Synthesis of Fe₂O₃ Nanoparticle-Decorated N-Doped Reduced Graphene Oxide as an Effective Catalyst for Zn-Air Batteries

Abstract

The advancement of Zn-air batteries requires effective and inexpensive electrocatalysts that facilitate the oxygen reduction reaction (ORR) and evolution reaction (OER). Herein, we report an effective electrocatalyst of Fe 2 O 3 nanoparticle-decorated N-doped reduced graphene oxide (Fe 2 O 3 /N-rGO), in which porous Fe 2 O 3 nanoparticles of ∼37 nm are anchored on the N-rGO surface uniformly. In an alkaline solution, the synthesized Fe 2 O 3 /N-rGO affords superior ORR and OER activity in comparison with Fe 2 O 3 and N-rGO, demonstrating the reinforced synergistic effect. Moreover, it exhibits a comparable limiting current density and a higher current retention ratio in the ORR than commercial Pt/C. A Zn-air battery with Fe 2 O 3 /N-rGO delivers a peak power density of 80.1 mW cm −2 , and the energy density reaches 730.2 Wh kg Zn −1 . In addition, stable voltage gaps of ∼0.91 V during discharge and charge are achieved at 5 mA cm −2 , and the energy efficiency is maintained at ∼60% over 120 cycles, illustrating the remarkable stability for rechargeable Zn-air batteries.

Synthesis of Ultrasmall NiCo2O4 Nanoparticle-Decorated N-Doped Graphene Nanosheets as an Effective Catalyst for Zn–Air Batteries

“…As exhibited in Figure c, the Ni 2p spectra can be assigned to Ni 2+ (871.8 and 853.2 eV), Ni 3+ (873.4 and 855.7 eV), and two satellite peaks (879.1 and 861.4 eV). The N 1s spectra illustrated in Figure d are assigned to three peaks at 398.5, 400.1, and 401.7 eV, which correspond to the pyridinic N, pyrrolic N, and graphitic N, respectively . Compared with the content of the three N species in N-G (Figures d and S6c), NiCo 2 O 4 /N-G has more pyridinic N, revealing that more defects are generated, which is in keeping with the Raman analyses.…”

“…Hence, the existence of oxygen vacancies in the XPS analysis of NiCo 2 O 4 /N-G also supports the analysis from the Raman spectra, confirming its defect nature. The C 1s spectra exhibited in Figure f are separated into four peaks at 289.8, 286.5, 285.6, and 284.5 eV, which are assigned to the OC–O, C–O, C–N, and CC groups, respectively . The successful doping of N into the graphene skeleton is thus proved by the existence of the C–N group …”

“…The increasing energy needs and climate change resulting from the consumption of traditional fossil energy have promoted the rapid expansion of sustainable energy technologies, such as fuel cells, supercapacitors, and metal–air batteries. − Rechargeable Zn–air batteries (ZABs) with high safety, low prices, and a remarkable theoretical energy density of up to1086 Wh kg –1 have gained significant concerns. − A ZAB is a half-open system in which the positive reactant (O 2 ) is directly obtained from the surrounding air, beneficial for a high energy density. − Nevertheless, the sluggish kinetics of O 2 -involved reactions (oxygen reduction reaction, ORR, and oxygen evolution reaction, OER) in the air electrode lead to a large discharge–charge voltage gap, which greatly restricts the performance improvement of ZABs. , Although the precious metal-based electrocatalysts (e.g., Pt/C and Ir/C) demonstrate superior ORR and OER catalytic activity, the large-scale applications are restricted by scarcity and poor stability. − Consequently, alternative bifunctional electrocatalysts with superior ORR and OER activity, low prices, and excellent durability are greatly needed for the development of ZABs. − …”

Co3O4–NiCo2O4 Hybrid Nanoparticles Anchored on N-Doped Reduced Graphene Oxide Nanosheets as an Efficient Catalyst for Zn–Air Batteries

“…Moreover, Raman spectra show two conspicuous peaks near 1382 and 1585 cm –1 (see Figure b), which are the D and G bands of the material, respectively. According to related literature, the intensity ratio between D and G bands of materials reflects lattice defects in materials . The I D / I G value of Co 3 O 4 –NiCo 2 O 4 /N-RGO (1.08) is larger than those of N-RGO (1.04), NiCo 2 O 4 /N-RGO (1.00), and Co 3 O 4 /N-RGO (1.03), implying an increase in the number of defects in Co 3 O 4 –NiCo 2 O 4 /N-RGO .…”

Constructing the Triple‐Phase Boundaries of Integrated Air Electrodes for High‐Performance Zn–Air Batteries

“…[ 18 ] The fabrication of a conventional air electrode is based on the physical deposition of the catalyst material on a substance (e.g., drop casting and spray coating). [ 19–24 ] For these methods, additional auxiliary material like polymer binder, carbon black, and pore former is necessary, [ 25–27 ] which is adverse to the battery performance. First, the polymer binder with low electric conductivity will severely decrease the active surface area and volume, and cause microstructure destruction and undesirable boundaries, resulting in poor electron transfer and mass transport.…”