Sulphur–carbon composites for Li/S batteries

Abstract

Structural and electrochemical properties of various types of sulphur–carbon composites were reviewed to propose approaching ways for the development of lithium/sulphur battery with high energy density and good cycle performance. To improve the electrochemical properties of a sulphur cathode, carbon and polymer materials are applied to sulphur composites: multiwalled nanotube (MWNT), graphene, CMK-3 and activated carbon; and polyaniline (PANi), polyacrylonitrile and polythiophene (PTh). These can serve conducting paths and a polysulphide reservoir to enhance the electrical conductivity of the sulphur cathode and effectively prevent dissolution of polysulphides. And the composites are categorised in two parts such as mixed type sulphur composites and embedded type sulphur composites. Among the sulphur–carbon composites, the hollow carbon capsule/S composite prepared by a geometric control and an infusion method of sulphur in sulphur carbon composite electrode, demonstrated the best electrochemical properties.     

Electrodeposited Ni–Co–S nanosheets on nickel foam as bioelectrochemical cathodes for efficient H2 evolution

High overpotential and soaring prices of the cathode electrode are the bottlenecks for the development of microbial electrolysis technology for hydrogen production. In this study, a novel one-step electrodeposition method has been attempted to fabricate electrodeposited cathodes in situ growth of Ni–Co–S, Ni–S, Co–S catalyst on nickel foam (NF) to reduce the overpotential of electrodes. Finally, a uniform nanosheet with a high specific surface area and more active sites is formed on the NF surface, resulting in a lower overpotential than plain NF. At 0.8 V, the Co–S/NF cathode produces a favorable 42% increase in hydrogen yield (0.68 m³·m⁻³·d⁻¹), 40% upsurge in current density (10.6 mA/cm³) and 39% rise of cathodic recovery rate (58.0 ± 3.2%) than bare NF, followed by Ni–Co–S/NF and Ni–S/NF cathode. All the electrodeposited electrodes demonstrate enhanced current density and reduced electron losses, thereby achieving efficient hydrogen production. These innovative varieties of electrodes are highly advantageous as they are relatively inexpensive and easy to manufacture with great potential in reducing costs and further real time application in large scale.     

Vermicular Ni3S2–Ni(OH)2 heterostructure supported on nickel foam as efficient electrocatalyst for hydrogen evolution reaction in alkaline solution

Alkaline solution is considered to be more suitable for industrial application of hydrogen production by water electrolysis. However, most of the low-cost electrocatalyts such as Ni₃S₂ has poor ability to dissociate HO–H, resulting in unsatisfied hydrogen evolution performance in alkaline media. In this paper, a novel vermicular structure of Ni₃S₂–Ni(OH)₂ hybrid have been successfully prepared on nickel foam substrate (v-Ni₃S₂–Ni(OH)₂/NF) through a facile two-step containing hydrothermal and electrodeposition processes. The heterostructure consists of rod-like Ni₃S₂ and Ni(OH)₂ nanosheets, in which Ni(OH)₂ is coated on the surface of Ni₃S₂. This structure not only constructs a fast electron transfer channel but also possesses rich heterointerface, thus accelerating the Volmer step and allowing more active sites of Ni₃S₂ to functioning well. As a result, v-Ni₃S₂–Ni(OH)₂/NF exhibited excellent electrocatalytic activity toward HER in 1.0 M KOH solution. It only needs 78 mV and 137 mV to drive current density of 10 mA cm⁻² and 100 mA cm⁻². Moreover, the catalytic stability of this electrocatalyst in alkaline solution is also satisfactory.     

Direct synthesis of binder-free Ni–Fe–S on Ni foam as superior electrocatalysts for hydrogen evolution reaction

Designing the efficient, low-cost and stable electrocatalyst is of great significance for storage and conversion of the renewable energy to hydrogen. Herein, the binder-free Ni–Fe–S electrocatalysts were directly electrodeposited on Ni foam, which exhibited the excellent hydrogen evolution reaction performance with the overpotential of 51.4 mV at the current density of 10 mA cm^?2. Based on the analysis and results of as-synthesized Ni, Ni–Fe and Ni–S, the boosted electrocatalytic activity can be attributed to the composite effect between Ni and the introduced Fe and S. Additionally, the Ni–Fe–S electrocatalysts also displayed the low cell voltage (1.59 V at 10 mA cm^?2), remarkable durability and high Faraday efficiency in overall water electrocatalysis. Moreover, the water electrolysis device with Ni–Fe–S bi-electrodes can be driven by a small wind power generation and producing 4 mL H₂ in 39 min, indicating the prepared Ni–Fe–S electrocatalyst has the great potentials in producing hydrogen via renewable energy.     

Graphite–FeSi alloy composites as anode materials for rechargeable lithium batteries

Iron–silicon are prepared by annealing elemental mixtures at 1000 °C followed by mechanical milling. Graphite–Fe₂₀Si₈₀ alloy composites have been prepared by ball-milling a mixture of Fe₂₀Si₈₀ alloy and graphite powder. The microstructure and electrochemical performance of the composites are characterized by X-ray diffraction and an electrochemical method. The FeSi₂ matrix is stable for extended cycles and acts as a buffer for the active centre, Si. The Fe₂₀Si₈₀ alloy electrode delivers large initial capacity, but the capacity degrades rapidly with cycling. Fe₂₀Si₈₀ alloy–graphite composite electrodes, however, show good cycleability and a high reversible capacity of about 600 mAh g⁻¹. These composites appear to be promising candidates for negative electrodes in lithium rechargeable batteries.     

Synthesis and characterization of high-density non-spherical Ni(OH)2 cathode material for Ni–MH batteries

Positive electrode active materials of non-spherical nickel hydroxide powders with a high tap-density for alkaline Ni–MH batteries have been successfully synthesized using a polyacrylamide (PAM) assisted two-step drying method. The tap-density of the powders reaches 2.32 g cm⁻³, which is significantly higher than that of nickel hydroxide powders obtained by the conventional co-precipitation method. X-ray diffraction (XRD), infrared spectroscopy (IR), scanning electron microscopy (SEM), thermogravimetric/differential thermal analysis (TG-DTA), Brunauer–Emmett–Teller (BET) testing, laser particle size analysis, tap-density testing, cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and a charge–discharge test were used to characterize the physical and electrochemical properties of the synthesized material. The results show that the as-prepared nickel hydroxide materials have an irregular tabular shape, a high density of structural disorder, and a high specific surface area. The charge–discharge tests indicate that nickel hydroxide powders synthesized by the new method have better electrochemical performance than those obtained by the conventional co-precipitation method. This performance improvement could be attributable to a more compact electrode microstructure, a lower amount of intercalated anions, better reaction reversibility, a higher proton diffusion coefficient, and lower electrochemical impedance, as indicated by TG-DTA, CV, and EIS. The results clearly show that better electrochemical activity can be achieved using nickel hydroxide that has a higher tap-density. Moreover, the new synthesis process is simple, cost-effective, and facile for large-scale production.     

Novel MoSe2–Ni(OH)2 nanocomposite as an electrocatalyst for high efficient hydrogen evolution reaction

Nowadays, there is a great demand for low-cost and highly active electrocatalyst for the production of clean renewable energy. However, most of the electrocatalysts are noble metal-based which are very costly and unstable. To counter this, electrochemical water splitting in energy storage systems is been widely applied, using non-noble metal-based nanostructured electrocatalysts. In this work, a novel noble metal-free MoSe₂–Ni(OH)₂ nanocomposite electrocatalyst is synthesized using a multi-step hydrothermal technique for efficient hydrogen evolution reaction (HER). The morphology, structural, chemical composition, and functional features of the synthesized nanomaterials were characterized using different techniques that include scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction analysis (XRD), X-ray photoelectron spectroscopy (XPS), and Raman analysis. The new developed MoSe₂–Ni(OH)₂ nanocomposite combines a high active surface area with a high chemical stability, generating a novel material with a synergistic effect that enhances water splitting process performance. Thus, an outstanding low Tafel slope of 54 mV dec⁻¹ is accomplished in the hydrogen evolution reaction.     

Graphene/Ni–Fe layered double hydroxide nano composites as advanced electrode materials for glucose electro oxidation

NickelIron Layered Double Hydroxide nano composites were electrochemically synthesized on graphene/glassy carbon electrode at a constant potential. The surface morphology and the structure of the electrodes were characterized by scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), elemental mapping analysis, X-ray diffraction (XRD) and Atomic force microscopy (AFM). This electrode was studied for glucose electro-oxidation reaction using cyclic voltammetry, chronoamperometry and electrochemical impedance spectroscopy (EIS) techniques. Results confirmed high catalytic activity, stability of the graphene/NiFe LDH electrode and glucose electro oxidation reaction on this electrode is under the effect of diffusion process. Also in comparison of some previous reported methods for the glucose electro oxidation, graphene/NiFe LDH shows a high diffusion coefficient as an electro catalyst for glucose electro oxidation. Electrical equivalent circuits for electrodes is obtained by using the Zview software. The low electrochemical charge transfer resistance (R_ct) was obtained on the graphene/NiFe LDH due to the presence of NiFe LDH nano composite.     

Structural optimization of graphite for high-performance fluorinated ethylene–propylene composites as bipolar plates

This paper presents a novel method of structural optimization by using graphite particles ranging in size from 35 to 500 μm to fabricate conductive fluorinated ethylene–propylene composites for high-temperature bipolar plates. To investigate the effects of dispersion and packing density, the large graphite particles were decorated with fluorinated ethylene–propylene powders by ball milling, and the master batch of well-dispersed small graphite particles and polymer master batch was mixed with large graphite particles. The resulting fluorinated ethylene–propylene/graphite composite bipolar plates, which contained 65 wt% graphite, exhibited high electrical conductivity of 550 S cm^?1. In particular, by modulating the electrical transportation paths between the large graphite particles with the well-dispersed fluorinated ethylene–propylene/graphite master batch, the orientation and dispersion of the graphite particles in the matrix resulted in enhanced electrical conductivity and mechanical properties. The preparation of structurally optimized fluorinated ethylene–propylene/graphite composite bipolar plates with well-dispersed graphite particles of different sizes provides a robust and scalable strategy for realizing high-performance and large-area bipolar plates.     

Effect of nickel hydroxide composition on the electrochemical performance of spherical Ni(OH)2 positive materials for Ni–MH batteries

A special method “conduit synthesis technology” has been utilized to produce spherical nickel hydroxide powders with different chemical compositions. Three kinds of powers A, B, C were prepared by chemically coprecipitating Ni, Co, Zn, Ca, Mg and Cu. It was found that powder B produced better performance than the others. The discharge capacities of powder B could achieve 280 mAh g⁻¹ for both 1C and 2C rates at 65 °C, respectively. The cyclic voltammetry analysis showed that the difference between the oxidation potential and the oxygen evolution potential of powder B is 122 mV. It indicated that Co could improve conductivity of electrons, restrict the oxygen evolution reaction and thus promote the high rate charge/discharge and high-temperature performance. Ca and Mg might effectively enhance the oxygen evolution potential in the charge process. Furthermore, the proper addition of Zn, Ca and Cu could lower the ionization energy and elevated the transition energy, and thus the transfer of electrons in electrode materials was accelerated and the electrochemical performance of nickel hydroxide electrode was improved. It was a promising way to improve the electrochemical performance of spherical nickel hydroxide for Ni–MH batteries.     

Potentiostatic electrodeposited of Ni–Fe–Sn on Ni foam served as an excellent electrocatalyst for hydrogen evolution reaction

Ni–Fe–Sn electrocatalyst supported on nickel foam (Ni–Fe–Sn/NF) with high efficiency of hydrogen evolution reaction (HER) has been successfully fabricated through one-step potentiostatic electrodeposition route. The optimized Ni–Fe–Sn/NF displayed an extremely low overpotential of, respectively, 144 and 180 mV at 50 and 100 mA cm^?2 for HER in alkaline condition. Moreover, it could retain its superior stability for at least 12 h. The remarkable electrocatalytic activity of our electrocatalyst is ascribed to the high conductivity originated from synergistic effects between Ni, Fe, and Sn during HER process.     

Sprouts-like Fe(OH)2 hetero-nanostructures assembly on selenium layered nickel foam (NiF–Se) as an efficient and durable catalyst for electro-oxidation of urea

In this study, we develop selenium (Se)-iron hydroxide (NiF–Se@Fe(OH)₂) hetero-nanostructured catalyst system for fuel cell, and environmental-relevant urea-electro-oxidation reaction. For the rational engineering, the Se layers are initially deposited on the Ni foam substrate; then we grow Fe(OH)₂ hetero-nanostructures with various morphologies by introducing different ratios of Fe precursor sample. The Fe(OH)₂ ball-like nanorods to rock-like nanosheets are synthesized on the Se layered Ni foam surface by a simple hydrothermal process. The microscopic characterizations, and spectral analysis reveal the formation of Se integrated Fe(OH)₂ hetero-nanostructures such as ball-like nanorods, sprouts-like nanowire network, nanoflowers and rock-like nanosheets through effective Ni–O bond and Fe–Se bond for its typical synergism. The Se induces an interesting morphology transformation from crystalline nanorods to rock-like nanosheets structures that lead to the potential constituents for catalyst electrode that effectively merge the qualities such as high conductivity, large specific surface area, and larger catalytic active sites for electro-oxidation reaction of urea. Among them, NiF–Se@Fe(OH)₂ (8 mmol Fe(NO₃)₂) sprouts-like hetero-nanostructured network displays higher catalytic activity toward oxidation of urea (146.7 mA) with onset potential of 0.11 V vs. Ag/AgCl in 1 M NaOH + 0.1 M urea. Furthermore, the sprouts-like NiF–Se@Fe(OH)₂ nanowired network shows superior activity than the other aspect ratio's, excellent long-term stability, and reproducibility.     

Pulse-electrodeposited Ni–Fe–Sn films supported on Ni foam as an excellent bifunctional electrocatalyst for overall water splitting

The development of extremely active bifunctional non-noble electrocatalysts for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is pivotal for water splitting but remains challenging. Herein, self-supported Ni–Fe–Sn electrocatalysts were fabricated on nickel foam (NF) through a simple and facile pulse electrodeposition process. Under optimal conditions, the prepared Ni–Fe–Sn electrocatalysts exhibited excellent bifunctional properties in alkaline medium and required ultralow overpotentials of only 27 and 201 mV for HER and OER, respectively, to reach the current density of 10 mA cm^?2. Importantly, the same Ni–Fe–Sn electrocatalyst can be assembled as the anode and the cathode in a two-electrode system. It demanded a fairly low applied voltage of 1.55, 1.72, and 1.87 V to produce 10, 50, and 100 mA cm^?2, respectively, and exhibited excellent long-term stability. The excellent electrocatalytic water splitting performance of the Ni–Fe–Sn film was mainly associated with its intrinsic catalytic activity derived from the modulation of the electronic structures among Ni, Fe, and Sn by using the appropriate atomic ratio of Ni: Fe: Sn.     

Co3O4–C@FeMoP on nickel foam as bifunctional electrocatalytic electrode for high-performance alkaline water splitting

Exploring low-cost, highly efficient, and sustainable non-precious electrocatalysts for electrolytic H₂ generation is driving research for the sustainable green urban development. Herein, we present a simple synthetic approach, through a two-step process, to prepare the bifunctional electrode of Co₃O₄–C@FeMoP hybrid micro rods/nanosheets anchored on nickel foam (NF), in which the Co₃O₄–C microrods grown on NF surface are decorated by FeMoP nanosheet layers, which is directly grown through a simple hydrothermal followed by post-phosphorization processes. The obtained hybrid hierarchical Co₃O₄–C@FeMoP/NF shows a significant enhancement in the electrocatalytic activities of oxygen/hydrogen evolution reactions (OER/HER) in comparison to the individual Co₃O₄–C and FeMoP nanostructures, thanks to more heterointerface active sites provided by FeMoP nanostructures with three-dimensional (3-D) layered architectures. The Co₃O₄–C@FeMoP/NF catalyst exhibits a relatively small overpotential of 200 mV vs. RHE for OER to achieve 20 mA/cm² and 123 mV vs RHE at 10 mA/cm² for HER along with excellent durability in alkaline electrolytes. We demonstrate the bifunctional electrocatalytic electrode as the electrolyzer for the generation of H₂ via water splitting at small applied voltage of 1.61 V to achieve 10 mA/cm² and good stability for 24-h continuous running.     

Fabrication of ball-milled MgO–Mg(OH)2-hydromagnesite composites and evaluation as an air-stable hydrogen storage material

A phase stability map of metallic magnesium powder, exposed to environmental conditions for 12 months (Mg-12M) and subjected to different high-energy ball-milling speeds and milling times, was constructed. Mg-12M−160 [½MgO-⅓Mg(OH)₂-⅙hydromagnesite] and Mg-12M−640 [¼MgO-⅝Mg(OH)₂-⅛hydromagnesite] composites were obtained changing the milling conditions. The correlation among the accumulated energy (ΔE_accum), the impact energy (ΔE_hit), and the phase stability under different high-energy ball-milling conditions were generated. The Mg-12M−160 composite had a hydrogen storage capacity of 0.63 wt% at −196 °C and 8.3 bar, although further hydrogen adsorption at higher pressures is expected. Structural defects play a significant role in the adsorption capacity. A representation of the possible absorption mechanism is proposed.     

Synthesis and electrochemical characteristics of Li(Ni · M)O2 (M = Co,Mn) cathode for rechargeable lithium batteries

The synthesis and electrochemical characteristics of LiNiO₂ and Li(Ni · M)O₂ (M = Co or Mn) as the cathode materials for rechargeable lithium batteries were investigated. It was clarified from these investigations that LiNiO₂ has been produced from crystalline NiO, which was derived from Ni(OH)₂ and LiOH, and that the property of NiO had some influence on the LiNiO₂ preparation. It was assumed that the formation of the layered structure has been inhibited by the existence of the Ni vacancy and Ni³⁺ ion in NiO. The synthesis of a solid solution of Li(Ni · Co)O₂ suggested that a part of the Ni replacement by Co might inhibit the formation of the Ni vacancy of NiO and promote the formation of the layered structure. The capacity fading with increase in cycle number was suppressed by the replacement of a part of Ni with Co. We considered that the capacity fading was suppressed by the development of the layered structure wherein formation of Ni vacancy was suppressed by replacement with Co. LiNi_0.8Co_0.2O₂ prepared under the stream of oxygen gas showed a small irreversible capacity at first cycle and higher cycling capacity of ∼ 180 mA h g⁻¹.     

Controlled synthesis of Mn3O4/Co9S8–Ni3S2 on nickel foam as efficient electrocatalyst for oxygen evolution reaction

Advances in electrochemical interfaces have greatly facilitated the development of new energy systems that can replace traditional fossil fuels. Oxygen evolution reaction (OER) is the core reaction in the new energy conversion system to produce hydrogen. Here, nanorods structure of Mn₃O₄/Co₉S₈–Ni₃S₂/NF-4 was designed and assembled. The Mn₃O₄ has served as an appropriate matrix to build a composite structure with Co₉S₈–Ni₃S₂ to enhance the stability of catalyst. And the introduction of Mn regulated the electronic structure of Ni and Co, which increased the OER activity of matericals. Further characterization and electrochemical testing have suggested that between polymetallic can effectively optimize conductivity and enhance reaction kinetics. Mn₃O₄/Co₉S₈–Ni₃S₂/NF-4 can achieve overpotential of 188 mV at the current density of 10 mA cm^?2 in alkaline solution, with small Tafel slope of 43.2 mV dec^?1 and satisfactory stability of 30 h at 10 mA cm^?2. This work may show a feasible reference in the design of high-efficient OER catalysts.     

Ternary TiO2/Ni–Ni(OH)2/NiPi nanotube arrays with synergetic effect for enhanced photoelectrocatalytic H2-evolution

Dual co-catalysts have an essential effect on improving the photoelectrochemical (PEC) performance of semiconductor materials. In this study, Ni–Ni(OH)₂ or/and Nikel phosphate (NiPi) nanocrystals co-catalysts were deposited on the surface of as-prepared TiO₂ nanotube arrays (TNTAs) by a simple electrodeposition route for PEC hydrogen production. The TNTAs loading with Ni and NiPi bifunctional co-catalysts exhibited remarkably enhanced PEC performance, with about an 8.3-fold increase in the photocurrent; and an 11.7-fold improvement in H₂ evolution rate in comparison to bare TNTAs. The constructed ternary TNTAs/Ni–Ni(OH)₂/NiPi comprised the advantage of Ni–Ni(OH)₂ and NiPi nanoparticles to enhance visible-light absorption and promote oxygen evolution reaction (OER) kinetics. The internal electric field is generated between supported p-type Ni(OH)₂ and n-type TiO₂ under light irradiation, which will drive holes to flow to Ni(OH)₂ and oxidize it as the OER active layer. Also, the photo-generated holes remaining in the TiO₂ valence band can migrate to NiPi co-catalysts to cause OER. Therefore, the photogenerated electron-hole pairs can be successfully separated under the synergetic influence of Ni–Ni(OH)₂ and NiPi co-catalyst, leading to a superior PEC water splitting ability.     

Pt–Ni nanoparticles electrodeposited on rGO/CFP as high-performance integrated electrode for methanol oxidation

A novel carbon fiber paper loaded with reduced graphene oxide (rGO) was used as the substrate, on which Pt–Ni nanoparticles were electro-deposited as to prepare an integrated electrode by two electrochemical methods (cyclic voltammetry and square wave pulse). The electrochemical tests indicated two integrated electrodes had excellent performance towards methanol oxidation. Especially, Pt-Ni-CV(A)-rGO/CFP electrode showed the highest electrocatalytic activity, and mass activity reached 5.33 A·mg^?1_Pt, which was about 5.6 times that of the commercial Pt/C catalyst (JM). Further, after annealing under a reducing atmosphere, two electrodes exhibited completely different changes in the aspects of morphology and electrocatalytic performance. It can be attributed to the changes of element distribution and morphology of nanoparticles after annealing. The as-prepared Pt–Ni-rGO/CFPs composite electrode is promising for integrated electrode of proton exchange membrane fuel cells. This work opens an avenue for the preparation of high-performance integrated electrode.     

Highly-dispersed surfactant-free bimetallic Ni–Pt nanoparticles as high-performance catalyst for hydrogen generation from hydrous hydrazine

Highly-dispersed surfactant-free bimetallic Ni–Pt nanoparticles (NPs) with a particle size as small as 2.4 nm were successfully synthesized using NaBH₄ as reducing agent in the presence of NaOH, which exhibit excellent catalytic performance with very fast kinetics for selective decomposition of hydrous hydrazine to hydrogen at room temperature. NaOH plays an important role in the formation of highly-dispersed Ni–Pt nanoparticles. The present results bring light to new opportunities in the development of high-performance metal nanoparticle catalysts and encourage the effective application of hydrous hydrazine as a promising hydrogen storage material.