Thermal analysis of some organoclays

Thermogravimetric (TG) and differential thermal analysis (DTA) curves of methyltributylammonium smectite (MTBAS), methyltrioctylammonium smectite (MTOAS), and di(hydrogenatedtallow)dimethylammonium smectite (DHTDMAS), and also corresponding sodium smectite (NaS) and tetraalkylammonium chlorides (TAAC) were determined. The TAACs was decomposed exactly by heating up to 500°C. The adsorbed water content of 8.0% in the pure NaS was decreased down to 0.2% depending on the size of the non-polar alkyl groups in the tetraalkylammonium cations (TAA⁺). The thermal degradation of the organic partition nanophase formed between 2:1 layers of smectite occurs between 250–500°C. Activation energies (E) of the thermal degradations in the MTBAS, MTOAS and DHTDMAS are 13.4, 21.9, and 43.5 kJ mol⁻¹, respectively. The E value increases by increasing of the interlayer spacing along a curve depending on the size of the alkyl groups in the TAA⁺.     

Electrochemical reduction of CO2 with high current density in a CO2 + methanol medium II. CO formation promoted by tetrabutylammonium cation

The cation of the supporting electrolyte was found to play an important role in the electrochemical reduction of highly concentrated CO₂ in a CO₂ + methanol medium. Electroreduction of CO₂ with tetrabutylammonium (TBA) salts yielded CO as the main product, while methyl formate was predominantly formed when lithium salts were used as supporting electrolytes. The latter supporting electrolytes showed a higher overvoltage than the former. When TBA salt was used, the reduction of CO₂ was catalysed by TBA ion to yield CO^−.₂. This intermediate may be stabilized by forming an ion pair, {TBA⁺---CO^−.₂}, or by being adsorbed on the electrode surface as CO^−._2ad. Then CO^−.₂ reacts with CO₂ to produce CO. The hydrophobic atmosphere at the electrode provided by TBA ion may be adequate for CO production. Lithium ion, on the other hand, suppressed the reduction of CO₂.     

FTIR spectroscopy study of the electrochemical reduction of CO2 on various metal electrodes in methanol

The electrochemical reduction of CO₂ on Sn, Cu, Au, In, Ni, Ru and Pt electrodes in methanol containing 0.1 M sodium perchlorate was studied by cyclic voltammetry and in-situ FTIR spectroscopy. Dissolved CO₂ increases the cathodic current at potentials below −1.3 V vs. Ag|0.01 M Ag⁺ with Sn, Au, Cu, In and Ni electrodes. It is concluded from the FTIR spectra obtained that there is no reduction of CO₂ on any of the metals studied, and that the only reaction product detected by Fourier transform (FT) IR spectroscopy, i.e. CO²⁻₃, is formed by reaction of CO₂ with hydroxyl anions produced in the electroreduction of residual water.In order to identify the electroreduction products of CO₂ it was necessary to obtain the FTIR spectra of sodium oxalate and sodium carbonate in methanol. They were obtained by the electroreduction of oxalic acid and the alkalinization of CO₂-saturated methanol respectively. It could be proved that the electroreduction of carboxylic acids to carboxylate anions in organic solvents does not require either a H-chemisorbing metal electrode, or the presence of water in the solvent.     

Solvation effect of the cation of the supporting electrolyte in hexamethylphosphoramide

Polarographic reductions of sodium and potassium ions in hexamethylphosphoramide (HMPA) have been examined in various supporting electrolytes. The supporting electrolytes, which have much the same solvated radii and much the same electrocapillary curves, sometimes have a significantly different influence on the polarographic reductions of metal ions. The Li⁺ and Hex₄N⁺ ions provide a typical example. Their effective radii are seen to have much the same characteristics. However, the polarographic reduction of the sodium ion shows a difference in shape between that occurring in Li⁺ solution and that in Hex₄N⁺ solution. Another example is found in the case of Et₄N⁺, Me₄N⁺ and 5N6⁺, whose r_eff and the electrocapillary curves are much the same. However, the polarographic reductions of the sodium and potassium ions are different in these solutions. The solvation number of the solvent molecule of the supporting electrolyte cation seems to exert a great influence on these reductions. The electrocapillary curves were also examined with the tetradodecylammonium ion, tetradecylammonium ion and tetraphenylphosphonium ion used as the supporting electrolytes. The inhibition of the reduction of metal ion for these cations is evidence for their lack of solvation. The effects of the solvated asymmetrical tetraalkylammonium ions on the polarographic behaviour were also examined. When some methyl groups cooperate with the tetraalkylammonium ion, the chemical character is between that of the Et₄N⁺ ion and that of the Me₄N⁺ ion.     

Dual-Role of Polyelectrolyte-Tethered Benzimidazolium Cation in Promoting CO2/Pure Water Co-Electrolysis to Ethylene

Electrochemical CO₂ reduction reaction (CO₂RR), as a promising route to realize negative carbon emissions, is known to be strongly affected by electrolyte cations (i.e., cation effect). In contrast to the widely-studied alkali cations in liquid electrolytes, the effect of organic cations grafted on alkaline polyelectrolytes (APE) remains unexplored, although APE has already become an essential component of CO₂ electrolyzers. Herein, by studying the organic cation effect on CO₂RR, we find that benzimidazolium cation (Beim⁺) significantly outperforms other commonly-used nitrogenous cations (R₄N⁺) in promoting C₂₊ (mainly C₂H₄) production over copper electrode. Cyclic voltammetry and in situ spectroscopy studies reveal that the Beim⁺ can synergistically boost the CO₂ to *CO conversion and reduce the proton supply at the electrocatalytic interface, thus facilitating the *CO dimerization toward C₂₊ formation. By utilizing the homemade APE ionomer, we further realize efficient C₂H₄ production at an industrial-scale current density of 331 mA cm⁻² from CO₂/pure water co-electrolysis, thanks to the dual-role of Beim⁺ in synergistic catalysis and ionic conduction. This study provides a new avenue to boost CO₂RR through the structural design of polyelectrolytes.     

Electroprecipitation of Ag(II)/Ag(III) tetraphenylsulfonate porphyrin and electrocatalytic behavior of the films

The electrochemical precipitation on glassy carbon and gold electrodes of Ag(II) tetraphenylsulfonate porphyrin (Ag(II)TPPS) from aqueous HClO₄ solutions, is reported. Electrochemical quartz crystal microbalance (EQCM) results indicate the possible formation of an Ag(II)–Ag(III) porphyrin dimer species. This species is oxidized and reduced in two consecutive steps: oxidation at +0.31 and +0.36 V (vs. SCE) and reduction at +0.11 and +0.07 V. The films show catalytic behavior toward O₂ reduction in 10⁻² M HClO₄ at relatively low potentials (E<−0.1 V) but catalyze NO reduction at relatively high-reduction potentials (E<0.4 V). The electrochemical results seem to indicate that the catalytic cycle in the case of NO involves formation of Ag(II)TPPS–Ag(II)TPPS(NO)⁺ and its electroreduction to regenerate Ag(II)TPPS–Ag(III)TPPS and NO-reduction products.     

SDS‐modified Nanoporous Silver as an Efficient Electrocatalyst for Selectively Converting CO2 to CO in Aqueous Solution

Selectively electrochemical conversion of CO₂ into organic fuel using renewable electricity is one of the most sought‐after processes. In this paper, we report the electrochemical reduction of CO₂ (CO₂RR) on the nanoporous Ag electrodes made of compacted Ag nanoparticles (AgNPs), which were prepared by one‐step reduction in the water phase with or without the surfactant sodium dodecyl sulfate (SDS). The scanning electron microscope (SEM) characterizations show that the compacted Ag electrodes have the nanoporous morphology formed by stacking AgNPs. Compared with the nanoporous Ag electrode without SDS modification (C‐AgNPs), the SDS‐modified AgNPs electrode (C‐AgNPs‐SDS) is highly effective in improving selective CO production in a wide range of potentials (–0.69 V — –1.19 V, vs. RHE), with a Faradaic efficiency of 92.2% and a current density of –8.23 mA·cm^–2 for CO production at –0.79 V (vs. RHE). C‐AgNPs‐SDS is also catalytically stable with only less than 7% deactivation after 8 h of continuous electrolysis.     

Aqueous Photoelectrochemical CO2 Reduction to CO and Methanol over a Silicon Photocathode Functionalized with a Cobalt Phthalocyanine Molecular Catalyst

We report a precious-metal-free molecular catalyst-based photocathode that is active for aqueous CO₂ reduction to CO and methanol. The photoelectrode is composed of cobalt phthalocyanine molecules anchored on graphene oxide which is integrated via a (3-aminopropyl)triethoxysilane linker to p-type silicon protected by a thin film of titanium dioxide. The photocathode reduces CO₂ to CO with high selectivity at potentials as mild as 0 V versus the reversible hydrogen electrode (vs RHE). Methanol production is observed at an onset potential of −0.36 V vs RHE, and reaches a peak turnover frequency of 0.18 s⁻¹. To date, this is the only molecular catalyst-based photoelectrode that is active for the six-electron reduction of CO₂ to methanol. This work puts forth a strategy for interfacing molecular catalysts to p-type semiconductors and demonstrates state-of-the-art performance for photoelectrochemical CO₂ reduction to CO and methanol.     

On the crystallization mechanism of ETS-10 titanosilicate synthesized in gels containing TAABr

Thermal analysis of the products resulted during crystallization of ETS-10 by using starting co gels with molar composition 5.0 Na₂O-3.0 KF-TiO₂-6.4 HCl-TAABr-7.45 SiO₂-197.5 H₂O, where tetralkylammonium (TAA) are tetramethyl (TMA), tetraethyl (TEA), tetrapropyl (TPA) and tetrabutylammonium (TBA), was performed. The effect of TAA⁺ cations (ionic radius in hydrated forms, shapes and hydrophilic/hydrophobic character) on the crystallization of ETS-10 is evident from the induction time, t_i (TMA⁺ ? TEA⁺ < TPA⁺ < TBA⁺), the rate of crystallization, R (TMA⁺ < TEA⁺ < TPA⁺ < TBA⁺), morphology and size of crystallites. Organic cations play a “pore filling” role rather than as a “structure-directing” agent. The relatively flexible molecules of the symmetric tetraalkylammonium cations mixed with alkali cations (Na⁺, K⁺) participate directly at prenucleation and nucleation steps by their interaction with the silicate and titanate in aqueous colloidal dispersion.     

Investigation of the interaction between cobalt sulfide coatings and Ag(I) ions using cyclic voltammetry in KClO4 and NaOH aqueous solutions and X-ray photoelectron spectroscopy

Cobalt sulfide coatings have been investigated by means of cyclic voltammetry in 0.1 M KClO₄ and 0.1 M NaOH solutions and analyzed using X-ray photoelectron spectroscopy. They have been shown to contain CoS(OH), CoS and Co(OH)₂. After treating such Co sulfide coatings with AgNO₃ solution, their composition changes: both the cobalt and oxygen content decreases and Ag (up to 85 at%) appears in the coating as Ag₂S, Ag₂O and metallic Ag. Co(II) compounds react with Ag⁺ ions according to an exchange reaction [CoS+2Ag⁺+2H₂O→Ag₂S+Co(OH)₂+2H⁺]. In the course of the reaction of Co(OH)₂ with silver ions, a redox process occurs, giving metallic silver [Co(OH)₂+Ag⁺+H₂O→Ag°+Co(OH)₃+H⁺ or Co(OH)₂+Ag⁺→Ag°+CoO(OH)+H⁺]. Ag₂S reduction takes place at more positive potentials than Cu reduction; therefore sulfide layers of cobalt modified with silver ions, unlike unmodified ones, may be plated with Cu from both acid and alkaline electrolytes. Electronic Publication     

Bimetallic Cooperativity and Hydrogen Bonding Allow Efficient Reduction of CO2

Reducing CO₂ selectively to one of the several C1 products is challenging, as the thermodynamic reduction potentials for the different n e⁻/n H⁺ reductions of CO₂ are similar and so is the reduction potential for H⁺ reduction. Recently, Halime, Aukauloo, and co-workers have taken inspiration from the active site of nickel CO dehydrogenase (Ni-CODH) to design bimetallic iron porphyrins bridged by a urea moiety. These complexes show fast and selective reduction of CO₂ to CO and the results suggest a Ni-CODH type mechanism at play where one of the two metals binds and reduces the CO₂ while the other stabilizes the reduced species by forming a bridged complex, facilitating the C−O bond cleavage.     

From Monomers to π Stacks,from Nonconductive to Conductive: Syntheses,Characterization, and Crystal Structures of Benzidine Radical Cations

Salts that contain radical cations of benzidine (BZ), 3,3′,5,5′‐tetramethylbenzidine (TMB), 2,2′,6,6′‐tetraisopropylbenzidine (TPB), and 4,4′‐terphenyldiamine (DATP) have been isolated with weakly coordinating anions [Al(OR_F)₄]^? (OR_F=OC(CF₃)₃) or SbF₆^?. They were prepared by reaction of the respective silver(I) salts with stoichiometric amounts of benzidine or its alkyl‐substituted derivatives in CH₂Cl₂. The salts were characterized by UV absorption and EPR spectroscopy as well as by their single‐crystal X‐ray structures. Variable‐temperature UV/Vis absorption spectra of BZ ^{. +}[Al(OR_F)₄]^? and TMB ^{. +}[Al(OR_F)₄]^? in acetonitrile indicate an equilibrium between monomeric free radical cations and a radical‐cation dimer. In contrast, the absorption spectrum of TPB ^{. +}SbF₆^? in acetonitrile indicates that the oxidation of TPB only resulted in a monomeric radical cation. Single‐crystal X‐ray diffraction studies show that in the solid state BZ and its methylation derivative (TMB) form radical‐cation π dimers upon oxidation, whereas that modified with isopropyl groups (TPB) becomes a monomeric free radical cation. By increasing the chain length, π stacks of π dimers are obtained for the radical cation of DATP. The single‐crystal conductivity measurements show that monomerized or π‐dimerized radicals (BZ ^{. +}, TMB ^{. +}, and TPB ^{. +}) are nonconductive, whereas the π‐stacked radical (DATP ^{. +}) is conductive. A conduction mechanism between chains through π stacks is proposed.     

Selective and Efficient Reduction of Carbon Dioxide to Carbon Monoxide on Oxide‐Derived Nanostructured Silver Electrocatalysts

In this work, the selective electrocatalytic reduction of carbon dioxide to carbon monoxide on oxide‐derived silver electrocatalysts is presented. By a simple synthesis technique, the overall high faradaic efficiency for CO production on the oxide‐derived Ag was shifted by more than 400 mV towards a lower overpotential compared to that of untreated Ag. Notably, the Ag resulting from Ag oxide is capable of electrochemically reducing CO₂ to CO with approximately 80 % catalytic selectivity at a moderate overpotential of 0.49 V, which is much higher than that (ca. 4 %) of untreated Ag under identical conditions. Electrokinetic studies show that the improved catalytic activity is ascribed to the enhanced stabilization of COOH^. intermediate. Furthermore, highly nanostructured Ag is likely able to create a high local pH near the catalyst surface, which may also facilitate the catalytic activity for the reduction of CO₂ with suppressed H₂ evolution.     

Bis(4‐aminopyridine)silver(I) nitrate and tris(2,6‐diaminopyridine)silver(I) nitrate

The bis(4‐aminopyridine)silver(I) cation in [Ag(C₅H₆N₂)₂]NO₃ has the Ag atom on a twofold axis and displays an N—Ag—N angle of 174.43 (15)° and an Ag—N distance of 2.122 (3) Å. The two ligands are planar and the angle between the two ligand planes is 79.45 (9)°. The pyridine rings are stacked in piles with an interplanar distance of 3.614 (5) Å, a distance that strongly suggests that pyridine π–π interactions have an appreciable importance with respect to the non‐bonded crystal organization. The tris(2,6‐diaminopyridine)­silver(I) cation in [Ag(C₅H₇N₃)₃]NO₃ has Ag—N distances of 2.243 (2), 2.2613 (17) and 2.4278 (18) Å, and N—Ag—N angles of 114.33 (7), 134.91 (7) and 114.33 (7)°. The Ag⁺ ion is situated 0.1531 (2) Å from the plane defined by the three pyridine N atoms.     

Syntheses and Crystal Structures of Copper and Silver Complexes with the Ylide Ph3PCHP(O)PPh2 as Ligand

The reactivity of the hydrolysis product of hexaphenylcarbodiphosphorane, PPh₃CHP(O)Ph₂, towards different soft Lewis acids, such as CuI and Ag[BF₄] are reported. While CuI exclusively binds at the ylidic carbon atom, reaction of the silver cation in CH₂Cl₂ leads to proton abstraction from the solvent to give the cation [PPh₃CH₂P(O)Ph₂]⁺. Surprisingly, Ag⁺ replaces the methyl group of [PPh₃CHMeP(O)Ph₂]⁺ to produce a dimeric complex, in which Ag⁺ is coordinated to C and O forming an eight membered ring. The compounds were characterized by spectroscopic methods and X‐ray diffraction.     

Equilibrium Study on Ion-Pair Formation in Water and Distribution Between Water and m-Xylene of Tetraalkylammonium Picrates

The 1:1 ion-pair formation constants (K _IP) of tetraalkylammonium (Me₄N⁺, Et₄N⁺, Pr₄N⁺, Bu₄N⁺, and Bu₃MeN⁺) picrates in water were determined by capillary electrophoresis at 25°C. The ion-pair extraction constants (K _ex,ip) of the picrates from water to m-xylene were determined by a batch-extraction method at 25°C, and the distribution constants (K _D) of the neutral ion-pairs were calculated from the relationship K _D = K_ex,ip/K _IP. The tetraalkylammonium ion having more methylene groups generally forms a slightly more stable ion-pair with the picrate ion in water, which is attributed to the lower hydration of the cation. For Me₄N⁺, Et₄N⁺, Pr₄N⁺, and Bu₄N⁺, the distribution of the ion pair into m-xylene increases in that order, and a linear relationship was found between log K _D and the number of methylene groups in the cation. This is consistently explained by the regular solution theory. It was also revealed that the ion pairs have a strong specific interaction with water. The ion pair of Bu₃MeN⁺ has a higher distribution constant than that expected from the relationship between log K _D and the number of methylene groups for the symmetrical tetraalkylammonium ions. The cation dependence of the ion pair extractability is mostly governed by that of the distribution of the ion pair.     

Electrochemical Oxidation of Lithium Carbonate Generates Singlet Oxygen

Solid alkali metal carbonates are universal passivation layer components of intercalation battery materials and common side products in metal‐O₂ batteries, and are believed to form and decompose reversibly in metal‐O₂/CO₂ cells. In these cathodes, Li₂CO₃ decomposes to CO₂ when exposed to potentials above 3.8 V vs. Li/Li⁺. However, O₂ evolution, as would be expected according to the decomposition reaction 2 Li₂CO₃→4 Li⁺+4 e^?+2 CO₂+O₂, is not detected. O atoms are thus unaccounted for, which was previously ascribed to unidentified parasitic reactions. Here, we show that highly reactive singlet oxygen (¹O₂) forms upon oxidizing Li₂CO₃ in an aprotic electrolyte and therefore does not evolve as O₂. These results have substantial implications for the long‐term cyclability of batteries: they underpin the importance of avoiding ¹O₂ in metal‐O₂ batteries, question the possibility of a reversible metal‐O₂/CO₂ battery based on a carbonate discharge product, and help explain the interfacial reactivity of transition‐metal cathodes with residual Li₂CO₃.     

Raman spectroscopy of silver pertechnetate

The title compound, AgTcO₄, contains close Ag—O contacts, and Raman spectroscopy shows a reduction in the Tc—O stretching frequencies on changing the pertechnetate counter‐cation from K⁺ to Ag⁺.     

Ag[Fe(CO)5]2+: A Bare Silver Complex with Fe(CO)5 as a Ligand

Attempts to prepare Fe(CO)₅⁺ from Ag[Al(OR^F)₄] (R^F=C(CF₃)₃) and Fe(CO)₅ in CH₂Cl₂ yielded the first complex of a neutral metal carbonyl bound to a simple metal cation. The Ag[Fe(CO)₅]₂⁺ cation consists of two Fe(CO)₅ molecules coordinating Ag⁺ in an almost linear fashion. The ν(CO) modes are blue‐shifted compared to Fe(CO)₅, with one band above 2143 cm^?1 indicating that back‐bonding is heavily decreased in the Ag[Fe(CO)₅]₂⁺ cation.     

Charge carriers and dc polarization phenomena in solid Na2WO4

Ionic transport measurements based on the Tubandt method have been performed in all three solid phases of Na₂WO₄ at temperatures between 550 and 600°C in air. It is shown that t_Na⁺ = 1.00 in all cases. Ag is oxidized anodically to Ag⁺ at Ag/Na₂WO₄ interfaces. Cathodically only (air) oxygen reduction occurs, resulting in the formation of a poorly conducting layer of Na₂O and Na₂CO₃ at the cathode.