Electrochemical Reaction Sites Research Articles

A novel cobalt chloride hydrate modified Co-MOF derived carbon microspheres as anode materials for lithium ion batteries

• The Cl-doped ZIF-67-derived carbon microspheres were prepared by a novel chlorination method in high-temperature. • The electrochemical performance of CCH@CM has been greatly improved compared to ZIF-67. • CCH@CM continues the microporous structure of ZIF-67 while minimizes volume expansion. • Cobalt Chloride Hydrate (CCH) grown in situ provides maximum active sites for electrochemical reactions with Li-ions. In this work, the carbon-microsphere loaded with cobalt chloride hydrate (CCH@CM) was prepared via a collaborative and chlorination strategy derived from ZIF-67 precursor, which exhibits a superior electrochemical performance as a lithium-ion battery anode material. The synthesized CCH@CM obtained a high initial discharge capacity (947 mAh g −1 ) and the capacity attenuation rate is close to zero after 200 cycles at the current density of 100 mA g −1 . The porous structure derived from ZIF-67 not only can provide a conductive path, which increases the transport of electrons and lithium ions, but also alleviate volume expansion. The presences of -Cl-/H 2 O groups provide active sites for the anchoring of Li + . As the first successful synthesizing the cobalt chloride hydrate (CCH) from ZIF-67, good electrochemical performance provides a promising for the large-scale application in lithium ion batteries.

Co‐MOF derived MoSe 2 @ CoSe 2 /N‐doped carbon nanorods as high‐performance anode materials for potassium ion batteries

Potassium ion batteries (KIBs) have attracted considerable attention as a next-generation large-scale energy storage system. Due to the large diameter of K+ ions, developing advanced electrode materials to achieve high-performance KIBs is challenging. In this paper, one-dimensional (1D) hybrid nanostructures comprising a MoSe2 core and a CoSe2/N-doped carbon shell (denoted as MC-Se@NC) are successfully synthesized by thermal treatment of Co-based metal-organic framework (ZIF-67)-coated MoO3 nanorods. The unique 1D morphology and synergistic effect between the different elements provide sufficient electrochemical reaction sites and facilitate the reaction kinetics. Further, the N-doped carbon coating alleviates the volume fluctuation and pulverization of the active materials during cycling and improves the electrode conductivity. Accordingly, when applied to KIBs, the MC-Se@NC anode delivers a high reversible capacity of 327 mA h g−1 at 0.5 A g−1 after 150 cycles, and remarkable rate capability of 190 mA h g−1 at 2.0 A g−1. Furthermore, to explore the practical application of MC-Se@NC anode, a K-ion full cell consisting of MC-Se@NC anode and Prussian blue cathode is fabricated and characterized. As a demonstration, a light-emitting diode (LED) is successfully powered by the K-ion full cell. These excellent electrochemical properties of MC-Se@NC present possibilities for the commercialization of KIB-based large-scale energy storage systems.

3D‐Architectured MoS2‐Microflower‐Modified Electrodes toward Electrochemical Determination of Imidacloprid

AbstractWe report the fabrication and analytical performance studies of electrochemical sensors based on hydrothermally grown 3D MoS2‐microflower‐modified Glassy Carbon (GCE) and Carbon Paste Electrodes (CPE) for the sensitive detection of the insecticide imidacloprid (IMI). As compared to MoS2/GCE, the fabricated MoS2/CPE demonstrates a faster electron transfer and better catalytic ability. MoS2/CPE sensor delivers its best performance towards the determination of IMI in PBS solution of pH 7.4, owing to its porous nature which can accommodate a higher number of active electrochemical reaction sites. The sensor exhibits a sensitivity value of 2.296 μA μM−1 cm−2 with lower detection and quantification limits of 12±0.24 nM and 40±0.8 nM respectively. The proposed sensor also exhibits linearity in the detection of IMI from 1 to 100 μM.

Rational construction of hollow nanoboxes for long cycle life alkali metal ion batteries

• A series of hollow nanoboxes of metal oxide were prepared by changing the ratio of different Co and Zn. • The application of hollow nanoboxes in alkaline metal ion battery was studied. • The assembled Li/Na ion full-cells shows good cycling performance, demonstrating practical application value. Hollow nanostructures are extremely attractive in energy storage and show broad application prospects. But the preparation method is accompanied by a complicated process. In this article, the CoZn–based hollow nanoboxes with electrochemical synergy are prepared in a simple way. This structure can effectively shorten the transmission distance of ions and electrons, and alleviate the volume expansion during the cycle. In particular, bimetallic oxides are rich in oxygen vacancies, providing more active sites for electrochemical reactions. In addition, the stepwise oxidation–reduction reaction can also improve the volume change of the electrode material. According to the kinetic analysis and density functional theory (DFT) calculation, it is confirmed that the synergistic effect of the bimetallic oxide can accelerate the reaction kinetics. Based on these characteristics, the electrode exhibits stable cycle performance and long cycle life in alkali metal ion batteries, and can provide reversible capacities of 302.1 (LIBs, 2000 cycles), 172.5 (SIBs, 10000 cycles) and 109.6 (PIBs, 5000 cycles) mA h g –1 at a current density of 1.0 A g –1 , respectively. In addition, by assembling (LiCoO 2 //CoZn–O 2 ) and (Na 3 V 2 (PO 4 ) 3 //CoZn–O 2 ) full–cells, the practical application value is demonstrated. The sharing of this work introduces a simple way to synthesize hollow nanoboxes, and shows excellent electrochemical performance, which can also be expanded in other areas.

Ag/C composite catalysts derived from spray pyrolysis for efficient electrochemical CO2 reduction

• Ag/C composite and Ag electrocatalysts were synthesized by spray pyrolysis. • Composites had higher CO productivity and stability than Ag particles did. • Ag reaction sites on and within the carbon black support were used efficiently. • Carbon black support is a superior choice for CO 2 reduction by electrocatalyst. In this study, Ag/C composite catalysts with different weight ratios (20, 50, and 75 wt% Ag) were synthesized by spray pyrolysis to improve the performance of electrochemical CO 2 reduction for CO production. Among the electrocatalysts tested, the Ag75/C composite catalyst (75 wt% of Ag nanoparticles dispersed in carbon black support) showed the highest electrochemical CO 2 reduction performance, along with high stability that surpassed that of pure Ag particles. Above all, this is because Ag nanoparticles were dispersed on the surface of (and inside) the carbon black support. This enlarged the Ag surface area, thereby increasing the number of electrochemical CO 2 reduction sites. Additionally, the carbon black support has a hierarchically porous structure that improved the transport of the catholyte, reactant, and products, enabling enhanced electrochemical CO 2 reduction to CO. Furthermore, the use of carbon black support in the Ag/C composite catalysts allows the binder to bind more carbon microspheres than Ag nanoparticles, reducing the Ag surface area covered by the binder in comparison with that for pure Ag particles. Thus, the charge transfer resistance of a Ag/C composite catalyst was much lower than that of pure Ag particles due to the improved interconnection, contact, and number of electrochemical reaction sites provided by the combination of carbon black support and Ag nanoparticles. All of these interpretations imply that carbon black is an appropriate support able to play a key role in improving CO productivity via electrochemical CO 2 reduction.

Hollow FeS2 nanospheres encapsulated in N/S co-doped carbon nanofibers as electrode material for electrochemical energy storage

Pyrite iron sulfide (FeS2) is a fascinating electrode material for energy reserve devices because of its high theoretical capacity, non-polluting nature and abundant resources. However, the practical application has been extremely inhibited owing to its poor rate capacity and short cyclability caused by volume change during charge/discharge processes. In this article, a novel nanocomposite that is hollow FeS2 nanospheres encapsulated in N/S co-doped carbon nanofibers (FeS2CNFs) was synthesized through electrostatic spinning. The FeS2CNFs nanocomposite demonstrates a terrific specific capacity of 511 F g−1 at 1 A g−1 for all-solid-state supercapacitors. The FeS2CNFs as electrode material for sodium-ion batteries (SIB) displays a specific capacity of 827.7 mAh g−1 and possesses a capacity of 490.6 mAh g−1 at 0.05 A g−1 after 200 cycles. The results indicate that this encapsulated structure can guarantee the integrity of electrode materials. And the abundant defects in carbon nanofibers caused by N/S co-doping may increase electrochemical reaction sites to facilitate charge transfer. The N/S co-doped FeS2CNFs nanocomposite exhibits a great potential for applying in SIB and supercapacitors.

Microwave-assisted synthesis of well-defined nitrogen doping configuration with high centrality in carbon to identify the active sites for electrochemical hydrogen peroxide production

While nitrogen (N)-doped carbon can facilitate the four-electron transfer in oxygen reduction reaction (ORR), its effect on the two-electron path is yet to be investigated. To date, the random N-C bond configurations in N-doped carbons make it difficult to identify the active sites for electrochemical reactions. Here, we report a preparation of well-controlled N-C configurations with high centrality as model catalysts for identification of active sites for two-electron transfer ORR. Specifically, the synthesized Pyrrolic-N doped single-wall carbon nanotube and graphene utilizing a microwave-assisted pulse heating method, exhibit excellent activity for two-electron path (H2O2 selectivity of 93.5% and 98.35%). X-ray adsorption near-edge structure spectroscopy measurements indicate that carbon atoms adjacent to Pyrrolic-N are the active sites for two-electron transfer. This work provides a viable way for the fabrication of tailored N configurations in carbon materials and significantly advances our understanding of the N moieties for the electrochemical H2O2 generation.

Fabrication of hierarchical flower-shaped cobalt silicate spheres with boosting performance for lithium storage

As a new type of electrode material, transition metal silicates anode has drawn increasing attention owing to high theoretical capacity, sufficient reserves and nontoxicity. Herein, a unique flower-shaped cobalt silicate was fabricated via an alkali-assisted hydrothermal synthesis method, which feathered large specific surface area and abundant meso-pores. Serving as an anode material for lithium ion batteries, the hierarchical CoSiO 2 material exhibited excellent cycling stability (1111 mAh g −1 at 0.1 A g −1 after 200 cycles) and superior rate capability (411 mAh g −1 at 10 A g −1 ). The novel structure of F–CoSiO 2 anode not only provided abundant active sites for electrochemical reactions and effectively facilitated the migration of Li ions during charge-discharge process, but also contributed to the primary pseudocapacitive charge storage behaviors. This work may open up opportunities in structure design and represent the enormous potential of hierarchical transition metal silicate as practical advanced electrode for lithium storage. • A novel flower-shaped CoSiO 2 anode material for lithium ion batteries was designed and fabricated firstly. • The 3D architecture assembled by 2D nanosheets generated large surface area and abundant mesopores. • The hierarchical structure greatly shortened mass diffusion and fascinated the transport of Li ions. • The CoSiO 2 material exhibited remarkable cycling and rate performance.

Binder-free SnS2 sheet array with high sulfur vacancy concentration for enhanced lithium storage performance

Vacancy could not only offer extra active sites for electrochemical reactions, but also induce the change of band gap of electrode materials to enhance the electronic conductivity. In this work, binder-free SnS2 sheet array with high S vacancy concentration was fabricated on carbon paper (CP) by hydrothermal synthesis. When employed as the anode for lithium-ion battery, the SnS2/CP delivers greatly improved capacity, coulombic efficiency, high-rate discharge-ability as well as cycling performance from that of SnS2 powders. The results were analyzed and discussed with density functional theory based theoretical calculation, electrochemical impedance spectra combining diverse physicochemical techniques.

Size dependence of perovskite-type BaNbO2N particles on sunlight-driven photoelectrochemical water splitting

The size of particulate semiconductors is a critical factor in photoelectrochemical (PEC) water splitting activity because the surface area determined by the particle size establishes the electrochemical reaction sites as well as the resulting photoactivity. Herein we demonstrate the size dependence of perovskite-type BaNbO2N particles, responsive to intensive-visible-light up to 740 nm, on the PEC water splitting activity. The layered perovskite Ba5Nb4O15 particles in different sizes, as a starting oxide for synthesis of BaNbO2N, were synthesized by polymerized complex method, followed by calcination at different temperatures (1073, 1173, 1273, and 1373 K). The size of Ba5Nb4O15 particles was dependent on the calcination temperature so that low-temperature calcination led to smaller BaNbO2N particles. Although the different Ba5Nb4O15 particles experienced nitridation at 1123 K for 13 h, the sizes of the resulting BaNbO2N particles were nearly unchanged from those of the starting oxides. The sizes and Brunauer-Emmett-Teller surface areas of porous BaNbO2N particles largely influenced the PEC water splitting activity. As a result, photoelectrode employing the small BaNbO2N particles, prepared from the calcination at 1173 K, produced the highest photocurrent of 2.20 mA cm−2 at 1.23 VRHE during the sunlight-driven water splitting, showing the size dependence of oxynitride particles on photoactivity. Therefore, findings from this study support that the size reduction of oxynitride particles largely improved the PEC water splitting activity.

Rational design of hierarchical Ni-Mo bimetallic Selenide/N-doped carbon microspheres toward high–performance potassium ion batteries

Potassium ion batteries (KIBs) have received a lot of attention in large-scale energy storage applications because of abundant potassium resources. However, owing to the poor structural durability of electrode materials and sluggish reaction kinetics, the commercialization of KIBs is challenging. Herein, we design a hierarchically structured Ni–Mo bimetallic selenide/N-doped carbon microsphere (NMSe/NC) as an advanced anode material for KIBs. The hierarchical Ni-Mo/polydopamine microsphere precursor, obtained from the spontaneous chemical reaction of NiMoO4 nanorods with dopamine hydrochloride, is converted into heterostructured-Ni–Mo selenide crystals confined in a hierarchical NC matrix via a two-step thermal treatment. The unique hierarchical surface structure and the synergistic effect of Mo and Ni species provide sufficient electrochemical reaction sites and promote the reaction kinetics. Furthermore, the proximate contact between the active materials and the N-doped carbon matrix can facilitate electron transportation and enhance the structural robustness of the electrode. Consequently, the resulting NMSe/NC hierarchical microspheres delivered a high reversible capacity of 332 mA h g−1 after 200 cycles (current density: 0.5 A g−1) and a remarkable rate capability of 206 mA h g−1 (current density: 2.0 A g−1). The excellent electrochemical performance of NMSe/NC indicates their potential for KIB commercialization in large-scale energy storage systems in the future.

Electrocatalytic surface nanoionics with strained interfaced and colossal conductivity for enhancing durability and performance of solid oxide fuel cell

For an oxygen electrode in solid oxide fuel cells (SOFCs) consisting of mixed electrical and ionic conducting lanthanum strontium cobalt ferrite (LSCF), it degrades due to its low chemical stability and cation surface segregation. To mitigate such degradation, for the first time in the field of SOFCs, we demonstrate a conformal ultra-thin (∼10 nm) coating consisting of subjacent discrete nano-Pt capped with a superjacent conformal CoO x layer, applied on LSCF/SDC composite electrode, using atomic layer deposition (ALD). The coating layer reduces the cell series resistance by up to 40%, presents extraordinary stability with an intact morphology after 816 h operation. The superjacent CoO x surface nanoionics consists of randomly orientated but single-layered nanograins, with high-density intergranular and surface grain boundaries serving as the electrochemical reaction sites and facilitating mass transport. The ALD coating turns the original perovskite surface that is vulnerable to cation segregation and degradation into an embedded strained interface phase with enormous conductivity. The coating layer appears to suppress Sr outward diffusion and confines a 2 nm Sr-enriched interface layer between the coating layer and the LSCF backbone. The conductivity of the coating layer is estimated to be ∼1.27 × 10 4 S/cm and two orders magnitude higher than that of LSCF. • Conformal CoO x nanoionics with discrete Pt nano-particles on LSCF/SDC. • Heterogeneous CoO x /Pt reduces the cell series resistance by 40%. • CoO x /Pt ALD layer possesses extraordinary nanostructure stability over 816 h. • CoO x /Pt ALD layer suppresses Sr outward diffusion. • Conductivity of the ALD layer is two orders magnitude higher than that of LSCF.

Interface engineering of hierarchical NiCoP/NiCoSx heterostructure arrays for efficient alkaline hydrogen evolution at large current density.

The development of non-noble metal electrocatalysts with high activity and long-term stability for the hydrogen evolution reaction (HER), especially at large current density, is of great significance for industrial hydrogen production from water using renewable electricity. Constructing heterostructures with interfacial interactions is an effective strategy to improve the catalytic performance for large-current-density HER. Herein, we innovatively present a facile two-step electrodeposition method to immobilize a hierarchical NiCoP/NiCoSx heterostructure on Ni foam (NF) for alkaline HER. The strong interfacial coupling effect between NiCoP and NiCoSx not only offers abundant active sites for fast electrochemical reaction, but also enhances the charge transfer ability accompanied by high electrical conductivity. Consequently, the obtained self-supporting NiCoP/NiCoSx/NF exhibits an excellent catalytic performance with low overpotentials of 68, 144 and 222 mV to deliver current densities of 10, 100 and 500 mA cm-2 in 1 M KOH, along with good stability for more than 110 h, outperforming most of the reported non-noble metal based HER catalysts. Density functional theory (DFT) results further confirm that this bimetal phosphide/sulfide heterostructure can synergistically optimize the Gibbs free energy of H* during the HER process, thus accelerating the HER reaction kinetics. This work provides a new strategy toward the rational design of large-current-density electrocatalysts, which have great potential in practical large-scale hydrogen production.

High-performance Li-ion battery driven by a hybrid Li storage mechanism in a three-dimensional architectured ZnTiO3-CeO2 microsphere anode.

ZnTiO3 and ZnTiO3-CeO2 microspheres with particle sizes of about 100-300 nm were synthesized for the first time by a simple solvothermal process followed by calcination. The results indicate that CeO2 modification does not alter the morphology of the microspheres. ZnTiO3-CeO2 (0, 3, 6, and 9 wt%) show an initial charge (discharge) capacity of 171.01 (253.2), 204.6 (507.5), 213.4 (451.6) and 126.2 (367.2) mA h g-1 at 500 mA g-1, respectively. After 500 cycles, the corresponding charge (discharge) capacities were 191.1 (192.3), 298.7 (300.3), 322.4 (328.5) and 211.2 (212.3) mA h g-1, respectively. Obviously, the charge (discharge) capacities of the ZnTiO3-CeO2 composites are superior to those of pristine ZTO, which demonstrates that the Li storage performance of the CeO2-modified ZTO electrodes is improved. The CeO2 shell provides a good electronic contact between ZnTiO3 and CeO2, decreasing charge transfer resistance and facilitating the charge transportation of the ZnTiO3-CeO2 composite. In addition, the formed phase interface between CeO2 and ZnTiO3 may provide more active sites for electrochemical reactions, improving the reversibility of Li-ion intercalation and decreasing the electrochemical polarization during cycling, especially at high current densities. Therefore, such ZnTiO3-CeO2 microspheres can be regarded as hopeful candidates for anode materials for Li-ion batteries.

Ultrasonication-assisted fabrication of porous ZnO@C nanoplates for lithium-ion batteries

Lithium-ion batteries have made significant commercial and academic progress in recent decades. Zinc oxide (ZnO) has been widely studied as a lithium-ion battery anode due to its high theoretical capacity of 987 mAh g-1, natural abundance, low cost, and environmental friendliness. However, ZnO suffers from poor electronic conductivity and large volume variation during the battery discharge/charge process, leading to capacity deterioration during long-term cycling. Herein, porous ZnO@C nanoplates are developed to offer short ion diffusion pathways and good conduction networks for both Li ions and electrons. The porous nanoplates provide abundant active sites for electrochemical reactions with minimized charge transfer impedance. As a result, the porous ZnO@C nanoplates deliver higher performance for lithium-ion storage compared with a bare ZnO anode. Furthermore, with the introduction of reduced graphene oxide (rGO), the ZnO@C@rGO composite anode achieves a capacity of 229.3 mAh g-1 at a high current density of 2 A g-1.

Ni-cermet with straight pore paths as cathode for solid oxide electrolysis cell enabling energy-efficient and coking-resistant conversion of CO2

The use of typical nickel (Ni)-based solid oxide electrolysis cells (SOECs) for carbon dioxide (CO2) reduction is largely limited due to declined electrolysis performance in CO2-lean atmosphere and coking in CO-rich atmosphere. The present study is intended to investigate the electrochemical performance and coking behavior of the Ni cermet cathode in relation to its pore structure. In CO2-lean atmosphere (PCO2 = 0.3 atm), the cell with the straight pore paths (Cell-1) shows significantly higher electrolysis current density than the one with the tortuous pore paths (Cell-2) (1.12 vs. 0.61 A cm−2 under 1.5V at 750 °C). Cell-1 also demonstrates better resistance to coking than Cell-2. The critical current density at which coking starts to occur is found to be between 1.0 and 1.5 A cm−2 for Cell-1, whereas it is between 0.5 and 1.0 A cm−2 for Cell-2. Electrochemical impedance spectroscopy (EIS) measurement in combination with distribution relaxation time (DRT) analysis reveals that the Ni-cermet cathode with the straight pore paths allow facile transport of CO2 to the electrochemical reaction sites mitigating the concentration polarization, and the produced CO can be removed rapidly from the reaction sites keeping its concentration below the coking threshold.

Improvement on the electrochemical performance by morphology control of nanostructured La0.6Sr0.4CoO3−δ-Gd0.1Ce0.9O1.95 cathodes for IT-SOFC

Spherical GDC particles favour high number of electrochemical reaction sites (ers) and the breathing structure for fast ionic conduction in LSC phase, driven by the indirect modification of the cobalt's chemical speciation in LSC.

Development of Binder Free Interconnected 3D Flower of NiZn2O4 as an Advanced Electrode Materials for Supercapacitor Applications

The design and development of electrode materials for energy-storage applications is an area of prime focus around the globe because of the shortage of natural resources. In this study, we developed a method for preparing a novel three-dimensional binder-free pseudocapacitive NiZn2O4 active material, which was grown directly over nickel foam (NiZn2O4@3D-NF), using a simple one-step hydrothermal process. The material was characterized by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. Cyclic voltammetry, galvanostatic charge–discharge, and electrochemical impedance spectroscopy techniques were employed to evaluate the pseudocapacitive performance of the NiZn2O4 active material in a three-electrode assembly cell. The prepared NiZn2O4@3D-NF electrode exhibited an excellent specific capacitance, of 1706.25 F/g, compared to that of the NiO@3D-NF (1050 F/g) electrode because it has the bimetallic characteristics of both zinc and nickel. The NiZn2O4@3D-NF electrode showed better cyclic stability (87.5% retention) compared to the NiO@3D-NF electrode (80% retention) after 5000 cycles at a fixed current density, which also supports the durability of the NiZn2O4@3D-NF electrode. The characteristics of NiZn2O4@3D-NF include corrosion resistance, high conductivity, an abundance of active sites for electrochemical reaction, a high surface area, and synergism between the bimetallic oxides, which make it a suitable candidate for potential application in the field of energy storage.

Electrochemical performance and redox stability of solid oxide fuel cells supported on dual-layered anodes of Ni-YSZ cermet and Ni–Fe alloy

A Ni–Fe alloy layer in combination with a cermet layer composed of Ni and yttria-stabilized zirconia (YSZ) cermet layer was explored as an anode for solid oxide fuel cells (SOFCs). The cell supported on the dual-layered anode with straight pore paths showed a maximum power density of 1070 mW cm−2 at 800 °C, while 737 mW cm−2 for the one supported on the anode with tortuous pore paths. Electrochemical impedance measurement and distribution of relaxation time analysis revealed that the straight pore paths allowed fast gas phase transport thus mitigating the concentration polarization, and improved the accessibility of electrochemical reaction sites hence reducing the activation polarization. The cell supported on the Ni-YSZ/Ni–Fe dual-layered anode remained intact after 8 redox cycles, whereas the cell supported on the Ni-YSZ single layered anode failed after one redox cycle. It is concluded that the Ni-YSZ/Ni–Fe dual-layered composite explored in the present study is suitable for use as the supporting anode for SOFCs.

Effective Carbon Pores to Improve the Electrochemical Performance of Phosphorus as an Anode for Sodium Ion Batteries

We propose here that carbon pores provide key reaction sites for stable electrochemical reactions in phosphorus sodium ion batteries (SIBs). Phosphorus showing a high theoretical capacity (2596 mA ...