Repetitive Potential Cycling Research Articles

Electrodeposited Carbonyl Functional Polymers as Suitable Supports for Preparation of the First-Generation Biosensors.

The aim of this electrochemical study was to ascertain which type of electrochemically deposited carbonyl functionalized polymer represents the most suitable electrode substrate for direct covalent immobilization of biological catalysts (enzymes). For this purpose, a triad of amperometric biosensors differing in the type of conductive polymers (poly-vanillin, poly-trans-cinnamaldehyde, and poly-4-hydroxybenzaldehyde) and in the functioning of selected enzymes (tyrosinase and alkaline phosphatase) has been compared for the biosensing of neurotransmitters (dopamine, epinephrine, norepinephrine, and serotonin) and phenyl phosphates (p-aminophenyl phosphate and hydroquinone diphosphate). The individual layers of the polymers were electrochemically deposited onto commercially available screen-printed carbon electrodes (type C110) using repetitive potential cycling in the linear voltammetric mode. Their characterization was subsequently performed by SEM imaging and attenuated total reflectance FTIR spectroscopy. Molecules of enzymes were covalently bonded to the free carbonyl groups in polymers via the Schiff base formation, in some cases even with the use of special cross-linkers. The as-prepared biosensors have been examined using cyclic voltammetry and amperometric detection. In this way, the role of the carbonyl groups embedded in the polymeric structure was defined with respect to the efficiency of binding enzymes, and consequently, via the final (electro)analytical performance.

Oxygen Reduction Reaction on Pt-Y/C Catalysts: Activity and Long-Term Stability Study

Pt-Y/C catalysts were prepared by a modified formic acid method and their structural characteristics and activity for oxygen reduction reaction (ORR) were evaluated. X-ray diffraction analysis showed that no alloy was formed between the metals and X-ray photoelectron spectroscopy (XPS) experiments showed that yttrium is presented as Y2O3, Y(OH)3 and Y-O-Pt species. CO stripping voltammetry and in situ X-ray absorption spectroscopy confirmed the interaction between Pt nanoparticles and yttrium species. The Pt-Y/C 7:3 material showed the higher specific activity (103 μA cmPt -2) for ORR. Following repetitive potential cycling, the activity for the ORR of the Pt-Y/C 7:3 catalyst declined in a similar proportion to the Pt/C material. Transmission electron microscopy analysis after stability for both catalysts showed that Pt/C particle size slightly increased and that for Pt-Y/C 7:3 remained the same. XPS made in ultrathin catalyst layer, agreeing with energy-dispersive X-ray spectroscopy analysis, revealed that the intensities of the Y 3d peaks were suppressed relative to the initial one and that yttrium in the form of Y2O3 and Y(OH)3 were dissolved, while the species Y-O-Pt still remain in the catalyst, maintaining the higher activity.

CO Tolerance and Stability of Graphene and N-Doped Graphene Supported Pt Anode Electrocatalysts for Polymer Electrolyte Membrane Fuel Cells

Pt electrocatalysts supported on pristine graphene nanosheets (GNS) and nitrogen-doped graphene nanoplatelets (N-GNP) were prepared through the ethylene glycol process, and a comparison of their CO tolerance and stability as anode materials in polymer electrolyte membrane fuel cells (PEMFCs) with those of the conventional carbon (C)-supported Pt was made. Repetitive potential cycling in a half cell showed that Pt/GNS catalysts have the highest stability, in terms of the highest sintering resistance (lowest particle growth) and the lowest electrochemically active surface area loss. By tests in PEMFCs, the Pt/N-GNP catalyst showed the highest CO tolerance, while the poisoning resistance of Pt/GNS was lower than that of Pt/C. The higher CO tolerance of Pt/N-GNP than that of Pt/GNS was ascribed to the presence of a defect in graphene, generated by N-doping, decreasing CO adsorption energy.

Electropolymerized Porous Polymer Films on Flexible Indium Tin Oxide Using Trifunctional Furan Substituted Benzene Conjugated Monomer for Biosensing

In recent years, conducting polymers are playing a significant role in the field of display devices, transistors, solar cells, sensors, and electrochromic windows due to their outstanding optoelectronic and semiconducting properties due to their conjugated backbone. One potential application that is not as widely explored using these materials is biosensing, where advantage is taken of the porosity that can be generated by the polymerization of a three-dimensional network. There are various approaches for producing conjugated microporous polymers using trifunctional or multifunctional monomers synthesized via chemical or electrochemical methods. In this work, we have used electropolymerization to synthesize conjugated polymer films on a working electrode of flexible indium tin oxide (FITO) using a trifunctional conjugated monomer 1,3,5-tri(furan-2-yl)benzene (TFB). There are several parameters that influence the formation of a porous polymer film, and the most critical ones are substrate conductivity, roughness, method of electropolymerization, and choice of an electrolyte. These porous electropolymerized films were characterized using UV–vis spectroscopy (UV–vis), X-ray photoelectron spectroscopy (XPS), surface profilometry, four-point probe conductivity measurements, and scanning electron microscopy (SEM). The polymer films that were electropolymerized using chronoamperometry rather than repetitive potential cycling demonstrated a more suitable morphology to trap DNA/RNA analytes for biosensing applications.

Electrochemically Reduced Graphene Oxide – Noble Metal Nanoparticles Nanohybrids for Sensitive Enzyme-Free Detection of Hydrogen Peroxide

Electrochemically reduced graphene oxide (ERGO) is a versatile material for the electrode modification, which enables modification of the physicochemical properties of the surface by the reduction and reoxidation of oxygen groups. The oxygen functional groups and structural defects of ERGO deposited on a layer of metal nanoparticles facilitate the electron transport and enhance the electrocatalytic properties of the nanoparticles. ERGO layers show moderate-intrinsic electrocatalytic properties towards the electrochemical reduction of hydrogen peroxide. In this contribution, we present studies of ERGO layers on the top of the nanoparticle layer composed of gold nanoparticles stabilized with silicotungstate ligands (Au/SiW12), silver nanoparticles stabilized with silicotungstate ligands (Ag/SiW12), and silver nanoparticles stabilized with phosphomolybdate ions (Ag/PMo12). The nanoparticles are prepared by the reduction of the chloroauric acid or silver nitrate by the partially reduced forms of H4SiW12O40 or H3PMo12O40 acid. The films of nanoparticles are conditioned by the repetitive potential cycling at pH = 6 before the deposition of the graphene oxide (GO) layer. The GO layer is reduced by scanning the potential between − 0.4 and − 1.2 V vs. SCE. Combination of ERGO with Au/SiW12 or Ag/SiW12 nanoparticles results in synergistic enhancement of amperometric responses to hydrogen peroxide. The electrocatalytic current values observed for the NPs-ERGO layers are higher than the sum of the current for the pure NPs layers and the ERGO layer deposited on a glassy carbon electrode. The Ag/PMo12 nanoparticles show poor electrocatalytic currents due to possible formation of aggregate structures. Infrared and Raman spectroscopies are applied to investigate the electrocatalytic layers.

Preparation of Sb-Doped SnO2 Nanoparticle with High Surface Area for Use As a Stable Anode Catalyst Support for PEM Electrolyzers.

Proton exchange membrane (PEM) water electrolysis has been considered as one of the most promising technologies for large H2 production. While the cost and stability of PEM are the main obstacles for the commercial application. Here we report a cost-effective catalyst, which consists of IrO2 nanoparticles supported on Sb-doped SnO2 (ATO). ATO support is synthesized by using templating process and hydrothermal method to improve its thermal stability. It has a mesoporous structure, small particle size, and high surface area. After loading IrO2 via Adams fusion method, the IrO2/ATO catalyst shows high electrochemical stability, according to repetitive potential cycling. This catalyst also shows a good electrochemical performance in single cell. Firstly, we prepared a series of ATO samples and named them as the Brunauer Emmett Teller model (BET) surface area. The surface area and pore size distribution of the obtained ATO samples were calculated by BET and nonlocal density functional theory (NLDFT). As shown in Fig.1a, the pore size become smaller with the increases of BET surface area, and the high surface area may be contributed to high synthesize temperature and long synthesize time. Secondly, we use the as-prepared ATO samples as catalysts support for IrO2, the catalysts named as BET surface area-IrO2 (e.g. 107-IrO2) and the IrO2 loading is 40 wt%. Fig.1b shows the cyclic voltammetry (CV) performance of different catalysts, it is quite clear that when supported by ATO, the voltammograms of these supported catalysts are dissimilar in shape from that of unsupported IrO2. The electrochemically active surface area (ECSA) of 170-IrO2 is obvious higher than the other ATO supported catalyst and a little higher than pure IrO2. This indicate that the 170 sample has the appropriate surface area as well as pore size distribution and it is best used as for IrO2 catalyst support. Finally, the accelerated degradation testing (ADT) was performed to investigated the durability of the 170-IrO2 catalyst in rotating disk electrode (RDE) test. As shown in Fig.1c the CV curves almost overlap before and after 9000 cycles’ ADT. Fig.1d shows the Linear sweep voltammetry (LSV) results of the catalyst samples before and after ADT. It is quite obvious that the 170-IrO2 catalyst is maintained stable with only a little loss in the catalytic activity. We have successfully made a series of ATO through templating process followed by hydrothermal method with different BET surface area and used as catalyst support for IrO2. The 170-IrO2 catalyst demonstrates high electrochemical performance and good stability. Herein, the as-synthesized ATO is considered to be a promising oxygen evolution catalyst support for solid polymer electrolyte water electrolyzer applications. Figure 1

Surface voltammetric dealloying investigation on PdCu/C electrocatalysts toward ethanol oxidation in alkaline media

Voltammetric dealloying is employed here to investigate the correlations between catalytic performance and surface composition and structure, taking ethanol oxidation reaction (EOR) on Pd-Cu alloy surface as a case study. First, home-made PdCu/C with a mean particle size of ca. 3.11 ± 0.6 nm is dealloyed by repetitive potential cycling in 0.5 M H2SO4. With dealloying cycles rising, the Cu component is gradually leached out and the corresponding Pd/Cu atomic ratio gradually increases from ca. 2.1 to 4.0; meanwhile, SEM images display that Pd-rich porous shell is formed due to dealloying-induced surface structural rearrangement, being verified by the appearance of ear-like peaks at − 0.015 V (vs. SCE) in CVs collected in 0.5 M H2SO4; furthermore, XPS spectra indicate that core-level binding energies of Pd 3d5/2 first positively shift to 336.1 eV and then oppositively move down to 334.9 eV, indicating that the d-band center of Pd composition is modulated by the dealloying treatment. Moreover, the voltammetric peak current densities for EOR follow the order of PdCu/C-DA15 > as-prepared PdCu/C ˃ > PdCu/C-DA30 ˃ commercial Pd/C ˃ PdCu/C-DA75, due to the modest downshift of Pd d-band center resulted by charge transfer and surface atomic rearrangement. In addition, the EOR durability gradually decays with the continuous loss of Cu, indicating that electro-oxidation of surface species also follows the so-called bi-functional mechanism. This work might provide some new insights into the catalysis enhancement by tuning the surface/interfacial structure of catalysts.

Electrochemical determination of ATP at rhodamine6G capped gold nanoparticles modified carbon felt electrode at pH 7.2

We report the electrochemical determination of adenosine-tri-phosphate (ATP) using rhodamine6G capped gold nanoparticles (FCGN) modified carbon felt (CF) as working electrode in phosphate buffer solution (PBS; 0.2 M) as a supporting electrolyte at pH 7.2. It was found that FCGN-modified-CF electrode not only enhanced the oxidation currents, but also showed uniform shift in the current with repetitive potential cycles. Selective determination of ATP in the presence of high concentration of AMP, ADP, H2PO4– and HP2O73– and the effect of pH on electrochemical behavior of ATP was also examined. Cyclic voltammetry (CV) and differential pulse voltammetry (DPV) studies demonstrate typical peaks ca. + 0.60 V and +2.25 (vs. SCE), respectively with excellent selectivity and sensitivity. The interface property of FCGN-modified-CF electrode was investigated by impedance spectroscopy. Under optimum experimental conditions, the calibration plots are linear in the 10–100 nM range with detection limit of (LoD) ∼ 8.0 nM. Furthermore, the sensitivity of Rh6 G–Au NPs towards ATP was reconfirmed by fluorescence titration study, which is in accord with electrochemical experimental findings.

Pt nanoparticles sputter-deposited on TiO2/MWCNT composites prepared by atomic layer deposition: Improved electrocatalytic activity towards the oxygen reduction reaction and durability in acid media

Acid-treated multi-walled carbon nanotubes (MWCNTs) were decorated with TiO2 using the atomic layer deposition (ALD) technique followed by uniform distribution of platinum nanoparticles (PtNPs) through magnetron sputtering. Surface analyses were performed by scanning electron microscopy (SEM), scanning transmission electron microscopy (STEM) and X-ray photoelectron spectroscopy (XPS). Electrochemical decontamination and characterization of the Pt-TiO2/MWCNT electrodes were carried out by CO stripping followed by cyclic voltammetry in acid media. The oxygen reduction reaction (ORR) was studied in O2-saturated 0.05 M H2SO4 solution using the rotating disk electrode (RDE) method. Durability of the prepared catalysts was examined by repetitive potential cycling. Electrochemical data obtained was analyzed and compared to that of the commercial Pt/C catalyst. It was revealed that the Pt-TiO2/MWCNT catalysts possess higher ORR activity and better durability as compared to that of the commercial Pt/C.

Electrochemically reduced graphene oxide on gold nanoparticles modified with a polyoxomolybdate film. Highly sensitive non-enzymatic electrochemical detection of H2O2

Gold nanoparticles (AuNPs) were prepared via the chloroauric acidreduction using Keggin-type anions (PMo12O403−). The layer of AuNPs was deposited on the glassy carbon electrode (GC) and conditioned using repetitive potential cycling between 0.3 and −0.4 V vs. SCE in the buffer solution at pH = 6. The changes in the polyoxometalate structure upon cycling are studied using Raman spectra. Graphene oxide (GO) was drop-cast on a thin layer of AuNPs on a GC electrode. Then, GO was reduced by scanning the electrode potential between −0.4 and −1.2 V vs. Ag/AgCl. The resulting layer of the electrochemically reduced graphene oxide(ERGO) on AuNPs shows non-enzymatic sensitivity to hydrogen peroxide. The sensitivity of the ERGO/AuNPs/GC/electrode to H2O2equals 741 mA mM−1 cm‐2 (limit of detection is equal to 56 nM) for the H2O2concentration lower than 0.1 mM, and 381.5 μA mM−1 cm‐2 at the higher concentration of H2O2. The electrocatalytic activity of the bare AuNPs layer and the activity of ERGO deposited directly on the GC electrode are significantly lower, which pointing to a synergistic effect between ERGO and AuNPs. The electrodes are characterized using Raman spectra. The mechanism of the ERGO-AuNPs synergistic electrocatalysis is proposed.

Electrochemical synthesis of nickel–cobalt oxide nanoparticles on the glassy carbon electrode and its application for the voltammetric determination of 4-nitrophenol

In this article, a new voltammetric sensor for determination of 4-nitrophenol (4-NP) based on nickel–cobalt oxide nanoparticle (Ni–CoOX NPs)-modified glassy carbon electrode (GCE) was presented. The nickel–cobalt nanoparticles (Ni–Co NPs) were firstly electrodeposited on the GCE by repetitive potential cycling method, and then, the deposited NPs were converted to Ni–CoOX NPs by sweeping the potential of the electrode from 0.0 to 0.6 V in 0.1 M NaOH solution. The obtained electrocatalyst (Ni–CoOX NPs) was analysed via scanning electron microscopy and energy-dispersive X-ray spectroscopy. 4-Nitrophenol showed a well-defined reduction peak at about −733 mV at the Ni–CoOX NPs/GCE in the phosphate buffer solution (pH 6.0). Compared with the bare GCE, the reduction peak current was clearly enhanced and the overpotential was significantly decreased at the Ni–CoOX NPs/GCE. The diffusion coefficient (D) of 4-nitrophenol at the modified electrode was also determined utilizing chronoamperometry. The current response of the modified electrode was linear with the 4-NP concentration in the range from 7 to 682 µM, with a detection limit of 4.8 µM (S/N = 3), using differential pulse voltammetry.

Effect of atomic composition on the compressive strain and electrocatalytic activity of PtCoFe/sulfonated graphene

The aim of this work is improvement of the stability and durability of sulfonated graphene supported PtCoFe electrocatalyst (PtCoFe/SG) for application in proton exchange membrane fuel cells (PEMFCs). The durability investigation of PtCoFe/SG is evaluated by a repetitive potential cycling test. The compressive strain in the lattice of PtCoFe/SG towards the electrocatalytic oxygen reduction reaction is studied. The synthesized electrocatalysts are examined physically and electrochemically for their structure, morphology and electrocatalytic performance. It is shown that presence of SO3 groups on the graphene cause better adsorption of PtCoFe nanoparticles on the support and increase stability of electrocatalysts. Also, it is shown that Co:Fe atomic ratio in the synthesized electrocatalysts plays important role in their electrocatalytic performance. In the optimum Co:Fe atomic ratio, the compressive strain goes through the ideal value of the binding energy; further increase in Co/Fe atomic fraction introduces the excessive compressive strain and the activity of electrocatalyst decreases. The electrocatalyst synthesized in the optimum conditions is utilized as cathode in PEMFC. The power density of the PEMFC in low metal loading (0.1mgcm−2 Pt) reaches to a maximum of 530mWcm−2 at 75°C. It suggests that PtCoFe/SG with 7:3 Co:Fe atomic ratio promises to improve the power density of PEMFCs.

Platinum Particles Electrochemically Deposited on Multiwalled Carbon Nanotubes for Oxygen Reduction Reaction in Acid Media

Platinum nanoparticles supported on multiwalled carbon nanotubes (Pt/MWCNT) were prepared using controlled electrochemical deposition from Ar-saturated H2PtCl6 solution. The electrodeposition parameters were varied to observe change in the surface morphology and electrocatalytic activity of the Pt/MWCNT catalysts for oxygen reduction reaction (ORR). Surface morphology of the prepared catalysts was studied by scanning electron microscope (SEM) and scanning transmission electron microscope (STEM). For electrochemical characterization of the Pt/MWCNT electrocatalysts, CO-stripping and cyclic voltammetry (CV) experiments were performed in 0.05 M H2SO4 solution. The ORR was studied in acid medium using the rotating disk electrode (RDE) method. The results obtained were analyzed and compared to those of commercial Pt/C. The size, shape and distribution of Pt particles as well as the electrochemical behavior of Pt/MWCNT modified electrodes showed strong dependence on the deposition parameters. The catalyst materials prepared by electrochemical deposition showed higher specific activities than commercial Pt/C catalyst. The Pt/MWCNT cathode materials showed remarkable stability during repetitive potential cycling in 0.05 M H2SO4.

Iridium Oxide-reduced Graphene Oxide Nanohybrid Thin Film Modified Screen-printed Electrodes as Disposable Electrochemical Paper Microfluidic pH Sensors.

A facile, controllable, inexpensive and green electrochemical synthesis of IrO2-graphene nanohybrid thin films is developed to fabricate an easy-to-use integrated paper microfluidic electrochemical pH sensor for resource-limited settings. Taking advantages from both pH meters and strips, the pH sensing platform is composed of hydrophobic barrier-patterned paper micropad (µPAD) using polydimethylsiloxane (PDMS), screen-printed electrode (SPE) modified with IrO2-graphene films and molded acrylonitrile butadiene styrene (ABS) plastic holder. Repetitive cathodic potential cycling was employed for graphene oxide (GO) reduction which can completely remove electrochemically unstable oxygenated groups and generate a 2D defect-free homogeneous graphene thin film with excellent stability and electronic properties. A uniform and smooth IrO2 film in nanoscale grain size is anodically electrodeposited onto the graphene film, without any observable cracks. The resulting IrO2-RGO electrode showed slightly super-Nernstian responses from pH 2-12 in Britton-Robinson (B-R) buffers with good linearity, small hysteresis, low response time and reproducibility in different buffers, as well as low sensitivities to different interfering ionic species and dissolved oxygen. A simple portable digital pH meter is fabricated, whose signal is measured with a multimeter, using high input-impedance operational amplifier and consumer batteries. The pH values measured with the portable electrochemical paper-microfluidic pH sensors were consistent with those measured using a commercial laboratory pH meter with a glass electrode.

Iridium Oxide-reduced Graphene Oxide Nanohybrid Thin Film Modified Screen-printed Electrodes as Disposable Electrochemical Paper Microfluidic pH Sensors

A facile, controllable, inexpensive and green electrochemical synthesis of IrO2-graphene nanohybrid thin films is developed to fabricate an easy-to-use integrated paper microfluidic electrochemical pH sensor for resource-limited settings. Taking advantages from both pH meters and strips, the pH sensing platform is composed of hydrophobic barrier-patterned paper micropad (µPAD) using polydimethylsiloxane (PDMS), screen-printed electrode (SPE) modified with IrO2-graphene films and molded acrylonitrile butadiene styrene (ABS) plastic holder. Repetitive cathodic potential cycling was employed for graphene oxide (GO) reduction which can completely remove electrochemically unstable oxygenated groups and generate a 2D defect-free homogeneous graphene thin film with excellent stability and electronic properties. A uniform and smooth IrO2 film in nanoscale grain size is anodically electrodeposited onto the graphene film, without any observable cracks. The resulting IrO2-RGO electrode showed slightly super-Nernstian responses from pH 2-12 in Britton-Robinson (B-R) buffers with good linearity, small hysteresis, low response time and reproducibility in different buffers, as well as low sensitivities to different interfering ionic species and dissolved oxygen. A simple portable digital pH meter is fabricated, whose signal is measured with a multimeter, using high input-impedance operational amplifier and consumer batteries. The pH values measured with the portable electrochemical paper-microfluidic pH sensors were consistent with those measured using a commercial laboratory pH meter with a glass electrode.

Activity and Long-Term Stability Study of Pt-Y/C Electrocatalysts for Oxygen Reduction Reaction

Pt-Y/C catalysts were prepared by a modified formic acid method and their activities for oxygen reduction reaction (ORR) were evaluated. X-ray diffraction analysis showed that no alloy was formed between the metals, while x-ray photoelectron spectroscopy revealed that yttrium is present as Y2O3, Y(OH)3, and Y-O-Pt. The Pt-Y/C 7:3 material had the highest specific activity (94 µA cmPt -2) for ORR, and was superior to other Pt-Y/C materials. Following repetitive potential cycling, ORR activity of the Pt-Y/C 7:3 catalyst decreased in a similar proportion to that of Pt/C. X-ray photoelectron spectroscopy results of the aged ultrathin catalyst layer were in agreement with energy-dispersive x-ray spectroscopy data. These studies revealed that the intensities of the Y 3d peaks were suppressed due to voltammetric cycling and that while Y2O3 and Y(OH)3 dissolved, Y-O-Pt remained in the catalyst.

Pt–rare earth catalysts for ethanol electrooxidation: modification of polyol synthesis

Pt–Ln/C (Ln = La, Ce, Pr, and Eu) catalysts were obtained by using a modification of the polyol method and tested for ethanol oxidation. Transmission electron microscopy (TEM) results showed that the Pt–Ln/C catalysts had particles with average size of 3 nm, which is the smallest particle size reported for Pt–rare earth catalysts; and the particles are homogeneously distributed on the carbon support. X-ray diffraction analysis showed no alloy formation between Pt and rare earth elements, and X-ray photoelectron spectroscopy (XPS) confirmed that Ln is present in its oxide form. X-ray absorption spectroscopy (XAS) results confirmed that the presence of the second metal affects the Pt electronic structure. CO oxidation in the presence of rare earths takes place mostly through the lower-potential pathway, and these catalysts showed better activity toward ethanol oxidation than Pt/C with the same particle size. Durability tests performed by repetitive potential cycling under an Ar atmosphere revealed good structural stability of the Pt–Ln/C catalysts.

Electrodeposition of tantalum on carbon black in non-aqueous solution and its electrocatalytic properties

In this work, we synthesized tantalum (Ta) nanoclusters on carbon black (Ta/CB) via simple electrodeposition in non-aqueous solvent, acetonitrile (ACN) at ambient temperature. Transmission electron microscopy (TEM) images showed that the electrodeposited Ta nanoclusters consisted of tiny Ta nanoparticles. X-ray photoelectron spectroscopy (XPS) result represented that the outermost Ta formed the native oxide on Ta/CB due to its ambient exposure to air. Electrochemical catalytic properties of prepared Ta/CB on glassy carbon electrode (Ta/CB/GC) were investigated toward reductions of oxygen and hydrogen peroxide, and oxidations of ascorbic acid and dopamine. For oxygen reduction reaction (ORR) in acid, Ta/CB/GC represented a decent electrocatalytic performance which was better or comparable to bare Pt. The operational stability in acidic condition was maintained up to 500 repetitive potential cycles presumably due to the protective native Ta oxide layer. Ta/CB/GC also showed high amperometric sensitivity (4.5 (±0.16) mA mM−1 cm−2, n = 5) for reduction of hydrogen peroxide in 0.1 M phosphate buffer solution (PBS, pH 7.4). In addition, Ta/CB/GC was demonstrated for the possibility of simultaneous detection of ascorbic acid and dopamine using differential pulse voltammetry (DPV).

Effect of MO2 (M = Ce, Mo, Ti) layer on activity and stability of PtCo/C catalysts during an oxygen reduction reaction

The performance of PtCo/C catalysts in the presence of a metal oxides layer for an oxygen reduction reaction (ORR) was investigated. Different types of metal oxides (CeO2, MoO2 and TiO2) and metal loadings (0.03–0.45mg/cm2) were incorporated on the PtCo/C catalyst layer. Their activity was analyzed in acid solution and proton exchange membrane (PEM) fuel cell under a H2/O2 environment at 60°C and ambient pressure, while the stability was tested in an N2-saturated H2SO4 solution using repetitive potential cycling. It was found that the addition of metal oxides on a catalyst layer had no influence for PtCo/C morphology. However, they significantly affected the electrochemical surface area (ESA), internal contact resistance (ICR) and hydrophilic/hydrophobic properties of the catalysts layer. Furthermore, they significantly affected the ORR activity and stability in acid solution and PEM fuel cell operation. Among all studied metal oxides, the TiO2 exhibited the best property for use as the catalyst interlayer in PEM fuel cell for both activity and stability enhancement.

Preparation of Supercapacitors on Flexible Substrates with Electrodeposited PEDOT/Graphene Composites.

Composite films consisting of poly(3,4-ethylenedioxythiophene) (PEDOT) and graphene oxide (GO) were electrochemically polymerized by electrooxidation of EDOT in ionic liquid (BMIMBF4) onto flexible electrode substrates. Two polymerization approaches were compared, and the cyclic voltammetry (CV) method was found to be superior to potentiostatic polymerization for the growth of PEDOT/GO films. After deposition, incorporated GO was reduced to rGO by a rapid electrochemical method of repetitive cathodic potential cycling, without using any reducing reagents. The films were characterized in 3-electrode configuration in BMIMBF4. Symmetric supercapacitors with aqueous electrolyte were assembled from the composite films and characterized through cyclic voltammetry and galvanostatic discharge tests. It was shown that PEDOT/rGO composites have better capacitive properties than pure PEDOT or the unreduced composite film. The cycling stability of the supercapacitors was also tested, and the results indicate that the specific capacitance still retains well over 90% of the initial value after 2000 consecutive charging/discharging cycles. The supercapacitors were demonstrated as energy storages in a room light energy harvester with a printed organic solar cell and printed electrochromic display. The results are promising for the development of energy-autonomous, low-power, and disposable electronics.