Nanopore electrode

Paek SM, Yoo E, Honma I (2009) Enhanced cyclic performance and hthium storage capacity of Sn02/graphene nanoporous electrodes with thrce-dimensionally delaminated flexible... 

The simplest photoelectrochemical cells consist of a semiconductor working electrode and a metal counter electrode, both of which are in contact with a redox electrolyte. In the dark, the potential difference between the two electrodes is zero. The open circuit potential difference between the two electrodes that arises from illumination of the semiconductor electrode is referred to as the photovoltage. When the semiconductor and counter electrode are short circuited, a light induced photocurrent can be measured in the external circuit. These phenomena originate from the effective separation of photogenerated electron-hole pairs in the semiconductor. In conventional photoelectrochemical studies, the interface between the flat surface of a bulk single crystalline semiconductor and the electrolyte is two dimensional, and the electrode is illuminated from the electrolyte side. However, in the last decade, research into the properties of nanoporous semiconductor electrodes interpenetrated by an electrolyte solution has expanded substantially. If a nanocrystalline electrode is prepared as a film on a transparent conducting substrate, it can be illuminated from either side. The obvious differences between a flat (two dimensional) semiconductor/ electrolyte junction and the (three dimensional) interface in a nanoporous electrode justify a separate treatment of the two cases. 

It is reasonable to assume that in a nanoporous electrode (Fig. 7), the time required for a photogenerated minority carrier to reach the semiconductor surface by drift or diffusion is not very different from that estimated for a flat semiconductor/ electrolyte interface. However, the photogenerated majority carrier must travel through the porous structure to reach the back contact. Much work has been devoted recently to the study of electronic transport through nanostructured electrodes (cf. sections 3 and 5). It has been found that the characteristic time required for a majority carrier to travel through the porous network can be extremely long (in the ms to s range). 

Figure 28. Electron transport through a nanoporous electrode under steady-state illumination conditions. A potential gradient is built up by trapped electrons.

Macroporous semiconductor electrodes resemble in many respects the bulk electrodes described earlier. However, there are clear differences between porous and nonporous systems that become even more pronounced in nanoporous electrodes. Porous systems are considered in Sect. 2.1.5. 

Fig. 17 Schemes of the semiconductor/electrolyte interface for a macroporous and a nanoporous electrode, (a) An n-type macroporous electrode under moderate depletion structural units contain a depleted region and a bulk region (free electrons in the nondepleted region), (b) A macroporous n-type electrode at a strongly positive potential the entire porous electrode is depleted of free electrons, (c) A nanoporous electrode in which depletion occurs without band bending.

FIGURE 2.31 (a) Capacitance of a nanoporous electrode as a function of the pore size for a... 

FIGURE 2.57 Capacitance (C) of a nanoporous electrode as a function of the pore width (d) up to 15a. Peak positions are labeled in terms of the ion diameter (O = 0.5 nm). (Reprinted with permission from Jiang, D. E., Z. Jin, and J. Wu. 2011. OseiUation of capacitance inside nanopores. Nano Letters 11 5373-5377. Copyright 2011 Ameriean Chemical Society.)... 

Mysyk, R., V. Ruiz, E. Raymundo-Pinero, R. Santamaria, and F. Beguin. 2010. Capacitance evolution of electrochemical capacitors with tailored nanoporous electrodes in pure and dissolved ionic liquids. Fuel Cells 10 834-839. 

In addition, traditional top-down nanofabrication methods such as focused ion beam (FIB], can be used to fabricate nanopore array electrodes [225], FIB milling thus represents a simple and convenient method for fabrication of prototype nanopore electrode arrays. These electrode nano-arrays can be used in electrochemical nanofabrication for applications in sensing and fundamental electrochemical studies. 

Hereafter, electrochemical growth of new material in the pores of the film is reliant on optimizing many of the same parameters demanded by other nanoporous electrode structures, such as anodized alumina and track-etched membranes [45]. 

Paek, S. M., Yoo, E. ]., and Honma, I. (2009]. Enhanced cyclic performance and lithium storage capacity of SnOj/graphene nanoporous electrodes with three-dimensionally delaminated flexible structure. Nano Lett, 9, pp. 72-75. 

Vatamanu J, Borodin O, Smith GD (2010) Molecular dynamics simulations of atomically flat and nanoporous electrodes with a molten salt electrolyte. Phys Chem ChemPhys 12 170-182... 

The truncated conical-shaped glass nanopore electrode (for brevity, hereafter referred to as a glass nanopore electrode or GNE) comprises a Pt microdisk electrode sealed at the bottom of a conical-shaped pore in glass (1). The radius of the pore orifice can be varied between 5 nm and 1 pm. The GNE was developed as a structurally simple platform for nanopore-based sensors and for investigating molecular transport through orifices of nanoscale dimensions. 

Riihle S, Greenshtein M, Chen S-G, Merson A, Pizem H, Sukenik CS, Cahen D, Zaban A (2005) Molecular adjustment of the electronic properties of nanoporous electrodes in dye-sensitized solar cells. J Phys Chem B 109(40) 18907-18913... 

Moving up the scale to the level of flooded nanoporous electrodes, Michael s group has developed the first theoretical model of ionomer-free ultrathin catalyst layers—a type of layer that promises drastic savings in catalyst loading. Based on the Poisson-Nernst-Planck theory, the model rationalized the impact of interfacial charging effects at pore walls and nanoporosity on electrochemical performance. In the end, this model links fundamental material properties, kinetic parameters, and transport properties with current generation in nanoporous electrodes. 

Pikul, J.H., Zhang, H., Cho, J. Braun, P. King, W.P. High-power lithium ion microbatteries from interdigitated three-dimensional bicontinuous nanoporous electrodes. Nature Commun. 4 (2013), 1732. 

Wang Z.-S., Hnang C.-H., Huang Y.-Y., Hou Y.-J., Xie P.-H., Zhang B.-W, Cheng H.-W. A highly efficient solar cell made from a dye-modified ZnO-covered TiOa nanoporous electrode. Chan. Mater. 2001 13 678-682... 

Zaban A., Chen S.G., Chappel S., Gregg B.A. Bilayer nanoporous electrodes for dye sensitized solar cells. Chem. Commun. 2000 2231-2232... 

M. A5mb, A. Ivanov, E. Instuli, M. Cecchini, G. Chansin, C. McGilvery, G. Baldwin, J. Hong, G. McComb, J. B. Edel and T. Albrecht, Nanopore/electrode structures for single-molecule biosensing, Electrochimica Acta, 2010, 55(27), 8237-8243. 

T. Albrecht, How to Understand and Interpret Current Flow in Nanopore/ Electrode Devices, ACS Nano, 2011, 5(8), 6714-6725. 

A. Rutkowska, J. B. Edel and T. Albrecht, Mapping the Ion Current Distribution in Nanopore/Electrode Devices, ACS Nano, 2013, 547 555. 

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