Platinum supported on titanium–ruthenium oxide is a remarkably stable electrocatayst for hydrogen fuel cell vehicles

Abstract

We report a unique and highly stable electrocatalyst-platinum (Pt) supported on titanium-ruthenium oxide (TRO)-for hydrogen fuel cell vehicles. The Pt/TRO electrocatalyst was exposed to stringent accelerated test protocols designed to induce degradation and failure mechanisms identical to those seen during extended normal operation of a fuel cell automobile-namely, support corrosion during vehicle startup and shutdown, and platinum dissolution during vehicle acceleration and deceleration. These experiments were performed both ex situ (on supports and catalysts deposited onto a glassy carbon rotating disk electrode) and in situ (in a membrane electrode assembly). The Pt/TRO was compared against a state-of-the-art benchmark catalyst-Pt supported on high surfacearea carbon (Pt/HSAC). In ex situ tests, Pt/TRO lost only 18% of its initial oxygen reduction reaction mass activity and 3% of its oxygen reduction reaction-specific activity, whereas the corresponding losses for Pt/HSAC were 52% and 22%. In in situ-accelerated degradation tests performed on membrane electrode assemblies, the loss in cell voltage at 1 A · cm −2 at 100% RH was a negligible 15 mV for Pt/TRO, whereas the loss was too high to permit operation at 1 A · cm −2 for Pt/HSAC. We clearly show that electrocatalyst support corrosion induced during fuel cell startup and shutdown is a far more potent failure mode than platinum dissolution during fuel cell operation. Hence, we posit that the need for a highly stable support (such as TRO) is paramount. Finally, we demonstrate that the corrosion of carbon present in the gas diffusion layer of the fuel cell is only of minor concern.noncarbon catalyst supports | PEFC | start-stop protocol | TiO 2 -RuO 2 | carbon corrosion C arbon has traditionally been the most common material of choice for polymer electrolyte fuel cell (PEFC) electrocatalyst supports (1) due to its low cost, high abundance, high electronic conductivity (30 S · cm −1 ), and high Brunauer, Emmett, and Teller (BET) surface area (200-300 m 2 · g −1 ), which permits good dispersion of the platinum (Pt) catalyst (2-4). The (in) stability of the carbon-supported platinum electrocatalyst is a key issue that currently precludes widespread commercialization of PEFCs for automotive applications. Carbon is known to undergo electrochemical oxidation to carbon dioxide, as shown in Eq. 1. The standard electrode potential for this reaction is 0.207 V vs. standard hydrogen potential (SHE; all potentials henceforth reported vs. SHE, unless otherwise stated). Under normal PEFC operating conditions, the electrode potential is <0.1 V at the anode and between 0.6 V and 0.8 V at the cathode. Despite the fact that the cathode potential is usually significantly higher than the standard potential for carbon oxidation (with an effective overpotential of 0.4-0.6 V), the actual rate of carbon oxidation is very slow due to intrinsic kinetic limitations; in other words, a very low standard heterogeneous rate constant (5).During operation of automotive PEFC stacks, fuel/air ...

Fabrication, In-Situ Performance, and Durability of Nanofiber Fuel Cell Electrodes

“…7,20 End-of-life and beginning-of-life polarization curves from carbon corrosion tests with JM-Pt(Vulcan) catalyst are shown in Figures 10a and 10b for feed gas relative humidities of 100% and 40%, respectively. The spray-coated MEA showed severe performance losses due to carbon corrosion, significantly more than the nanofiber electrode.…”

“…Current efforts are focused on metal oxides and thermally treated carbon supported catalysts. [7][8][9][10] …”

Influence of the Working and Counter Electrode Surface Area Ratios on the Dissolution of Platinum under Electrochemical Conditions

“…3 Application of nanostructured Pt materials, such as Pt nanoparticles (PtNPs), reduces the cost of catalysts and improves their utilization. [4][5][6][7][8][9][10][11] Yet, nanostructured materials, including Pt nanoparticles, possess high surface Gibbs energy that enhances their activity towards both desired as well as undesired reaction. These interrelated characteristics give rise to gradual degradation of Pt-NPs through chemical and electrochemical reactions.…”

Pt/RuO2-TiO2Electrocatalysts Exhibit Excellent Hydrogen Evolution Activity in Alkaline Media

“…20 Ruthenium-titanium oxide (RTO) has been investigated as a catalyst support for platinum and the derivative Pt/RuO 2 -TiO 2 (Pt/RTO) catalyst has shown excellent stability and activity in polymer electrolyte fuel cells. 21,22 In this work, we postulate that using this mixed-metal-oxide support for platinum (in place of carbon) will yield a HER electrocatalyst with excellent activity in alkaline media and that the support will serve a similar function as the hydroxides described in the above paragraphs, namely to enhance water dissociation at the Pt-support edges. The overarching objective of this work was therefore to synthesize a Pt catalyst supported on RuO 2 /TiO 2 and to demonstrate its enhanced activity for HER when compared against a commercial Pt/C catalyst.…”