Production of N‐doped Reduced Graphene Oxide/Fe₃O₄ Hybrids and Effect of Order of Production Steps on Electrocatalytic Performances for Oxygen Reduction Reaction

Abstract

Oxygen reduction reactions (ORRs) occur at cathodes in fuel cells and require efficient electrocatalysts. Because of the cost and limited durability and stability of commercial Pt/C catalysts, the development of efficient Pt‐free electrocatalysts is an active research topic. Here, we describe the solution‐based production of Fe3O4 nanoparticles/N‐doped graphene‐based materials from FeCl2, graphene oxide (G−O), and hydrazine. Orders of production steps were varied by; i) reacting FeCl2 and G−O first and then adding hydrazine (Fe/G−N), ii) reacting G−O, FeCl2, and hydrazine at the same time (Fe/G/N), or iii) reacting G−O and hydrazine first and then adding FeCl2 (G/N−Fe). The hybrids produced showed better ORR electrocatalytic activity in alkaline media than single components such as N‐doped graphene‐based materials or Fe3O4. Furthermore, the electrocatalytic properties of the resulting hybrids were found to depend on orders of addition. Fe/G/N was found to be the best electrocatalyst and had better onset and half‐wave potentials, thermodynamic current density, and 4‐electron selectivity. All three hybrids show good cyclic durability and methanol tolerance.

Co(O)4(N)‐type single‐atom‐based catalysts and ligand‐driven modulation of electrocatalytic properties for reducing oxygen molecules

“…SEM measurements reveal that the NrGO, Co‐NrGO‐1, and Co‐NrGO‐2 samples consist of crumpled thin materials (Figure 1B,C), typical for reduced graphene oxide materials 25–29 . The TEM images show that the samples contain thin graphene‐based layers (Figure 1D,E).…”

“…24 SEM measurements reveal that the NrGO, Co-NrGO-1, and Co-NrGO-2 samples consist of crumpled thin materials (Figure 1B,C), typical for reduced graphene oxide materials. [25][26][27][28][29] The TEM images show that the samples contain thin graphene-based layers (Figure 1D, E). Because Co-containing nanoparticles can be generated during wet processes, many SEM and TEM measurements were conducted at different locations in the same sample and different batches (Figure S4).…”