Effect of various Fe/Co ratios and annealing temperatures on a Fe/Co catalyst supported with nitrogen-doped reduced graphene oxide towards the oxygen reduction reaction

• Published in: Journal of alloys and compounds Vol. 816; p. 152573
• Main Authors: Samad, Shuaiba, Loh, Kee Shyuan, Wong, Wai Yin, Sudarsono, Wulandhari, Lee, Tian Khoon, Wan Daud, Wan Ramli
• Format: Journal Article
• Language: English
• Published: Lausanne Elsevier B.V 05.03.2020; Elsevier BV
• Subjects: Annealing; Bimetallic catalyst; Bimetals; Catalyst support; Catalysts; Chemical properties; Chemical synthesis; Cobalt; Configurations; Electron microscopy; Emission analysis; FeCo/nitrogen doped reduced graphene oxide; Ferric chloride; Field emission microscopy; Graphene; High temperature; Iron chlorides; Microscopy; Morphology; Nanoparticles; Nitrogen; Organic chemistry; Oxygen reduction reaction; Oxygen reduction reactions; Precursors; Synergistic effect; Transition metals; X ray photoelectron spectroscopy; FeCo/nitrogen doped reduced graphene oxide; Bimetallic catalyst; Oxygen reduction reaction; Catalyst support
• ISSN: 0925-8388; 1873-4669; 1873-4669
• DOI: 10.1016/j.jallcom.2019.152573

A bimetallic catalyst improves the physical and chemical properties of a bimetal because of an increased synergistic effect of the two different metals compared with those of their corresponding single particles. Therefore, in this study, a bimetal consisting of iron and cobalt (FeCo) supported with nitrogen-doped reduced graphene oxide (FeCo/NG) was successfully synthesised as a potential catalyst using a thermal annealing method for the oxygen reduction reaction (ORR). Dicyandiamide was used as the N precursor. Thermal annealing was performed at a high temperature (600 °C–800 °C) using transition metal precursors of FeCl3 and Co(NO3)2.6H2O with different Fe/Co molar ratios. The morphology analysis by means of field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) showed that the average size of the FeCo nanoparticles is between 20 nm and 130 nm. With increasing annealing temperature, the size of the nanoparticles drastically grew, and they were well dispersed on the NG surface. XPS analysis revealed that the pyridinic-N configuration had the highest percentage of 62.61% compared to that of the others. This configuration acted as the active site for the enhanced ORR in an alkaline medium. The catalyst with a 1:2 molar ratio synthesised at 700 °C (1:2FeCo/NG700) exhibited the highest performance in 0.1 M KOH medium with a comparable potential of 0.74 V vs. RHE compared to those of the other catalysts. It exhibited a higher current density of 0.605 mA cm−2 compared with that of commercial Pt/C (0.75 V vs. RHE, 0.569 mA cm−2). Based on linear sweep voltammetry (LSV) analysis, the average number of electron transfers (n) of 1:2FeCo/NG700 was between 3.60 and 3.99 in the potential range of 0.0–1.0 V vs. RHE; this revealed that the 1:2FeCo/NG700 catalyst undergoes 4-electron pathways. These findings show that FeCo/NG is an active catalyst towards ORR in an alkaline medium, thereby justifying its use as a non-precious bimetallic catalyst for PEMFC application. [Display omitted] •Dicyandiamide (DCDA) as a N-precursor for bimetallic catalyst.•Effect of Fe/Co ratios and temperature on the synthesised catalyst are discussed.•FeCo-Nx moieties contributed to the enhancement of ORR performance.