Iron-Nanoparticle-Loaded Nitrogen-Doped Carbon Nanotube/Carbon Sheet Composites Derived from MOF as Electrocatalysts for an Oxygen Reduction Reaction

Exploring highly active, stable, and inexpensive electrocatalysts for the oxygen reduction reaction (ORR) is pivotal in developing high-performance energy conversion devices. Moreover, the production of catalysts containing transition metals with the appropriate nitrogen doping level is a potential approach to increase ORR catalytic efficiency, especially under acidic conditions. In this study, a hierarchical graphitic porous carbon-containing Fe and N was obtained via pyrolysis of a bimetal MOF (Fe/ZIF-8) composited with pyrrole. Further experimental and theoretical results confirmed that the synergistic effects between Fe-based nanoparticles and N-doping in the networks are likely form one of the main reasons for better ORR performance. Under optimized conditions, the resultant Fe-bNCNT/NC-900 (iron-based nanoparticles enwrapped in bamboo-like nitrogen-doped carbon nanotubes (bNCNTs) grown on N-doped sheet-like carbon) exhibits high electrocatalytic activity, high selectivity (direct 4e(-) reduction of oxygen to water), and stability in both acidic and alkaline electrolytes. Under acidic conditions, the half-wave potential (E-1/2 = 0.770 V-RHE) of Fe-bNCNT/NC-900 is comparable to commercial Pt/C (E-1/2 = 0.800 V-RHE). However, this catalyst shows better activity with a half-wave potential of 0.920 V-RHE, which is more than Pt/C (E-1/2 = 0.880 V-RHE) in an alkaline electrolyte. The E-1/2 of Fe-bNCNT/NC-900 under acidic and alkaline conditions experienced a 170 and 28 mV loss after 20 000 continuous cycles, and these results show the prepared catalyst has promising stability.