Non-precious metal on zirconium oxide/nitrogen-doped graphene nanocomposite (M/ZrO2-NG) as electrocatalyst for oxygen reduction reaction

Abstract

Nanocomposite electrocatalysts (M/ZrO2-NG; M: Fe, Co, Fe-Co) consisting of transition metals deposited on zirconium oxide/N-doped graphene were synthesized in the present study. These electrocatalysts were found to be efficient for the oxygen reduction reaction (ORR). A one-step low-temperature solvothermal method was utilized to synthesize nitrogen-doped graphene (NG), which displayed a certain level of alkaline media ORR activity. To enhance both the activity and stability of ORR, ZrO2 was hybridized with NG. Next, a hydrothermal synthesis method was employed to deposit iron and cobalt nanoparticles on ZrO2-NG. The as-prepared electrocatalysts were characterized using various physicochemical, morphological, and electrochemical analyses. FESEM, EDS mapping, HRTEM, XPS, XRD, and FTIR analyses were used to characterize the synthesized NG, ZrO2-NG, and M/ZrO2-NG electrocatalysts. The characterization results indicated that transition metal nanoparticles were homogeneously dispersed on the ZrO2-NG nanocomposite. The electrochemical analysis revealed that the Fe-Co/ZrO2-NG electrocatalyst had the optimal performance with Eonset and E1/2 of 0.872 ± 0.010 and 0.782 ± 0.006 VRHE, respectively, which was comparable to the commercial Pt/C (Eonset = 0.942 ± 0.013 and E1/2 = 0.852 ± 0.009 VRHE). Additionally, chronoamperometric results indicated that the Fe-Co/ZrO2-NG electrocatalyst exhibited better stability (92 % maintenance of its initial current density) than the commercial Pt/C. The high activity and good stability of the optimized nanocomposite electrocatalyst were attributed to the synergistic effect between the zirconium oxide nanoparticles and nitrogen-doped graphene, in addition to the presence of Fe and Co nanoparticles.