In situ fabrication of porous graphene electrodes for high-performance lithiumoxygen batteries

These years, LiO₂ batteries attract wide interest because of its high theoretical energy density. However, the catalytic activity and porous structure of cathode remains a great challenge. In this work, we developed a hierarchical porous graphene foam to serve as a battery cathode, which has much richer active sites for cathodic reaction and channels for Li⁺ transfer and O₂ diffusion. The cathode exhibits a superior specific capacity as high as 9559 mAh g^?1 at 57 mA g^?1 and remains a high-rate capability of 3988 mAh g^?1 at an increased current density of 285 mA g^?1. Benefiting from the well-designed cathode structure, the battery can be stably operated for 150 cycles with a stable voltage profile and voltage efficiency up to 65%. The well-designed graphene has a potential to be a superior free-standing cathode to other carbon-based materials due to its good combination of its hierarchical and porous structure, large surface area, abundant defects and excellent mechanical stability.     

Old-loofah-derived hard carbon for long cyclicity anode in sodium ion battery

Hard carbon was prepared via the carbonization of the old loofah sponge at 800 °C for 1 h in the inert N₂ atmosphere for sodium ion battery (SIB) anode. The resultant old-loofah-derived hard carbon was investigated by scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS), Raman, galvanostatic charge/discharge, cyclic voltammetry (CV) and alternating current (AC) impedance. The results suggested that the old-loofah-derived hard carbon powders consisted of many irregular micro-particles with the mean particle size of 12 μm. Furthermore, the old-loofah-derived hard carbon anode also delivered satisfactory electrochemical performances in SIB. For example, the initial discharge specific capacity was as high as about 695 mAh g^?1 at 25 mA g^?1, and the reversible discharge specific capability after 1000 cycles was still about 171 mAh g^?1 even at 1000 mA g^?1, indicating long cycle stability and the promising feasibility of the old-loofah-derived hard carbon anode. The disordered micro-structure and large interlayer distance may jointly contribute into the satisfactory electrochemical performances.     

Sulfur/alumina/polypyrrole ternary hybrid material as cathode for lithium-sulfur batteries

Recently, lithium-sulfur batteries (LSBs) have received extensive attention due to its high energy density of 2600 Wh kg^?1. At the same time, sulfur is earth-abundant, economical and non-poisonous. Nevertheless, the poor electrochemical performance restricts its commercial application, including the inferior cycling stability caused by the significant dissolution of lithium polysulfides and the low specific capacity because of the poor electrical conductivity of sulfur. In this work, we adopt a simple and amicable process to prepare sulfur/alumina/polypyrrole (S/Al₂O₃/PPy) ternary hybrid material to overcome these defects. In this strategy, each composition of the ternary hybrid material plays an essential role in cathode: alumina and PPy can provide strong adsorption for the dissolved intermediate polysulfides. Meanwhile, PPy also works as a conductive and flexible additive to expedite electron transport, and is coated on the surface of the as-prepared SAl₂O₃ composite by in situ chemical polymerization. The sulfur is encapsulated uniformly and perfectively by the two components, which is confirmed by field emission scanning electron microscope. The ternary hybrid material manifests good electrochemical performance as expected, and displays high initial discharge capacity of 1088 mA h g^?1 and a discharge capacity of 730 mA h g^?1 after 100 cycles at a current density of 200 mA g^?1. Besides, S/Al₂O₃/PPy also shows good rate capability. The synergy between alumina and PPy is the decisive factor, which gives rise to good electrochemical performance of cathode for high-performance LSBs.     

3D SnO2/sulfonated graphene composites with interpenetrating porous structure as anode material for lithium-ion batteries

Combine SnO₂ nanoparticles with some conductive carbonaceous materials has been regarded as one of the most effective strategies to solve the problems of poor conductivity and volume change. In this work, a SnO₂/sulfonated graphene composite with 3D interpenetrating porous structure (3D SnO₂/SG) was synthesized. The elaborate designed 3D SG structure not only generates an excellent electronic conductivity, but also buffers the volume expansion of the SnO₂ particles. As a result, the desirable 3D possesses enhanced performance when used as anode material in lithium battery. For example, the electrochemical results showed that the 3D SnO₂/SG presents a high reversible specific capacity (928.5 mA h g^?1 at the current density of 200 mA g^?1). Even after 120 cycles, the specific capacity of 679.7 mA h g^?1 (at the current density of 400 mA g^?1) are still maintained.     

Nanoporous (Pt1-xCox)3Al intermetallic compound as a high-performance catalyst for oxygen reduction reaction

Nanocatalysts that boost the sluggish kinetics of oxygen reduction reaction with a long-term durability are crucial for widespread use of low-temperature fuel cells. Here we report a nanoporous intermetallic compound typically composed of platinum–cobalt–aluminum intermetallic core with in-situ grown atomic-layer-thick Pt skin as a novel oxygen-reduction-reaction nanocatalyst with remarkably enhanced performance. Both Pt and Co atoms thermodynamically prefer to locate nearby Al element within face-centered cubic Pt₃Al matrix via the formation of strong PtAl and CoAl bonds, which not only enable synergistic ligand and compressive strain effects to moderately weaken the oxygen adsorption energy of Pt skin, but alleviate the evolution of surface Pt atoms to protect against the further dissolution of less-noble Co and Al. As a result, the nanoporous platinum–cobalt–aluminum nanocatalyst exhibits specific activity of 3.40 mA cm^?2_Pt and mass activity of 2.2 A mg^?1_Pt for the oxygen reduction reaction at 0.9 V versus reversible hydrogen electrode (～13- and ～20-fold enhancement relative to commercially available platinum nanoparticles supported carbon) with an exceptional durability, showing genuine potential as cathode catalyst in next-generation electrochemical energy conversion devices.     

Electrodeposited PCo nanoparticles in deep eutectic solvents and their performance in water splitting

A facile one-step route has been developed to electrodeposite PCo nanoparticles on a nickel foam in deep eutectic solvents. The as-prepared catalyst exhibits excellent performance towards both hydrogen evolution reaction and oxygen evolution reaction. Only 62 mV and 320 mV overpotentials were required to reach a current density of 10 mA cm^?2 for hydrogen evolution reaction and oxygen evolution reaction, respectively. That current density is measured at the voltage of 1.59 V for an overall water splitting when used as both anode and cathode. The scanning electron microscopy images indicate a high dispersion of the PCo sample on the Ni foam. The prepared material possesses a relative high ECSA and a low charge transfer resistance, indicating a large number of active sites for water splitting.     

Solvothermal synthesis of Li3VO4: Morphology control and electrochemical performance as anode for lithium-ion batteries

In this work, orthorhombic Li₃VO₄ with the controllable morphology has been synthesized by tuning the solvent composition (volume ratios of ethanol to deionized water) in a solvothermal approach. The resulting Li₃VO₄ samples with various morphologies (coral-shaped particle, self-assembled hierarchical microsphere, cube-like particle, sheet-like structure) show then different electrochemical performances when employed as anodes for Li-ion battery applications. The Li₃VO₄ with self-assembled hierarchical microsphere morphology (volume ratio of ethanol to deionized water at 15:15) exhibits the best electrochemical performance. The subsequent carbon coating process on microsphere samples is claimed to significantly improve both the capacities at both low (350–430 mAh g^?1 at 100 mA g^?1) and high current (180–350 mAh g^?1 at 2 A g^?1) conditions, and their excellent cycling stability.     

Performance and durability of an anode-supported solid oxide fuel cell with a PdO/ZrO2 engineered (La0.8Sr0.2)0.95MnO3-δ-(Y2O3)0.08(ZrO2)0.92 composite cathode

PdO/ZrO₂ co-infiltrated (La_0.8Sr_0.2)_0.95MnO_3-δ-(Y₂O₃)_0.08(ZrO₂)_0.92 (LSM-YSZ) composite cathode (PdO/ZrO₂+LSM-YSZ), which adsorbs more oxygen than equal amount of PdO/ZrO₂ and LSM-YSZ, is developed and used in Ni-YSZ anode-supported cells with YSZ electrolyte. The cells are investigated firstly at temperatures between 650 and 750 °C with H₂ as the fuel and air as the oxidant and then polarized at 750 °C under 400 mA cm^?2 for up to 235 h. The initial peak power density of the cell is in the range of 438–1207 mW cm^?2 at temperatures from 650 to 750 °C, corresponding to polarization resistance from 1.04 to 0.35 Ω cm². This result demonstrates a significant performance improvement over the cells with other kinds of LSM based cathode. The cell voltage at 750 °C under 400 mA cm^?2 decreases from initial 0.951 to 0.89 V after 170 h of current polarization and remains essentially stable to the end of current polarization. It is identified that the self-limited growth of PdO particles is responsible for the cell voltage decrease by reducing the length of triple phase boundary affecting the high frequency steps involved in oxygen reduction reaction in the cathode.     

Core/shell Fe3O4@Fe encapsulated in N-doped three-dimensional carbon architecture as anode material for lithium-ion batteries

Core-shell Fe₃O₄@Fe nanoparticles embedded into porous N-doped carbon nanosheets was prepared by a facile method with NaCl as hard-template. The three-dimensional carbon architecture built by carbon nanosheets enhance the conductivity of the encapsulated Fe₃O₄@Fe nanoparticles and strengthen the structure stability suffering from volume expansion during extraction and insertion of lithium ions. Rich Pores enhance the surface between electrode and electrolyte, which short the transmission path of ions and electrons. The core-shell structure with Fe as core further improves charge transferring inside particles thus lead to high capacity. The as-prepared Fe₃O₄@Fe/NC composite displays an irreversible discharge capacity of 839 mAh g^?1 at 1 A g^?1, long cycling life (722.2 mAh g^?1 after 500th cycle at 2 A g^?1) and excellent rate performance (1164.2 and 649.2 mAh g^?1 at 1 and 20 A g^?1, respectively). The outstanding electrochemical performance of the Fe₃O₄@Fe/NC composite indicates its application potential as anode material for LIBs.     

NiCoO2 nanosheets grown on nitrogen-doped porous carbon sphere as a high-performance anode material for lithium-ion batteries

NiCoO₂ nanosheets grown on nitrogen-doped porous carbon spheres (NiCoO₂@N-PCs) have been synthesized via a facile approach using gelatin nanospheres (GNSs) as the template, carbon and nitrogen sources. Due to the synergistic effect between the NiCoO₂ nanosheets and N-PCs, the NiCoO₂@N-PCs composite exhibits an ultrahigh discharge capacity of 978 mAh g^?1 at a current density of 200 mA g^?1 with minimal capacity loss even after 80 cycles. The superior properties of NiCoO₂@N-PCs illustrate that amorphous carbon matrix could significantly improve the electrochemical performance of high-capacity metal oxide anode nanomaterials. Findings from this study suggest that these GNSs may be used to synthesize functional metal oxides, including MnO₂, Fe₂O₃, CoO and NiO@N-PCs nanostructures.     

Enhanced electrochemical kinetics of magnesium-based hydrogen storage alloy by mechanical milling with graphite

Magnesium nickel alloy (Mg₂Ni) which used as the negative electrode material in the nickel-metal hydride (Ni/MH) secondary battery is modified by graphite via mechanical milling. The effects of graphite on the Mg₂Ni are systematically investigated by X-ray diffraction (XRD), scanning electron microscope (SEM) and a series of electrochemical tests. The results show that the cycle stability of the Mg₂Ni alloy is improved with the addition of 10 wt.% graphite and the discharge capacity at the 20th cycle increase from 116.9 mA g^?1 to 178.5 mA g^?1. The Tafel polarization test indicates better corrosion resistance of the Mg₂Ni/graphite composite. Meanwhile, the results of electrochemical tests indicate that both the charge-transfer reaction rate on the surface of the alloy and the hydrogen diffusion rate inside the bulk of alloy are boosted with the introduction of graphite.     

Co(OH)2 nanoparticles deposited on reduced graphene oxide nanoflake as a suitable electrode material for supercapacitor and oxygen evolution reaction in alkaline media

In this work, cobalt hydroxide nanoparticles are simply synthesized (size is about 50 nm) and deposited on the reduced graphene oxide nanoflake by the hydrothermal method. Then, the ability of glassy carbon electrode modified with this low-cost nanocomposite is examined as a supercapacitor and oxygen evolution electrocatalysts in 2.0 mol L^?1 KOH by a three-electrode system. The modified electrode as a pseudocapacitor with potential windows of 0.35 V, exhibits a powerful specific capacitance (235.20 F g^?1 at 0.1 A g^?1 current density), energy density, stability (about 90% of the initial capacitance value maintain after 2000 cycles at 1.0 A g^?1) and fast charge/discharge ability. Furthermore, the modified electrode displays a good electrocatalytic activity for oxygen evolution reaction with a current density of 10.0 mA cm^?2 at 1.647 V, small Tafel slope of 56.5 mV dec^?1, good onset potential of 1.521 V vs. RHE and suitable durability.     

PdCo bimetallic nano-electrocatalyst as effective air-cathode for aqueous metal-air batteries

For wide application of metal-air batteries, the key factor is the development of catalysts for air cathodes. In the present study, PdCo/C bimetallic nanocatalysts are prepared by a facile borohydride reduction method. To improve the activity and stability, the catalysts are heat-treated at 200 °C in H₂/Ar atmosphere from 4 h to 24 h. The optimal heat-treatment time is found to be 8 h, at which the highest activity for both oxygen reduction reaction and oxygen evolution reaction is obtained. With the 8 h heat-treated PdCo/C catalyst, the rechargeable zinc-air battery exhibits a high power density of 180 mW cm^?2 and retains stability for more than 50 h at a discharge-charge current density of 10 mA cm^?2, while the magnesium-air battery obtains a power density of more than 200 mW cm^?2 and remains stable within 8 h at a discharge current density of 65 mA cm^?2.     

Mass production of Nickel@Carbon nanoparticles attached on single-walled carbon nanotube networks as highly efficient water splitting electrocatalyst

Herein, we develop a direct current arc discharge method which enables large-scale synthesis of nickel@carbon attached single-walled carbon nanotube networks as an electrocatalyst for highly efficient water splitting. Mass amount of Ni@C/SCN (～80 g) could be easily obtained. After optimization, the catalyst exhibits a superior performance of electrochemical water splitting, which allows a current density of 10 mA cm^?2, with an overpotential of only 260 mV for OER and 198 mV for HER. The electrolyzer can achieve a current density of 10 mA cm^?2 at 1.8 V.     

M (Co,Ni), N and S tridoped carbon nanoplates as multifunctional catalysts for rechargeable Zn-air batteries and water electrolyzers

Exploration of multifunctional non-precious metal catalysts towards oxygen reduction reaction (ORR), oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) is very important for many clean energy technologies. Here, two trifunctional catalysts based on M (Co, Ni), N and S tridoped carbon nanoplates (Co/N/S-CNPs and Ni/N/S-CNPs) are reported. Due to the relatively higher catalytic site content, graphitization degree and smaller charge-transfer resistance, the Co/N/S-CNPs catalyst shows higher activity and stability for ORR (onset potential of 0.99 V and half-wave potential of 0.87 V vs. RHE (reversible hydrogen electrode)), OER (overpotential at 10 mA cm^?2 of 0.37 V) and HER than the Ni/N/S-CNPs catalyst. Furthermore, when constructed with the Co/N/S-CNPs and commercial 20 wt% Pt/C + Ir/C cathodes, respectively, Zn-air battery (ZnAB) based on the Co/N/S-CNPs cathode displays better performance, including a higher power density of 96.0 mW cm^?2 and cycling stability at 5 mA cm^?2. In addition, an alkaline electrolyzer assembled with the Co/N/S-CNPs catalyst as a bifunctional catalyst can reach 10 mA cm^?2 at 1.65 V for overall water splitting and maintain excellent stability even after cycling for 12 h. The present work proves the potential of the Co/N/S-CNPs catalyst for many clean energy devices.     

AuNi alloy nanoparticles supported on reduced graphene oxide as highly efficient electrocatalysts for hydrogen evolution and oxygen reduction reactions

Bimetallic nanoparticles of Au and Ni in the form of alloy nanostructures with varying Ni content are synthesized on reduced graphene oxide (rGO) sheets via a simple solution chemistry route and tested as electrocatalysts towards the hydrogen evolution (HE) and oxygen reduction (OR) reactions using polarization and impedance studies. The AuNi alloy NPs/rGO nanocomposites display excellent electrocatalytic activity which is found to improve with increasing Ni content in the AuNi/rGO alloy nanocomposites. For HER, the best AuNi alloy NPs/rGO electrocatalyst, the one with the highest Ni content, exhibits high activity with an onset overpotential approaching zero versus the reversible hydrogen electrode and an overpotential of only 37 mV at 10 mA cm^?2. Additionally, a low Tafel slope of 33 mV dec^?1 and a high exchange current density of 0.6 mA cm^?2 are measured which are very close to those of commercial Pt/C catalyst. Also, in the ORR tests, this electrocatalyst displays comparable activity to Pt/C. The Koutecky–Levich plots referred to a 4-electron mechanism for the reduction of dissolved O₂ on the AuNi alloy NPs/rGO catalyst. The electrocatalyst thus demonstrates excellent activity towards HER and ORR. Additionally, it exhibits outstanding operational durability and activation after 10,000^th cycles assuring its practical applicability.     

Facile synthesis of nitrogen-doped Sn@NC composites as high-performance anodes for lithium-ion batteries

Owing to its high capacity of 994 mAh g^?1, low cost, and environmental friendliness, tin (Sn) is considered as an advanced anode material for high-capacity lithium-ion batteries (LIBs). Here, a facile strategy to fabricate core-shell structured Sn@NC composites with one-step and large-scale production is introduced in a liquid-phase reaction under room temperature. When used as anode materials for LIBs, the optimal Sn@NC composite delivers a high reversible discharge capacity of 761.2 and 476 mAh g^?1 at a current density of 200 and 1000 mA g^?1 after 200 cycles, respectively. A high capacity of 328.3 mAh g^?1 can also be obtained even at a current density of 2000 mA g^?1. The excellent cycling stability and rate performance of the composite can be ascribed to the synergistic effect of the nanometer size of Sn powder and porous structure of the carbon shell, both of which can effectively reduce the absolute volume change of electrode during the repeated charge-discharge cycles, and thus lead to excellent electrochemical performances at both rate capability and cycling life.     

Synergistic effect of sulfur on electrochemical performances of carbon‐coated vanadium pentoxide cathode materials with polyvinyl alcohol as carbon source for lithium‐ion batteries

Vanadium pentoxide (V₂O₅) is a common cathode material for lithium‐ion battery, but its low electronic and ionic conductivity seriously affect its electrochemical performances. In this paper, a type of carbon‐coated V₂O₅ and S composite cathode material with PVA as the carbon source is utilized to lithium‐ion batteries. X‐ray diffraction and Raman test results illustrate that sulfur can make the V₂O₅ lose part of oxygen atoms and become nonstoichiometric vanadium oxide (V₂O_5‐x). Electrochemical test results show that sulfur can provide a considerable proportion of the specific capacity of the whole cathode. This illustrates that the synergistic effect of sulfur can optimize the structure of vanadium pentoxide in order to increase more electron transfer channels, and at the same time, it also can provide additional specific capacity for the whole cathode. When the ratio of V₂O₅ and sulfur is 1:3, the discharge specific capacity can reach 923.02, 688.37, and 592.70 mAh g^?1 at 80, 160, and 320‐mA g^?1 current density, respectively, and after 100 times charge and discharge cycles at 320‐mA g^?1 current density, the capacity retention rate can achieve to more than 60%.     

Temperature-hydrogen pressure phase boundaries and corresponding thermodynamics for ZrCoH system

The thermodynamically and kinetically stable regions of the temperature–H₂ pressure phase boundaries for the ZrCoH system were established using the Temperature-Concentration-Isobar (TCI) method. Based on this, the enthalpy change and entropy change values of dehydrogenation and disproportionation reactions were successfully obtained. The average enthalpy change (ΔH) and entropy change (ΔS) estimated from the phase boundaries for dehydrogenation of ZrCoH₃ to ZrCo are respectively 103.07 kJ mol^?1H₂ and 148.85 J mol^?1 H₂ K^?1, which are well agreement with the data reported in literature. The average ΔH and ΔS were estimated to be ?120.91 kJ mol^?1H₂ and -149.32 J mol^?1 H₂ K^?1 for the disproportionation of ZrCoH₃, whereas the ΔH and ΔS were calculated to be ?84.6 kJ mol^?1H₂ and -92.29 J mol^?1 H₂ K^?1 for disproportionation of ZrCo. In addition, it was found from the established phase boundaries that the anti-disproportionation property of ZrCo alloy can be enhanced if the phase boundaries of hydrogenation/dehydrogenation are far away from the phase boundaries of disproportionation by adjusting the thermodynamics. Meanwhile, it is possible to keep ZrCo away from disproportionation even at high temperature of 650 °C under hydrogen atmosphere, if the temperature-H₂ pressure trajectory is carefully controlled without crossing the phase boundaries of disproportionation. Therefore, the established phase boundaries can be used as a guide to the eye avoiding disproportionation and improving the anti-disproportionation property of ZrCo alloy.     

Synthesis of NiS coated Fe3O4 nanoparticles as high-performance positive materials for alkaline nickel-iron rechargeable batteries

In this paper, ethyl xanthate nickel (EXN) was used as nickel and sulfur sources to modify Fe₃O₄ powder nanoparticles dissolved in pyridine. After short heat treatments, the generated NiS nanoparticles were not only compactly and uniformly coated on the surface of Fe₃O₄ but also induced the decreased particle size of Fe₃O₄. The microstructure, morphology and particle size of the resulting NiS coated Fe₃O₄ particles were characterized X-ray diffraction (XRD), Scanning electron microscopy (SEM), Transmission electron microscopy (TEM), and Raman spectroscopy. The results showed that thickness of the NiS coating on Fe₃O₄ particles was about 6 nm. The NiS coated Fe₃O₄ particles were tested as positive materials for nickel-iron batteries and found to effectively inhibit the iron anode passivation and improve the efficiency of charge capacity. The NiS (1.5%) – Fe₃O₄ nanoparticles delivered a significant power density of 557.2 mA h g^?1 at a current density of 120 mA g^?1, with a charging efficiency of 79.6%. Furthermore, discharge capacities of 550.2 and 436.8 mA h g^?1 were achieved respectively at 300 and 600 mA g^?1, with charging efficiencies reaching up 85.9% and 76.5% of the initial capacity after 100 cycles.