Increase In Active Surface Area Research Articles

Ion energy dependence of helium plasma irradiation effects on the photoelectrochemical properties of tungsten oxide

Abstract Tungsten samples with fuzz nanostructures on the surface were generated using helium plasma with different incident ion energies, and then fuzz tungsten oxide electrodes were prepared by calcination. The photoelectrochemical (PEC) properties and stability of the samples were measured, and the dependence on the incident ion energy was discussed. The mechanism of the fuzz structure to enhance the PEC performance of tungsten oxide was analyzed by scanning electron microscope (SEM), X-ray diffraction (XRD), and electrochemical impedance spectroscopy (EIS). The results show that fuzzy sample fabricated with higher ion energy has greater PEC performance, which is mainly caused by the increase in active surface area.

Enhanced Electrochemical Performance of MWCNT-Assisted Molybdenum-Titanium Carbide MXene as a Potential Electrode Material for Energy Storage Application.

Two-dimensional (2D) materials such as MXenes have attracted considerable attention owing to their enormous potential for structural flexibility. Here, we prepared a Mo2TiC2Tx-layered structure from parent Mo2TiAlC2Tx MAX by chemically selective etching of the aluminum layer. The prepared MXene was employed in composite formation with CTAB-grafted multiwalled carbon nanotubes (MWCNTs) to have a structure with improved electrochemical performance. The samples were characterized to analyze the structure, morphology, elemental detection, vibrational modes, and surface chemistry, followed by an electrochemical performance of the Mo2TiC2Tx MXene and MWCNTs@Mo2TiC2Tx composite using the GAMRAY Potentiostat under a 1 M KOH electrolyte. The specific capacitance of pristine Mo2TiC2Tx was 425 F g-1, which was enhanced to 1740 F g-1 (almost 4 times) at 5 mV s-1 due to the increase in active surface area and conductive paths between the MXene sheets. The charge storage mechanism was studied by further resolving the cyclic voltammograms. MWCNTs@Mo2TiC2Tx showed much improved electrochemical performance and reaction kinetics, making it an ideal material candidate for supercapacitor applications.

Surfactants effect on the electrochemical properties of FeSe2 electrode for supercapacitor with first principles insights into quantum capacitance

Nanostructured material like FeSe2 has been synthesized through a simple and cost-effective hydrothermal method. The effect of cationic, non-ionic, and anionic surfactants has been studied on the structural, morphological, and electrochemical properties of FeSe2 electrode material. The FeSe2 electrode material prepared with the assistance of CTAB surfactant displayed a superior specific capacitance value of 401 F g −1 at a scan rate of 10 mV s −1 and 337 F g −1 at a current density of 3.3 A g −1, respectively. The maximum energy density of the symmetric supercapacitor cell fabricated with the same material is evaluated to be 47 Wh kg−1 at a power density of 1667 W kg−1. The addition of the surfactant cetyltrimethylammonium bromide (CTAB) during the synthesis process is found to have a significant impact on the charge storage capability of the material, which is attributed to an increase in active surface area, porosity, reduced crystallite size, and reduced bulk resistance, etc. The real-time use of CTAB-based FeSe2 symmetric cells has been verified via illuminating different voltage light-emitting diodes. Further, the electronic properties and the quantum capacitance of FeSe2 material synthesized without the assistance of any surfactant have been analyzed theoretically using first-principles density functional theory calculations. Acquired results unveil the potential growth of FeSe2 electrode material in energy storage applications.

Using coupled Ni and Zn oxides based on ZIF8 as efficient electrocatalyst for OER

In the present work, we report the synthesis and characterization of efficient and stable electrocatalysts for oxygen evolution reaction (OER) in alkaline medium constructed using Ni and/or Co oxides dispersed on Zn oxide based on the zeolitic imidazole framework (ZIF8) operated through a combined application of solvothermal and calcination methods. Once subjected to calcination, the calcined, solvothermally treated Ni/ZIF8, named Ni/ZIF8-900A composite, recorded the most impressive improvement in OER electrocatalytic activity among the electrocatalysts synthesized in this study. Ni/ZIF8-900A recorded an overpotential (η) of 0.34 V at 10 mA cm−2; this was the same value obtained for RuO2 and was relatively close to the value obtained for IrO2 (0.29 V) - both widely regarded as state-of-the-art electrocatalysts. Long-term electrochemical tests revealed that Ni/ZIF8-900A had a negligible loss in electrocatalytic activity, demonstrating its high electrocatalytic efficiency in OER in alkaline medium. The physicochemical characterization of the Ni/ZIF8-900A composite showed that the catalyst is characterized by overlapping and merged structures of ZnO and Ni0.8Zn0.2O, as well as a high Ni content on its surface (Ni(1):Zn(2) in %w/w) in comparison with the Ni content in the bulk composition (Ni(1):Zn(14) in %w/w). The large amount of Ni3+ on the Ni/ZIF8-900A surface (before and after the stability tests) and the presence of N atoms bonded to the metals were found to be responsible for the improved OER activity of the electrocatalyst. The electrochemical results showed that when exposed to oxidative potentials during OER experiments, the surface structure of the Ni oxide/oxyhydroxide-enriched Ni/ZIF8-900A catalyst is activated. The outstanding OER electroactivity of the Ni/ZIF8-900A composite can be attributed to surface activation fueled by oxide formation, which resulted in an increase in active surface area along the composite and caused a possible displacement of Ni3+ states to Ni4+ states on the oxides formed.

Co-doping of SiO2 and ZrO2 for the synthesis of energy-saving PbO2 anode material for trivalent chromium electroplating

In this study, the electrodes (PbO2, PbO2–SiO2, PbO2–ZrO2 and PbO2–SiO2–ZrO2) were prepared by galvanostatic electrodeposition in a lead nitrate system and used as anode materials for trivalent chromium plating. Physical characterizations show that the successful doping of SiO2 and ZrO2 can refine the grain of PbO2. Electrochemical tests show that the PbO2–SiO2–ZrO2 electrode has good electrocatalytic activity and corrosion resistance, which is mainly attributed to the increase of active surface area. In the process of trivalent chromium plating, the initial and increasing range of the cell voltage of the PbO2–SiO2–ZrO2 electrode were the lowest, and the amount of hexavalent chromium generated was much smaller than that obtained using the pure PbO2 electrode, which had obvious advantages in energy savings. This study provides a concise method for PbO2 electrode modification and provides a reference for the subsequent use of anode materials for trivalent chromium plating and electrodeposition of other metals.

Electrophoretic Deposition of Platinum Nanoparticles using Ethanol-Water Mixtures Significantly Reduces Neural Electrode Impedance

Platinum electrodes are critical components in many biomedical devices, an important example being implantable neural stimulation or recording electrodes. However, upon implantation, scar tissue forms around the electrode surface, causing unwanted deterioration of the electrical contact. We demonstrate that sub-monolayer coatings of platinum nanoparticles (PtNPs) applied to 3D neural electrodes by electrophoretic deposition (EPD) can enhance the electrode's active surface area and significantly lower its impedance. In this work we use ethanol-water mixtures as the EPD solvent, in contrast to our previous studies carried out in water. We show that EPD coating in 30 vol.% ethanol improves the device's electrochemical performance. Computational mesoscale multiparticle simulations were for the first time applied to PtNP-on-Pt EPD, revealing correlations between ethanol concentration, electrochemical properties, and coating homogeneity. Thereto, this optimum ethanol concentration (30 vol.%) balances two opposing trends: (i) the addition of ethanol reduces water splitting and gas bubble formation, which benefits surface coverage, and (ii) increased viscosity and reduced permittivity occur at high ethanol concentrations, which impair the coating quality and favoring clustering. A seven-fold increase in active surface area and significantly reduced in vitro impedance of the nano-modified neural stimulation electrode surfaces highlight the influence of ethanol-water mixtures in PtNP EPD.

Quantifying instant water cleaning efficiency using zinc oxide decorated complex 3D printed porous architectures

Industrialization harms the quality of water; therefore, cleaning and monitoring water sources are essential for sustainable human health and aquatic life. An increase in active surface area and porosity can result in quick and efficient cleaning activity. 3D printing can build porous architecture with controlled porosity and active surface area. Here, catalytically active ZnO nanosheets were grown on the surface of 3D printed architecture (Schwarzites and Weissmuller) with different porosity and surface area. The Weissmuller structure along with ZnO, has shown better catalytic performance due to its higher porosity (~69%) and high active surface area, compared to Schwarzites structure. Synergistic effect of adsorption and photodegradation has resulted in ~95% removal efficiency of mixed dye within 10 min by Weissmuller structure. The dye degradation efficiency was determined using colorimetric measurements with a regular smartphone for real-time quantitative investigation of dye removal efficiency. Most importantly, decorated 3D printed structures exhibit high structural stability without residuals (ZnO nanosheets) in water after performing the recycling experiment. Therefore, the decorated 3D printing structures and colorimetric detection method will offer a user-friendly versatile technique for analysis of removal efficiency of toxic components in different polluted water sources without using high-end sophisticated instruments and complicated procedures.

Simultaneous Femtomolar Detection of Paracetamol, Diclofenac, and Orphenadrine Using a Carbon Nanotube/Zinc Oxide Nanoparticle-Based Electrochemical Sensor

The development of an efficient, selective, and highly sensitive electrochemical sensor for the simultaneous analysis of multiple drugs is a tough challenge. Herein, we report an applied electrochemical sensing platform comprising both acid- and base-functionalized carbon nanotubes (CNTs) with zinc oxide nanoparticles between the layers (COOH-CNTs/ZnO/NH2-CNTs) for the detection of paracetamol, diclofenac, and orphenadrine (PAR, DIC, and ORP) drugs with ultrahigh sensitivity and selectivity as evidenced by intense and well-resolved voltammetric signals. Prior to electrochemical analysis, the nanocomposite/glassy carbon electrode (GCE) surface was characterized by multiple spectroscopic techniques. The performance of fCNTs/ZnO/fCNTs/GCE was probed by electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), and square-wave anodic stripping voltammetry (SWASV). The functionalized porous architecture with a large effective surface area provided a conduit for efficient mass transport and active sites for anchoring adsorbate molecules, thus leading to substantially lower oxidation overpotentials and amplified current signals. The fCNTs/ZnO/fCNTs/GCE exhibited a 6-fold increase in active surface area than bare GCE. Under optimized SWASV conditions, the designed sensor demonstrated simultaneous detection of PAR, DIC, and ORP with an unprecedented femtomolar limit of detection (46.8, 78, and 60 fM, respectively) within a time span of just 1 min. Besides the specificity, stability, and reliability studies of the designed sensing platform in multiple biological and pharmaceutical samples, % recoveries of 96–102% highlight the novelty and figures of merit of the designed electrochemical sensor. Moreover, computational studies were carried out that support the experimental outcome of a favorable charge transfer process between functional groups of the drugs and the sensor surface.

Synthesis of AlCl3-Graphite Intercalation Compounds for Lithium-Ion Capacitor Anode

Lithium-ion capacitors (LIC) are hybrid energy storage devices combining electric double layer capacitors (EDLC) and lithium-ion batteries (LIB). In typical LIC systems, faradaic reaction on anode restricts high power performance because of slow reaction rate than that of non-faradaic reaction on cathode. The conventional graphite anode suffers from low rate capability for LIC and shows low theoretical capacity which is not suitable for high energy density. To achieve high rate performance and high capacity, ferric chloride-graphite intercalation compounds (FeCl3-GICs) are reported as LIB anodes[1]. Intercalated FeCl3 enlarges interlayer spacing of graphite and reacts like following reaction (FeCl3+3Li++3e- ↔ Fe+3LiCl). We focused on aluminum chloride-GICs (AlCl3-GICs), lighter than FeCl3-GICs, as new anode materials for LIB and LIC. AlCl3-GICs have possibility of high rate performance and higher capacity at low potential by following reaction (AlCl3+3Li++3e-↔Al+3LiCl, Al+2.25Li++2.25e-↔Li2.25Al). In this paper, AlCl3-GICs were synthesized and evaluated their material characteristics and electrochemical properties. AlCl3-GICs was synthesized via vapor phase intercalation mehod[2]. First, graphite, AlCl3 and N-chlorosuccinimide as chlorinating agent were mixed under Ar atomosphere. Then, mixed powder was heated under vacuum at various temperatures (115, 135, 150, 200 ℃), forming AlCl3-GICs (named as 115, 135, 150, 200, respectively). Electrochemical properties were evaluated by galvanostatic charge/discharge test at various current densities with assembled Li//AlCl3-GIC cells. As experimental condition, electrolyte was 1M LiPF6 in EC/DEC (1/1 vol.), voltage range was 0.01–3.0 V and current density values were 0.1–2.0 A g-1. Fig. 1 shows XRD patterns of obtained AlCl3-GICs. Peaks derived from GICs were confirmed for all AlCl3-GICs. The different intensity ratio of pristine(002)/GIC(00x) of the AlCl3-GICs synthesized with different heating temperature indicated various intercalated structures. Fig. 2 shows rate performance of the Li//AlCl3-GIC cells. From this result, it was confirmed that AlCl3-GICs could react with Li+ and showed over 70 mAh g-1 even at high current density such as 2.0 A g-1 (over 4 C-rate). The results demonstrated high rate performance of AlCl3-GICs as anode for LIB and LIC. We have considered that the high rate capability can be due to improvement of Li+ diffusibility caused by enlarging interlayer spacings and/or increase of active surface area. Especially, 115 shows the discharge capacity of 432 mAh g-1, which is higher than theoretical capacity of graphite (372 mAh g-1) and the highest capacities among GICs at all current densities. Therefore, AlCl3-GICs have possibility as the anode for high performance LIC. In the poster, details of characteristics and application to LIC will be discussed. Acknowledgements This work is partially supported by the Advanced Low Carbon Technology Research and Development Program of the Japan Science and Technology Agency (JST-ALCA, JPMJAL1008, JPMJAL1301). Reference [1] Y. Sun et al., Energy Technol., 7, 1801091 (2019).[2] H. Shioyama, Tanso, 161, 35-37 (1993). Figure 1

LaFeO<sub>3</sub> Modified RuO<sub>2</sub> for Enhancing Electrochemical Performances

LaFeO3nanoparticles-modified RuO2and RuO2samples were fabricated by a thermal decomposition and was characterized by powder X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDS) and cyclic voltammetry tests. XRD results reveal that the RuO2and RuO2-LaFeO3samples are mainly a rutile structure. Compared with the RuO2sample, the RuO2-LaFeO3sample has smaller crystalline grain size. Cyclic voltammetry analysis shows the voltammetric behaviour and the characteristic potentials of the RuO2and the RuO2-LaFeO3samples are similar in 1.0 M KOH solution. Voltammetric charge analysis reveals that the RuO2-LaFeO3sample has higher concentrated of surface active species and larger exposed surface area than the RuO2sample. Capacitive measurement results show the Double-layer capacitance (Cdl) and the electrochemical surface area (ECSA) values of the RuO2-LaFeO3sample are approximately 2 times larger than those of the RuO2sample, indicating that the electrochemical active surface area increase when integrating of RuO2with LaFeO3nanoparticles.

Patterning flat-sheet Poly(vinylidene fluoride) membrane using templated thermally induced phase separation

The presence of surface patterns on separation membranes, when properly designed, can enhance the membrane performance by increasing the active surface area, tuning the surface wettability, and promoting mass transfer in the boundary layer. This work reports a new method of patterning microporous membranes, namely, lithographically templated thermally induced phase separation (lt-TIPS). Templated by surface-patterned elastomeric molds, the TIPS of poly (vinylidene fluoride) (PVDF) and tributyl O-acetylcitrate (ATBC) lead to successful pattern replication onto the PVDF membranes. We systematically examined the TIPS processing conditions, including PVDF/ATBC concentration (20 wt%, 25 wt% and 30 wt%) and quenching temperature (25 °C and 100 °C), on the fidelity of pattern replication, as well as structure and properties of the PVDF membranes. Experimental results show that lower solution concentration and direct quenching to 25 °C lead to higher fidelity of pattern replication. Lower concentration and higher quenching temperature result in membranes with larger pores and higher porosity. In comparison with non-patterned PVDF membranes, the patterned PVDF membranes display similar pore structures, mechanical characteristics and crystallinity. In contrast, the presence of the surface pattern significantly increases the water contact angle and pure water flux, as expected from the increase in active surface area. The work shows that lt-TIPS is an effective method for patterning membranes, complementary to existing imprinting and phase-inversion based methods.

Grain size effect on photocatalytic activity of TiO2 thin films grown by atomic layer deposition

We have studied the effect of grain size on the photocatalytic activity of TiO2 thin films grown by atomic layer deposition technique. A number of thin films of different crystallinity (anatase, rutile, amorphous) and grain sizes (55 nm to 715 nm) were grown on Si substrates under different processing conditions, by varying the reactor temperature, deposition time or buffer layers. The films are characterized by scanning electron microscopy, grazing incidence x-ray diffraction, x-ray photoelectron spectroscopy, secondary ion mass spectrometry and atomic force microscopy. The photocatalytic activity was examined by measuring the degradation rates of methylene blue in aqueous solutions under the ultraviolet light irradiation. The photocatalytic activity exhibits a maximum for grains of average size of 200 nm, indicating existence of two competing effects, which occur when the average grain size decreases: increase of active surface area (which promotes a high photocatalytic activity) and increase of grain boundaries (which degrades the photocatalytic activity).

Use of Electrochemical Impedance Spectroscopy to Reveal Ageing Mechanisms in Silicon Anodes for Lithium-Ion Batteries

The key for the exploitation of renewable energy and thus the replacement of fossil fuels and traditional energy sources is the achievement of effective energy storage strategies. In this regard, rechargeable Lithium-ion batteries (LIBs) play a significant role due to the high gravimetric and volumetric energy, high power density, long cycle life and low self-discharge property. However, the new applications of LIBs need higher energy densities than the present LIB technology can offer. Replacing the commercially used carbon anodes with Silicon anodes can increase the capacity more than ten times. Unfortunately, implementing Silicon anodes is still challenging due to the poor cycling stability caused by the severe volume changes of Silicon upon lithiation and delithiation during charge and discharge respectively. To improve the cycling stability a fundamental understanding of the complex processes and the degradation mechanisms is necessary. The processes in a Silicon anode during cycling have been studied by using electrochemical impedance spectroscopy (EIS) as it is a powerful, noninvasive technique to resolve the various processes in an electrode. For the investigation, a Silicon electrode using 1 M LiPF6 in EC/DEC electrolyte was cycled between the voltage potential limits of 50 mV and 1 V at a constant current. EIS measurements have been conducted at different state of charge during 200 discharge/charge cycles. The experimentally obtained impedance data were analyzed by a semi-mathematical model based on a porous electrode model. The model simulates the impedance response of a porous Silicon electrode, composed of spherical intercalation particles. The radii of the particles are dynamically changing because of expansion and contraction due to lithiation and delithiation, respectively. The impedance of a single particle is calculated considering diffusion of the Lithium cations (Li+ ions) in the particles, the solid electrolyte interphase (SEI) film and interfacial process. The particle size distribution of the Silicon powder and porous electrode theory is used to simulate the total impedance of the Silicon anode. All complex spectra obtained from experiments and simulation showed the same elements reported in literature for Silicon anodes before[1,2]. The mathematical model was used to identify important parameters to analyze the experimental data on a fundamental basis. Evaluating the experimental data revealed the large impact of the porosity reduction on the impedance during cycling. It was shown that after an expected increase in active surface area with lithiation due to the expansion of the Silicon particles, the active surface area suddenly drops. This drop in active surface area was found to correlate to a critical porosity of 0.1. It was concluded that the decrease in porosity leads to a diffusion limitation of the ions in the electrode bulk and therefore to a severe decrease in accessible surface area. Increased surface area and reduced porosity after the same lithiation time with progressive cycling indicates that the expansion of the Silicon particle is not fully reversed with delithiation. This indicates an ageing mechanism of trapped Lithium in the electrode[3]. Discontinuous diffusion behavior were correlated to cracking of the Si particle which leads to new ions diffusion pathways. Furthermore, the results indicate a formation of new SEI with lithiation and a partially redissolution with delithiation, which was also reported by Philippe et al.[4]. The attached figure shows the ratio of the experimentally obtained active surface area Aexp and the modelled active surface area Amod (based on expansion due to lithiation) and the diffusion coefficient of Li+ ions in the electrode. The results are shown for cycle 12 during the lithiation from 1 V to 50 mV (a) and for the cycle 1 to 200 after a lithiation to 50 mV (b).

Tuning electrical properties of polythiophene/nickel nanocomposites via fabrication

Polythiophene/nickel nanocomposites were synthesized by the electrochemical oxidative polymerization of thiophene in the presence of nickel nanoparticles. The nanocomposites were characterized by scanning electron microscopy, energy dispersive X-ray analysis, atomic force microscopy and Raman spectroscopy. It was found that both PTh and PTh/Ni nanocomposites show granular structures with grains that agglomerate. The increasing of the Ni content results in a decreasing in size and an increasing in density of insular PTh/Ni agglomerations. All composite samples present smaller grains and agglomerations as compared to pure PTh. As the Ni content increases both Ra and RMS are slightly increasing. Surface area was also estimated and the results showed a slightly increase of active surface area. Their electrochemical properties were further evaluated utilizing cyclic voltammetry. As-grown nanocomposites of PTh/nickel with the highest content of nickel exhibited enhanced electrochemical activity, the highest specific capacitance of 3000 F g−1 and the fastest discharging process of 200 s.

Electrochemical Roughening of Thin-Film Platinum Macro and Microelectrodes.

This protocol demonstrates a method for electrochemical roughening of thin-film platinum electrodes without preferential dissolution at grain boundaries of the metal. Using this method, a crack free, thin-film macroelectrode surface with up to 40 times increase in active surface area was obtained. The roughening is easy to do in a standard electrochemical characterization laboratory and incudes the application of voltage pulses followed by extended application of a reductive voltage in a perchloric acid solution. The protocol includes the chemical and electrochemical preparation of both a macroscale (1.2 mm diameter) and microscale (20 µm diameter) platinum disc electrode surface, roughening the electrode surface and characterizing the effects of surface roughening on electrode active surface area. This electrochemical characterization includes cyclic voltammetry and impedance spectroscopy and is demonstrated for both the macroelectrodes and the microelectrodes. Roughening increases electrode active surface area, decreases electrode impedance, increases platinum charge injection limits to those of titanium nitride electrodes of same geometry and improves substrates for adhesion of electrochemically deposited films.

Defect-Enhanced Phase Transformation Kinetics in Intercalation Compounds

Point, line and/or planar defects are ubiquitously present in all materials and intentional introduction and control of defects plays a key role in the development of advanced materials with better performance and new functionality. Well-known examples include doping semiconductors to modify the band structure and using phase or grain boundaries to strengthen alloys. Like other materials, battery intercalation compounds contain various types of defects, and “defect engineering” is a promising strategy for this class of materials, which nonetheless has not yet been widely explored. In particular, recent studies find that antisite defects in battery compounds, can promote Li transport by opening up alternative diffusion channels with lower migration energies in numerous lithium-ion battery electrode materials, which enhances the rate performance of batteries. Antisite defects are also reported to improve the stability and cyclability of cubic LixTi2O4. These examples demonstrate that the rational tailoring of antisite defects provides a potentially general approach to improving battery electrode properties. Here we present a computational study that reveals a new mechanism of antisite defects enhancing the rate capability of intercalation compounds by accelerating surface-reaction-limited (SRL) phase transformation during battery charge/discharge. Antisite defects are generated when the sites of intercalating ions are occupied by other cations that are usually less mobile. A prominent effect of antisite defects in battery electrodes is to block the existing paths of intercalating ions and generate new migration pathways at the same time. For intercalation compounds with strong anisotropic transport properties, such effect usually leads to the reduction in the diffusion anisotropy of intercalating ions, which has already been observed in practically synthesized lithium iron phosphate olivine (LiFePO4). In this work, we discovered that although antisite defects in LiFePO4 impede Li movement in the fast [010] diffusion direction, their ability to enhance transport along other slower diffusion directions leads to an unexpected increase in the phase transition rate when it is kinetically limited by surface reaction. Figure 1. compares the discharge simulations of two LiFePO4 particles with different antisite defect concentrations. Orders-of-magnitude improvement in SRL phase transformation kinetics is observed in “defect-rich” particle due to the increase of active surface area for Li intercalation. More transparent understanding of such mechanism was obtained by solving 1D depth-average model numerically and analytically. Meanwhile, it is revealed that the presence of defects causes Li intercalation time to increase less pronouncedly with particle sizes, and can reduce the risk of electrochemical shock under galvanostatic (dis)charge conditions by homogenizing the reaction flux. Due to the kinetic competition between surface reaction and bulk diffusion, an optimal defect concentration is predicted to exist for a given particle geometry to maximize the Li (de)intercalation rate. Criteria for the co-design of defect content and particle morphology are proposed. Counter-intuitively, we find that (100)-oriented LiFePO4 platelike particles may exhibit even better rate performance than (010)-oriented plate particles in the SRL kinetic regime, which are commonly viewed as the most desirable LiFePO4 particle morphology. While we demonstrate the possibility of using antisite defects to accelerate phase transitions in LiFePO4, it has general applicability to other phase-changing battery materials that exhibit ion diffusion anisotropy. Figure 1

Improving electrochemical performance of reduced graphene oxide by counteracting its aggregation through intercalation of nanoparticles

Herein, we report the fabrication and characterization of hybrid electrode material for supercapacitor applications. CaCO3 nanoparticles (Nps) are used as intercalator to avoid the restacking behavior of reduced graphene oxide (rGO) nanosheets. CaCO3 Nps and rGO sheets are fabricated employing precipitation technique and microwave irradiation method, respectively. The intercalation process is performed by magnetic stirring followed by ultra-sonication technique. As prepared CaCO3 Nps, rGO and rGO intercalated with 2.5 wt.% and 5 wt.% CaCO3 Nps are characterized using X-ray diffraction analysis, Fourier transform infrared spectroscopy and field emission scanning electron microscopy to evaluate the crystalline characteristics, molecular vibrations, and morphology, respectively. The prepared electrode materials are coated separately on the glassy carbon electrode and their electrochemical performance displayed remarkable capacitance values for rGO nanosheets intercalated with 2.5 wt.% and 5 wt.% CaCO3 Nps. From the obtained results, it is clear that the specific capacitance of 2.5 wt.% CaCO3 intercalated rGO displays higher specific capacitance of 84.5 F/g at 5 mV/s with high retention stability. The mechanism behind the improvement in the electrochemical behavior is due to the increase in active surface area which is explained via Brunauer–Emmett–Teller analysis and energy-dispersive X-ray spectroscopic analysis.

Cobalt‐Vanadium Hydroxide Nanoneedles with a Free‐Standing Structure as High‐Performance Oxygen Evolution Reaction Electrocatalysts

AbstractIt is a great challenge to develop electrocatalysts with high efficiency and low cost toward oxygen evolution reaction (OER) for the electrolysis of water. Herein, novel CoV‐hydroxide nanoneedle arrays with freestanding structure is successfully fabricated as new electrocatalysts for OER. Remarkably, the incorporation of V into Co hydroxide can significantly modulate the nanoneedle morphology, which results in the increase of active surface area, and augment the intrinsic activity by tuning the electronic structure. Particularly, we find that the freestanding Co hydroxide nanoneedles with 25 % Co substituted by V (Co0.75V0.25‐HNNs) show the optimum OER catalytic activity and have a low overpotential (268 mV at 10 mA cm−2), a small Tafel slope (80 mV dec−1) and long‐term stability, which are comparable to the other Co‐based and V‐based electrocatalysts for OER reported in literature.

(Invited) 3D Multifunctional Carbon Nanotube Networks

In the field of nanomaterials research, carbon nanotubes, proved to possess unique physicochemical properties that have been applied to improve the performance of existing processes or even design novel technologies. This paper illustrates that is possible to assemble carbon nanotubes into macroscopic self-standing structures with a distinctive isotropic three-dimensional arrangement. The final properties at the macroscopic scale take advantage of those of the individual nanoscale components and of the overall increase of active surface area. In particular, the carbon nanotubes assemblies possess good electric conductivity, and outstanding mechanical properties, enabling a much broader range of applications in energy and environmental areas than the individual carbon nanotubes. The synthesis method and the relevant structural characteristics are described, as well as the relationship between the observed microscopic properties and some potential applications.

Nickel catalysts supported on silica microspheres for CO2 methanation

Nickel catalysts supported on silica microspheres were prepared by the application of porous resin beads (Amberlite XAD7HP) as hard template using different order of nickel nitrate and tetraethoxysilane (TEOS) introduction. Large nickel oxide nanoparticles distributed over silica microspheres were formed when nickel precursor was introduced directly to the polymer template prior to the silica framework development or added into the silica-polymer composites. On the other hand, an impregnation of as-prepared silica microspheres after template removal led to the formation of small nickel oxide nanoparticles. The catalysts showed hierarchical pore structure. Low-temperature nitrogen adsorption/desorption and photoacoustic Fourier-transform infrared spectroscopy studies revealed slight changes of porosity and surface properties of catalysts affected by the synthesis methods. X-ray diffraction, scanning and transmission electron microscopy, temperature-programmed reduction and hydrogen desorption studies were used for determination of the properties of metallic nickel nanoparticles. It was stated that the activity and selectivity of catalysts in the CO2 methanation reaction was related to the active surface area and the size of nickel nanoparticles. An increase in CO2 conversion and selectivity to methane at low temperatures (220–350 °C) with an increase in active surface area and decrease in nickel crystallite size was observed.