Huijie Hou

Microfabricated Microbial Fuel Cell Arrays Reveal Electrochemically Active Microbes

Microbial fuel cells (MFCs) are remarkable “green energy” devices that exploit microbes to generate electricity from organic compounds. MFC devices currently being used and studied do not generate sufficient power to support widespread and cost-effective applications. Hence, research has focused on strategies to enhance the power output of the MFC devices, including exploring more electrochemically active microbes to expand the few already known electricigen families. However, most of the MFC devices are not compatible with high throughput screening for finding microbes with higher electricity generation capabilities. Here, we describe the development of a microfabricated MFC array, a compact and user-friendly platform for the identification and characterization of electrochemically active microbes. The MFC array consists of 24 integrated anode and cathode chambers, which function as 24 independent miniature MFCs and support direct and parallel comparisons of microbial electrochemical activities. The electricity generation profiles of spatially distinct MFC chambers on the array loaded with Shewanella oneidensis MR-1 differed by less than 8%. A screen of environmental microbes using the array identified an isolate that was related to Shewanella putrefaciens IR-1 and Shewanella sp. MR-7, and displayed 2.3-fold higher power output than the S. oneidensis MR-1 reference strain. Therefore, the utility of the MFC array was demonstrated.

Conjugated Oligoelectrolytes Increase Power Generation in E. coli Microbial Fuel Cells

A series of conjugated oligoelectrolytes with structural variations is used to stain E. coli. By taking advantage of a high-throughput screening platform that incorporates gold anodes, it is found that MFCs with COE-modified E. coli generate significantly higher power densities, relative to unmodified E. coli. These findings highlight the potential of using water-soluble molecules inspired by the work on organic semiconductors to improve electrode/microbe interfaces.

Air-cathode microbial fuel cell array: a device for identifying and characterizing electrochemically active microbes.

Microbial fuel cells (MFCs) have generated excitement in environmental and bioenergy communities due to their potential for coupling wastewater treatment with energy generation and powering diverse devices. The pursuit of strategies such as improving microbial cultivation practices and optimizing MFC devices has increased power generating capacities of MFCs. However, surprisingly few microbial species with electrochemical activity in MFCs have been identified because current devices do not support parallel analyses or high throughput screening. We have recently demonstrated the feasibility of using advanced microfabrication methods to fabricate an MFC microarray. Here, we extend these studies by demonstrating a microfabricated air-cathode MFC array system. The system contains 24 individual air-cathode MFCs integrated onto a single chip. The device enables the direct and parallel comparison of different microbes loaded onto the array. Environmental samples were used to validate the utility of the air-cathode MFC array system and two previously identified isolates, 7Ca (Shewanella sp.) and 3C (Arthrobacter sp.), were shown to display enhanced electrochemical activities of 2.69 mW/m(2) and 1.86 mW/m(2), respectively. Experiments using a large scale conventional air-cathode MFC validated these findings. The parallel air-cathode MFC array system demonstrated here is expected to promote and accelerate the discovery and characterization of electrochemically active microbes.

Microfabricated devices in microbial bioenergy sciences.

Microbes provide a platform for the synthesis of clean energy from renewable resources. Significant investments in discovering new microbial systems and capabilities, discerning the molecular mechanisms that mediate microbial bioenergy production, and optimizing existing microbial bioenergy systems have been made. However, further development is needed to achieve the economically feasible large-scale production of value-added energy products. Microfabricated lab-on-a-chip systems provide cost- and time-efficient opportunities for analyzing microbe-mediated bioenergy synthesis. Here, we review developments in the application of lab-on-a-chip systems to the bioenergy sciences. We focus on systems that support the analysis of microbial generation of bioelectricity, biogas, and liquid transportation fuels. We conclude by suggesting possible future directions.

A microfluidic microbial fuel cell array that supports long-term multiplexed analyses of electricigens

Microbial fuel cells (MFCs) are green energy technologies that exploit microbial metabolism to generate electricity. The widespread implementation of MFC technologies has been stymied by their high cost and limited power. MFC arrays in which device configurations or microbial consortia can be screened have generated significant interest because of their potential for defining aspects that will improve performance featuring high throughput characteristics. However, current miniature MFCs and MFC array systems do not support long-term studies that mimic field conditions, and hence, have limitations in fully characterizing and understanding MFC performances in varieties of conditions. Here, we describe an MFC array device that incorporates microfluidic technology to enable continuous long-term analysis of MFC performance at high throughput utilizing periodic anolyte/catholyte replenishment. The system showed 360% higher power output and 700% longer operating time when compared to MFC arrays without catholyte replenishment. We further demonstrate the utility of the system by reporting its successful use in screening microbial consortia collected from geographically diverse environments for communities that support enhanced MFC performance. Taken together, this work demonstrates that anolyte/catholyte replenishment can significantly improve the long-term performance of microfabricated MFC arrays, and support the characterization of diverse microbial consortia.

A novel hollow sphere bismuth oxide doped mesoporous carbon nanocomposite material derived from sustainable biomass for picomolar electrochemical detection of lead and cadmium

A novel ultrasensitive, selective and low cost electrochemical sensor based on a hollow sphere bismuth oxide doped mesoporous carbon aerogel nanocomposite derived from a sustainable biomass material was successfully fabricated for simultaneous Pb2+ and Cd2+ detection at picomolar levels. In this nanocomposite material, we successfully brought together the advantages of an extraordinarily large surface area biomass derived carbon matrix with mesopores for analyte pre-enrichment and the excellent electroanalytical activity of the bismuth oxide hollow sphere structure for highly sensitive heavy metal sensing. Under optimized conditions, this electrode material exhibited a very low detection limit of 1.72 pM for Pb2+ and 1.58 pM for Cd2+ under ambient conditions, the lowest ever limit of detection recorded for the detection of both Pb2+ and Cd2+ using activated carbon. Furthermore, two wide linear ranges from 0.5 pM to 10 pM and from 10 pM to100 pM were observed due to the differences of adsorption dynamics at different metal ion concentration ranges. The nanocomposite sensor material demonstrated excellent reproducibility and great resistance to interference. Furthermore, the application for real water analysis was demonstrated and the result was highly consistent with the measurement from inductively coupled plasma optical emission spectroscopy (ICP-OES).

Pretreatment of eucalyptus with recycled ionic liquids for low-cost biorefinery

It is urgent to develop recycled ionic liquids (ILs) as green solvents for sustainable biomass pretreatment. The goal of this study is to explore the availability and performance of reusing 1-allyl-3-methylimidazolium chloride ([amim]Cl) and 1-butyl-3-methylimidazolium acetate ([bmim]OAc) for pretreatment, structural evolution, and enzymatic hydrolysis of eucalyptus. Cellulose enzymatic digestibility slightly decreased with the increased number of pretreatment recycles. The hydrolysis efficiencies of eucalyptus pretreated via 4th recycled ILs were 54.3% for [amim]Cl and 72.8% for [bmim]OAc, which were 5.0 and 6.7-folds higher than that of untreated eucalyptus. Deteriorations of ILs were observed by the relatively lower sugar conversion and lignin removal from eucalyptus after 4th reuse. No appreciable changes in fundamental framework and thermal stability of [amim]Cl were observed even after successive pretreatments, whereas the anionic structure of [bmim]OAc was destroyed or replaced. This study suggested that the biomass pretreatment with recycled ILs was a potential alternative for low-cost biorefinery.

A thermoresponsive hydrogel poly(N-isopropylacrylamide) micropatterning method using microfluidic techniques

Poly(N-isopropylacrylamide) (PNIPAAm) is a thermoresponsive hydrogel that has been widely used in various biomedical applications, including tissue engineering. Making PNIPAAm into a microscale structure is an effective method of increasing its thermoresponsiveness and modulating surface properties compared to bulk PNIPAAm. The commonly used method of direct photolithography combined with a photomask is challenging in creating pure PNIPAAm patterns smaller than 10 µm. Also, each time when there is a need to change the sizes of resulting PNIPAAm patterns, a new photomask is required. Here, a microfluidically controlled micropatterning method utilizing hydrophilic spots on a hydrophobic substrate was developed to create pure PNIPAAm microstructures. This method enabled the fabrication of pure PNIPAAm microstructures with a wide range of sizes from 70 µm to sub-10 µm out of the same substrate preparation by simply varying the flow speed of the hydrogel precursor solution through a microfluidic channel. Hydrogel microstructures with diameters of 12 to 59% of the hydrophilic pattern diameters were successfully fabricated using this fabrication scheme. The smallest hydrogel pattern fabricated using this method was 2.3 µm in diameter using a 5 µm diameter hydrophilic pattern at a flow speed of 100 mm s−1. This simple and versatile fabrication scheme could be an ideal method for creating large arrays of hydrogel micropatterns with varying sizes.

Long-term stability of FeSO4 and H2SO4 treated chromite ore processing residue (COPR): Importance of H+ and SO42−

In this study, the long-term stability of Cr(VI) in the FeSO4 and H2SO4 (FeSO4-H2SO4) treated chromite ore processing residue (COPR) after 400 curing days and the stabilization mechanisms were investigated. FeSO4-H2SO4 treatment significantly reduced toxicity characteristic leaching procedure (TCLP) and synthetic precipitation leaching procedure (SPLP) Cr(VI) concentrations to lower than the regulatory limit of 1.5mgL-1 (HJ/T 301-2007, China EPA) even for the samples curing 400days, achieving an outstanding long-term stability. Our independent leaching tests revealed that H+ and SO42- have synergistic effect on promoting the release of Cr(VI), which would make Cr(VI) easier accessed by Fe(II) during stabilization. The contributions of H+ and SO42- to Cr(VI) release ratio were 25%-44% and 19%-38%, respectively, as 5mol H2SO4 per kg COPR was used. X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and alkaline digestion analyses were also employed to interpret the possible stabilization mechanism. Cr(VI) released from COPR solid was reduced to Cr(III) by Fe(II), and then formed stable FexCr(1-x)(OH)3 precipitate. This study provides a facile and reliable scheme for COPR stabilization, and verifies the excellent long-term stability of the FeSO4-H2SO4 treated COPR.

Facile synthesis of mesoporous graphene platelets with in situ nitrogen and sulfur doping for lithium–sulfur batteries

The interaction between lithium polysulfides and doped heteroatoms could prevent the loss of soluble polysulfides in the cathode and mitigate the shuttle effect in lithium–sulfur batteries. Herein, a facile synthesis of mesoporous graphene platelets (NSGs) with in situ nitrogen and sulfur doping by the pyrolysis of a self-assembled L-cysteine precursor on sodium chloride crystal surface for structure-directing is presented. The mesoporous lamellar structure of the NSG possesses a uniform distribution of pyrrolic N, pyridinic N, and thiosulphate structured heteroatoms originating from in situ doping, which promotes the confinement of intermediate polysulfides. Combining the strong interactions with soluble polysulfide, flexible mesoporous architecture, and high conductivity of graphene, the prepared NSG material exhibited a high initial capacity of 1433 mA h g−1 at a 2C rate as well as a reversible capacity of 684 mA h g−1 after 200 cycles. This demonstrates that the in situ nitrogen and sulfur doped thin lamellar structure of graphene would be a promising cathode material for high performance lithium–sulfur batteries.