Oxygen vacancies endow atomic cobalt-palladium oxide clusters with outstanding oxygen reduction reaction activity

Considering the technological importance of fuel cells, developing highly efficacious, durable, and Platinum (Pt)-free catalysts are crucial. In this work, we propose a novel nanocatalyst (NC) comprising oxygen vacancies (O^V) enriched atomic CoPdO_x clusters (CoPdO_x^V) anchored Pd nanoparticles (NP)s on cobalt-oxide support (denoted as CPCo). As-prepared CPCo NC with an additional 3 wt% of Co decoration (denoted as CPCo-3) delivers an exceptionally high mass activity (MA) of 4394 mAmg_Co⁻¹ at 0.85 V vs RHE and 426 mAmg_Co⁻¹ at 0.90 V vs RHE in alkaline oxygen reduction reaction (ORR) (0.1 M KOH), which surpasses the commercial J.M.-Pt/C (20 wt%) catalyst by 65-times. More importantly, the CPCo-3 NC exhibits outstanding durability in an accelerated durability test (ADT) with a progressively increased MA by 40 % (6,140 mAmg_Co⁻¹) as that of the initial condition after 20 k cycles. Through in-depth physical characterization, electrochemical analysis, and in-situ X-ray absorption spectroscopy (XAS), we demonstrated the conceptual framework of potential synergism between the CoPdO_x^V and neighbouring metallic Pd-sites. In this event, the surface-anchored CoPdO_x^V species coupling with O^V promotes the O₂ splitting, while the neighbouring Pd-sites simultaneously trigger the O^ads relocation (i.e. OH⁻ desorption) step. In addition, the cobalt oxide support underneath assists the electron injection to surface Pd-sites. This work not only marks a step ahead for designing high-performance transition metal oxide catalysts for fuel cells but also uncovers the material's aspects of cobalt that shall spark motivation for the other catalytic applications.