In situ formation of sub nanometer cobalt particle with platinum nanocrystal for high performance oxygen reduction reaction electrocatalyst

Abstract

Hitherto, platinum (Pt) is the most active electrocatalyst for the oxygen reduction reaction (ORR) of the proton exchange membrane fuel cells (PEMFCs). Enhancing the performance and reducing the use of costly Pt is of great significance for the wider adoption of PEMFCs. The present research demonstrates in situ synthesized Pt nanocrystal immobilized with sub nanometer sized cobalt (Co) particles (≤ 0.3 nm) loaded on ketjenblack carbon (KB) support via a simple polyol method as a highly active ORR electrocatalyst. The as synthesized Pt_4.1Co/KB catalyst featured a more positive halfwave potential of 0.925 V with a resultant of 1.8 times higher mass activity than Co free Pt/KB catalyst at 0.9 V in 0.1 M HClO₄ and insignificant decay in ORR performance after 30,000 potential cycles. The excellent electrocatalytic performance of Pt_4.1Co/KB has also been proven in a practical H₂/air fuel cell, demonstrating a maximum peak power density of 1.08 W/cm², comparable to the standard Pt/C-TKK (47 %) catalyst. The improved ORR performance of Pt_4.1Co/KB is attributed to the incorporation of sub nanometer sized Co particles, which synergistically enhance the activity and stability. Computational studies using periodic density functional theory calculations also suggest that the integration of ultrafine Co nanoparticles shifted the Pt contribution to the density of states towards higher energy levels, thereby facilitating the ORR process for the Pt_4.1Co/KB catalyst. This work provides a distinctive development of an efficient and robust ORR catalyst for advancing PEMFCs.