Elucidating Synergistic Effects of Different Metal Ratios in Bimetallic Fe/Co-N-C Catalysts for Oxygen Reduction Reaction

Abstract

Lowering or eliminating the noble-metal content in oxygen reduction fuel cell catalysts could propel the large-scale introduction of commercial fuel cell systems. Several noble-metal free catalysts are already under investigation with the metal-nitrogen-carbon (Me-N-C) system being one of the most promising. In this study, a systematic approach to investigate the influence of metal ratios in bimetallic Me-N-C fuel cells oxygen reduction reaction (ORR) catalysts has been taken. Different catalysts with varying ratios of Fe and Co have been synthesized and characterized both physically and electrochemically in terms of activity, selectivity and stability with the addition of an accelerated stress test (AST). The catalysts show different electrochemical properties depending on the metal ratio such as a high electrochemical mass activity with increasing Fe ratio. Properties do not change linearly with the metal ratio, with a Fe/Co ratio of 5:3 showing a higher mass activity with simultaneous higher stability. Selectivity indicators plateau for catalysts with a Co content of 50% metal ratio and less, showing the same values as a monometallic Co catalyst. These findings indicate a deeper relationship between the ratio of different metals and physical and electrochemical properties in bimetallic Me-N-C catalysts.

Iron, Cobalt, and Nickel Phthalocyanine Tri-Doped Electrospun Carbon Nanofibre-Based Catalyst for Rechargeable Zinc–Air Battery Air Electrode

“…The FeCoNi-CNF-materials coated electrodes exhibited higher oxygen reduction current density in the studied potential range compared to two TM Pc functionalized catalysts. The benefit of combining Fe-Nx and Co-Nx sites in the nanocarbon catalyst is generally recognised to be advantageous for achieving higher ORR activity compared to single TM-Nx-containing materials [ 15 , 17 , 75 ]. Moreover, in a study by Sonkar et al, the functionalization of reduced graphene oxide catalyst with NiPc provided enhanced oxygen reduction performance and a 4e − ORR pathway [ 52 ].…”

“…Furthermore, this technique enables versatile introduction of different transition metals (TMs) and their compounds into CNFs, which have been confirmed to provide the active sites for ORR (e.g., TM-Nx) and OER (e.g., TM oxides) [ 8 , 9 , 13 , 14 ]. Despite the problems with uniform distribution of several TMs at once in one nanocarbon catalyst, multiple TM-containing materials have been proposed to be more efficient non-PGM bifunctional oxygen catalysts than single TM-based ones [ 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 ]. In addition to dual TM-embedded CNF catalysts employed for RZAB air electrode application [ 23 , 24 , 25 ], triple TM combination with various nanocarbon supports have been also investigated [ 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 ].…”

Metal Particle Detection Methods and Their Use for Freeze-Dried Vaccine Inspection: A Review

“…In XPS, X-rays are sent through the sample and eject electrons from its atoms, yielding chemical information. However, only electrons from a depth of a few nanometers can be detected [342], and the method can only be applied in solids or powders and requires high vacuum [341], [342]. In electron microscopes, beams of accelerated electrons are sent to the sample, and the scattered and transmitted electrons are detected.…”

Recent Advances on PEM Fuel Cells: From Key Materials to Membrane Electrode Assembly

“…By tuning the content of doped Fe into zeolitic imidazolate framework (ZIF)-8 precursors, exclusively atomically dispersed FeN 4 sites have been achieved, which present a significantly improved active site density and half-wave potential (E 1/2 ) of (0.88 ± 0.01) V vs. RHE [52]. Recently, dual single-atom catalysts were proposed to achieve better ORR intrinsic activity, e.g., Fe/ Co-N-C [53,54].…”