Hybrid Nanostructures of Bimetallic NiCo Nitride/N-Doped Reduced Graphene Oxide as Efficient Bifunctional Electrocatalysts for Rechargeable Zn–Air Batteries

Abstract

A nonprecious electrocatalyst with high efficiency in both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is extremely crucial for the development of high-performing metal–air batteries. In this work, a nonprecious-metal bifunctional catalyst of ultrafine and uniform Ni2.25Co0.75N nanoparticles anchoring on N-doped reduced graphene oxide (denoted as Ni2.25Co0.75N/NrGO) was prepared by the thermal ammonolysis of the corresponding hydroxide/graphene oxide precursor. As a result of the intimate combination of redox-active metal nitrides and electroconductive N-doped reduced graphene oxide (NrGO), the Ni2.25Co0.75N/NrGO hybrid not only exhibited high OER activity but also showed outstanding ORR kinetics and durability, comparable to commercial RuO2 and Pt/C electrocatalysts, respectively. Furthermore, Zn–air batteries assembled by using the as-prepared Ni2.25Co0.75N/NrGO hybrid electrocatalysts yielded a high power density and gravimetric energy density of 193 mW cm–2 and 864 W h kg–1, respectively, characteristic with a low charge/discharge voltage gap of 0.72 V and excellent cyclability up to 166 h at 10 mA cm–2 in an aqueous system. More importantly, the ORR experiment and X-ray photoelectron spectroscopy coupled with density functional theory calculations verified that the electronic transfer from bimetallic NiCo nitride to NrGO may enhance the ability in forming O2 adsorption and *OOH on NrGO, which is the possible origination of the ORR high activity.

Rational Design and Synthesis of Hierarchical Porous Mn–N–C Nanoparticles with Atomically Dispersed MnNx Moieties for Highly Efficient Oxygen Reduction Reaction

“…Transition-metal-coordinated nitrogen–carbon materials (M–N–C) have been extensively studied and developed rapidly due to their promising catalytic performance. − Meanwhile, tremendous efforts have been made to reveal specific catalytic active sites and catalytic mechanism for the ORR in M–N–C catalysts. The active sites proposed mainly include: MN x C y moieties, metal carbides, metal nitrides, etc. , The most active sites have been identified as MN x C y moieties, which can readily activate O 2 and subsequently break the O–O bond with a lower energy barrier than on other metal-free active sites, therefore significantly improving the ORR catalytic activity. − Actually, the nature of the transition metal in M–N–C also affects the bonding energies of O 2 and other ORR intermediates on MN x C y sites, resulting in significantly different activity and durability.…”

Strongly Coupled MnO2 Nanosheets/Silver Nanoparticles Hierarchical Spheres for Efficient Oxygen Reduction Reaction Electrocatalysis

“…), and v is the kinematic viscosity of the electrolyte (v = 0.01 cm 2 s −1 in 0.1 M KOH solution). 28 In order to study the H 2 O 2 yield of materials in the catalytic ORR process, a rotating ring disk electrode (RRDE) was also conducted in 0.1 M KOH saturated with O 2 . The H 2 O 2 yield and n were calculated by eqs 3 and 4.…”

“… where j is the measured current density, j K is the kinetic limiting current density, j L is the diffusion-limited current density, and ω is the electrode rotation rate. F is the Faraday constant (96 485 C/mol), C 0 is the bulk concentration of O 2 in 0.1 M KOH solution (1.26 × 10 –6 mol cm –3 ), D 0 is the diffusion coefficient of O 2 in 0.1 M KOH solution (1.93 × 10 –5 cm 2 s –1 ), and v is the kinematic viscosity of the electrolyte ( v = 0.01 cm 2 s –1 in 0.1 M KOH solution) …”

Oxygen Reduction Reaction Promoted by the Strong Coupling of MoS2 and SnS

“…The H 2 O 2 yield and n for ORR were further evaluated by conducting the rotating ring-disk electrode (RRDE, the diameter is 5.6 mm) test and were calculated according to the formulas and . − where I d is the disc current, I r is the ring current, and N is the collection efficiency (0.37), respectively.…”