Mesoscale Control of PGM Electrocatalysts Using Self-Assembled Block Copolymer Templates

Abstract

Platinum Group Metals (PGMs) are state-of-the-art electrocatalysts for electrochemical energy conversion technologies. This talk presents a templating approach for the fabrication of dense and periodic platinum and iridium oxide nanowires and standing cylinders with tuned feature sizes (e.g., 12 to 40 nm) and long-range order from self-assembled block copolymer thin films. Unlike previous studies, we show that a starting template utilizing an ion-containing block copolymer electrolyte over a non-ionic block copolymer yields thicker and denser metal/metal oxide nanostructures. PGM geometry and chemical composition were characterized using electron microscopy, atomic force microscopy, grazing incidence x-ray scattering, x-ray photoelectron spectroscopy, and inductively coupled plasma – optical emission spectrometry. The structural characterization tools show high-fidelity pattern transfer from the block copolymer template to the PGM nanostructure. Additionally, the templating process was conducive for preparing the nanostructured PGMs on glassy carbon disks and interdigitated electrodes (IDEs) for electrochemical reactivity assessments. The former substrates were used to assess HER and ORR in a conventional rotating disk electrode setup, while the latter platform was amenable for hydrogen pump and water electrolysis demonstrations with thin film low-temperature and high-temperature polymer electrolytes. Electrochemical measurements revealed a commensurate trend between PGM surface area and mass activity. In summary, the block copolymer templating approach represents a unique platform for high throughput comparative analyses of the intrinsic catalytic activity as a function of meso-scale geometry. It is also an effective platform to understand electrocatalytic reactivity differences for a given catalyst with different types of electrolytes.