Engineering ORR Electrocatalysts from Co₈Pt₄ Carbonyl Clusters via ZIF-8 Templating

To reduce the costs of proton exchange membrane fuel cells, the amount of Pt necessary to drive efficient oxygen reduction reaction (ORR) should be minimized. Particle nanostructuring, (nano-)alloying, and metal-doping can yield higher activities per Pt mass through tailoring catalysts owning a high number of active sites and precise electronic properties. In this work, the atom-precise [NBnMe₃]₂[Co₈Pt₄C₂(CO)₂₄] (Co₈Pt₄) cluster is encapsulated and activated in a zeolitic imidazolate framework (ZIF)-8, which unlocks the access to defined, bare Pt−Co nanoclusters, Co_8±xPt_4±yNC@ZIF-8, for the fabrication of highly active ORR catalysts. Upon controlled C-interfacing and ZIF-8-digestion, Co-doped Pt NPs (Pt₂₇Co₁) with a homogenous and narrow size distribution of (1.1±0.4) nm are produced on Vulcan® carbon. Restructuring of the Pt₂₇Co₁/C catalyst throughout the ORR measurement was monitored via high-angle annular dark field-scanning transmission electron microscopy and X-ray photoelectron spectroscopy. The measured ORR mass activity of (0.42±0.07) A mg_Pt⁻¹ and the specific activity of (0.67±0.06) mA cm_ECSA⁻² compare favourably with the catalyst obtained by direct C-interfacing the pristine Co₈Pt₄ cluster and with state-of-the-art Pt/C reference catalysts. Our results demonstrate the potential of ZIF-8-mediated Pt−Co NP synthesis toward devising ORR catalysts with high Pt-mass activity.