Fabrication and Cell Analysis of a Pt/SiO₂Platinum Thin Film Electrode

Abstract

A platinum thin film electrode was fabricated on the surface of SiO 2 nanofibers by atomic layer deposition (ALD) and its cell performances were analyzed with an MEA using it as the cathode to reveal general features of platinum thin film electrodes. Although the Pt/SiO 2 cell showed comparable performance to the conventional Pt/C cell under suitable condition in spite of the much smaller electrochemical surface area (ECSA), it showed poor performance under overly dry or wet conditions as is the case with the 3M's nanostructured thin film (NSTF) electrode. An analysis applying a transmission line model of the electrode to the Pt/SiO 2 nanofiber electrode indicated that the performance loss of the Pt/SiO 2 electrode under dry condition is mainly due to the increase in the reaction resistance rather than that in the ohmic resistance. The increment in the reaction resistance was suppressed by addition of ionomer to the Pt/SiO 2 electrode. Furthermore, performance loss under wet condition due to cathode flooding was drastically alleviated by addition of a hydrophobic polymer to the Pt/SiO 2 electrode. A polymer electrolyte fuel cell (PEFC) is a promising power source for automotive application. For the wider commercialization of the fuel cell vehicles (FCVs), however, there still remains challenge to reduce the amount of precious Pt used as the electrocatalyst. For that purpose, it is essential to develop a novel electrode which enables high oxygen reduction reaction (ORR) activity, high durability, and high power density. 1,2Conventional PEFCs generally use platinum particles supported on high surface area carbon particles as electrode catalysts. Great efforts have been made in improving performance of those particulate catalysts by reducing particle size, 3 alloying, 4-9 or applying core-shell structure.10-12 However, the chemical and electrochemical stabilities of the carbon supports, 13,14 as well as the dissolution of platinum particles, [15][16][17] raise concern about the durability of the catalyst. Furthermore, the oxygen reduction reaction (ORR) activity per surface area of platinum (the specific activity) decreases with reducing the particle size.3,17-22 These problems limit further improvement of the dispersed catalysts.Recently, platinum thin film electrodes, such as 3M's nanostructured thin film (NSTF), have attracted much attention as alternative catalysts for PEFCs. 23 The structure of the NSTF electrode is totally different from that of the conventional Pt/C electrode in following three points: low platinum surface area (10 -25 cm 2 Pt /cm 2 planar ), support material without electrical conductivity, and containing no ionomer. Although NSTF electrodes showed higher efficiency and power density than conventional Pt/C electrodes under suitable operating conditions, 24,25 it has been reported that they tend to show larger performance loss under dry or wet conditions. [26][27][28] The aim of this research is to examine all those properties of NSTF on other thin film electrodes and reveal their general fe...

Review—Electromobility: Batteries or Fuel Cells?

“…Alternative support materials have also been considered such as carbon nanotubes, 135 hollow graphitic spheres, 140 and conductive metal oxides. 141 Recently, Inaba et al published MEA measurements with SiO 2 nanofiber supported Pt, 142 showing reasonable performance at intermediate humidification and poor performance under other commonly employed operating conditions. So far, none of these alternative supports seem to have the maturity to be used in commercial MEAs, and cumbersome and costly system mitigation strategies are still needed to assure long-term durability.…”

Vertically Oriented Polymer Electrolyte Nanofiber Catalyst Support for Thin Film Proton‐Exchange Membrane Fuel Cell Electrodes

“…A significant performance improvement could also be achieved by including a hydrophobic component to prevent the buildup of water in the large hydrophilic pores between the fibers. Recent work on other extended surface metal electrodes has shown the addition hydrophicity to dramatically increase performance and robustness of operation . In addition, the roughness of the electrodes can be optimized in terms of nanofiber diameter, orientation, areal density, and aspect ratio.…”

“…Recent work on other extended surface metal electrodes has shown the addition hydrophicity to dramatically increase performance and robustness of operation. [33,34] In addition, the roughness of the electrodes can be optimized in terms of nanofiber diameter,o rientation, areal density,and aspect ratio.…”

High Specific and Mass Activity for the Oxygen Reduction Reaction for Thin Film Catalysts of Sputtered Pt3Y

“…It is also possible that the use of a thin film catalyst can reduce the detrimental effect of carbon corrosion found for carbon‐supported nanoparticles . Consequently, the use of electrodes with sputtered or atomic layer deposited nanostructured thin films (NSTFs) has been identified as a promising method for mass produced fuel cells . Sputtering is, moreover, particularly suitable for the growth of alloy thin films as the method enables deposition with high control over composition and catalyst loading.…”