Breaking the activity-stability trade-off in oxygen reduction via encapsulating Pd nanoparticles within defectively porous Fe, N-doped carbon nanotube

Pd nanoparticles were encapsulated within the Fe, N-doped carbon nanotubes. • The catalyst provides metallic Pd and Fe-N x as dual active sites to ORR. • Thinner, mesoporous and defective carbon walls of the nanotubes were constructed. • The catalyst shows outstanding ORR properties and practical performance. The cost, activity and durability of Pd-based catalyst can be balanced by supporting Pd on carbon materials. Herein, we report an oxygen reduction reaction (ORR) catalyst fabricated by encapsulating Pd nanoparticles within Fe, N doped carbon nanotubes, in which metallic Pd and Fe-N x serve as dual active sites. The porosity of carbon nanotube walls was tailored through a sequential process involving pyrolysis, acid leaching, and a second pyrolysis step. The resulting catalyst, Pd@FeNC7A8, exhibits smaller nanotubes with thinner carbon walls, more mesopores and greater defectivity, collectively enhancing the accessibility of the encapsulated Pd nanoparticles. Consequently, the Pd@FeNC7A8 exhibits reduced diffusion/mass-transport resistance with 33 Ω·s −1/2 of Warburg coefficient, compared with 43 Ω·s −1/2 of the control catalyst, Pd@FeNC48A, with compact carbon structure. Pd@FeNC7A8 catalyst delivers 0.904 V of half wave potential, 5.209 mA cm −2 of limited current density, and 48 mF cm −2 of electrochemical active surface area, outperforming Pd@FeNC48A in ORR performance. It also exhibits superior methanol resistance and durability compared with Pt/C. Moreover, the Pd@FeNC7A8-based the Zn-air battery demonstrates a higher discharge voltage, greater power density and specific capacity compared to its Pt/C-based counterpart, highlighting the potential of this catalyst in practical applications. Download: Download high-res image (144KB) Download: Download full-size image