Effects of Pt metal loading on the atomic restructure and oxygen reduction reaction performance of Pt-cluster decorated Cu@Pd electrocatalysts

Abstract

Surface tailoring as well as inner structure design at the atomic scale are of primary importance for the activity and durability of nanocatalysts (NCs) in electrochemical applications. In this study, a novel structural candidate containing a Cu core and Pt cluster decorated Pd shell with a balance struck between the performance and cost considerations for the oxygen reduction reaction (ORR) is proposed. The carbon nanotube supported NCs are synthesized using a wet chemical reduction method with different ratios of Pt from 5 to 14 wt%. Our results demonstrate a robust assessment for programming the ORR performance by Pt loading control in the NCs. For the optimum case (∼5.0 wt% of Pt), the mass activity (M.A.) is ∼639 mA mg_Pt⁻¹. This value is improved by 9-folds compared to that of commercial Pt NC (J.M.-Pt/C) at 0.85 V vs. RHE and can be attributed to the formation of a high density of surface truncations in the NC surface. When the Pt loading is ∼9 wt%, the NC forms multi-faceted twin particles with low surface defects and thus has the highest stability (+/− 0.5% of current vibration) in an accelerated degradation test (ADT) among the experimental samples. Further increasing Pt to 14 wt%, restructures the NC into a local ordered crystal with certain amounts of Pt island clusters in the surface. Such a phenomenon results in a vibration of the current density by surface restructure upon oxidation and reduction of Pt oxides in a ADT test and possesses a residual current density of 92% compared to its original value after 40 k cycles. Most importantly, our observations bring fundamental and practical insights into the role of surface defects in electrocatalysis and present a new strategy to surmount a dilemma between the reliability and activity of ORR NCs.