Co-, Ni-Catalyzed Borylation of Carbon Nanofibers for Oxygen Reduction Reaction in an Anion Exchange Membrane Fuel Cell

In an attempt to develop nonprecious metal electrocatalyst, herein, we report borylation of graphitic carbon nanofiber (GNF) and codoping of Co, Ni toward a oxygen reduction reaction (ORR) catalyst and their application in anion exchange membrane fuel cells (AEMFCs). Boron (B) doping in a carbon matrix creates a C–B bond with lower bond energy to facilitate insertion of metal atoms in the carbon matrix beneficial for ORR activity. Ni and Co doping individually and in combination with the B/GNF increases positive charge clouds surrounding metal centers and facilitates O2 adsorption and catalytic activity. The DFT studies on the catalysts are extensively carried out to measure the band gaps, atomic compositions of frontier molecular orbitals, and charge clouds distribution on the catalysts and correlated with the electrochemical findings. Further, Ni and Co doping creates positive charge cloud, facilitating O2 adsorption through lowering the band gap. Synergistic effect of Ni and Co in the catalyst (Ni20Co20@B/GNF-H) toward ORR activity is clearly established and later demonstrated in an anion exchange membrane fuel cells (AEMFCs) as a potential cathode catalyst. Ni20Co20@B/GNF-H showed an eminent ORR activity, competent CH3OH tolerance in alkaline medium without much decrease in ORR activity even after 10,000 potential cycles. Assessing the fuel cell performance evaluation in AEMFC, Ni20Co20@B/GNF-H catalyst, delivers a peak power density of ∼70 mW cm–2 at a load current density of ∼138 mA cm–2 under ambient pressure and temperature. This nonprecious boron-functionalized GNF-H catalyst opens an era toward the development of a low cost, highly efficient metal based cathodic ORR electrocatalyst for AEMFC applications.