Pulse Potential Method Research Articles

Three-dimensional anodic aluminum templates via a single-step pulsed potential method

Recent advances in the fabrication of three-dimensional Anodic Aluminum Oxide templates have opened novel opportunities in the generation of photonic structures and material nanostructuration. So far these structures have been produced from the standard two-step pulsed potential anodization and modulated current density anodization approaches. However, their fabrication is slow, with the two-step approach relying on intermediate oxide removal steps that often use toxic etchants. In this work, we report the fabrication of 3D Anodic Aluminum Oxide templates from a single-step pulsed potential method, completely removing the need for intermediate etching steps, and decreasing total fabrication times to less than 24 hours. Structural coloration was also successfully demonstrated and analyzed in these templates, for 99.999% and 99.5% Al precursors, presenting the same morphology and optical functionality as templates produced from two-step processes.

High-performance and sodiation mechanism of a pulse potential-electrodeposited Sb-Zn alloy as an anode for sodium-ion batteries

Antimony-based alloys have attracted extensive attention as promising anode materials in sodium-ion batteries (SIBs) due to their high theoretical capacity. However, the current process used to fabricate Sb-based alloys results in an almost powdery product, which leads to inadequate ion penetration and impedes electron transport when the alloys mix with nonconductive binders. Here, we have developed an advanced pulse potential electrodeposition method to prepare binder-free Sb-Zn alloys on copper foil and form a self-supported anode of SIBs. The Sb-Zn alloy anodes exhibited remarkably stable and robust Na-ion storage performance. Compared with the constant potential electrodeposition method, the Sb-Zn composite prepared using pulse potential electrodeposition exhibits higher charge/discharge capacities, a higher rate capability and superior cycle performance. The initial charge/discharge capacities of the Sb-Zn alloy anode are 377 mAh·g−1/453 mAh·g−1, and the first coulombic efficiency reaches to 83%. The specific capacity retention is 70% after 320 cycles at a charge/discharge current density of 300 mA·g−1. The reaction mechanism and reaction kinetics were determined by performing operando X-ray diffraction spectroscopy and cyclic voltammetry investigations. This work provides a potential new starting point for large scalable manufacturing of high-performance Sb-based anodes for SIBs.

Pulsed electro-synthesized tunable crystallite sizes ZnMn2O4/Mn2O3 nanocomposite as high-performance cathode material for aqueous zinc-ion batteries

Rechargeable aqueous zinc ion batteries (ZIBs) are one of the most promising candidates for large-scale energy storage, due to their high capacity, high hydrogen evolution potential, safe and cost-effective components while benefiting from the abundance of active materials. However, ZIBs still suffer from suitable cathode materials with high capacity and superior cycling stability. Herein, we study a new strategy for the synthesis of tunable crystallite sizes ZnMn2O4/Mn2O3 nanocomposite using the pulsed potential method. The effect of synthesis potential on structural, morphological, and electrochemical properties of nanocomposite was investigated via different characterization techniques. According to our results, the functional and electrochemical properties of ZnMn2O4/Mn2O3 nanocomposite are profoundly affected by the synthesis potential. The crystallite sizes of synthesized nanocomposites can be tuned from 20.2 nm to 29.3 nm, depending on the applied potential. However, the exposed surface area of nanomaterials is ranged between 50.3 m2 g−1 and 132.0 m2 g−1. The developed nanocomposite was investigated as the cathode material for aqueous zinc ion batteries. The ZnMn2O4/Mn2O3 nanocomposite exhibited an excellent discharge capacity of 216.8 mAh g−1 at 0.2 A g−1 after 200 cycles. In addition, the developed cathode showed to preserve 97.8% of its initial capacity for 2000 cycles at 2 A g−1. Apart from the high specific capacity and long cycle stability, the facile synthesis method can offer the ZnMn2O4/Mn2O3 nanocomposite as a high-performance cathode material for durable zinc ion batteries.

Robust Fe2+-doped nickel-iron layered double hydroxide electrode for electrocatalytic reduction of hexavalent chromium by pulsed potential method

• A 3D porous Fe 2+ -NiFe LDH/NF was synthesized using a spontaneous redox reaction. • Pulsed potential remarkably improved electrocatalytic Cr(VI) reduction performance. • Anodic potential accelerated the adsorption of Cr(VI) and desorption of Cr(III). • Cathodic potential can regenerate Fe 2+ and reduced. • Bare Ni foam can reduce Cr(VI) directly under cathodic potential. Electrocatalytic reduction of Cr(VI) to less toxic Cr(III) is deemed as a promising technique. Conventional electrocatalytic reduction is always driven by a constant cathodic potential, which exhibits a repelling action to Cr(VI) oxyanions in wastewater and consequently suppresses reduction kinetics. In order to remarkably accelerate Cr(VI) electrocatalytic reduction, we applied a pulsed potential on an Fe 2+ -NiFe LDH/NF electrode synthesized by in situ growth of Fe 2+ -doped NiFe LDH nanosheets on Ni foam using a spontaneous redox reaction. Under anodic potential section, HCrO 4 – anions are adsorbed on the electrode surface and reduced to Cr(III) by Fe 2+ . Then, Cr(III) ions are desorbed from the electrode surface under coulombic force. The regeneration of Fe 2+ and direct reduction of Cr(VI) are achieved under cathodic potential section. The pulsed potential can achieve complete elimination of Cr(VI) within 60 min at an initial concentration of 10 mg L −1 , and the removal efficiency shows a 60% increase with respect to that under constant cathodic potential.

A Robust Electrochemical Sensor for Determination of Thiamethoxam Based on Electrochemical Reduced Graphene Oxide-Cationic Pillar[6]arene Composite Film

On the surface of a glassy carbon electrode, electrochemically reduced graphene oxide-cationic pillar[6]arene (ErGO-CP6) composite film was constructed using a pulsed potential method. UV–vis spectra, SEM, Raman spectra and electrochemical experiments were applied to characterize the composite film. It was then used as a new electrochemical sensing platform for determination of thiamethoxam. Due to the synergistic effect of ErGO and CP6, this composite film shows a higher sensitivity and better selectivity toward thiamethoxam than that of ErGO film. The linear range from 1.0 × 10−7 to 1.3 × 10−5 mol l−1 was obtained by differential pulse voltammetry. Meanwhile, the method was applied to cucumber and tomato samples in a recovery test. The recovery was between 92.0% and 98.7%, and the results are satisfactory. This study presents a promising electrochemical sensing platform for rapid and sensitive analysis of thiamethoxam.

Polyaniline-Decorated Carbon as Composite Carrier for Improving PtNi Catalyst Durability

Polyaniline (PANI) was synthesized on carbon cloth with a diffusion layer by an electrochemical technique and characterized by Fourier-transform infrared spectrometry, x-ray photoelectron spectroscopy, and scanning electron microscopy. PANI polymerized by a potentiostatic and a pulse potential method showed different morphologies. The former showed a granular shape and the latter a reticular structure. The reticular PANI was more suitable as a catalyst carrier based on the results of a cyclic voltammetry test. A PtNi catalyst electrodeposited on the reticular PANI-decorated carbon cloth (PtNi/PANI(PP)-C) had a smaller particle size and a homogeneous distribution. PtNi/PANI(PP)-C exhibited a higher electrochemical active surface area and better electrocatalytic activity according to the cyclic voltammetry and single cell polarization tests. Linear sweep voltammetry measurements indicated that PtNi/PANI(PP)-C showed excellent oxidation-reduction reaction activity through a four-electron transfer pathway. The results of an accelerated durability test showed that the performance degradation of PtNi/PANI(PP)-C was slower than that of PtNi/C. The reticular PANI-decorated carbon carrier improved the electrochemical activity and durability of the catalyst.

An analytical study on nucleation and growth mechanism of nanostructured Ni-Se coating by the chronoamperometry and pulse potential techniques

The current paper aimed to investigate the mechanism of Ni-Se electrodeposition and contribute a comprehensive understanding of Ni-Se deposition by pulse potential technique. Firstly, electrochemical mechanisms including the reactions and nucleation mechanism of Ni-Se on glassy carbon electrode were studied using cyclic voltammetry (CV) and chronoamperometry (CA) techniques, respectively. Moreover, to investigate the nucleation and growth mode influenced by different concentrations and applied deposition potential, experimental results were fitted into Bewick 2D nucleation and Scharifker-Hills 3D nucleation models. Current transient curves showed the electrodeposition of Ni-Se phase follows both the 2D nucleation and 3D progressive nucleation and diffusion-controlled growth. This work reports how the deposition of Ni-Se nuclei by pulse potential method on different substrates and the dependence of pulse parameters on the nucleation, growth, morphology, and stoichiometry of the nanostructured Ni-Se coating.

Pulse potential method-assisted construction and regulation of a trivalent chromium conversion coating on hot-dip coated steel sheet

A pulse potential method (PPM) was used to regulate the formation of Cr(III) conversion coating (TCC) on hot-dip Zn-55 % Al-1.6 % Si. The micromorphology analysis and the contact angel measurement showed that the application of PPM changed the micro-features and hydrophobicity on the surface of TCC. Surface XPS analysis indicated that PPM increased the proportion of hydroxides and greatly reduced the content of Cr(VI) on TCC. Better corrosion resistance of the TCC was measured using multiple electrochemical methods when the pulse square-wave potential Ep = −0.10 V. The results corroborated the positive role of PPM in improving the temporary corrosion resistance of hot-dip coating.

Characterisation of backwall crack depth using the pulsed potential drop method

The alternating current potential drop (ACPD) technique has been used for monitoring backwall cracks in electrical conductors. However, previous systems required too much labour when ACPD measurements were made over a large frequency range (1 Hz-10 kHz). In this paper, a pulsed potential drop (PPD) method is found to be superior, not only in efficiency and stability but also in accurate crack detection. The detected signal excited by the pulsed current appears to be more sensitive to depth variations and, therefore, can be used for estimating crack depth in PPD testing. Experiments have been performed on AISI 1045 plates with machined cracks; the results obtained from these tests show the feasibility of crack monitoring using the PPD method.

The Controlled Preparation of Ordered Iridium Oxide Nanotubes Arrays for Oxygen Evolution Reaction

Ordered electrode is believed to be the next generation of MEA. One-dimensional-arrays material possesses high surface area, oriented electron transfer pathway and facile mass transfer pathway, which shows great potential as electrocatalyst. For OER electrode, IrO2 is still the irreplacable choice at present status. To construct IrOx based nanotube/nanowire arrays could increase the performance of OER electrode with reduced loading amount of Iridium. Titanium oxide nanotube arrays (TNTA) is a promising candidate for the preparation of 1-D arrays electrode as its prominent stability, ordered structure and sufficient conductivity with simple modification. In order to achieve the open-end nanotube structure for the fully utilization of noble metal catalyst, controlled electrochemical deposition is applied.In our previous work, IrOx nanotube arrays performs similar current density with 1/20 loading amount of commercial IrO2 nanoparticle at the same potential. To achieve the length control of IrOx nanotube arrays, the electrodeposition of IrOx on TNTA with cyclic voltametry method was studied. By altering the scan rate, continuous IrOx nanotube arrays with different length ranged from 500 nm to 1400 nm was achieved. This phenomenon may probably due to that the deposition in the tube is diffusion controlled, while the deposition at the mouth of TNTA keeps constant due to sufficient supplement of precursor form the bulk electrolyte. In a single cycle, as the depositing goes on, the concentration gradient along the tube forms and results in uneven deposition. Different scan rate results in different duration of depositing in a single cycle. And longer duration means more uneven deposition, and leads to shorter nanotube.At present, to obtain IrOx nanotube arrays with uniform tube wall, control deposition with pulsed potential deposition method is studied. By altering the relaxation and deposition time, IrOx with uniform thickness and tunable length can be achieved. And the thickness of IrOx tube wall can be controlled, too. By achieving uniform and thinner tube wall, the utilization rate of Iridium can be further increased.

Pulse electrodeposition of nickel selenide nanostructure as a binder-free and high-efficient catalyst for both electrocatalytic hydrogen and oxygen evolution reactions in alkaline solution

Herein, we report a pulse potential electrodeposition method (PPE) as a fast and one-step route for the production of effective and binder-free Ni–Se catalysts for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in alkaline solution. The results demonstrated that the fabricated electrocatalysts by PPE show more desirable electrocatalytic performance than constant potential electrodeposition method (CPE). The electrodeposited NiSe nanostructures with large electrochemically active surface area of 2965 on the nickel foam (NF) at the frequency of 0.01 Hz exhibited high electrocatalytic activity for HER and OER. It delivers the current density of 10 mA/cm2 at the overpotential of 65 mV for HER and 100 mA/cm2 at 306 mV for OER in 1 M KOH. In addition, the Tafel slope for HER and OER was 89 and 61 mV/dec respectively. Morphological stability of NiSe nanostructure catalyst leads to an increase the electrocatalytic stability during long-term electrolysis.

High-efficiency and sustainable photoelectric conversion of CO2 to methanol over CuxO/TNTs catalyst by pulse potential method

Herein, we report a special pulse potential method to increase methanol production and keep the CuxO/TiO2 nanotube array (TNT) catalyst active during photoelectrocatalysis reduction of CO2. The CuO/TNT catalyst was prepared via electrodeposition of copper on anodized titanium oxide followed by heat treatment. The variation of valence of copper in the photoelectrocatalytic reduction process was studied intensively by high-resolution transmission electron microscopy, XPS, and AES characterizations. Results show that the photocatalytically active CuO is apt to be reduced to elementary Cu during photoelectrocatalysis process, leading to rapid decay of photocatalytic activity. While for the case of pulse potential regime, another photocatalytically active oxide, Cu2O, will be produced on the surface during anodic pulse, which can effectively maintain the photocatalytic activity of catalyst. CV study indicates that the oxidation of Cu is prior to the oxidation of methanol, so the methanol oxidation hardly ever happens during anodic pulse stage. The catalyst applied in pulse potential regime provided a much larger photocurrent than that in constant potential regime over an extended period of time. As a result, the yield of methanol produced in optimized pulse potential condition is greatly increased, nearly twice that in constant potential regime.

Pulse-potential electrochemical fabrication of coaxial-nanostructured polypyrrole/multiwall carbon nanotubes networks on cotton fabrics as stable flexible supercapacitor electrodes with high areal capacitance

Flexible supercapacitors (FSCs) with a high areal capacitance are essential for future wearable energy-storage devices due to the limitation of available area on the surface of the human body (< 2 m2). To achieve the performance with high areal capacitance, the surface structure of electrodes should be designed carefully. In this paper, a hierarchical composite electrode based on coaxial-nanostructured polypyrrole (PPy) and multiwall carbon nanotube (MWCNT) was electrochemical co-deposited on the surface of the MWCNT-coated cotton fabric (MCF) by a facile pulse potential method. The pulse potential co-deposition conditions-lower potential (EL), the number of cycles (NC) and EL duration time (tL)-played crucial roles in the uniform distribution of MWCNT within PPy/MWCNT composites, thickness of PPy shell and porous morphology. The three-dimension porous networks of PPy/MWCNT/MCF electrodes not only enhanced the efficiency of faradaic redox reactions but also facilitated the accessibility of the electrolyte to electrode surface, accordingly presenting an ultrahigh areal specific capacitance of 5.05 F cm−2 (0.001 V s−1) and unexceptionable cycling stability of 129.20% specific capacitance retention (1000 cycles, 0.02 V s−1). This work provides a new route to develop FSCs electrodes and shows a promising application in wearable energy-storage technology.

Direct Electrodeposition to Fabricate 3D Graphene Network Modified Glassy Carbon Electrode for Sensitive Determination of Tadalafil

In this work, pulse potential method (PPM) was presented to fabricate directly three-dimensional graphene (3DG) network on the surface of glassy carbon electrode (GCE). The morphological characteristic of 3DG network were investigated by means of Raman spectra, scanning electron microscopy (SEM) and electrochemical experiments. The 3DG network as a new voltammetric material was used to develop a high-sensitive electrochemical sensor for determination of tadalafil. Electrochemical tests showed that the 3DG network can help to enhance response due to the large accessible surface area as well as its excellent conductivity. Under the optimum conditions, the electrochemical response showed a linear relationship with tadalafil concentrations in the range of [Formula: see text]–[Formula: see text][Formula: see text]mol[Formula: see text]L[Formula: see text], and a low detection limit of [Formula: see text][Formula: see text]mol[Formula: see text]L[Formula: see text] was achieved for tadalafil. Moreover, the fabricated electrochemical sensor exhibited excellent selectivity, stability, reproducibility and repeatability, which make it very suitable for analytical applications for the trace level determination of tadalafil.

Methanol Oxidation on Galvanostatically Electrodeposited Nipt Nanoparticles: Correlation between Deposition Current Density and Catalytic Activity

Among the different types of fuel cells, alkaline direct alcohol fuel cells (ADAFC) have attracted significant attention. Compared to hydrogen fuel cells, ADAFC are easy to handle, store and transport and have high volumetric energy density, which makes them strong candidates to power portable devices and consumer electronics [1]. The alkaline medium of ADAFCs favors faster reaction kinetics, low over-potentials and non-noble metals can be used as catalysts [2]. Nickel based materials have shown to be good catalysts for alcohol oxidation reaction in alkaline media [3, 4]. Furthermore, studies on NiPt nanoparticles suggest that the presence of Ni enhances the catalytic properties of Pt [5,6]. The present work proposes a methodology of galvanostatic electrodeposition of bimetallic NiPt nanoparticles on gold. Traditionally, nanoparticles are electrodeposited by double pulse potential method; however, previous works in our group proved that galvanostatic control leads to the formation of smaller particles and narrower size distribution [7]. Electrodepositions were carried out applying a two second current pulse in a platting bath containing 50 mM NiSO4 + 1.5 mM K2PtCl4 + 500mM NaCl at pH 2.0. Figure1a depicts the electrode potential response to pulses of different current densities. Increasing the current density pulses results in shorter times for each of the three stages transition present. During a galvanostatic experiment, the working electrode potential adjusts to a value that ensures a charge transfer rate for an electrochemical process whose kinetics is consistent with the current demanded by the experiment. Thus, it can be inferred that each potential drop is associated to a different electrochemical process. Cycling at 1M KOH generates a layer of NiOOH, which is the active species on the electro-oxidation of methanol on Ni in alkaline media. The catalytic properties of the deposited material were tested by cyclic voltammetry in 1M KOH + 0.5 M methanol. A typical voltammogram is shown in Figure1b. The forward scan exhibits three anodic peaks: Iaf, IIaf and IIIaf. The first one corresponds to the oxidation of methanol on Pt, while the second and third peaks are caused by the formation of NiOOH and oxidation of methanol on NiOOH, respectively. During the backward scan Ni and Pt surfaces regenerate their active sites by desorption of poisonous species [8, 9] generating two anodic peaks (Iab and IIIab). Following Fetohi et al. [6], the Iaf/ Iab ratio and the electrocatalytic intensity (EI= Iaf+ Iab) were calculated. Larger values of the Iaf/ Iab are desired since this indicates that the catalyst has a good tolerance to poisoning. As shown on Figure1c, better poisoning tolerances are achieved when the deposits are produced at higher current densities. It is noteworthy that the Iaf/ Iab obtained for the electrodeposited materials are larger than 15, while for electrodeposited Pt this ratio is 1.8. The EI parameter was introduced by Ding et al. [5] to evaluate electrocatalytic ability of the deposited material. Figure1d shows how the best EI is achieved when the deposit is obtained by applying a pulse of 4.0 mAcm-2. Applying the same criterion to peaks IIIaf and IIIab suggest the highest catalytic activity of NiOOH is also achieved for the same deposit. Galvanostatic control resulted on the deposition of NiPt particles with high tolerance to CO poisoning. Electrocatalytic activity of the deposits can be tuned by adjusting the intensity of the current pulse. Fig. 1 a) Potential transients during galvanostatic deposition of NiPt from 50 mM NiSO4 + 1.5 mM K2PtCl4 +500mM NaCl with a pH of 2.0. b) Cyclic Voltammogram of NiPt deposit in 0.5 M Methanol in 1 M KOH at 50 mVs-1. c) Dependence of the Iaf/ Iab ratio and d) Dependence of the electrocatalytic intensity on the deposition current density. References I. Ozoemena, RSC Adv., 6, 89523 (2016).R. Varcoe, and R. C. T. Slade Fuel Cells, 5, 187 (2005).Fleischmann, K. Korinek and D. Pletcher, J.Electroanal.Chem.Interfacial Electrochem. 31,39 (1971).S. Ferdowsi, S. A. Seyedsadjadi, A. Ghaffarinejad, J. Nanostruct. Chem., 5, 17, (2015).Ding, Y. Zhao, L. Liu, Y. Cao, Q. Wang, H. Gu, X. Yan, Z. Guo, Int. J. Hydrog. Energy, 39, 17622 (2014).E. Fetohi, R.S. Amin,*, R.M. Abdel Hameed, K.M. El-Khatiba, Electrochim. Acta, 242, 187 (2017).T. Martínez, G. Zavala, and M. Videa, J. Mex. Chem. Soc., 53, 7 (2009).Danaee, M. Jafariana, F. Forouzandeh, F. Gobal, M.G. Mahjani, Int. J. Hydrog. Energy, 33, 4369 (2008).-Y. Zhao, C.-L. Xu, D.-J. Guo, H. Li, H.-L. Li, J. Power Sources, 162, 492 (2006). Figure 1

Effect of electrodeposition modes on ruthenium oxide electrodes for supercapacitors

With developments in energy storage devices, supercapacitors are gaining more attraction because of their potential to excel batteries shortly. In this work, ruthenium oxide (RuO2) has been deposited on stainless steel and studied the influence of surface modification of solid electrodes on capacitance properties. Hydrous ruthenium oxide was plated by different modes such as potential sweep method (cyclic voltammetric), constant potential method (chronoamperometry) and optimised potential pulse method using a recently reported precursor material namely ruthenium nitrosylsulfate (RuNS). The structural information and morphology of electrodeposits were characterised by X-ray diffractometer and scanning electron microscope respectively. The XRD studies indicate a poor crystalline state for RuO2 in all the modes of deposition but can contribute to a higher surface area when compared to a highly crystalline form. The SEM analysis revealed the formation of surface modification concerning the change of potential mode. Mud-cracked morphology, spherical particles and dendrimeric morphology observed on chronoamperometry, potential pulse and cyclic voltammetry respectively. Electrochemical studies were also conducted on the samples to assess their performance for supercapacitor applications. The spherical particles of hydrous RuO2 show high performance of capacitance behaviour 1180 F/g in 0.5 M H2SO4 at the scan rate of 5 mV/s. Dendrimeric morphology and mud-cracked morphology shows 573 F/g and 546 F/g respectively in same 0.5 M H2SO4 at the scan rate of 5 mV/s. The studies reveal that RuO2 electrodes can be exploited for their outstanding capacitive behaviour by properly controlling the morphology of the deposits.

Electrochemical redox induced rapid uptake/release of Pb(II) ions with high selectivity using a novel porous electroactive HZSM-5@PANI/PSS composite film

A porous electroactive composite based film made of core@shell nanospheres is uniformly fabricated on the conductive substrate by artfully applying the alternative assembly of the polyaniline/polystyrene (PANI/PSS) and the high-crystalline protonated Zeolite Socony Mobil-5 (HZSM-5) nanospheres via a potential pulse method. The isolated HZSM-5 nanospheres are interconnected and linked up by the chains of PANI/PSS that act as bridges for electron transportation. In this composite film, the HZSM-5 nanospheres provide the protons to further improve the electroactivity of PANI based on the unique proton “round-trip” transfer effect during the electrochemical redox process. The obtained HZSM-5@PANI/PSS composite based film shows fast electrochemical uptake/release ability for the removal of Pb2+ ions from the aqueous solution because of the strong driving force resulting from the electric field, and the adsorption equilibrium time is less than 60 min. When the initial concentration of Pb2+ ions is 100 mg L−1, the ion adsorption quantity reaches 240.6 mg g−1 and retains 97.1% of its initial value after 5 uptake/release cycles. Especially, the selectivity factors of the HZSM-5@PANI/PSS film for Pb2+/Ni2+, Pb2+/Co2+, Pb2+/Cd2+, and Pb2+/Zn2+ reach up to 21.97, 26.19, 24.61, and 39.29, respectively. Such high selectivities for Pb2+ ions are realized by artfully using the significantly lower Gibbs energy of dehydration of Pb2+ ions than that of other listed metal ions, which makes the Pb2+ ions easily adsorbed into the composite film based on the confinement effect of the HZSM-5. Furthermore, the consumed energy for dehydration is supplied by the electric field, resulting in the decrease of the ions transport resistance and the increase of the adsorption capacity of the composite film.

Controlled Selectivity of CO2 Reduction on Copper by Pulsing the Electrochemical Potential.

We demonstrate a simple strategy to enhance the CO2 reduction reaction (CO2 RR) selectivity by applying a pulsed electrochemical potential to a polycrystalline copper electrode. By controlling the pulse duration, we show that the hydrogen evolution reaction (HER) is highly suppressed to a fraction of the original value (<5 % faradaic efficiency) and selectivity for the CO2 RR dramatically improves (>75 % CH4 and >50 % CO faradaic efficiency). We attribute the improved CO2 RR selectivity to a dynamically rearranging surface coverage of hydrogen and intermediate species during the pulsing. Our finding provides new insights into the interplay of transport and reaction processes as well as timescales of competing pathways to enable new opportunities to tune CO2 RR selectivity by adjusting the pulse profile. Additionally, the pulsed potential method we describe can be easily applied to other catalysts materials to improve their CO2 RR selectivity.

Microelectrode Glucose Detection at the Human Mucosa

Earlier work by this research group developed the ability to detect cholesterol at the human oral mucosa using a microelectrode double potential pulse method. Hydrogen peroxide produced by the oxidase enzyme accumulates at the electrode-tissue interface and is oxidized serially by sequential potential step perturbations. A second step measures the background prior to significant generation of hydrogen peroxide providing semi-real-time signal correction. The corrected signal contains unremoved background that arises from reversible surface chemistry coupled to the potential perturbation where the short time between the first potential step for hydrogen peroxide oxidation and the second potential step for background measurement does not allow compete re-establishment of the surface condition that is reached during accumulation of hydrogen peroxide over longer time. The magnitude of the reversible charge correlates with the amount of exposed platinum surface atoms that serve as the catalyst for hydrogen peroxide oxidation. Normalization of data from different electrodes is possible using the negative charge that passes upon returning the potential to the initial potential after the first step. Data for detection of glucose at the human mucosa is presented.

Facile fabrication of 3D graphene–multi walled carbon nanotubes network and its use as a platform for natamycin detection

In this work, a three dimensional graphene-multiwalled carbon nanotubes (3DG-MWCNTs) network is successfully fabricated on the surface of glassy carbon electrode (GCE) using pulse potential method (PPM) in a graphene oxide-multi walled carbon nanotubes (GO-MWCNTs) homogeneous dispersion. Scanning electron microscopy (SEM) images and electrochemical experiments confirmed the 3D structure of interpenetrated graphene-MWCNTs network and excellent electrochemical performance. The 3DG-MWCNTs network was presented to develop a sensitive voltammetric sensor for detection of natamycin. Systematic electrochemical tests demonstrate that the 3DG-MWCNTs network modified electrode can effectively increase response to the oxidation of natamycin due to the large accessible surface area as well as its excellent conductivity. Under optimized conditions, the voltammetric sensor showed a linear relationship in the range of 5.0 × 10−8–2.5 × 10−6 mol L−1 and a low detection limit of 1.0 × 10−8 mol L−1. Moreover, the proposed method was also applied for detection of natamycin content in real samples (commercial red wine and beverage).