电化学技术降解有机废水研究进展

综述了电催化氧化、光电催化、超声电化学、三维电极电化学技术降解有机废水的研究与应用进展,重点介绍了电化学技术协同降解有机废水的发展现状,对各种电化学方法进行了阐述,探讨了电化学技术降解有机废水的发展趋势,展望了降解有机废水今后的重点研究方向。     

The electrochemistry of lithium in ionic liquid/organic diluent mixtures

The electrochemistry of lithium is investigated in a number of electrolytes that consist of a lithium salt dissolved in a combined ionic liquid-organic diluent medium. We find that ethylene carbonate and vinylene carbonate improve electrochemical behaviour, while toluene and tetrahydrofuran are less promising.We also present insights into the electrode passivation caused by these diluents in an ionic liquid electrolyte during lithium cycling. We observe that during lithium cycling those electrolytes with carbonate based diluents are the most able to utilise their previously reported improved lithium ion diffusivities. Conversely, tetrahydrofuran, the most promising diluent of those studied in terms of its known ability to increase lithium ion diffusivity is found not to be as advantageous as a diluent. It appears that the poor electrochemical interfacial properties of the tetrahydrofuran electrolyte prevented the realisation of the benefits of the high solution lithium ion diffusivity.     

Electrocatalysis and electron transfer mechanisms in the reduction of organic halides at Ag

The reductive cleavage of a series of organic halides, including both aromatic and aliphatic compounds, has been investigated in acetonitrile at glassy carbon (GC) and silver electrodes. Ag exhibits extraordinary electrocatalytic activities for the reduction of most of the investigated halides. During the reductive cleavage of a carbon–halogen bond, electron transfer (ET) and bond breaking may occur either in a single step or in two distinct steps. The compounds examined in this study are representative of both dissociative electron transfer (DET) mechanisms. In general a link between the DET mechanism and electrocatalysis at Ag is observed for the whole set of data. There is no catalysis at all when the ET involves a substituent that gives a stable radical anion. Furthermore, there is no catalysis for all aromatic chlorides. Instead, a remarkable electrocatalysis is observed for all compounds undergoing a concerted DET mechanism, regardless of the nature of the halogen atom.     

Use of ion exchange membranes in preparative organic electrochemistry. L Anodic methoxylation of some olefins

Electro-oxidation of a solution of an olefm in methanol can be carried out, in the absence of supporting electrolyte, at a platinum grid lying on a cationic exchange membrane. 1,1-diphenylethylene,trans-stilbene, cyclohexene, acenaphthylene, 2-methyl-3-phenylindenone, and furan have been investigated. The corresponding dimethyl ethers are generally the main products of electrolysis; the yield depends on the olefin structure. Up to 80% of 2,5-dimethoxy-2,5-dihydrofuran is reached from furan.The results are compared to those obtained by classical electrochemical processes.     

Use of ion exchange membranes in preparative organic electrochemistry. II. Anodic dimethoxylation of furan

Anodic dimethoxylation of furan can be performed by electro-oxidation of a solution of furan in methanol in the absence of supporting-electrolyte at a platinum grid lying on a cation exchange membrane. Yields of up to 80% of 2,5-dimethoxy-2,5-dihydrofuran are reached. The process is studied by investigating the influence of different factors (cell voltage, substrate concentration, nature of the membrane) on electrolysis results such as chemical yield, current efficiency and energy consumption.     

Cobalt nanoparticle decorated N-doped carbons derived from a cobalt covalent organic framework for oxygen electrochemistry

The low cost and highly efficient construction of electrocatalysts has attracted significant attention owing to the use of clean and sustainable energy technologies. In this work, cobalt nanoparticle decorated N-doped carbons (Co@NC) are synthesized by the pyrolysis of a cobalt covalent organic framework under an inert atmosphere. The Co@NC demonstrates improved electrocatalytic capabilities compared to N-doped carbon without the addition of Co nanoparticles, indicating the important role of cobalt. The well-dispersed active sites (Co–N_x) and the synergistic effect between the carbon matrix and Co nanoparticles greatly enhance the electrocatalytic activity for the oxygen reduction reaction. In addition, the Co content has a significant effect on the catalytic activity. The resulting Co@NC-0.86 exhibits a superb electrocatalytic activity for the oxygen reduction reaction in an alkaline electrolyte in terms of the onset potential (0.90 V), half-wave potential (0.80 V) and the limiting current density (4.84 mA·cm^–2), and a high selectivity, as well as a strong methanol tolerance and superior durability, these results are comparable to those of the Pt/C catalyst. Furthermore, the superior bifunctional activity of Co@NC-0.86 was also confirmed in a home-built Zn-air battery, signifying the possibility for application in electrode materials and in current energy conversion and storage devices.     

Electrocatalysis: present and future

The development of electrocatalytic materials and our knowledge of the factors which determine catalytic activity are reviewed. To the present, the main aim has been to produce electrocatalysts which minimize overpotentials, particularly for gas evolving or consuming electrode reactions. In the future, however, materials which optimize the selectivity of more complex reactions may increase in importance. It must be recognized that the development of electrocatalysts has been essentially empirical and there remains a gulf between those who develop electrode materials and those who seek to understand the physical chemistry of electrocatalysis.     

Electrocatalysis on solid oxide electrolytes

Conclusion Based on the preceding discussion, it is tentatively concluded that the oxide electrolyte cell acts as an oxygen concentration cell and the presence of point defects, such as interstitial protons on the oxide electrolyte surface, enhances the electrochemical reduction of O₂ at the cathode and may be responsible for catalysing the anodic oxidation of H₂.In order to obtain a much better understanding of the fundamentals of electrode processes involving point defects like interstitial protons and F-centres (V ₀ ^x ), it is necessary to investigate the current-overpotential characteristics by performing systematic experiments using various metals as electrodes and a variety of oxides (e.g. ceria) over a wide range of compositions as electrolytes. It is planned to examine the influence of the morphology of the surface on the current-overpotential characteristics by making electron-microscopic, and Auger spectroscopic, measurements. In future work, the magnitude of the individual cathodic and anodic overpotentials will be measured by the introduction of reference electrodes to the system. Having reference electrodes available will greatly facilitate the interpretation of the data and confirmation of proposed electrochemical mechanisms. Also, with the experimental arrangement of Fig. 1 variation of flow-rates normal to the disc, resulting in stagnation flows, will allow gas phase masstransfer rates to be varied, thus allowing the mechanism of the limiting current behaviour in the plateaus of Figs. 3 and 4 to be ascertained.     

Recent advances in electrochemistry of diamond

Conductive boron-doped chemically vapour-deposited diamond thin film and honeycomb electrodes were examined for various possible applications in electroanalysis and electric double layer capacitor applications, respectively. The possibility of voltammetric study of electrochemical reactions occurring at high oxidation and high reduction potentials was demonstrated at diamond electrodes, taking histamine and carbon tetrachloride as respective examples. High sensitivity and high stability of this electrode were demonstrated for the determination of histamine and sulfadiazine by flow injection analysis method. Nanostructured honeycomb diamond electrodes, prepared by oxygen plasma etching, exhibited a wide potential window similar to that of as-grown film but a capacitance 200 times higher than that of the as-grown film. These results indicate the usefulness of diamond electrode for electroanalysis and double layer capacitor applications.     

Electrocatalysis and the oxygen evolution reaction

The oxygen evolution reaction has been investigated on a number of electrodes which are electrocatalysts for the chlorine evolution reaction, by making measurements in NaClO₄ solution. Steady state current—potential and impedance—potential measurements, obtained using automated equipment, have been used as the preferred experimental method. Analysis of the impedance has been undertaken by means of curve fitting, and the resulting parameter curves of the double-layer capacity, the charge transfer resistance, and the electrolyte ohmic resistance displayed as a function of potential. Some speculation is made about the interpretation of the parameter curves. The ohmic loss parameter, R_w, is used to correct the potentials to the true values. In comparison to some other gas evolution reactions, such as hydrogen and chlorine, R_w does not depend strongly on potential. The corrected log i—E curve is also considered. It is suggested that a more complete picture of the electrical performance of these electrodes can be obtained by using these electrochemical methods.     

The electrochemistry of alloys

The features of the dissolution of the components of alloys forming solid solutions were examined. It was shown on the example of the anodic dissolution of alpha-brass that the process of the selective dissolution of zinc observed in the initial period is limited by the stage of its non-stationary diffusion from the bulk of the alloy and is subsequently replaced by uniform dissolution. During prolonged corrosion of brass, secondary selective dissolution is observed, which is due to the re-deposition of copper.It was established that intensive preferential dissolution of iron from Fe-Cr alloys takes place in the passive region and leads to the enrichment of the passivating chromium film. The results obtained from an investigation of the dissolution of the components of Fe-Cr-Mo alloys in the active region permit the conclusion that the favourable effect of small additions of molybdenum on the corrosion stability of alloys is due to the fact that this element, in view of its great inclination to passivation, blocks the most active centres of the surface in the process of its dissolution.In order to establish the mechanism of the active dissolution of Fe-Cr, alloys, the effect of the potential and pH of sulphate solutions on the partial dissolution rates of iron and chrome from these alloys in the active state was established. It was shown that the Tafel slopes and the order of magnitude of the reaction for the H⁺ ions for both components were the same and close to the corresponding values for pure iron (at low concentrations of chromium in the alloy) or for pure chromium (when the chrome content in the alloys was 13% or more). A mechanism was suggested for the active dissolution of alloys that explained the discovered regularities.     

Information sources for electrochemistry

The many types of information sources available for electrochemists are reviewed. The primary literature of electrochemistry and the role of the secondary literature in providing access to the primary are described. The complementary natures of the many databases that contain information on electrochemistry are emphasized.This paper was originally presented in part at the 1983 Spring Meeting of the Electrochemical Society in San Francisco, California, USA.     

Anodic electrochemistry of chalcopyrite

The anodic behaviour of chalcopyrite in 1 M H₂SO₄ and 1 M HCl was studied by linear sweep voltammetry and potentiostatic electrolysis. Voltammograms with a fresh surface showed a small prewave, attributed to a surface oxidation process, followed by a region of active dissolution characterized by a steeply rising anodic current. At still higher potentials the behaviour differed in the two electrolytes, but, contrary to a previous report, there was no evidence of a photosensitive limiting current. Anodic characteristics of chalcopyrite specimens from different sources, including synthetic material, were similar. The anode reaction was found to involve 6·7±0·3 F per mole of chalcopyrite, from which it was calculated that 86% of the sulphide sulphur was oxidized to the elemental form (some of which was plastic sulphur) and 14% to sulphate. The surfaces of oxidized electrodes were examined and photographed after varying periods of potentiostatic electrolysis. Chalcopyrite dissolution occurred at localized sites, the number of which depended strongly on potential. Current-voltage and potentiostatic current-time curves were interpreted in terms of the kinetics of nucleation, growth and overlap of these discrete corrosion centres.