Electrodes architectures

R. Ghen and T. S. Zhao. A novel electrode architecture for passive direct methanol fuel cells. Electrochemistry Communications 9 (2007) 718-724. 

Three-dimensional electrode nanoarchitectures exhibit unique structural features, in the guise of amplified surface area and the extensive intermingling of electrode and electrolyte phases over small length scales. The physical consequences of this type of electrode architecture have already been discussed, and the key components include (i) minimized solid-state transport distances (ii) effective mass transport of necessary electroreactants to the large surface-to-volume electrode and (iii) magnified surface—and surface defect—character of the electrochemical behavior. This new terrain demands a more deliberate evaluation of the electrochemical properties inherent therein. 

J. Jiang, Y. Li, J. Liu, X. Huang, C. Yuan, X. W. D. Lou, Recent Advances in Metal Oxide-Based Electrode Architecture Design for Electrochemical Energy Storage. Adv. Mater. 2012,24,5166-5180. 

Another important breakthrough in this field was realized by a flow-through porous electrode architecture with vanadium redox electrolytes [6]. As shown in Fig. 4, the fuel and oxidant were supplied into the inlet ports and guided to flow through the porous carbon electrodes in the... 

Novel concepts of electrode fabrication focus on ways to realize well-defined 3D porous electrode architectures, in which the distribution of TPB is fine-tuned for maximum fuel cell performance. In principle, this means electrode manufacture... 

To print high-aspect-ratio electrode architectures, the composition and rheology of each ink must be optimized to ensure a reliable flow through the nozzles and to promote adhesion between the printed features. 

This phenomenon of Pt corrosion in bromine environments has prompted some interesting and innovative work to develop non-Pt-based catalytic solutions in systems such as the H/Br RFB [40, 41]. Similarly, non-Pt methods need to he adopted for catalyzing the Br2/Br redox reaction in Zn/Br RFBs to avoid such problems that would most likely lead to severe degradation of the system. Alternatively, novel electrode architectures could be used to circumvent the introduction of foreign metals into the system. For instance, conductivity tests of porous carbon electrodes have demonstrated that they perform comparably to Pt electrodes [42]. 

DIAMOND THIN FILM DEPOSITION, ELECTRODE ARCHITECTURES, SUBSTRATE MATERIALS,... 

An interesting feature of DET biosensors is a simple and robust electrode architecture (e.g., no leaking of soluble redox mediators). Additionally, many interfering substances affecting the detection in first- and second-generation biosensors do not interfere with biosensors based on DET. The number of possible analytes is of course restricted to the number of available enzymes, but by use of modem protein engineering techniques the spectmm of analytes will be broadened in future. An example is the modification of the substrate specificity of cellobiose... 

Other major domains of future development will be multiple nanoelectrode arrays applied in dye-sensitized solar cells, fuel cells and sensing technologies. Aiming to restore lost body functions of disabled people, the extensive research (both in vitro and in vivo) already registered in medical sciences wDl progress further. As three-dimensional electrode architectures are used to connect neurons to electroiuc circuits, they will play a relevant role in the new generations of advanced (hi-tech) bioiuc prosthetics and implants. 

This is a major issue, since nanomaterials will be intensively used for next generation of secondary lithium batteries. New electrode architectures and/or the use of additives/inhibitors in the electrol54es would be surely of great interest in order to alleviate degradation (ageing) or slowdown mechanisms inside the battery system. 

Modification of a snbstrate snrface by spontaneous adsorption (24), now more commonly referred to as self-assembly, is one of the most utilized modification pathways. These films are typically bound to the snbstrate by chanisorption however, intermolecular forces within the film are also important Chemisorption is the strong adsorption of a molecule onto a snrface throngh the spontaneous formation of a chemical bond (1). This chemical bond forms between a fnnctional group in the molecule and a site on the electtode. Monomolecular layers prepared by chemisorption are known as self-assembled monolayers (SAMs). These adlayers can be used to impart the desired function to the electrode directly, or can serve as a foundation for more complex electrode architectures. 

While CNTs possess limited surface areas compared to other microporous carbon blacks, they maintain rigid mechanically robust structures that can result in favorable three-dimensional electrode architectural configurations. The network arrangement can provide a porous structure that can readily facilitate the transport of electrolyte species and provide highly electronically conductive pathways to the redox centers of the active materials. The structure, porosity, and pore size distribution of this scaffold-like architecture can also be tailored by using CNTs with varying diameters, surface properties, and wall thicknesses or by modifying preparation techniques. 

Many of the advancements for improving current densities in bioelec-trocatalytic systems have come about as a result of the utilization of high surface area electrode architectures. Categories of high surface area electrodes range from porous carbon electrodes such as carbon fiber paper, carbon felt, carbon cloth, and graphene to metallic nanoparticles, nanorods, and carbon nanotubes. All such materials provide an increased electrical contact interface between the electrode and bulk... 

Probably, nanostructured electrode materials and sophisticated electrode architectures are the key factors for the successfiil development of state-of-the-art devices with optimized performance for on-/in-line applications. 

Lytle, J.C., Wallace, J.M., Sassin, M.B., Barrow, A.J., Long, J.W., Dysart, J.L., Rolison, D.R., 2011. The right kind of interior for multifunctional electrode architectures carbon nanofoam papers with aperiodic submicrometre pore networks. Energy Environmental Science 4 (5), 1913-1925. 

The myriad of approaches discussed has been used to produce bands, disks/pores, interdigitated arrays, and various other electrode architectures with critical dimensions approaching 100 nm." However, only recently... 

Achieving DET with GOx has therefore been a major field of study in the development of BFCs. Over the past decade, there have been various reports on DET with GOx occurring on the surfaces of carbonaceous materials such as graphene and carbon nanotubes (CNTs) [8,21-25]. The incorporation of CNTs into the electrode architecture is thought to allow electrical contact between the active site of GOx and the electrode surface. The diameter of a CNT can be as small as 1 nm for a single-walled CNT (SWCNT) in contrast, a GOx molecule is 8nm. Their comparable sizes theoretically allow CNTs to be positioned within proximity of the cofactor and reduce the electron tunneling distance [8,22]. 

This chapter provides examples of various biocatalysts, nanomaterials, and fabrication processes that yield functional bioelectrodes for anodic or cathodic processes. Most of the descriptions of electrode materials in this chapter focus on the fabrication of electrode architectures suitable for direct electron transfer (DET) processes, with an emphasis on enzyme-based electrodes however, examples of materials that are also suitable for microbial anodes are also included because of the parallels in development of such conductive architectures (see Sections 10.4.2 and 10.5.2). 

The complexity of the bio-electronic interface necessitates that material selection and electrode fabrication be understood to obtain an optimal result. In the design of an anode or a cathode, the materials should enhance stability of the immobilized biocatalyst and foster electron transfer (ET) between the biocatalyst and the conductive material. As a result, various materials and methodologies have been described in the literature to coordinate redox biocatalysts and electrodes [24,25]. In addition, several factors should be considered when selecting materials, including the electro-chemically accessible surface area (EASA), mechanical stability, and conductivity. The electrode architecture can be designed to enhance mass transport of fuel to the biocatalyst, and, in some instances, to include mediators to shuttle electrons between... 

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