Investigation of the “permanent” electrochemical promotion of catalysis (P-EPOC) by electrochemical mass spectrometry (EMS) measurements

The phenomenon of electrochemical promotion of catalysis (EPOC) is most often fully reversible. Subsequent to long-lasting polarization, however, the new steady-state open-circuit catalytic activity after current interruption may remain significantly higher than that before polarization. This phenomenon has been reported as “permanent electrochemical promotion of catalysis” (P-EPOC). The catalytic oxidation of C₂H₄ was studied over a Pt/YSZ/Au electrochemical cell under excess O₂ at 375 °C, combining cyclic voltammetry and mass spectrometry. It has been found that after positive current interruption, the catalytic rate remains in a highly active P-EPOC steady-state, where it is almost double than the initial open-circuit rate. During this highly active steady-state, the application of a similar negative current for a similar time period has been found to result in the return of the catalytic rate to the initial open-circuit state. Similar reversibility of the rate has been observed after cyclic voltammetry experiments where after a complete potential oscillation the open-circuit rate is almost the same to that before polarization. These establish the reported mechanism for the origin of P-EPOC, on promoting species storage and concomitant migration to the metal/gas interface after positive current interruption, through the three phase boundaries.     

Zirconia-based amperometric sensor using ZnO sensing-electrode for selective detection of propene

The sensing characteristics to propene (C₃H₆) were examined at 600 °C under wet condition for the amperometric sensor using a yttria-stabilized zirconia (YSZ) tube and ZnO (+8.5 wt%Pt) sensing-electrode (SE). In order to improve the sensitivity to C₃H₆, the “pulsed-potential method” was adopted here. It was found that the current response varied almost linearly with C₃H₆ concentration in the range of 0–200 ppm when SE was polarized at +1.0 V (vs. Pt/air reference electrode) for a period of 0.3 s. By using the present “pulsed-potential method”, the sensitivity to 100 ppm C₃H₆ was increased about 1000 times, compared with the normal “constant-potential method”. The excellent selectivity to C₃H₆ was also obtained for the present sensor without influence of other hydrocarbons, NO_x, CO, H₂, etc.     

Hydrogen generation from catalytic glucose oxidation by Fe-based electrocatalysts

Iron phosphide films (Fe₂P) grown in situ on stainless steel mesh (SSM) exhibit excellent electrocatalytic performance toward the glucose oxidation reaction (GOR) with robust durability. During GOR, the Fe₂P could be further transformed into the oxidized Fe species with high catalytic activity. The integrated two-electrode glucose electrolytic cell utilizing Fe₂P/SSM and Pt/C exhibited a cell voltage 300 mV lower than water splitting alone, indicating an efficient pathway for H₂ production. These features suggest that the replacement of the sluggish oxygen evolution reaction (OER) with the thermodynamically more favourable GOR in the Pt/C ||Fe₂P/SSM configuration is an attractive alternative for electrolytic H₂ generation.     

Platinum nanocube catalysts for methanol and ethanol electrooxidation

We prepared Pt nanocube catalyst with about 3.6 nm in size by a polyol process in the presence of PVP as a stabilizer and Fe ion as a kinetic controller. The crystal structure of Pt nanocube with {1 0 0} faces was confirmed by field-emission transmission electron microscopy. In a cyclic voltammogram, we found that the Pt nanocube catalyst showed relatively high ratio of the forward anodic peak current to the reverse anodic peak current resulting in less accumulation of residues on the catalyst. The Pt nanocube catalyst with the edge of stepped {1 0 0} faces was preferable to breakage of CH₃OH and CH₃CH₂OH compared to polycrystalline Pt nanocatalyst. In an electrochemical measurement for methanol and ethanol electrooxidation, the Pt nanocube catalyst showed an excellent catalytic activity, i.e., lower onset potential and higher current density, compared to the polycrystalline Pt nanocatalyst.     

Anisotropic catalytic activity of the orientation controlled Nd2NiO4 + δ/YSZ hetero-epitaxial system for SOFC cathode

Electrode–electrolyte hetero-epitaxial systems for solid oxide fuel cells (SOFCs) with two different configuration of Nd₂NiO_4 + δ(110)//YSZ(100) and Nd₂NiO_4 + δ(100)//YSZ(110) were successfully fabricated by pulsed laser deposition. Thin films of Nd₂NiO_4 + δ approximately 20 nm thick were grown on a commercial single crystal of YSZ. The preferred two-dimensional diffusion paths of the oxide ions were perpendicular to the substrate for both configurations and showed oxygen reduction capability different from each other. This opens up new research direction focusing on the details of anisotropic catalytic activity of SOFC cathode depending on the crystalline surface.     

Fused ring systems derived from reactions of half-open titanocenes with diynes: Syntheses,characterization, cage rearrangements,and structural studies

The reactions of several α,ω-diynes with half-open titanocene complexes [M(C₅H₅)(2,4-C₇H₁₁)(PR₃)] (C₇H₁₁ = dimethylpentadienyl) lead to 5 + 2 + 2 ring constructions, yielding nine-membered rings fused to four-membered and larger rings. These reactions tolerate significant functionalization, even allowing for the presence of heteroatoms such as oxygen and nitrogen. The nine-membered rings provide both allyl and diene coordination to the Ti(C₅H₅) fragments, resulting in 16 electron configurations. On standing, these species undergo cage rearrangements, via CC bond activation reactions. Structural data have been obtained for a number of the fused ring species, as well as one of the rearrangement products.     

Visible light photocatalysis by a Titania–Rhodium(III) complex

Titania hybrid photocatalysts containing 0.5, 1.0, 2.0, and 5.0 wt% of rhodium(III) were prepared by chemisorption of RhCl₃ × 3H₂O onto anatase hydrate powder (TH). Analytical data suggest that a titania–trichlororhodate complex is produced containing a [TiO₂]–O–Rh bond.Similar results are found in the case of modification by RhBr₃ × 3H₂O. Diffuse reflectance spectra exhibit an absorption shoulder throughout the visible region down to 700 nm. Photoelectrochemical measurements indicate that the quasi-Fermi level of electrons is gradually shifted to more anodic potentials with increasing rhodium loading reaching a value of ?0.34 V at pH 7 (vs. NHE) in the case of 5.0%RhCl₃/TH. This is more anodic by 210 mV as compared to unmodified TH. Upon visible light irradiation this photocatalyst induces a fast mineralization of 4-chlorophenol whereas cyanuric acid, which is known to be mineralized in the presence of the analogous Pt(IV) modified titania, is not degraded.     

Barium carbonate nanoparticle as high temperature oxygen reduction catalyst for solid oxide fuel cell

BaCO₃ nanoparticles are demonstrated as outstanding electrocatalysts to enhance the high temperature oxygen reduction reaction (ORR) in solid oxide fuel cells (SOFCs). BaCO₃ nanoparticles are formed from thermal decomposition of barium acetate, Ba(Ac)₂ infiltrated to porous cathode skeleton and shows good chemical compatibility with cathode materials. BaCO₃ nanoparticles can greatly reduce the area specific resistance (ASR) of typical SOFC cathode materials, including La_0.8Sr_0.2FeO_3 -δ (LSF), La_0.6Sr_0.4Co_0.2Fe_0.8O_3 -δ (LSCF) and La_0.8Sr_0.2MnO_3 -δ (LSM). For example at 700 °C, ASR for LSF on yttria-stabilized zirconia (YSZ) electrolyte decreases from 2.95 Ω cm² to 0.77 Ω cm² when 12.9 wt.% BaCO₃ nanoparticles are deposited on the surface of the porous LSF electrode. Impedance spectra analysis shows that the decrease in ASR mainly comes from the reduction of the low frequency resistance. Furthermore, BaCO₃ nanoparticles are found to greatly enhance the oxygen chemical exchange coefficient. Most importantly, it has been found that the catalytic activity of BaCO₃ nanoparticles is even higher than those of the precious metals such as Pd, Rh, Pt and Ag, infiltrated into LSF, LSCF and LSM electrodes supported on YSZ electrolytes.     

Oscillations of pH at the Fe│H2SO4 interface during anodic dissolution

An unmodified Pt microelectrode and a Pt microelectrode coated with polyaniline were used in conjunction with a scanning electrochemical microscope (SECM) to study anodic dissolution in the Fe│H₂SO₄ system. The concentrations of Fe^2 + (c_Fe2 +) measured with the unmodified microelectrode and the pH values measured with the polyaniline-modified microelectrode were recorded in situ during current oscillations in the Fe│H₂SO₄ system and were found to change periodically at the Fe│H₂SO₄ interface. The changes in c_Fe2 + may be caused by the periodic formation and dissolution of surface film(s), which could be salt films and/or oxide films. If a salt film is formed, it is unlikely to affect the pH. Since the pH changes periodically during the current oscillations, it can be deduced that the surface film is mainly composed of oxide, and that the formation and dissolution of the oxide film play a key role in the current oscillations of the system.     

Double cyclometallation of bridging 3,6-bis(2-thienyl)-1,2,4,5-tetrazine in a dinuclear mesityl(dimethylsulfoxide)platinum(II) complex: Structure and properties

3,6-Bis(2-thienyl)-1,2,4,5-tetrazine (bttz) reacts with trans-Pt(dmso)₂(mes)₂, mes = mesityl = 2,4,6-trimethylphenyl, under twofold cyclometallation to yield structurally characterized (μ-bttz-2H⁺)[Pt(dmso)(mes)]₂ with uncoordinated thiophene sulfur atoms and bttz deprotonated in the 3,3′ positions. The structural features include cis-positioned carbanionic ligands, twisted mesityl substituents, S-coordinated dmso ligands with the SO bonds lying in the molecular plane, shortened inter-ring bonds, and rather short Pt–C bonds at 1.998(9)/2.00(1) Å (Pt–C_mes) and 1.985(9)/1.99(1) Å (Pt–C_bttz-2H+). Reversible reduction to {(μ-bttz-2H⁺)[Pt(dmso)(mes)]₂}^? causes a high-energy shift of the charge transfer bands and the appearance of an unresolved EPR signal at g = 1.9905.     

Titanium-supported nanoporous bimetallic Pt–Ir electrocatalysts for formic acid oxidation

Novel titanium-supported nanoporous network bimetallic Pt–Ir/Ti electrocatalysts (S1:Pt₅₉Ir₄₁/Ti, S2:Pt₄₄Ir₅₆/Ti, S3:Pt₂₂Ir₇₈/Ti) have been successfully fabricated by the hydrothermal process. The nanoparticles of Pt and Ir were deposited on the titanium substrates in the presence of formaldehyde as a reduction agent. The electrocatalytic activity of these electrocatalysts towards formic acid oxidation in 0.5 M H₂SO₄ + 0.5 M HCOOH solutions was investigated using cyclic voltammograms (CVs), linear sweep voltammograms (LSVs), chrono amperometry and electrochemical impedance spectroscopy (EIS). The CVs of S1, S2 and S3 exhibit two anodic peaks in the forward scan and one anodic peak in the reverse scan which are similar to the pure Pt. Their LSVs show that the three samples present significantly high current densities of formic acid oxidation compared to the Pt electrode. It is observed from the chrono amperometric measurements at potential 600 mV that the sample S2 delivers a steady-state current density that is 545 times larger than that for the pure Pt electrode. EIS analysis shows that the impedances on both the imaginary and real axes of S1, S2 and S3 are much lower than those of the pure Pt. Among the three samples (S1, S2 and S3), S2 exhibits the highest electrocatalytic activity towards the formic acid oxidation.     

(Liquid + liquid) equilibria of ternary and quaternary systems containing n-hexane,toluene, m-xylene,propanol, sulfolane,and water at T = 303.15 K

(Liquid + liquid) equilibrium data for ternary and quaternary systems containing n-hexane (C₆H₁₄), toluene (C₇H₈), m-xylene (C₈H₁₀), propanol (C₃H₈O), sulfolane (C₄H₈SO₂), and water (H₂O) were measured at T = 303.15 K. Phase diagrams of {w₁C₄H₈SO₂ + w₂C₇H₈ + (1 − w₁ − w₂)C₆H₁₄}, {w₁C₄H₈SO₂ + w₂C₈H₁₀ + (1 − w₁ − w₂)C₆H₁₄}, {w₁C₄H₈SO₂ + w₂C₃H₈O + w₃C₇H₈ + (1 − w₁ − w₂ − w₃)C₆H₁₄} and also systems containing water: {w₁C₄H₈SO₂ + w₂H₂O + w₃C₇H₈ + (1 − w₁ − w₂ − w₃)C₆H₁₄} and {w₁C₄H₈SO₂ + w₂H₂O + w₃C₈H₁₀ + (1 − w₁ − w₂ − w₃)C₆H₁₄} (w = mass fraction) were obtained at T = 303.15 K. The (liquid + liquid) equilibrium data of the systems were used to obtain interaction parameters in non-random two-liquid (NRTL) and universal quasi-chemical theory (UNIQUAC) activity coefficient models. These parameters can be used to predict equilibrium data of ternary and quaternary systems. The root mean square deviations (RMSDs) using these models were calculated and reported. The partition coefficients and the selectivity factors of solvents for extraction of toluene or m-xylene from n-hexane at T = 303.15 K are calculated and presented. The experimental selectivity factors of sulfolane for the system {w₁C₄H₈SO₂ + w₂C₇H₈ + (1 − w₁ − w₂)C₆H₁₄} at T = 298.15 K and T = 323.15 K were taken from the literature and the influence of temperature on the extraction of toluene was also investigated. The phase diagrams for the ternary and quaternary systems including both the experimental and correlated tie lines are presented. The tie-line data of the studied systems were also correlated using the Hand equation and the correlation parameters are calculated and reported.     

Novel nano-structured Pd+yttrium doped ZrO2 cathodes for intermediate temperature solid oxide fuel cells

Novel nano-structured Pd+yttrium doped ZrO₂ (YSZ) electrodes have been developed as cathodes of intermediate temperature solid oxide fuel cells (IT-SOFCs). Nano-sized Pd particles were introduced into the rigid and porous YSZ structure by PdCl₂ solution impregnation. The results show that Pd nanoparticles (20–80 nm) were uniformly distributed in the porous YSZ structure; and such nano-structured composite cathodes were highly active for the O₂ reduction reaction, with polarization resistances (R_E) of 0.11 and 0.22 Ω cm² at 750 and 700 °C and activation energy of 105 kJ mol⁻¹ that is significantly lower than those for the conventional perovskite-based cathodes (130–201 kJ mol⁻¹).     

Activity of Pt anode catalyst modified by underpotential deposited Pb in a direct formic acid fuel cell

We characterized the electrocatalytic activity of platinum electrode modified by underpotential deposited lead (PtPb_upd) for a formic acid (HCOOH) oxidation and investigated the influence on the power performance of direct formic acid fuel cells (DFAFC). Based on the electrochemical analysis using cyclic voltammetry and chronoamperometry, PtPb_upd electrode modified by underpotential deposition (UPD) exhibited significantly enhanced catalytic activity for HCOOH oxidation below anodic overpotential of 0.4 V (vs. SCE). Multi-layered PtPb_upd electrode structure of Pt/Pb_upd/Pt resulted in more stable and enhanced performance using 50% reduced loading of anode catalyst. The performance of multi-layered PtPb_upd anode is about 120 mW/cm² at 0.4 V and it also showed a sustainable cell activity of 0.52 V at an application of constant current loading of 110 mA/cm².     

Density functional theory investigation of the photodissociation channels of acetophenone

The photodissociations of acetophenone (C₆H₅COCH₃) have been investigated by density functional theory (DFT) approach. The experimentally observed three photodissociation channels were clarified from the theoretical calculations on the related reactants, transition states (TSs), and products. Two of the three channels, C₆H₅COCH₃ → C₆H₅CO + CH₃ and C₆H₅COCH₃ → C₆H₅ + CH₃CO, were assigned to Norrish I reactions on the potential energy surfaces (PESs) of the lowest triplet state (T₁). And, the first one is more favorable for lower barrier. The subsequent decompositions, C₆H₅CO → C₆H₅ + CO and CH₃CO → CH₃ + CO, were also studied by the similar calculations as above. The third photodissociation channel, C₆H₅COCH₃ → C₆H₅CH₃ + CO, has been documented on the PESs of the ground state (S₀). The third one played a minor role in the photodissociations of C₆H₅COCH₃ for much higher barrier than the first two.     

Synthesis,characterization and electrocatalytic activity for ethanol oxidation of carbon supported Pt,Pt–Rh,Pt–SnO2 and Pt–Rh–SnO2 nanoclusters

Nanoclusters of Pt, Pt–Rh, Pt–SnO₂ and Pt–Rh–SnO₂ were successfully synthesized by polyol method and deposited on high-area carbon. HRTEM and XRD analysis revealed two phases in the ternary Pt–Rh–SnO₂/C catalyst: solid solution of Rh in Pt and SnO₂. The activity of Pt–Rh–SnO₂/C for ethanol oxidation was found to be much higher than Pt/C and Pt–Rh/C and also superior to Pt–SnO₂/C. Quasi steady-state measurements at various temperatures (30–60 °C), ethanol concentrations (0.01–1 M) and H₂SO₄ concentrations (0.02–0.5 M) showed that Pt–Rh–SnO₂/C is about 20 times more active than Pt/C in the potential range of interest for the fuel cell application.     

Electrochemical investigation of corrosion and corrosion inhibition of iron in hydrochloric acid solutions

The inhibition effect of 1-methyl pyrazole (MPA) on the acidic corrosion of iron in 1.0 M HCl was studied at different concentrations (10^?3–10^?2 M) by potentiodynamic polarization and electrochemical impedance spectroscopy, and EIS measurements. It is found from the polarization studies that methyl pyrazole (MPA) behaves mainly as anodic inhibitor in HCl. Values of polarization resistance (R_p) and double layer capacitance (C_dl) in the absence and presence of MPA in 1.0 M HCl are determined. The adsorption of MPA on iron surface from HCl is found to obey Temkin adsorption isotherm.     

Fabrication of a large area cathode-supported thin electrolyte film for solid oxide fuel cells via tape casting and co-sintering techniques

A large area cathode-supported electrolyte film, comprising porous (La_0.8Sr_0.2)_0.95MnO₃ (LSM95) cathode substrate, LSM95/Zr_0.89Sc_0.1Ce_0.01O_2?x (SSZ) cathode active layer, and SSZ electrolyte, has been successfully fabricated by tape casting and co-sintering techniques. The interface reaction between cathode and electrolyte was inhibited by using A-site deficient LSM. A dense enough SSZ thin film with a thickness of ～26 μm was obtained at 1250 °C. By using Pt as anode, the obtained single cell reached the maximum power density of 0.54 W cm^?2 at 800 °C in O₂/humidified H₂, with open circuit voltage (OCV) value of 1.08 V.     

Density functional study of the complete pathway for the Heck reaction with palladium diphosphines

The reaction mechanism for the complete catalytic cycle of the Heck reaction (between phenyl bromide, C₆H₅Br, and ethylene, C₂H₄, in the presence of the base, NEt₃ to form the product styrene, C₆H₅–C₂H₃), catalyzed by diphosphinopalladium complexes, Pd(PR₃)₂ {R = H, Me, Ph}, was investigated by using density functional theory (DFT). The relative free energies of the fully-optimized species in gas phase at 298.15 K and 1 atm were corrected for solvation in DMSO at 1 mol/L by using conductor-like polarizable continuum model (CPCM). The calculations indicate a four-step mechanism for the catalysis, including oxidative addition of C₆H₅Br, migratory insertion of C₆H₅ to C₂H₄, β-hydride transfer/olefin elimination of product, and catalyst regeneration by removal of HBr. Our calculations demonstrate that Pd π-complexes can be formed with phenyl bromide and ethylene before the oxidative addition occurs. Subsequently, various reaction paths were studied for the oxidative addition of phenyl bromide to palladium complexes, coordinated by phosphine(s) and/or ethylene. Interestingly, all pathways lead to palladium monophosphine as the active catalyst. Careful exploration was made on two possible pathways for the migratory insertion and β-hydride-transfer/olefin elimination: (1) the neutral path with bromide bound to Pd and (2) the cationic path with prior bromide ion dissociation. The neutral path is preferred to the cationic path, especially when the more bulky phosphines such as triphenylphosphine are involved.     

Adjustable bidirectional extracellular electron transfer between Comamonas testosteroni biofilms and electrode via distinct electron mediators

Bidirectional extracellular electron transfer of strain Comamonas testosteroni I2 was for the first time investigated with electrochemical active biofilms developed under different conditions. The electrochemical active biofilm developed under microbial fuel cell conditions was capable of anodic electron transfer via attached redox species with standard potential of 0.04 V (vs. SCE). Meanwhile the above redox species lost its catalytic capability when the biofilm was developed under a constant potential (− 0.4 V vs. SCE). Instead, the microbe adjusted its electron transfer strategy to a soluble shuttle (standard potential − 0.20 V vs. SCE) and enabled a cathodic current. Air exposure experiment verified that the soluble shuttle at negative potential had a positive response to the oxygen; meanwhile the anodic electron transfer via the attached species was rarely influenced.