Impact of salinity on cathode catalyst performance in microbial fuel cells (MFCs) (original) (raw)
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Microbial fuel cell performance with non-Pt cathode catalysts
2007
Various cathode catalysts prepared from metal porphyrines and phthalocyanines were examined for their oxygen reduction activity in neutral pH media. Electrochemical studies were carried out with metal tetramethoxyphenylporphyrin (TMPP), CoTMPP and FeCoTMPP, and metal phthalocyanine (Pc), FePc, CoPc and FeCuPc, supported on Ketjenblack (KJB) carbon. Iron phthalocyanine supported on KJB (FePc-KJB) carbon demonstrated higher activity towards oxygen reduction than Pt in neutral media. The effect of carbon substrate was investigated by evaluating FePc on Vulcan XC carbon (FePcVC) versus Ketjenblack carbon. FePc-KJB showed higher activity than FePcVC suggesting the catalyst activity could be improved by using carbon substrate with a higher surface area. With FePc-KJB as the MFC cathode catalyst, a power density of 634 mW m −2 was achieved in 50 mM phosphate buffer medium at pH 7, which was higher than that obtained using the precious-metal Pt cathode (593 mW m −2 ). Under optimum operating conditions (i.e. using a high surface area carbon brush anode and 200 mM PBM as the supporting electrolyte with 1 g L −1 acetate as the substrate), the power density was increased to 2011 mW m −2 . This high power output indicates that MFCs with low cost metal macrocycles catalysts is promising in further practical applications.
Water formation at the cathode and sodium recovery using Microbial Fuel Cells (MFCs)
Sustainable Energy Technologies and Assessments, 2014
Microbial Fuel Cells (MFCs) utilise biodegradable carbon compounds in organic waste to generate electric current. The aim of this work was to enhance MFC performance by using low cost and catalyst (platinum)-free cathode materials. The results showed that the range of Pt-free cathodes including activated carbon, plain carbon fibre veil with and without microporous layer (MPL) in two-chamber MFCs generated power with simultaneous catholyte generation in the cathode chamber. This is the first time to report a clear catholyte formation on the cathode half cell, which was directly related to MFC power performance. The importance of this phenomenon may be attributed to the oxygen reduction reaction, water diffusion and electroosmotic drag. The synthesised catholyte in situ on the open-to-air cathode appeared to be sodium salts (9% w/v concentration), which was recovered from the anolyte feedstock containing sludge and sodium acetate. An overlooked benefit of catholyte formation and accumulation contributes greatly to the overall wastewater treatment, water recovery, bioremediation of salts and carbon capture.
Energy and Environmental Science, 2017
Differences in microbial fuel cell (MFC) architectures, materials, and solution chemistries, have previously hindered direct comparisons of improvements in power production due to new cathode materials. However, one common reactor design has now been used in many different laboratories around the world under similar operating conditions based on using: a graphite fiber brush anode, a platinum cathode catalyst, a single-chamber cube-shaped (4-cm) MFC with a 3-cm diameter anolyte chamber, 50 mM phosphate buffer, and an acetate fuel. Analysis of several publications over 10 years from a single laboratory showed that even under such identical operational conditions, maximum power densities varied by 15%, with an average of 1.36 ± 0.20 W m-2 (n=24), normalized to cathode projected area (34 W m-3 liquid volume). In other laboratories, maximum power was significantly less, with an average of 0.91 ± 0.26 W m-2 (n=10), despite identical conditions. One likely reason for the differences in power is cathode age. Power production with Pt catalyst cathodes significantly declined after one month of operation or more to 0.87 ± 0.31 W
Optimization of a Pt-free cathode suitable for practical applications of microbial fuel cells
Bioresource Technology, 2009
Microbial fuel cells (MFCs) are considered as a promising way for the direct extraction of biochemical energy from biomass into electricity. However, scaling up the process for practical applications and mainly for wastewater treatment is an issue because there is a necessity to get rid of unsustainable platinum (Pt) catalyst. In this study, we developed a low-cost cathode for a MFC making use of sputter-deposited cobalt (Co) as the catalyst and different types of cathode architecture were tested in a singlechambered air-cathode MFC. By sputtering the catalyst on the air-side of the cathode, increased contact with ambient oxygen significantly resulted in higher electricity generation. This outcome was different from previous studies using conventionally-coated Pt cathodes, which was due to the different technology used.
Neutral hydrophilic cathode catalyst binders for microbial fuel cells
Energy Environ. Sci., 2011
Improving oxygen reduction in microbial fuel cell (MFC) cathodes requires a better understanding of the effects of the catalyst binder chemistry and properties on performance. A series of polystyrene-bpoly(ethylene oxide) (PS-b-PEO) polymers with systematically varying hydrophilicity were designed to determine the effect of the hydrophilic character of the binder on cathode performance. Increasing the hydrophilicity of the PS-b-PEO binders enhanced the electrochemical response of the cathode and MFC power density by 1515%, compared to the hydrophobic PS-OH binder. Increased cathode performance was likely a result of greater water uptake by the hydrophilic binder, which would increase the accessible surface area for oxygen reduction. Based on these results and due to the high cost of PS-b-PEO, the performance of an inexpensive hydrophilic neutral polymer, poly(bisphenol A-co-epichlorohydrin) (BAEH), was examined in MFCs and compared to a hydrophilic sulfonated binder (Nafion). MFCs with BAEH-based cathodes with two different Pt loadings initially (after 2 cycles) had lower MFC performance (1360 and 630 mW m À2 for 0.5 and 0.05 mg Pt cm À2) than Nafion cathodes (1980 and 1080 mW m À2 for 0.5 and 0.05 mg Pt cm À2). However, after long-term operation (22 cycles, 40 days), power production of each cell was similar (151200 and 700-800 mW m À2 for 0.5 and 0.05 mg Pt cm À2) likely due to cathode biofouling that could not be completely reversed through physical cleaning. While binder chemistry could improve initial electrochemical cathode performance, binder materials had less impact on overall long-term MFC performance. This observation suggests that long-term operation of MFCs will require better methods to avoid cathode biofouling.
Scientific Reports, 2015
For the first time, a new generation of innovative non-platinum group metal catalysts based on iron and aminoantipyrine as precursor (Fe-AAPyr) has been utilized in a membraneless single-chamber microbial fuel cell (SCMFC) running on wastewater. Fe-AAPyr was used as an oxygen reduction catalyst in a passive gas-diffusion cathode and implemented in SCMFC design. This catalyst demonstrated better performance than platinum (Pt) during screening in "clean" conditions (PBS), and no degradation in performance during the operation in wastewater. The maximum power density generated by the SCMFC with Fe-AAPyr was 167 ± 6 μW cm −2 and remained stable over 16 days, while SCMFC with Pt decreased to 113 ± 4 μW cm −2 by day 13, achieving similar values of an activated carbon based cathode. The presence of S 2− and SO 4 2− showed insignificant decrease of ORR activity for the Fe-AAPyr. The reported results clearly demonstrate that Fe-AAPyr can be utilized in MFCs under the harsh conditions of wastewater. Energy and water availability are critical challenges to sustainable development in the 21 st century. Treatment of wastewater using available technologies is generally energy-consuming and, consequently, expensive 1. Microbial fuel cells (MFCs) represent a promising technology for wastewater treatment, while directly generating electrical energy 2-3. Recently, the energy output from MFCs has been successfully applied for powering small electronic devices such as sensors 4-5 , pumps 6 , clocks 7 and mobile phones 8. One barrier to long-term application of MFCs in wastewater treatment is the cathode material and design. Existing materials generally suffer from low durability 9-10 (as from poisoning by contaminants), and high costs (as with platinum-based materials) 11-12. The most common and preferred cathode for MFCs and for fuel cells in general is based on an oxygen reduction reaction (ORR), where oxygen is supplied from air. ORR can occur via either 2e − per O 2 (H 2 O 2 pathway) or 4eper O 2 (H 2 O pathway), with the latter pathway being preferred due to the larger number of electrons transferred and the production of H 2 O as a final product. Cathode overpotential 13 and catalyst poisoning 10 are substantial problems that lead to dramatic kinetic losses in ORR in both short and long term operations 14-15. The overpotential is mainly caused by the low catalytic activity of the catalysts in the pH range of 6-8 16 , which is the typical pH range of wastewater. Despite Pt has been the most utilized catalyst for oxygen reduction reaction at the cathode 17 , Pt is not suitable as a cathode catalyst for MFCs systems 18. Two different materials have been evaluated as alternative efficient catalysts, one based on carbonaceous materials 19 and the other one on inexpensive transition metals 20. In fact, modified carbonaceous materials (e.g. activated carbon and activated carbon nanofibers)
Energy, 2018
Power output limitation is one of the main challenges that needs to be addressed for full-scale applications of the Microbial Fuel Cell (MFC) technology. Previous studies have examined electrochemical performance of different cathode electrodes including the development of novel iron based electrocatalysts, however the long-term investigation into continuously operating systems is rare. This work aims to study the application of platinum group metals-free (PGM-free) catalysts integrated into an airbreathing cathode of the microbial fuel cell operating on activated sewage sludge and supplemented with acetate as the carbon energy source. The maximum power density up to 1.3 Wm À2 (54 Wm À3) obtained with iron aminoantipyrine (Fe-AAPyr) catalyst is the highest reported in this type of MFC and shows stability and improvement in long term operation when continuously operated on wastewater. It also investigates the ability of this catalyst to facilitate water extraction from the anode and electroosmotic production of clean catholyte. The electrochemical kinetic extraction of catholyte in the cathode chamber shows correlation with power performance and produces a newly synthesised solution with a high pH > 13, suggesting caustic content. This shows an active electrolytic treatment of wastewater by active ionic and pH splitting in an electricity producing MFC.
Electrochimica Acta, 2017
The oxygen reduction reaction (ORR) is one of the major factors that is limiting the overall performance output of microbial fuel cells (MFC). In this study, Platinum Group Metal-free (PGM-free) ORR catalysts based on Fe, Co, Ni, Mn and the same precursor (Aminoantipyrine, AAPyr) were synthesized using identical sacrificial support method (SSM). The catalysts were investigated for their electrochemical performance, and then integrated into an air-breathing cathode to be tested in "clean" environment and in a working microbial fuel cell (MFC). Their performances were also compared to activated carbon (AC) based cathode under similar conditions. Results showed that the addition of Mn, Fe, Co and Ni to AAPyr increased the performances compared to AC. Fe-AAPyr showed the highest open circuit potential (OCP) that was 0.307 AE 0.001 V (vs. Ag/AgCl) and the highest electrocatalytic activity at pH 7.5. On the contrary, AC had an OCP of 0.203 AE 0.002 V (vs. Ag/AgCl) and had the lowest electrochemical activity. In MFC, Fe-AAPyr also had the highest output of 251 AE 2.3 mWcm À2 , followed by Co-AAPyr with 196 AE 1.5 mWcm À2 , Ni-AAPyr with 171 AE 3.6 mWcm À2 , Mn-AAPyr with 160 AE 2.8 mWcm À2 and AC 129 AE 4.2 mWcm À2. The best performing catalyst (Fe-AAPyr) was then tested in MFC with increasing solution conductivity from 12.4 mScm À1 to 63.1 mScm À1. A maximum power density of 482 AE 5 mWcm À2 was obtained with increasing solution conductivity, which is one of the highest values reported in the field.
Ion exchange membrane cathodes for scalable microbial fuel cells
2008
One of the main challenges for using microbial fuel cells (MFCs) is developing materials and architectures that are economical and generate high power densities. The performance of two cathodes constructed from two low-cost anion (AEM) and cation (CEM) exchange membranes was compared to that achieved using an ultrafiltration (UF) cathode, when the membranes were made electrically conductive using graphite paint and a nonprecious metal catalyst (CoTMPP). The best performance in single-chamber MFCs using graphite fiber brush anodes was achieved using an AEM cathode with the conductive coating facing the solution, at a catalyst loading of 0.5 mg/cm 2 CoTMPP. The maximum power density was 449 mW/ m 2 (normalized to the projected cathode surface area) or 13.1 W/m 3 (total reactor volume), with a Coulombic efficiency up to 70% in a 50 mM phosphate buffer solution (PBS) using acetate. Decreasing the CoTMPP loading by 40-80% reduced power by 28-56%, with only 16% of the power (72 mW/m 2 ) generated using an AEM cathode lacking a catalyst. Using a current collector (a stainless steel mesh) pressed against the inside surface of the AEM cathode and 200 mM PBS, the maximum power produced was further increased to 728 mW/m 2 (21.2 W/m 3 ). The use of AEM cathodes and brush anodes provides comparable performance to similar systems that use materials costing nearly an order of magnitude more (carbon paper electrodes) and thus represent more useful materials for reducing the costs of MFCs for wastewater treatment applications.