Electrochemical Reduction Method Research Articles

Electrochemical Performance of Ba0.5Sr0.5Co0.8Fe0.2O3−δ in Symmetric Cells With Sm0.2Ce0.8O1.9 Electrolyte for Nitric Oxide Reduction Reaction

The emission of nitric oxide from the combustion process of fossil fuels causes air pollution problems. In addition to traditional removal methods, nitric oxide can be removed by the electrochemical reduction method. In this study, Ba0.5Sr0.5Co0.8Fe0.2O3−δ powders were synthesized using a solid-state reaction method. Symmetrical cells, with Sm0.2Ce0.8O1.9 as the electrolyte and Ba0.5Sr0.5Co0.8Fe0.2O3−δ as the electrodes, were prepared as the electrochemical reactor for nitric oxide reduction. In the process of electrochemical reduction, nitric oxide reduction occurs at the cathode and oxygen evolution occurs at the anode. To study the nitric oxide reduction performance of the electrode, impedances of the symmetrical cell in different atmospheres were analyzed. For the nitric oxide conversion in symmetric cells, two different modes, dual chamber and single chamber, were applied. Results demonstrated that the denitrification performance of the double chamber was better but the single chamber mode had other advantages in its simple structure. Presliminary stability results of the single chamber symmetric cell show that the electrochemical reduction of nitric oxide in symmetric cells with BSCF performed most reliably.

Efficient electrochemical N2 fixation by doped-oxygen-induced phosphorus vacancy defects on copper phosphide nanosheets

By a two-step method of doped-oxygen induction and electrochemical reduction, a phosphorus vacancy-modified cuprous phosphide catalyst is designed which exhibits excellent electrocatalytic NRR performance.

Synthesis of Dimethyl Octahydroquinazolinones by using Electrochemically Prepared Copper Oxide Nanoparticles

Present work involves the synthesis of substituted dimethyl octahydroquinazolinones by using electrochemically prepared copper oxide nanoparticles as catalyst in microwave. Copper oxide nanoparticles were prepared in appreciable yield by using electrochemical reduction method of synthesis in the presence of tetrabutylphosphonium bromide for capping. The prepared nanoparticles were analyzed by UV, FTIR, TGA, X-ray diffraction and electron microscopic studies. The nanoparticles of copper oxide then were successfully used as a catalyst in multicomponent reaction between diketones, substituted aldehydes and urea/thiourea to synthesize substituted dimethyl octahydroquinazolinones.

Removal and Recovery of Uranium from Groundwater Using Direct Electrochemical Reduction Method: Performance and Implications.

Removal of uranium from groundwater is of great significance as compared to in situ bioimmobilization technology. In this study, a novel direct electro-reductive method has been developed to efficiently remove and recover uranium from carbonate-containing groundwater, where U(VI)O2(CO3)34- and Ca2U(VI)O2(CO3)3 are the dominant U species. The transferred electron calculations and XPS, XRD analyses confirmed that U(VI) was reduced to U(IV)O2 and accumulated on the surface of the Ti electrode (defined as Ti@U(IV)O2 electrode) with high current efficiencies (over 90.0%). Moreover, over 98.0% of the accumulated U(IV)O2 could be recovered by soaking the Ti@U(IV)O2 electrode in the dilute nitric acid. Results demonstrated that the accumulated U(IV)O2 on the surface of the Ti electrode played a key role in the removal of U(VI), which can promote the electro-reduction of U(VI). Therefore, the electrode could be used repeatedly and has a high removal capacity of U(VI) due to the continuous accumulation of active U(IV)O2 on the surface of the electrode. Significantly, the uranium in both real and high salinity groundwater can be efficiently removed. This study implies that the proposed direct electro-reductive method has great potential for the removal and recovery of uranium from groundwater and uranium-containing wastewater.

A facile method to enhance the performance of soil bioelectrochemical systems using in situ reduced graphene oxide

Bioelectrochemical systems offer a potential solution for the treatment of a broad variety of environmental contaminants. Unfortunately, when applied to the remediation of soil and sediments, the low electrical and hydraulic conductivities of these media limit their effective applicability in full-scale installations. Interestingly, these drawbacks may be overcome by including conductive particles within the soil porosity in order to maximize the outreach of the electrode through the contaminated medium, thereby minimizing electron- and mass-transfer limitations.Herein, we increase the electrical conductivity of a model porous aquifer using amendments of graphene oxide (GO), followed by its reduction to produce reduced graphene oxide (rGO) by means of microbial or electrochemical reduction methods. Both approaches promoted the formation of rGO-sand composites with superior electrical features compared to controls not amended with GO, with conductivity being positively correlated to the GO application rates, within the applied range of 10–2000 mgGO kgsand−1. The electrochemical reduction yielded significantly higher conductivity than the biological method. This result is putatively ascribed to a higher degree of reduction achieved by the former approach. When applied to laboratory scale soil bioelectrochemical systems fed with sodium acetate as a model contaminant, the GO-amended reactors delivered 32x higher anodic current compared to unamended controls. We conclude that GO amendments to porous soils improve the outreach of the electrochemical process to include microbial cells in distal soil locations.

Electrochemical Reduction of Carbon Dioxide on Lanthanum Based Transition Metal Oxide Electrocatalysts

Among the various methods available for reduction of CO2, the electrochemical reduction method stands out due to it being capable of producing industrially important fuels, organic chemicals and pure oxygen. Such process takes place in an electrochemical cell, where carbon dioxide is reduced to at room temperature and atmospheric pressure, using only water, carbon dioxide and electricity at specific electrochemical potentials. Here, electrocatalysts have an important role to play, for enhancing the kinetics of the process and also for rendering the formation of desired products feasible at some selected potentials. In the present research, we are exploring the usage of La-based transition metal (TM) oxides, crystallizing in perovskite structure, as electrocatalysts. The synthesis of these metal oxides is cost effective and tuning the performance via doping is facile. Furthermore, these perovskites are stable in stoichiometric, as well as non-stoichiometric, forms and due to the basicity of La exhibits affinity for CO2. Accordingly, here we have investigated the efficiency and effectiveness of different La-based TM oxides, as electrocatalysts, towards the formation of industrially relevant products upon reduction of CO2. It may be mentioned here that, in order to enhance the efficiency of the electrocatalysts, as well as the mass transport of CO2 to the surface of the electrocatalysts, we have designed a new electrolysis cell where gas diffusion electrode (GDE) containing the electrocatalysts is used as working electrode. All the La-based TM oxides (i.e., LaCoO3, LaCrO3, LaFeO3, LaMnO3, LaNiO3) were synthesized via citrate solution-combustion route and calcined in air atmosphere at 850 oC for 6 h, with the heating rate being 10 oC/minute. Phase evolution of the TM oxides before and after usage, as electrocatalysts, were checked using X-ray diffraction (XRD; EMPYREAN PANalytical diffractometer) having Cu Kα radiation and scanning at a rate of 1 o/min between 10 to 90o. Inorganic Crystal Structure Database was used for the phase analysis of the powder catalysts. The composition of the perovskite catalysts (in terms of the ratios of the metals) were quantitatively analyzed by energy dispersive spectroscopy (EDS; QUANTA 200). Morphologies of the oxide particles were observed using scanning electron microscopy (SEM) JEOL JSM-7600F. The specific surface area of the perovskite catalysts were measured via BET using Micromeritics 3 FLEX Surface Characterization. The electrochemical CO2 reduction reaction was performed in an electrolysis cell via chronoamperometry using Biologic potentiostat (Model VSP 300). The reduction reactions were carried out on gas diffusion electrode (GDE) using basic aqueous electrolyte. The applied potentials were -1.1 V, -1.3 V, -1.5 V, -1.7 V, -1.9 V and -2.1 V vs. Hg/HgO, as reference electrode. The chronoamperometry experiments were performed for 3 h at each potential. The current densities obtained during the electrochemical CO2 reduction experiments were obtained for all the La-based TM oxide electrocatalysts used, viz., LaCoO3, LaCrO3, LaFeO3, LaMnO3, LaNiO3. The liquid products present in the electrolyte after the experiments were analyzed by high performance liquid chromatography (HPLC) using Agilent 1260 infinity series model with Aminex HPX-87H column. The gaseous products were analyzed by gas chromatography - thermal conductivity detector (GC-TCD) using Nucon 5700 gas chromatography. XRD scans recorded with the as-synthesized and calcined La-based TM oxides indicate that the oxides were phase pure (as shown in Fig. 1). The crystal structure was established as perovskite. The composition of the as-synthesized and calcined perovskite electrocatalysts, as determined using EDS, were in good agreement with the target compositions. The current densities were fairly stable during the 3 h long experiments for all the potentials studied; with an example being shown in Fig. 2. All the electrocatalysts produced formate (HCOO-), acetate (CH3COO-) and hydrogen as the products of electrochemical CO2 reduction. Furthermore, ethanol (C2H5OH) and 1-propanol (C3H7OH) were also formed on LaCoO3, with LaMnO3 being able to produce 1-propanol (C3H7OH) as one of the products. Hence, as per the present set of results in the context of the formation of desired products, LaCoO3 and LaMnO3 seem to be more promising among the La-TM-oxide electrocatalysts studied here. Keywords: CO2 reduction, transition metal oxide, electrocatalyst, chronoamperometry, reaction product. Figure 1

Structure and Properties of Nanocomposite Nickel/Graphene Oxide Coatings Produced by Electrochemical Reduction Method

Structure and Properties of Nanocomposite Nickel/Graphene Oxide Coatings Produced by Electrochemical Reduction Method

Photoelectrochemical degradation of 2,4-dichlorophenoxyacetic acid using electrochemically self-doped Blue TiO2 nanotube arrays with formic acid as electrolyte

Blue TiO2 nanotube arrays (Blue-TNTs) were fabricated via an electrochemical reduction method with formic acid as the electrolyte. The optimum reduction conditions were obtained as bias potential of −1.3 V, reduction time of 5 min and formic acid of 3 M. Blue-TNTs were remarkably corroded compared with the intact TNTs. Similar crystal structures of the two catalysts were observed using X-ray diffraction, while red-shift was observed for Blue-TNTs using Raman spectra. X-ray photoelectron spectroscopy indicated of the presence of Ti3+ in Blue-TNTs that resulted from the reduction of Ti4+ and reduced the resistance of the catalyst. Blue-TNTs exhibited much stronger light-absorption than intact TNTs over the entire ultraviolet-visible region, especially in the visible region. The catalyst was used toward the photoelectrochemical oxidation of 2,4-dichlorophenoxyacetic acid (2,4-D) for the first time where the influencing factors were studied. Photoelectrocatalysis with Blue-TNTs presented a 2,4-D degradation rate constant (0.0295 min−1) more than twice the sum of that of electrocatalysis (0.0055 min−1) and photocatalysis (0.0089 min−1). Blue-TNTs fabricated in formic acid showed a better photoelectrocatalytic performance for 2,4-D removal compared with that prepared in ethylene glycol, Na2SO4 and NaNO3 solution. Blue-TNTs is considered to be a promising photoelectric anode for contaminant degradation.

Preparation of Pt dendrites on Poly(diallyldimethylammonium chloride)-functionalized reduced graphene oxide as an enhanced electrocatalyst for the hydrogen evolution reaction in alkaline media

Herein, we describe the synthesis of Pt dendrites with electrochemically active high-index planes on poly(diallyldimethylammonium chloride)-functionalized reduced graphene oxide (PFG) using a newly developed high-voltage electrochemical reduction (HVER) method. Subsequently, the catalytic activities of the prepared samples for the hydrogen evolution reaction (HER) in 1 M NaOH are characterized. The HVER method facilitates the preparation of nanoparticles in short reaction times. This method allows Pt particles to be formed by electron transfer from the cathode to a Pt precursor. Importantly, Pt particles deposited on PFG (Pt/PFG), prepared by the addition of PVP, are revealed to comprise both two- (2D) and three-dimensional (3D) dendrite structures, featuring abundant step and edge sites. The various factors affecting the morphology and the ratio of 2D to 3D dendrites of Pt were determined by TEM analysis. The ratio of 2D to 3D Pt dendrites depends on the amount of PVP employed and has a direct influence on the electrochemically active surface area (ECSA) and HER activity. Namely, the prepared Pt/PFG sample with the highest density of 2D Pt dendrites exhibits the highest HER activity due to its high ECSA. The performance of Pt/PFG13 (prepared keeping the PVP:Pt ratio as 13:1) was compared with that of commercial 40 wt% Pt/C, and the Pt/PFG13 sample exhibited superior current density (−424 mA/cmgeo2 for Pt/PFG13 and –242 mA/cmgeo2 for commercial 40 wt% Pt/C at −1.5 V vs. Hg/HgO; approximately 1.8 times higher) and catalytic stability, implying that these parameters are positively correlated with the increased number of step and edge sites.

Structures and photoelectrochemical performances of reduced TiO2 NTAs obtained by hydrogen thermal and electrochemical reduction methods

Reduced TiO2 nanotube arrays were obtained by hydrogen-thermal and electrochemical reduction methods respectively, and the photoelectrochemical performances were studied. Phase structures, elemental compositions, and surficial morphologies were characterized with X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM) to investigate the structural differences between as-prepared TiO2 NTAs and reduced TiO2 NTAs, including two different reducing products. The photoelectrochemical performances of TiO2 NTAs were found to be enhanced by both two reducing methods. The different mechanisms of hydrogen-thermal reduction and electrochemical reduction were investigated by comparing optical absorption, charge transport, separation efficiency of charge carriers, and surficial reactions during the photoelectrochemical processes. For hydrogen-thermal-reduced TiO2 NTAs, the improved photoelectrochemical performances are induced by high optical absorption and low recombination of charge carries, whereas for electrochemical reduced TiO2 NTAs, the enhanced performances are attributed to low charge transport resistance.

Direct electrochemical reduction of copper sulfide in molten borax

In this study, for the first time, direct copper production from copper sulfide was carried out via direct electrochemical reduction method using inexpensive and stable molten borax electrolyte. The effects of current density (100–800 mA/cm2) and electrolysis time (15–90 min) on both the cathodic current efficiency and copper yield were systematically investigated in consideration of possible electrochemical/chemical reactions at 1200°C. The copper production yield reached 98.09% after 90 min of electrolysis at a current density of 600 mA/cm2. Direct metal production was shown to be possible with 6 kWh/kg energy consumption at a 600 mA/cm2 current density, at which the highest current efficiency (41%) was obtained. The suggested method can also be applied to metal/alloy production from single- and mixed-metal sulfides coming from primary production and precipitated sulfides, which are produced in the mining and metallurgical industries during treatment of process solutions or wastewaters.

In-situ Reduction Synthesis of Bi/BiOI Heterostructure Films with High Photoelectrochemical Activity

The Bi/BiOI heterostructure films grew perpendicular to the FTO substrates were synthesized in-situ through an electrochemical deposition and hydrogen reduction method. The metallic Bi nanoparticles were decorated onto the surface of BiOI nanosheets via an in-situ reduction, induced 6.3 times improvement of photocurrent density, compared to the pristine BiOI at 1.23 V vs. reversible hydrogen electrode(RHE). The enhancement of photoelectrochemical performance was attributed not only to the efficient separation of charge resulted from surface plasmon resonance effect, but also to the fast charge transfer at the interface due to the in-situ reduction of the films. This work provided a simple and facile strategy to in-situ construct heterostructure films, and showed an effective method to improve the photoelectrochemical activity of Bi-based semiconductors.

Three-dimensional interconnected cobalt sulfide foam: Controllable synthesis and application in supercapacitor

Transition metal sulfides have been considered as the promising electroactive materials for the supercapacitors with high specific capacitances. Herein, cobalt sulfide foam (CSF) with three-dimensional (3D) porous hierarchical structure was controllably synthesized on the electrode by the facile electrochemical reduction of elemental sulfur in the precursor of sulfur incorporated polypyrrole (S/PPy) composite with a electrochemical reduction method followed with in-situ reacting with Co2+ ions in the electrolyte, and used for high-performance supercapacitors. Since such a CSF material provided smooth ion diffusion pathways for the fast ion transfer between electrode and electrolyte and simultaneously the anchoring of conductive PPy to the cross-linked cobalt sulfide (CoS) nanosheets enabled good electrical contact between the current collector and the active material for the fast electron transfer. By synergetic combination of these advantages, the optimum electrode delivered exceptional rate capability (84.8% capacity retention from 1 to 20 mA cm−2) and excellent cycling stability (86.8% capacity retention after 10000 cycles). An asymmetric supercapacitor assembled with the CSF as the positive electrode and activated carbon as the negative electrode displayed outstanding electrochemical performance. It is expected to provide a green and simple method for the preparation of transition metal sulfide-based electrodes for the practical energy storage.

Continuous efficient removal and inactivation mechanism of E. coli by bismuth-doped SnO2/C electrocatalytic membrane.

The Bi-SnO2/C electrocatalytic membrane was fabricated via a simple electrochemical reduction and hydrothermal method. Under the action of electric field, the Sn2+ and Bi3+ were firstly adsorbed and reduced to metallic Sn and Bi on the carbon membrane surface by cathodic reduction reaction, and the Bi-SnO2/C membrane was obtained subsequently through hydrothermal oxidation process. Confirmed by SEM, TEM, XRD, and XPS characterizations, the nano-Bi-SnO2 is homogeneously distributed on the membrane surface and is firmly attached to the carbon membrane via C-O-Sn chemical bond. Through CV, LSV, and EIS electrochemical analysis, the Bi-SnO2/C membrane possesses the higher electrocatalytic activity and stability than carbon membrane. Therefore, the Bi-SnO2/C membrane could continuously efficiently remove and inactivate Escherichia coli in water through flow-through mode. As a result, the sterilization efficiency can reach more than 99.99% under the conditions of cell voltage 4V, flow rate 1.4mL/min, and E. coli initial concentration 1.0 × 104CFU/mL, owing to the synergistic effect of the membrane separation and electrocatalytic oxidation. Moreover, it was found that the oxidation groups of ⋅OH radicals generated by Bi-SnO2/C membrane play the crucial role for bactericidal performance. This work presents a low-cost, highly active, and stable electrocatalytic membrane towards continuous bacterial inactivation, which exhibits promising potential in water disinfection and is beneficial for practical large-scale applications.

Selective bilirubin sensor fabrication based on doped IAO nanorods for environmental remediation

In this approach, low-dimensional facile IAO nanorods were prepared by using the hydrothermal technique, which is efficiently applied to develop a non-enzymatic sensor coated with GCE probe by electrochemical reduction method.

Improve Corrosion Resistance of Zircaloy by Copper–Graphene Nanocomposite Coatings

In this study, the corrosion behavior of Zircaloy was investigated in the presence and absence of copper–graphene nanocomposites coating. The coating was prepared employing Hummers’ and electrochemical reduction methods. The morphology of copper–graphene nanocomposites coating was studied using scanning electron microscopy (SEM). Corrosion behavior was investigated employing dynamic polarization and electrochemical impedance spectroscopy (EIS) tests in a solution containing lithium hydroxide (LiOH), boric acid (H3BO3), and deionized water. The results showed that corrosion resistance of Zircaloy increased with introduction of copper–graphene nanocomposites coatings. The lowest corrosion rate was attained in the Zircaloy with copper–graphene nanocomposites coating (corrosion rate: 0.040 mm/year). An approximately 20 times decrease in the corrosion rate was observed in the Zircaloy with copper–graphene nanocomposites coating when compared to the un-coated Zircaloy (corrosion rate: 0.831 mm/year).

Au/ZnO nanocomposites decorated ITO electrodes for voltammetric sensing of selenium in water

Herein, we report an electrochemically synthesized Au/ZnO nanocomposite (NC) onto a disposable ITO electrode for selective detection of selenium (IV), the utmost toxic chemical species of selenium, in water using the square wave anodic stripping voltammetry as transduction technique. The NC is synthesized via one-step electrochemical reduction method. Raman, XPS, and EDAX analysis confirm the synthesis of the nanocomposite, while XRD and HR-TEM investigations reveal their crystalline nature, with a uniform distribution of spherical Au nanoparticles onto hexagonal ZnO. CV and EIS analysis of fabricated electrodes support their electro-analytical application. The analytical characteristics of the fabricated NC were optimized in terms of deposition potential, deposition time, electrolyte, pH and square wave characteristics (frequency, step-size, amplitude, etc.) to achieve a detection and quantification limit of 2.89 ppb and 8.75 ppb, respectively, with 2.55% (n = 3) RSD and 0.19 μA/ppb sensitivity. The NC is also tested against a variety of cations and anions, commonly found in water, such as Pb (II), Cu (II), Mg (II), Fe (III), Cd (II), iodide, phosphate, sulphate, bromide, etc. The observed electrode insulation towards these interfering ions is assigned to a high adsorption coefficient of ZnO towards selenium (IV) in the fabricated NC electrodes. The sensor performance is also validated against ion chromatography technique and spiked water sample collected from the field. The presented sensor electrodes could be a potential substitute for existing mercury and bulk electrodes for their easy integration into the field-deployable electrochemical analyzer for selenium screening in water.

Electrochemical synthesis of AuPt nanoflowers in deep eutectic solvent at low temperature and their application in organic electro-oxidation

Deep eutectic solvents (DESs), called a new generation of green solvents, have broad applied in synthesis of nanomaterials due to their remarkable physicochemical properties. In this work, we used a unique strategy (adding moderate water (10%) to DES) to effectively prepare nanomaterials. Flower-like AuPt alloy nanoparticles were successfully synthesized using one-step electrochemical reduction method at a low potential of −0.30 V (vs. Pt) and a low temperature of 30 °C. In this process, the DES acted as solvent and shape-directing agent. More importantly, we used the electrode modified with the as-prepared nanomaterials as the anode to the electrochemical oxidation synthesis. The glassy carbon electrode modified with the AuPt nanoflowers was directly employed to the electro-oxidation of xanthene (XT) to xanthone (XO) under a constant low potential of 0.80 V (vs. Ag/AgCl) and room temperature, with a high yield of XO. Moreover, the synthesis process was milder and more environment-friendly than conventional organic syntheses. This new strategy would have a promising application in electroorganic synthesis fields.

Morphologically Tunable MnO2 Nanoparticles Fabrication, Modelling and Their Influences on Electrochemical Sensing Performance toward Dopamine

The morphology or shape of nanomaterials plays an important role in functional applications, especially in the electrochemical sensing performance of nanocomposites modified electrodes. Herein, the morphology-dependent electrochemical sensing properties of MnO2-reduced graphene oxide/glass carbon electrode (MnO2-RGO/GCE) toward dopamine detection were investigated. Firstly, various morphologies of nanoscale MnO2, including MnO2 nanowires (MnO2 NWs), MnO2 nanorods (MnO2 NRs), and MnO2 nanotubes (MnO2 NTs), were synthesized under different hydrothermal conditions. Then the corresponding MnO2-RGO/GCEs were fabricated via drop-casting and the subsequent electrochemical reduction method. The oxidation peak currents increase with the electrochemical activity area following the order of MnO2 NWs-RGO/GCE, MnO2 NTs-RGO/GCE, and MnO2 NRs-RGO/GCE. The spatial models for MnO2 NWs, MnO2 NTs, and MnO2 NRs are established and accordingly compared by their specific surface area, explaining well the evident difference in electrochemical responses. Therefore, the MnO2 NWs-RGO/GCE is selected for dopamine detection due to its better electrochemical sensing performance. The response peak current is found to be linear with dopamine concentration in the range of 8.0 × 10−8 mol/L–1.0 × 10−6 mol/L and 1.0 × 10−6 mol/L–8.0 × 10−5 mol/L with a lower detection limit of 1 × 10−9 mol/L (S/N = 3). Finally, MnO2 NWs-RGO/GCE is successfully used for the determination of dopamine injection samples, with a recovery of 99.6–103%. These findings are of great significance for understanding the relationship between unlimited nanoparticle structure manipulation and performance improvement.

Indirect Electrochemical Reduction of Indigo and Dyeing

The method of electrochemical reduction utilizes electrons as agent to achieve the reduction of indigo, vat dyes and pollution emissions, as well as the recycling of electrolyte. In this study, Ca2+-Fe3+-triethanolamine (TEA) redox system was used as the mediator to achieve the indirect electrochemical reduction of indigo. The optimization of parameter was analyzed by reduction efficiency (RE) and current efficiency (CE). The result showed that indigo could be reduced by electrochemical method and the best optimization recipe was 20 g/L NaOH + 5 g/L Fe2(SO4)3 + 30 g/L TEA + 5 g/L Calcium gluconate + 3 g/L indigo in 1 A·dm-2 current density at 50°C. This work suggested that Ca2+-Fe3+-TEA redox system in reduction of indigo was an effective way with higher CE (75.9 %).