Preparation and Characterization of Platinum-Cobalt Nanosheets for Oxygen Reduction Reaction

Enhancing the efficiency of Pt-based electrocatalysts for the oxygen reduction reaction (ORR) is crucial for the broader use of polymer electrolyte fuel cells. Pt-based electrocatalysts are commonly used at the cathode side of polymer electrolyte fuel cells to facilitate the ORR, which is the most sluggish process during cell operation. Pt nanosheet prepared via topotactic reduction of platinum oxide nanosheets showed large electrochemically active surface area (ECSA)and high mass specific activity (MA).1 The addition of cobalt into the Pt nanosheet is expected to enhance and improve overall electrocatalytic performance as PtCo alloy nanoparticles are known to have higher specific activity than pure Pt. In this study, we present the synthesis and characterization of cobalt-doped platinum-oxide nanosheets ((Pt,Co)Ox NS) and their transformation into carbon-supported Pt-Co nanosheets for potential electrochemical applications. The (Pt,Co)Ox NS colloid was obtained through exfoliation in aqueous solution by modification of our previous synthesis process.1 The results demonstrated enhanced electrocatalytic activity of the (Pt,Co)Ox NS composite compared to pure platinum-oxide nanosheets. For the pure platinum-oxide nanosheets, the ECSA was 97 m2 (g-Pt)-1. Moreover, employing the Koutecky-Levich equation, the MA was determined to be 321 A g-1 at 0.9 V vs. RHE, and the specific activity was 332 µA cm-2. For the PtCo nanosheets, the ECSA was similar at 91 m2 (g-Pt)-1. However, owing to the Co electronic effect, the specific activity rose to 576 µA cm-2, leading to an overall increase in MA to 524 A g-1 at 0.9 V vs. RHE. This improvement is attributed to the synergistic effect between cobalt and platinum, which enhances the oxygen reduction process. Reference: D. Takimoto, S. Toma, Y. Suda, T. Shirokura, Y. Tokura, K. Fukuda, M. Matsumoto, H. Imai, and W. Sugimoto, Nat Commun 14, 19 (2023)