Elsevier

Journal of Energy Chemistry

Volume 66, March 2022, Pages 348-355
Journal of Energy Chemistry

In-situ growth of CoNi bimetal anchored on carbon nanoparticle/nanotube hybrid for boosting rechargeable Zn-air battery

https://doi.org/10.1016/j.jechem.2021.08.007Get rights and content

Abstract

Exploring highly efficient non-precious metal based catalysts for bifunctional oxygen electrode is crucial for rechargeable metal-air batteries. In this study, with MOFs as precursors, a facile coprecipitation method is designed to realize in-situ growth of the CoNi anchored carbon nanoparticle/nanotube (CoNi/N-CNN) hybrid, which can achieve the simultaneous maximum exposure of both oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) active centers. Benefiting from the unique structure, the CoNi/N-CNN catalyst exhibits excellent electrocatalytic performance for ORR (Eonset = 1.183 V, E1/2 = 0.819 V) and a low operating voltage of 1.718 V at 10 mA cm−2 (Ej=10) for OER. Delightfully, the home-made rechargeable Zn-air battery with CoNi/N-CNN delivers a high discharge power density up to 209 mW cm−2, and an outstanding charge–discharge cycling stability. The boosted bifunctional electrocatalytic activity can be ascribed to the strong coupling effect between Co/Ni center sites and defect-rich N-anchored carbon featured with porous and nanotube structure, which can introduce uniformly dispersed active sites, tailored electronic configuration, superb conductivity and convenient charge transfer process. The hybrid non-precious bimetal based electrocatalyst provides the possibility to develop the low-cost and high-efficient ORR/OER bifunctional electrocatalysts in rechargeable metal-air battery.

Graphical abstract

Bimetal based electrocatalyst derived from trimetallic precursor can provide desirable ORR/OER activities owing to the superb micro/mesoporosity framework, abundant CoNi alloy and highly conductive carbon nanoparticle/nanotube (CoNi/N-CNN) hybrid.

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Introduction

The development of low-price and high-efficient energy conversion techniques has spurred wide research attention due to the increasing demands for environmental-friendly and advanced renewable energy [1], [2], [3]. Among them, rechargeable Zn-air battery has been regarded as one of the most promising candidates to meet next-generation energy storage and conversion equipment with a high theoretical energy density of 1084 Wh kg−1, high safety and cost effective [4], [5], [6]. Since the 4e reaction on oxygen electrode surface needs high energy of 498 kJ mol−1, the sluggish kinetics of oxygen reduction reaction (ORR) during discharging process and high over potential of oxygen evolution reaction (OER) during charging process extremely hinder the overall energy conversion efficiency [7], [8], [9]. Precious materials, such as Pt/C, Ir/C, IrO2, and RuO2, have been regarded as the best catalysts for ORR/OER. However, the rarity, high cost and unsatisfactory stability greatly limit their industrial application [10], [11], [12]. Therefore, it is particularly important to develop non-precious metal based bifunctional oxygen electrode catalysts with highly-efficient and low-cost [13], [14].

To this end, a combination of highly conductive nitrogen co-coped carbon with non-precious metals has manifested colossal potentials in accelerating ORR and OER due to the synergistic effects between carbon and non-precious metal elements [15], [16], [17]. It has been shown that the bifunctionality of metal@N-doped carbon materials can be ascribed to exuberant diversity of the active species including M−Nx synergistic structure, as well as special N-doped collocation (N–C) [18], [19], [20], [21], [22]. However, the conventional synthetic strategies face great challenges in the regulations of composition and structure of the metal@N-doped carbon, including the aggregation of the metal and non-uniform distributed active centers. Metal-organic frameworks (MOFs) featuring of connected metal nodes/clusters with organic linkers have been considered as potential precursors to synthesize the metal@N-doped carbon based catalysts with adjustable pore size and uniform metal active sites [23], [24]. Unfortunately, the bifunctional catalytic activity of the metal@N-doped carbon catalysts consisting of single metal sites still needs to be further improved [25]. It has been reported that ZIF-67–900 and Co@Co3O4@C–CM possess high ORR activity, but cannot afford excellent OER activity [26], [27]. To further enhance the catalytic performance of oxygen cathode, bimetal@N-doped carbon based catalysts have aroused great concern due to the enriched metal active sites and tailored electronic configuration [24], [28], [29], [30]. Up to now, various kinds of bimetallic@N-doped carbon materials including FeMn, FeCo, CoMg, CoMn, ZnCo and CuCo have been developed for ORR and OER [5], [31]. However, controllable constructing robust bimetallic@N-doped carbon with uniformly dispersed metal active sites as bifunctional ORR/OER catalyst is still a big challenge [32].

Owing to a strong electron coupling effect, CoNi alloy can provide rich valence state changes, and specifically intrigues the surface properties alternation and the intrinsic polarity shift in the process of oxygen reactions [30], [33]. Triggered by this, exploring Co anchors with another transition metal, for example, Ni maybe a potential strategy to boost the catalytic activity for both of ORR and OER, attributing to that Ni holds first-rate OER performance [34], [35]. In this study, we report the sea anemone-like CoNi bimetal anchored on carbon nanoparticle/nanotube (CoNi/N-CNN) hybrid by adjusting the metal precursor to prepare robust and high-efficient bifunctional oxygen electrocatalysts applied in rechargeable Zn-air battery. The as-obtained CoNi/N-CNN exhibits a positive half-wave potential of ORR (0.819 V) and a low overpotential of OER (488 mV at 10 mA cm−2), as well as a high peak power density of 209 mW cm−2 when it displayed in the rechargeable Zn-air battery as well. The boosting bifunctional electrocatalytic activity can be ascribed to the synergetic effect between CoNi center sites and defect-rich N-anchored carbon. Meanwhile, the carbon layer and carbon nanotubes can improve electrical conductivity. Furthermore, the micro/mesoporosity framework derived from the porous characteristics of the MOFs precursor and the evaporation of Zn ions during the pyrolysis process is convenient for mass transfer. The hybrid non-precious bimetal based electrocatalyst derived from trimetallic precursor may provide the possibility to develop and construct the low-cost and high-efficient bifunctional oxygen electrocatalysts [36], [37].

Section snippets

Synthesis process of the CoNi/N-CNN, CoNi/N-CNN-x, Co/N-CNN and Ni/N-CNN

In a typical preparation method, 0.59 g Zn(NO3)2 6H2O, 0.24 g Co(NO3)2 6H2O and 0.24 g Ni(NO3)2 6H2O were dissolved in 8 g deionized water, and 22.7 g 2-methylimidazole was dissolved in 80 g deionized water. Then, the two new solutions were mixed under stirring condition. The precursor solution was continually stirred for 6 h at 22 ± 2 °C to form uniformly dispersed solution. After centrifugation and washing with deionized water and ethanol for several times, the Co/Ni-ZIF was obtained after

Synthesis and structural characterization

The synthesis procedure for the bimetallic MOF derived CoNi/N-CNN is schematically shown in Fig. 1(a). The CoNi/N-CNN catalyst is synthesized by a simple coprecipitation method following with a calcination process. The morphological and structural properties of the as-prepared electrocatalyst are investigated by SEM, HRSEM, TEM and HRTEM measurements. Fig. 1(b) gives the typical SEM image of the special architecture of the CoNi/N-CNN featuring sea anemone-like structure. To better understand

Conclusion

In conclusion, through a facile and efficient coprecipitation process, in-situ growth of the CoNi anchored micro/mesoporous carbon nano frameworks (CoNi/N-CNN) featuring of sea anemone-like structure is successfully realized by direct pyrolysis of MOF precursor. The as-prepared CoNi/N-CNN exhibits excellent catalytic activity for the ORR and OER processes, as well as stability, superior to those of commercial Pt/C-RuO2 electrocatalyst. The home-made Zn-air battery with CoNi/N-CNN as cathodic

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgments

This work was financially supported by the “Scientific and Technical Innovation Action Plan” Hong Kong, Macao and Taiwan Science & Technology Cooperation Project of Shanghai Science and Technology Committee (19160760600) and the National Natural Science Foundation of China (21972017).

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