bluuebunny/crossref_metadata_2025 huggingface dataset:
Selectivity Control in the Electroreduction of CO2 over Nanostructured Catalysts
Authors: Mistry Hemma , Varela Ana Sofia , Reske Rulle , Strasser Peter , Roldan Beatriz
Published: February 2020

The electrocatalytic reduction of CO2to industrial chemicals and fuels is a promising pathway to sustainable electrical energy storage and to an artificial carbon cycle, but is currently hindered by the low energy efficiency and low activity displayed by traditional electrode materials. In order to overcome these challenges, we have explored how catalyst nanostructure and oxidation state can be used to control the activity and selectivity of the reaction.

      Using the inverse micelle synthesis method, nanoparticles (NPs) with well-defined size and interparticle distance supported on glassy carbon electrodes were prepared and tested as catalysts for CO2 electroreduction. Previously, we have reported the dramatic effect of the size of these NPs size on activity and selectivity for Cu1 and Au2 NPs. Here, we will show that interparticle distance is also a critical parameter for controlling reactivity.3 For largely spaced NPs, we find that selectivity to CO is enhanced, since this reaction intermediate is less likely to readsorb on neighboring NPs after formation. Large NPs which are highly spaced have slightly higher hydrocarbon selectivity than smaller NPs, since there is more chance for the intermediates to readsorb on the same particle. On the contrary, for closely spaced NPs we find that hydrocarbon selectivity is enhanced, since the re-adsorption of reaction intermediates on neighboring NPs can facilitate the multi-step pathway required for hydrocarbon production. These results are also corroborated by theoretical diffusion calculations. This study addresses previously unexplored aspects of how product selectivity can be controlled using mesoscale transport processes during CO2 electroreduction. In addition, it shows that IP distance is a critical design parameter to consider when developing improved NP catalysts for CO2electroreduction.

      Another critical parameter for selectivity control in nanostructured electrocatalysts is the oxidation state. We will discuss new oxide-derived metal catalysts that can reduce CO2 with lowered overpotential and improved hydrocarbon selectivity. We will also discuss critical insights into the catalyst reaction mechanism which were unraveled using structural and chemical information on the sample during the reaction using operando X-ray absorption fine structure spectroscopy.

References

1) R. Reske, H. Mistry, F. Behafarid, B. Roldan Cuenya, P. Strasser, J. Am. Chem. Soc. (2014) 136: 6978-6986.

2) H. Mistry, R. Reske, Z. Zeng, Z. Zhao, J. Greeley, P. Strasser, B. Roldan Cuenya, J. Am. Chem. Soc. (2014) 136: 16473-16476.

3) H. Mistry, F. Behafarid, R. Reske, A. S. Varela, P. Strasser, B. Roldan Cuenya, ACS Catal. (2015), DOI: 10.1021/acscatal.5b02202.
Enhancement in Production of Electricity from Wastewater Using Microbial Fuel Cell
Authors: Joshi Jarina
Published: February 2020

A two compartment model of microbial fuel cell was designed. The cells were made from wastewater as electrolyte. Saccharomyces cerevisae was cultured in anodic compartment.  The maximum power of 10.745w/m3 was obtained on the 5th day when cellulose acetate was used as the proton exchange membrane (PEM) utilizing waste water as a substrate while supplying external resistance of 500 ohm. There was slight decrease in the power when PEM used  was coated  cellulose acetate i.e 9.156w/m3 and the power dramatically decreased when nafion membrane was used producing the power of 4.34w/m3. The continuous flow of 1%hydrogen peroxide at the rate of 1 ml/min in anodic compartment  in similar conditions increased the power to 22.145w/m3.
Tailoring Microbial Fuel Cells for Production of Hydrogen Peroxide
Authors: Young Michelle , Ki Dongwon , Stadie Mikaela , Thompson Julia , Chowdhury Nadratun , Popat Sudeep , Rittmann Bruce , Torres César I
Published: February 2020

Microbial fuel cells (MFCs) have been studied for over a decade for possible applications of generating electrical power from wastewater treatment. The power densities achieved so far – although increased by orders of magnitude since the first studies – are still well below those required to compete with other anaerobic treatment processes.

We are exploring the use of MFCs for the production of hydrogen peroxide (H2O2). H2O2 is a powerful oxidant and disinfectant that can be used onsite at a treatment plant. Its production in MFCs is possible by allowing the 2-e- oxygen reduction reaction (ORR) to occur at the cathode. We have studied several aspects of the selection of cathode catalyst, design of the MFCs, and their operation, to optimize the rates and concentrations of H2O2 that can be achieved in a continuous-flow catholyte scheme.

First, we determined the thickness of the Vulcan carbon catalyst necessary for the cathode to promote the 2-e- vs. the 4-e- ORR, as higher thicknesses tend to lead to the consumption of H2O2 within the catalyst layer. Next, we studied various anion exchange membranes (AEMs) for their compatibility with H2O2. Although high-conductivity AEMs are desirable to decrease Ohmic overpotentials, we had to select an AEM that has a relatively low conductivity, because of its higher compatibility with H2O2 that would allow long-term operation. We also optimized the catholyte composition and hydraulic retention time (HRT) within the MFCs to allow for H2O2 production at a high cathodic Coulombic efficiency, by avoiding its disintegration within the cathode chamber.

Through these advances, we have been able to show consistent H2O2 production in MFCs fed with acetate as the electron donor on the anode to concentrations of >0.3%. These concentrations are significantly higher than those needed for many of the possible onsite applications of H2O2, for e.g. disinfection. Our results should pave the way for further development and scale-up of MFCs for the production of H2O2.
On Design, Operation, and Characterization of Microbial Electrochemical Cells with Reduced Overpotentials
Authors: Ki Dongwon , Popat Sudeep , Torres César I
Published: February 2020

One of the main performance challenges in microbial electrochemical cells (MXCs) is the low voltage efficiency in comparison to other fuel and electrolysis cells.  For example, in the case of microbial fuel cells (MFCs), a theoretical maximum of 1.1 V is available when coupling acetate oxidation at the anode to O2 reduction at the cathode, while at current densities of > 5 A m-2, only < 0.3 V is produced, representing > 0.8 V of overpotential. Similarly, although the theoretical applied voltage in microbial electrolysis cells (MECs) is only 0.14 V, the actual applied voltage can be as high as 1.2 V, representing close to 1 V of overpotential. Thus, there is a need to consider design and operation tactics for MXCs that help reduce the overall overpotential in the system. In this study, we aimed to improve the design and operation of MECs to achieve current densities >10 A m-2 with reduced applied voltages, using a thorough analytical framework involving electrochemical techniques such as chronoamperometry, voltammetry and electrochemical impedance spectroscopy. We developed a design that allows high surface area for the anode using carbon fibers, but without creating a large distance between the anode and the cathode (<0.5 cm) to reduce Ohmic overpotential. We determined that Ohmic overpotential, at current densities >10 A m-2 remained <0.1 V even when using an anion exchange membrane to separate the anode and the cathode. We observed the largest overpotential from cathode related phenomena. The increase in pH in the cathode chamber, often to ~13, results in >0.3 V of Nernstian concentration overpotential. We showed how by adding CO2 to the cathode, this overpotential could be reduced to negligible.  We revealed that the benefit of CO2 was primarily on the pH and not necessarily on the cathode activation overpotential through electrochemical impedance spectroscopy on the cathode.  We also tested two different cathode materials (stainless steel and nickel) to compare the cathode activation overpotentials.  Overall, through our design and operation improvements, we were able to reduce the applied voltages from 1.1 to ~0.85 V, at 10 A m-2.  However, the cathode overpotential is still a major problem in our reactor design possibly due to local concentration gradients on cathodes, resulting in Nernstian concentration overpotential.  To overcome this, it is required to optimize mass transport further between the anode and the cathode, possibly through novel designs and/or improved hydrodynamics at the local surfaces, estimating cathode overpotential ~0.2 V.  Then, we estimate that the total applied voltage in MECs at high current densities (e.g. >10 A m-2) could be reduced as low as 0.7 V.
Metallization of DNA Origami to Form Electrically Conductive ~10 Nm Diameter Nanowires
Authors: Uprety Bibek , Harb John N.
Published: February 2020

DNA based bottom-up nanotechnology is seen as a promising technology for the development of future generations of nanodevices. The bottom-up approach takes advantage of molecular self-assembly to create useful architectures of nanometer dimensions. DNA, with its small size, functional groups and complementary base pairs, is a powerful template for nanodevice fabrication via bottom-up assembly. Recent advances in the field of “DNA origami” have enabled fabrication of nanostructures by folding single-stranded DNA into a variety of 2- and 3-D shapes. However, electrically conductive structures are required for many nanodevice applications.

In this study, we report the fabrication of electrically conductive DNA origami-templated nanowires with the use of gold nanorods (Au NR’s) as a step towards DNA nanodevices.  Our process begins with a seeding step where Au NR’s bind to the DNA origami backbone. The seeds are then connected by electroless deposition to make continuous wires. The use of nanorods as seeds provides two key advantages over previous work with particulate seeds.  First, the surfactant-enabled anisotropic growth used to initially fabricate the nanorods appears to persist through the electroless plating process on the DNA template. This permits improved control of the width of the final metallized structure since growth in the axial direction is preferred. The average final width of our Au-metallized DNA wires was ~10nm. Continuous 400 nm long DNA wires were obtained by filling gaps between seed particles that ranged from 10.6 nm on average to gaps as wide as 25 nm. The second advantage of nanorods is the reduction in the number of connection points between seed particles by a factor of three relative to that observed for 5 nm seed particles. The reduced number of connection points is expected to increase the conductivity of the wires. Initial electrical characterization of the DNA wires shows that they are conductive, and more detailed measurements are in progress. Site-specific placement of Au NR's on a DNA origami template, demonstrated in this study, is capable of providing the controlled placement needed to enable future nanodevice applications.

In summary, we have demonstrated a metallization process to fabricate thin, high aspect ratio, conductive wires on DNA-origami templates with the use of Au NR’s and electroless plating. Continuing efforts seek to interface these thin nanowires with appropriate semiconducting elements to enable fabrication of self-assembled nanoscale devices.

References:

 

Uprety, B.; Gates, E. P.; Geng, Y.; Woolley, A. T.; Harb, J. N. Site-Specific Metallization of Multiple Metals on a Single DNA Origami Template. Langmuir
2014, 30, 1134-1141.

Gates, E.P.; Jensen, J.K.; Harb, J.N.; Woolley, A.T. Optimizing Gold Nanoparticle Seeding Density on DNA Origami. RSC Advances
2015, 5, 8134-8141.
The Role of Shewanella Oneidensis MR-1 Structural Proteins in Electrochemical Performance and Biofilm Development
Authors: Cornejo Jose Alberto , Artyushkova Kateryna , Babanova Sofia , Ista Linnea K , Ajo-Franklin Caroline Marie , Atanassov Plamen
Published: February 2020

Microbial exoelectrogens present promising avenues for the development of bioremediation, biofuel cells and synthetic biology. Our research interests are focused on achieving efficient electron transfer from these organisms embedded in biohybrid constructs while reducing ohmic loses in the system. A crucial aspect for attaining this goal is to fully understand bacterial motility and attachment to the solid support of interest in which respiration occurs. Therefore, biofilm formation is of central interest in anode respiring microorganisms relying on extracellular electron transfer (EET). Microbial appendages have been proposed to be involved in cell attachment as well as in different modes of cell motility prior to the biofilm formation process as observed in select microorganisms [1]. Amongst them, Shewanella oneidensis has been thoroughly used as a model for further understanding microbial electrochemical phenomena. A crucial area of study contributing to the development of microbial electrochemical systems consists in identifying key components involved in the assembly and functionality of pili and flagella in this organism.

Therefore, in this study we utilized motility mutants of S. oneidensis MR-1 that lack key proteins involved in the secretion of type IV pili and flagella. Electrochemical techniques were explored to compare the performance and current generation from microbial fuel cells containing motility-impaired mutants as well as wild type S. oneidensis. Furthermore, we studied and quantified the anodic biofilm morphological characteristics based on microscopic techniques. We found that type IV pili mutants exhibited the highest deficiencies in electrochemical performance and current production based on chronoamperometric studies. Specifically, these deficiencies were more pronounced on PilD and PilT protein-lacking mutants. These complexes are essential inner membrane proteins responsible for pili assembly and contraction [2]. On the other hand, flagella-lacking S. oneidensis mutants did not present significant restrains in current output and biofilm formation.

We conclude that the discussed structural protein assemblies present relevant roles in bacterial surface attachment. Our findings present direct implications in the development of fully engineered biohybrid assemblies, bacteria-anode interactions, and bacterial electron transfer quantification.

Figure 1. SEM images of wild type, pili-lacking and flagella-lacking mutants of S. oneidensisattachedto carbon felt fibers.

 
 

References:

1. K.M. Thormann, R.M. Saville, S. Shukla, D.A. Pelletier, A.M. Spormann, Initial phases of biofilm formation in Shewanella oneidensis MR-1. J Bacteriol, 2004. 186: 8096–8104. 

2. R.M Saville, N. Dieckmann , A.M. Spormann, Spatiotemporal activity of the mshA gene system in Shewanella oneidensis MR-1 biofilms. FEMS Microbiol Lett. 2010. 308:76–83.

Figure 1
Characterization of Electrochemical Activity in Four Alkaline Hot Springs in Heart Lake Geyser Basin, Yellowstone National Park
Authors: Mohamed Abdelrhman , Medina Adan , Ha Phuc Thi , Peyton Brent , Beyenal Haluk
Published: February 2020

Yellowstone National Park is well known among microbiologists for its unique microbial ecology, where microorganisms adapt to extreme environments (temperature and pH) associated with geothermal features including hot springs, geysers, and fumaroles. Recently, we developed a portable, battery-operated potentiostat to control the potential of electrodes in in Heart Lake Geyser Basin. The goal of this work is to compare the electrochemical activity in polarized and non-polarized electrodes deployed in alkaline hot springs. We used carbon fabric electrodes (3 inch x 3 inch) working electrode, graphite felt (5 inch x 5 inch x 0.25 inch) counter electrode, and Ag/AgCl reference electrode. A carbon fabric electrode (3 inch x 3 inch) was used as a non-polarized control. These electrodes were immersed in four hot springs with temperature ranging between 45οC and 91οC, and pH between 8 and 8.8. In total, eight polarized electrodes and controls were deployed; one anode and one cathode in each hot spring. The cathodes were deployed approximately 1 foot below the surface of the water, and polarized at -0.6 VAg/AgCl. The anodes were deployed near the bottom of each hot spring at depth 3-10 feet, and polarized at +0.4 VAg/AgCl.  All electrodes were deployed for a period of 30 days, and then harvested for electrochemical analysis. Cyclic voltammetry reveals the presence of multiple anodic and cathodic peaks in both polarized and control electrodes. Increased temperature seems to activate redox couples, with anodic (positive current) peaks at -0.2 and 0.35 VAg/AgCl, and two corresponding cathodic (negative current) peaks at -0.4 and 0.25 VAg/AgCl. Temperature-controlled experiments shows that the peak height increases with temperature, which alludes to the presence of thermally-activated electrochemical reactions.
(Invited) Disentangling the Roles of Free and Cytochrome-Bound Flavins in Extracellular Electron Transport from Shewanella Oneidensis MR-1
Authors: Xu Shuai , Jangir Yamini , El-Naggar Mohamed
Published: February 2020

In addition to its natural environmental significance, the process of extracellular electron transfer (EET) can be exploited at electrode interfaces to enable microbial electrochemical technologies for renewable energy recovery, biofuel production, bioremediation, and wastewater treatment. Success in these applications hinges on a better understanding of the electron transfer pathways that link electrochemically active microbes, such as Shewanella oneidensis MR-1, to electrodes. Here, we report electrochemical measurements that reveal both flavin-dependent and flavin-independent EET pathways from S. oneidensis MR-1. Significantly, differential pulse voltammetry captured the redox signatures of both free and cytochrome-bound flavins simultaneously in one experimental system for the first time, allowing us to compare their relative contributions while studying the impact of cell-removal, flavin addition, different culture conditions, and a mutant disrupted in flavin secretion. Our results indicate that endogenous flavins accelerate EET from Shewanella to carbon cloth electrodes primarily as cytochrome-bound cofactors, rather than free soluble shuttles, thereby supporting one of the two debated models of Shewanella EET. Our measurements also highlight the extent to which different electrode materials can impact detection of microbial redox signatures. This communication motivates additional structural studies to study the binding location and precise interaction of flavins at cytochrome-electrode interfaces.
Deep Oxidation of Multiple (Poly)Saccharides at a Bi-Enzymatic Bioelectrode
Authors: Milton Ross D , Yuan Mengwei , Hickey David P , Sugawara Atsuya , Peterbauer Clemens , Haltrich Dietmar , Minteer Shelley D.
Published: February 2020

As perhaps the most commonly utilized fuel for enzymatic fuel cells (EFCs), glucose oxidation is largely under-exploited. Theoretically, the oxidation of glucose and its downstream metabolites is able to deliver a maximum of 24e- to a bioanode, however the vast majority of EFCs reported to date only perform a single 2e- oxidation of glucose.

Commercially available glucose oxidase (GOx) from Aspergillus sp. oxidizes the anomeric (C1) carbon of glucose. Recently, mediated bioelectrocatalysis of pyranose dehydrogenase from Agaricus meleagris (AmPDH) via an osmium redox hydrogel has been demonstrated, whereby AmPDH is reported to be able to oxidize glucose and other saccharides at combinations of their respective C1/C2/C3 positions.1

Another attractive property of an EFC is the ability to utilize a single biocatalyst to oxidize a range of fuels. We recently reported the use of an engineered commercially-available glucose oxidase with broader substrate specificity at an electrode surface that resulted in an EFC configuration that was able to oxidize multiple (poly)saccharides, including lactose from dairy milk and starch.2

This study reports the ability of a ferrocene redox hydrogel to mediate bioelectrocatalytic saccharide oxidation by AmPDH. Further, AmPDH and broad substrate specificity glucose oxidase were combined to yield an EFC that was able to operate on multiple (poly)saccharides while theoretically increasing the extent of oxidation of each substrate, resulting in a more-versatile EFC with greater efficiency.

References

1.              M. E. Yakovleva, C. Gonaus, K. Schropp, P. Oconghaile, D. Leech, C. K. Peterbauer and L. Gorton, Phys. Chem. Chem. Phys., 2015, 17, 9074-9081.

2.              R. D. Milton, F. Wu, K. Lim, S. Abdellaoui, D. P. Hickey and S. D. Minteer, ACS Catal., 2015, 5, 7218-7225.

Figure 1
Direct Electron Transfer Mechanisms Applied Toward the Development of an Enhanced Photoelectrochemical Biofuel Cell
Authors: Lopez Ryan J. , Shreve Andrew , Atanassov Plamen
Published: February 2020

Photoelectrochemical biofuel cells (PEBFCs) are hybrid devices which combine the utility of enzymatic redox catalysts with the photon absorbing characteristics of a dye-sensitized solar cell (DSSC).  The pairing of these two technologies has been demonstrated to result in a system that improves on the performance of either a traditional enzymatic fuel cell (EFC) or DSSC operating independently1.  Furthermore, due to the increased potential provided by a PEBFC relative to an EFC the range of oxidizers used in the cathode can be broadened to produce a variety of useful reduced fuels.  Traditionally, PEBFCs have relied on NAD+/NADH intermediates for charge transfer between the anodic redox enzyme and the porphyrin sensitizer.  However, recent work by our group has shown that quinoprotein glucose dehydrogenases are capable of efficient, mediator free direct electron transfer (DET) to immobilized heme porphyrins2.  DET allows for a further reduction in the electrode overpotential compared to many mediated systems and therefore provides more usable potential for energy conversion.  

In the current work a PEBFC utilizing DET mechanisms was developed with the goal of providing efficient electron transfer between the enzymatic catalyst and the porphyrin sensitizer on the anode.  The electron transfer was enhanced by photo-excitation of the sensitizer and induced charge separation to a covalently bound n-type semi-conductor (Figure 1).  The resulting oxidized sensitizer then readily accepts electrons from the quinoproteins adsorbed to the electrode surface.  The open circuit potential (Voc) of the illuminated photo anode was more negative than the same anode in a dark condition by approximately 80 mV (top of Figure 2).  The generated current of the illuminated photoanode was also considerably higher at all potentials tested (bottom of Figure 2).  To complete the PEBFC, the photoanode is coupled with a cathode utilizing an oxidase enzymatic catalyst and overall performance in terms of surface characteristics, Voc, and total power are characterized.  Further applications with regards to possible uses in energy conversion and reforming of simple, abundant substrates such as glucose to more readily useable fuels such as hydrogen will be discussed.

1.            M. Hambourger, G. Kodis, M. D. Vaughn, G. F. Moore, D. Gust, A. L. Moore and T. A. Moore, Dalton Transactions, 9979 (2009).

2.            R. J. Lopez, S. Babanova, K. Artyushkova and P. Atanassov, Bioelectrochemistry, 105, 78 (2015).

Figure 1
NADH Bioelectrocatalysis at a Naphthoquinone Redox Polymer
Authors: Abdellaoui Sofiene , Milton Ross D , Quah Timothy , Minteer Shelley D.
Published: February 2020

Nicotinamide adenine dinucleotide-dependent (NAD) enzymes are used by a wide-spread of dehydrogenases which have been used in a large portion of enzymatic fuel cells (EFCs) to date. The oxidation of an EFC’s fuel (such as glucose) results in the generation of enzymatically-generated diffusive reduced cofactor (NADH). Various electrocatalysts and mediators have been employed to electro-oxidize NADH at low potential, such as phenothiazines and rhodium catalysts.1, 2 Naphthoquinones and anthraquinones have also been employed for NADH oxidation in high power EFCs, however their use typically requires an additional enzyme to mediate electron transfer between the quinone and NADH (diaphorase).3

            We report the use of a naphthoquinone redox polymer to oxidize NADH, enzymatically generated from glucose oxidation by NAD-dependent glucose dehydrogenase. The naphthoquinone redox polymer serves as a support for enzyme immobilization. Additionally, NADH is oxidized without the requirement of diaphorase.4

References

1.         L. Gorton and E. Dominguez, Rev. Mol. Biotechnol., 2002, 82, 371-392.

2.         B. Reuillard, A. Le Goff and S. Cosnier, Anal. Chem., 2014, 86, 4409-4415.

3.         H. Sakai, T. Nakagawa, Y. Tokita, T. Hatazawa, T. Ikeda, S. Tsujimura and K. Kano, Energy & Environmental Science, 2009, 2, 133-138.

4.         S. Abdellaoui, R. D. Milton, T. Quah and S. D. Minteer, Chem. Commun., 2016, DOI: 10.1039/C5CC09161F.

Figure 1
Establishing Direct Electron Transfer in Cyanobacteria for Photocurrent Generation
Authors: Sekar Narendran , Ramasamy Ramaraja P.
Published: February 2020

Cyanobacteria are used as anode catalyst in photo-bioelectrochemical cells to generate electricity in a sustainable, economic and environmental friendly manner. Though cyanobacteria (CB) have huge advantage for solar energy conversion through its robust photosynthesis, they could not perform extracellular electron transfer effectively as other electricigens. This is because, unlike electricigens such as Geobacter sp., CB do not possess any special key players on their outer membrane to carry out direct electron transfer. In this work, we genetically engineered a cyanobacterium named Synechococcus elongatus PCC7942 to express an outer membrane c-type cytochrome called OmcS1. The genetically modified CB (Eng-CB) enhanced the photocurrent generation significantly in photo-bioelectrochemical cells compared to that of wild type without the addition of any redox mediator. A specific redox peak corresponding to OmcS (~ 0.1 V vs Ag/AgCl) was observed in Eng-CB in a low-scan rate cyclic voltammetry (1 mV/s) and the same was found absent in the wild type. Both these evidences confirmed the establishment of direct electron transfer in Eng-CB. Also, extracellular electron transfer of the Eng-CB was investigated biochemically based on its ability to reduce the exogenously added soluble redox compound like potassium ferricyanide during its growth in BG11 medium. The enhanced ferricyanide reduction as well as photocurrent generation by the Eng-CB under both light and dark conditions elucidates the fact that the heterologously expressed OmcS could interact with both photosynthetic and respiratory electron transport chains. This work demonstrates the importance of interdisciplinary and integrated approach to enhance the photocurrent generation using CB and aid in advancing the understanding of biological interfaces with the electrode leading to for rapid development of photosynthetic microbial fuel cell technology. 

References:

1. N. Sekar, R. Jain, Y. Yan, R. P. Ramasamy (2015) Biotechnol Bioeng.  doi: 10.1002/bit.25829

Figure 1
Geobacter Sulfurreducens Electrodes for Nitrate Reduction in Ground Water
Authors: Knoche Krysti L. , Renner Julie N , Minteer Shelley D.
Published: February 2020

Nitrate accumulation in ground water is a major global problem, especially in farming communities where fertilizers are used. A nitrate reducing microbial fuel cell fed by hydrogen from a PEM-based water electrolysis cell has been proposed as a low cost alternative to current water treatment methods. To this end, Geobacter sulfurreducens anodes are electrochemically evaluated for their ability to reduce nitrate. G. sulfurreducens was subcultured in a nitrate-based media, then cast on 1 cm2 Toray paper electrodes and immobilized with 4% pectin cross-linked with magnesium chloride. Cyclic voltammograms in Figure 1 demonstrate bioelectrocatalytic nitrate reduction by the G. sulfurreducens anode. Preliminary data gathered from the microbial fuel cell system built by Proton OnSite shows a decrease in nitrate correlating with an increase in ammonia and nitrite with operation.

Figure 1
The Effect of Cation Exchange Membrane on Long-Term Electromethanogenic Performance
Authors: Carpenter Kayla , Ishii Shino , Ishii Shunichi , Phadke Sujal , Babanova Sofia , Flynn Michael , Hogan John , Bretschger Orianna
Published: February 2020

Bioelectrochemical systems offer a method to microbially harness the energy from unwanted compounds, such as wastewater, and use towards biosynthesis of beneficial compounds. Understanding the effects of the cation exchange membrane and other potential environmental stimuli is critical for developing bioelectrochemical systems that are robust and reliable. In this study, an electron-consuming community enriched from rice paddy soil was fed with a stable electron source via potentiostatic control of the working electrode to -700 mV vs. Ag/AgCl, and carbon dioxide as the sole inorganic carbon source. A subpassage technique was used as a selective pressure to enhance electron consumption and methanogenesis within the system. After relatively stable operation over a 250-day period along with sampling of the community to determine taxonomic composition, the cation exchange membrane was changed from Nafion®-117 to Ultrex®. While methane production remained consistent for an additional 450-day operation, there was a striking decrease in measured current consumption of the system (Fig. 1), which may also correlate to a change in the cathode microbial community and mechanism of energy recovery from the electrode (Fig. 2).

Results suggest that the properties of the cation exchange membrane are correlated to electrical system performance. Nafion is a physically thinner cation exchange membrane than the Ultrex material, and the physical differences in the membrane properties may impact the diffusion of protons and other molecules between the counter and working compartments. For example, it is possible that free radicals are formed at the counter electrode surface during poised-potential operation and may diffuse into the working chamber via the membrane. However, the presence of a thicker member (e.g. the Ultrex) in the system may minimize this diffusion effect and also limit the proton transfer, thereby leading to reduced electrochemical activity and alternative mechanisms for methane formation at the working electrode.

The taxonomic composition of the electromethanogic community was characterized using 16S rRNA gene sequences. The communities associated with the working electrode changed significantly when the membrane was switched from Nafion to Ultrex (Fig. 2).  The relative abundance of methanogens (Euryarchaeota) increased from below detection to occupying nearly 60% of the community during the first subpassage after the membrane change. The relative abundance of the methanogenic population varied throughout operation with Ultrex membranes, but remained detectable and in high relative abundance for several subpassages. Interestingly, the relative abundance of Clostridia, α-,  δ-, and ε-Proteobacteria also significantly changed throughout the duration of operation with the Ultrex membrane.

Figure 1
A PEMFC System Operating with Biohydrogen
Authors: Dai Ngan Hue , Nguyen Duong Tam Anh , Man Tran Van
Published: February 2020

Increasing energy demands, depletion of fossil fuel resource and environmental pollution require the researches of alternative fuel as well as energy conversion devices. Proton Exchange Membrane Fuel Cells (PEMFCs), available applied for emergency and/or transport power supply, are the systems in which hydrogen is used as the fuel for anode. In this study, we design a combined system of PEMFC stack operating with biohydrogen as fuel and pure oxygen or air as oxidant. The biohydrogen is produced from a raw bamboo biomass treatment process. This process conclude two steps (i) advanced oxidation and (ii) fermentation.
On-Body Energy Harvesting: Wearable Biofuel Cells
Authors: Jia Wenzhao , Banodkar Amay , Wang Joseph
Published: February 2020

The presentation will discuss describe the development of textile- and tattoo-based flexible biofuel cells and batteries. We will illustrate the favorable electrochemical behavior of these wearable devices, and demonstrate the ability to generate substantial levels of electrical power from the human perspiration in a non-invasive and continuous fashion. Mechanical stress studies indicate that the printed devices survive large mechanical deformations. Technical challenges and prospects for using textile- and tattoo-based electrochemical biofuel cells and batteries will be discussed, along with several demonstrations and prospects for future on-body applications.

        

REFERENCES

[1] “Epidermal Biofuel Cells: Energy Harvesting from Human Perspiration”, W. Jia, G. Valdés-Ramírez, A. J. Bandodkar, J. R. Windmiller, J. Wang, Angew Chemie Int. Ed., 52(2013)7233.

[2] “Wearable Electrochemical Sensors and Biosensors: A Review”, J. R. Windmiller and J. Wang,  Electroanalysis, 25(2013)29.
(Invited) Photovoltaic Proprieties and Photocatalytic Activity of Perovskite Oxide-Based Systems
Authors: Nechache Riad
Published: February 2020

Photocatalytic water splitting with semiconductor materials has been investigated as a clean and

renewable process for directly converting sunlight into chemical energy. In particular, multiferroics MFs have recently

been used for applications in both photocatalysis (PC) and photovoltaics (PV) due to their ferroelectric properties and

narrow band gaps, allowing them to harness the majority of solar radiation in the visible range. As typical MFs,

BiFeO3 (BFO) and Bi2FeCrO6 (BFCO) have been recognized as potential materials for PV and visible-light PC

applications owing to their suitable band gap (1.4-2.8 eV) and good chemical stability. However, the investigations on

such materials for photocatalytic water splitting are still limited and efforts have to be undertaken to demonstrate their

full potential. An efficient PV system is at the basis on an effective PC process. Thus, the control of PV properties of

MFs is a critical issue for achieving highly efficient photocatalytic system. Here we will present, the controlled growth

and characterization of BFCO and BFO thin films and nanostructures via pulsed laser and hydrothermal techniques.

The PV properties of such systems and their photocatalytic activity will be also discussed
Insulator-Metal-Insulator-Semiconductor (IMIS) Photoelectrodes for Water Splitting
Authors: Esposito Daniel , Labrador Natalie Yumiko , Li Xinxin , Koberstein Jeffrey , Liu Yukun
Published: February 2020

One promising approach to achieving stable and efficient photoelectrochemical (PEC) water splitting is the composite photoelectrode architecture known as a metal-insulating-semiconductor (MIS) photoelectrode. [1,2,3,4]  Within the MIS design, metal catalyst is deposited on top of a thin insulating layer ( < 2 nm thick) that separates the metal from the semiconducting absorber layer. The insulating layer is particularly important because it can protect the underlying semiconductor from corrosion and avoid fermi-level pinning while still enabling efficient charge transfer between the semiconductor and metal through quantum mechanical tunneling. Through this composite design, the MIS architecture is able to decouple efficiency and stability, and has been applied to c-Si and InP photoelectrodes with great success in recent years, [1,2,3,4] For example, InP MIS photocathodes for the hydrogen evolution reaction have achieved photoelectrode conversion efficiencies up to 14%,[2] and n-Si MIS photoanodes have been demonstrated with stable operation in the highly oxidative environment of the oxygen evolution reaction for > hrs.[1]. Despite these encouraging results, further improvement in MIS photoelectrode performance is needed if this technology is to become commercially viable. In particular, improved photovoltage and maximized photo-current density generated by MIS photoelectrodes is essential for achieving DOE solar-to-hydrogen conversion efficiency targets.

            In this work, electrodeposition has been explored as a potentially low-cost and scalable means of depositing ultra-low loadings (1 to 20 ng cm-2) of Pt nanoparticles onto SiO2-covered p-Si photoelectrodes. As-deposited MIS photoelectrodes are found to exhibit very poor durability, but we describe how this issue can be overcome through application of a thin secondary insulating layer to form an insulator-metal-insulator-semiconductor (IMIS) geometry. Surprisingly, it is found that the secondary insulating layer also results in a substantial improvement in the fill factor and short circuit current of IMIS devices compared to MIS photoelectrodes of identical loading. The combination of electrodeposition with the IMIS architecture thus offers an exciting opportunity for improving both the efficiency and durability of photoelectrochemical energy conversion. After presenting a side-by-side comparison of MIS and IMIS photoelectrode performance, we highlight reasons for the differences in their performance.     

References:

[1] Y.W. Chen, P. McIntyre, et al., Nat. Mater., 10 (2011)

[2] M.H. Lee, et al., Angew. Chem. Int. Ed., 51 (2012).

[3] J.C. Lee, A. Bard, J. Ekerdt, et al., Nature Nanotech., 10, 84-90 (2015)

[4] D.V. Esposito,I. Levin, T.P. Moffat, and A.A. Talin.Nature Materials, 12, 562-568 (2013).
Improved Efficiency of Betanin-Sensitized Solar Cells Prepared with Electrophoretically-Deposited Nanoparticulate TiO2 Photoanodes and Reflective Pt Cathodes
Authors: Valdez-Nava Jesús Israel , Ortega-Díaz David , Feria-Socarras Isabel Virginia , Godínez Mora-Tovar Luis Arturo , Fuentes Rosalba , Méndez Perla Fabiola , Manríquez Juan
Published: February 2020

In this investigation we prepared betanin-sensitized solar cells by means of electrophoretically-deposited nanoparticulate TiO2 photoanodes and reflective Pt cathodes. This strategy allowed constructing improved betanin-based dye-sensitized solar cells having efficiencies of 8.8% (Eoc
=0.607V, ff=0.47). Our results indicated that, despite the surface coverages of betanins on the TiO2 films are typically low; the incident photon-to-current efficiencies which were obtained for the betanin-sensitized TiO2 photoanodes were significantly increased. This phenomenon was promoted due the photons of light were highly diffused when they passed through the electrophoretic-deposited TiO2 films, while a significant quantity of non-harvested photons on the dyed-TiO2 were forced to come back to these electrodes by optical reflection that took place on the Pt cathodes.
(Invited) Chalcogenide Tetrahedral Cluster Based Framework Materials for Photocatalytic Application
Authors: Feng Pingyun , Lin Qipu , Sasan Koroush , Chen Xitong , Mao Chengyu
Published: February 2020

The self-assembly of metal chalcogenide tetrahedral clusters can lead to a family of porous semiconducting materials with uniform pore sizes and high surface area. The single-sized tetrahedral clusters act as building blocks to form well-ordered three-dimensional superlattices in the presence of either organic or inorganic species (including optically active metal complexes) as structure directing agents. The structural analysis based on single crystals reveals detailed information that could help for the understanding of the unique optical and photocatalytic properties of the materials. The diversity of superlattices is achieved by modifying the cluster size, the cluster composition, and the inter-cluster linkage mode. The electronic band structures of the materials can be tuned over a wide range by controlling the chemical compositions and sizes of the clusters. Physical properties such as porosity and gas adsorption properties of the materials have been studied and will be presented. These porous semiconducting materials exhibit high surface area and uniform porosity. They can be used as photocatalytic materials for converting water and carbon dioxide into useful chemicals, as well as electrocatalytic materials for oxygen reduction reaction.
(Invited) Numerical Modeling of a Particle-Suspension Reactor for Solar Water Splitting
Authors: Bala Chandran Rohini , Breen Sasuke , Shao Yuanxun , Ardo Shane , Weber Adam Z
Published: February 2020

Sunlight-driven water splitting offers the potential to store and transport transient solar energy in the form of stable chemical bonds as hydrogen. Existing technologies for solar water splitting—multijunction photovoltaic systems coupled to water electrolyzers and photoelectrochemical cells—have demonstrated efficiencies up to 18%, but are not cost-competitive with hydrogen from fossil fuels on an energy density basis. Particle-suspension reactor designs consisting of microscale photocatalysts suspended freely in the electrolyte are projected to be cost-competitive with hydrogen from gasoline and hence motivate this study. Of specific focus here is a vertically stacked, particle-suspension reactor (see figure below) evolving hydrogen (HER) and oxygen (OER) in separate compartments in the presence of a redox mediator/shuttle via a Z-scheme mechanism. Porous separators between the two reactor vessels facilitate ion transport while attenuating crossover of product gases. The tandem design facilitates the use of wide bandgap semiconductors in the top compartment and relatively narrow bandgap materials in the bottom compartment. A transient, two-dimensional, computational model has been developed to simulate the coupled light absorption, species transport and electrochemical reactions in a unit cell of the proposed reactor. The model is used to identify reactor dimensions that reduce mass transport limitations of the redox shuttle and maximize incident light absorption. Sensitivity of model results to optical properties of the photocatalyst and species diffusivities are studied. Results indicate sustainable solar-to-hydrogen conversion efficiencies of at least 1% for a chosen reactor design in the absence of forced convection, which is not only feasible with state-of-the-art photocatalytic materials but is close to a value that could be reasonably cost competitive with hydrogen from fossil sources.

Acknowledgments: This work was supported by the Assistant Secretary for Energy Efficiency and Renewable Energy, Fuel Cell Technologies Program of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231 and University of California, Irvine under award no DE-EE0006963.

Figure 1
Controlling the Product Syngas H2:CO Ratio through Pulsed Bias Electrochemical Reduction of CO2 on Copper
Authors: Kumar Bijandra , Brian Joseph Patrick , White Robert , Kumari Sudesh , Spurgeon Joshua M
Published: February 2020

Copper is one of the most commonly studied materials for the electrochemical conversion of carbon dioxide (CO2) into valuable chemical products. Numerous efforts have been made to enhance the product selectivity - an important characteristic essential for efficient chemical production from CO2 - of Cu with only marginal progress. Here, we introduce a pulsed-bias technique for the electrochemical reduction of CO2 on Cu catalyst which led to 100% selectivity for CO formation over other carbon products and only produced syngas (CO + H2). X-ray photoelectron spectroscopy (XPS) and controlled CO2 electrochemical reduction experiments suggest that in-situ oxidation and reduction of the Cu causes the preference for CO formation over other carbon products on polycrystalline Cu. Moreover, the observed pulse waveform dependency of the H2 to CO product ratio can also be beneficial by allowing tunable CO2 reduction products as a controllable syngas feedstock for different industrial applications (e.g., Fischer-Tropsch process, and hydroformylation of alkenes to aldehydes) without an additional hydrogen source. This study opens a new route for the selective conversion of CO2 into syngas on robust and cost-effective Cu catalysts, which could be adopted at large scale in the chemical industry. 

Keywords: Copper, Catalyst, CO2reduction, Syngas, Selectivity, Electrochemistry
Efficient Solar Water Splitting Via Tunable Photoanode-Photocathode-Catalyst Interface Devices
Authors: Porter Spencer H , Hwang Shinjae , Li Mengjun , Yakshinskiy Boris , Amarasinghe Voshadhi , Taghaddos Elaheh , Laursen Anders B. , Gardner Graeme , Manichev Viacheslav , Safari Ahmad , Garfunkel Eric , Greenblatt Martha , Dismukes Gerard Charles
Published: February 2020

Current photoelectrochemical devices for water electrolysis suffer from low stability and efficiency. Aims to address both those needs have been realized using a system that uses two sequential solar light absorbers (semiconductors) — in conjunction with oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) catalysts. Each absorber has a built-in electric field (band-bending) achieved by doping to allow matching of valence (VB) and conduction (CB) band energy levels to the electrochemically required OER and HER potentials. To improve charge separation efficiency and lifetime, methods for creation of thin films of OER (LiCoO2) and HER (Ni-P) catalysts have been developed. The OER catalyst is coupled to a mid bandgap light absorber (~1.7-2.5 eV), while the photocathode is comprised of the Ni-P on p-Si (100). During device fabrication, interfacial effects and surface morphologies for each electrode were analyzed by x-ray photoelectron spectroscopy, atomic force microscopy, helium ion microscopy, x-ray diffraction, and Rutherford backscattering. Photoelectrochemical measurements inclusive of faradaic efficiency and IPCE for each electrode individually as well as a single overall water splitting device have been measured. Various device architectures are considered and discussed to achieve the most cost-effective PEC design.

Figure 1
Uniform Porous Multilayer-Junction Thin Film for Enhanced Gas-Sensing Performance
Authors: Sun Xuhui , Zhang Pingping , Zhang Hui
Published: February 2020

Highly-uniform In2O3/CuO bilayer and multilayer porous thin films were successfully fabricated using self-assembled soft template and simple sputtering deposition technique. The sensor based on the In2O3/CuO bilayer porous thin film shows obviously improved sensing performance to ethanol at the lower working temperature, compared to single layer counterpart sensors. The response of In2O3/CuO bilayer sensors exhibit nearly 3 and 5 times higher than those of the single layer In2O3 and CuO porous film sensors over the same ethanol concentration, respectively. The sensing mechanism based on p-n hetero-junction, which contributed to the enhanced sensing performance was also experimentally confirmed by a control experiment which the SiO2 insulation layer was inserted between the In2O3 and CuO layers to break the p-n junction. In addition, the sensing performance can be further enhanced by increasing the number of In2O3/CuO junction layers. The facile process can be easily extended to the fabrication of other semiconductor oxide gas sensors for practical sensing applications.