Negative capacitance at the low-frequency domain and inverted hysteresis are familiar features in perovskite solar cells, where the origin is still under discussion. Here we use Impedance Spectroscopy to analyse these responses in methylammonium lead bromide cells treated with lithium cation at the electron selective layer/perovskite interface and in iodide devices exposed to different relative humidity conditions. Employing the Surface Polarization Model, we obtain a time constant associated to the kinetics of the interaction of ions/vacancies with the surface, τkin, in the range of 10 0 -10 2 s for all the cases exhibiting both features. These interactions lead to a decrease in the overall recombination resistance, modifying the low-frequency perovskite response and yielding to a flattening of the cyclic voltammetry. As consequence of these results we find that that negative capacitance and inverted hysteresis lead to a decrease in the fill factor and photovoltage values.
Analysis of photoelectrochemical oxidation of benzyl alcohol reveals a non-electrochemical UV-light process, with a huge impact on the reaction performance.
store energy due to its high-density energy per weight unit. [3] Additionally, the reduction of CO 2 , to energy-rich chemicals (CO, formic acid, methane, methanol, etc.), has been recently gaining increasing attention these days. In this line, there are other alternative chemical transformations, such as the synthesis of products for the chemical industry, which despite being much less developed, [4] may present an intrinsic economical interest. [5] An interesting transformation for the chemical industry is the reduction of nitrobenzene to aniline, a species widely employed as building block for the production of dyes, explosives, pesticides and drugs. [6] Traditionally, the production of aniline has been achieved by organic synthesis using homogeneous catalysis, [7] heterogeneous catalysis, [8] photocatalysis, [9] photoelectrocatalysis, [10] as well as biocatalysis.. [11] In the industry, the standard method to synthesize aniline is the catalytic vapour-phase hydrogenation using fixed-bed or fluidized-bed vapor-phase processes. For example, in the industrial procedure developed by Bayer, nitrobenzene and hydrogen are mixed at 100-700 kPa (in 1:120 molar ratio) and injected into a reactor that contains Pd on activated charcoal as catalyst. This process requires initial thermal activation of 250-300 °C. [12] With the aim to produce aniline through a more sustainable process, we focus on the electrocatalytic reduction of nitrobenzene, working under ambient conditions of temperature and pressure. [13] The electrochemical reduction of nitrobenzene to aniline is a complex reaction that takes place through 3-steps, involving 6 electrons and 6 protons that may yield to other side-reactions as shown in Figure 1. Each step involves the insertion of 2eand 2H + species in the NO 2 group of the molecule until leading to the complete substitution of the oxygens by hydrogen atoms, with the formation of one molecule of aniline and two molecules of water. During the electro-reduction, two intermediate species, namely, nitrosobenzene and phenylhydroxylamine are formed. [14] To reach an effective reduction and hydrogenation, this organic transformation requires the formation (and stabilization) [15] of abundant H * radicals in the electrode surface. This requirement highlights the importance of developing materials capable of producing H * in order to succeed in this electro-transformation.Interest in the electrochemical reduction of organic compounds as an alternative to hydrogen electrosynthesis is driven, among other reasons, by the fact that the products obtained in this process may have more economic value than H 2 . Furthermore, the technique, coupled with renewable sources of electricity, may open the door for large volume green chemical synthesis. In the present article, the electrochemical reduction and hydrogenation of nitrobenzene to aniline at neutral pH is focused upon, using copper electrodes with and without palladium decoration. Both electrodes present good activity, with a decrease in the overpotential for ni...
Society is demanding clean energy to substitute the greatly pollutant carbon-based fuels. As an alternative, the green hydrogen produced by electrocatalysis constitutes a nice strategy as its products and reactants...
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