Scalable Synthesis of N–Doped Graphene–Oxide–Supported FeCo(OH)x Nanosheets for Efficient Co–Doped Fe3O4 Nanoparticle-Based Oxygen Reduction Reaction Electrocatalysis

Abstract

Developing efficient and cost-effective materials is crucial for advancing electrochemical oxygen reduction reaction (ORR). This study presents a synthesis route for high-performance spinel Fe and Co oxide nanoparticles on N-doped reduced graphene oxide (NRGO). This solvothermal synthesis in formamide yields well-dispersed, ultrafine FeCo(OH)x nanoparticles (∼5 nm) anchored on NRGO. These nanoparticles can be employed for the formation of spinel FexCo3-xO4 oxide nanoparticles, potentially because of their high surface area and intense interaction with the NRGO support. By introducing Co2+ ions into formamide, our method prevents rapid Fe2+ oxidation to Fe3+, promoting the formation of well-defined Fe3O4 nanoparticles, not Fe2O3. This, in turn, facilitates the successful decoration of highly dispersed spinel FexCo3-xO4 oxide nanoparticles (∼30 nm) onto the NRGO support, even after calcination at 900°C, which represents the critical temperature for conventional graphitization. This unique approach results in significantly reduced particle aggregation compared with that of conventional methods. The (Co)Fe3O4–NRGO nanocomposite exhibits remarkable ORR activity, achieving an electron number of ∼3.7 and a current density of 5.01 mA·cm−2 at E = 0.75 VRHE, comparable to those of commercial Pt/C catalysts. Furthermore, the catalyst exhibits remarkable stability, maintaining a reducing current density that is 42% lower after 40,000 s of uninterrupted operation at 0.75 VRHE compared with a 75% reduction observed with Pt/C. This exceptional performance is attributed to the strong interaction between the (Co)Fe3O4 nanoparticles and NRGO, facilitated by the Co ion precursor during annealing.