Although great progress has been made in the field of electrochemical CO2 reduction reaction (eCO(2)RR), inducing product selectivity is still difficult. We herein report that a thiocyanate ion (SCN-) switched the product selectivity of copper catalysts for eCO(2)RR in an H-cell. A cuprous thiocyanate-derived Cu catalyst was found to exhibit excellent HCOOH selectivity (faradaic efficiency = 70-88%) over a wide potential range (-0.66 to -0.95 V vs RHE). Furthermore, it was revealed that the formation of CO and C2H4 over commercial copper electrodes could be dramatically suppressed with the presence of SCN-, switching to HCOOH. Density functional theory calculations disclosed that SCN- made the formation of HCOO* easier than COOH* on Cu (211), facilitating the HCOOH generation. Our results provide a new insight into eCO(2)RR and will be helpful in the development of cheap electrocatalysts for specific utilization.

Selective CO2 electroreduction to C2+ products, especially ethanol, is regarded as a potential technology for CO2 utilization but is still a formidable challenge. Herein, we report the highly dispersive trace Ag decorated copper/copper oxide composite (Cu/Cu2O-Ag-x) for efficient electrochemical CO2 reduction to C2+ products, mainly containing ethylene and ethanol. Physical measurements confirm that the Ag decoration is an effective strategy to tune the surface electronic structure but without changing the valence and morphology of Cu. The performance evaluation of electrochemical CO2 reduction in a flow cell demonstrates that the activity and selectivity for ethanol production on Cu/Cu2O can be promoted by the trace Ag modification. The best catalyst, Cu/Cu2O with merely 0.6 at.% silver decoration, exhibits a significant enhancement in C2+ selectivity (60.9 %) as compared to the Ag-free Cu/Cu2O catalyst (50.4 %). Originated from the formed Cu-Ag sites and thus enhanced affinity with oxygen-adsorbed intermediates on Cu/Cu2O-Ag-x catalysts, the ethanol formation is favored with a greatly improved Faradaic efficiency (19.2 %) as well as partial current density (305 mA cm(-2)), which are superior to those of Ag-free counterpart (9.1 %, 105 mA cm(-2)). Moreover, the products selectivity remains stable even electrolysis at 900 mA cm(-2) over 8 h, demonstrating the preeminent electrocatalytic stability.

The development of cost-effective and durable oxygen evolution reaction (OER) catalysts is an essential prerequisite for hydrogen production through proton exchange membrane water electrolysis. Herein, a series of Fdoped pyrochlore yttrium ruthenate Y2Ru2O7-delta-xFx (YRuOF) are designed via low-temperature fluorination of precursor oxides with polyvinylidene fluoride. Both X-ray photoelectron spectroscopy and transmission electron microscopy results confirm that F is doped into the pyrochlore crystal lattice, inducing the oxygen vacancies (VO). Importantly, the OER catalytic activity is positively correlated with VO concentration. The density functional calculation (DFT) reveals that the existence of VO enhances the metal-oxygen covalency of pyrochlore, which is conducive to the lattice oxygen evolution mechanism, hence greatly accelerating the OER kinetic. Consequently, the optimized YRuOF catalyst exhibits a greatly enhanced OER activity with an overpotential of -235 mV at 10 mA cm-2 in comparison with that on undoped pyrochlore (-296 mV). Furthermore, such a Fdoped YRuOF catalyst has a very good OER stability. This study provides an ideal perspective to develop highly efficient and durable YRuOF for the oxygen evolution reaction.

Efficient Fe/N/C electrocatalysts for oxygen reduction reaction (ORR) have been prepared from a nonporous 8-fold interpenetrated metal-organic framework (Fe-Zn-TTPA) bearing dense Zn(II)-carboxylate coordination units. During pyrolysis, the Zn(II)-carboxylate moieties gradually decompose into nanosized zinc oxide (ZnO) particles, serving as thermally removal templates to tune the texture of carbon matrix via carbothermal reduction. With the assistance of in situ formed nanosized ZnO templates, the optimal Fe/N/C electrocatalyst, namely, Fe/N/C-1000-0.05, show well-dispersed ORR-active sites of iron carbide (Fe3C) nanoparticles and Fe-N-x species hosted by a hierarchical porous carbon matrix with dominant mesopores. In alkaline electrolyte, a higher ORR activity than the benchmark Pt/C was achieved (E-onset = 0.98 V vs reversible hydrogen electrode (RHE);E-1/2 = 0.86 V vs RHE). Moreover, Zn-air battery using Fe/N/C-1000-0.05 as a cathode catalyst exhibits a peak power density of 130 mW cm(-2) and outstanding durability with a slight decay by 3.1% at a current density of 5 mA cm(-2) for 70 h.

A Cu@Cu-N-C composite electrocatalyst with metallic Cu NPs and Cu(II)-N-x species embedded into the carbon matrix was pyrolyzed from ZIF-8 precursor through the formation of Cu(OH)(2)@ZIF-8. The optimal Cu@Cu-N-C catalyst obtained at 1000 degrees C features a hollow polyhedral morphology, which is resulted from the carbothermal reaction of in-situ generated Cu2O and ZnO with carbon beyond 800 degrees C. The best-performance Cu@Cu-N-C exhibits an impressive catalytic bifunction towards oxygen reduction reaction (ORR) and carbon dioxide reduction (CO2RR) which is assumed to be imparted by the unique Cu(0)Cu(II)-N-x active sites. In alkaline electrolyte, it shows the ORR performance (E-1/2 = 0.83 V vs RHE) comparable to Pt/C (E-1/2 = 0.85 V vs RHE), and the assembled zinc-air (Zn-air) battery displays an excellent durability with the open circuit voltage (1.23 V) decaying only by ca. 4.2% in 80 hat 20 mA cm(-2). For CO2RR, it also delivers an outstanding catalytic performance converting CO2 into CO with a high Faradaic efficiency (90% at -0.5 V vs RHE). Control experiments have indicated that the potential synergistic interactions between Cu (0) (from Cu NPs) and Cu-N-x sites have promoting effects on both ORR and CO2RR. (C) 2019 Elsevier Ltd. All rights reserved.

An overoxidized poly(3,4-ethylenedioxythiophene) film-modified screen-printed carbon electrodes (SPCE/PEDOTox) was prepared and characterized by field emission scanning electron microscopy (FESEM), X-ray photoelectron spectroscopy (XPS) and water contact angle techniques. The obtained film is a porous structure with highly abundant oxygen functionality. The SPCE/PEDOTox could adsorb cations strongly and perform catalytic oxidation of biomolecules. The potential-induced adsorption of dopamine was observed for SPCE/PEDOTox. A simple medium-exchange procedure was developed for the selective determination of dopamine by the use of the dopamine-adsorbed electrode. Under optimal differential pulse voltammetry (DPV), the proposed assay can be employed in the determination of submicromolar concentration of dopamine without the coexisting interferences of ascorbic acid (1000-fold) and uric acid (10-fold). (C) 2014 Elsevier Ltd. All rights reserved.

The electrochemical oxidation of pyrogallol at electrogenerated poly(3,4-ethylenedioxythiophene) (PEDOT) film-modified screen-printed carbon electrodes (SPCE) was investigated. The voltammetric peak for the oxidation of pyrogallol in a pH 7 buffer solution at the modified electrode occurred at 0.13 V, much lower than the bare SPCE and preanodized SPCE. The experimental parameters, including electropolymerization conditions, solution pH values and applied potentials were optimized to improve the voltammetric responses. A linear calibration plot, based on flow-injection amperometry, was obtained for 1-1000 mu M pyrogallol, and a slope of 0.030 mu A/mu M was obtained. The detection limit (S/N= 3) was 0.63 mu M.

A novel modified screen-printed carbon electrode (SPCE) was constructed by spin-coating room temperature ionic liquid, 1-butyl-3-methylimidazolium chloride ([BMIM][Cl]), into electropolymerized conducting polymer matrix of poly(3,4-ethylenedioxythiophene) (PEDOT). The resulting surface morphology was characterized by scanning electron microscopy. X-ray photoelectron spectroscopy was employed to confirm the successful surface modification. Cyclic voltammograms have shown that the composite film-modified electrode combined the advantages of conducting polymer and ionic liquids, and exhibited good electrocatalytic activity for biomolecules. The results showed lowering the overpotentials and enhancing current responses, without showing any fouling effect. The proposed method was applied to the simultaneous determination of dopamine (DA), ascorbic acid (AA) and uric acid (UA) in pH 7.0 PBS.

In this study, we report a simple, low-cost and rapid electrochemical sensor based on the anodically pretreated screen-printed carbon electrodes (SPCE*) for the determination of pyrogallol in pH 7.0 buffer solutions. Cyclic voltammetric studies show that SPCE* lowers overpotentials and improve electrochemical behaviour of pyrogallol, compared to untreated SPCE. All experimental parameters were optimized to improve voltammetric responses; excellent analytical features were achieved by flow-injection amperometric methods. A linear calibration plot was obtained for 10-1000 mu M pyrogallol with a slope of 0.0562 mu A/mu M. The detection limit (S/N = 3) was 0.33 mu M. Interferences from some inorganic salts and organic compounds were studied. The assay was applied to the determination of pyrogallol in tap water and lake water, respectively.

This work provides an easy way to fabricate a composite film-modified electrode, and used as an electrochemical nitrite sensor. A functionalized ionic liquid, 1-butyl-3-methylimidazolium ferricyanide (BMIMFC), has been synthesized and modified onto a screen-printed carbon electrode (SPCE) by deposition methods. Poly(3-(aminopropyl)trimethoxysilane) sol-gel (SG) is then used as the second modified layer. The surface morphology of the modified electrode (SPCE/BMIMFC/SG) is characterized using scanning electron microscopy (SEM). The modified electrodes exhibit a very stable redox couple, and its redox potential is pH-dependent. In strongly acidic solutions, attractive electrocatalytic activity for the reduction of nitrite is achieved. As an amperometric nitrite sensor, the modified electrode shows a wide linear range (20-510 μM), a suitable sensitivity (0.0040 μA/μM) and a low detection limit (1.3 μM, S/N = 3). Unlike previous reports on the electrocatalytic reduction of nitrite, the present detection assays indicate insignificant interference from dissolved oxygen and common salts, promising the convenient operation of the nitrite sensor.

In this study, a hybrid nanocomposite consisting of a conducting polymer and gold nanoparticles (AuNPs) is fabricated onto a screen-printed carbon electrode (SPCE). A thin layer of poly(3,4-ethylenedioxythiophene) (PEDOT) is coated electrochemically on a bare SPCE; then, the nano-sized AuNPs are embedded by electrochemical deposition. The resultant SPCE/PEDOT/AuNPs-modified electrode is characterized by electrochemical methods, field emission scanning electron microscopy (FE-SEM) and X-ray photoelectron spectroscopy (XPS). The SPCE/PEDOT/AuNPs-modified electrode possesses great catalytic activity for the oxidation of cysteine in various pH buffer solutions (pH 2.0–8.0). The selectivity of the method is demonstrated by the separation of the oxidation peaks at up to 240mV for cysteine and glutathione in pH 6.0 buffer solutions. The effects of the oxidizable interferences are also investigated. Flow-injection amperometry is performed for 0.5–200μM of cysteine in pH 4.0 buffer solutions, and a linear calibration plot with a slope of 0.115μA/μM is obtained. The detection limit (S/N=3) is 0.05μM. Additionally, the proposed methods obtain satisfactory results in the detection of cysteine-containing medicine samples.

This study reports that disposable, electrochemically pretreated screen-printed carbon electrodes (SPCE*) can be employed for the simultaneous determination of aminophenol isomers in aqueous buffer solution. In sharp contrast to untreated SPCE, voltammetric studies indicate that the oxidation peak potential of each analyte in an aminophenol isomer mixture may be separated at the activated SPCE*. The individual oxidation peak currents are greatly increased by first-order derivative techniques. All experimental parameters were optimized to improve responses. The derivative oxidation peak currents is proportional to the concentration of isomer over the range from 0.2 to 100μM for 2-aminophenol (2AP), from 3.0 to 200μM for 3-aminophenol (3AP), and from 0.2 to 200μM for 4-aminophenol (4AP), with detection limits of 0.07, 0.16 and 0.05μM, respectively. The proposed methods have excellent analytical characteristics that include ease of handling, high sensitivity, wide linear dynamic range and low detection limits. The assay was applied to the simultaneous determination of aminophenol isomers in river water with good recovery results.

Hydroquinone (HQ) and catechol (CA) are two positional isomers of dihydroxybenzene. They usually coexist in environmental samples and bring about pollution in our living environment. This research has developed a cheap, sensitive, and rapid method for the electrochemical determination of HQ and CA in aqueous pH 6.0 buffer solution without previous separation. By employing both anodically pretreated screen-printed carbon electrodes (SPCE*) and square wave voltammetric techniques, a direct and simultaneous determination of the two positional isomers was achieved. The oxidation peak potentials for HQ and CA were completely separated at the SPCE*, exhibiting well-defined and quasireversible redox peaks and showing greatly enhanced activity. Under optimized conditions, the linear calibration ranges for HQ and CA were in the ranges of 0.1-50 and 0.1-70 μM, with detection limits (S/N = 3) of 0.05 and 0.05 μM, respectively. This method was applied to the direct determination of HQ and CA in river water with satisfactory recovery results.

Flotation experiments with different reagents taken at Wugou Coal Preparation Plant,leading to a selection of a new collector and a high-efficient modified frother,and concurrently,effective measures taken for adjustment of operation parameters;thereby,flotation efficiency increased and reagent consumption reduced.

The electrocatalytic oxidation of cysteine at screen-printed electrode (SPE) modified with electrogenerated poly(3,4-ethylenedioxythiophene) film (PEDOT) was investigated. Cyclic voltammetric studies showed that the SPE/PEDOT electrode lowers the overpotentials and improves electrochemical behavior of cysteine oxidation, as compared to the bare SPE. The catalytic oxidation responses were studied and the reaction mechanisms were discussed. Excellent analytical features, including high sensitivity, low detection limit and satisfactory dynamic range, were achieved by flow-injection amperometry under optimized conditions.