Electroless Deposition Of Platinum Research Articles

Analysis of Platinum Distribution within a Nafion 212 Membrane during Electroless Deposition

Ionic polymer metal composite (IPMC) is an electrically-responsive material made of perfluorinated sulfonic acid (PFSA) ionomers electroless plated with noble metal, such as platinum. Recently, interest in thin IPMC has been rising because of its potential applications in micro-electromechanical systems. However, little effort has been made so far on studying metal electroless deposition within thin PFSA membranes (thinner than 100 um). In this paper we study the platinum distribution within a thin Nafion membrane (Nafion 212, 50 µm-thick) using standard manufacturing recipe. We compare the obtained distribution with the distribution reported in literature based on thick Nafion membrane (Nafion 117, 180 µm-thick). We show that in Nafion 212 the maximum Pt concentration is situated in the bulk of the membrane, while in Nafion 117 the maximum peak is situated at the liquid-membrane boundary, suggesting a different rate determining deposition mechanism. Electroless deposition of platinum in Nafion 212 Ionic polymer metal composite (IPMC) is rising interest in the microelectromechanical system (MEMS) since smaller and thinner IPMC substrates would expand the applications. IPMCs are mostly made of a perfluorinated sulfonic acid ionomers (PFSA) membrane, such as commercially-available Nafion, coated with platinum. The prevalent way of manufacturing IPMC relies on the chemical reduction of platinum on the surface of the PFSA membrane, i.e. electroless deposition (1). Most of the reports on IPMC manufacturing rely on Nafion 117 (thickness of 0.180 mm, equivalent weight 1100 g/mol) while Nafion 212 has been poorly studied (thickness 0.050 mm, equivalent weight 1100 g/mol). This contribution aims at filling this gap.Materials and methodsA PFSA membrane (Nafion 212 membrane) has been coated with platinum using the standard recipe already describe elsewhere (1). An immersion-reduction step was performed in an immersion bath composed of tetraammineplatinum chloride (Pt(NH3)4Cl2, 0.2%), and reduction baths made of sodium borohydride (NaBH4, 5%). After the first immersion (30 min and 2 hours, respectively), the samples were immerged in the reduction bath until the end of the precipitation. Samples were then frozen in liquid nitrogen and cut, and analyzed with electrons dispersive x-ray spectroscopy (EDS) and processing of scanning electron microscopy (SEM) images (Fig 1a).Figure 1. a) EDS detection of platinum (yellow) overlapped with SEM picture of the cross-section of IPMC. Platinum distribution and Rayleigh fit for single reduction step (NaBH4) of platinum in a Nafion 212 membrane, after 30 minutes (b) and 2 hours (c) of immersion.Results and discussionThe distribution of platinum within Nafion 117 has already been studied by Millet et al. (2). The Pt distributions thereby reported strongly differs from the profiles we obtained (Fig 2). In the aforementioned profiles, the maximum Pt concentration is located at the liquid-substrate boundary of the Nafion membrane (2), whereas the Pt distribution in Nafion 212 reaches the maximum inside the Nafion membrane, between 0.5 µm and 1 µm below the surface (Fig 1b 1c).As reported by Millet et al., two limiting types of kinetics may be encountered in a dynamic exchange process, such that the deposition rate-determining mechanism is either diffusion in the liquid-film boundary (F-mechanism), or diffusion in the membrane (M-mechanism).The position of the peaks in our experimental data suggests that the mechanism determining the Pt precipitation rate inside Nafion 212 is diffusion inside the membrane while using Nafion 117 with the same reducing agent concentration leads to a precipitation rate determined by diffusion at the liquid/film boundary. It has been proven experimentally that ionic conductivity and water uptake of Nafion 212 is higher than for Nafion 117 (3). Thus we can hypothesize that the different behavior of thinner Nafion could explain the different empirical Pt distribution obtained using same reducing agent concentration. We could obtain a good fit of the Pt distribution (R2=0.919 and R2=0.945) within Nafion 212 with the Rayleigh distribution for immersion time of 30 minutes and 2 hours respectively (Eq 1.):f(x,σ 2) = (x/σ 2) exp(-x/2σ 2) [1]The scale parameter σ was found to be 4.19 and 4.58 for the sample immerged for 30 minutes and 2 hours, respectively. Further investigation of the precipitation mechanism inside Nafion 212 membrane and estimations of the phenomenological equations of mass transport correlated to Rayleigh distribution is reserved for future work.References K. Kim, M. Shahinpoor, Smart Mater. Struct., 12, 1, p. 65 (2003).P. Millet, R. Durand, E. Dartyge, G. Tourillon, and A. Fontaine J. Electrochem. Soc., 140, 5, pp. 1373-1380 (1993).A. Kusoglu, A.Z. Weber Chem. Rev. 117, 3 pp. 987-1104 (2017). Figure 1

Synthesis of nanoporous acicular-mullite ceramic and electroless platinum coating for particulate matter entrapment and catalytic combustion

Crystal-structured acicular-mullite ceramic with high porosity and interpenetrated networks was fabricated for diesel particulate filter (DPF), followed by electroless deposition of platinum (Pt) catalysis throughout ceramic surfaces from an aqueous Pt (IV) solution. The integrated material was characterized and compared with commercial cordierite particulate matter (PM) filter, exhibiting many excellent properties in surface area, porous ratio, and loading capacity for both soot and catalyst. The resulting surface density of Pt nanoparticles attained as high as 8.0 × 109/cm2 due to the 3-dimensional architecture, while maintaining a pore ratio, 63.72%, relative to 52.60% in its counterpart. Deposited Pt nanoparticles artfully serve as catalysis for combustion of carbon soot, potentially implemented for diesel engine filter, reducing the particulate matter emission for environmental protection. The catalytic performance was evaluated by a regular thermal gravity analysis (TGA) measurement, showing that the significant drop of soot conversion temperature, and soot convert rate could be further improved by co-precipitating CeO2 catalyst additive. This material, thereby, could readily adapt itself into large-scale production.

Increasing durability of Pt-surface-enriched nanosize structure catalysts by multi-step platinum deposition

The sluggish reaction of oxygen reduction in proton-exchange membrane fuel cells (PEMFCs) and the durability of platinum-based catalysts have been major economical and technological barriers to the widespread application of PEMFCs. We report here on two Pt-surface-enriched nanosize structure (Pt-SENS) catalysts with iridium core, synthesized with the use of single-step and successive step-by-step electroless deposition of platinum. The synthesized catalysts were studied by energy-dispersive X-ray spectroscopy (SEM-EDS), X-ray photoelectron spectroscopy (XPS), and transmission scanning electron microscopy (STEM). Electrochemical analysis demonstrated improved oxygen reduction reaction (ORR) mass activity of the homemade catalysts by 25–30% compared with commercial 50%Pt/C catalyst and improved durability, by a factor of ~ 3, of the catalyst synthesized by successive step-by-step deposition following accelerated stress test (AST). Higher mass activities are attributed to better platinum utilization as a result of a Pt-surface-enriched structure, while greater durability is attributed to the stabilization of surface platinum by stronger Pt–Ir bonds induced by iridium atoms in the core.

Cisplatin-loaded porous Si microparticles capped by electroless deposition of platinum.

The loading and release of the anti-cancer drug platinum cis-dichlorodiamine (cisplatin) from mesoporous silicon (pSi) microparticles is studied. The pSi microparticles are modified with 1-dodecene or with 1,12-undecylenic acid by hydrosilylation, and each modified pSi material acts as a reducing agent, forming a deposit of Pt on its surface that nucleates further deposition, capping the mesoporous structure and trapping free (unreduced) cisplatin within. Slow oxidation and hydrolytic dissolution of the Si/SiO(2) matrix in buffer solution or in culture medium leads to the release of drugs from the microparticles. The drug-loaded particles show significantly greater toxicity toward human ovarian cancer cells (in vitro), relative to an equivalent quantity of free cisplatin. This result is consistent with the mechanism of drug release, which generates locally high concentrations of the drug in the vicinity of the degrading particles. Control assays with pSi particles loaded in a similar manner with the therapeutically inactive trans isomer of the platinum drug, and with pSi particles containing no drug, result in low cellular toxicity. A hydrophobic pro-drug, cis,trans,cis-[Pt(NH(3))(2)(O(2)C(CH(2))(8)CH(3))(2)Cl(2)], is loaded into the pSi films from chloroform without concomitant reduction of the pSi carrier.

Electroless deposition of platinum on indium tin oxide glass as the counterelectrode for dye-sensitized solar cells

A platinum (Pt) layer is electroless-deposited on indium tin oxide (ITO) glass substrate as the counterelectrode for dye-sensitized solar cells (DSSCs). Compared with other methods of depositing Pt layer, electroless deposition is simple, low-temperature, and easy to scale-up for industrial application. The Pt concentration of the electroless plating solution is found to play an important role in the cell performance. With increasing the Pt concentration, i.e. the Pt loading on the ITO surface, the resultant Pt layer exhibits a porous structure. Owing to the porous structure, the Pt layer can provide more active surface area for triiodide reduction and thus reduces the charge-transfer resistance. The cell performance is promoted accordingly with increasing the Pt concentration. Energy conversion efficiency of 6.46%, short-circuit current density of 15.04 mA cm −2, open-circuit voltage of 0.68, and fill factor of 0.63 can be achieved for the DSSC employing electroless-Pt counterelectrode.

Molecular Monolayers Enhance the Formation of Electrocatalytic Platinum Nanoparticles on Vertically Aligned Carbon Nanofiber Scaffolds

We demonstrate the use of molecular monolayers to enhance the nucleation of electrocatalytically active platinum nanocrystals onto vertically aligned carbon nanofiber (VACNF) scaffolds. The photochemical functionalization of VACNFs with bifunctional organic alkenes produces monolayer-modified VACNFs exposing large amounts of carboxylic acid groups. Subsequent electroless deposition of platinum leads to high densities of ∼8 nm diameter Pt nanocrystals uniformly deposited along the length of the nanofibers. Electrochemical measurements show that the molecular monolayers do not impede redox behavior of the electrode, and measurements of the electrocatalytic oxidation of methanol show very high catalytic efficiency. Our results suggest that the use of molecular functionalization layers provides an improved way to integrate nanostructured carbon with metals for a variety of catalytic and electrocatalytic applications.

Platinum electroless deposition on nafion membrane for PEM fuel cells

The aim of this research was to study the deposition of platinum on Nafion117 membrane by using an electroless technique. The investigated parameters were electroless time (30 to 90 min) and Pt : N2H4 ratio (from 1 : 1 to 1 : 3.85). The results indicated that the platinum deposition on the 1st side of membrane was lower than that on the 2nd side because of the effect of N2H4 on the property of membrane. Platinum deposition increased when the Pt : N2H4 ratio decreased. The optimum condition was found at electroless time of 60 min and Pt : N2H4 ratio of 1 : 1.95. At this condition, more than 89% of platinum was deposited on both surfaces. The coated membrane was used to make a membrane electrode assembly (MEA) of a proton exchange membrane fuel cell (PEMFC) which was tested at 60 ‡C in a saturated H2/O2 system. The maximum current density was 80 mA/cm2 at 0.3 V.

Ionic actuators based on novel sulfonated ethylene vinyl alcohol copolymer membranes

Sulfonated ethylene vinyl alcohol copolymers have been synthesized and artificial muscles have been produced from this new class of ionomeric membrane materials. FTIR spectroscopy confirmed the modification through introduction of peaks characteristic of ester linkages between sulfosuccinic acid and vinyl alcohol. Solid-state 23Na NMR showed the ionic functionalities aggregate during membrane casting, yet small angle X-ray scattering showed that nano-phase separation between the ionic domains and matrix occurs only at elevated sulfonate content. Ionic polymer metal composites were produced through an electroless deposition of platinum generating membranes that display actuation under applied electrical stimulus. The perfluorosulfonate ionomer Nafion ® has been used as a benchmark to gauge the performance of the artificial muscles produced in this study. Results showed the modified EVOH IPMC's behave similar to Nafion ®, yet actuation kinetics in the new ionomer are significantly slower. Pulsed gradient spin echo NMR showed water diffusion coefficients in modified EVOH to be 1/3 those in Nafion ® though the water content in the new ionomer is more than double. Slower actuation kinetics are, therefore, attributed to slower water diffusion caused by a disorganized morphology in the sulfonated ethylene vinyl alcohol.

Platinum Electroless Deposition on Silicon from Hydrogen Fluoride Solutions: Electrical Properties

Current transport through mesa structures formed by Pt electroless deposition on p-Si wafers has been studied. The silicon treatment in the solution of sodium chloroplatinate in dilute HF acid is shown to result in both Pt nucleation on the Si surface (cathodic process) and Si wafer etching by fluoride ions (anodic process). These processes occurred simultaneously, forming the developed Pt/Si interface. Auger electron spectroscopy and C-V curves reveal the formation of a dielectric interface layer between Pt and Si of hundreds of nanometers that extends with the time of treatment. The electrical properties of mesa structures exhibit Schottky barrier behavior. Both conditions of current transport along the deposited layer and parameters of Schottky contact are defined vs. the deposition time and compared with that for thermally deposited Pt contact. © 2001 The Electrochemical Society. All rights reserved.

Electroless deposition of platinum on proton-conductive perfluorinated membranes modified with ethylene diamine

Perfluorinated, non-hydrolysed, carbon-chain flat-sheet membranes were treated with ethylene diamine (EDA) to investigate the influence of EDA-treatment on the process of the Pt deposition on these membranes. The electrical resistances of the modified membranes were also measured, to determine the degree of modification of the membranes. Pt-containing membranes were characterised using SEM to compare the profile of the Pt deposition on Pt-containing membranes that were not modified. Dielectric analysis (DEA) was used to investigate the dipole and ion mobility of hydrolysed EDA-modified membranes.

Different Behavior in the Deposition of Platinum from HF Solutions on n‐ and p‐Type (100) Si Substrates

Platinum electroless deposition on silicon from HF solutions was studied by scanning electron microscopy and transmission electron microscopy, focusing the interest on the different evolution of the deposit on n‐ and p‐doped samples. In both cases the final result was that a complete platinum layer was eventually formed, but the process was hindered on n+ substrates which exhibited an induction period and displayed a more local behavior compared to p substrates. The results are discussed in terms of a global electrochemical process in which silicon is oxidized and platinum reduces injecting holes to the silicon valence band.

Atomic Force Microscopy Study of the Silicon Doping Influence on the First Stages of Platinum Electroless Deposition

The first stages of platinum electroless deposition on (100) Si from hydrogen fluoride solutions are studied by tapping mode atomic force microscopy (AFM), transmission electron microscopy (TEM), and x‐ray photoelectron spectroscopy (XPS). Tapping mode AFM and TEM provide a morphological characterization of the samples, while XPS accounts for the compounds present on the surface. During immersion in an aqueous HF solution containing a platinum salt, platinum nucleates on the silicon substrate while the surface is etched. The deposited nuclei are polycrystalline, highly pure, and strongly silicidated at room temperature. Metal deposition takes place by means of a redox reaction in which silicon atoms oxidize, supplying the electrons for the metal to reduce. For all substrates, platinum silicide is formed during deposition at room temperature, suggesting a competition between the deposition of pure metal by an electrochemical mechanism and the formation of the silicide by direct reaction. For equal deposition times, more platinum deposits on p‐type substrates than in n+. p‐Type substrates, moreover, undergo a general increase in roughness in the bare silicon areas, while n‐type substrates present a lower and more local etching. This seems to indicate that electroless platinum deposition is somehow hindered on n+ substrates.

First stages of platinum electroless deposition on silicon (100) from hydrogen fluoride solutions studied by AFM

The first stages of platinum electroless deposition on p-Si (100) from hydrogen fluoride (HF) solutions are studied by atomic force microscopy (AFM), transmission electron microscopy (TEM), electron dispersive spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). Platinum nuclei are deposited on a silicon substrate by simple immersion in an aqueous HF solution containing a platinum salt. Tapping-mode AFM and TEM have been used to characterize the samples morphologically, and EDS and XPS to identify the chemical nature of the main features. Platinum silicide formation has been detected for the first time in this kind of process, suggesting a competition between the deposition of pure metal and the formation of its silicide.

Modification of the Silicon Surface by Electroless Deposition of Platinum from HF Solutions

ABSTRACTPlatinum electroless deposition on Si(lOO) from HF solutions is hindered on n+ substrates as compared to p-substrates defining an induction period and displaying a more local behavior. The results are discussed in terms of a global electrochemical process. Platinum reduces injecting holes to the silicon valence band and silicon atoms oxidizes. The final morphological situation is a porous silicon layer which contains platinum nuclei formed by filling pits originated in the first stages of the deposition process.

First Stages of the Platinum Electroless Deposition on Silicon (100) from Hf Solutions.

AbstractElectroless metal deposition based upon the addition of fluoride anions to the metal salt aqueous solution have been developed recently on the assumption that the cleanness of the substrate will be guaranteed and the deposit will be of high purity. In this work, platinum is deposited on silicon (100) from fluorinated solution at two different pH's. The influence of pH is analyzed using Tapping Mode Atomic Force Microscopy (TMAFM) to characterize the main morphological properties of the deposit. Combined TMAFM and Transmission Electron Microscopy (TEM) images are presented and X-ray Photoelectron Spectroscopy (XPS) allows us to identify the chemical nature of the silicon surface.