Long-term Electrochemical Stability Research Articles

Synthesis of Ni–Co–ZrO2 nanocomposites doped with ceria particles via electrodeposition as highly protective coating

A novel Ni–Co–ZrO2 nanocomposites doped with ceria particles has been synthesized by pulse electrodeposition as highly protective coating. The effect of current density and duty cycle on its structure and properties were evaluated. The composite coatings are compact with hill-valley like structure. The average roughness (Sa) was about 73–98 nm and the duty cycle of 70% benefits low roughness and fine-grained structure. The crystallite size of these coatings is 17–20 nm. The nanocrystalline coating exhibits the preferred orientation of Ni (111) texture. AFM and XPS were utilized to analyze the surface properties. EIS results indicated that the electrodeposition parameters greatly affect the corrosion behavior of the nanocomposites. The electrochemical behavior varied with immersing time. Duty cycle of 30%, current density of 2 A dm−2 were the appropriate parameters for the best corrosion and wear resistance and optimal long-term electrochemical stability in 3.5 wt% NaCl corrosive solution. This coating shows good potential for engineering application in aggressive medium.

Structural composite supercapacitor using carbon nanotube mat electrodes with interspersed metallic iron nanoparticles

A carbon nanotube (CNT) mat interspersed with metallic iron nanoparticles is investigated as a structural supercapacitor electrode material that could be incorporated into fiber-reinforced composites. Both ionic liquid and aqueous potassium hydroxide electrolytes are trialed to examine pseudocapacitive mechanisms and the long-term electrochemical stability of the CNT mat in symmetrical supercapacitors. High-resolution transmission electron microscopy showed the high level of interconnection of the CNTs and evenly distributed metallic iron nanoparticles, which enhances the structural and electrical performance of the electrode. Raman and X-ray photoelectron spectroscopies combined with thermogravimetric and surface area analyses are used to characterize the physico-chemical properties of the CNT mat and identify the different electrochemical mechanisms contributing to the supercapacitive behavior. Three electrode experiments demonstrated the relative contributions of the cathode and anode processes to the total capacitance. Symmetrical supercapacitor coin-cell trials used a structural glass-fiber separator and showed the ionic liquid electrolyte facilitated stable pseudocapacitance with the available iron nanoparticles, leading to specific energy and power as high as 18.3 Wh.kg−1 at 0.15 kW kg−1 and 5.6 Wh.kg−1 at 2.4 kW kg−1 after 5000 cycles. It is envisioned these materials can readily be incorporated into composite materials for structural energy storage technology.

Facile synthesis and electrochemical properties of a novel Ni-B/TiC composite coating via ultrasonic-assisted electrodeposition.

A novel Ni-B/TiC composite coating was synthesized by ultrasonic-assisted direct current electrodeposition. Ultrasonic technology was adopted to prevent the agglomeration of nanoparticle, improve the structure and corrosion resistance, using an ultrasonic bath at frequency 40 KHz and acoustic power 300 W. The influences of current density and deposition time on its structure and electrochemical behaviors were studied. Under ultrasonic dispersion, the composite coatings are smooth, compact with protrusion structure sparsely distributed on it. The average roughness (Sa) was about 13.6-26.1 nm. The crystallite size is 10-21 nm. The preferred orientation is Ni (1 1 1) texture. EIS results indicated that the corrosion resistance was greatly improved by ultrasonic-assisted method. The corrosion mechanism is consistent with one-time constant EEC model of Rs(CPEdlRct). With the increase of immersion time, the Rct of the composite coating often first increased and then decreased. Under ultrasonic, current density 2 A dm-2 and deposition time 20 min were the appropriate parameters for the optimal corrosion resistance and excellent long-term electrochemical stability in 3.5 wt% NaCl corrosive solution. This coating shows good application prospect for corrosion protection in aggressive environment.

High-Performance MoO₃ Nanoplate Electrode for Asymmetric Supercapacitor with Long-Term Electrochemical Stability.

In the present study, by controlling the content of ammonium molybdate via a facile hydrothermal method, we achieved MoO₃ electrodes with different morphologies, i.e., triangular nanoplates, triangular prisms and four prisms. As the electrode material of supercapacitors, the MoO₃ electrodes with triangular nanoplates show the highest specific capacitance (104 mAh g-1 at 2 mA cm-2) as well as a good cycling performance with 92.4% retention rate after 8000 cycles at 10 mA cm-2. Subsequently, an asymmetric supercapacitor is fabricated using the MoO₃-0.15 and activated carbon (AC) as cathode and anode, respectively. The fabricated supercapacitor shows a high energy density of 24.8 Wh kg-1 at a power density of 358 W kg-1. Significantly, the device manifests a long-term cycling stability with retention rate of 103% even after 16000 cycles. According to the noted facts, the promising prospects of MoO₃ electrode for practical applications in supercapacitor are definitely confirmed.

Al3+ ion intercalation pseudocapacitance study of W18O49 nanostructure

Intercalation pseudocapacitance is of essential significance for designing high performance electrode materials, which offers exceptional charge storage characteristics. In this study, we elucidate the pseudocapacitive behavior of Al3+ ions intercalation within the distinctive tunnels of monoclinic W18O49 nanostructure. 3D sea urchin-like W18O49 is synthesized through one-step solvothermal approach. Its physicochemical properties are investigated by X-ray diffraction, X-ray photoelectron spectroscopy, Field emission scanning electron microscopy and Brunauer-Emmett-Teller surface area analysis. Cyclic voltammetry, galvanostatic charge-discharge and electrochemical impedance spectroscopy techniques are used to investigate the electrochemical characteristics of W18O49 electrode in different electrolyte systems. It shows high specific capacitance of 350 F g−1 at 1 A g−1, superior electrochemical long-term stability in the Al3+ electrolyte with 92% capacitance retention at 8000 cycles. The excellent electrochemical performance is predominantly due to the Al3+ ions intercalation/de-intercalation with W18O49 nanostructure that is proven by ex situ X-ray diffraction analysis. The work marks a notable achievement in the effort of substituting commonly acidic proton electrolyte for W18O49 supercapacitor.

Nitrogen-doped hierarchical porous carbons prepared via freeze-drying assisted carbonization for high-performance supercapacitors

Functionalized carbon electrodes with hierarchical porous structure play an essential role in the fabrication of high-performance supercapacitors. Here, we report a novel freeze-drying assisted carbonization approach for the preparation of nitrogen-doped hierarchically porous carbons (NHPCs). Using urea as both the pore-forming agent and the nitrogen source, and sodium alginate (SA) as the carbon precursor, we are able to modulate the porosity and N-doping concentration of the NHPCs by simply altering the carbonization temperature and the dosage of urea. The prepared NHPCs exhibit specific surface area as high as 1179 m2 g−1 with 70% micropore and high N- and O-doping concentration of 6.7 wt% and 13.8 wt%, respectively. Carbon electrodes based on these NHPCs show a high gravimetric capacitance (305 F g−1 at 1 A g−1) and an excellent rate ability (retaining 73.8% at 20 A g−1) in three-electrode systems. The NHPCs symmetric supercapacitor delivers excellent energy density of up to 23.8 W h kg−1 as well as long-term electrochemical stability (95.8% capacitance retention over 10, 000 cycles). The abundance of the raw materials combined with the simple fabrication procedure makes the SA-derived NHPCs as promising electrode materials for the next generation advanced supercapacitors.

Bioinspired silver nanoparticles/reduced graphene oxide nanocomposites for catalytic reduction of 4-nitrophenol, organic dyes and act as energy storage electrode material

Facile and a novel technique for bioinspired synthesis of silver nanoparticles (AgNPs) using an aqueous extract of mango (Mangifera indica) flower as stabilizing and reducing agent was demonstrated. The formation of AgNPs and AgNPs/rGO nanocomposites were confirmed through extensive experimental characterization and numerical analysis. Both, AgNPs and AgNPs/rGO nanocomposites showed excellent catalytic performance in catalytic hydrogenation of 4-nitrophenol and azo bond in dye molecules. The rGO supported Ag nanocomposites exhibited improved catalytic activity compared to AgNPs due to the enhancement of surface area. Electrochemical analysis of AgNPs/rGO nanocomposites showed specific capacitance (SC) of ∼532 F g−1 at a current density of 1.0 A g−1. About 92% retention in SC after 2000 charge-discharge cycles suggested long-term electrochemical cyclic stability as supercapacitor electrode materials. The biogenic nano-particles and composites implied that the rGO reinforced Ag excellent applicants as hydrogenation refining materials. All these observations demonstrated a novel, eco-cost effective and estimable candidates as hydrogenation refining materials and electrode materials.

Cu-based N-doped/undoped graphene nanocomposites as electrocatalysts for the oxygen reduction

The development of efficient electrocatalysts for the energy-related reactions, based on earth-abundant elements, is extremely important for a sustainable energetic future. Herein, we report the application of Cu nanoparticles supported on undoped and N-doped graphene—Cu/GOE and Cu/GOE-u composites, respectively—as electrocatalysts for the oxygen reduction reaction (ORR). All the materials showed ORR electrocatalytic activities in alkaline medium. The Cu/GOE-u composite exhibited the most promising performance, with an onset potential of 0.84 V and a current density of jL = − 4.4 mA cm−2 (vs. 0.84 V and − 2.8 mA cm−2 for Cu/GOE), which revealed the great influence of the created Cu–Nx/C active sites on the ORR electrocatalytic activity. The pure GOE-u support showed worse performance than the GOE, demonstrating that the N-doping advantage is not linear and also depends on the type and amount of accessible active sites created. The N-doping allowed an increase in the selectivity for the 4-electron process, resulting in a % of H2O2 produced < 25% for Cu/GOE-u (vs. almost 75% for Cu/GOE). Both nanocomposites revealed good tolerance to methanol crossover, and the Cu/GOE-u displayed a moderate long-term electrochemical stability, with current retention of 84% after 20,000 s.

Green synthesis of porous graphitic carbons from coal tar pitch templated by nano-CaCO3 for high-performance lithium-ion batteries

A green and cost-effective strategy was developed to synthesize porous graphitic carbons from coal tar pitch using commercially available CaCO3 nanoparticles as template without any further activation. The prepared porous graphitic carbons have well-developed hierarchical porous structure with moderate specific surface area (∼236.3 m2 g−1) and large pore volume (∼2.871 cm3 g−1), cross-linked carbon skeleton with relatively high levels of graphitic feature and enriched in oxygen/nitrogen-containing functional groups. Such unique microstructure characteristics of porous graphitic carbons not only can endow sufficient available space or active sites for Li-ions storage, but also can provide favorable and efficient channels for the Li-ions/electrons transportation. The prepared porous graphitic carbon PGC-3 applied as anode for lithium-ion batteries (LIBs) shows a large reversible capacity of 707 mAh g−1 at 0.05 A g−1, and presents a superior rate capability with high reversible capacities of 299 mAh g−1 and 248 mAh g−1 even at the extremely high current densities of 3 A g−1 and 5 A g−1, respectively. Moreover, such porous graphitic carbon also exhibits an outstanding long-term electrochemical stability and excellent cycling performance with over 93.5% capacity retention after 1000 cycles. This study paves a promising and universal way for large-scale production of porous graphitic carbons porous from coal tar pitch for high performance anode materials used in LIBs.

Novel piperidinium functionalized anionic membrane for alkaline polymer electrolysis with excellent electrochemical properties

To improve low-efficiency and durability for alkaline membrane water electrolysis, novel piperidinium functionalized SEBS (SEBS-Pi) alkali membrane was prepared. The membrane not only displayed high conductivity (>10 mS cm−1 at 30 °C), but possessed excellent thermal stability and mechanical properties. Alkali resistance test lasts 576 h in 1 M KOH at 80 °C, high retentions of IEC as well as conductivity and no obvious change in FT-IR spectra suggest good alkaline resistance of SEBS-Pi membrane. Good three phase reaction boundary in catalyst layers and packing between the membrane and catalyst layers are formed when SEBS-Pi is used as both membrane and ionomer. A good performance of water electrolysis is achieved (400 mA cm−2 at 2 V, 50 °C). During a long-term electrochemical stability test carried out with current density of 400 mA cm−2 at 50 °C for 105 h, the voltage remained almost constant (around 2.08 V), indicating good cell durability. All these indicate that SEBS-Pi has a good potential for applications in water electrolysis.

Controllable designing of superlattice units of tiled structure and standing structure as efficient oxygen evolution electrocatalyst: self-assembled graphene and hydroxide nanosheet

Layered double hydroxides (LDHs), as an effective oxygen evolution reaction (OER) electrocatalyst, face many challenges in the practical application. One is that bulk materials limit the exposure of active sites, and the other is that controllable assembly of specific structures is difficult to achieve. In this work, based on the exfoliation–assembly strategy, we, for the first time, report novel tiled/standing structures of NiAl-LDH/RGO nanohybrids as highly efficient catalyst for water oxidation in 1.0 M KOH solution. Interestingly, based on our mass protocol, we were surprised to find that there are dynamic evolution structures between NiAl-LDH nanosheets and GO nanosheets (GO-NS). Unambiguous evidences prove the LDH-NS tiling/standing on GO-NS that forms a periodic (LDH/GO)n superlattice, which was proposed for the first time. NiAl-LDH/RGO-5 (NG-5) nanohybrids possess the lattice unit where LDH-NS are well-organized standing on GO-NS, exhibits excellent electrocatalytic performances with low overpotential of 180 mV and 220 mV at current density of 50 mA cm−2 and 100 mA cm−2, and low onset potential of 1.345 V (vs. RHE). In addition, at potential of 1.7 V (vs. RHE), NG-5 composite can drive large current densities of 595 mA cm−2; it is better than those of pure NiAl-LDH (123 mA cm−2). Furthermore, NG-5 composite exhibits an excellent long-term electrochemical stability for 10 h remained 95.28%. The outstanding electrocatalytic properties above suggest that NG-5 composite is a candidate for the substitution of noble-metal-based catalyst for OER.

Fabrication and electrochemical characteristics of nanowire-net structured cobalt hydroxide

Cobalt hydroxide (Co(OH)2) nanostructures were prepared on fluorine-doped tin oxide (FTO) substrates via an inexpensive and simple wet-chemical method. At a growth temperature of 60 °C, heterogeneous nucleation caused the nanowire-net structured Co(OH)2 to form a compact bottom layer on the surface of FTO substrate, and homogeneous nucleation resulted in the growth of a porous nanowire-net layer in the solution as the top layer. At 90 °C, vertically well-aligned Co(OH)2 nanosheets were grown from the heterogeneous nucleation on the surface of FTO substrate. Cyclic voltammetry (CV) revealed that the entirely binder-free Co(OH)2 prepared at 60 °C had a high capacitance of 254F/g (38.08 mF/cm2) at a scan rate of 2 mV/s and good rate capability compared to the nanosheet-structured Co(OH)2 prepared at 90 °C. Furthermore, it had excellent long-term electrochemical stability of ∼97% after 1000 cycles at a scan rate of 50 mV/s. These results suggested that the nanowire-net structured Co(OH)2 had significant application potential in the field of energy storage.

Rational design of metal organic framework derived hierarchical structural nitrogen doped porous carbon coated CoSe/nitrogen doped carbon nanotubes composites as a robust Pt-free electrocatalyst for dye-sensitized solar cells

A novel hierarchical structural hybrid of nitrogen-doped porous carbon (NPC) coated hollow CoSe nanoparticles anchored on nitrogen-doped carbon nanotubes (NCNTs) is enabled from the zeolitic imidazolate framework ZIF-67. In this composite, polypyrrole-derived NCNTs as a nitrogen-rich template effectively alleviates the irreversible aggregation of ZIF-67 derivatives. The hollow CoSe embedded NPC nanoparticles(CoSe@NPC) as high catalytic activity centres endow sufficiently available active sites for the reduction of triiodide, while NCNTs serve as both the bridge and the dispersant for the CoSe@NPC. Moreover, the outstanding catalytic metal-nitrogen bonds(Co-N-C) species take the role of high-speed transport pathway to facilitate transfer of electrons from the carbon skeleton to active sites. Benefiting from the above advantages, the hybrid of CoSe@NPC anchored on NCNTs shows fabulous electrocatalytic activity with an energy conversion efficiency of 7.58%, which is even higher than that of Pt counter electrode (7.27%). More remarkably, the composite also demonstrates a good long-term electrochemical stability in iodine-based electrolyte. The present work proves the rationality of the preparation of ZIFs-derived materials with special structures and their application in dye-sensitized solar cells system.

One‐Step Preparation of Cobalt‐Nanoparticle‐Embedded Carbon for Effective Water Oxidation Electrocatalysis

AbstractThe sluggish kinetics of the oxygen evolution reaction (OER) impedes the whole water splitting efficiency and it is thus highly desirable to develop cost‐effective OER electrocatalysts. In this Communication, we report the one‐step preparation of cobalt‐nanoparticle‐embedded carbon as a superior OER electrocatalyst with a low overpotential of 232 mV to drive a current density of 10 mA cm−2 in 1.0 M KOH. Notably, this catalyst also exhibits excellent long‐term electrochemical stability. The catalytic mechanism is also investigated by density functional theory calculations.

Biomass-derived nanoporous carbons as electrocatalysts for oxygen reduction reaction

Electrocatalysts (ECs) for the oxygen reduction reaction (ORR) are crucial in fuel cells and for this reason developing cost-effective metal-free ECs with high electrocatalytic activity and high-volume production remains a huge challenge. Herein, we report the application as ORR electrocatalysts of a series of high grade nanoporous carbons, prepared by chemical activation of acid-chars obtained from the H2SO4 digestion and polycondensation (acid-mediated carbonization) of a biomass residue (Agave sisalana).All the nanoporous carbons presented good ORR electrocatalytic activities in alkaline medium. The AC1 carbon exhibited the most promising ORR performance with Eonset = 0.84 vs. RHE, jL, 0.26 V, 1600 rpm = -3.12 mA cm−2 and nO2 = 3.6 electrons. The Tafel slopes of all carbons varied between 47 mV dec−1 (AC3) and 250 mV dec−1 (AC1). Furthermore, the carbons revealed superior tolerance to methanol when compared with commercial Pt/C and a competitive long-term electrochemical stability, with current retentions of 75–85 % after 20,000 s.The results obtained in this work suggest a promising method based on sustainable and economical biomass residues towards the development and engineering of novel value-added biomass-derived carbons as effective metal-free electrocatalysts for alkaline fuel cells.

Facile design and synthesis of nickle-molybdenum oxide/sulfide composites with robust microsphere structure for high-performance supercapacitors

This study has reported a simple strategy for the fabrication of nickle-molybdenum oxide/sulfide composites (Ni-Mo-O-S) with microsphere structure, using a simple two-step method including a facile hydrothermal process and a post solution sulfidation treatment. The electrochemical performance of the as-prepared Ni-Mo-O-S composites is carefully evaluated as the working electrode. Additionally, the effects of material preparation conditions on the specific capacitance of the as-prepared composites are also fully investigated and summarized, including the S2− concentration, sulfidation temperature and reaction time. In this work, high-performance electrode materials could be easily achieved under a wide range of preparation conditions. Specifically, the Ni-Mo-O-S composites could deliver a high specific capacitance of 2177.5 F·g−1 at a current density of 1 A·g−1, and after cycling for 5000 times, the specific capacitance could retain 86.25% of its initial value. Besides, the corresponding hybrid supercapacitor (Ni-Mo-O-S//AC HSC) achieves a high energy density of 50.61 Wh·kg−1 at a power density of 850 W·kg−1, and possesses excellent longterm electrochemical cycling stability (93.38% capacitance retention after 10,000 cycles). Our work has provided a low-cost, feasible and promising way to prepare high-performance electrode materials for supercapacitors.

Freestanding nitrogen-doped d-Ti3C2/reduced graphene oxide hybrid films for high performance supercapacitors

A facile method has been developed to prepare a freestanding binder-free nitrogen-doped delaminated-Ti3C2/reduced graphene oxide hybrid films for high-performance supercapacitor electrodes. This film exhibits a high specific capacitance of 247 F g−1 (∼445.2 F cm−3) at 1 A g−1 in 6 M KOH, which is still well maintained after 10000 cycles at 10 A g−1, demonstrating excellent long-term electrochemical stability. In addition, a flexible symmetric supercapacitor has been assembled with such films that delivers a maximum energy density of 15.7 W h kg−1 (at 309.3 W kg−1) and a power density of 3738.7 W kg−1 (at 11.1 W h kg−1) in PVA/H2SO4 gel. This impressive electrochemical performance can be attributed to the enhanced conductivity and high pseudocapacitance offered by the heteroatoms of nitrogen and the alleviated self-restacking of MXene layers by the introduction of reduced graphene oxide nanosheets.

Surface Functionalization of a Conventional Polypropylene Separator with an Aluminum Nitride Layer toward Ultrastable and High-Rate Lithium Metal Anodes.

Lithium (Li) metal as a next-generation anode has received great interest from industry and academic institutes due to its attractive benefits of a high theoretical capacity (3860 mAh g-1) and the lowest negative potential (-3.04 V vs SHE) among the anode candidates. However, major issues associated with dendritic Li growth, infinite volume expansion of Li, and low Coulombic efficiency cause severely degraded cycle stabilities and fatal safety issues (such as short-circuit). Herein, we first designed a functional membrane, comprising an aluminum nitride (AlN) layer and a polypropylene (PP) separator, in order to curb the sharp Li dendrite growth, restrain the propagation of dendritic Li toward the PP separator, and consequently improve the electrochemical stabilities of Li metal batteries. When the designed membrane was introduced in either the Li/Cu half-cell or the Li/LCO full-cell, Li dendrite growth was significantly suppressed and side reactions associated with electrode degradation was effectively prevented by the material benefits of the AlN layer, thus leading to the significantly enhanced cycle performances. Low temperature stability tests further demonstrated the optimiztic potentiality of the designed membrane for enabling the stable operation of Li metal batteries under harsh conditions. Our approach of adopting a metal nitride layer to the PP separator can be a compelling strategy to improve the long-term electrochemical stability of the Li metal electrode.

Enhancement of alkaline water splitting activity by Co-P coating on a copper oxide nanowire.

Hydrogen is the most attractive source of energy in the 21st century. However, high-efficiency mass production of hydrogen still faces many challenges. Although electrochemical water splitting is an ideal way to produce hydrogen, it requires low-cost and efficient electrocatalysts. In this work, a hybrid shell/core Co-P/CuO nanowire array was fabricated by Co-P film electrodeposition on a CuO nanowire array. Because of the synergy between Co-P and CuO nanowire arrays, Co-P/CuO shows remarkable activity toward the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER). This bifunctional electrocatalyst achieving 20 mA cm-2 requires a cell voltage of only 1.645 V, and has superb long-term electrochemical stability and high faradaic efficiency.

Graphene oxide/cobalt-based nanohybrid electrodes for robust hydrogen generation

Low-cost nanostructured hybrid materials and the optimization of their structural design present an opportunity to achieve high performance and stable renewable energy devices. Here we used electrospinning to homogeneously embed graphene oxide (GO) nanosheets within the one-dimensional structure of cobalt-based nanohybrids (CoNHs). In particular, we focus on the performance of these nanohybrids in Na2S/Na2SO3 aqueous electrolyte (pH = 13) due to its wide application in photocatalytic and photoelectrochemical (PEC) devices. We demonstrate that the addition of GO can remarkably reduce the charge transfer resistance from 4.4 Ω to 2.5 Ω for the 0 wt% GO/CoNHs and the 12 wt% GO/CoNHs, respectively. Furthermore, the CoNHs display outstanding electrochemical long-term stability, as the overpotential required to keep J = −10 mA cm−2 is invariable for over 42 h. The structural characterization of the nanohybrids indicates that during continuous operation, the CoNHs rebuild and regenerate in situ leading to the formation of two-dimensional nanostructures comprising a mixture of cobalt chalcogenides (Co3S4 and CoS2). The integration of the CoNHs in a quantum-dot based PEC cell and an alkaline electrolyzer (1 M KOH) demonstrates the versatility and viability of these alternative electrodes toward active and solar-driven fuel generation.