Colloidal Electrode Research Articles

Polyethylene glycol-based colloidal electrode via water competition for ultra-stable aqueous Zn-I batteries

Polyethylene glycol-based colloidal electrode via water competition for ultra-stable aqueous Zn-I batteries

Sustainable iron production via highly efficient low-temperature electrolysis of 3D conductive colloidal electrodes

Low temperature electrolysis at 100 °C with 3D-conductive Fe2O3 colloidal electrodes is used to produce high purity Fe powder and other metal powders with no direct CO2 emission.

Sustainable Iron Production by Low Temperature Electrolysis of Fe2O3 Colloidal Electrode

Fe is one of the most important metals that has been used in nearly every construction of man. Currently, Fe is manufactured by a carbothermic reduction by which Fe2O3 ores and carbon are reduced at >2000°C in a blast furnace. This conventional method is environmentally hazardous as it emits almost 2 tons of CO2 per every ton of crude iron produced, accounting for 5% of global CO2 emission. With the goal of zero CO2 emission and sustainable development, more advanced technologies of Fe manufacturing are urgently required. Herein, we introduce a novel and sustainable Fe production using a low temperature electrolysis (100°C) of Fe2O3 colloidal electrode. The Fe2O3 colloid with an electronic-ionic conductive network was successfully fabricated which contains Fe2O3 electrochemically active species, carbon and NaOH solution. Carbon acts as an electronic conductor while NaOH solution serves as an ionic conductor. This electrode design helps increase reactive areas for the Fe2O3 reduction process resulting in fast reaction rate. In addition, some organic and inorganic additives were added to enhance an electrolysis efficiency via promoting the reaction and suppressing H2 evolution parasitic reaction. This method can produce high purity Fe powder with a high current efficiency of 95%. Our zero CO2 emission method is much greener, and less energy consumptive than the conventional carbothermic process, which potentially revolutionizes the iron and steel industry that has a history of environmental consciousness for many decades.

Crystallization design of multicale electrode materials forelectrochemical energy storage

<p indent="0mm">Electrochemical energy storage devices include solid/gas/liquid interface reactions, electron, ion and mass transmission processes, which were across a range of micro-meso-macro scales. The macro-electrochemical properties of electrode materials are the comprehensive manifestations of different scale influence factors. From the crystallization point of view, this article introduces the crystal structure, interface structure and three-dimensional structure which are beneficial to ion and electron transfer, and develops a new type of colloidal electrode material, which strengthens the electrochemical properties of electrode material. Guided by functional application, integrating atomic molecules, materials and devices to design multiscale electrode materials is one of the directions to solve the problems faced by electrochemical energy storage devices.

High specific capacitance of manganese-based colloidal system with rare earth modification

Ever-increasing global energy consumption has increased aggregate demand on electrochemical energy storage devices with high energy density. Over the past few decades, manganese oxides have attracted wide attention due to their abundant reserves, low cost, environmental friendliness, and high theoretical capacity. However, most reported manganese-based materials have exhibited capacity far below the theoretical capacity, which was only on the basis of Mn3+/Mn4+ couple. The rich chemistry of manganese enables it to exist in various valence states, such as Mn0, Mn2+, Mn3+, Mn4+, and Mn7+, providing great opportunity for discovering new manganese-based electrode systems. Herein, we formed a Mn2+/Mn4+ couple from a manganese-based colloidal system with rare earth (RE) modification, which was formed in-situ on nickel (Ni) foam in KOH electrolyte under an electric field assistance. The Mn-based colloidal electrode, with Mn:Ce mass ratio of 1:0.5, achieved a high specific capacitance of 2985 F g–1 at 3 A g–1, which was higher than the theoretical capacity of 2193 F g–1 on the basis of the Mn3+/Mn4+ couple. After the addition of Ce3+, the prepared sample exhibited improved rate capability performance. Our manganese-based colloidal electrode with RE modification delivered a high specific capacitance of 1223 F g–1 at 20 A g–1, with 54.5% retention of 2243 F g–1 at 3 A g–1 at Mn:Ce mass ratio of 1:0.05. Colloidal electrode systems involving Mn-based colloids are a novel way to engineer the electrochemical performance of inorganic materials.

A Flexible and Ultrahigh Energy Density Capacitor via Enhancing Surface/Interface of Carbon Cloth Supported Colloids

AbstractPseudocapacitors are now reaching the energy density limits set by the surface redox reaction of their electrode materials, requiring new cation paradigms for a fast cation Faradaic reaction with high capacitance. In this work, a flexible and ultrahigh energy density capacitor is reported via enhancing surface/interface of active colloids and supported carbon cloth. A flexible asymmetrical capacitor assembled with Ni2+ colloidal cathode and Fe3+ colloidal anode displays a high energy density of 353 W h kg−1 at the power density of 2250 W kg−1, outperforming recent reported pseudocapacitors, and shows superior cycling stability after 10 000 charge–discharge cycles at current density of 30 A g−1. This work demonstrates that the optimized surface/interface of carbon cloth and colloids can lead to the enhancement of both stability and activity of colloidal electrode.

Colloidal paradigm in supercapattery electrode systems

Among decades of development, electrochemical energy storage systems are now sorely in need of a new design paradigm at the nano size and ion level to satisfy the higher energy and power demands. In this review paper, we introduce a new colloidal electrode paradigm for supercapattery that integrates multiple-scale forms of matter, i.e. ion clusters, colloidal ions, and nanosized materials, into one colloid system, coupled with multiple interactions, i.e. electrostatic, van der Waals forces, and chemical bonding, thus leading to the formation of many redox reactive centers. This colloidal electrode not only keeps the original ionic nature in colloidal materials, but also creates a new attribute of high electroactivity. Colloidal supercapattery is a perfect application example of the novel colloidal electrode, leading to higher specific capacitance than traditional electrode materials. The high electroactivity of the colloidal electrode mainly comes from the contribution of exposed reactive centers, owing to the confinement effect of carbon and a binder matrix. Systematic and thorough research on the colloidal system will significantly promote the development of fundamental science and the progress of advanced energy storage technology.

SURFACE–INTERFACE REACTION OF SUPERCAPACITOR ELECTRODE MATERIALS

Facing the challenge of low energy density of conventional electric double layer supercapacitors, researchers have long been focusing on the development of novel pseudocapacitive electrode materials with higher energy densities. Since capacitive charge storage reaction mostly occurs on the interface of electrode and electrolyte, the interface chemistry determines the achievable power and energy densities of a supercapacitor. Consequently, understanding of surface–interface reaction mechanism is a key towards efficient design of high-performance supercapacitor electrode materials. In this paper, we have reviewed the recent advances in the understanding of surfaces–interfaces in the system of pseudocapacitive supercapacitors. With significant research advancements in the understanding of surface–interface of supercapacitors, novel colloidal electrode materials with improved surface–interface structures have been developed in our previous work, which have the potential to deliver both high energy and power densities. This review aims to provide an in-depth analysis on the surface–interface control approaches to improve the energy and power densities of supercapacitors.

In situ electrochemical activation of Ni-based colloids from an NiCl2 electrode and their advanced energy storage performance.

The formation of electrochemical activated cations in electrode materials to induce multiple-electron transfer reactions is a challenge for high-energy storage systems. Herein, highly electroactive Ni-based colloidal electrode materials have been synthesized by in situ electrochemical activation of a NiCl2 electrode. The highest specific capacitance of the activated Ni-based electrodes was 10 286 F g-1 at a current density of 3 A g-1, indicating that a three-electron Faradaic redox reaction (Ni3+ ↔ Ni) occurred. Upon potential cycling and constant potential activation, a decrease in the charge transfer resistance can be found. Activation and utilization of multiple-electron reactions is an efficient route to increase the energy density of supercapacitors. This newly designed colloidal pseudocapacitor is compatible with inorganic pseudocapacitor chemistry, which enables us to use metal cations directly via their commercial salts rather than their oxide/hydroxide compounds.

Low temperature electrolysis for iron production via conductive colloidal electrode

In the process of low temperature electrolysis of Fe2O3, an electrical-ionic conductive colloidal electrode containing the electrochemically active species, the liquid electrolyte and a percolating electrical conductor has been successfully fabricated and used to produce Fe.

A colloidal pseudocapacitor: Direct use of Fe(NO3)3 in electrode can lead to a high performance alkaline supercapacitor system

An electrochemical system including functioned Fe(NO3)3 and alkaline electrolyte is constructed to study the charge storage mechanism upon both thermodynamic calculations and electrochemical measurements. The thermodynamic calculation results demonstrate that increasing KOH concentration of alkaline electrolyte can enhance electrolyte activity but decrease the peak potential, which agrees well with that of electrochemical measurement. The present results indicate that the proposed pseudocapacitive redox reactions are between Fe3+ and Fe2+ in our salt electrode of Fe(NO3)3 system, in which the solid Fe3+ in FeOOH colloids serves as the active anode component and free Fe3+ on the colloidal electrodes serves as the cathode component. The active central ions of Fe3+ in Fe(NO3)3⋅9H2O can be fixed on the electrodes by the surrounding ligands (OH− and NO3−) and can be in-situ transformed into colloidal Fe4NO3(OH)11 and goethite (α-FeOOH). Electrochemical results indicate that the current proposed colloidal pseudocapacitor system warrants the high-efficiency utilization of electroactive central Fe3+ ions, showing high energy density of 58.4Wh/kg at the power density of 8.4kW/kg as an anode material. Meanwhile, our designed pseudocapacitor system can function well as a supercapacitor cathode. This colloidal pseudocapacitor system can offer a facile and efficient route for the design of advanced supercapacitors.

Fine microstructure of high performance electrode in alkaline anion exchange membrane fuel cells

The electrode fabrication and resulting microstructure are the main determinates of the performance of alkaline anion exchange membrane fuel cells (AAEMFCs). In the present work, the electrode microstructure is adjusted by the ionomer content in catalyst layers as well as the dispersion solvent for catalyst inks. The ionomer content shows a strong influence on the cell active, ohmic and mass-diffusion polarization losses. Especially, an in-suit proof for the ionomer as the hydroxide conductor is first given by the cell cycle voltammogram, and the optimum content is 20 wt.%. Meanwhile, it is found that the ionomer either dissolves in the dielectric constant ɛ = 18.3–24.3 solutions (including ethanol, propanol and isopropanol) or disperses in the n-butyl acetate (ɛ = 5.01) colloid. Compared with these electrodes using the solution method, the colloidal electrode tends to form the larger catalyst/ionomer agglomerates, increased pore volume and pore diameter, continuous ionomer networks for hydroxide conduction, and correspondingly decreased ohmic and mass-diffusion polarization losses. Ultimately, when employing the optimum ionomer content and the colloid approach, the highest peak power density we achieved in AAEMFC is 407 mW cm−2 at 50 °C, which can be taken as a considerable success in comparison to the current results in publications.

Efficient electrocatalytic oxidation of water: minimization of catalyst loading by an electrostatic assembly of hydrous iridium oxide colloids

Exploiting an effective catalyst has been an essential and significant task in the development of electrochemical water oxidation. A highly electrocatalytic iridium oxide colloidal electrode, prepared by the electrostatic assembly fashion, is reported herein. Poly(allylamine hydrochloride) (PAH) was utilized to facilitate the formation of stable PAH/iridium oxide colloid clusters, resulting in a high catalytic utility (turnover efficiency of 6.36 ± 0.25 s−1 at low overpotential, η = 0.28 V) towards the oxygen evolution reaction (OER), with the smallest Ir loading (Γcov = 2.3 × 10−9 mol cm−2) of any yet reported. A variety of examinations and approaches were conducted to gain better understanding of such electrostatically assembled architecture and to identify hexahydroxyiridate(IV), [Ir(OH)6]2−, as the key active catalytic species.

Preparation of Pt Colloids via a Wet-Chemical Method for Methanol Sensor

Pt colloids were synthesized by a wet-chemical method. The Pt colloids were modified on the glassy carbon electrode (GCE). The electrochemical behavior and electrocatalyst for methanol of the colloidal Pt-modified electrode in H2SO4medium were investigated. The results show that the as-prepared Pt colloids are good electrocatalysts for methanol oxidation and the oxidation current increases with methanol concentration in the range of 0.002 to 0.5 M. The colloidal Pt-modified electrode is simple, easy-to-use and reusable, showing promising applications in the electrocatalyst and determination of methanol.

Cathodic behaviour of CoFe2O4 spinel electrodes in alkaline medium

Spinel type CoFe2O4 thin films have been prepared, on stainless steel supports, by thermal decomposition of aqueous solutions of mixed cobalt and iron nitrates in 1:2 molar ratio at 400 °C. The electrochemical behaviour of the CoFe2O4/1 M KOH interface was investigated by cyclic voltammetry, chronoamperometry and impedance techniques. The studies allowed finding out the redox reactions occurring at the oxide surface. The results were compared with colloidal electrodes prepared by alkaline precipitation of Fe(II) or Fe(III) hydrous oxi-hydroxides on platinum electrodes. In addition, it has been concluded that the processes are diffusion-controlled and the diffusion of the hydroxide ion, through the oxide, acts as the rate-determining step. The diffusion coefficient of OH− through the oxide film was determined using cyclic voltammetry, chronoamperometry and electrochemical impedance spectroscopy techniques.

Mechanisms of Pu(VII) reduction in aqueous alkaline solutions in the presence of catalysts

Published data on the Pu(VII) stability in alkaline media suggest that one-electron oxidation of OH− ion or H2O with Pu(VII) ions is thermodynamically impossible. The more probable pathway of Pu(VII) reduction is formation of a dimer from thermodynamically excited and nonexcited Pu(VII) ions, followed by decomposition of the dimer into two Pu(VI) ions and H2O2 molecule, which reacts with Pu(VII) and Pu(VI). The released energy is spent for Pu(VII) excitation. In the presence of difficultly soluble hydroxides of Fe(III), Co(III), and other d elements, and also of Pt and PbO2, hydroxides of elements in higher oxidation states appear at the surface of colloidal particles and electrode materials under the action of Pu(VII). The neighboring OH groups dimerize and are eliminated in the form of H2O2.

Photoelectrochemical Analysis of Anion-Doped TiO2 Colloidal and Powder Thin-Film Electrodes

The photoelectrochemical characteristics of anion-doped powder and colloidal electrodes were investigated under UV and visible illumination. The solar absorption of was improved by synthesizing reduced forms of using anions of the main group elements (C, N, and P) to substitute for oxygen in the titania lattice. Analytical methods, including scanning electron microscopy, X-ray diffraction, elemental analysis, Raman, and UV–visible spectroscopy were employed to characterize these materials. The photoactivity of the electrodes was evaluated using a three-electrode configuration quartz photoelectrochemical cell using simulated solar irradiance. All anion-doped electrodes investigated, specifically C-, N-, and P-doped, increased the visible absorption of n-, leading to higher photoactivity under solar light. The addition of methanol to the electrolyte reduced the rapid charge recombination and hence enhanced the photocurrents. Although the efficiency is not yet comparable to single-crystal n-, optimization of the parameters studied here showed that significant increases in photoactivity could be achieved over the native powder.

Immunosensors Based on Layer‐by‐Layer Self‐Assembled Au Colloidal Electrode for the Electrochemical Detection of Antigen

AbstractColloidal Au particles have been deposited on the gold electrode through layer‐by‐layer self‐assembly using cysteamine as cross‐linkers. Self‐assembly of colloidal Au on the gold electrode resulted in an easier attachment of antibody, larger electrode surface and ideal electrode behavior. The redox reactions of [Fe(CN)6]4−/[Fe(CN)6]3− on the gold surface were blocked due to antibody immobilization, which were investigated by cyclic voltammetry and impedance spectroscopy. The interaction of antigen with grafted antibody recognition layers was carried out by soaking the modified electrode into a phosphate buffer at pH 7.0 with various concentrations of antigen at 37 °C for 30 min. Further, an amplification strategy to use biotin conjugated antibody was introduced for improving the sensitivity of impedance measurements. Thus, the sensor based on this immobilization method exhibits a large linear dynamic range, from 5–400 μg/L for detection of Human IgG. The detection limit is about 0.5 μg/L.

Spectroelectrochemical Measurements at Colloidal Au Multilayer Optically Transparent Electrodes

AbstractApplication of thin colloidal Au multilayers on glass substrates as optically transparent electrodes is reported herein. Evaluation of the electrode by scanning electron microscopy and as an optically transparent thin layer electrode (OTTLE) illustrate its use for spectroelectrochemical applications. A spectroelectrochemical Nernst plot acquired for the oxidation of o‐tolidine yielded a value of E°=0.605 V (vs. Ag/AgCl) and n=1.88. Both of these values are in excellent agreement with previously published values obtained using a traditional Au minigrid OTTLE. The colloidal Au multilayer electrode is expected to offer many advantages over the minigrid OTTLE in specific applications. These advantages include direct control over microscopic surface topography, large electrochemical surface area, applicability to many different electrode geometries, and increased microscopic surface roughness for SERS and SPR applications.

Electrochemical Behavior of Au Colloidal Electrode through Layer-by-Layer Self-Assembly

Electrodes formed by Au colloidal nanoparticles have been obtained by layer-by-layer self-assembly using 1,6-hexanedithiol as cross-linkers. Cyclic voltammograms show that the peak-to-peak separation decreases as the number of Au colloidal layers increases. After seven layers of Au colloidal particles have been deposited, the multilayer electrodes have the electrochemical properties of metallic Au and show ideal microelectrode behavior. An equivalent circuit for the electrochemical impedance spectroscopy was established to model the working electrode. It is evident that by increasing the layer number of Au colloidals, the interfacial electron transfer is promoted, implying the electron-transfer process changes from a kinetically limited process to a diffusionally limited process.