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 the electrochemical oxygen reduction reaction (ORR). By introducing Co²⁺ ions into formamide, our method prevents rapid Fe²⁺ oxidation to Fe³⁺, promoting the formation of well-defined Fe₃O₄ nanoparticles rather than Fe₂O₃. 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 Fe_xCo_3−xO₄ oxide nanoparticles, potentially due to their high surface area and strong interaction with the NRGO support. This, in turn, facilitates the successful decoration of highly dispersed spinel Fe_xCo_3−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 V_RHE, 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 V_RHE 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.