Simultaneous Electro-oxidation Research Articles

Spatially separated redox active sites over Re-Ni@Ni(OH)2 core-shell structure for enhancing furfural oxidation coupled with hydrogen evolution

The design of bifunctional catalysts with spatially separated active sites holds significance importance in achieving simultaneous electrooxidation and hydrogen evolution reaction (HER). Herein, a core-shell Re-Ni@Ni(OH)2/CC heterostructure is demonstrated for the electrocatalytic furfural oxidation reaction (FOR) coupled with HER. Experimental results and theoretical analyses reveal that Re not only modulates the heterointerface between Re-Ni core and Ni(OH)2 shell, facilitating furfural (FF) adsorption at Ni(OH)2 sites, but also tunes electronic structure of Ni. This leads to a negative shift in the d-band center from Fermi level, effectively weakening hydrogen adsorption at Ni sites in Re-Ni@Ni(OH)2 heterostructure, thereby improving the HER process. As a result, the synthesized Re-Ni@Ni(OH)2/CC exhibits a low cell voltage of 1.40 V @10 mA cm−2 for the FOR||HER. This study highlights the importance of modulating metal’s electronic structure and identifying active sites, which has great potential for improving bifunctional electrocatalytic reactions.

Comparison between Electrooxidation of 1-Naphthol and 2-Naphthol in Different Non-Aqueous Solvents and Suppression of Layer Growth of Polymers

The two naphthol isomers were investigated in different organic solvents by taking cyclic voltammograms, and fouling took place on a platinum electrode surface, except for dimethyl sulfoxide and dimethyl formamide. Studies in allyl alcohol rarely used in electrochemical investigations pointed to the importance of the carbon–carbon double bond as electrode deactivation was remarkably faster compared with its saturated analog solvent. Similarly, the use of the other unsaturated solvent mesityl oxide in the electropolymerization of naphthols resulted in different findings compared with methyl isobutyl ketone. As dimethyl formamide was the best choice concerning the solubility of products, it was successfully tested in electrode renewal after deactivation in an aqueous solution. The increase in dimethyl formamide content led to more and more improved reproducibility of the currents of the outlined aromatic compounds. Naphthol isomers were assessed in the suppression of layer growth originating from the electrooxidation of another monomer phloroglucinol. Its simultaneous electrooxidation with naphthol monomers had a dramatic effect on layer morphology and it was found that instead of a coherent organic layer originating from the homopolymerization of phloroglucinol, the copolymerization with naphthols led to the development of more porous and rougher deposits. The suppressed electropolymerization thus increased sensitivity towards a chosen redox active compound, 4-methoxyphenol.

Electrochemical Oxidation of Phenol Released from Spent Coordination Polymer Impregnated with Ionic Liquid

Coordination polymer (CP)-type adsorbents impregnated with ionic liquids that are used to remove phenol from wastewater must be regenerated. A simple washing of the adsorbent releases about 70% from the spent adsorbent. In order to increase and study the phenol release, an electrochemical method was used. For this purpose, an electrochemical commercial graphite electrode was used as the working electrode, and the electrolyte support was a 3% NaCl solution. During the electrochemical investigation, the spent CP was immersed in a saline solution. The PH content in the electrolyte affected the direct electrooxidation (EO); the formation of BQ appeared to be accelerated by a lower concentration and a slower release of PH. After 90 min, an efficiency of PH electrooxidation (EOPH) of 36.22% from Cu-PA and EOPH of 42.14% from Cu-PA-IL, respectively, was achieved. These results were significantly higher than the EOPH of the solution resulting from washing the wasted adsorbent with a saline solution (22.58%). This work highlights the potential for the simultaneous electrooxidation of desorbed PH and the recovery of spent adsorbent in this situation. The number of cycles in which the adsorbent can be used without losing its absorbance ability is three.

Coupling surfactants with 3D hollow raspberry-like NiS/carbon microsphere with S vacancies for enhanced sensitivity monitoring of serotonin and L-tryptophan

Serotonin (ST) is a monoamine neurotransmitter synthesized from L-tryptophan (L-Try). Solving their simultaneous detection problem is necessary for assisting in diagnostics diseases. In this work, we designed NiS/carbon hybrids with NiS nanoparticles embedded on 3D hollow porous carbon microspheres (NiS/CS) via successive carbonization and sulfidation Ni-MOF for constructing electrocatalysts for the simultaneous electrooxidation of ST and L-Try. The formation of robust contact with surface S vacancies in NiS/CS nanointerfaces demonstrated a remarkably enhanced electrocatalytic activity towards ST and L-Try and the corresponding electrochemical signals appeared as two well resolved oxidation peaks with the significant peak-to-peak separation. Importantly, the dual amplification effect of the high electrocatalytic performance function of NiS/CS and the hydrophobic properties of surfactant CTAB coupling made CTAB/NiS/CS/GCE exhibit high sensitivity recognition to ST and L-Try, effectively shielding other coexisting interference. The developed sensor provided a 0.01–200.0 μmol/L linear response range and the low detection limit of 3.35 and 2.94 nmol/L for ST and L-Try, respectively. Finally, this sensing methodology enabled accurate determination of ST and L-Try amount in serum, urine and injection samples and with successful recovery outcomes.

Electro-oxidation of Ni (II)-citrate complexes at BDD electrode and simultaneous recovery of metallic nickel by electrodeposition

The simultaneous electro-oxidation of Ni (II)-citrate and electrodeposition recovery of nickel metal were attempted in a combined electro-oxidation-electrodeposition reactor with a boron-doped diamond (BDD) anode and a polished titanium cathode. Effects of initial nickel citrate concentration, current density, initial pH, electrode spacing, electrolyte type, and initial electrolyte dosage on electrochemical performance were examined. The efficiencies of Ni (II)-citrate removal and nickel metal recovery were determined to be 100% and over 72%, respectively, under the optimized conditions (10 mA/cm2, pH 4.09, 80 mmol/L Na2SO4, initial Ni (II)-citrate concentration of 75 mg/L, electrode spacing of 1 cm, and 180 min of electrolysis). Energy consumption increased with increased current density, and the energy consumption was 0.032 kWh/L at a current density of 10 mA/cm2 (pH 6.58). The deposits at the cathode were characterized by scanning electron microscopy (SEM), energy-dispersive spectrometry (EDS), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). These characterization results indicated that the purity of metallic nickel in cathodic deposition was over 95%. The electrochemical system exhibited a prospective approach to oxidize metal complexes and recover metallic nickel.

Monolayer assembly of gold nanodots on polyelectrolyte support: A multifunctional electrocatalyst for reduction of oxygen and oxidation of sulfite and nitrite

AbstractThe present work demonstrates a monolayer self‐assembly of methionine‐capped gold nanodots (AuNDs) on the glassy carbon electrode (GCE) and its application in various electrocatalytic reactions. Positively charged poly(acrylamide‐co‐diallyldimethylammonium chloride) (PADA)‐modified GCE was used as electrode substrate and monolayer assembly of negatively charged AuNDs was performed over PADA‐modified GCE by simple dipping method. The successful modification of AuNDs on GCE was confirmed by characteristic cyclic voltammetry behavior of gold oxidation and reduction. Further to optimize the dipping time duration of AuNDs self‐assembly, dipping time‐dependent electrocatalysis was performed. Interestingly, the prepared AuNDs self‐assembled electrodes exhibit very good electrocatalytic activity in the reduction of oxygen with excellent methanol tolerance and simultaneous electrooxidation of pollutants and food additives, nitrite, and sulfite ions.

Bifunctional Pt/Au Janus electrocatalysts for simultaneous oxidation/reduction of furfural with bipolar electrochemistry.

The sustainable conversion of biomass-derived compounds into high added-value products is a very important contemporary scientific challenge. In this context, we report here the simultaneous electro-oxidation/-reduction of a biomass-derived compound in a one-pot approach using bipolar electrochemistry. Bifunctional Pt/Au Janus electrocatalysts are employed for a selective conversion of furfural into both, furfuryl alcohol and furoic acid, which can't be achieved when using non-Janus particles. The results emphasize the benefits of bipolar electrochemistry in the frame of electrosynthesis processes.

Electrochemical investigation of allopurinol polymerised carbon paste electrode interface for epinephrine and folic acid sensing in pharmaceutical samples

ABSTRACT The performance of simultaneous electro oxidation of epinephrine (EP) and folic acid (FA) was achieved at allopurinol polymerised carbon paste electrode (AlpM-CPE) by cyclic voltammetry (CV) method at physiological pH. The modified electrode showed remarkable sensing activity towards the electrooxidation of EP, involving irreversible 2-electronstransfer with adsorption-controlled kinetics. The results of varying few experimental parameters, for instance – scan rate, solution pH, concentration of the target analyte was examined. It was observed that, the anodic peak current (Ipa) is proportional to the concentration of EP in the range 51.02–318.18 μM with a calculated limit of detection (LOD) 0.46 µM by CV technique. The analytical applicability of the fabricated AlpM-CPE was examined for the resolve of EP in pharmaceutical sample and a good recovery results were observed.

Electrooxidation of urea and creatinine on nickel foam-based electrocatalysts

Electrooxidation of urea and creatinine is desirable for wastewater remediation and portable dialysis to remove the two solutes from aqueous waste streams. Urine concentrations of urea (330 mM) and creatinine (18 mM) are relevant for wastewater remediation, while portable dialysis must be able to remove blood serum concentrations of urea (10 mM) and creatinine (0.18 mM) from dialysate. Three nickel foam-based electrocatalysts (clean Ni foam, Ni hydroxide, and Ni hydroxide doped with 1 mol% iron) were examined as substrates for the simultaneous electrooxidation of urea and creatinine. Electrodes were hydrothermally fabricated and characterized by loading, scanning electron microscopy, and elemental mapping. Cyclic voltammetry and chronoamperometry were used to electrochemically evaluate the three catalysts. All electrochemical experiments were performed at room temperature and pH 14. The results indicate that creatinine in urea solutions suppresses the oxidation current relative to urea-only solutions on Ni foam and Ni hydroxide catalysts. On iron-doped Ni hydroxide, an enhanced oxidation current occurs in cyclic voltammetry of creatinine/urea solutions, with the effect greater for dialysate-relevant concentrations. In chronoamperometry measurements, a slight decrease in oxidation current is observed for urea/creatinine solutions as compared with urea alone. This behavior is attributed to concurrent reactions of urea and creatinine subject to site blocking by adsorbed creatinine fragments that becomes evident at long timescales.

One Pot Hydrothermal Synthesis of Large Area Nano Cube Like ZnSnO3 Perovskite for Simultaneous Sensing of Uric Acid and Dopamine Using Differential Pulse Voltammetry

We report ultra-selective zinc stannate nano cubes (ZnSnO3) modified glassy carbon electrode (GCE) for simultaneous detection of Uric Acid (UA) and Dopamine (DA) using differential pulse voltammetry (DPV) technique. The ZnSnO3 nano cubes were synthesized via one-pot hydrothermal technique. The orthorhombic phase formation of nano cubes structured ZnSnO3 was confirmed through X-ray diffraction (XRD) and scanning electron microscopy (SEM) imaging. The sensor exhibited very distinct oxidation potentials and excellent sensitivity with wide dynamic ranges of detection ranging from 10 nM to $5~\mu \text{M}$ and $1~\mu \text{M}$ to 5 mM with a very low limit of detections of 2.6 nM and 550 nM towards DA and UA respectively. The sensing mechanism can be ascribed to the simultaneous electro-oxidation process of DA and UA at the 3d orbital SnO6 octahedra sites facilitated with the Sn2+/Sn4+ oxidation states of Sn in line with the stress induced electrical property transformation of ZnSnO3 due to its piezoelectric nature. The as fabricated ZnSnO3/GCE sensor was further successfully evaluated for simultaneous detection of UA and DA in the simulated blood serum samples. This simple strategy for developing ZnSnO3 perovskite modified electrode paves way to develop electrochemical sensing platforms for bioanalytical applications.

Efficient removal of refractory organics in landfill leachate concentrates by electrocoagulation in tandem with simultaneous electro-oxidation and in-situ peroxone

Leachate concentrates, an effluent produced from nanofiltration and/or reverse osmosis, contains a high amount of salts and dissolved organics especially refractory organics. Thus, the treatment of leachate concentrates would consume high energy or a large amount of chemicals. The present study is to develop an effective treatment method by using coupled electrochemical methods with the least possible energy consumption. The leachate concentrates was pretreated by electrocoagulation (EC), with aluminum or iron electrodes as anodes, to decrease the dissolved organic content. EC with Al electrode was found to be more efficient by consuming 1.25 kWh/m3 energy to remove 70% of total organic carbon (TOC). EC effluent was further subjected to a novel simultaneous electro-oxidation and in-situ peroxone process, which used a Ti-based nickel and antimony doped tin dioxide (NATO) as anode and a carbon nanotube coated carbon-polytetrafluoroethylene (CNT-C/PTFE) as cathode for oxygen reduction reaction (ORR). Compared with a traditional EO with cathode for hydrogen evolution reaction (HER-EO), ORR-EO obtained higher efficiency and an energy consumption of 26.25 kWh/m3, which was much lower than 35.5 kWh/m3 for HER-EO. Results showed that after ORR-EO, a final TOC of 57.3 mg/L was obtained. Thus, EC in tandem with ORR-EO process has an excellent capability and economic merit in the field of treating leachate concentrates.

Sensitive electrochemical platform based on nano-cylindrical strontium titanate/N-doped graphene hybrid composite for simultaneous detection of diphenhydramine and bromhexine

Herein, we report a nano-cylindrical strontium titanate/N-doped graphene (SrTiO3/N-GNS) hybrid composite synthesized by a solvothermal method. The composite material has been explored by various physicochemical and electrochemical characterization techniques. It is found that the nano-cylindrical SrTiO3 nanoparticles with highly crystalline mesoporous structure are consistently present in between as well as on the surface of N-GNS sheets resulted in 3-dimensional continuous structure. The electrochemical investigations reveal that SrTiO3/N-GNS hybrid composite displays excellent electrocatalytic behavior towards simultaneous electro-oxidation of two commonly encountered anti-allergic drugs viz. Diphenhydramine (DPH) and Bromhexine (BRO) in phosphate buffer of pH 7.0 employing adsorptive stripping differential pulse voltammetry. The new application of SrTiO3/N-GNS hybrid as an electrochemical sensor shows wide linear working range from 0.038 to 100.0 μM for DPH and 0.030–90.0 μM for BRO with detection limit of 2.1 and 1.9 nM respectively. Also, the developed sensor manifests adequate recoveries in synthetic pharmaceutical samples and human body fluids. These findings suggest that SrTiO3/N-GNS composite is and could serve as a potential candidate for highly sensitive electrochemical sensing applications.

Paired electro-oxidation of insecticide imidacloprid and electrodenitrification in simulated and real water matrices

Groundwater is one of the main freshwater resources on the Earth, but its contamination by NO3− and pesticides jeopardizes its suitability for consumption. In this work, the simultaneous electro-oxidation of insecticide imidacloprid (IMC) and electroreduction of NO3− in softened groundwater containing a large amount of Cl− has been addressed. The assays were carried out in a stirred undivided tank reactor containing either a boron-doped diamond (BDD) or IrO2 anode, and Fe cathode, which showed greater electrocatalytic activity than stainless steel to reduce NO3−. Comparative assays in simulated water mimicking the anionic composition of groundwater were made to assess the influence of natural organic matter (NOM) on the decontamination process. The BDD/Fe cell had much greater performance than the IrO2/Fe one, although the former produced larger amounts of ClO3− and ClO4−. In all cases, the NO3−, Cl− and IMC decays agreed with a (pseudo)-first-order kinetics. In the BDD/Fe cell, total NO3− removal was reached at j ≥ 10 mA cm−2 in softened groundwater, at similar rate in the presence and absence of IMC, but it was decelerated using the simulated matrix. The N-products formed upon NO3− electroreduction contributed to IMC degradation, but its decay was inhibited by NOM because of the partial consumption of oxidants like hydroxyl radical and active chlorine. Operating at 5 mA cm−2 for 240 min, total removal of the insecticide and 61.5% total organic carbon (TOC) decay were achieved, also attaining a low NO3− content that was suitable for humans. Eight heteroaromatic products were identified, allowing the proposal of a reaction sequence for IMC degradation in groundwater.

Nonylphenol Degradation by Simultaneous Electrooxidation on BDD Anode and Oxidation by H2O2 in a Continuous Flow Electrochemical Reactor

Nonylphenol Degradation by Simultaneous Electrooxidation on BDD Anode and Oxidation by H2O2 in a Continuous Flow Electrochemical Reactor

In situ anchoring of a Co3O4 nanowire on nickel foam: an outstanding bifunctional catalyst for energy-saving simultaneous reactions

Bifunctional CoNW/NF as an efficient and monolithic electrocatalyst for simultaneous electrooxidation of 5-hydroxymethylfurfural and the hydrogen evolution reaction.

Simultaneous electro-oxidation and in situ electro-peroxone process for the degradation of refractory organics in wastewater.

During electro-oxidation (EO) wastewater treatment, the applied voltage must polarize both a dimensionally stable anode with a sufficiently high potential to effectively produce hydroxyl radicals (OH), as well as a cathode with a sufficiently low potential to catalyze the H2 evolution reaction (HER). Nevertheless, H2 does not contribute to pollutant degradation and yet increases energy consumption. Inspired by fuel cell technology, in which the O2 reduction reaction (ORR) is catalyzed on the cathode, herein, a carbon nanotube-coated carbon-PTFE gas diffusion electrode was fabricated to catalyze ORR during EO for the treatment of leachate concentrates. In comparison to conventional HER-EO, ORR-EO was shown to save 17.7-23.2% energy consumption. Further, as the cathodic ORR byproduct, H2O2 can react with the ozone generated from the Ti/SnO2-Sb2O5 anode to catalyze the peroxone process, which enhances OH generation for the degradation of organic products. This in situ electro-peroxone process was determined by salicylic acid OH trapping and liquid chromatography. The novel simultaneous EO and in situ electro-peroxone process described herein has great application potential and economic merit in the degradation of refractory organics in wastewater.

A simple ultrasensitive electrochemical sensor for simultaneous determination of gallic acid and uric acid in human urine and fruit juices based on zirconia-choline chloride-gold nanoparticles-modified carbon paste electrode

The determination of gallic acid (GA) and uric acid (UA) is essential due to their biological properties. Numerous methods have been reported for the analysis of GA and UA in various real samples. However, the development of a simple, rapid and practical sensor still remains a great challenge. Here, a carbon paste electrode (CPE) was modified by nanocomposite containing zirconia nanoparticles (ZrO2NPs), Choline chloride (ChCl) and gold nanoparticles (AuNPs) to construct ZrO2-ChCl-AuNPs/CPE as electrochemical sensor for the simultaneous electro-oxidation of GA and UA. Characterization was performed by Fourier transform infrared spectroscopy, X-ray diffraction, field emission scanning electron microscopy and energy dispersive X-ray spectroscopy. The modified electrode was investigated by different methods including electrochemical impedance spectroscopy and cyclic voltammetry. Kinetic parameters such as charge transfer coefficient, standard heterogeneous electron transfer rate constant and other parameters were calculated via voltammetry techniques. Differential pulse voltammetry was used for simultaneous determination of GA and UA applying the ZrO2-ChCl-AuNPs/CPE electrode. At the optimum conditions, this sensor showed a linear response in the ranges 0.22– 55 and 0.12–55 µM for GA and UA, respectively. In addition, low detection limits of 25 and 15 nM were obtained for GA and UA, respectively. Furthermore, ZrO2-ChCl-AuNPs/CPE was successfully applied for the independent determination of GA in green tea and fruit juice as well as the simultaneous determination of GA and UA in human urine samples.

A highly stable and sensitive GO-XDA-Mn2O3 electrochemical sensor for simultaneous electrooxidation of paracetamol and ascorbic acid

Highly stable electrochemical sensor based on strong π- π interactions between GO and XDA was fabricated for simultaneous as well as for individual detection of paracetamol (PCT) and ascorbic acid (AA). The oxidation potential of PCT and AA was greatly resolved with the decoration of Mn2O3 nanospheres. We believe that, presence of metal oxide on the surface of GO-XDA will offer higher electrochemical performance with its large surface area and fast electron transfer ability. Therefore, a comparative study was executed in the presence and absence of Mn2O3 nanospheres on the surface of GO-XDA. The GO-XDA-Mn2O3 modified electrode showed electrocatalytic oxidation of PCT in a very wide linear range of 1×10−6–1×10−3M with limit of detection (LOD) and sensitivity of 5.6×10−8M, 527.04μAmM−1cm−2 respectively and AA with 1×10−5 –8×10−3M linear range, LOD and sensitivity of 6.0×10−7M, 655.74μAmM−1cm−2 respectively. Furthermore, astonishing stability was found when GO-XDA-Mn2O3 nanocomposite was stored for over a week. The proposed sensor displayed incredible selectivity, sensitivity and excellent recovery results for real samples with appreciable consistency and precision suggesting practical utility of the GO-XDA-Mn2O3 as an effective and reliable electrochemical sensor for simultaneous as well as individual determination of PCT and AA.

Investigation of a Combined Hydrogen and Oxygen Spillover Mechanism for Syngas Electro-Oxidation on Ni/YSZ

An accurate, comprehensive model for the individual and simultaneous electro-oxidation of H2 and CO on Ni-YSZ is necessary to predict SOFC performance for a range of gaseous fuels. A mechanism that combines hydrogen (H) spillover to YSZ with oxygen (O) spillover to nickel is implemented in a previously-validated 1D-MEA model with detailed gas-phase transport and surface reforming kinetics in the anode. This model is then successfully fitted to a wide range of experimental polarization data for fuel mixtures. The H and O spillover pathways are then investigated in depth for two anode fuel mixtures: 20% H2 + 80% N2 and 20% H2 + 80% CO. Although these studies confirm that H spillover is typically the dominant source of current, they also show that the current produced by O spillover is non-negligible at higher currents. Furthermore, it is observed that H2 adsorption to nickel becomes the rate-limiting step at high currents in the hydrogen pathways, while the current produced by O spillover to CO(Ni) is never limited by the rate of CO adsorption. The model is then successfully compared to two independent lower temperature data sets. Together these results demonstrate that it is important to model both spillover pathways on Ni/YSZ and to account for rate-limiting H2 adsorption at high currents.

Simultaneous electro-oxidation of phenol, CN−, S2− and NH4+ in synthetic wastewater using boron doped diamond anode

Electrochemical decontamination of phenolic synthetic wastewater containing CN−, S2− and NH4+ using a boron-doped diamond (BDD) electrode was investigated. The removal of phenol, its oxidation byproducts, total organic carbon (TOC), chemical oxygen demand (COD), and the inorganic species were evaluated in relation to specific energy consumption (SEC) and average current efficiencies (ACE) in single, binary, ternary and quaternary matrices of the inorganic species cohabiting phenol in solution. The total amount of COD removal, ACE and SEC were found to depend on the nature of ions in solution and were also proportional to the degree of inorganic species in the matrix. The decay kinetics of phenol as well as the inorganic species in different matrices mainly follow first order kinetics. ACE for binary and higher matrices values of 44.3–58.8% and 58.9–79.3%, respectively, indicate 132–207% and 208–315% increase in ACE, respectively, as compared to the 19.1% ACE when phenol was present alone. The SEC of 57.0 kWh/kg-COD estimated for the single phenol matrix dropped from 57kWh/kg-COD to between 15.1–20.6 and 7.83–15.2kWh/kg-COD for the multicomponent matrices which corresponds to a percent decrease of 63.2–73.5% and 73.3–86.3%, respectively. Presence of the inorganic species insignificantly affected phenol oxidation, though they delayed the attainment of steady state of complete decontamination depending on the species in the matrix. This study demonstrates the viability of oxidation at BDD anodes as an alternative treatment means for effective decontamination of phenolic wastewater containing inorganic species.