Programmable Exposure of Pt Active Facets for Efficient Oxygen Reduction.

To produce efficient ORR catalysts with low Pt content, PtNi porous films (PFs) with sufficiently exposed Pt active sites were designed by an approach combining electrochemical bottom-up (electrodeposition) and top-down (anodization) processes. The dynamic oxygen-bubble template (DOBT) programmably controlled by a square-wave potential was used to tune the catalyst morphology and expose Pt active facets in PtNi PFs. Surface-bounded species, such as hydroxyl (OH* , *=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 ).