Direct synthesis of a carbon nanotube interpenetrated doped porous carbon alloy as a durable Pt-free electrocatalyst for the oxygen reduction reaction in an alkaline medium

Abstract

Direct synthesis of highly durable carbon nanotube interpenetrated porous carbon alloy electrocatalysts for the oxygen reduction reaction (ORR) from a single precursor, trimetallic zeolitic imidazole framework (t-ZIF), is reported. The use of a single precursor improves the uniform distribution of active reaction centres which is crucial for ORR catalysts. The t-ZIF has Fe, Co and Zn metal centres and 2-methylimidazole as a ligand. Carbonisation of the t-ZIF under an inert atmosphere produces nitrogen and Fe/Co–N_x doped carbon/carbon nanotubes alloyed with metal/metal oxide particles encased inside the carbon structures (FeCo-NCZ). The presence of Zn in the t-ZIF induces porosity in carbon during the carbonisation process. The peculiar morphology with a reasonably high surface area provides efficient mass transport and interpenetrated carbon nanotube assisted fast electron transport in the catalyst. X-ray photoelectron spectroscopy reveals that FeCo-NCZ is enriched with different possible active reaction centres such as pyridinic, graphitic and Fe/Co–N_x type nitrogen coordination on the catalyst surface. The ORR activity of FeCo-NCZ in oxygen saturated 0.1 M KOH was comparable to/higher than that of the reference Pt/C catalyst. The displayed onset potential (1.04 V vs. the RHE) and half-wave potential (0.91 V vs. the RHE) of FeCo-NCZ are more positive compared to those of Pt/C and other control-samples. It is noteworthy that the dioxygen reduction kinetics of FeCo-NCZ are comparable to those of Pt/C as evident from the Tafel slope and oxygen reduction follows a four electron pathway. More interestingly, FeCo-NCZ shows better fuel tolerance and electrochemical stability even at 60 °C compared to Pt/C under alkaline conditions.