PNNL

Abstract

Pt-based materials are the state-of-the-art catalysts for oxygen reduction reaction (ORR), but their high cost and scarcity remain the major obstacles for large-scale applications in renewable energy industries. To produce efficient ORR catalysts with low Pt content, PtNi porous films (PFs) with sufficiently exposed Pt active sites were rationally designed through a programmable approach combining electrochemical bottom-up (electrodeposition) and topdown (anodization) processes. The unique dynamic oxygen-bubble template (DOBT) programmably controlled by square-wave potential was utilized to tune the catalyst morphology and expose Pt active facets in PtNi PFs. The surface-bounded species such as hydroxyl anions (OH*, * represents surface site) on the exposed PtNi PFs surfaces were adjusted by the applied anodic voltage, further affecting the dynamic oxygen (O2) bubbles adsorption on Pt. As a result, PtNi PF with enriched Pt (111) facets (denoted as Pt3.5%Ni PF) was obtained, showing prominent ORR activity with an onset potential of 0.92 V (vs. RHE) at an ultra-low Pt loading (0.015 mg cm-2). The adsorbed OHads coverage estimation shows fewer OHads on Pt3.5%Ni PF than other PtNi PFs, indicating that enriched Pt (111) facets in the catalysts enable facilitated O2 adsorption for oxygen reduction and thus leading to superior ORR activity