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Приведён краткий обзор проблемы электрохромизма в неупорядоченных тонких пленках сложных оксидов вольфрама на основе экспериментальных результатов, опубликованных ранее. Рассмотрены проблемы ионно-электронного упорядочения в сложных оксидах вольфрама MWO ( M = Na, K и x = 0,3), их взаимосвязь с динамикой процесса электрохромного окрашивания в этих конденсированных системах. Рассмотрены возможные пути решения обозначенных проблем. Отправной точкой нашего похода к исследованию электрохромизма и разработки физических основ технологии электрохромных устройств явился отказ от общепринятого электрохимического рассмотрения этого явления. Мы убеждены в том, что электрохромный эффект является чисто твердотельным эффектом, происходящим в конденсированной системе с сильной электронной корреляцией. Электронная структура твердого тела, имеющаяся на границе раздела твердое тело-электролит в значительной степени, управляет характером и скоростью реакций, которые протекают на его поверхности. В случае окислов роль, которую играет электронная структура особенно сложна. Все изложенное указывает на необходимость рассмотрения влияния глубоких уровней в объеме оксидной вольфрамовой бронзы и на ее поверхности, граничащей с электролитом на процесс электрохромного окрашивания. A brief review of the problem of electrochromism in disordered thin films of complex tungsten oxides is given on the basis of experimental results published earlier. The problems of the ion-electron ordering in complex tungsten oxides MWO (M = Na or K and x = 0,3) are regarded as well as their relationship with the dynamics of the process of electrochromic coloring in these condensed systems. Possible ways of solving the indicated problems are considered. The starting point of our campaign to study the electrochromism and to develop the physical grounds of the technology of electrochromic devices was the rejection of the generally accepted electrochemical consideration of this phenomenon. We are convinced that the electrochromic effect is a purely solid-state one occurring in a condensed system with a strong electron correlation. The electronic structure of a solid at the solid-electrolyte interface largely controls the nature and rate of reactions that take place on its surface. In the case of oxides, the role played by the electronic structure is particularly complex. All of the above indicates the need to consider the effect of deep levels in the bulk of the oxide tungsten bronze and on its surface, bordering the electrolyte, on the process of electrochromic coloring.

В работе рассмотрены вопросы получения тонких пленок натрийвольфрамовых бронз кубической структуры методом электрокристаллизации. Приведены основные параметры полученных пленок. Сняты спектры отражения пленок для неокрашенных и окрашенных пленок. Исследование приповерхностного слоя монокристаллов натрий-вольфрамовых бронз методами протонографии и ядерных реакций показало их высокое структурное совершенство. Анодная и катодная поляризации монокристаллов приводят к изменению структуры их приповерхностного слоя. Обеднение по натрию приповерхностного слоя присутствует и при катодной и при анодной поляризации, и глубина обеднения растет с ростом времени поляризации величины напряжения. Электронографией исследованы тонкие пленки натрийвольфрамовых бронз, установлена аморфная структура свеженапыленных пленок для всех температур подложки. Отжиг электронным лучом приводит к кристаллизации пленок. The paper considers the problems of obtaining thin films of sodium-tungsten bronzes of a cubic structure by the method of electrocrystallization. The main parameters of the obtained films are presented. The reflection spectra of the films were recorded for uncolored and colored films. Investigation of the near-surface layer of sodium-tungsten bronze single crystals by protonography and nuclear reactions showed their high structural perfection. The anodic and cathodic polarizations of single crystals lead to a change in the structure of their surface layer. Depletion in sodium of the nearsurface layer is present at both cathodic and anodic polarization, and the depletion depth increases with increasing polarization time of the voltage value. Thin films of sodium-tungsten bronzes have been investigated by electron diffraction, and the amorphous structure of freshly deposited films has been established for all substrate temperatures. Annealing with an electron beam leads to crystallization of the films.

Serious concerns about climate change make the reutilization of CO2 particularly attractive; one option for reutilization is the electroreduction of CO2 in acetonitrile solutions on a range of electrode materials. Among them, transition-metal oxides stand out as cost-effective alternatives. In this context, the electrocatalytic activity of nanostructured WO3 electrodes for carbon dioxide reduction in both humid and dry acetonitrile media has been addressed by using electrochemical and spectroelectrochemical measurements. Importantly the cathodic faradaic process starts at potentials as high as −0.16 V vs SHE. Gas chromatography measurements show CO as being the main product in both dry and humid acetonitrile, together with formate in the presence of humidity. Interestingly, purging with CO2 causes not only the appearance of cathodic faradaic currents but also an increase in capacitive currents, which are directly associated with an enhanced electrochromic effect. The ICP-MS determination of tungsten upon electrolysis confirms a minor electrodissolution of WO3 electrodes. On the basis of these observations, a mechanism is proposed in which WO3 is not only the electrode material but also a mediator in the CO2 reduction process. We are grateful for the financial support of MINECO through project MAT2015-71727-R (FONDOS FEDER). N.E.M.R. acknowledges COLCIENCIAS National Doctoral Scholarship (567) and the Vicerrectorado de Investigación y Transferencia del Conocimiento de la Universidad de Alicante, and A.K.D.-G. thanks the Mexican government (CONACYT) for the award of a doctoral grant.

Electrochromic effect and molecularly imprinted technology have been used to develop a sensitive and selective electrochromic sensor. The polymeric matrices obtained using the imprinting technology are robust molecular recognition elements and have the potential to mimic natural recognition entities with very high selectivity. The electrochromic behavior of iridium oxide nanoparticles (IrOx NPs) as physicochemical transducer together with a molecularly imprinted polymer (MIP) as recognition layer resulted in a fast and efficient translation of the detection event. The sensor was fabricated using screen-printing technology with indium tin oxide as a transparent working electrode; IrOx NPs where electrodeposited onto the electrode followed by thermal polymerization of polypyrrole in the presence of the analyte (chlorpyrifos). Two different approaches were used to detect and quantify the pesticide: direct visual detection and smartphone imaging. Application of different oxidation potentials for 10 s resulted in color changes directly related to the concentration of the analyte. For smartphone imaging, at fixed potential, the concentration of the analyte was dependent on the color intensity of the electrode. The electrochromic sensor detects a highly toxic compound (chlorpyrifos) with a 100 fM and 1 mM dynamic range. So far, to the best of our knowledge, this is the first work where an electrochromic MIP sensor uses the electrochromic properties of IrOx to detect a certain analyte with high selectivity and sensitivity., This work was supported by the European Commission Programme, H2020-WATER, INTCATCH Project (689341). This work is also funded by the CERCA Programme/Generalitat de Catalunya. ICN2 is supported by the Severo Ochoa program from Spanish MINECO (Grant No. SEV2013-0295). R.A. acknowledges the financial support from CONACYT (Mexico).