Performance Of Biocathode Research Articles

An In2O3/In2S3 photoanode-driven whole-cell biocathode sensor for sensitive detection of nitrate

Whole-cell biocathode sensor is a new form of self-regenerable biosensor and promising for environmental monitoring especially in the scenario with low organic substrate. However, external power supply such as electrochemical workstation is required to drive the biocathode reaction, which greatly limits its application. Herein, a new strategy based on the visible-light-driven whole-cell biocathode was proposed and validated for self-powered sensitive detections. To be specific, 1-OH phenazine was selected as the optimal electron shuttle for a Shewanella oneidensis MR-1 inoculated biocathode, which efficiently mediate the cathodic reaction at an electrode potential below −0.6 V (vs. SCE). Meanwhile, an In2O3/In2S3 photoanode with nanoflower-like structure was fabricated to match the kinetic of the biocathode. The photo-driven biocathode reduction was convinced by comparing with the performance of biocathode in the conventional three-electrode system. With this basis, a self-powered whole-cell biocathode sensor was developed for nitrate detection. An extreme low limit of detection of 0.028 μM (S/N=3) and linear detection range of 0.1–20 μM was achieved. Moreover, this biocathode sensor also exhibited excellent selectivity, reusability, accuracy, stability and was reliable for the detection of complex environmental samples. Therefore, this work developed a new photo-driven whole-cell biocathode sensor with excellent detection capacity of nitrate, which opens up new prospects for the development of high-performance biosensors.

Joint response mechanism of bioanode and biocathode in single chamber biocathode microbial electrochemical systems started-up with a constant and low resistance

Microbial electrochemical systems (MESs), particularly biocathode MESs, are recognized as environmentally friendly technologies in wastewater treatment. Rapid start-up and achievable high current and power density are desirable for scaled-up MES. The high output current can be obtained under low external resistance, but the response behaviors of bioanode and biocathode during start-up stage under low external resistance need to be clarified. In this study, a 10 L single-chamber biocathode microbial electrochemical system with microbial separator was successfully started within 11 days under a low external resistance of 20 Ω. The maximum power density reached 116.6 mW/m2 on the 9th day. However, the competition between oxygen-reducing bacteria and filamentous bacteria in the biocathode caused the decreased output power and power overshoot. Reducing the external resistance not only eliminated the power overshoot but also enhanced the electroactivity and organic removal efficiency of the bioanode. Additionally, it alleviated the constraint of filamentous bacteria on oxygen mass transfer, thereby enhancing the performance of the biocathode. The comprehensive regulation of the bioanode and the biocathode performance was achieved by reducing external resistance. This study analyzed the joint response mechanism of the bioanode and biocathode, aiming to provide guidance for the application of biocathode microbial electrochemical systems.

A wearable and flexible lactic-acid/O2 biofuel cell with an enhanced air-breathing biocathode

The performance of biocathode in an enzymatic biofuel cell (EBFC) in the real application is somehow overlooked. Herein, a wearable and flexible lactic-acid/O2 EBFC enhanced with an air-breathing biocathode is designed to solve the limitation of biocathode that arises from the low solubility and slow mass transfer of the dissolved oxygen. To improve the oxygen supply efficiency for the air-breathing biocathode, a superhydrophobic base electrode creating an efficient air-solid-liquid triphase interface is developed. The designed EBFC with an ‘island-bridge’ configuration is integrated by assembling the current collectors of air-breathing biocathode and bioanode on a commercial laminating film (LF) screen-printed with a noninterfering circuit. It is found that the biocathode/bioanode area ratio should exceed 9:1 so that the designed EBFC (1A//9C) can achieve the optimal performance. This EBFC delivers an open circuit voltage of ca. 0.75 V and outputs a maximum power density of ca. 1.78 mW cm−2. In addition, a scaled-up EBFC (total bioanode area: 1.5 cm2) successfully powers a self-developed low-power device of heartrate in the pulse operation mode when applied on a volunteer's arm.

Simultaneous removal of multiple heavy metals using single chamber microbial electrolysis cells with biocathode in the micro-aerobic environment

The simultaneous and efficient removal of various heavy metals from wastewater to satisfy the requirements of zero discharge has been a research hotspot and difficult point. In the laboratory scale (0.5 L), the biocathode microbial electrolytic cells (BCMECs) were constructed with the pre-screened heavy metal-tolerant electroactive bacterial, mainly of the Sphingomonas, Azospira and Cupriavidus. The BCMECs system showed a more satisfactory removal effect for multiple heavy metals and organic pollutants. At the auxiliary voltage of 0.9 V and initial concentration of 20 mg L−1, the removal efficiency of Cu, Pb, Zn, Cd and COD were 98.76 ± 0.32%, 98.01 ± 0.76%, 73.58 ± 4.83%, 84.39 ± 5.95%, 77.55 ± 1.51%, respectively. It was found by various characterization techniques (CV, EIS, XPS et al.) that the constructed biocathode has the function of electrocatalytic reduction of heavy metal ions in a micro-aerobic, film-free environment. The positive shift (0.030–0.229 V) of the initial potential for heavy metal reduction and the absence of a significant increase (＜ 10 Ω) in the interfacial resistance indicated a reduction in the total free energy of the reduction reaction, which promotes the reaction and improves the efficiency of heavy metal removal. Bacterial community analysis revealed that the Proteobacteria has been dominant in different heavy metal environments. With the increase of heavy metal concentration, Sphingomonas, Azospira and Cupriavidus showed stronger tolerance and became the dominant genus. This study emphasized the important performance of biocathodes and the effective treatment of heavy metal wastewaters by BCMECs and provided a reasonable way for industrial and mining enterprises to innovate the water treatment process.

3D-printed GA/PPy aerogel biocathode enables efficient methane production in microbial electrosynthesis

Microbial electrosynthesis (MES), which utilizes electroactive microorganisms as biocatalysts, is a promising technology for CO2 conversion. However, the low performance of biocathodes significantly hinders its practical application, which mainly originates from the low microorganism loading on the electrodes, sluggish interfacial electron transfer between biocatalysts and inorganic electrodes, and limited mass transport within the electrodes. Herein, a hierarchical porous 3D-printed (3DP) graphene aerogel (GA)/polypyrrole (PPy) cathode was fabricated using 3D printing. The interconnected channels of the 3DP GA scaffold efficiently promoted ion and gas transport, whereas the PPy coating enhanced interfacial electron transfer and biocompatibility. The 3DP GA/PPy cathode reached a CH4 production rate of 1672 ± 131 mmol/m2/d at −1.1 V, which was 2.14 times higher than that of a traditional carbon felt biocathode. This study provides a framework for the development of high-performance MES via rational electrode design for practical applications.

Microbial electrosynthesis for CO2 conversion and methane production: Influence of electrode geometry on biofilm development

AbstractElectromethanogenesis is a process of microbial electrosynthesis (MES) in which electroactive microorganisms reduce carbon dioxide (CO2) to produce methane (CH4), using a cathode as an electron donor. The efficiency of this reaction is greatly determined by the establishment of a robust microbial community on the biocathodes, which eventually affects the global performance of the bioreactor. Moreover, the development of the biofilm depends on several characteristics of the electrodes, more specifically their material and geometry. Since electrode geometry is a crucial parameter, this study aims at evaluating the sole influence of the electrode shape by installing carbon‐based electrodes with two different constructions (brush and carbon felt) of biocathodes in an electromethanogenic reactor for CO2 capture. The overall performance of the reactors showed coulombic efficiencies around 100%, with high‐quality biogas reaching methane concentrations above 90%. The results reveal that the electrode geometry affects the individual biocathode performance, and the carbon brush showed a bigger contribution to current generation and electrical capacitance, exhibiting higher peak hydrogen production compared to the carbon felt, which could be reflected in higher CO2 capture and methane generation. Both geometries showed a greater proliferation of archaea over bacteria (between 53 and 85%), which was more significant on the brush than on the carbon felt. Archaea community was dominated by Methanobacterium in carbon felt electrodes and codominated with Methanobrevibacter in brush electrodes, while bacteria analyses showed a very similar community for both geometries. © 2022 The Authors. Greenhouse Gases: Science and Technology published by Society of Chemical Industry and John Wiley & Sons Ltd.

Metal nanoparticles increased the lag period and shaped the microbial community in slurry-electrode microbial electrosynthesis.

Concerns about energy crisis and CO2 emission have motivated the development of microbial electrosynthesis (MES); recent studies have showed the potential of novel slurry-electrode MES. In this study, the effect of nonprecious metal nanoparticles (NPs) on the performance of slurry-electrode MES was systematically evaluated in terms of chemical production, physicochemical properties, electrochemical characterization, and microbial community. Ni and Cu NPs increased the lag period from 6 to 15 days for acetate production, while Mo NPs showed no apparent effect. However, these metal NPs slightly affected the final total acetate production (ca. 10 g L-1), Faradic efficiency (ca. 50%), net water flux across the anion exchange membrane (ca. 6 mL d-1), or electrochemical characterization of catholyte. BRH-c20a was enriched as the dominated microbe (>48%), and its relative abundance was largely affected by the addition of metal NPs. This study demonstrates that metal NPs affect the performance of biocathodes, mainly by shaping the microbial community.

A mathematical model for CO2 conversion of CH4-producing biocathodes in microbial electrosynthesis systems

Microbial electrosynthesis systems are a novel device for simultaneous CO2 reduction and CH4 production, and the CH4-producing biocathode in this system is the key component. This work presents a mathematical model to insight into the process of CH4 production on the biocathode. The model couples bioelectrochemical reaction, charge balance, mass transfer, dissolution of gaseous CO2 and interconversion of hydrated CO2, H2CO3, HCO3− and CO32−. To our knowledge, this is the first theoretical report for CH4-producing biocathodes in microbial electrosynthesis systems. This model is capable of predicting the response of CH4-producing biocathodes with operating time under various conditions and describing the effects of different parameters on CH4 production. The results suggest that the most important processes which influence the performance of biocathodes are the interconversions of hydrated CO2, H2CO3 and HCO3−.

Effect of start-up process using different electrochemical methods on the performance of CO2-reducing methanogenic biocathodes

Microbial electrosynthesis of methane holds great promise for renewable energy storage, but its present methane production performance requires to be much improved. In this work, three electrochemical methods including galvanostatic (GS), applying constant voltage (ACV), potentiostatic (PS) were used to investigate the effect of the start-up process on the performance of biocathode. The methanogenic biocathodes for CO2 reduction were evaluated based on the kinetics, performance, morphology, and microbial community. The methane production rate of the ACV biocathode was 145% and 238% higher than that of the GS and PS, respectively. The EIS analysis indicated that the high performance of ACV biocathode was mainly due to its much low charge transfer resistance, which was only 45% of the PS and 71% of the GS. Our study concluded that enough reducing equivalents (e− or H2) are more significant for the enrichment of high-performance methanogenic biofilms than changing the potential-dependent microbial community.

GO/PEDOT modified biocathodes promoting CO2 reduction to CH4 in microbial electrosynthesis

A GO/PEDOT film effectively enhances methanogenic biofilm formation and promotes the CH4 producing performance of biocathodes.

Improvement of bioelectricity generation and microalgal productivity with concomitant wastewater treatment in flat-plate microbial carbon capture cell

The unprecedented increase in global population has triggered the energy crisis, climate change and waste disposal issues which are necessitated the advancements in waste to energy technologies. The present study is directed towards evaluating the potential of microbial carbon capture cells (MCC) for simultaneous power generation, wastewater treatment and microalgal biomass production. Chlorella sorokiniana was used to establish the biocathode using anodic effluent as feed. The developed MCC was affected by physico-chemical parameters such as inlet pH, light intensity and photoperiod. The inoculum age of 12 h, inoculum size of 20%v/v, inlet pH 7.5, light intensity of 140 µmol m−2 s−1 and photoperiod of 12:12 (Light:dark) were asserted as most suitable conditions for achieving high performance of biocathode. The electricity generation was dependent upon the O2 availability at cathode and a drastic drop in voltage was observed under O2 limited conditions. Supplementation of anodic off-gas alone to cathode was not sufficient to sustain the growth of microalgae. However, combining internal anodic CO2 channelling with external CO2 pumping at cathode enhanced the performance of MCC. The experimental results revealed maximum open circuit voltage of 637 mV with a maximum power density of 2.32 W m−3. The maximum microalgal dry cell mass of 812 mg L−1 was achieved with an overall COD removal efficiency and energy recovery of 92–95% and 59%, respectively. These sustainability studies show that such a strategy can be applied for real time industrial flue gas treatment along with wastewater treatment in the future.

Operation strategy of cubic-meter scale microbial electrochemistry system in a municipal wastewater treatment plant

A 1.5 m3 pilot biocathode microbial electrochemistry system (MES) is developed with separate plug-in modular design and operated in a municipal wastewater treatment plant for treating effluent of primary sedimentation tank. Comprehensive operation strategies are investigated for the operation of pilot MES and for the high-efficiency operation of further full-size MES. Controlling with wastewater distribution system, an alternating direction parallel flow mode is achieved in pilot biocathode MES at 48 h interval and prevents the substrate limitation to downstream anodes along flow path. Intermittent aeration strategy with various air-liquid (A/L) ratios is optimized to save aeration energy of biocathode. Consequently, the optimized energy requirement is only 7.3% of that in a typical activated sludge process (0.3 kWh m−3). The dynamic microbial separator in pilot MES effectively blocks the oxygen leakage from cathode to anode compartment under tested A/L ratios (2.9–40) and enables aeration process to mainly affect biocathode performance. The incomplete polytetrafluoroethylene-coated (PTFE-coated) carbon brushes are well performed as biocathodes of pilot MES, improving the maximum power output by 15% under oxygen-limited condition. The hydrophobic surface provides oxygen source for cathode reduction due to the high air-affinity and supports a great amount of biomass on cathode brushes.

A variety of hydrogenotrophic enrichment cultures catalyse cathodic reactions

Biocathodes where living microorganisms catalyse reduction of CO2 can potentially be used to produce valuable chemicals. Microorganisms harbouring hydrogenases may play a key role for biocathode performance since H2 generated on the electrode surface can act as an electron donor for CO2 reduction. In this study, the possibility of catalysing cathodic reactions by hydrogenotrophic methanogens, acetogens, sulfate-reducers, denitrifiers, and acetotrophic methanogens was investigated. The cultures were enriched from an activated sludge inoculum and performed the expected metabolic functions. All enrichments formed distinct microbial communities depending on their electron donor and electron acceptor. When the cultures were added to an electrochemical cell, linear sweep voltammograms showed a shift in current generation close to the hydrogen evolution potential (−1 V versus SHE) with higher cathodic current produced at a more positive potential. All enrichment cultures except the denitrifiers were also used to inoculate biocathodes of microbial electrolysis cells operated with H+ and bicarbonate as electron acceptors and this resulted in current densities between 0.1–1 A/m2. The microbial community composition of biocathodes inoculated with different enrichment cultures were as different from each other as they were different from their suspended culture inoculum. It was noteworthy that Methanobacterium sp. appeared on all the biocathodes suggesting that it is a key microorganism catalysing biocathode reactions.

Repeated transfer enriches highly active electrotrophic microbial consortia on biocathodes in microbial fuel cells

Cathodic oxygen reduction catalyzed by autotrophic bacteria instead of a precious metal is a promising method to make use of microbial fuel cells (MFCs) in wastewater treatment with electricity production. However, the ecology of electrotrophic microbial consortia in wastewater systems that function as the catalyst for cathodic oxygen reduction is complicated and the electron transfer mechanisms are still unknown, which prevents further improvements of the biocathode performance. Enriched by the repeated transfer of a mature electrotrophic microbial consortia to new cathodes over 10 generations in 230 days, the start-up time was shortened from 21.4 to 7.6 days and the maximum current densities over the potential range of 0.5 to − 0.3 V increased by up to 112%, from 75 ± 5 A m−3 to 159 ± 3 A m−3, which was further confirmed in half-cell biocathode systems. The electrotrophic microbial consortia approached a relatively stable state after 8 generations. Acinetobacter, which is a member of Proteobacteria, was selectively enriched after 10 generations, which was closely related to the current production. Nitrospiraceae and Nitrosomonas may jointly perform a nitrogen cycling metabolic process and promote cathodic bioelectron transfer. Our findings confirmed that the electrotrophic microbial consortia on the cathode was able to be specifically evolved, leading to higher electroactivity, and also revealed which bacteria in fresh water are closely related to cathodic electron transfer.

Effects of surface charge, hydrophilicity and hydrophobicity on functional biocathode catalytic efficiency and community structure

The bioelectrotransformation efficiency of various organic matters and corresponding electrode biofilm community formation as well as electron transfer efficiency in bioelectrochemical systems (BESs) with different modified electrodes has been extensively studied on the anode side. However, the effects of cathode interface characteristics towards the BESs bioelectrotransformation performance remain poorly understood. In this study, the nitrobenzene-reducing biocathode catalytic efficiency and community structure in response to different modified electrodes (control: hydrophobic and no charge; –SH: hydrophobic and single negative charge; –NH2: hydrophilic and single positive charge –NH–NH2: hydrophilic and double positive charges) were investigated. The biocathode transformation efficiency of nitrobenzene (NB) to aniline (AN) (ENB-AN) was affected by the nature of electrode interface as well as the biocathode community formation and structure. Cathodes with hydrophilic surface and positive charges have performed well in the bioelectrotransformation experiments, and especially made an outstanding performance when inorganic NaHCO3 was supplied as carbon source and cathode as the sole electron donor. Importantly, the hydrophilic surfaces with positive charges were dominated by the electroactive nitroaromatic reducers (Enterococcus, Desulfovibrio and Klebsiella) with the relative abundance as high as 72.20 ± 1.87% and 74.86 ± 8.71% for –NH2 and –NH–NH2 groups respectively. This could explain the higher ENB-AN in the hydrophilic groups than that of the hydrophobic –SH modified group. This study provides new insights into the effects of electrode interface characteristics on the BESs biocathode performance and offers some suggestions for the future design for the improvement of bioelectroremediation performance.

The Effect of Oxygen Mass Transfer on Aerobic Biocathode Performance, Biofilm Growth and Distribution in Microbial Fuel Cells

AbstractMicrobial fuel cells (MFCs) are a sustainable technology for the direct conversion of biodegradable organics in wastewater into electricity. In most MFCs, the oxygen reduction reaction (ORR) is used as the cathode reduction reaction. Aerobic biocathodes, which use bacteria as biocatalysts to catalyze the cathode ORR, provide self‐sustained, robust and highly active alternatives to chemical catalysts. However, further study of the effect of oxygen mass transfer to the biofilm and cathode materials design is needed. In the current work, two aerobic biocathodes were enriched in half‐cells, and oxygen mass transfer to the biofilm and the biofilm distribution in the porous electrode structure were investigated. It was found that mass transfer of oxygen to the aerobic biocathode was a significant factor affecting cathode ORR, evidenced by a strong correlation between the air flow rate and current. Additionally, it was found that the biofilm penetrates between 20–30% into the porous carbon electrode structure, which is likely due to oxygen mass transfer limitations. The performance of a MFC with biocatalysts at both anode and cathode (64 µW cm−2 peak power at an air flowrate of 1 L min−1) showed strong correlation with air flowrate, confirming the observation in the half‐cell system.

Effect of Binary Hydrophilic Binders of SBR Latex and Water-Soluble Polymer on Gas-Diffusion Biocathode Performance

Performance of gas-diffusion biocathodes to electrochemically reduce oxygen for biofuel cells was improved by introduction of a new water-soluble binder for carbon powder to form electrode layer on ozone-hydrophilized carbon paper (CP) electrode base. Four kinds of water-soluble binders for carbon powder were compared and sodium polyglutamate (PGluNa) was selected for use in combination with styrene-butadiene rubber (SBR) latex to form a hydrophilic binder. The biocathode with the binder revealed the largest cathodic current among the four biocathodes with different binders in cyclic voltammetry at 0 V vs. Ag/AgCl. Glutaraldehyde (GA) was adopted as a crosslinker of bilirubin oxidase (BOD) to improve the stability of the biocathodes, which stabilized the cathodic current as expected, however excessive GA caused denaturation of BOD to decrease the enzyme activity. Long-term stability test of the biocathode utilizing a binder of PGluNa by chronoamperometry revealed good stability of oxygen reduction current for 1 h.

Enhanced oxygen reducing biocathode electroactivity by using sediment extract as inoculum

Autotrophic bacteria are able to catalyze cathodic oxygen reduction as a renewable and sustainable inexpensive catalyst. However, the performance of biocathode varied over reactors, and we still not know how inoculums affect this system. Using three different inoculum of wastewater (WW), sediment extract (SE) and soil extract (SO) in parallel reactors, we found that SE achieved the shortest setup time (17–25% shorter) as well as the highest power density compared to those of SO and WW. Cyclic voltammetry (CV) further revealed that the current densities of SE biocathodes (100±1A/m3) was 150% and 67% higher than those of WW biocathodes (40±1A/m3) and SO biocathodes (65±1A/m3). Community analysis showed the selective pressure on biocathode facilitated the growth of Proteobacteria, Bacteroidetes, Firmicutes and Actinobacteria families. Different from WW and SO biocathodes, Nitrospirae was selectively enriched in SE biocathodes, corresponding to an obvious increase in Unidentified Nitrospiraceae population at genus level, which may play an important role on the cathodic electroactivity. These results confirmed that sediment extract is a better bacteria source than soil and wastewater for the acclimation of autotrophic electroactive bacteria, and the community comparison provided broader knowledge on biocathode microbiology.

Bioanode as a limiting factor to biocathode performance in microbial electrolysis cells

The bioanode is important for a microbial electrolysis cell (MEC) and its robustness to maintain its catalytic activity affects the performance of the whole system. Bioanodes enriched at a potential of +0.2V (vs. standard hydrogen electrode) were able to sustain their oxidation activity when the anode potential was varied from −0.3 up to +1.0V. Chronoamperometric test revealed that the bioanode produced peak current density of 0.36A/m2 and 0.37A/m2 at applied potential 0 and +0.6V, respectively. Meanwhile hydrogen production at the biocathode was proportional to the applied potential, in the range from −0.5 to −1.0V. The highest production rate was 7.4L H2/(m2 cathode area)/day at −1.0V cathode potential. A limited current output at the bioanode could halt the biocathode capability to generate hydrogen. Therefore maximum applied potential that can be applied to the biocathode was calculated as −0.84V without overloading the bioanode.

Sulfate reduction and microbial community of autotrophic biocathode in response to acidity

Abstract Microbial electrolysis cells (MECs) with autotrophic biocathode are a promising technology for removal of pollutants in wastewater. The aim of this study was to investigate the effect of initial acidity of wastewater on performance of sulfate-reducing biocathodes. MECs with biocathodes were operated with initial pH values of catholyte ranged from 3.0 to 7.0. The optimum initial pH value was 6.0 with a maximum sulfate reductive rate and biomass of 57 mg L −1 d −1 and 2.1 ± 0.4 mg g −1 , respectively. With initial pH 7.0, the pH value of catholyte increased to 9.8 ± 0.2 after an operation cycle, which resulted in low performance of the biocathode. A considerable sulfate reductive rate of 31 ± 0.85 mg L −1 d −1 was achieved with initial pH 3.0. Desulfovibrio sp . grew dominantly with abundance of 46%–66% in the cathode biofilm with initial pH values from 3.0 to 6.0 and contributed to the sulfate reduction. Clostridium and Parapedobacter also had high abundance in pH 6.0 cathode, indicated that interspecies electron transfer between electrochemical active and sulfate-reducing bacteria could play an important role in sulfate removal. The results suggest that acidity of catholyte is an important factor to be considered to utilize autotrophic biocathode MECs for wastewater treatment.