Abiotic Anode Research Articles

H2 mediated mixed culture microbial electrosynthesis for high titer acetate production from CO2

Microbial electrosynthesis (MES) converts CO2 into value-added products such as volatile fatty acids (VFAs) with minimal energy use, but low production titer has limited scale-up and commercialization. Mediated electron transfer via H2 on the MES cathode has shown a higher conversion rate than the direct biofilm-based approach, as it is tunable via cathode potential control and accelerates electrosynthesis from CO2. Here we report high acetate titers can be achieved via improved in situ H2 supply by nickel foam decorated carbon felt cathode in mixed community MES systems. Acetate concentration of 12.5 g L−1 was observed in 14 days with nickel-carbon cathode at a poised potential of −0.89 V (vs. standard hydrogen electrode, SHE), which was much higher than cathodes using stainless steel (5.2 g L−1) or carbon felt alone (1.7 g L−1) with the same projected surface area. A higher acetate concentration of 16.0 g L−1 in the cathode was achieved over long-term operation for 32 days, but crossover was observed in batch operation, as additional acetate (5.8 g L−1) was also found in the abiotic anode chamber. We observed the low Faradaic efficiencies in acetate production, attributed to partial H2 utilization for electrosynthesis. The selective acetate production with high titer demonstrated in this study shows the H2-mediated electron transfer with common cathode materials carries good promise in MES development.

High-rate microbial electrosynthesis using a zero-gap flow cell and vapor-fed anode design

Microbial electrosynthesis (MES) cells use renewable energy to convert carbon dioxide into valuable chemical products such as methane and acetate, but chemical production rates are low and pH changes can adversely impact biocathodes. To overcome these limitations, an MES reactor was designed with a zero-gap electrode configuration with a cation exchange membrane (CEM) to achieve a low internal resistance, and a vapor-fed electrode to minimize pH changes. Liquid catholyte was pumped through a carbon felt cathode inoculated with anaerobic digester sludge, with humidified N2 gas flowing over the abiotic anode (Ti or C with a Pt catalyst) to drive water splitting. The ohmic resistance was 2.4 ± 0.5 mΩ m2, substantially lower than previous bioelectrochemical systems (20–25 mΩ m2), and the catholyte pH remained near-neutral (6.6–7.2). The MES produced a high methane production rate of 2.9 ± 1.2 L/L-d (748 mmol/m2-d, 17.4 A/m2; Ti/Pt anode) at a relatively low applied voltage of 3.1 V. In addition, acetate was produced at a rate of 940 ± 250 mmol/m2-d with 180 ± 30 mmol/m2-d for propionate. The biocathode microbial community was dominated by the methanogens of the genus Methanobrevibacter, and the acetogen of the genus Clostridium sensu stricto 1. These results demonstrate the utility of this zero-gap cell and vapor-fed anode design for increasing rates of methane and chemical production in MES.

Algae-Assisted Microbial Desalination Cell: Analysis of Cathode Performance and Desalination Efficiency Assessment

Algae-assisted microbial desalination cells represent a sustainable technology for low-energy fresh water production in which microalgae culture is integrated into the system to enhance oxygen reduction reaction in the cathode chamber. However, the water production (desalination rate) is low compared to conventional technologies (i.e., reverse osmosis and/or electrodialysis), as biocathodes provide low current generation to sustain the desalination process. In this sense, more research efforts on this topic are necessary to address this bottleneck. Thus, this study provides analysis, from the electrochemical point of view, on the cathode performance of an algae-assisted microbial desalination cell (MDC) using Chlorella vulgaris. Firstly, the system was run with a pure culture of Chlorella vulgaris suspension in the cathode under conditions of an abiotic anode to assess the cathodic behavior (i.e., cathode polarization curves in light-dark conditions and oxygen depletion). Secondly, Geobacter sulfurreducens was inoculated in the anode compartment of the MDC, and the desalination cycle was carried out. The results showed that microalgae could generate an average of 9–11.5 mg/L of dissolved oxygen during the light phase, providing enough dissolved oxygen to drive the migration of ions (i.e., desalination) in the MDC system. Moreover, during the dark phase, a residual concentration of oxygen (ca. 5.5–8 mg/L) was measured, indicating that oxygen was not wholly depleted under our experimental conditions. Interestingly, the oxygen concentration was restored (after complete depletion of dissolved oxygen by flushing with N2) as soon as microalgae were exposed to the light phase again. After a 31 h desalination cycle, the cell generated a current density of 0.12 mA/cm2 at an efficiency of 60.15%, 77.37% salt was removed at a nominal desalination rate of 0.63 L/m2/h, coulombic efficiency was 9%, and 0.11 kWh/m3 of electric power was generated. The microalgae-assisted biocathode has an advantage over the air diffusion and bubbling as it can self-sustain a steady and higher concentration of oxygen, cost-effectively regenerate or recover from loss and sustainably retain the system’s performance under naturally occurring conditions. Thus, our study provides insights into implementing the algae-assisted cathode for sustainable desalination using MDC technology and subsequent optimization.

A single microbial electrochemical system for CO2 reduction and simultaneous biogas purification, upgrading and sulfur recovery

In this work, a single microbial electrochemical system was developed for multiple goals simultaneously – CO2 reduction, biogas purification, upgrading and sulfur recovery. This system consists of a methanogen-inoculated biocathode for CO2 reduction and a ferrous ion (Fe2+)-mediated abiotic anode for hydrogen sulfide (H2S) oxidation. In the cathodic chamber, methane production rate of 20.6 ± 1.0 μmol·h−1 and high upgrading level (up to 98.3% methane content) were achieved. In the anodic chamber, H2S was completely removed and selectively converted into elemental sulfur particles. The system showed stable performance during continuous operation for treating both pure CO2 and mixed gases, with a cathodic coulombic efficiency of up to 85.2%. This simple system holds a great potential for practical application for biogas upgrading and sulfur recovery from waste water/gases.

Recovery of elemental sulfur with a novel integrated bioelectrochemical system with an electrochemical cell

Several industrial activities produce wastewater with high sulfate content that can cause significant environmental issues. Although bioelectrochemical systems (BESs) have recently been studied for the treatment of sulfate contained in this wastewater, the recovery of elemental sulfur with BESs is still in its beginnings. This work proposes a new reactor configuration named BES-EC, consisting of the coupling of a BES with an electrochemical cell (EC), to treat this type of wastewater and recover elemental sulfur. The reactor consisted of four electrodes: i) an abiotic anode, ii) a biocathode for the autotrophic sulfate reduction, iii) an anode of an electrochemical cell (EC) for the partial oxidation of sulfide to elemental sulfur (the biocathode and the EC anode were placed in the same chamber) and iv) an abiotic EC cathode. Several cathode potentials and sulfate loads were tested, obtaining high sulfate removal rates (up to 888 mg SO42−-S L−1 d−1 at −0.9 V vs. SHE with a specific energy consumption of 9.18 ± 0.80 kWh kg−1 SO42−-S). Exceptionally high theoretical elemental sulfur production rates (up to 498 mg S0-S L−1 d−1) were achieved with the EC controlled at a current density of 2.5 A m−2. Electron recovery around 80% was observed throughout most of the operation of the integrated system. In addition, short experiments were performed at different current densities, observing that sulfate removal did not increase proportionally to the higher applied current density. However, when the BES was controlled at 30 A m−2 and the EC at 7.5 A m−2, the proportion of elemental sulfur produced corresponded to 92.9 ± 1.9% of all sulfate removed.

The enhancement of iron fuel cell on bio-cathode denitrification and its mechanism as well as the microbial community analysis of bio-cathode

To address the issue of insufficient electrons during denitrification, an iron fuel cell (IFC) bioreactor using iron as abiotic anode was designed. The nitrogen removal efficiency (NRE) of IFC (2.54 ± 0.016%) was significantly lower than microbial fuel cell (MFC) (32.58 ± 0.033%) with same bio-cathode under autotrophic conditions, which was due to the permeation of acetate on proton exchange membrane (PEM) affected the process of enriching autotrophic denitrifying bacteria by MFC. When used in heterotrophic conditions, the NRE of the closed-circuits of IFC was 29.04%, 10.53%, 8.33% higher than open-circuits, respectively, when the COD/nitrogen (C/N) ratios was 1, 2 and 3. The enhancement of IFC was the iron anode could convert a portion of nitrate to nitrite according to the abiotic cathode control experiments. The mainly functional bacteria of bio-cathode was Paracoccus (53.04%). In conclusion, the IFC could be a theoretical model for using inorganic electron donor during denitrification.

Bioelectrochemical Denitrification for the Treatment of Saltwater Recirculating Aquaculture Streams.

Maintaining low concentrations of nitrogen compounds (ammonium, nitrate and nitrite) in recirculating aquaculture waters is extremely important for a larger and healthier fish production, as well as for water discharge purposes. Although ammonium removal from aquaculture streams is usually done within a nitrifying step, nitrate removal via denitrification is still partially limited by the low organic matter availability. Therefore, an easy-to-operate autotrophic denitrifying bioelectrochemical system is herein proposed for the treatment of seawater aquaculture streams. The nitrate-containing synthetic stream flows sequentially through a biological denitrifying cathode (placed at the lower portion of a tubular reactor) and an abiotic anode (generating electrons and oxygen from water splitting, at the upper portion). Experimental results with synthetic seawater showed that the system reached denitrification rates of 0.13 ± 0.01 kg N m–3 day–1, operating with minimum ammonium and nitrite accumulation, as well as minimum chlorine formation in the abiotic anode, despite the high chloride concentration. There results support the technical potential for simultaneous bioelectrochemical denitrification and partial re-oxygenation of aquaculture waters either for recirculation or discharge purposes.

Evaluation of gas and carbon transport in a methanogenic bioelectrochemical system (BES).

Bioelectrochemical systems (BESs) may be used to upgrade anaerobic digester biogas by directly converting CO2 to CH4 . The objective of this study was to evaluate gas (N2 , CO2 , CH4 , and H2 ) and carbon transport within a methanogenic BES. Four BES configurations were evaluated: abiotic anode with abiotic cathode (AAn-ACa), bioanode with abiotic cathode (BAn-ACa), abiotic anode with biocathode (AAn-BCa), and bioanode with biocathode (BAn-BCa). Transport of N2 , a gas commonly used for flushing anoxic systems, out of the anode headspace ranged from 3.7 to 6.2 L/d-atm-m2 , normalized to the proton exchange membrane (PEM) surface area and net driving pressure (NDP). CO2 was transported from the cathode to the anode headspace at rates from 3.7 to 5.4 L/d-atm-m2 . The flux of H2 from cathode to anode headspace was 48% greater when the system had a biocathode (AAn-BCa) than when H2 was produced at an abiotic cathode (BAn-ACa), even though the abiotic cathode headspace had 75% more H2 than the AAn-BCa biocathode at the end of 1 day. A 7-day carbon balance of a batch-fed BAn-BCa BES showed transient microbial carbon storage and a net transport of carbon from anode to cathode. After a 7-day batch incubation, the CH4 production in the biocathode was 27% greater on a molar basis than the initial CO2 supplied to the biocathode headspace, indicating conversion of CO2 produced in the anode. This research expands the current understanding of methanogenic BES operation, which may be used in improving the assessment of BES performance and/or in the development of alternative BES designs and mathematical models. Biotechnol. Bioeng. 2017;114: 961-969. © 2016 Wiley Periodicals, Inc.

Gold particles growth on carbon felt for efficient micropower generation in a hybrid biofuel cell

In this study, homogeneously dispersed gold particles growth onto carbon felt were fabricated by electrodeposition method followed by a thermal treatment at 1000°C under nitrogen. The thermal treatment induced the dewetting of gold and the formation of well-crystallized gold particles that exhibited large surface area. The structural properties of the resulted Au@CF material were evaluated by SEM, XRD and TGA. We studied the electrocatalytic properties of this new gold material through the abiotic glucose oxidation in alkaline medium and the enzymatic dioxygen electroreduction by the enzyme bilirubin oxidase. Finally, we showed the potentiality of the resulting Au@CF material to build a 3-dimensional glucose hybrid biofuel cell by assemblying an abiotic anode with an enzymatic cathode. The system exhibited high electrochemical performance with an open circuit voltage of 0.71V and a maximum power density of 310μWcm−2 at 352mV (by taking into account the projected surface area), in spite of a low gold loading (0.2wt%). The advance presented in this work is the efficiency of the synthesis technique to get a new free-standing material for electrocatalysis based on gold particles with high reactive surface area for electron transfer and macropores for diffusion transport.

One‐Pot Route to Gold Nanoparticles Embedded in Electrospun Carbon Fibers as an Efficient Catalyst Material for Hybrid Alkaline Glucose Biofuel Cells

AbstractTraditional strategies to develop Au metal nanoparticle catalysts for glucose oxidation comprise Au nanoparticles (NPs) supported on electrode surfaces. In this work, the fabrication of a new material capable of acting as an abiotic anode for the electrooxidation of glucose was developed. The material is composed of electrospun carbon fibers containing gold nanoparticles formed in situ from a polyacrylonitrile (PAN) solution with HAuCl4. This approach allows the pre‐reduction of the gold salt by PAN under mild conditions without the need for extra energy and leads to very stable carbon–gold bonding with well‐dispersed AuNPs, not previously reported. The gold‐modified carbon fibers (Au@CFs) were characterized by SEM, energy‐dispersive X‐ray spectroscopy, XRD, and electrochemical analysis. The Au@CF electrodes showed electrochemical activity toward glucose oxidation in alkaline media. Combined to a bilirubin oxidase modified biocathode (BOD@CFs), the resulting hybrid glucose biofuel cell showed open‐circuit voltage and power density values of 0.75 V and 65 μW cm−2, respectively, which remained intact after 3 weeks.

Autotrophic denitrification performance and bacterial community at biocathodes of bioelectrochemical systems with either abiotic or biotic anodes

Two-chamber bioelectrochemical systems (BESs) have recently been developed for nitrate removal from nitrate-contaminated water. In this study, we compared the nitrate removal performance of biocathodes of BESs when using abiotic and biotic anodes. Acetate was used as electron donor in BESs with biotic anode, whereas a direct current power supply was used as energy source in BESs with abiotic anode. The nitrogen removal efficiency increased from 18.1% to 43.0% when the voltage supplied to the BES with abiotic anode increased from 0.7V to 0.9V, whereas no higher removal efficiency was obtained at a higher supplied voltage (1.1V). The highest efficiency (78.0%) of autotrophic nitrogen removal was achieved when electron transfer from the biotic anode chamber of BESs was used. Unexpectedly, control of the cathode potential did not enhance nitrate removal in BESs with biotic anode. Special attention was paid to elucidate the differences of bacterial communities catalysing autotrophic denitrification in the biocathodes of BESs with abiotic and biotic anodes. Data from denaturing gradient gel electrophoresis and phylogenetic analysis suggested that denitrification in BESs with abiotic anode could be attributed to Nitratireductor sp., Shinella sp., and Dyella sp., whereas the dominant bacterial denitrifiers in BESs with biotic anode were found to be Pseudomonas sp., Curtobacterium sp., and Aeromonas sp. These results implied that biocathodes of BESs with biotic anode are more efficient than those of BESs with abiotic anode for nitrate removal from nitrate-contaminated water in practical applications.

Impedance and Thermodynamic Analysis of Bioanode, Abiotic Anode, and Riboflavin-Amended Anode in Microbial Fuel Cells

Department of Environmental Engineering, Sangmyung University, Cheonan 330-720, KoreaReceived June 28, 2012, Accepted July 17, 2012Understanding exoelectrogenic reactions of the bioanode is limited due to its complexity and the absence ofanalytics. Impedance and thermodynamics of bioanode, abiotic anode, and riboflavin-amended anode wereevaluated. Activation overpotential of the bioanode was negligible compared with that of the abiotic anode.Impedance spectroscopy shows that the bioanode had much lower charge transfer resistance and highercapacitance than the abiotic anode in low frequency reaction. In high frequency reaction, the impedanceparameters, however, were relatively similar between the bioanode and the abiotic anode. At open-circuitimpedance spectroscopy, a high frequency arc was not detected in the abiotic anode in Nyquist plot. Additionof riboflavin induced a phase angle shift and created curvature in high-frequency arc of the abiotic anode, andit also drastically changed impedance spectra of the bioanode.Key Words : Bioanode, Abiotic anode, Impedance, Anode biofilm, Microbial fuel cellIntroductionAnode biofilm is a crucial component in microbial fuelcells (MFCs) for electrogenesis. The main enzymatic com-ponents for electrogenesis of anode biofilm are exoelec-trogens, microorganisms that are capable of extracellularelectron transfer.

Effect of Anode Size, Membrane and Membrane Size on Power Generation and Wastewater Treatment in Microbial Fuel Cells

Using wastewater as substrate, taking anaerobic sludge as inoculant, microbial fuel cells (MFCs) have emerged in recent years, which can generate electricity and accomplish wastewater treatment simultaneously. Based on the evaluation indexes of output voltage, coulombic efficiency, power density and TOC removal rate, three abiotic factors, anode size, membrane and membrane size, affecting MFC performance were investigated with an orthogonal experiment (L4 (23)). The results show that the impact order of factors through analyzing the value “R” was “anode size > membrane > membrane size”. The optimal set with these three factors for the performance of MFCs was big size anode, Naf-117 and big size membrane. Meanwhile, the high TOC removal rate (more than 90%) and high acetates consumed rate (100%) show the MFCs have strong ability of wastewater treatment. Cation exchange membrane Yumi-28 has compared ability of wastewater treatment and energy-production potential in MFC work.

Direct Biological Conversion of Electrical Current into Methane by Electromethanogenesis

New sustainable methods are needed to produce renewable energy carriers that can be stored and used for transportation, heating, or chemical production. Here we demonstrate that methane can directly be produced using a biocathode containing methanogens in electrochemical systems (abiotic anode) or microbial electrolysis cells (MECs; biotic anode) by a process called electromethanogenesis. At a set potential of less than -0.7 V (vs Ag/AgCl), carbon dioxide was reduced to methane using a two-chamber electrochemical reactor containing an abiotic anode, a biocathode, and no precious metal catalysts. At -1.0 V, the current capture efficiency was 96%. Electrochemical measurements made using linear sweep voltammetry showed that the biocathode substantially increased current densities compared to a plain carbon cathode where only small amounts of hydrogen gas could be produced. Both increased current densities and very small hydrogen production rates by a plain cathode therefore support a mechanism of methane production directly from current and not from hydrogen gas. The biocathode was dominated by a single Archaeon, Methanobacterium palustre. When a current was generated by an exoelectrogenic biofilm on the anode growing on acetate in a single-chamber MEC, methane was produced at an overall energy efficiency of 80% (electrical energy and substrate heat of combustion). These results show that electromethanogenesis can be used to convert electrical current produced from renewable energy sources (such as wind, solar, or biomass) into a biofuel (methane) as well as serving as a method for the capture of carbon dioxide.

Harnessing electric power from monosaccharides—a carbohydrate–air alkaline fuel cell mediated by redox dyes

Although carbohydrates play a central role in the biochemical pathways of biological systems, current technologies do not allow us to seriously consider the direct oxidation of monosaccharides such as glucose as a prominent source of power for electronic devices. Here we show a simple, inexpensive approach to harness chemical energy from glucose, converting it directly to electric power without a precious metal, enzyme or microorganism catalyst to promote monosaccharide oxidation. The design of this abiotic anode using inexpensive chemical dyes in alkaline solutions with high-surface-carbon materials is capable of harnessing electrical power from glucose. In conjunction with a commercial air-breathing electrode the resulting cell can generate maximum power at about 0.3 V and more than 9 mA cm−2; thus more than 2.5 mW cm−2. This power density surpasses any existing biotic or abiotic design. This approach might open the door to a broader possibility in using such monosaccharides in energy storage and harvesting to power small devices.