Anodic Deposition Research Articles

Electrochemical fabrication of metal–organic frameworks membranes and films: A review

Abstract Electrochemical fabrication is an important method for the preparation of metal-organic frameworks (MOFs) membranes and films. The method can be further divided into five categories: anodic deposition, cathodic deposition, conversion of electrosynthesized MOFs precursors, electrophoretic deposition, and galvanic displacement. In this article, the electrochemical fabrication methods and the applications of MOFs membranes and films were reviewed, and the existing challenges and outlook in this field were analyzed.

Electrochemically assisted hydrogel deposition, shaping and detachment

This work describes a facile approach allowing Dibenzoyl-l-Cystine (DBC) based hydrogel controlled deposition and controlled detachments over a conducting support. The method itself is an electrochemically assisted approach, where the water oxidation at the electrode surface results in a local pH drop inducing DBC gelation and hydrogel formation. We have comprehensively described the possibility of the hydrogel shaping by alternating the anodic deposition potential, DBC concentration and finally the working electrode geometry. The latter includes macro-electrodes in a form of platinum discs having diameter equal to 200 and 500 μm; hexagonal arrays of circular platinum microelectrodes with a diameter of a single electrode equal to 5 or 10 μm and custom made platinum microelectrodes, having the shape of circles, triangles and squares, that are used to shape the microgels. Over the course of our work we were able to define the conditions to form a number of different hydrogel shapes such as: (i) flat and planar deposits; (ii) hemispherical deposits with an oxygen bubble pocket; (iii) spongy hydrogel structures or (iv) hemispherical micro-cups build from radially oriented DBC fibres directionally growing from the support. Furthermore, we were also able to remotely form and then detach the hydrogel deposit in the initial formulation solution using only an electrochemical trigger. Our work represents a solid proof of concept and opens a number of new avenues for the electrochemically assisted soft matter fabrication down to micrometre scale.

Feasibility of removal of graphene oxide particles from aqueous suspensions by DC/AC electrocoagulation

Graphene oxide (GO) particulates offer an inexpensive route for the formation of graphene flakes. Their fine size and high degree of dispensability in aqueous media have raised environmental safety concerns in processing plants. This manuscript describes a novel electrocoagulation based method that enables the removal of GO particles from acidic aqueous suspensions in the form of copper-ion containing GO films. Specifically, copper ions were generated near a copper anode and adsorbed onto negatively surface-charged GO particles, driving the anodic deposition of GO films. The experimental variables included the type of electric field (DC and AC) and the use of a copper-ion induced bulk pre-coagulation step. A direct current (DC) potential gradient of 3 V/cm applied to a baseline suspension with a GO concentration of 0.8 mass percent solids removed approximately 3% of the GO particles in a minute in the form of compact films of thickness ranging from approximately 10 to 50 microns containing copper ions. Use of AC fields led to lower deposition rates and copper content. On the other hand, pre-coagulation of GO dispersions with copper ions led to films with enhanced copper concentrations. Characterization of GO films using XPS and Raman techniques has shown that copper is present in the bivalent form in GO.

(Invited) Metal Oxides and Composites for Chemical Sensing

In the field of advanced sensor technology, metal oxide nanostructures are promising materials due to their high charge carrier mobility, easy fabrication and excellent stability. In particular, most of them exhibit a reversible interaction between their surfaces and the surrounding atmosphere. This interaction may lead to a change of some different properties of the material, such as electrical conductance, capacitance, work function or optical characteristics. All metal oxides are in principle sensitive to gases if they are prepared in a sufficiently porous form (high surface to volume ratio and electrical properties controlled by surface states), but in order to be active material in chemical sensors they need to fulfill specific requirements such as sensitivity, selectivity, stability, fast response and recovery time.Further conductometric sensors are the cheapest devices that could be integrated into portable olfaction systems, due to their easy readout, small size and low cost. Depending on the materials they are based on, they could offer high sensitivity, but they often lack selectivity between different chemical species. Moreover, they sometimes have stability issues, due to high temperature required during normal operation (200-400°C). Furthermore, one dimensional (1D) semiconductor metal oxides such as nanowires (NWs) have been attracted great deal of attention in the field of chemical sensors due to their unique chemical/physical properties. In chemical sensor, surface of the active materials determines the sensor sensitivity toward specific gas analyte. The enhancement in the sensor response can be achieved by increasing the active surface area of the sensor. But there is still a lot of work going on regarding the preparation of nanostructured oxides, like controlling their morphology and position at the nanoscale level. Moreover, a major challenge is the reliable integration of quasi-1D nanostructures on specific transducers used to fabricate chemical sensors, assuring stable electrical contacts over long-term operation.Various strategies have been used to increase the gas response and selectivity, including modulating the sensing temperature, morphological control, catalyst doping/loading and catalytic filtering of interference gases. Another effective strategy to enhance the sensor response and selectivity is to construct the heterojunction between two different oxides that enables the control of conductivity at p-p, p-n, and n-n interfaces, and synergistic catalytic effects between different materials.The results of bringing together the properties of two different nanostructure materials into a single sensing platform by using a common, simple, low cost and high yield growth method will be presented. Herein, we report on the novel preparation and characterization of different nanostructures and hetrostructures morphologies such as NiO, WO3, Bi2O3 and ZnO NWs, (fig. 1)TiO2 nanotubes and NiO/ZnO branched 1D-1D nano-heterostructures and NiO/SnO2, CuO/ZnO Core-shell, SnO2/Go and WO3-doped with Nb (fig. 1). Several growth techniques have been used for the growth of different nanostructures: vapour phase evaporation and condensation, thermal oxidation, electrochemical anodization, hydrothermal synthesis and atomic layer deposition. The surface morphology of the nanostructures was investigated by using scanning electron microscopy (SEM) while, for structural characterization GI-XRD, the transmission electron microscopy (TEM), and XPS, Raman spectroscopy, UV-Vis spectroscopy. Finally, heterostructures based conductometric gas sensing devices have been fabricated and tested towards different gases spices such as (NO2, H2, CO, VOC’s) and their performance have been compared with literature and the host materials. Further in our recent work, the sensing properties of ZnO NWs were improved by functionalizing with 3-aminopropyl) trimethoxysilane (APTES). The whole process creates the amino (-NH2) terminated ZnO surface (SAM). These functionalized conductometric sensing devices showed excellent performance toward acetone and ethanol as compared to the pristine ZnO NWs.

(Invited) Promoted Nitrogen Photofixation over Periodic WS2@TiO2 Nanoporous Film

Atmospheric nitrogen fixation using a photocatalytic system is a promising approach to produce ammonia. However, most of the recently explored photocatalysts for N2 fixation are in powders, which suffer from particle agglomeration, difficulty in the collection, and unsatisfied conversion efficiency. To the best of our knowledge, rare research about the N2 photofixation over periodic nanostructured films has been reported. Compared with the powdered photocatalysts, the film materials have the inherent advantages over powders, including but not limited to easy transportation and collection. Moreover, the periodic nanostructured films are beneficial for providing photogenerated charge carriers with short diffusion length and favorable transport pathways, leading to superior photocatalytic performances. In this work, we reported the efficient photofixation of N2 over a periodic WS2@TiO2 nanoporous film, which was fabricated through a facile method combing anodization, E-beam evaporation and chemical vapor deposition (CVD). Oxygen vacancies were introduced into the TiO2 to improve the N2 adsorption and activation. The as-prepared WS2@TiO2 film with an optimized WS2 content shows highly efficient photocatalytic performance for N2 fixation with an NH3 evolution rate of 1.50 mmol g-1 h-1, representing one of the state-of-the-art catalysts. This study aims to explore efficient film materials for not only N2 photofixation but also other solar energy conversion applications.

Oxygen Evolution Anodes by Anodic Deposition Method for Hydrogen Production

Oxygen Evolution Anodes by Anodic Deposition Method for Hydrogen Production

Effect of gamma irradiation on the critical heat flux of nano-coated surfaces

An anodic electrophoretic deposition (EPD) technique is used to create a uniform TiO2 thin film coating on boiling thin steel plates (1.1 mm by 90 mm). All of the effective parameters except time of the EPD method are kept constant. To investigate the effect of gamma irradiation on the critical heat flux (CHF), the test specimens were irradiated in a gamma cell to different doses ranging from 100 to 300 kGy, and then SEM and BET analysis were performed. For each coated specimen, the contact angle and capillary length were measured. The specimens were then tested in a boiling pool for CHF and boiling heat transfer coefficient. It was observed that irradiation significantly decreases the maximum pore diameter while it increases the porosity, pore surface area and pore volume. These surface modifications due to gamma irradiation increased the CHF of the nano-coated surfaces compared to that of the unirradiated surfaces. The heat transfer coefficient (HTC) of the nano-coated surfaces irradiated at 300 kGy increased from 83 to 160 kW/(m2 K) at 885 kW/m2 wall heat flux by 100%. The CHF of the irradiated (300 kGy) and unirradiated surfaces are 2035 kW/m2 and 1583 kW/m2, respectively, an increase of nearly 31%.

Common mechanism for helical nanotube formation by anodic polymerization and by cathodic deposition using helical pores on silicon electrodes

We report that platinum-assisted chemical etching formed self-organized helical pores in silicon substrates can be utilized as platforms for the electrochemical production of nanohelices of conducting polymers (polypyrrole) and metals (gold). Surprisingly, the nanohelices thus created are tubes although the polymerization and deposition were carried out by anodic and cathodic reactions, respectively. Based on our results, we propose a common mechanism for the formation of tubular nanohelices by both anodic polymerization and cathodic deposition through the accumulation of reactants in microporous silicon which covers the wall surface of the helical pores.

Electrochromic modulation of plasmonic resonance in a PEDOT-coated nanodisk metasurface

The electrochromic modulation of plasmonic metasurfaces showing structural colors is a promising strategy to realize dynamic electronic reflective displays. However, hybridizing electrochromic polymers with large-area plasmonic metasurfaces remains challenging. In this study, we present a poly(3,4-ethylenedioxythiophene) (PEDOT)-coated gold nanodisk (PCGN) metasurface, which is fabricated based on techniques of large-area anodic aluminum oxide template-assisted deposition and electrochemical polymerization. Experimental and numerical results demonstrated that fast and reversible electrochromic modulation was realized within the PCGN metasurface. The wavelength control of the localized surface plasmon resonance of the PCGN metasurface originated from the electrically driven refractive index change of the PEDOT layer. The PCGN metasurface is promising for the high yield manufacturing of devices applied in dynamic reflective displays.

Calcium and phosphorous enrichment of porous niobium and titanium oxides for biomaterial applications

Anodic oxidation of niobium has been investigated in an electrolyte solution containing calcium phosphate and calcium acetate. The oxide layer morphology has been determined by combining 3D Atomic Force Microscopy images and cross-sectional Field Emission SEM measurements. The surface sensitivity of high-resolution X-ray Photoemission Spectroscopy has been exploited to evaluate the chemical composition of the outermost oxide surface, a key feature in view of implant development. Anodic Spark Deposition (ASD) results in the formation of micrometer-thick oxide layers showing a porous morphology suitable for osseointegration purposes. Increasing the maximum potential attained during oxidation leads to an increase of the oxide thickness and pore size accompanied by a noticeable surface enrichment with calcium and phosphorus. Remarkably, a maximal Ca/P ratio of 1.8 was achieved for anodization at 250 V, promising for osseointegration thanks to the similarity with hydroxyapatite stoichiometry. Parallel experiments performed on titanium under the same conditions indicated a maximal Ca/P ratio of 1.3 and pores of smaller dimensions. The comparative analysis suggests that niobium may represent a promising alternative to titanium to be explored for implant development.

Stress variations during polarization of iron thin film electrode in pH 8.4 borate buffer solution

The stress variations during polarization of iron thin film electrode in pH 8.4 borate buffer solution have been measured by a cantilever bending method to investigate the correlation between stress evolution and electrochemical reaction of the iron electrode. The stress variations toward compressive direction during active dissolution of iron result from the relaxation of the residual tensile stress due to the decrease in thickness of the iron electrode. The stress variations toward tensile direction in the pre-passive region are brought by the anodic deposition of ferrous ions once dissolved into solution. The successive potential steps for each interval of 1 h in the passive region between 0.20 and 0.90 V induce the stress variations toward compressive direction at potentials more positive than 0.30 V in connection with the growth of the inner (barrier) layer in the passive film. The electrostriction stress in the inner layer of the passive film formed on iron at 0.90 V has been estimated from the stress relaxation in the cathodic potential sweep after 1-h passivation at 0.90 V. In addition, the stress variations toward compressive direction during cathodic reduction of the passive film are attributed to the volume expansion due to the formation of iron (II) hydroxide at the intermediate step of the cathodic reduction at pH 8.4. Furthermore, the rapid stress variations toward compressive direction during hydrogen evolution at potentials more negative than 0.52 V are caused by the volume expansion in near the surface region of the iron thin film electrode due to hydrogen adsorption or absorption.

The Design of ZnO Nanorod Arrays Coated with MnOx for High Electrochemical Stability of a Pseudocapacitor Electrode.

Tremendous efforts have been made on the development of unique electrochemical capacitors or pseudocapacitors due to the overgrowing electrical energy demand. Here, the authors report a new and simple strategy for fabricating hybrid MnOx-coated ZnO nanorod arrays. First, the vertically aligned ZnO nanorods were prepared by chemical bath deposition (CBD) as a template providing a large surface area for active material deposition. The manganese oxide was subsequently coated onto the surface of the ZnO nanorods to form a hybrid MnOx-coated ZnO nanostructure by anodic deposition in a manganese acetate (MnA)-containing aqueous solution. The hybrid structure of MnOx-coated ZnO nanorod arrays exhibits a large surface area and high conductivity, essential for enhancing the faradaic processes across the interface and improving redox reactions at active MnOx sites. A certain concentration of the deposition solution was selected for the MnOx coating, which was studied as a function of deposition time. Cyclic voltammetry (CV) curves showed that the specific capacitance (SC) of the MnOx-coated ZnO nanostructure was 222 F/g for the deposition times at 10 s when the concentration of MnA solution was 0.25 M. The unique hybrid nanostructures also exhibit excellent cycling stability with >97.5% capacitance retention after 1200 CV cycles. The proposed simple and cost-effective method of fabricating hybrid nanostructures may pave the way for mass production of future intelligent and efficient electrochemical energy storage devices.

Electrochemical deposition as a universal route for fabricating single-atom catalysts

Single-atom catalysts (SACs) exhibit intriguing catalytic performance owing to their maximized atom utilizations and unique electronic structures. However, the reported strategies for synthesizing SACs generally have special requirements for either the anchored metals or the supports. Herein, we report a universal approach of electrochemical deposition that is applicable to a wide range of metals and supports for the fabrication of SACs. The depositions were conducted on both cathode and anode, where the different redox reactions endowed the SACs with distinct electronic states. The SACs from cathodic deposition exhibited high activities towards hydrogen evolution reaction, while those from anodic deposition were highly active towards oxygen evolution reaction. When cathodically- and anodically-deposited Ir single atoms on Co0.8Fe0.2Se2@Ni foam were integrated into a two-electrode cell for overall water splitting, a voltage of 1.39 V was required at 10 mA cm−2 in alkaline electrolyte.

Flexible 3D Electrodes of Free-Standing TiN Nanotube Arrays Grown by Atomic Layer Deposition with a Ti Interlayer as an Adhesion Promoter.

Nanostructured electrodes and their flexible integrated systems have great potential for many applications, including electrochemical energy storage, electrocatalysis and solid-state memory devices, given their ability to improve faradaic reaction sites by large surface area. Although many processing techniques have been employed to fabricate nanostructured electrodes onto flexible substrates, these present limitations in terms of achieving flexible electrodes with high mechanical stability. In this study, the adhesion, mechanical properties and flexibility of TiN nanotube arrays on a Pt substrate were improved using a Ti interlayer. Highly ordered and well-aligned TiN nanotube arrays were fabricated on a Pt substrate using a template-assisted method with an anodic aluminum oxide (AAO) template and atomic layer deposition (ALD) system. We show that with the use of a Ti interlayer between the TiN nanotube arrays and Pt substrate, the TiN nanotube arrays could perfectly attach to the Pt substrate without delamination and faceted phenomena. Furthermore, the I-V curve measurements confirmed that the electric contact between the TiN nanotube arrays and substrate for use as an electrode was excellent, and its flexibility was also good for use in flexible electronic devices. Future efforts will be directed toward the fabrication of embedded electrodes in flexible plastic substrates by employing the concepts demonstrated in this study.

Rational Construction of MnCo2O4.5 Deposited TiO2 Nanotube Array Heterostructures with Enhanced Photocatalytic Degradation of Tetracycline

AbstractA novel type of heterostructured photocatalyst, MnCo2O4.5 deposited TiO2 nanotube arrays (TNAs), was successfully synthesized via a two‐step anodization and chemical bath deposition method. The decoration of MnCo2O4.5 nanoparticles on anatase TNAs significantly enhances its photocatalytic degradation activity of tetracycline (TC). The optimized 140MnCo2O4.5/TiO2 nanotube arrays (140 M/TNA) catalyst exhibited the highest photocatalytic degradation of TC with an efficiency of 93.1 % after 2 h illumination. Meanwhile, the material showed good stability after a 5 cycle test. The mechanism of increased activity is attributed to the MnCo2O4.5/TiO2 heterostructure, which extends the response range to visible light and promotes electron–hole separation. Further radical capture experiment reveals that .O2− is vital as an active species for degrading TC in this system. The photocatalyst obtained via this rational synthesis strategy can effectively remove organic pollutants from waste water under visible light irradiation.

Study of 1D Titanate‐Based Materials –New Modification of the Synthesis Procedure and Surface Properties‐Recent Applications

AbstractThis paper represents a general study of titanate nanotubes (TiNTs) which are among the most important materials in the field of catalysis. This research work covers more than 100 publications about the formulation, characterisation and most recent applications of TiNTs. TiNTs can be prepared by different methods, namely the anodic deposition, sol‐gel template synthesis and alkaline hydrothermal treatment. The present study focuses on the preparation of this tubular structure by alkaline treatment, using the latest and most recent processes that have been introduced in this method (stirring, acid nature, annealing temperature, etc). The surface properties, such as the point of zero charge (P.Z.C), acid‐base nature and light absorption, of TiNTs are also evoked. In the end, some recent and important TiNTs applications in the field of renewable energies are reported (H2 production and methanation). In addition, NO reduction, CO oxidation, photocatalysis and organic synthesis are also mentioned. Therefore, it may be said that this paper is a structured study about TiNTs for the purpose of making the reader aware of their importance, understand their synthesis, and know their scope of applications. To conclude, the most important data, acquired through various characterization techniques, are provided.

Recycling of Gold Using Anodic Electrochemical Deposition from Molten Salt Electrolyte

Recycling of precious metals is becoming increasingly important as our living standards improve and electronic technologies advance. Conventional recycling processes involve multi-step hydrometallurgical treatments, in which precious metals are dissolved in aqueous solutions using a combination of strong complexing agents and oxidizing agents. However, these processes are time consuming and produce a large amount of hazardous liquid waste. Here, we present a new recycling process for Au, which is based on the direct anodic electrochemical deposition of anionic Au ions dissolved in a molten salt electrolyte. Moreover, this process is simple and does not generate harmful waste. In this process, Au is alloyed with Na to facilitate its dissolution in a molten mixture of NaCl–NaI. The existence of Au as an anionic species (Aun−) in the molten salt was proven and its anodic deposition (oxidation reaction) by application of an anodic current was demonstrated. During the anodic deposition of Au, Na is deposited on the cathode and can be recovered and reused in the process. It is expected that this electrodeposition technique to recycle Au from scrap metal could result in the development of a new environmentally friendly Au recycling process that does not generate hazardous waste.

Electrodeposition of MoS2 from Dichloromethane

The electrodeposition of MoS2 from dichloromethane (CH2Cl2) using tetrabutylammonium tetrathiomolybdate ([NnBu4]2[MoS4]) as a single source precursor is presented. The electrodeposition of MoS2 from CH2Cl2 requires addition of a proton donor to the electrolyte and trimethylammonium chloride (Me3NHCl) was used for this purpose. Electrochemical Quartz Crystal Microbalance (EQCM) experiments have been employed for a detailed study of the electrochemical mechanism and to study the role of the proton donor. EQCM reveals cathodic electrodeposition of MoS2 and anodic deposition of MoS3 as well as an additional corrosion process where the deposited MoS3 strips back into solution. The electrodeposited MoS2 films are amorphous in nature. All the films were found to be homogeneous in composition across the electrode area and to be reproducible between experiments. Annealing of the as-deposited films under a sulfur atmosphere results in crystalline MoS2 as confirmed by energy dispersive X-ray spectroscopy (EDX), Raman spectroscopy and X-ray diffraction. The deposited films were smooth and planar, as observed with scanning electron microscopy (SEM), indicating a layer-by-layer growth typical of transition metal dichalogenides.

Facile and Scalable Modification of a Cu Current Collector toward Uniform Li Deposition of the Li Metal Anode.

The development of lithium metal anodes has been severely impeded by the detrimental lithium (Li) dendrite growth which can largely shorten the lifespan of the battery. Here, we propose a one-step redox strategy to fabricate reduced graphene oxide (rGO) and Cu2O co-modified Cu current collector (rGO-Cu2O/Cu), which can guide the uniform Li ion nucleation and suppress the formation of the Li dendrite. The lithiophilic Cu2O in situ grown on the Cu substrate via direct chemical oxidation of Cu foil by the GO solution can decrease the Li nucleation overpotential and regulate the preferential nucleation of Li ions, while the rGO produced at the same time can facilitate the electron transport. As the consequence of the synergistic effects, rGO-Cu2O/Cu could be fully discharged with largely enhanced Coulombic efficiency of 98% and extended cycling life of the symmetrical cell up to 300 h. The full battery assembled with LiFePO4 also exhibits satisfying electrochemical performance, indicating the promising practical application of this Li-plated rGO-Cu2O/Cu anode. Furthermore, the processable rGO-Cu2O/Cu which can make Li metal anode moldable into various shapes with a controllable size will be favorable to manufacture diverse device architectures.

Anodic Oxidation of Ethynylferrocene Derivatives in Homogeneous Solution and Following Anodic Deposition onto Glassy Carbon Electrodes

AbstractEight ferrocene derivatives linked by either an ether, amine, or phenylacetylene moiety to a terminal ethynyl group were covalently deposited on glassy carbon electrodes by anodic electrochemical methods. The lithio activation method, in which the terminal hydrogen of the ethynyl group is replaced by a lithium atom before anodic oxidation, was successfully employed in all cases. Direct oxidation of the inactivated ethynyl group also resulted in surface deposition. Surface coverages between 1×10−10 mol cm−2 and 14×10−10 mol cm−2 were achieved. Cyclic voltammetry scans of the modified electrodes in pure electrolytes differed depending on the size of the supporting electrolyte anion, as little as half the current being measured for a [B(C6F5)4]− vs. [PF6]− solution, suggesting differences in ion transport near the electrode surface. An ether‐linked ethynylferrocenium ion (5+) was isolated after electrolytic and chemical oxidation of 5 and characterized by X‐Ray crystallography as its [SbCl6]− salt.