In the past 10–15 years, the microbial fuel cell (MFC) technology has captured the attention of the scientific community for the possibility of transforming organic waste directly into electricity through microbially catalyzed anodic, and microbial/enzymatic/abiotic cathodic electrochemical reactions. In this review, several aspects of the technology are considered. Firstly, a brief history of abiotic to biological fuel cells and subsequently, microbial fuel cells is presented. Secondly, the development of the concept of microbial fuel cell into a wider range of derivative technologies, called bioelectrochemical systems, is described introducing briefly microbial electrolysis cells, microbial desalination cells and microbial electrosynthesis cells. The focus is then shifted to electroactive biofilms and electron transfer mechanisms involved with solid electrodes. Carbonaceous and metallic anode materials are then introduced, followed by an explanation of the electro catalysis of the oxygen reduction reaction and its behavior in neutral media, from recent studies. Cathode catalysts based on carbonaceous, platinum-group metal and platinum-group-metal-free materials are presented, along with membrane materials with a view to future directions. Finally, microbial fuel cell practical implementation, through the utilization of energy output for practical applications, is described.

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Among the most appealing features of oligothiophenesÐwhich are actively investigated for a broad range of electronic applications [1±7] Ðare their chemical stability and ease of functionalization, which allows the fine tuning of relevant properties. Unsubstituted oligothiophenes are p-type, hole-transporting, semiconductor materials and one of the research objectives in the field of organic-based devices is to achieve the kind of functionalization capable of giving stable derivatives displaying n-type semiconductor properties [8±10] for the preparation of electron-transporting layers. One of the possible ways to achieve this objective is functionalization with strongly electron-withdrawing groups, which can be designed to increase the electron affinity of the material.[11]We report here a new strategy towards functionalization of oligothiophenes that consists of the chemical transformation of thienyl sulfurs into the corresponding S,S-dioxides. We show that this kind of functionalizationÐwhich implies the dearomatization of the thiophene ringsÐleads to very stable oligomers with increased electron delocalization and has also a dramatic effect on their electron affinity as deduced from their electrochemical reduction potential. It is worth mentioning that the synthesis and the characterization of unsubstituted thiophene S,S-dioxide has been reported only very recently [12] and that only S,S-dioxides derived from polysubstituted thiophene are stable at room temperature.[13±15] So far, no electrochemical data on this kind of compound have yet been published. The oligothiophene S,S-dioxides were prepared either by action of m-chloroperoxybenzoic acid (m-CPBA) on the parent oligothiophenes [16] or by assembly of the appropriate building blocks via the Stille reaction, according to the improved procedure recently described by us. [17] As an example, the synthesis of a,w-bis(dimethyl(t-butyl)silyl)-2,2¢:5¢,2²:5²,2²¢-quaterthiophene-1,1-dioxide, 5, is illustrated in Scheme 1.As shown in Table 1, which includes the main optical and electrochemical data for a series of structurally correlated tetramers and pentamers, the maximum absorption wavelength of 5 (OTTT) is red shifted by 48 nm with respect to that of the parent quaterthiophene (TTTT), indicating a greater delocalization of the electronic charge. Moreover, while the oxidation potential of OTTT only increases by 0.09 V with respect to that of TTTT, the reduction potential is shifted by 0.84 V towards less negative values, resulting in a substantial increase of the electron affinity and also a decrease of the energy gap, DE el , of OTTT with respect to that of the precursor quaterthiophene.A similar trend in the variation of the oxidation and reduction potentials evaluated by cyclic voltammetryÐfol-lowing the dearomatization of one terminal ring by formation of the corresponding S,S-dioxideÐwas observed for the entire series of oligomers from the dimer to the pentamer bearing ±SiMe 2 t Bu or ±(CH 2 ) 5 CH 3 groups at the a,w positions. This trend is shown in Figu...