Beads-on-string hierarchical structured electrocatalysts for efficient oxygen reduction reaction

Abstract

Rational design of hierarchically structured electrocatalysts is particularly important for electrocatalytic oxygen reduction reaction (ORR). Here, ZIF-67 crystals are stringed on core–shell Ag@C nanocables using a coordination-modulated process. Upon pyrolysis, Ag@C strings of Co nanoparticles embedded with three-dimensional porous carbon with beads-on-string hierarchical structures are developed. Due to the advantages of the rich electrochemical active sites of Co-based “beads” and the efficient electron transfer pathways via Ag@C “strings,” the resultant NH3–Ag@C@Co–N–C-700 catalyst shows an improved electrocatalytic activity toward ORR. NH3–Ag@C@Co–N–C-700 shows a high onset potential of 0.99 V versus RHE, a high half-wave potential of 0.88 V versus RHE, and a large limiting current of 5.8 mA cm−2, which are better than those of commercial Pt/C electrocatalysts. Additionally, the NH3–Ag@C@Co–N–C-700 catalyst shows high stability and preeminent methanol tolerance, which makes NH3–Ag@C@Co–N–C-700 a promising catalyst for oxygen electrocatalysis in fuel cell applications.