Nickel disulfide nanosheet as promising cathode electrocatalyst for long-life lithium–oxygen batteries
Graphical abstract
Introduction
Rechargeable lithium–oxygen batteries (LOBs) attract significant attention for application in next-generation automobile technologies owing to their high theoretical specific energy density of 3505 W h kg−1, which is approximately 5–10 times higher than those of conventional lithium-ion batteries (LIBs) [[1], [2], [3]]. In an LOB system using an aprotic electrolyte, the electrochemical reaction between Li-ion and oxygen can be expressed as: 2Li+ + 2e− + O2 ↔ Li2O2 (E0 = 2.96 V vs. Li/Li+), during which an oxygen reduction reaction (ORR) and an oxygen evolution reaction (OER) occur upon the discharging and charging processes, respectively [1,2]. However, some critical issues such as the low energy efficiency and the short cycle life hinder their applications [4]. In particular, the sluggish kinetics of the ORR and OER lead to a high potential gap between the ORR and OER. In order to overcome this obstacle, it is necessary to use an effective electrocatalyst in an oxygen-electrode (or cathode) [5,6]. Extensive studies have been carried out to develop suitable electrocatalysts for LOBs, such as noble metals (Au, Pt, Ru) and transition-metal oxides, carbides, and nitrides [[7], [8], [9], [10], [11], [12]]. However, considering the significant drawbacks, including the high cost and the low catalytic activity and stability, it is required to develop novel electrocatalysts for LOBs.
Transition-metal sulfides (TMSs) attract interest as energy conversion and storage materials owing to their low costs, earth-abundance, and higher electron conductivities and electrochemical activities compared to those of their oxide counterparts [[13], [14], [15], [16]]. Recently, they have been reported as LOB electrodes. For example, Sennu et al. synthesized Co3S4 with a high reversibility of 95.72% during the first discharging and charging process [17]. Dou et al. and Lin et al. reported an excellent intrinsic oxygen affinity of Co9S8; nanocage- and sisal-shaped Co9S8 structures exhibited discharge capacities of 7000 and 6875 mA h g−1, respectively, at a current density of 50 mA g−1 [13,18]. Additionally, Ma et al. reported a flower-like NiS, which exhibited a full-discharge capacity of 6733 mA h g−1 at a current density of 75 mA g−1 [19]. However, although NiS2 has been reported in diverse applications such as water splitting electrocatalysts and supercapacitors [20,21], it has not been reported as an electrocatalyst for LOBs.
To the best of our knowledge, for the first time, we utilized a two-dimensional (2D) single-crystalline NiS2 nanosheets (NiS2-NSs) as an effective ORR/OER electrocatalyst for LOBs. As the number of crystal boundaries in a single-crystalline structure is smaller than that of a polycrystalline structure, the single-crystal structure promotes electron movement and exhibits an excellent catalytic activity [22,23]. In addition, the 2D morphology is suitable for large numbers of Li-ion and O2 species [24,25]. Single-crystalline NiS2-NSs were obtained through a hydrothermal reaction and a subsequent solid/gas phase reaction. The synthesized NiS2-NSs electrode exhibited effective formation and decomposition of the discharge products and excellent cycle stability. In addition, a NiS2-NSs electrode without conducting agent exhibited a good electrocatalytic performance.
Section snippets
Synthesis of a Ni(OH)2-NSs precursor
The Ni(OH)2-NSs precursor was synthesized by a simple hydrothermal method. First, Ni(OCOCH3)2·4H2O (8 mmol, 98%, Sigma-Aldrich) was completely dissolved in deionized water (100 mL) under magnetic stirring. Second, the pH of the solution was adjusted to 9.1–9.2 using an ammonia solution (28–30%). Third, the solution was transferred to a 200-mL Teflon-lined autoclave and heated at 170 °C for 12 h. After the hydrothermal reaction, the product was washed several times with deionized water and
Results and discussion
Fig. 1a shows the XRD patterns of the Ni(OH)2-NSs and NiS2-NSs. After the hydrothermal reaction, a crystalline Ni(OH)2 phase (hexagonal polymorph, JCPDS No. 14–0117) was obtained; no secondary peaks were observed (lower panel in Fig. 1a). After the thermal reaction of the Ni(OH)2-NSs precursor with the sulfur powder, the Ni(OH)2 phase was completely transformed to the NiS2 phase (cubic polymorph, JCPDS No. 11–0099); no secondary peaks were observed (upper panel in Fig. 1a). However, there were
Conclusion
In summary, we developed single-crystalline NiS2-NSs as an electrocatalyst in an oxygen-electrode for rechargeable LOBs. The single-crystalline Ni(OH)2-NSs were synthesized by the hydrothermal synthesis and then reacted with evaporated sulfur through the gas/solid phase reaction to form the single-crystalline NiS2-NSs. As an electrocatalyst in the oxygen-electrode, the NiS2-NSs exhibited excellent ORR/OER performances with a low potential gap of 1.42 V after 100 cycles. Particularly, they
Conflicts of interest
There are no conflicts to declare.
Acknowledgements
This work is supported by the National Research Foundation of Korea (NRF) Grant funded by the Ministry of Science and ICT, South Korea (2019R1A2B5B02070203) and by Creative Materials Discovery Program through the National Research Foundation of Korea (NRF) funded by Ministry of Science and ICT, South Korea (2018M3D1A1058744).
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NiS<inf>2</inf>/CdS photocatalysts with high specific surface area and excellent H<inf>2</inf> evolution performance
2024, International Journal of Hydrogen EnergySynergistic coupling of a self-defense redox mediator and anti-superoxide disproportionator in lithium-oxygen batteries for high stability
2023, Chemical Engineering JournalCitation Excerpt :In recent years, beyond searching for solid catalysts for highly efficient ORR/OER activity, a new approach is to introduce soluble redox mediators (RMs) into nonaqueous electrolytes. The use of RMs, such as lithium iodide (LiI), 2,5-di-tert-butyl-1,4-benzoquinone (DBBQ), anthraquinone (AQ), and 2,2,6,6-tetramethylpiperidin-1-yl (TEMPO), to efficiently consume the generated solvated superoxide intermediates is an excellent solution [9–16]. Moreover, Bi-CoPc as a redox mediator promotes the decomposition of discharge products at low charge potential [17].
Metal-organic frameworks-derived hollow dodecahedral carbon combined with FeN<inf>x</inf> moieties and ruthenium nanoparticles as cathode electrocatalyst for lithium oxygen batteries
2021, Journal of Colloid and Interface ScienceCitation Excerpt :However, on account of the sluggish kinetics of oxygen reduction/evolution reaction (ORR/OER), LOBs are confronted with large overpotential, inferior cycle stability and low round-trip efficiency [13–16]. Using reasonable catalyst is the most effective measure to reduce the overpotential [17–19] and improve the cycle life [20–22]. Carbon material is an excellent support material with high conductivity, light mass, controllable morphology and abundant pores [23].
Photocatalytic H<inf>2</inf> evolution integrated with selective amines oxidation promoted by NiS<inf>2</inf> decorated CdS nanosheets
2021, Journal of CatalysisCitation Excerpt :The loading of NiS2 cannot change the chemical structures of CdS nanosheets, as compared to the Cd 3d and S 2p spectra of pristine CdS. For Ni 2p spectrum (Fig. 3c), the peaks at 853.6 eV for Ni 2p3/2 and 870.9 eV for Ni 2p1/2 are assigned to Ni2+ species of NiS2; the peaks at 855.3 for Ni 2p3/2 and 872.6 eV for Ni 2p1/2 are attributed to Ni-O bands produced by surface oxidation of NiS2 in air [41,42]. There is a negative shift of 0.4 eV observed for the binding energy of Ni2+ as compared to those of pristine NiS2 nanoparticles (Fig. 3d), indicating a strong electronic interaction between NiS2 and CdS after the formation of an intimate interface [43,44].
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These authors contributed equally to this work.