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

Abstract

Developing oxygen electrocatalysts with outstanding activity and low cost is vital to the promotion of the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) of Zn–air batteries. Herein, an NiCo2O4 nanoparticle-decorated nitrogen-doped graphene nanosheet (NiCo2O4/N-G) is synthesized as a bifunctional electrocatalyst. The ultrasmall NiCo2O4 nanoparticle with an average particle size of 4 nm can introduce plentiful reaction active sites. Furthermore, the N-G nanosheets with small dimensions of 200 nm possess an extremely large specific surface area and can effectively restrict the aggregation of NiCo2O4 nanoparticles and promote species transport. Compared with NiCo2O4 and N-G, NiCo2O4/N-G exhibits a higher ORR and OER electrocatalytic activity in alkaline electrolytes, and it demonstrates almost comparable ORR activity but superior stability to commercial Pt/C. Using the NiCo2O4/N-G catalyst, a home-built Zn–air battery demonstrates a peak power density of 108.3 mW cm–2, an excellent discharge capacity of up to 792.6 mAh gZn –1, and a superior energy density of up to 879.9 Wh kg. Moreover, stable charge–discharge voltage gaps and an energy efficiency of ∼63% at 10 mA cm–2 can sustain for over 540 cycles during cycling, indicating excellent cycling stability.

CoO Enhanced Oxygen Evolution Kinetics of LaMnO3 Perovskite As a Potential Cathode for Rechargeable Zn-Air Batteries

“…It has been reported that the ORR electrocatalytic activity of Co-based catalysts is closely related to the abundance of Co 2+ because the exposure of Co 2+ active sites could promote the oxygen adsorption on catalysts surface and accelerate the electron transfer process . It was obviously noted that the Co 2+ cations were the predominant active species in the LaMnO 3 –CoO composite according to the fitting XPS spectra . Therefore, we can speculate that the composite containing more Co 2+ can present a higher electrocatalytic activity.…”

“…31 It was obviously noted that the Co 2+ cations were the predominant active species in the LaMnO 3 −CoO composite according to the fitting XPS spectra. 32 Therefore, we can speculate that the composite containing more Co 2+ can present a higher electrocatalytic activity. In Figure 2d, three oxygen counterparts were located at 529.5, 531.3, and 533.3 eV, which were attributed to the lattice oxygen (O latt ), surface absorbed oxygen (O ads ), and oxygen-containing groups (O w ), respectively.…”

Hyper-Crosslinked Polymer-Derived Nitrogen-Doped Hierarchical Porous Carbon as Metal-Free Electrocatalysts for High-Efficiency Oxygen Reduction

“…Py-NHCP-1000 displays a stable potential platform of 1.49 V, and it is close to Pt/C (1.50 V). In addition, the peak power density of Py-NHCP-1000 is up to 165 mW cm –2 according to the polarization plots revealed in Figure c, which considerably precedes that of the Pt/C catalyst (127 mW cm –2 ) as well as those of most of the non-noble metal catalysts reported recently, − signifying its possible application potential for energy conversion. From the galvanostatic discharge curves shown in Figure d, an ignorable voltage drop is observed after 36 h, which reveals a high stability of ZAB with the Py-NHCP-1000 catalyst.…”

Assessment of the Feasibility of Zn–Air Batteries with Alkaline Electrolytes Working at Sub-Zero Temperatures

“…These data are fit to a line, the slope of which is the geometric C dl . The oxygen reduction reaction (ORR) activity at different temperatures was tested using the linear sweep voltammetry method . 4 mg of commercial Pt/C, 2 mg of XC-72 carbon, and 20 μL of Nafion solution (5 wt %) were dispersed into 380 μL of isopropanol and then sonicated for 30 min to form a homogeneous ink.…”

“…The oxygen reduction reaction (ORR) activity at different temperatures was tested using the linear sweep voltammetry method. 31…”