Synergistic catalytic enhancement of metal-organic framework derived nanoarchitectures decorated on graphene as a high-efficiency bifunctional electrocatalyst for methanol oxidation and oxygen reduction

Abstract

Designing highly efficient, long-lasting, and cost-effective cathodic and anodic functional materials as a bifunctional electrocatalyst is essential for overcoming the bottleneck in fuel cell development. Herein, a novel two-step synthesis strategy is developed to synthesize metal-organic framework (MOF) derived nitrogen-doped carbon (NC) with improved spatial isolation and a higher loading amount of cobalt (Co) and nickel carbide (Ni3C) nanocrystal decorated on graphene (denoted as Co@NC-Ni3C/G). Benefiting from multiple active sites of high N-doping level, uniform dispersion of Co and Ni3C nanocrystals, and a large active area of graphene, the Co@NC-Ni3C/G hybrids exhibit excellent methanol oxidation reaction (MOR) and oxygen reduction reaction (ORR) efficiency in an alkaline environment. For MOR, the optimized Co@NC-Ni3C/G-350 catalyst achieved a current density of 44.8 mA cm−2 at an applied potential of 1.47 V (V vs. RHE), which is significantly higher than Co@NC-Ni3C (42.07 mA cm−2) and Co@NC (24.1 mA cm−2) in 0.5 M methanol + 1.0 M KOH solutions. In addition, during the CO retention test, the Co@NC-Ni3C/G-350 catalyst exhibits excellent CO tolerance capacity. Excitingly, the as-prepared Co@NC-Ni3C/G-350 hybrid exhibits significantly improved ORR catalytic efficiency in terms of positive onset and half-wave potential (Eonset = 0.90 V, E1/2 = 0.830 V vs. RHE), small Tafel slope (34 mV dec−1) and excellent durability (only reduced 0.016 V after 5000 s test). This work provides new insights into MOF-derived functional nanomaterials for anode and cathode co-catalysts for methanol fuel cells.