(712e) The Durability of Platinum Overlayers Formed By Self-Terminating Electrodeposition for PEM Fuel Cell Application

Proton exchange membrane fuel cells (PEMFCs) are an energy-efficient alternative to combustion engines for automotive applications. However, they are still on the cusp of mass adoption, mainly due to higher costs. Significant advances have been made in PEMFC system design over the last three decades concerning cost reduction and structural redesign. The membrane electrode assembly (MEA), especially the electrode, is considered 'the heart' of a PEMFC and is designed to accommodate the need for efficient transport of electrons, reactants, and heat as well as constraints imposed by the platinum cost. Advances in PEMFC electrode design over the years range from using platinum black films with a loading of 10 g_pt/cm² in the 1970s to present-day Pt/ PGM (Platinum Group Metal) nanoparticle coated carbon-black particles (Pt/C) that use about 0.3 mg_pt/cm². The electrocatalyst architecture based on highly dispersed nanoparticles on carbon black particles enables significant gain in specific surface area of the catalyst. However, durability problems associated with corrosion of carbon support and subsequent loss of active surface area during start-up and shut down cycles have led to renewed interest in carbon-free nanostructured electrodes that employ a thin coating of Platinum or PGM-based catalytic layer on mesostructured conductive support ((Debe 2012), (Liu et al. 2012))

In this context, we carried out systematic ex-situ investigations on the durability of platinum thin films comprising of atomic overlayers formed by Self-Terminating platinum electrodeposition (Liu et al. 2012). We characterized the sequential growth of platinum film using XPS and AFM measurements; and analyzed the electrocatalytic performance as a function of the number of self-terminating pulses. We found that using eight pulses of electrodeposition, corresponding to ~10 nm thick platinum film, can meet stringent ex-situ durability targets set for a potential electrocatalyst in Fuel Cell Vehicles (FCVs) application by the Department of Energy (DOE), USA. Our results also show that samples with platinum deposited using four pulses (< 4 µg/cm² loading) or even one pulse (< 1 µg/cm² loading) are electrochemically active. For eight and more pulses of platinum, we observed ~ 20% loss in Electrochemically Active Surface Area (ECSA) during the first 3000 durability cycles and 10-15% ECSA loss over the next 27000 cycles, indicating stabilization of the activated platinum morphology over time. In this presentation we will present results for the minimum number of pulses of platinum electrodeposition needed to form a complete overlayer of electrochemically active platinum and compare estimates of platinum loss using ICP-OES and Cyclic Voltammetry. These studies pave the way for an additive, roll-to-roll, and cost-effective manufacturing process of ultra-low platinum loaded MEAs for PEMFCs by building on our earlier results on printing silver nanostructures using a simple inkjet printer by Print-Expose-Develop technique (Parmar and Santhanam 2014) in conjunction with the ability to controllably form overlayers of platinum on metallic substrates by Self-terminating electrodeposition.