Aqueous HClO4 Research Articles

Voltammetry in Microemulsion Formed by Electron Donor Solution in Organic Solvent|Ionic Liquid Microdroplets in Aqueous Electrolyte

Oxygen reduction reaction (ORR)1 or hydrogen evolution reaction (HER)2 at liquid|liquid interface provide the possibility of separation of their products: hydrogen peroxide or hydrogen.3,4 Typically, these reactions are studied at single interface formed between immiscible electrolyte solutions in quiescent conditions. In such geometry the frequency of successful reaction events when highly hydrophobic electron donor (i.e. decamethylferrocene (DMFc) or excited form of decamethylruthenocene (DMRc)) dissolved in organic phase meet proton from aqueous phase is rather limited. Importantly, electrochemical recycling of electron donor at electrode positioned close to the liquid|liquid interface increases efficiency of this reaction.5,6 The use of microemulsion is promising higher efficiency alternative, because of extended interfacial area of numerous organic droplets. As efficient electron exchange between oxidized form of electron donor and the electrode is crucial for biphasic ORR and HER one has to focus on electrochemical studies of DMFc or DMRc in emulsions.are important. Voltammetric signal of various redox probes as ferrocene or ferrocene surfactants in quiescent emulsions is similar to that in single phase with some variation of peak density currents or redox potential.7-11 Other studies focused on chronoamperometric experiments to detect collisions of redox probe (e.g. ferrocene12) containing droplets with the electrode surface. It was found that the addition of an hydrophobic ionic liquid, typically trihexyltetradecyl-phosphonium bis(trifluoro-methylsulfonyl) amide to the organic phase as stabiliser and electrolyte, does not influence the magnitude of the electrochemical signal.13 Here we will report results of electrochemical studies of emulsion prepared from aqueous HClO4 and DMFc or DMRc and trihexyltetradecylphosphonium bis(trifluoromethylsulfonyl) imide (IL-PI) solution in toluene. As aqueous phase acid solution was selected, because in biphasic ORR or HER it serves as a source of protons. During the measurements the microemulsion was stirred to achieve faster droplets transport towards the electrode surface. Results will be compared with these obtained in a single organic phase.Voltammograms obtained with glassy carbon disc electrode indicate reversible oxidation/reduction of the redox probe similar to the seen with an electrode immersed in single organic phase. During continuous scanning redox only small change of peak currents is seen. Importantly, when after experiment in emulsion working electrode was transferred to aqueous HClO4, the voltammetric signal is still seen, but the peak currents are significantly smaller. This may indicate the redox reaction in liquid film formed on the electrode surface. Formation of liquid organic film is confirmed by the results of chronoamperometric experiments. When the electrode is set at potential corresponding to the oxidation of the redox probe, of the current is seen after c.a. 100 s drop, what may indicate the gradient of redox probe concentration. As DMFc is insoluble in water this points out on gradient of organic phase close to the glassy carbon surface.14 In turn voltammetric current related to electroreduction of highly hydrophilic hexacyanoferrate(III) is significantly diminished in emulsion as compared to pure aqueous electrolyte indicating partial coverage of the GC surface by hydrophobic film.Other effects related with electrochemical behavior of studied emulsions will be also presented and discussed.

Metal Free, Direct and Selective Deoxygenation of α‐Hydroxy Carbonyl Compounds: Access to α,α‐Diaryl Carbonyl Compounds

An efficient, metal free, direct and selective deoxygenation of α‐hydroxy carbonyl compounds is achieved with the aid of catalytic amount of aqueous HClO4 (70 %) and triethylsilane as hydride source. A variety of α‐hydroxy‐α,α‐diaryl carbonyl compounds are selectively deoxygenated to give α,α‐diaryl carbonyl compounds in good to excellent yields. Intermediacy of α‐keto carbenium ion is proposed on the basis of some control experiments and atmospheric pressure chemical ionization mass spectral analysis.

Ionic Liquid-Modified Microporous ZnCoNC-Based Electrocatalysts for Polymer Electrolyte Fuel Cells

Non-platinum group metal (non-PGM) oxygen reduction reaction (ORR) catalysts have been widely reported, but their application in proton exchange membrane fuel cells (PEMFCs) is challenging because of their poor performance in acidic environments. Here, [BMIM][NTf₂] ionic liquid (IL) modification of microporous ZnCoNC catalysts (derived from ZIF-ZnCo) is investigated to study their behavior in PEMFCs and to elucidate the catalytic mechanisms in practical operation. The high O₂ solubility of ILs enhances the utilization of active sites with porous ZnCoNC, and their hydrophobic nature facilitates the water transport during fuel cell operation. The half-cell measurement in aqueous HClO₄ shows that with the 20 wt % IL modification, the electron-transfer number increases from 2.58 to 3.88, approaching the desired 4-electron-transfer ORR. The power density obtained shows 140% improvement in single-cell PEMFC tests. The catalyst also yields an interesting performance in alkaline anion-exchange membrane fuel cells.

Enhanced Oxygen Reduction Activity by Selective Anion Adsorption on Non-Precious-Metal Catalysts

Non-precious-metal catalysts (NPMC) are promising alternatives to platinum-based catalysts for the oxygen reduction reaction (ORR), which is the cathode reaction in fuel cells. In this paper, we focus on an iron–nitrogen–carbon (Fe/N/C) catalyst, in comparison to platinum, and investigate how these different types of catalysts behave toward selective anion poisoning. The catalysts are studied with respect to their ORR activity, using the rotating disk electrode (RDE) technique in aqueous HClO4, H2SO4, H3PO4, and HCl electrolytes, and the results are supported by density functional theory (DFT) calculations. We find that the ORR on the Fe/N/C catalyst is less affected by anion poisoning than platinum. Surprisingly, it is seen that phosphoric acid not only does not poison the Fe/N/C catalyst, but instead promotes the ORR; this finding is in sharp contrast to the poisoning effect observed on platinum. This is a highly important finding, as modern high-temperature proton exchange fuel cells (HT-PEMFCs) employ...

Cu(aq)]2+ is structurally plastic and the axially elongated octahedron goes missing.

High resolution (k = 18 Å-1 or k = 17 Å-1) copper K-edge EXAFS and MXAN (Minuit X-ray Absorption Near Edge) analyses have been used to investigate the structure of dissolved [Cu(aq)]2+ in 1,3-propanediol (1,3-P) or 1,5-pentanediol (1,5-P) aqueous frozen glasses. EXAFS analysis invariably found a single axially asymmetric 6-coordinate (CN6) site, with 4×Oeq = 1.97 Å, Oax1 = 2.22 Å, and Oax2 = 2.34 Å, plus a second-shell of 4×Owater = 3.6 Å. However, MXAN analysis revealed that [Cu(aq)]2+ occupies both square pyramidal (CN5) and axially asymmetric CN6 structures. The square pyramid included 4×H2O = 1.95 Å and 1×H2O = 2.23 Å. The CN6 sites included either a capped, near perfect, square pyramid with 5×H2O = 1.94 ± 0.04 Å and H2Oax = 2.22 Å (in 1,3-P) or a split axial configuration with 4×H2O = 1.94, H2Oax1 = 2.14 Å, and H2Oax2 = 2.28 Å (in 1,5-P). The CN6 sites also included an 8-H2O second-shell near 3.7 Å, which was undetectable about the strictly pyramidal sites. Equatorial angles averaging 94° ± 5° indicated significant departures from tetragonal planarity. MXAN assessment of the solution structure of [Cu(aq)]2+ in 1,5-P prior to freezing revealed the same structures as previously found in aqueous 1M HClO4, which have become axially compressed in the frozen glasses. [Cu(aq)]2+ in liquid and frozen solutions is dominated by a 5-coordinate square pyramid, but with split axial CN6 appearing in the frozen glasses. Among these phases, the Cu-O axial distances vary across 1 Å, and the equatorial angles depart significantly from the square plane. Although all these structures remove the dx2-y2 , dz2 degeneracy, no structure can be described as a Jahn-Teller (JT) axially elongated octahedron. The JT-octahedral description for dissolved [Cu(aq)]2+ should thus be abandoned in favor of square pyramidal [Cu(H2O)5]2+. The revised ligand environments have bearing on questions of the Cu(i)/Cu(ii) self-exchange rate and on the mechanism for ligand exchange with bulk water. The plasticity of dissolved Cu(ii) complex ions falsifies the foundational assumption of the rack-induced bonding theory of blue copper proteins and obviates any need for a thermodynamically implausible protein constraint.

Synergistic effect of (RuCl 3 + IrCl 3 ) catalyzed oxidative conversion of rizatriptan benzoate to rizatriptan-N-oxide with N-haloamine: Exploration of scope, reaction behavior and kinetic data

Abstract Synergistic effect of (RuCl3 + IrCl3) as a binary mixture and alone have been investigated in the oxidation of rizatriptan benzoate (RTB) with chloramine-T (CAT) in aqueous HClO4 medium at 303 K. The kinetic patterns were found to be different in all the three catalyzed reactions. Activation parameters have been calculated. Under the identical set of experimental conditions, the reaction rate reveals that all the three catalyzed reactions are about 25 to 75-fold faster than the uncatalyzed reactions. The observed catalytic reaction rate sequence follows the order: (RuCl3 + IrCl3) > IrCl3 > RuCl3. The observed reactivity sequence may be attributed due to the fact that IrCl3–Carbon σ complexes are less strong, less localized and less covalent than RuCl3–Carbon complexes. Consequently, the present redox system is of great importance as the drug rizatriptan is transformed into rizatriptan-N-oxide On the basis of kinetic data, most plausible mechanisms were proposed.

Kinetic Studies of Charge Transfer Formation of Erythromycin and 2, 3 Dichloro-5, 6-Dicyano -1,4- Benzoquinone

The kinetics of erythromycin with 2, 3 dichloro-5,6-dicyano -1,4- benzoquinone [DDQ] is described for the determination of erythromycin. It was carried in aqueous HClO4 (2M) medium at ionic strength of 0.01moldm-3, Kinetics of the reactions infer that the rate of formation of the charge transfer complex did not vary significantly with increase in concentration of erythromycin indicating likely zeroth order dependence of the rate with respect to concentration of the drug. However, the linearity of the pseudo-first order plot points to first order dependence of rate on [DDQ]

Improvement in the durability of carbon black-supported Pt cathode catalysts by silica-coating for use in PEFCs

Commercially available Pt metal catalysts supported on carbon black (Pt/CB) for polymer electrolyte fuel cell (PEFC) cathodes were covered with silica layers to improve their durability under the severe cathode operating conditions. The Pt metal particles in the Pt/CB catalyst grew in size during the accelerated durability tests (potential cycling between 0.6 and 1.0 V vs. RHE in an aqueous HClO4 electrolyte). Thus, the Pt/CB catalyst was seriously deactivated for the oxygen reduction reaction over the course of the durability tests. In contrast, the silica layers, which wrapped around the Pt metal particles in the silica-coated Pt/CB catalyst, prevented the migration of the Pt metal particles on the carbon supports and the diffusion of Pt cations out of the silica layers. Thus, the silica-coated Pt/CB catalysts maintained a high activity for the oxygen reduction reaction over the course of the durability tests. In addition, the silica-coated Pt/CB prepared from methyltriethoxysilane showed a higher activity than that prepared from tetraethoxysilane. The porous structures and hydrophobicity of silica prepared from methyltriethoxysilane promoted the diffusion of oxygen and water molecules in the silica layers of the silica-coated Pt catalysts.

Differential pulse anodic stripping voltammetric analysis of selenium (IV) at a gold electrode modified with O-Phenylenediamine-Nafion

Differential pulse anodic stripping voltammetric analysis (DPASVA) of selenium(IV) using a gold electrode modified with O-Phenylenediamine-nafion (GEMO-PN) has been studied. Various parameters (electrolyte, deposition time, pulse duration, pulse amplitude, etc.) affecting the Se(IV) determination were examined. Selenium(IV) was determined in an aqueous HClO4 (0.2 M) medium of pH 0.22 at an accumulation potential of -350 mV (vs. Ag/AgCl) and an accumulation time of 200 s. Under the optimum conditions, liner calibration graph, Ip=f(CSe4+), was obtained in the concentration ranges of 5x10-8 M (3.948 ng/mL) to 1x10-6 M (78.96 ng/mL) with relative standard deviations (RSD) 3.8%, and the detection limit was 0.048 ng/mL. This method showed a good accumulation efficiency for selenium and good resistance to interferences from metal ions as well as those associated with selenium in pharmaceuticals. The results for the determination of Se4+ using (GEMO-PN) were more sensitive and accurate than that obtained using bare gold electrode; the sensitivity was increased about 2000 times.

Characterization of Platinum Electrode Surfaces by Electrochemical Surface Forces Measurement

The surface forces between platinum, Pt, electrodes and those between the Pt electrode and mica in aqueous HClO4 were measured at various potentials (E) applied to the electrodes using an electrochemical surface forces apparatus (EC-SFA). This apparatus uses the twin-path surface forces apparatus, recently developed for opaque samples. The influence of the proton adsorption on the surface interactions was studied. The Pt electrodes were prepared by the template-stripping procedure using glass templates. The electrode surfaces were smooth (RMS roughness: 0.26 nm for a 5 μm × 5 μm area) and polycrystalline based on the atomic force microscopy and cyclic voltammetry results, respectively. When the applied potential E was decreased from 0.5 to 0.2 V (vs Ag/AgCl), the electric double layer (EDL) repulsion between the Pt electrodes decreased. The absolute values of the surface potentials, |ψ0|, calculated using the EDL theory were 58 and 43 mV at E = 0.5 and 0.2 V, respectively. The EDL force at E = 0.2 V was t...

Carbonization of polymers of intrinsic microporosity to microporous heterocarbon: Capacitive pH measurements

A nitrogen-containing polymer of intrinsic microporosity (PIM-EA-TB-H2; nitrogen adsorption surface area 846m2g−1) is vacuum carbonized at 700°C and thereby directly without post-treatment converted into a microporous heterocarbon (cPIM; N2 adsorption surface area 425m2g−1). Nitrogen functionalities in the polymer backbone are retained in the heterocarbon and appear responsible for unusual time-, electrolyte-, and pH-dependent properties. Electrochemical characterization suggests a high specific capacitance (typically 50Fg−1) but only after prolonged immersion in aqueous HClO4. The time-dependent increase in capacitance during immersion is assigned to slow hydration and ingress of HClO4 into hydrophobic micropores (H2SO4 or H3PO4 are more hydrophilic and much less effective). Once hydrated, the microporous heterocarbon exhibits pH-dependent capacitance “switching” over a wide pH range and analytical applications as “capacitive” pH sensor are proposed.

DEVELOPMENT AND VALIDATION OF DIFFERENTIAL PULSE ANODIC STRIPPING VOLTAMMETRIC ANALYSIS OF SELENIUM (IV) IN BULK AND IN DOSAGE FORMULATIONS AT A GOLD ELECTRODE MULTI-MODIFIED WITH A MIXTURE OF 3, 3′-DIAMINOBENZIDINE.4HCL AND VITAMIN E

Objective: A simple, direct and very sensitive differential pulse anodic stripping voltammetric analysis (DPASVA) of selenium (IV) in bulk and in dosage formulations using a gold electrode multi-modified with a mixture of 3,3′-diaminobenzidine.4HCl (Dab) and vitamin E (VE)-Nafion (AuEMDabVEN) has been studied.Methods: The method involves the study of various parameters (electrolyte, deposition time, pulse duration, pulse amplitude, etc.) affecting the Se(IV) determination. The proposed method was validated for specificity, linearity, precision and accuracy, repeatability, sensitivity (LOD and LOQ), robustness and solution stability with an average recovery of 98.1-100.32%.Results: Se(IV)was determined in an aqueous HClO4 (0.2M) medium of pH 0.22 at an accumulation potential of-250 mV and an accumulation time of 200 s for CSe(IV) at 1x10-8 to 1x10-6 mol/l (0.7896-78.96 ng/ml) and 350 s for CSe(IV) at 1x10-9 to 1x10-8 mol/l (0.07896-0.7896 ng/ml) with relative standard deviations (RSD)2.4% and 4.8%, respectively.Conclusion: This method showed very sensitive results for the determination of Se(IV) using an AuEMDabVEN than that obtained using the individual Dab or VE. This method could be applicable for the quantitative determination of the bulk Se(IV) as well as dosage formulations.

Characterizing archaeological bronze corrosion products intersecting electrochemical impedance measurements with voltammetry of immobilized particles

Application of electrochemical impedance measurements to microparticulate deposits of copper corrosion products attached to graphite electrodes in contact with 0.10M aqueous HClO4 electrolyte is described. The impedance measurements were sensitive to the applied potential and the amount of solid sample and were modeled taking into account the contribution of the uncovered base electrode. Several pairs of circuit elements provide monotonic variations which are able to characterize different corrosion compounds regardless the amount of microparticulate solid on the electrode. Application to a set of archaeological samples from the archaeological Roman site of Gadara (Jordan, 4th century AD) permitted to establish a grouping of such samples suggesting different provenances/manufacturing techniques.

Platinum Electrodes for Oxygen Reduction Catalysis Designed by Ultrashort Pulse Laser Structuring

AbstractCompact platinum plates have been micro‐ and nanostructured by using a one‐step process with ultrashort laser pulses. Depending on the parameters of the laser treatment (power, line distance, and scan speed), distinct surface structures can be produced by different spot energy densities. The platinum plates structured this way were tested for their electrochemical activity in the oxygen reduction reaction in aqueous HClO4 by using cyclic voltammetry and rotating disk electrode approaches. The laser‐induced surface structuring yields a substantial enhancement in the electrochemical activity of platinum surfaces. The observed rise of the electrochemical activity by a factor of 1500 is attributed to the considerable increase of the surface area.

Activated carbon from orange peels as supercapacitor electrode and catalyst support for oxygen reduction reaction in proton exchange membrane fuel cell

Activated carbon is synthesized using orange peel as precursor through chemical activation using H3PO4 and its ability as electrocatalyst support for ORR reaction is examined. The prepared material was subjected to various structural, compositional, morphological and electrochemical studies. For ORR activity, the platinum loaded on activated carbon (Pt/OP-AC) was investigated by cyclic voltammograms (CVs) recorded in N2 and O2 saturated 0.1M aqueous HClO4. For supercapacitor performance, three electrode systems was tested in aqueous H2SO4 for feasibility determination and showed electrochemical double layer capacitance (EDLC) behaviour which is expected for activated carbon like materials. Electrochemical surface area (ECSA) of the activated carbon from orange peel is measured using CV. The physical properties of the prepared carbon are studied using SEM (scanning electron microscope), XRD (X-ray diffraction), Fourier transform infrared (FT-IR) spectroscopy and Raman spectroscopy. The AC derived from orange peels delivered a high specific capacitance of 275Fg−1 at 10mVs-1 scan rate. Hence, this study suggested that orange peels may be considered not only as a potential alternative source for synthesizing carbon supported catalyst for fuel cell application but also highlight the production of low-cost carbon for further applications like supercapacitors.

Influence of phosphoric anions on oxygen reduction reaction activity of platinum, and strategies to inhibit phosphoric anion adsorption

Nafion-membrane-based proton exchange fuel cells (PEMFCs) typically operate at below 100 °C. However, H3PO4-doped polybenzimidazole (PBI)-based PEMFCs can operate at 100–200 °C. This is advantageous because of accelerated reaction rates and enhanced tolerance to poisons such as CO and SO2, which can arise from reformed gas or the atmosphere. However, the strong adsorption of phosphoric anions on the Pt surface dramatically decreases the electrocatalytic activity. This study exploits the “third-body effect”, in which a small amount of organic molecules are pre-adsorbed on the Pt surface to inhibit the adsorption of phosphoric anions. Pre-adsorbate species inhibit the adsorption of phosphoric anions, but can also partially occlude active sites. Thus, the optimum pre-adsorbate coverage is studied by correlating the oxygen reduction reaction (ORR) activity of Pt with pre-adsorbate coverage on the Pt surface. The influence of the pre-adsorbate molecule length is investigated using the organic amines, butylamine, octylamine, and dodecylamine, in both 0.1 mol/L HClO4 and 0.1 mol/L H3PO4. Such amines readily bond to the Pt surface. In aqueous HClO4 electrolyte, the ORR activity of Pt decreases monotonically with increasing pre-adsorbate coverage. In aqueous H3PO4 electrolyte, the ORR activity of Pt initially increases and then decreases with increasing pre-adsorbate coverage. The maximum ORR activity in H3PO4 occurs at a pre-adsorbate coverage of around 20%. The effect of molecular length of the pre-adsorbate is negligible, but its coverage strongly affects the degree to which phosphoric anion adsorption is inhibited. Butylamine adsorbs to Pt at partial active sites, which decreases the electrochemically active surface area. Adsorbed butylamine may also modify the electronic structure of the Pt surface. The ORR activity in the phosphoric acid electrolyte remains relatively low, even when using the pre-adsorbate modified Pt/C catalysts. Further development of the catalyst and electrolyte is required before the commercialization of H3PO4-PBI-based PEMFCs can be realized.

Electron Transfer Reactivity of the Aqueous Iron(IV)-Oxo Complex. Outer-Sphere vs Proton-Coupled Electron Transfer.

The kinetics of oxidation of organic and inorganic reductants by aqueous iron(IV) ions, Fe(IV)(H2O)5O(2+) (hereafter Fe(IV)aqO(2+)), are reported. The substrates examined include several water-soluble ferrocenes, hexachloroiridate(III), polypyridyl complexes M(NN)3(2+) (M = Os, Fe and Ru; NN = phenanthroline, bipyridine and derivatives), HABTS(-)/ABTS(2-), phenothiazines, Co(II)(dmgBF2)2, macrocyclic nickel(II) complexes, and aqueous cerium(III). Most of the reductants were oxidized cleanly to the corresponding one-electron oxidation products, with the exception of phenothiazines which produced the corresponding oxides in a single-step reaction, and polypyridyl complexes of Fe(II) and Ru(II) that generated ligand-modified products. Fe(IV)aqO(2+) oxidizes even Ce(III) (E(0) in 1 M HClO4 = 1.7 V) with a rate constant greater than 10(4) M(-1) s(-1). In 0.10 M aqueous HClO4 at 25 °C, the reactions of Os(phen)3(2+) (k = 2.5 × 10(5) M(-1) s(-1)), IrCl6(3-) (1.6 × 10(6)), ABTS(2-) (4.7 × 10(7)), and Fe(cp)(C5H4CH2OH) (6.4 × 10(7)) appear to take place by outer sphere electron transfer (OSET). The rate constants for the oxidation of Os(phen)3(2+) and of ferrocenes remained unchanged in the acidity range 0.05 < [H(+)] < 0.10 M, ruling out prior protonation of Fe(IV)aqO(2+) and further supporting the OSET assignment. A fit to Marcus cross-relation yielded a composite parameter (log k22 + E(0)Fe/0.059) = 17.2 ± 0.8, where k22 and E(0)Fe are the self-exchange rate constant and reduction potential, respectively, for the Fe(IV)aqO(2+)/Fe(III)aqO(+) couple. Comparison with literature work suggests k22 < 10(-5) M(-1) s(-1) and thus E(0)(Fe(IV)aqO(2+)/Fe(III)aqO(+)) > 1.3 V. For proton-coupled electron transfer, the reduction potential is estimated at E(0) (Fe(IV)aqO(2+), H(+)/Fe(III)aqOH(2+)) ≥ 1.95 V.

CO-Terminated Platinum Electrodeposition on Nb-Doped Bulk Rutile TiO2

Nanoparticulate platinum on carbon as oxygen reduction electrocatalyst suffers from two major drawbacks, namely, low specific activity of the Pt particles and corrosion instability of the carbon support under hydrogen starvation conditions (reverse current degradation). Both issues can be tackled by Pt thin films on TiO2 support. Platinum films were synthesized on commercially available Nb-doped bulk TiO2 electrodes via electrodeposition from Ar- (bulk amounts) and CO-saturated solutions (monolayer amounts). The platinized electrodes were tested for ORR activity in a voltammetric fashion, and the field-free semiconductor properties were evaluated by a combination of X-ray photoelectron spectroscopy (XPS), spectroscopic ellipsometry (SE), photoelectron yield spectroscopy (PYS), electrochemical impedance spectroscopy (EIS), and bulk conductivity measurements. The deposition of bulk amounts of Pt leads to a situation where the catalytic activity is directly correlated to the conductivity of the electrode. Raising the majority carrier density in the Nb-doped TiO2, via proton intercalation in aqueous HClO4 or glycol, drastically increased the activity. In case of monolayer deposits (CO-terminated deposition), intercalation has practically no effect on activity. Thus, the hypothesis is formed that unfavorable electronic interaction of the TiO2 support with small amounts of platinum drastically reduces ORR activity, an effect which is not observed for monolayer amounts of Pt deposited on gold.

Catalytic Activities of Sulfur Atoms in Amorphous Molybdenum Sulfide (MoSx) for the Electrochemical Hydrogen Evolution Reaction

In-situ Raman spectroscopy during cyclic voltammetry was used for the first time to investigate the hydrogen evolution reaction (HER) occurring on electrodeposited amorphous MoSx films, which consist of Mo3-based motiffs. A Raman peak at 2530 cm-1 was observed on these films during HER in aqueous HClO4 electrolyte. This peak was assigned as a MoS-H stretching vibration. This identification was corroborated by H/D isotopic exchange experiments. Hence, we could directly establish that sulfur atoms are the catalytic active sites in amorphous MoSx for proton reduction.We further distinguish the activities of the S atoms present in these amorphous films. Using X-ray photoelectron spectroscopy as a means to identity the types of S atoms present, we found that the turnover frequency for H2 production increases linearly with the percentage of S atoms with higher electron binding energies. These S atoms could be apical S2- and/or bridging S2 2-. Quantum chemical simulations using density functional theory rule out the apical S2- atoms as reaction sites for HER. In situ Raman spectroscopy of the model [Mo3S13]2- cluster further demonstrate the higher catalytic reactivity of the bridging S2 2- over terminal S2 2- (which have lower electron binding energy) for proton reduction.

Electrochemical characterisation of poly(3,4-ethylenedioxythiophene) film modified glassy carbon electrodes prepared in deep eutectic solvents for simultaneous sensing of biomarkers

Electrodeposition of the conducting polymer, poly(3,4-ethylenedioxythiophene) (PEDOT) in deep eutectic solvents (DES), prepared by the simple mixing and heating of an H-bond acceptor, choline chloride and H-bond donors such as urea, ethylene glycol and glycerol, is described. The PEDOT modified glassy carbon electrodes prepared in different DES and in the presence of conventional aqueous surfactants or HClO4 media were characterized during and after growth by electrochemical and quartz crystal microbalance studies. PEDOT synthesized in the best performing DES medium, choline chloride – urea (Reline) in the presence of HClO4, was used for the sensing of the biologically relevant molecules ascorbic acid, dopamine and uric acid. The sensing characteristics were compared with those of PEDOT-modified electrodes prepared in aqueous media.