Intensified gas diffusion in ordered mesoporous PtCo alloys for enhanced oxygen reduction electrocatalysis

Abstract

Oxygen reduction reaction (ORR) is the key electrochemical reaction in new energy devices. However, the performance of catalysts usually suffers from the sluggish kinetics of ORR. Herein, we constructed a three-dimensional (3D) ordered meso-structured channel in the PtCo alloy nanoparticles to enhance O₂ diffusion and accelerate the kinetics of ORR. The optimized PtCo-meso_4.5 catalyst with a pore channel size of 4.5 nm was found to achieve high ORR performance, exhibiting mass and specific activities that were 6.88 and 2.82 times greater than the Pt/C benchmark values, respectively. In an H₂-air fuel cell, the PtCo-meso_4.5 cathode delivered a current density of 1.44 A cm⁻² at 0.6 V and achieved a peak power density of 1.07 W cm⁻² as well as excellent stability (only 7.7% loss of current density at 0.6 V after 30k accelerated stability test cycles). The outstanding ORR performance of PtCo-meso_4.5 was attributed to the intensified O₂ gas diffusion in the 3D ordered mesoporous channels leading to the enhancement of mass/electron transport. Moreover, the PtCo alloy supplied enough active sites toward ORR, exhibiting a synergistic effect between the mesoporous structure and PtCo alloying sites, as revealed via the gas diffusion behaviors of PtCo alloys with different mesoporous sizes during the ORR process. This work provides a new idea for the design and synthesis of high-efficiency ORR electrocatalysts for fuel cells.