This paper reports successful hydrogen evolution using a dye-sensitized solar cell (DSSC)-powered microbial electrolysis cell (MEC) without a Pt catalyst on the cathode, indicating a solution for the inherent drawbacks of conventional MECs, such as the need for an external bias and catalyst. DSSCs fabricated by assembling a ruthenium dye-loaded TiO(2) film and platinized FTO glass with an I(-)/I(3)(-) redox couple were demonstrated as an alternative bias (V(oc) = 0.65 V). Pt-loaded (0.3 mg Pt/cm(2)) electrodes with a Pt/C nanopowder showed relatively faster hydrogen production than the Pt-free electrodes, particularly at lower voltages. However, once the applied photovoltage exceeded a certain level (0.7 V), platinum did not have any additional effect on hydrogen evolution in the solar-powered MECs: hydrogen conversion efficiency was almost comparable for either the plain (71.3-77.0%) or Pt-loaded carbon felt (79.3-82.0%) at >0.7 V. In particular, the carbon nanopowder-coated electrode without Pt showed significantly enhanced performance compared to the plain electrode, which indicates efficient electrohydrogenesis, even without Pt by enhancing the surface area. As the applied photovoltage was increased, anodic methanogenesis decreased gradually, resulting in increasing hydrogen yield.
"In this system, the MFC acted as an external energy source to produce hydrogen at the MEC cathode. A solar-powered MEC with a Pt catalyst-free cathode was reported for the production of hydrogen (Chae et al., 2009). Because both the MFC and solar cell use renewable energy, the application of them as the external energy sources for MEC operation can extend this technology in practical fields. "
[Show abstract][Hide abstract] ABSTRACT: Microorganisms naturally form biofilms on solid surfaces for their mutual benefits including protection from environmental stresses caused by contaminants, nutritional depletion or imbalances. The biofilms are normally dangerous to human health due to their inherited robustness. On the other hand, a recent study suggested that electrochemically active biofilms (EABs) generated by electrically active microorganisms have properties that can be used to catalyze or control the electrochemical reactions in a range of fields, such as bioenergy production, bioremediation, chemical/biological synthesis, bio-corrosion mitigation and biosensor development. EABs have attracted considerable attraction in bioelectrochemical systems (BESs), such as microbial fuel cells and microbial electrolysis cells, where they act as living bioanode or biocathode catalysts. Recently, it was reported that EABs can be used to synthesize metal nanoparticles and metal nanocomposites. The EAB-mediated synthesis of metal and metal-semiconductor nanocomposites is expected to provide a new avenue for the greener synthesis of nanomaterials with high efficiency and speed than other synthetic methods. This review covers the general introduction of EABs, as well as the applications of EABs in BESs, and the production of bio-hydrogen, high value chemicals and bio-inspired nanomaterials.
"Recently, based on the electron balance, the suppression of CH 4 production, a recognized factor related to typical electron losses within anode chambers, has been considered in order to increase the CE within bioelectrochemical systems (Chae et al., 2009a; Clauwaert and Verstraete, 2009; Freguia et al., 2008; Wagner et al., 2009). Glucose is a basic unit of organic compounds, most sugars and carbohydrates that abundantly exist in wastewater are composed of glucose molecules. "
[Show abstract][Hide abstract] ABSTRACT: Glucose-fed microbial fuel cells (MFCs) have displayed low Coulombic efficiency (CE); one reason for a low CE is metabolite generation, causing significant electron loss within MFC systems. In the present study, notable electron loss (15.83%) is observed in glucose-fed MFCs due to residual propionate, a glucose metabolite. In order to enhance the low CE caused by metabolite generation, a dual-anode MFC (DAMFC) is constructed, which are separately enriched by dissimilar substrates (glucose and propionate, respectively) to effectively utilize both glucose and propionate in one-anode chamber. In the DAMFC, propionate ceases to exist as a source of electron loss, and thus the CE increased from 33 ± 6 to 59 ± 4%.
"MEC ARB Acetate – 9.42 Chae et al. (2009) the existing systems. Particularly, the granule-based reactors, thermophilic processes, and integrated systems hold great promise for practical application, but many challenges are yet to be addressed. "
[Show abstract][Hide abstract] ABSTRACT: This chapter discusses high-rate hydrogen-producing bioreactors based on their HPR (hydrogen production rate), HY (hydrogen yield), biomass retention capability, and process stability. Development of bioreactors presents one important aspect of the fast progressing biohydrogen production technologies. It is widely accepted that the reactor configuration and operating mode can pose significant influences on the system biohydrogen production performance by directly affecting the hydrodynamics and bacteria properties. Both volumetric HPR and HY have been considered as important indexes to evaluate the performance of a biohydrogen production system. However, it is noted that the HY, defined by the amount of hydrogen produced per substrate consumed, is more dependent upon the microbial properties, substrate type, and environmental conditions rather than the reactor configurations. In fact, for dark-fermentation processes, HYs obtained with different systems are rather inconsistent so far and mostly no greater than those achieved with CSTRs (continuously stirred tank reactors). Thus, there is no reason to think that the reactor type would essentially influence the HY in dark-fermentation systems, and a comparison of these reactors here shall mainly be based on their HRPs. For the phototrophic and MEC (microbial electrolysis cells) hydrogen production processes, however, the HY is usually used for reactor evaluation because of the fewer microbial species and substrates involved as well as the relatively low HPR value of such systems. In addition, the operating stability is also a critical factor to be considered for the biological hydrogen production systems.
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