Specific adsorption of bromide and iodide anions from nonaqueous solutions on controlled-surface polycrystalline silver electrodes

Low-Concentration Redox-Electrolytes for High-Rate and Long-Life Zinc Metal Batteries

The uncontrolled zinc electrodeposition and side reactions severely limit the power density and lifespan of Zn metal batteries. Herein, the multi-level interface adjustment effect is realized with low-concentration redox-electrolytes (0.2 m KI) additives. The iodide ions adsorbed on the zinc surface significantly suppress water-induced side reactions and by-product formation and enhance the kinetics of zinc deposition. The distribution of relaxation times results reveal that iodide ions can reduce the desolvation energy of hydrated zinc ions and guide the deposition of zinc ions due to their strong nucleophilicity. As a consequence, the Zn||Zn symmetric cell achieves superior cycling stability (>3000 h at 1 mA cm-2, 1 mAh cm-2) accompanied by a uniform deposition and a fast reaction kinetics with a low voltage hysteresis (<30 mV). Additionally, coupled with an activated carbon (AC) cathode, the assembled Zn||AC cell delivers a high-capacity retention of 81.64% after 2000 cycles at 4 A g-1. More importantly, the operando electrochemical UV-vis spectroscopies show that a small number of I3 - can spontaneously react with the dead zinc as well as basic zinc saltsand regenerate iodide ions and zinc ions; thus, the Coulombic efficiency of each charge-discharge process is close to 100%.

Degradation Mechanism of Silver Metal Deposited on Lead Halide Perovskites

Lead halide perovskite solar cells have significantly increased in both efficiency and stability over the last decade. An important aspect of their long-term stability is the reaction between the perovskite and other materials in the solar cell. This includes the contact materials and their degradation if they can potentially come into contact through, e.g., pinholes or material diffusion and migration. Here, we explore the interactions of silver contacts with lead halide perovskites of different compositions by using a model system where thermally evaporated silver was deposited directly on the surface of the perovskites. Using X-ray photoelectron spectroscopy with support from scanning electron microscopy, X-ray diffraction, and UV-visible absorption spectroscopy, we studied the film formation and degradation of silver on perovskites with different compositions. The deposited silver does not form a continuous silver film but instead tends to form particles on a bare perovskite surface. These particles are initially metallic in character but degrade into AgI and AgBr over time. The degradation and migration appear unaffected by the replacement of methylammonium with cesium but are significantly slowed down by the complete replacement of iodide with bromide. The direct contact between silver and the perovskite also significantly accelerates the degradation of the perovskite, with a significant loss of organic cations and the possible formation of PbO, and, at the same time, changed the surface morphology of the iodide-rich perovskite interface. Our results further indicate that an important degradation pathway occurred through gas-phase perovskite degradation products. This highlights the importance of control over the interface materials and the use of completely hermetical barrier layers for the long-term stability and therefore the commercial viability of silver electrodes.

Reductive cleavage of carbon-chlorine bonds at catalytic and non-catalytic electrodes in 1-butyl-3-methylimidazolium tetrafluoroborate

Dissociative electron transfer (DET) to a series of organic chlorides at glassy carbon (GC), silver and copper electrodes has been studied in 1-butyl-3-methylimidazolium tetrafluoroborate. The overall results of this study show that the ionic liquid behaves like molecular solvents such as acetonitrile and dimethylfomamide. It is found that aromatic chlorides follow a stepwise mechanism, whereas concerted electron transfer/bond cleavage is the preferred reaction mechanism for alkyl and benzyl chlorides. Ag and Cu show catalytic effects only when the DET follows a concerted mechanism, but Ag proves to be a much better electrocatalyst than Cu. A series of substituted benzyl chlorides (Z-C6H4CH2Cl, Z = H, 3-OCH3, 3-F, 4-Cl, and 3-CF3) show interesting results providing some insight into the reaction dynamics. The process occurs by a concerted mechanism and, albeit a constant standard potential for the whole series, Ep on GC and Cu, which does not show catalytic activity, is significantly affected by the substituents. In contrast, Ag shows good catalytic activity and, as expected, Ep does not change with the substituent. This difference in behavior may be rationalized by considering ion-dipole interactions between R˙ and Cl(-) as opposed to adsorption of the fragments on the electrode surface.

Dissociative electron transfer to organic chlorides: electrocatalysis at metal cathodes

The reductive cleavage of a series of organic chlorides, including chloroaromatics, benzyl chlorides, activated chloroalkanes and polychloromethanes, was investigated at Ag, Cu, Pd and glassy carbon (GC) electrodes in CH(3)CN + 0.1 M (C(2)H(5))(4)NClO(4). The silver cathode was either a 2-mm diameter disc, fabricated from Ag wire, or nanoclusters of average diameter d = 304 nm, prepared by electrodeposition on GC. Ag, Cu and Pd electrodes have shown remarkable electrocatalytic properties for the reduction of several compounds. The peak potentials recorded at these electrodes, for example, at upsilon = 0.1 V s(-1) are positively shifted by 0.3-0.8 V with respect to the reduction potentials measured at a non catalytic electrode such as GC. Electrocatalysis is strictly related to the concerted nature of the dissociative electron transfer to the carbon-chlorine bond. No catalysis is observed when the dissociative electron transfer to RCl occurs according to a stepwise mechanism involving the intermediate formation of a radical anion. The catalytic surfaces affect the reaction scheme, offering a more favourable route possibly through the formation of strongly adsorbed activated complexes.

Electrosynthetic reduction of 1-iodoadamantane forming 1,1'-biadamantane and adamantane in aprotic solvents: insonation switches the mechanism from dimerisation to exclusive monomer formation

The combination of ultrasound and electrochemistry -sonoelectrochemistry can produce a variety of effects within an electrochemical system including enhanced mass transport, in situ cleaning of an electrode surface, diminution of the diffusion layer, and possible induction of new reactions by sonochemical enhancement of follow-up reactions post-electron transfer. Herein, we show that ultrasound provides a useful extra dimension to electrosynthesis via a switch in the sonoelectroorganic mechanism in which dimerisation is disfavoured by virtue of convective mixing promoted by insonation. Under 'normal' voltammetric conditions the reduction of 1-iodoadamantane at a silver cathode in tetrahydrofuran (THF) and acetonitrile (ACN) involves a single electron forming a mixture of monomeric and dimeric products; 58%/THF, 50%/ACN adamantane and 39%/THF, 50%/ACN 1,1'-biadamantane, respectively. However, under the conditions of insonation using a 10 kHz transducer, a single product is formed exclusively; 93%/THF, 96%/ACN adamantane. The effect of insonation upon the voltammetry at a silver macroelectrode is shown and compared to that under silent conditions. In addition, the previously observed characteristic series of oxidation and adsorption peaks following reduction of 1-iodoadamantane are reduced in magnitude under insonation. Overall, this work shows that the effect of insonation can switch the mechanism of follow-up chemical processes - favoring the formation of a monomer.