Fabrication of Block Copolymer Templated Extended Surface Model Electrocatalysts By Atomic Layer Deposition and Physical Vapor Deposition

Abstract

Templating platinum group metal (PGM) nanostructures from microphase separated block copolymers (BCPs) allows for electrocatalytic activity to be studied on highly ordered, model surfaces with precisely controlled feature sizes and morphologies, thereby allowing catalyst electroactivity and stability to be probed as a function of nanoscale geometry. In our previous work [1], BCP templated electrocatalysts fabricated via incipient wetness impregnation of PGM precursors were tested for hydrogen oxidation/evolution and water-splitting activity on interdigitated electrodes using liquid and solid polymer electrolytes. This talk presents the fabrication of such electrocatalysts via Atomic Layer Deposition (ALD) and Physical Vapor Deposition (PVD) techniques (e-beam evaporation and sputtering). Self-assembled lamellae of poly-(styrene-block-methylmethacrylate) (PSbPMMA) thin films on Si wafer and glassy carbon substrates were subjected to 5 - 15 ALD cycles with trimethylaluminium (TMA) precursor to induce selective growth of alumina in the PMMA domains via Sequential Infiltration Synthesis. Thereafter, the polymer template was removed via Reactive Ion Etching (RIE) with oxygen plasma. The resultant alumina nanostructures templated from self-assembled PSbPMMA was then used as a substrate either for Platinum ALD with (trimethyl)methylcyclopentadienylplatinum(IV) precursor atop a Titanium Nitride adhesive layer, or for sputtering of Pt atop a Ti adhesive layer to obtain conformal Pt coatings of up to 20 nm in thickness. When e-beam evaporation was used, The PMMA domains were selectively removed by successive wet and dry etch steps, followed by deposition and lift-off. The PGM electrocatalyst nanostructures were characterized via a combination of electron microcopy, X-ray diffraction, and X-ray photoelectron spectroscopy, and the Pt content of the catalysts were determined via microwave leaching and digestion of the electrocatalyst thin film followed by Inductively Coupled Plasma Mass Spectroscopy. The nanostructured electrocatalysts were tested for oxygen reduction (ORR) activity in a conventional rotating disk electrode setup using 0.1 M perchloric acid electrolyte, and the ORR mass activities and active surface area were obtained.[1] Bhattacharya, D., Arges, C. G., et al., Small, 2021, 17, 2100437