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Ledezma P.,Universities of Bristol and of the West of England | Degrenne N.,École Centrale Lyon | Bevilacqua P.,University Claude Bernard Lyon 1 | Buret F.,École Centrale Lyon | And 3 more authors.
Sustainable Energy Technologies and Assessments | Year: 2014

In this paper we present several preliminary results produced with a purposely-designed external-resistor (Rext) sweeping tool for microbial fuel cells (MFCs). Fast sampling rates show that MFCs exhibit differential steady-state stabilisation behaviours depending on Rext, with consequences for time constant (tc) selection. At high Rext (35kΩ), it is demonstrated that a tc≥10 min avoids underestimation not overestimation, whilst at low Rext (100Ω) 5min are sufficient, suggesting that sweeps with variable tc are possible. However, within the maximum power transfer range (2.5kΩ), steady-states are only observed at 20min tc but with a smaller confidence interval, questioning whether the polarisation technique is suitable to estimate maximum power transfer. Finally, a strategy towards the exploitation of a capacitive-like behaviour in MFCs is proposed, tapping into ≥10min periods with up to 50% higher current and energy transfer that could prove important for MFC-powered applications. © 2013 Elsevier Ltd.


Ledezma P.,Universities of Bristol and of the West of England | Greenman J.,University of the West of England | Ieropoulos I.,Universities of Bristol and of the West of England
Bioresource Technology | Year: 2012

The aim of this work is to study the relationship between growth rate and electricity production in perfusion-electrode microbial fuel cells (MFCs), across a wide range of flow rates by co-measurement of electrical output and changes in population numbers by viable counts and optical density. The experiments hereby presented demonstrate, for the first time to the authors' knowledge, that the anodic biofilm specific growth rate can be determined and controlled in common with other loose matrix perfusion systems. Feeding with nutrient-limiting conditions at a critical flow rate (50.8mLh -1) resulted in the first experimental determination of maximum specific growth rate μ max (19.8day -1) for Shewanella spp. MFC biofilms, which is considerably higher than those predicted or assumed via mathematical modelling. It is also shown that, under carbon-energy limiting conditions there is a strong direct relationship between growth rate and electrical power output, with μ max coinciding with maximum electrical power production. © 2012 Elsevier Ltd.


Ieropoulos I.,Universities of Bristol and of the West of England | Greenman J.,Microbiology Research Laboratory | Melhuish C.,Universities of Bristol and of the West of England
Bioelectrochemistry | Year: 2010

This study reports on the findings from the investigation into small-scale (6.25 mL) MFCs, connected together as a network of multiple units. The MFCs contained unmodified (no catalyst) carbon fibre electrodes and for initial and later experiments, a standard ion-exchange membrane for the proton transfer from the anode to the cathode. The anode microbial culture was of the type commonly found in domestic wastewater fed with 5 mM acetate as the carbon-energy (C/E) source. The cultures were mature and acclimatised in the MFC environment for approximately 2 months before being re-inoculated in the experimental MFC units. The cathode was of the O2 diffusion open-to-air type, but for the purposes of the polarization experiments, the cathodic electrodes were moistened with ferricyanide. The main aim of this study was to investigate the effects of connecting multiples of MFC units together as a method of scale up by using stacks and comparison of the effects of different PEM and MFC structural materials on the performance. Impedance matching (maximum-power-transfer) was achieved through calculation of total internal impedance. Three different PEM materials were compared in otherwise identical MFCs in sets of three. For individual isolated MFCs, Hyflon E87-03 was shown to produce twice, whilst E87-10 produced approximately 1.5 times the power output of the control (standard) PEM. However, when MFCs containing the E87-03 and E87-10 membranes were connected in a stack, the system suffered from severe instability and cell reversal. To study the effects of the various polymeric MFC structural materials, four small-scale units were manufactured from three different types of RP material; acrylo-butadiene-styrene coated (ABS), ABS coated (ABS-MEK) and polycarbonate (polyC). The stack of four (4) units prototyped out of polyC produced the highest power density values in polarisation experiments (80 mW/m2). © 2009 Elsevier B.V. All rights reserved.


Ledezma P.,Universities of Bristol and of the West of England | Stinchcombe A.,Universities of Bristol and of the West of England | Greenman J.,University of the West of England | Ieropoulos I.,Universities of Bristol and of the West of England
Physical Chemistry Chemical Physics | Year: 2013

This study reports for the first time on the development of a self-sustainable microbial fuel cell stack capable of self-maintenance (feeding, hydration, sensing & reporting). Furthermore, the stack system is producing excess energy, which can be used for improved functionality. The self-maintenance is performed by the stack powering single and multi-channel peristaltic pumps. © 2013 the Owner Societies.


Merino-Jimenez I.,University of Southampton | Merino-Jimenez I.,Pennsylvania State University | Merino-Jimenez I.,Universities of Bristol and of the West of England | Janik M.J.,Pennsylvania State University | And 2 more authors.
Journal of Power Sources | Year: 2014

A Pd-Ir alloy (1:1) coated on microfibrous carbon (11 μm diameter) supported on a titanium plate was evaluated as an electrode for the anodic oxidation of borohydride. The hydrogen generated, due to the parallel reaction of borohydride hydrolysis, was measured during the electrolysis obtaining less than 0.1 cm3 min-1 H2 between -1 and 0 V vs. Hg/HgO (-0.86 and 0.14 V vs. SHE), while the current densities for the oxidation of borohydride were up to 367 mA cm-2 in 0.5 mol dm-3 NaBH4 + 3 mol dm-3 NaOH. The low rate of hydrogen generation suggests that Pd-Ir could be a promising catalyst for borohydride oxidation. However, higher rates of hydrogen were generated at the open circuit potential, which is inconvenient in the direct borohydride fuel cell. Cyclic voltammetry allowed analysis of the oxidation peaks due to the borohydride oxidation. To obtain a further understanding of the borohydride oxidation mechanism at Pd-Ir electrodes, density functional theory (DFT) was used to examine the reaction mechanism at Pd2-Ir1(111) and Pd 2-Ir2(111) surfaces. The competition between borohydride oxidation and hydrogen evolution on the Pd-Ir alloys is compared with that on pure Pd(111), suggesting that the presence of Ir favors borohydride oxidation rather than hydrogen evolution. © 2014 Elsevier B.V. All rights reserved.


Pearson M.J.,Universities of Bristol and of the West of England | Fox C.,University of Sheffield | Sullivan J.C.,Universities of Bristol and of the West of England | Prescott T.J.,University of Sheffield | And 2 more authors.
Proceedings - IEEE International Conference on Robotics and Automation | Year: 2013

A biomimetic mobile robot called 'Shrewbot' has been built as part of a neuroethological study of the mammalian facial whisker sensory system. This platform has been used to further evaluate the problem space of whisker based tactile Simultaneous Localisation And Mapping (tSLAM). Shrewbot uses a biomorphic 3-dimensional array of active whiskers and a model of action selection based on tactile sensory attention to explore a circular walled arena sparsely populated with simple geometric shapes. Datasets taken during this exploration have been used to parameterise an approach to localisation and mapping based on probabilistic occupancy grids. We present the results of this work and conclude that simultaneous localisation and mapping is possible given only noisy odometry and tactile information from a 3-dimensional array of active biomimetic whiskers and no prior information of features in the environment. © 2013 IEEE.


Walter X.A.,Universities of Bristol and of the West of England | Walter X.A.,University of the West of England | Greenman J.,University of the West of England | Ieropoulos I.A.,Universities of Bristol and of the West of England
Bioresource Technology | Year: 2014

This study reports on the response of small-scale MFCs to intermittent loading, in terms of power output over time. The aim was to understand the evolution with time of power output under different duty cycles, in conditions close to practical implementation. Inexpensive ceramic membranes were compared to cation exchange membranes, under continuous flow and with a pre-digester connected. Results show that at the minute-scale, all the duty cycles investigated, produced 78% higher power bursts from the MFCs (500. μW) than when under continuous loading (280. μW). These results were recorded from MFCs employing ceramic membranes, whereas the difference in performance for MFCs employing commercially available cation-exchange-membranes was insignificant. When normalising to daily energy production, only specific duty cycles produced more power than continuous loading. Furthermore, the introduction of a pre-digester increased the MFC power outputs 10-fold, thus confirming that separating fermentation from electro-active respiration, significantly enhances the system performance. © 2014 Elsevier Ltd.


Walter X.A.,Universities of Bristol and of the West of England | Greenman J.,University of the West of England | Taylor B.,Universities of Bristol and of the West of England | Ieropoulos I.A.,Universities of Bristol and of the West of England
Algal Research | Year: 2015

Microbial fuel cells (MFCs) are energy transducers that convert organic matter directly into electricity, via the anaerobic respiration of electro-active microorganisms. An avenue of research in this field is to employ algae as the organic carbon fuel source for the MFCs. However, in all studies demonstrating the feasibility of this principle, the algal biomass has always been pre-treated prior to being fed to MFCs, e.g. centrifuged, dried, ground into powder, and/or treated by acid-thermal processes. The alternative presented here, is a flow-through system whereby the MFCs were continuously fed by fresh algal biomass. The system consisted of i) a culture of Synechococcus leopoliensis grown continuously in a photo-chemostat, ii) a pre-digester initiating the digestion of the phototrophs and producing a fuel devoid of oxygen, and iii) a cascade of 9 MFCs, hydraulically and electrically independent. This compartmental system could in theory produce 42W of electrical power per cubic metre of fresh culture (6·105cellsmL-1). © 2015.


Walter X.A.,Universities of Bristol and of the West of England | Greenman J.,University of the West of England | Ieropoulos I.A.,Universities of Bristol and of the West of England
Algal Research | Year: 2013

The rate of oxygen reduction reaction in the cathodic chambers of microbial fuel cells (MFCs) is a typical limiting aspect of its performance. Recently, research on biocathodes has gained more interest as it allows circumventing the utilisation of exogenous and unstable mediators at a lower cost. It is shown here that the growth of oxygenic phototrophs as a biofilm, increases the current output by two fold. This was possible by forcing the biofilm to grow onto the cathode, thus, producing the oxygen directly where it was consumed. This enhancement of the cathodic efficiency was stable for over 30. days. © 2013 Elsevier B.V.


PubMed | University of the West of England and Universities of Bristol and of the West of England
Type: | Journal: Bioresource technology | Year: 2014

This study reports on the response of small-scale MFCs to intermittent loading, in terms of power output over time. The aim was to understand the evolution with time of power output under different duty cycles, in conditions close to practical implementation. Inexpensive ceramic membranes were compared to cation exchange membranes, under continuous flow and with a pre-digester connected. Results show that at the minute-scale, all the duty cycles investigated, produced 78% higher power bursts from the MFCs (500W) than when under continuous loading (280W). These results were recorded from MFCs employing ceramic membranes, whereas the difference in performance for MFCs employing commercially available cation-exchange-membranes was insignificant. When normalising to daily energy production, only specific duty cycles produced more power than continuous loading. Furthermore, the introduction of a pre-digester increased the MFC power outputs 10-fold, thus confirming that separating fermentation from electro-active respiration, significantly enhances the system performance.

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