Origin of High Activity and Durability of Confined Ordered Intermetallic PtCo Catalysts for the Oxygen Reduction Reaction in Rotating Disk Electrode and Fuel Cell Operating Conditions

Abstract

Surface carbon confinement has emerged as an efficient method in promoting the performance of Pt-based catalysts, especially in the design of ordered intermetallic Pt alloy nanoparticles. However, to what function the carbon shell associated with the ordered phase has influenced the activity and particularly long-term durability both in rotating disk electrode (RDE) and fuel cell operating conditions has not been fully understood. In this research, we designed L10 PtCo nanoparticles coated by a thin nitrogen-doped carbon shell (I-PtCo@CN x ) with small particle size (about 5 nm), which exhibited almost 5 times increase in the Pt mass activity compared to commercial Pt/C. Remarkably, I-PtCo@CN x also showed improved longevity and high Co retention during the accelerated durability tests (ADT) compared with control samples. The increased performance originates from the compressed lattice of the ordered structure and the optimized electronic state by the interaction effect from the surface nitrogen-doped carbon shell (CN x ) detected by ex situ and operando X-ray absorption spectroscopy (XAS), which demonstrated fewer structure changes during reaction potentials. The order phase exhibited the ability to maintain the Co component against electrochemical dissolution, while CN x suppressed the generation of the oxidation species and hindered Ostwald ripening during the degradation, which led to higher durability in both RDE and membrane electrolyte assembly (MEA) tests.

Multiscale Regulation of Ordered PtCu Intermetallic Electrocatalyst for Highly Durable Oxygen Reduction Reaction

“…HADDF-STEM images of O-PtCu/HMCS and O-PtCu/C in Figures f, g, and S9 demonstrate the periodic layer-by-layer structure by the distinct Z -contrasts between Pt and Cu atoms, further proving the ordered PtCu structure in O-PtCu/HMCS and O-PtCu/C samples . Moreover, a Pt shell is formed in O-PtCu particles because of the surface segregation, which is consistent with other reported intermetallic materials. , The Pt layer on the surface helps expose more active sites, prevent the leaching of transition metals, and improve the Pt utilization efficiency . Atomic-level-resolution energy-dispersive X-ray (EDX) elemental mapping of the PtCu particle for the O-PtCu/HMCS (Figure h) provides additional compelling evidence for the ordered atomic arrangement.…”

“…Proton exchange membrane fuel cells (PEMFCs) have garnered broad interest as a promising technology to address the continuously growing demand for sustainable energy. , Unfortunately, the undesirable sluggish kinetics of the cathode reaction, oxygen reduction reaction (ORR), causes challenges for its practical application. , Thus, it necessitates the utilization of expensive Pt and Pt-based materials as the electrocatalyst to facilitate ORR . Numerous research efforts have been directed toward developing strategies for enhancing the activity of Pt-based catalysts, , and alloying Pt with transition metals has been established as an promising approach capitalizing on the strain effect, ligand effect, and ensemble effect. − Nevertheless, theses developed Pt–M alloy catalysts faces durability challenges, primarily resulting from the dissolution of transition metals in acidic media, which will lead to the collapse of catalyst particles and the loss of active sites. ,, Moreover, the leached transition metal ions contaminate the ionomers and membrane within the electrodes, consequently reducing their ionic conductivities. − …”

Proton Relay for the Rate Enhancement of Electrochemical Hydrogen Reactions at Heterogeneous Interfaces

“…Conventional design of heterogeneous electrocatalysts has focused on modifying the catalyst surface electronic structure through alloying, − crystalline structuring, and atomic ordering and orientation , to tune the covalent interactions of surfaces with reaction intermediates (e.g., surface binding or adsorption). − These approaches have led to significant progress in improving catalyst activity for a variety of electrocatalytic reactions, including the hydrogen evolution and oxidation reaction (HER/HOR), , the oxygen evolution and reduction reaction (OER/ORR), , CO 2 reduction reactions (CO 2 RR), , etc. In nature, the kinetics of these reactions are governed not only through covalent interactions but also through noncovalent interactions, the most important of which is tuning proton transfer near the catalyst surface. − …”