High active-site availability on Fe-N-C oxygen reduction electrocatalysts derived from iron(II) complexes of phenanthroline with a K2C2O4 promoter

The appropriate optimization of catalytically active sites and the number of exposed sites is extremely significant to boost the activity of carbon-based electrocatalysts towards the oxygen reduction reaction (ORR). Here, we propose a new method to design Fe-N-C catalysts with a high active-site accessibility for use in the ORR via a high-temperature calcination of Fe(II) ions coordinated with 1,10-phenanthroline dispersedly supported on a nanocarbon surface with the assistance of a K2C2O4 promoter. The optimized catalyst possesses a relatively high content of pyridinic-nitrogen ORR-active species and a homogeneous distribution of accessible nitrogen-rich active sites. As a result, compared to the commercial Pt/C catalyst, the obtained catalyst shows a similar ORR electrocatalytic activity with a half-wave potential of similar to 0.84 V (vs. RHE) and an ORR limited current density of similar to 5.8 mA cm(-2), as well as a better stability (an approximately 15-mV negative shift after an accelerated aging test) and tolerance to methanol in an O-2-saturated 0.1 mol l(-1) KOH solution. We also conclude that these active species (e.g., pyridinic-N, Fe-N and graphitic-N) may be the ORR catalytic sites for our catalysts. The improved ORR catalytic performance enables the prepared catalyst to be a promising replacement candidate for commercial Pt-based materials towards the ORR in alkaline media. (C) 2019 Elsevier B.V. All rights reserved.