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.     

ACo2O4 (A=Ni,Zn, Mn) nanostructure arrays grown on nickel foam as efficient electrocatalysts for oxygen evolution reaction

Developing highly efficient, low-cost and superior stable electrocatalysts for the oxygen evolution reaction (OER) is essential for coping with global energy shortage and environmental crisis. In this article, ACo₂O₄/NF (A = Mn, Zn, Ni) composites were synthesized via a facilely hydrothermal and calcination method and used as electrocatalytic water oxidation catalysts. The hybrid structure, chemical composition, oxidation state and surface morphology of ACo₂O₄/NF (A = Mn, Zn, Ni) has been confirmed by powder X-ray diffraction (XRD), energy dispersive X-ray (EDX), X-ray photoelectron (XPS), scanning electron microscopy (SEM), transmission Electron Microscope (TEM) and Brunaure-Emmett-Teller (BET) analysis. Such self-supported NiCo₂O₄/NF hybrid shows a smaller overpotential of 271 mV at current density of 10 mA cm^?2 in 1 M KOH, which is comparable to most reported NiCo₂O₄ materials (monomer or composite) for OER. Influence on catalytic activity of doping different metal ions in ACo₂O₄/NF was investigated systematically for the first time. Improved electrocatalytic activity of NiCo₂O₄/NF is attributed to the special homogeneous urchin-like structure and porous property.     

Three-dimensional reduced graphene oxide–Mn3O4 nanosheet hybrid decorated with palladium nanoparticles for highly efficient hydrogen evolution

A three-dimensional (3D) reduced graphene oxide–Mn₃O₄ nanosheet (Mn₃O₄@rGO) hybrid was achieved by simple electrodeposition technique. Small palladium nanoparticle were homogeneously anchored onto Mn₃O₄@rGO substrate through the reduction of palladium salt. The interpenetrating network architecture of Mn₃O₄@rGO greatly inhibited the aggregation of 2D sheets of Mn₃O₄ and rGO, and the open 3D orientation of the Mn₃O₄@rGO hybrid nanosheets on the electrode facilitated both mass transport and electron transfer as well as maximally exposed active sites. The introduction of Mn₃O₄ enhanced the structural and electrochemical stability of rGO. The as-synthesized Pd/Mn₃O₄@rGO hybrid was employed as an electrocatalyst for electrocatalytic hydrogen evolution reaction (HER). The electrocatalyst showed a low overpotential of 20 mV at 10 mA cm^?2, a small Tafel slope of 48.2 mV dec^?1, and a large exchange current density of 0.59 mA cm^?2. Importantly, the catalyst possessed superior durability with 85.87% of catalytic activity after a long-time test (10 h). This work presents a simple and efficient stratagy to construct high-performance electrocatalysts for energy and environmental applications.     

GO clad Co3O4 (Co3O4@GO) as ORR catalyst of anion exchange membrane fuel cell

GO cladded Co₃O₄ (Co₃O₄@GO core/shell) was synthesized as ORR catalyst for anion exchange membrane fuel cell (AEMFC) by ultrasonic method. The obtained GO/Co₃O₄ was characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), high-resolution transmission electron microscopy (HRTEM), and Fourier transform infrared spectroscopy (FT-IR). Physical characterizations confirmed the obtained catalyst was composed of GO lamina (2 nm) shell and 10 nm Co₃O₄ nanoparticle core. The optimal content of GO was 5%. At the moment, its onset potential and polarized current density were identical with that of commercial 20% Pt/C catalyst. The limited current density for ORR reached 4.30 mA cm^?2, which was smaller than that of 20% Pt/C (4.62 mA cm^?2). The prepared Co₃O₄@GO/C catalyst behaved excellent cycle stability after 1000th cycle. The results indicated the prepared Co₃O₄@GO/C maybe a potential, efficient and low cost catalyst for ORR in AEMFC.     

Construction of unique NiCo2S4@Ni3V2O8 hierarchical heterostructures arrays on Ni foam as an efficient electrocatalyst with high stability for water oxidation

The development of high efficiency and stable electrocatalysts for the electrochemical water oxidation reaction (WOR) is a grand bottleneck in chemical energy storage and conversion. This article describes a simple co-precipitation route to deposit hierarchical NiCo₂S₄@Ni₃V₂O₈ core/shell hybrid on conductive nickel foam electrode by a simple two-step process. When it is firstly used as the 3D substrates electrode, the NiCo₂S₄@Ni₃V₂O₈ material makes use of both components and provides excellent water oxidation activity, 35 mA cm^?2 was achieved at a overpotential of 290 mV, which is better than the benchmark of IrO₂ electrodes (320 mV of overpotential at 35 mA cm^?2) and 13 mA cm^?2 at 1.47 V with excellent durability. The enhanced water oxidation performance of the NiCo₂S₄@Ni₃V₂O₈ materials is mainly benefiting from its particular core/shell structure, which exhibits big surface areas, and fast electron and ion transfer. Ni₃V₂O₈ shell protects NiCo₂S₄ core from oxidation in the in alkaline electrolytes and improves stability of NiCo₂S₄@Ni₃V₂O₈.This indicates that most metal vanadates oxides-based electrodes are promising as an efficient electrocatalyst and shows the advantages of the interfacial effect, which provide a new idea toward high-performance flexible water oxidation fabrication of robust and cheap catalyst sample.     

A highly scalable spray coating technique for electrode infiltration: Barium carbonate infiltrated La0.6Sr0.4Co0.2Fe0.8O3-δ perovskite structured electrocatalyst with demonstrated long term durability

This work demonstrated a highly scalable spray coating process for cathode infiltration with excellent long-term stability for the oxygen reduction reaction. Barium carbonate (BaCO₃) nanoparticles have previously demonstrated excellent catalytic activity for the oxygen reduction reaction and were chosen as a model system to be applied by spray coating onto La_0.6Sr_0.4Co_0.2Fe_0.8O_3-δ (LSCF) and LSCF-SDC (Sm_0.2Ce_0.8O_2-δ) cathode materials. In this work, barium acetate solutions were modified by a surfactant to lower the surface tension and decrease the contact angle on LSCF which is a benefit for the infiltration process. In the LSCF electrode, BaCO₃ nano-particles exhibited significant interfacial contact with LSCF particles by the spray coating technique. As a result, the polarization resistance of BaCO₃ infiltrated LSCF was reduced from 2.5 to 1.2 Ωcm² at 700 °C. In addition, commercial full cell SOFCs with BaCO₃ infiltrated LSCF-SDC cathodes also demonstrated higher performance due to the reduced cathode resistance. At 750 °C, the electrode overpotential of the BaCO₃ infiltrated cell was much lower than that of baseline cell during long term testing (500 h). The polarization resistance of the BaCO₃ infiltrated LSCF-SDC electrode only increased by 1.6% after 500 h.     

Mo incorporated W18O49 nanofibers as robust electrocatalysts for high-efficiency hydrogen evolution

Creation of robust and stable electrocatalysts is a persistent objective for high-efficiency hydrogen evolution by water splitting. We present here the experimental realization of one-dimensional Mo incorporated W₁₈O₄₉ nanofibers (NFs) by a template-free solvothermal method. When utilized as electrocatalysts for hydrogen evolution through water splitting, the preliminary results demonstrate that the optimized catalytic electrode from 1 at% Mo doped W₁₈O₄₉ NFs yields an onset overpotential of 89 mV and Tafel slope of 49 mV dec^?1 as well as maximal exchange current density up to 1.60 × 10^?2 mA cm^?2. An overpotential as low as 462 mV is required to attain current density of 50 mA cm^?2 in comparison with 587 mV for pristine W₁₈O₄₉ NFs. Moreover, the Mo doped W₁₈O₄₉ NFs display relative stability by applying a potential of 503 mV and a current density of 80 mA cm^?2 over 24 h in 0.5 M H₂SO₄ aqueous solution, making them promising in practical applications.     

Highly efficient and stable bifunctional electrocatalyst for water splitting on Fe–Co3O4/carbon nanotubes

Replacement of precious platinum (Pt) or ruthenium oxide (RuO₂) catalysts with efficient, cheap and durable electrocatalysts from earth-abundant elements bifunctional alternatives would be significantly beneficial for key renewable energy technologies including overall water splitting and hydrogen fuel cells. Despite tremendous efforts, developing bifunctional catalysts with high activity at low cost still remain a great challenge. Here, we report a nanomaterial consisting of core-shell-shaped Fe–Co₃O₄ grown on carbon nanotubes (Fe–Co₃O₄/CNTs) and employed as a bifunctional catalyst for the simultaneous electrocatalysts on oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). The Fe–Co₃O₄/CNTs electrocatalyst outperforms the commercial RuO₂ catalyst in activity and stability for OER and approaches the performance of Pt/C for HER. Particularly, it shows superior electrocatalytic activity with lowering overpotentials of 120 mV at 10 mA cm^?2 for HER and of 300 mV at 10 mA cm^?2 for OER in 1 M KOH solution. The superior catalytic activity arises from unique core-shell structure of Fe–Co₃O₄ and the synergetic chemical coupling effects between Fe–Co₃O₄ and CNTs.     

Fe3O4/Ag microsheets assembled by interlaced nanothorns as high performance anode materials for lithium storage

Fe₃O₄/Ag nanocomposite is directly prepared by dealloying a well-designed FeAgAl source alloy in alkaline etching solution at room temperature. Selectively dissolving Al from FeAgAl alloy results in Fe₃O₄/Ag microsheets assembled by second order interlaced nanothorns. On account of the distinctive hierarchical micro-/nano-structure and the hybridization of well conductive Ag, Fe₃O₄/Ag composite shows much improved lithium storage performances with higher capacities, cycling stability, and coulombic efficiency compared with the pure Fe₃O₄ anode. Even the current rate is as high as 1 A g^?1, the capacity of Fe₃O₄/Ag composite still exceeds 600 mA h g^?1 after cycling 500 cycles compared with the remained value of only 294.8 mA h g^?1 for pure Fe₃O₄. Moreover, Fe₃O₄/Ag composite presents the excellent rate capabilities at whether low or high current densities. Owing to the superiorities of excellent properties and handy preparation, the Fe₃O₄/Ag anode exhibits encouraging prospect for lithium ion batteries.     

CuCo2O4 microflowers catalyst with oxygen evolution activity comparable to that of noble metal

It is of high significance to design efficient, low-cost and durable electrocatalysts for the reaction (OER) in alkaline solution. In this communication, we report the development of CuCo₂O₄ microflowers directly on nickel foam (CuCo₂O₄/NF) as an efficient and durable electrocatalyst for OER. Such CuCo₂O₄/NF demands overpotential of only 296 mV to drive a geometrical catalytic current density of 20 mA cm^?2, 73 mV and 145 mV less than that for Co₃O₄/NF and NF, respectively, which are better than that of RuO₂/NF. Furthermore, CuCo₂O₄/NF presents an excellent long-term electrochemical durability maintaining the activity at overpotential of 240 mV for 10 h.     

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.     

In-situ reduction synthesis of La2O3/NiM-NCNTs (M = Fe,Co) as efficient bifunctional electrocatalysts for oxygen reduction and evolution reactions

Highly active and stable bifunctional catalysts for both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) play a vital role in rechargeable zinc-air batteries. In this work, La₂O₃ and alloy nanoparticles (NiFe and NiCo) decorated nitrogen doped carbon nanotubes hybrids (denoted as La₂O₃/NiFe-NCNTs and La₂O₃/NiCo-NCNTs) were successfully prepared by the in-situ reduction procedure. The crystalline structure and morphology of hybrids were characterized by X-ray diffraction (XRD), X-ray photoelectron spectra (XPS), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). La₂O₃/NiFe-NCNTs revealed desirable bifunctional catalytic activities towards both oxygen reduction reaction (5.1 mA cm^?2 at 0.3 V vs. RHE) and oxygen evolution reaction (1.69 V vs. RHE at 10 mA cm^?2) in alkaline media. Furthermore, rechargeable zinc-air batteries fabricated with La₂O₃/NiFe-NCNTs as the bifunctional catalyst demonstrated a small charge-discharge voltage gap (1.04 V) and long-term stability after charge-discharge cycling for 100 cycles.     

Facile synthesis of laminated porous WS2/C composite and its electrocatalysis for oxygen reduction reaction

The Vulcan XC-72R modified WS₂ nanocomposite (WS₂/C）was prepared by solid reaction process combined with sonication. The as-prepared WS₂/C nanocomposite presents a laminated porous structure by SEM and TEM characterization. The electrochemical experiments show that the onset potential and the limiting-current density of WS₂/C is 0.78 V and 4.99 mA cm^?2, respectively, which is much higher than, WS₂ (3.12 mA cm^?2) and Vulcan XC-72R (2.79 mA cm^?2). The number of transfer electrons in ORR at the WS₂/C nanocomposite electrode is 3.70, which is close to four-electron process. Besides, the current density of WS₂/C nanocomposites remained at 90% after 20,000 s, indicating its superior electrochemical stability. All these facts reveal that the as-prepared WS₂/C nanocomposite can be regarded as a promising cathode ORR catalyst for fuel cell.     

Crossed FeCo2S4 nanosheet arrays grown on 3D nickel foam as high-efficient electrocatalyst for overall water splitting

Great efforts in developing low-cost, highly efficient and stable electrocatalysts are to tune the chemical compositions and morphological characteristics for enhancing efficiency of water splitting. In this communication, FeCo₂S₄ nanosheet was grown in situ on nickel foam (FeCo₂S₄/NF) via a facile hydrothermal sulfidization method and served as a high-efficient bifunctional electrocatalyst for overall water splitting. As-synthesized FeCo₂S₄/NF self-supported electrode delivers 20 mA cm^?2 at an overpotential of 259 mV toward OER and 10 mA cm^?2 at an overpotential of 131 mV toward HER in alkaline media. Moreover, when used as both anode and cathode in a two-electrode electrolyzer, only a small cell voltage of 1.541 V is needed to afford a current density of 10 mA cm^?2 for overall water splitting. Bifunctional electrode FeCo₂S₄/NF also revealed a distinguished electrochemical durability during a 12 h stability test at 1.63 V, which would provide a promising water splitting installation for commercial hydrogen production.     

In-situ growth of mesoporous Nb2O5 microspheres on g-C3N4 nanosheets for enhanced photocatalytic H2 evolution under visible light irradiation

Large-surface-area mesoporous Nb₂O₅ microspheres were successfully grown in-situ on the surface of g-C₃N₄ nanosheets via a facile solvothermal process with the aid of Pluronic P123 as a structure-directing agent. The resultant g-C₃N₄/Nb₂O₅ nanocomposites exhibited enhanced photocatalytic activity for H₂ evolution from water splitting under visible light irradiation as compared to pure g-C₃N₄. The optimal composite with 38.1 wt% Nb₂O₅ showed a hydrogen evolution rate of 1710.04 μmol h^?1 g^?1, which is 4.7 times higher than that of pure g-C₃N₄. The enhanced photocatalytic activity could be attributed to the sufficient contact interface in the heterostructure and large specific surface area, which leads to effective charge separation between g-C₃N₄ and Nb₂O₅.     

Monodisperse Pd nanoparticles assembled on reduced graphene oxide-Fe3O4 nanocomposites as electrocatalysts for borohydride fuel cells

5 nm palladium nanoparticles (Pd NPs) are synthesized and assembled on reduced graphene oxide-iron oxide nanocomposite (rGO-Fe₃O₄) to be used in oxygen reduction reaction (ORR) and borohydride oxidation reaction (BOR) studies in alkaline media. The structure and morphology of the resulting Pd/rGO-Fe₃O₄ hybrid material are evaluated by X-ray diffraction (XRD), transmission electron microscopy (TEM), and energy dispersive X-ray spectroscopy (EDS) analyses. The electrochemical behavior of Pd/rGO-Fe₃O₄ hybrid material for the ORR and BOR is investigated by voltammetry with rotating disk and rotating ring disk electrode and electrochemical impedance spectroscopy, enabling evaluation of the number of exchanged electrons, Tafel slope, exchange current density and activation energy. The results reveal that ORR at Pd/rGO-Fe₃O₄ proceeds as a 2-electron process with Tafel slope of 0.133 V dec^?1, while BOR proceeds as a 5.6-electron process with Tafel slope of 0.350 V dec^?1 and exchange current density of 1.38 mA cm^?2. The BOR activation energy was found to be 12.4 kJ mol^?1. Overall, this study demonstrates the good efficiency of Pd/rGO-Fe₃O₄ hybrid material for BOR.     

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.     

Co3O4 nanosheet arrays treated by defect engineering for enhanced electrocatalytic water oxidation

Due to its poor electrical conductivity and finite exposed active sites, the development of high activity Co₃O₄ oxygen evolution reaction (OER) electrocatalysts remains a major challenge. Oxygen vacancies can enhance the electrical conductivity of electrocatalysts and reduce the adsorption energy of H₂O molecules on surfaces, thereby significantly enhancing their electrocatalytic activity. Taking inspiration from this, we demonstrate a green and facile reduction strategy to prepare reduced Co₃O₄ nanosheet arrays (R-Co₃O₄ NSA) with large electrochemical surface area and rich in surface oxygen vacancies. Compared to pristine Co₃O₄ nanosheet arrays (P-Co₃O₄ NSA), R-Co₃O₄ NSA exhibits better OER performance, with a lower overpotential of 330 mV at a current density of 20 mA cm^?2 and a smaller Tafel slope of 72 mV dec^?1. Impressively, the excellent properties of R-Co₃O₄ NSA can rival to the state-of-the-art noble metal oxide electrocatalyst (IrO₂). This strategy of defect-engineering offers a briefness and cost-effective means for the development of highly efficient OER systems.     

Micro and nano-architectures of Co3O4 on Ni foam for electro-oxidation of methanol

Spinel Co₃O₄ material with different morphologies is directly grown on Ni foam by simple hydrothermal method and subsequent calcination processes. The direct growth of binder free active phase of Co₃O₄ on Ni foam is an effective approach to enhance the electrocatalytic activity of the material. The morphologies of Co₃O₄ strongly depend on the anion of the precursor salt used. Microflowers, microspheres and nanograss morphologies of Co₃O₄ are obtained using chloride, sulfate and acetate salts of cobalt, respectively. The BET surface areas of these cobalt oxide materials are found to increase in the order of microflower-Co₃O₄ (53 m² g^?1) < nanograss-Co₃O₄ (65 m² g^?1) < microsphere-Co₃O₄ (100 m² g^?1). The electrocatalytic activity of these Co₃O₄ materials has been tested for methanol oxidation by cyclic voltammetry and chronoamperometry. All three samples show low onset potentials (0.32–0.34 V) for methanol oxidation. The vanodic peak current of methanol oxidation is found to increase in the order of microflower-Co₃O₄ (28 A g^?1) < nanograss-Co₃O₄ (34.9 A g^?1) < microsphere-Co₃O₄ (36.2 A g^?1) at 0.6 V. This study highlights the significance of the morphology of cobalt oxide in the development of oxide based non-precious electrocatalysts for methanol oxidation.     

Hierarchical nitrogen-enriched porous carbon materials derived from Schiff-base networks supported FeCo2O4 nanoparticles for efficient water oxidation

Abundant metal oxides and their composites have attracted great interest in the application of electrochemical energy conversion and storage. In this work, we obtain a hybrid material of FeCo₂O₄ nanoparticles anchored on hierarchical nitrogen-enriched porous carbon material (denoted as FeCo₂O₄@NPC-450 °C) and study its activity for oxygen evolution reaction (OER). NPC-450 °C is prepared by carbonizing a Schiff-base network (SNW) and SNW is melamine-based material own high nitrogen content and rigid molecular backbone. Compared with FeCo₂O₄ and NPC-450 °C, FeCo₂O₄@NPC-450 °C hybrid exhibits remarkable OER performance with a small over potential of mere 330 mv at a current density of 10 mA cm ^?2 and a small Tafel slope of 50 mV dec^?1. Electrochemical measurements also show that FeCo₂O₄@NPC-450 °C present stability for at least 25 h in alkaline solutions. FeCo₂O₄@NPC-450 °C shows good performance for OER raises the possibility for cheap and easily prepared catalyst to replace precious metal catalysts.