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Schematic depiction of the case of a semi-permeable cation conductor causing a 'cationic diode' effect. In the closed state, the flow of cations is limited by electrolyte depletion within the cylindrical section
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Films of titanate nanosheets (approx. 1.8-nm layer thickness and 200-nm size) having a lamellar structure can form electrolyte-filled semi-permeable channels containing tetrabutylammonium cations. By evaporation of a colloidal solution, persistent deposits are readily formed with approx. 10-μm thickness on a 6-μm-thick poly(ethylene-terephthalate)...
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... ionic diode effect caused in asymmetrically coated microholes can be explained (at least to a first approximation) based on a combination of ion conductivity and concentration polarisation phenomena [35]. Figure 1 provides a schematic summary of the key processes. With a symmetric ionomer deposit on both sides of the microhole, transport of ions from the left or from the right compartment remains the same and a simple resistance is observed rather than rectifier behaviour. ...
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... working electrode in a classic four-electrode measurement cell [36]), a distinct change in current occurs with an 'open' potential domain (due to accumulation of electrolyte in the microhole region; current flows) and a 'closed' potential domain (due to depletion of electrolyte in the microhole region; current is blocked). This is illustrated in Fig. 1 for the case of a cationic ...
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... due to potential dependent com- positional changes. There are different types of mechanisms, for example based on double-layer changes within nanopores, based on diffusion-migration layer compositional changes and due to interfacial precipitation or blocking. The diffusion- migration layer-based processes in microhole diodes (as de- scribed in Fig. 1) can be contrasted with processes reported in work on nanochannel diodes [37], nano-cones [38] and on electrolytic microfluidic/nanofluidic channel diodes [39,40]. Other types of ionic diodes have been proposed based on gel- gel interfaces [41]. Ionic circuits have been proposed based on polymer gels [42,43]. Ionic diode switching ...
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... the asymmetric case, current rectification behaviour is ob- served with a higher current generated at positive applied po- tentials and a lower current generated at negative applied po- tentials. Figure 1 illustrates the corresponding cases of an open cationic diode (positive applied potential) and a closed cation- ic diode (negative applied potential) for the case of negatively charged titanate nanosheet material. Next, rectification phe- nomena are investigated with different concentrations of aque- ous NaCl electrolyte solution. ...
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Citations
... Similar cases of semi-permeable ion conducting materials leading to ionic diode behavior were observed with metal-organic framework (MOF) materials [78], with cellulosic materials [79], with TiO 2 nanosheet films [80], and with biological materials such as M13 bacteriophage aggregate deposits [81]. Figure 17 shows the shape of M13 phage with surface protein defining a positive surface charge when immersed in dilute aqueous acid. ...
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... Titanate nanosheet material was synthesised as described previously by Sasaki et al. [22] and by Harito et al. [29,30]. All chemicals were purchased form Sigma-Aldrich or Fisher Scientific and used without further purification. ...
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... The spectrum that corresponds to the non-calcined TiNT/RVC shows a large peak at 148 cm −1 and smaller peaks at 278 and 447 cm −1 , the former corresponds to the presence of the titanate phase of TiNT. The as synthesised titanate has different chemical properties from TiO 2 in which the titanate has a negative surface charge [41], interlayer structure, and more hydroxyl groups [42] hence it can be easily deposited to RVC by electrophoretic deposition. After calcination, the anatase phase gave rise to Raman bands at 151, 185 cm −1 , 390 cm −1 450 cm −1 and 629 cm −1 indicating that the heat treatment converted the substrate phase from titanate to anatase phase as reported in the literature [43]. ...
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... Incidentally, these cations play an increasing role in electrochemistry. Namely, as follows from the papers published during last year, TBAc were able to influence the rate of polyoxometalates electron transfer during reductive reactions at Pt electrode [11], "invert" the so-called diode effect (from cationic one to anionic) during the ion transport at a titanate nanosheet deposit [12] and initiate the layered-to-spinel phase transition in Li-rich layered cathode in lithium batteries [13]. The finding presented in a third of the above mentioned papers [13] together with ours in [10] encouraged us to enlarge the knowledge on the ability of TBAc to induce the phase transition in an electrochemical system. ...
Effect of surface structure of Au(1 0 0) electrode on the phase transitions within adsorbed adlayer of coumarin (CUM) in halide electrolytes in the presence of tetrabutylammonium cations (TBAc) was studied by means of cyclic voltammetry and differential capacity measurements. At the nearly unreconstructed surface of Au(1 0 0) electrode in chloride and bromide solutions, TBAc induced this transition, while at the reconstructed surface these cations caused a shift of it to more negative potentials. In KI as the supporting electrolyte, such phase transition was not detected at the reconstructed surface, but it was induced at the unreconstructed one. Additionally, new phase transitions in CUM adlayer have been found at the unreconstructed surface in bromide electrolyte, which are, however, completely inhibited by TBAc. Keywords: Single-crystal Au(1 0 0) electrode, Phase transition, Tetrabutylammonium cations, Halide anions, Coumarin
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