Nanoporous gold electrode prepared from gold compact disk as the anode for the microbial fuel cell

The electrodes (anode and cathode) have an important role in the efficiency of a microbial fuel cell (MFC), as they can determine the rate of charge transfer in an electrochemical process. In this study, nanoporous gold electrode, prepared from commercially available gold-made compact disk, is utilized as the anode in a two-chamber MFC. The performance of nanoporous gold electrode in the MFC is compared with that of gold film, carbon felt and acid-heat-treated carbon felt electrodes which are usually employed as the anode in the MFCs. Electrochemical surface area of nanoporous gold electrode exhibits a 7.96-fold increase rather than gold film electrode. Scanning electron microscopy analysis also indicates the homogeneous biofilm is formed on the surface of nanoporous gold electrode, while the biofilm formed at the surface of acid-heat-treated carbon felt electrode shows rough structure. Electrochemical studies show although modifications applied on carbon felt electrodes improve its performance, nanoporous gold electrode, due to its structure and better electrochemical properties, acts more efficiently as the MFC’s anode. The maximum power density produced by nanoporous gold anode is 4.71 mW m^?2 at current density of 16.00 mA m^?2, while this value for acid-heat-treated carbon felt anode is 3.551 mW m^?2 at current density of 9.58 mA m^?2.     

Hybrid Hydrogels of Porous Graphene and Nickel Hydroxide as Advanced Supercapacitor Materials

Graphene‐based hydrogels can be used as supercapacitor electrodes because of their excellent conductivity, their large surface area and their high compatibility with electrolytes. Nevertheless, the large aspect ratio of graphene sheets limits the kinetics of processes occurring in the electrode of supercapacitors. In this study, we have introduced in‐plane and out‐of‐plane pores into a graphene–nickel hydroxide (Ni(OH)₂) hybrid hydrogel, which facilitates charge and ion transport in the electrode. Due to its optimised chemistry and architecture, the hybrid electrode demonstrates excellent electrochemical properties with a combination of high charge storage capacitance, fast rate capability and stable cycling performance. Remarkably, the Ni(OH)₂ in the hybrid contributes a capacitance as high as 3138.5 F g^?1, which is comparable to its theoretical capacitance, suggesting that such structure facilitates effectively charge‐transfer reactions in electrodes. This work provides a facile pathway for tailoring the porosity of graphene‐based materials for improved performances. Moreover, this work has also furthered our understanding in the effect of pore and hydrogel structures on the electrochemical properties of materials.     

Phase transition in porous electrodes. II. Effect of asymmetry in the ion size

The electrochemical thermodynamics of electrolytes in porous electrodes is qualitatively different from that in the bulk with planar electrodes when the pore size is comparable to the size of the electrolyte ions. In this study, the effect of the ion size asymmetry on the thermodynamics in porous electrodes was studied by using Monte Carlo simulation. We used the electrolyte ions for which the size of the cations and that of anions is different. Due to the asymmetry in the ion size, the ionic structure and the way the surface charge is distributed on the electrode surfaces were found to be qualitatively different in the cathode and in the anode. In particular, for some ranges of applied voltage, the distribution of the surface charge induced on the electrode planes shows inhomogeneity, which is not intrinsic to the structure of the porous electrodes. The transition from the homogeneous to the inhomogeneous distribution of surface charge on changing the voltage is a second order phase transition.     

A review on the development of a porous carbon-based as modeling materials for electric double layer capacitors

Carbon electrodes are a key factor for electric double layer capacitors (EDLCs). Carbon gels have high porosity with a controllable pore structure by changing synthesis conditions and modifying preparation processing to improve the electrochemical performance of EDLCs. This review summarizes the preparation of carbon gels and their derivatives, the criteria to synthesize high surface area in each process, the development by some carbon forms, and EDLC applications. Porous carbons are also prepared as model materials by concentrating on how pore structure increases electrochemical capacitance, such as electronic and ion resistance, the tortuosity of pore channel, suitable micropore and mesopore sizes, and mesopore size distribution. This review emphasizes the significance of pore structures as the key factor to allow for the design of suitable pore structures that are suitable as the carbon electrode for EDLCs.     

Synthesis and electrochemical performance of nanoporous Li4Ti5O12 anode material for lithium-ion batteries

Nanoporous Li₄Ti₅O₁₂ (N-LTO) was prepared by sol–gel method using monodisperse polystyrene spheres as a template and followed by calcination process. The as-prepared N-LTO has a spinel structure, large special surface area, and nanoporous structure with the pore average diameter of about 100?nm and wall thickness of 50?nm. Electrochemical experiments show that N-LTO exhibits a high initial discharge capacity of 189?mAh?g^?1 at 0.1?C rate cycled between 0.5 and 3.0?V and excellent capacity retention of 170?mAh?g^?1 after 100?cycles. EIS and CV analysis show that N-LTO has a higher mobility for Li⁺ diffusion and a higher exchange current density, indicating an improved electrochemical performance. It is believed that the nanoporous structure has a larger electrode/electrolyte contact area, resulting in better electrochemical properties at high charge/discharge rates.     

From metal-organic framework to nanoporous carbon: toward a very high surface area and hydrogen uptake

In this work, with a zeolite-type metal-organic framework as both a precursor and a template and furfuryl alcohol as a second precursor, nanoporous carbon material has been prepared with an unexpectedly high surface area (3405 m(2)/g, BET method) and considerable hydrogen storage capacity (2.77 wt % at 77 K and 1 atm) as well as good electrochemical properties as an electrode material for electric double layer capacitors. The pore structure and surface area of the resultant carbon materials can be tuned simply by changing the calcination temperature.     

Phase transition in porous electrodes

It is shown by Monte Carlo simulation that electrochemical thermodynamics of electrolytes in a porous electrode is qualitatively different from that in the bulk with a planar electrode. In particular, first order phase transitions occur in porous electrodes when the pore size is comparable to the ion size of the electrolytes: as the voltage is increased from zero, the surface charge density and the ion density in the porous electrodes discontinuously change at a specific voltage. The critical points for those phase transitions are identified.     

Nanoconfinement effects in electrochemical reactions

Nanostructuring materials in the aims to enhance its catalytic activity has long been indispensable in electrocatalyst development. In particular, nanoporous electrodes with numerous pores in the nanoscale, are widely utilized owing to its enlarged surface area as well as activated surface characteristics. In the geometrical point of view, nanocavities of nanoporous electrodes offer unique spatial environment that confine reactant molecules, resulting in enhanced interaction between the reactant molecule and the electrode surface. Such electrocatalytic effects stemming from the morphology of nanoporous electrodes have been denoted as nanoconfinement effects. This review introduces the concept of nanoconfinement effects in electrochemical systems, the recent progress, and perspectives in this field.     

Protein adsorption on nanoporous TiO2 films: a novel approach to studying photoinduced protein/electrode transfer reactions

We have investigated the use of nanoporous TiO2 films as substrates for protein immobilisation. Such films are of interest due to their high surface area, optical transparency, electrochemical activity and ease of fabrication. These films moreover allow detailed spectroscopic study of protein/electrode electron transfer processes. We find that protein immobilisation on such films may be readily achieved from aqueous solutions at 4 degrees C with a high binding stability and no detectable protein denaturation. The nanoporous structure of the film greatly enhances the active surface area available for protein binding (by a factor of up to 850 for an 8 microns thick film). We demonstrate that the redox state of proteins such as immobilised cytochrome-c (Cyt-c) and haemoglobin (Hb) may be modulated by the application of an electrical bias potential to the TiO2 film, without the addition of electron transfer mediators. The binding of Cyt-c on the TiO2 films is investigated as a function of film thickness, protein concentration, protein surface charge and ionic strength. We demonstrate the potential use of immobilised Hb on such TiO2 films for the detection of dissolved CO in aqueous solutions. We further show that protein/electrode electron transfer may be initiated by UV bandgap excitation of the TiO2 electrode. Both photooxidation and photoreduction of the immobilised proteins can be achieved. By employing pulsed UV laser excitation, the interfacial electron transfer kinetics can be monitored by transient optical spectroscopy, providing a novel probe of protein/electrode electron transfer kinetics. We conclude that nanoporous TiO2 films may be useful both for basic studies of protein/electrode interactions and for the development of novel bioanalytical devices such as biosensors.     

由微孔棒状羟基磷灰石为模板合成的新型层次孔炭材料的电化学电容性能

电化学电容器已经成为极具潜力的可满足高功率需求的储能系统器件. 多孔炭具有大比表面积、高导电性、化学惰性、廉价及可调孔结构等优势, 因此成为电化学电容器最为常用的电极材料. 本文报道由微孔棒状羟基磷灰石为模板及蔗糖为碳源合成的新型具有层次孔道结构的孔炭材料的电化学电容器的性能. 采用X射线衍射分析仪、扫描电子显微镜、透射电子显微镜、X射线光电子能谱及BET表面分析仪表征了合成的多孔炭的形貌及表面特性. 采用循环伏安法、交流阻抗图谱分析及恒流充放电评价多孔炭材料在1 mol·L^-1硫酸中的电化学电容性能. 多孔炭具有高的比表面积(719.7 m²·g^-1)和大的孔容(1.32 cm³·g^-1), 其无序的孔道由任意分布的微孔、坍塌的中孔及类模板形状的相互交织的棒状中孔组成. 随着炭化温度的增加, 微孔及棒状中孔的密度随之降低, 在炭化温度高达900℃时, 孔径分布图上出现了三个峰. 正是由于这些特殊的结构特征, 由900℃炭化得到的多孔炭制成的电极展示出很好的电化学电容性能.     

Oxygen Evolution Reaction on Nanoporous Gold Modified with Ir and Pt: Synergistic Electrocatalysis between Structure and Composition

Active oxygen evolution reaction electrocatalysts for water splitting have received great attention because of their importance in the utilization of renewable energy sources. Here, the electrochemical oxygen evolution reaction activities of a nanoporous gold (NPG)‐based electrode in acidic media are investigated. The dependence of the oxygen evolution reaction activity on the NPG surface area shows that the large electrochemical surface areas of the NPG are effectively utilized to enhance electrocatalytic activity. The NPG surfaces are modified with Pt using atomic layer electrodeposition methods, and the resulting NPG@Pt exhibited enhanced electrocatalytic activities compared to those of the NPG and flat Pt electrodes. Ir‐modified NPG (NPG@Ir) electrodes are prepared by spontaneous exchange of Ir on NPG surfaces and exhibit enhanced electrocatalytic activity compared to that of flat Ir surfaces. The modification of NPG@Pt with Ir results in NPG@Pt/Ir electrodes, and their electrocatalytic activities exceed those of NPG@Ir. The enhanced oxygen evolution reaction activity on NPG@Pt/Ir over that on NPG@Ir surfaces is examined by X‐ray photoelectron spectroscopy. The oxygen evolution reaction activity on NPG@Pt/Ir surfaces demonstrates synergistic electrocatalysis between the nanoporous surface structure and active electrocatalytic components.     

Interactive effects of pore size control and carbonization temperatures on supercapacitive behaviors of porous carbon/carbon nanotube composites

Porous carbon-based electrodes were prepared by carbonization with poly(vinylidene fluoride) (PVDF)/carbon nanotube (CNT) composites to further increase the specific capacitance for supercapacitors. The specific capacitance, pore size distribution, and surface area of the PVDF/CNT composites were measured, and the effect of the carbonization temperatures was examined. The electrochemical properties were examined by cyclic voltammetry, impedance spectroscopy, and galvanostatic charge-discharge performance using a two-electrode system in TEABF(4) (tetraethylammonium tetrafluoroborate)/acetonitrile as a non-aqueous electrolyte. The highest specific capacitance of ～101 Fg(-1) was obtained for the samples carbonized at 600 °C. The pore size of the samples could be controlled to below 7 nm through the carbonization process. This suggests that micropores make a significant contribution to the specific capacitance due to improved charge transfer between the pores of the electrode materials and the electrolyte.     

焦粉活性炭/Al-Ni(OH)2复合电极材料的制备及其超级容器性能

以焦粉为原料,用HNO3预处理除灰,采用KOH浸渍-煅烧活化法制备焦粉活性炭(CPAC),通过场发射扫描电子显微镜、X射线衍射等表征其形貌,采用BET测试其比表面积、孔结构及孔径分布。初步考察了活化温度、活化时间等对焦粉活性炭电极材料电化学性能的影响。采用共沉淀法制备CPAC/Al-Ni(OH)2复合电极材料,通过恒电流充放电测试及循环伏安测试表征CPAC/Al-Ni(OH)2复合电极材料的电化学性能。结果表明,当活化温度为800℃、活化时间为3 h制得的焦粉活性炭电极材料的电化学性能最佳,比电容达到211 F/g。CPAC-800℃-3 h/Al-Ni(OH)2复合电极材料随Al掺杂量的增大呈现先增大后减小的趋势。在固定Al质量掺杂量为4%,炭镍质量比为1∶1时所得复合材料的比电容量最大:1173.6 F/g。恒电流充放电及循环伏安测试表明Al掺杂量为4%、炭镍比为1∶1的复合材料具有较好的电化学性能。     

高容量超级电容器电极材料的设计与制备

超级电容器寿命长,安全性高,并可以实现快速充放电,是化学电源研究的热点之一。然而,超级电容器的能量密度较低限制了其更多的应用。因此,超级电容器领域的研究关注点在如何提高超级电容器的能量密度。其中,提高比容量是提高能量密度的一种有效途径。本文通过对电极材料和电解液的优化来研究制备得到高容量超级电容器的方法。电极材料的比表面积、孔道结构和导电性对其电化学性能有着直接的影响。一方面,通过优化电极材料的孔道结构和比表面积可以增加活性位点并提高电解液离子传导率,从而得到高比电容。另一方面,电极材料导电性的提高有利于提升其电子传导率从而得到较高的比容量。本文分别对碳材料和金属氧化物/氢氧化物的优化达到了增加双电层电容和赝电容的目的。不仅如此,还可以通过在电解液中增加氧化还原电对从而得到高比电容。这一方法为高容量超级电容器的制备提供了新的思路。     

Highly conductive nanostructured C-TiO2 electrodes with enhanced electrochemical stability and double layer charge storage capacitance

The present work reports the structural and electrochemical properties of carbon-modified nanostructured TiO(2) electrodes (C-TiO(2)) prepared by anodizing titanium in a fluoride-based electrolyte followed by thermal annealing in an atmosphere of methane and hydrogen in the presence of Fe precursors. The C-TiO(2) nanostructured electrodes are highly conductive and contain more than 1 × 10(10) /cm(2) of nanowires or nanotubes to enhance their double layer charge capacitance and electrochemical stability. Electrogenerated chemiluminescence (ECL) study shows that a C-TiO(2) electrode can replace noble metal electrodes for ultrasensitive ECL detection. Dynamic potential control experiments of redox reactions show that the C-TiO(2) electrode has a broad potential window for a redox reaction. Double layer charging capacitance of the C-TiO(2) electrode is found to be 3 orders of magnitude higher than an ideal planar electrode because of its high surface area and efficient charge collection capability from the nanowire structured surface. The effect of anodization voltage, surface treatment with Fe precursors for carbon modification, the barrier layer between the Ti substrate, and anodized layer on the double layer charging capacitance is studied. Ferrocene carboxylic acid binds covalently to the anodized Ti surface forming a self-assembled monolayer, serving as an ideal precursor layer to yield C-TiO(2) electrodes with better double layer charging performance than the other precursors.     

Carbon materials for supercapacitor application

The most commonly used electrode materials for electrochemical capacitors are activated carbons, because they are commercially available and cheap, and they can be produced with large specific surface area. However, only the electrochemically available surface area is useful for charging the electrical double layer (EDL). The EDL formation is especially efficient in carbon pores of size below 1 nm because of the lack of space charge and a good attraction of ions along the pore walls. The pore size should ideally match the size of the ions. However, for good dynamic charge propagation, some small mesopores are useful. An asymmetric configuration, where the positive and negative electrodes are constructed from different materials, e.g., activated carbon, transition metal oxide or conducting polymer, is of great interest because of an important extension of the operating voltage. In such a case, the energy as well as power is greatly increased. It appears that nanotubes are a perfect conducting additive and/or support for materials with pseudocapacitance properties, e.g. MnO(2), conducting polymers. Substitutional heteroatoms in the carbon network (nitrogen, oxygen) are a promising way to enhance the capacitance. Carbons obtained by one-step pyrolysis of organic precursors rich in heteroatoms (nitrogen and/or oxygen) are very interesting, because they are denser than activated carbons. The application of a novel type of electrolyte with a broad voltage window (ionic liquids) is considered, but the stability of this new generation of electrolyte during long term cycling of capacitors is not yet confirmed.     

Electroanalysis based on stand-alone matrices and electrode-modifying films with silica sol-gel frameworks: a review

Silica sol-gel matrices and its organically modified analogues that contain aqueous electrolytes, ionic liquids, or other ionic conductors constitute stand-alone solid-state electrochemical cells when hosting electrodes or serve as modifying films on working electrodes in conventional cells. These materials facilitate a wide variety of analytical applications and are employed in various designs of power sources. In this review, analytical applications are the focus. Solid-state cells that serve as gas sensors, including in chromatographic detectors of gas-phase analytes, are described. Sol-gel films that modify working electrodes to perform functions such as hosting electrochemical catalysts and acting as size-exclusion moieties that protect the electrode from passivation by adsorption of macromolecules are discussed with emphasis on pore size, structure, and orientation. Silica sol-gel chemistry has been studied extensively; thus, factors that control its general properties as frameworks for solid-state cells and for thin films on the working electrode are well characterized. Here, recent advances such as the use of dendrimers and of nanoscale beads in conjunction with electrochemically assisted deposition of silica to template pore size and distribution are emphasized. Related topics include replacing aqueous solutions as the internal electrolyte with room-temperature ionic liquids, using the sol-gel as an anchor for functional groups and modifying electrodes with silica-based composites.

     

Influence of nanoporous carbon electrode thickness on the electrochemical characteristics of a nanoporous carbon|tetraethylammonium tetrafluoroborate in acetonitrile solution interface

Electrochemical characteristics for the nanoporous carbon|Et₄NBF₄+acetonitrile interface have been studied by cyclic voltammetry and impedance spectroscopy methods. The influence of the electrolyte concentration and thickness of the nanoporous electrode material on the shape of the cyclic voltammetry and impedance curves has been established and the reasons for these phenomena are discussed. A value of zero charge potential, depending slightly on the structure and concentration of the electrolyte, the region of ideal polarizability and other characteristics have been established. The nanoporous nature of the carbon electrodes introduces a distribution of resistive and capacitive elements, giving rise to complicated electrochemical behaviour. Analysis of the complex plane plots shows that the nanoporous carbon|Et₄NBF₄+acetonitrile electrolyte interface can be simulated by an equivalent circuit, in which two parallel conduction paths in the solid and liquid phases are interconnected by the double-layer capacitance in parallel with the complex admittance of the hindered reaction of the charge transfer or of the partial charge transfer (i.e. adsorption stage limited) process. The values of the characteristic frequency depend on the electrolyte concentration and electrode potential, i.e. on the nature of the ions adsorbed at the surface of the nanoporous carbon electrode. The value of the solid state phase resistance established is independent of the thickness of the electrode material.     

氯化锌活化对炭气凝胶微球的结构与电化学性能的影响

对炭气凝胶微球在高温下进行氯化锌活化改性,并用于制作超级电容器的电极。采用扫描电镜、N2物理吸附-脱附等对炭气凝胶微球的形貌结构进行表征,采用循环伏安、恒流充放电等测定了材料的电化学性能。结果表明,氯化锌活化有效地改善了炭气凝胶微球的孔结构,通过增加炭气凝胶微球的微孔面积和体积,提高了材料的比表面积和孔隙率。经过氯化锌活化,炭气凝胶微球的电化学性能也随之得到提高,电阻明显减小,比电容提高了2倍以上。     

Electrochemical impedance spectroscopy studies of organic-solvent-induced permeability changes in nanoporous films derived from a cylinder-forming diblock copolymer

In this paper we report electrochemical investigations of the influence of organic solvents dissolved in aqueous solution on the permeability of nanoporous films derived from a cylinder-forming polystyrene-poly(methyl methacrylate) diblock copolymer (CF-PS-b-PMMA). The nanoporous films (ca. 30 nm in pore diameter) were prepared on planar gold electrodes via UV-based degradation of the cylindrical PMMA domains of annealed CF-PS-b-PMMA films (30-45 nm thick). The permeability of the electrode-supported nanoporous films was assessed using cyclic voltammetry and electrochemical impedance spectroscopy (EIS). The faradic current of Fe(CN)(6)(3-/4-) decreased upon immersion in aqueous solutions saturated with toluene or methylene chloride (5.8 mM and 0.20 M, respectively). EIS data indicated that the decrease in faradic current mainly reflected an increase in the pore resistance (R(pore)). In contrast, R(pore) did not change in a saturated n-heptane solution, 0.17 M ethanol, or 5.8 mM aqueous solutions of methylene chloride, diethyl ether, methyl ethyl ketone, or ethanol. Atomic force microscopy images of a nanoporous film in aqueous solution with and without 5.8 mM toluene showed a reversible change in the surface morphology, which was consistent with a toluene-induced change in R(pore). The solvent-induced increase in R(pore) was attributed to the swelling of the nanoporous films by the organic solvents, which decreased the effective pore diameter. The reversible permeability changes suggest that the surface of CF-PS-b-PMMA-derived nanoporous films can be functionalized in organic environments without destroying the nanoporous structure. In addition, the solvent-induced swelling may provide a simple means for controlling the permeability of such nanoporous films.