Microbial anode materials

The combination of favorable properties of PANI and TiO opens the possibility for various applications of PANI/TiO nanocomposite materials, such as piezoresistivity devices [41], electrochromic devices [99,118], photoelectrochemical devices [43,76], photovoltaic devices/solar cells [44,50,60,61,93,119], optoelectronic devices/UV detectors [115], catalysts [80], photocatalysts [52,63,74,75,78,84,87,97,104,107,121,122,125], photoelectrocatalysts [122,123], sensors [56,61,65,69,85,86,95,120,124], photoelectrochemical [110] and microbial fuel cells [71], supercapacitors [90,92,100,109,111], anode materials for lithium-ion batteries [101,102], materials for corrosion protection [82,113], microwave absorption materials [77,87,89], and electrorheological fluids [105,106]. In comparison with PANI, the covalently bonded PANI/TiO hybrids showed significant enhancement in optical contrast and coloration efficiency [99]. It was observed that the TiO nanodomains covalently bonded to PANI can act as electron acceptors, reducing the oxidation potential and band gap of PANI, thus improving the long-term electrochromic stability [99]. Colloidal... 

There are clear differences between chemical and microbial fuel cell anodes. The most obvious difference is that anodes of MFCs must be able to support the growth of biological organisms. MFC anodes must also be highly conductive in order to efficiently collect electrons produced by bacteria as small increases in material resistance can have a significant impact on maximum power outputs. Other considerations when selecting an anode material include the expense of the material and the ability for it to be manufactured on a large scale. 

Table 9.1. Comparison of anode materials for microbial fuel cells. ...

Carbon nanotube/polyaniline composite as anode material for microbial fuel cells. Journal of Power Sources, 170, 79-84. 

Anode material Microbial source Substrate /max (pA cm" ) Reference... 

Liu, Y Harnisch, F., Schroder, U., Fricke, K., Climent, V., and Feliu, J.M. (2010) The study of electrochemically active mixed culture microbial biofilms on different carbon-based anode materials. Biosensors Bioelectronics, 25, 2167-2171. 

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). 

Anode performance Add redox mediators in anode chamber Use anode materials of high conductivity, good microbial compatibility and large surface area Anode modification with conductive polymers, metal oxides, etc. 

Y. Liu, F. Hamisch, K. Fricke, U. Schroder, V. Climent and J.M. Feliu, The study of electrochemically active microbial biofilms on different carbon-based anode materials in microbial fuel cells. Biosens. Bioelectron. 25,2010,2167-2171. 

Y. Qiao, C.M. Li, S.-J. Bao and Q.-L. Bao, Carbon nanotube/polyaniline composite as anode material for microbial fuel cells, /. Power Sources 170,2007,79-84. 

Many of the by-products of microbial metaboHsm, including organic acids and hydrogen sulfide, are corrosive. These materials can concentrate in the biofilm, causing accelerated metal attack. Corrosion tends to be self-limiting due to the buildup of corrosion reaction products. However, microbes can absorb some of these materials in their metaboHsm, thereby removing them from the anodic or cathodic site. The removal of reaction products, termed depolari tion stimulates further corrosion. Figure 10 shows a typical result of microbial corrosion. The surface exhibits scattered areas of localized corrosion, unrelated to flow pattern. The corrosion appears to spread in a somewhat circular pattern from the site of initial colonization. 

Due to the outstanding electrical and electrochemical properties of CNT/PANI, composite materials have also been applied as anode for a microbial fuel cell [335], high performance supercapacitors [333,336,337], and as modified electrode for the reduction of nitrite [331]. 

Electrode materials play an important role in the performance (power output) and cost of bacterial fuel cells. This problem was the topic of two review papers. In a review by Rismani-Yazdi et al. (2008), some aspects of cathodic limitations (ohmic and mass transport losses, substrate crossover, etc.), are discussed. In a review by Zhou et al. (2011), recent progress in anode and cathode and filling materials as three-dimensional electrodes for microbial fuel cells (MFCs) has been reviewed systematically, resulting in comprehensive insights into the characteristics, options, modifications, and evaluations of the electrode materials and their effects on various actual wastewater treatments. Some existing problems of electrode materials in current MFCs are summarized, and the outlook for future development is also suggested. 

Dumas, C.,Mollica, A., Feron, D., Basseguy, R., Etcheverry, L. Bagel, A. Marine microbial fuel-cell Use of stainless steel electrodes as anode and cathode materials. Electrochim. Acta 53 (2007), pp. 468-473. 

The mechanisms involved during microbial corrosion of metals are the following (1) stimulation of an anodic or cathodic process by bacterial metabolites, (2) breakdown of the protective layers, and (3) enhanced conductivity near the surface liquid environment. However, bacteria may also inhibit corrosion processes (O Fig. 12.8) by electrochemical processes (Hernandez et al. 1994 Jayaraman et al. 1997, 1999 Manila et al. 1997 Potekhina et al. 1999). Bacteria may also (1) neutralize the corrosive substances, (2) form protective layers on materials, or (3) decrease the corrosiveness of the aqueous environment. 

A. (2007) Marine microbial fuel cell use of stainless steel electrodes as anode and cathode materials. Electrochimica Acta,... 

Eor their exploitation at the anode of microbial BBSs, these compounds have to be oxidized at an electrocatalytic electrode surface. This anode concept has been used for the oxidation of hydrogen produced during glucose fermentation on a platinum polymer-based sandwich electrode. In a subsequent step, these noble metal-free materials were replaced by noble metal-free electrode electrocatalysts allowing the oxidation of not only H2 but also low-molecular organic acids such as formate and lactate [33-35]. furthermore, the exploitation of sulfur species [36-38] can be classified within this electron transfer concept, although it needs to be noted that sulfur species can be reversibly cycled over sulfide/sulfur in BESs [39]. 

Microbial fuel cells (MFCs) use bacteria as the catalysts to oxidize organic or inorganic matter and form electrical current [38 2]. Electrons produced by the bacteria on the anode are transported to the cathode, linked by a conductive material containing a resistor or operated under a load (i.e., producing electricity that mns a device) (Fig. 6.9) [43]. By convention, a positive current flows from the positive (cathode) to the negative (anode) terminal, a direction opposite to that of electron flow. The device must be capable of having the substrate oxidized at the anode replenished either continuously or intermittently otherwise, the system is considered... 

This chapter introduces the principles and applications of MFCs, with emphases on the nature of electricity-producing bacteria, anodic electron transfer mechanisms, power generation of MFCs and efficiency of electrode materials. Different types of MFCs and other microbial-electrochemical conversion devices are also discussed. 

Voltammetry studies. Voltammetry has various uses, for example to determine the standard redox potentials of redox active components Rabaey et al. 2005a), examine the electrochemical activity of microbial strains or consortia Kim et al. 2002 Niessen et al. 2004 Rabaey et al. 2004 Schroder et al. 2003), and test the performance of novel cathode materials Zhao et al. 2005). A potentiostat is needed to conduct voltammetry studies, of which there are two basic types. In linear sweep voltammetry (LSV) the potential of the working electrode (anode or cathode) is varied at a certain scan rate (expressed in V s" ) in one set direction. For cyclic voltammetry (CV), the scan is... 

---