Flow battery concept

The redox flow battery (RFB) concept was first proposed by L. H. Thaller at the NASA Lewis Research Center, Cleveland, Since then, it... 

Moro LMS (2013) Trends in redox flow battery technology and project REDOX2015. 2013 International conference on new concepts in smart cities fostering public and private alliances (SmartMILE). IEEE, Spain, pp 1 ... 

Redox flow batteries have been studied for almost 40 years, ever since the first concept reported by Thaller in 1976 [6]. NASA-Lewis Research Centre developed the first complete redox energy storage system based on the Fe(III)/Fe(II) and Cr(III)/Cr (II) redox couples as the positive and negative active species, respectively. Since then, redox flow batteries have been significantly developed, leading to various systems. Generally, two major principles can classify RFBs. 

An extension of hybrid redox flow batteries is the double hybrid soluble lead-acid flow batteries (SLFBs) where deposition and dissolution of redox active compounds are involved in both high potential and low potential electrode reactions. Fletcher et al. explored the concept of SLFBs in 2004 [112], and have reported their systematic study in a series of papers [113-120]. The electrode reactions of a SLFB are ... 

It follows that in batteries, the negative electrode is the anode and the positive electrode is the cathode. In an electrolyzer, to the contrary, the negative electrode is the cathode and the positive electrode is the anode. Therefore, attention must be paid to the fact that the concepts of anode and cathode are related only to the direction of current flow, not to the polarity of the electrodes in galvanic cells. 

Advances in microminiaturization of pumps, battery technology, and transcutaneous energy transmission may make these concepts a reality in the near future. It is now possible to make a pump that is as small as a pencil eraser deliver 5 1/min of blood flow and both axial and centrifugal pumps are being developed with magnetically levitated... 

None of the lightbulbs in a house are connected directly to a battery like the one in this example, but the concept is the same. When a light switch is turned on, the switch closes a circuit inside the wall of the house. Electrons can now flow through the houses wires, into the lightbulb, and back out. When the switch is turned off, the loop is broken again, and the light goes out. 

Anode — Electrode where -> oxidation occurs and electrons flow from electrolyte to electrode. At the other electrode, which is called a - cathode, electrons flow from electrode to electrolyte. It follows that in a -> battery, the anode is the negative electrode. In - electrolysis, to the contrary, the anode is the positive electrode. Note that the concepts of anode and cathode are related only to the direction of electron flow, not to the polarity of the electrodes. The terms anode and cathode as well as anion , cation electrolyte etc. were introduced by - Faraday, who considered that anions migrated toward the anode, while cations migrated toward the cathode (see also - Whewell). However, it should be noted that the redox species, which gives electrons to the anode, is not necessarily an anion. 

The following simple experiment demonstrates the essential concept of the critical threshold for percolation. A mixture of small plastic and metal balls of equal size is poured into a beaker with a crumpled-foil electrode at the bottom, another crumpled-foil electrode is pressed onto the top, and the electrodes are connected to a battery through an ammeter. Current is measured as a function of the composition (i.e., fraction of metal balls) of the conductor/insulator mixture. There is a critical composition below which no current flows and above which the conductivity increases nearly exponentially. At this threshold the two electrodes suddenly become spatially connected along a statistical pathway originating in the random medium. Percolation theory tells us that the critical composition is 0.25 fraction metal balls, a remarkably low concentration. This is perhaps not an intuitive result. 

Since various authors have referred to the electrochemical mechanism occurring around ore bodies as a geobattery or natural voltaic cell, it is appropriate to introduce the concept of voltaic cells. Voltaic cells are man-made electrical circuits in which the impetus for current flow comes directly from the chemical energy of partially-separated reactants within the cell. All batteries are voltaic cells. 

In terms of achievable specific energy (W/kg) and volumetric energy density (W/L), air-fed fuel cells have the advantage that one reaction partner, namely, oxygen, is derived from air, and consequently does not add to the weight and volume of the device. However, ambient air must be processed (cleaned, humidified, etc.), which has to be taken into account. This advantage is also expressed in the concept of metal air batteries, e.g., the Zn/Air or Al/Air battery, which on the anode (metal) consists as half a battery (closed mass flow) and on the cathode as half a fuel cell (open mass flow). 

This chapter will cover major topics of CL research, focusing on (i) electrocatalysis of the ORR, (ii) porous electrode theory, (iii) structure and properties of nanoporous composite media, and (iv) modern aspects in understanding CL operation. Porous electrode theory is a classical subject of applied electrochemistry. It is central to all electrochemical energy conversion and storage technologies, including batteries, fuel cell, supercapacitors, electrolyzers, and photoelectrochemi-cal cells, to name a few examples. Discussions will be on generic concepts of porous electrodes and their percolation properties, hierarchical porous structure and flow phenomena, and rationalization of their impact on reaction penetration depth and effectiveness factor. 

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