Ab-Initio and Experimental Study of Oxygen Reduction Reaction (ORR) Activity and Durability of Ordered PtNi/C Catalysts
Authors: Woo Seung-min , Jin Song , Seo Min Ho 
Published: December 2024

Developing durable and highly active low-Pt electrocatalysts for oxygen reduction reaction (ORR) in acidic media is necessary for highly effective polymer electrolyte membrane fuel cells (PEMFCs). Intermetallic structure is thermodynamically more stable than random alloy metal compounds. In oxygen reduction reaction (ORR), Pt3Ni1 with (111) facet is to be the most effective electrocatalyst for ORR. Therefore, to develop a highly efficienct electrocatalyst for oxygen reduction reaction (ORR) in effective polymer electrolyte membrane fuel cell (PEMFC), an ordered PtNi/C intermetallic alloy on a carbon black support has been designed. To enhance ORR performance and reduce Pt usage, a Pt-transition metal alloy catalyst has been developed. Alloying Pt with a second metal on a carbon support material can improve activity due to the change in lattice parameter and the electronic effect. According to the d-band theory, the downshift effect of the d-band induced by the upshift of the fermi level is predicted to improve ORR activity by weakening the binding energy. In case of alloying Pt and Ni, it can be predicted that the difference in electronegativity between Pt and Ni will induce a fermi level shift, resulting in a d-band center shift effect, which can enhance ORR activity. Compared to random alloy structured electrocatalysts, intermetallic structures of ordered PtNi were more thermodynamically stable. Moreover, intermetallic structure stabilizes the alloy, improving the durability of metal components against chemical corrosion in acidic media, such as HClO4 or H2SO4. Therefore, to improve catalyst’s durability, heat treatment was used to align the structure, making it structurally stable and reducing Pt-Pt distance. Heat treatment screening was carried out between 500℃ and 800℃ using a thermal shock method to minimize particle size growth. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and rotating disc electrode (RDE) were used to investigate the compositional difference and crystallinity of the intermetallic structure, electrochemical ORR activity and durability between disordered PtNi/C (d-PtNi/C) and ordered PtNi/C (o-PtNi/C). The electronic effect of the three Nicore@Ptshell models, namely ordered Nicore@Ptshell (o-PtNi), disordered Nicore@Ptshell (d-PtNi), and pure Pt147 (pure Pt), was estimated through density functional theory (DFT). The d-band theory and Bader charge analysis were used to estimate ORR activity and charge transfer, respectively. Additionally, the durability in acidic media of each model was estimated through dissolution potential calculations (Udiss). This work has supported by the National Research Foundation of Korea (NRF) grant funded by the Ministry of Science and ICT in Republic of Korea (MSIT) (NRF-2022R1A2C2093090). This work was supported by the Technology Innovation Program (20019175) funded by the Ministry of Trade, Industry & Energy (MOTIE, Korea). This research was supported by the Ministry of Trade, Industry, and Energy (MOTIE), Korea, under “Digital manufacturing platform" (No. P0022331) supervised by the Korea Institute for Advancement of Technology (KIAT).