (PANI) coatings and the understanding of their anti-corrosion performance and mechanisms. Anodic polarization currents were measured from various locations over the WBE surface in order to produce anodic polarization current maps under PANI deposition.