Highly Robust Low-PGM MEAs Based upon Composite Supports _ Final Report

Technical Report · Tue Nov 12 00:00:00 EST 2019

OSTI ID:1573917

Dameron, Arrelaine

This Small Business Innovation Research Phase I project investigated high performance, highly durable supports for low Platinum Group Metal (PGM) fuel cells using low-cost techniques to achieve the 2020 targets for cost ($$\$$40/kW$ at the system level, $$\$$40/kW$$ at the MEA level), start-up/shutdown durability (5,000 cycles), and less than 10% loss in power after 5,000 hours. Although carbon is currently used as a support due to its low cost, high conductivity and availability in high surface area formats, it also oxidizes or corrodes (at defect sites, C#) over time in the presence of water, via formation and oxidation of active (C#OH) carbon surface oxide species with H2O, and OH spill-over from Pt: 1) C^# + H₂O → C^#OH + H⁺ + e^- a. C^#OH + H₂O → CO₂ + 3H⁺ + 3e^- 2) Pt + H₂O → PtOH + H⁺ + e^- a. C^#OH + PtOH → CO₂ + 2H⁺ + 2e^- + Pt * Adapted from FCPAD review, fc136_borup_2016_o.pdf The only viable approaches to obviate this issue are to either supplant the carbon with a corrosion-resistant alternative, or to isolate the carbon from direct exposure to corrosive agents through physical or chemical means. In order to reach the DOE performance and durability goals for fuel cells, the carbon corrosion issue is currently being addressed with non-carbon alternatives (e.g. Ta- or Nb-doped TiO₂, nitrides, Indium tin oxide, etc.). However, when conductive metal oxides or corrosion-resistant nitrides are used as supports, there is typically a reduction in surface area of materials that adversely affect conventional Pt deposition processes, which can lead to accelerated ripening of Pt and loss of activity/performance. When conventional carbons have been encapsulated with materials, there had historically been a trade-off between coating cost and precision and/or coverage of the coating materials. Low-cost coating processes such as sol-gel techniques can apply rough, granular coatings that do not provide robust protection at the carbon interface; higher-cost precision processes such as Physical Vapor Deposition (PVD) are difficult to scale to meet DOE cost targets. This program will apply a recently developed low-cost Atomic Layer Deposition (ALD) technique to apply ultra-thin conductive barrier coatings onto carbon particles to prepare drop-in ready materials suitable for use in highly robust Membrane Electrode Assemblies (MEAs) and without sacrificing cost or performance, and extend system durability shortcomings shown in Figure 1. PneumatiCoat Technologies has demonstrated a high-throughput, low-cost method of applying ALD coatings to particles, allowing this precision coating technique to be implemented at very low $$/kg for fuel cells, catalysts and Li-ion batteries. This work addressed the following barriers to support commercial adoption of Fuel Cells: Durability: A demonstrated approach to applying pinhole-free, corrosion-resistant barrier coatings at the nano-scale, which has increased the lifetime of Li-ion battery cathode materials by 250% (which have severe electrochemical, morphological, structural and corrosion-derived degradation pathways). Performance and Cost: A proven low-cost encapsulation technique applied to low cost carbons used today, which can be applied before and/or after the electrocatalyst nanostructures are applied; Phase I Technical Objectives: 1) Demonstrate a successful overcoat method on low PGM Pt/C catalysts with ALD TiO₂, specifically targeting uniform coverage of the carbon support with gas phase access to the Pt catalysts. 2) Evaluate the activity, ohmic resistance and cycling stability of overcoated catalyst materials by RDE & MEA testing. 3) Demonstrate improved cycling durability with MEA testing of optimized encapsulated catalysts without significant loss in activity. 4) Down select to a viable encapsulated Pt/C catalyst material based on electrochemical performance, process engineering and techno-economic considerations. FN is confidently stating that the Technical Feasibility has been completely demonstrated and significant improvements to high capacity and high voltage cathode materials are directly attainable using PCT’s low-cost high rate manufacturing systems for applying ALD coatings to these materials at the powder level. The general metrics for materials production can be boiled down to cost, performance and scalability, and above all, whether there is commercial interest in a finished product. This Phase I project has elucidated that PCT’s semi-continuous ALD coating systems provide highly-compelling cost, performance and scalability metrics relative to both non-ALD coating processes and batch production systems for coating particles by ALD. PCT’s approach is the only viable solution that can meet the automotive industry’s mandate to raw materials suppliers, which states that encapsulation coatings cannot add more than $1/kg to the cost of active materials. The overall objective of the Phase I project was to apply optimal encapsulation coatings to Li-ion battery cathode materials for head-to-head comparison of processes and coating techniques, to further the mission of reducing the total cost of ownership of battery systems. Screening designs were deployed to pair best coating materials for each Gen 3 cathode material, and subsequent optimization runs were to be executed to define specific down-selected coating processes for the high capacity and high voltage materials.

• Research Organization: Forge Nano Inc (FMK Pneumaticoat Technologies LLC)
• Sponsoring Organization: USDOE Office of Science (SC)
• DOE Contract Number: SC0017192
• OSTI ID: 1573917
• Type / Phase: SBIR (Phase I)
• Report Number(s): DOE-17192; 7205311827
• Country of Publication: United States
• Language: English