bluuebunny/crossref_metadata_2025 huggingface dataset:
Surface-Enhanced Raman Spectroelectrochemistry with Screen-Printed Electrodes for Quantitative Analysis
Authors: Fanjul Bolado Pablo , Martín Yerga Daniel , Junquera Pérez Alejandro , González García María Begoña , Hernández Santos David
Published: February 2020

Electrochemically roughened silver surfaces have been widely employed for Surface-enhanced Raman scattering (SERS) assays. In most cases, the roughening process is usually performed ex situ with a specific electrolyte solution and, afterwards, the analyte is adsorbed on the substrate for the detection. This procedure has several possible issues: the final state of the substrate could not be the optimum for enhancing the SERS effect, the surface could become passivated between the roughening and the detection steps, decreasing the SERS activity, and the step for the analyte adsorption could take several minutes. Moreover, one of the main issues of SERS-based assays is the reproducibility between experiments and these substrates have been mainly used for qualitative studies. However, there is a strong scientific interest for increasing the applicability of SERS assays for quantitative studies with reproducible and simple methods. Screen-printed electrodes could be promising SERS substrates because they are mass-fabricated using the well-established thick-film technology leading to precise, disposable, low-cost and easy-to-use devices.

In this work, the real-time in situ electrochemical roughening of readily-available metal screen-printed electrodes is proposed to obtain a quantitative and precise SERS detection of several species at low concentrations using a fast and cost-effective methodology. The roughening and the analytical detection are carried out simultaneously, solving the typical issues of the ex situ preparation. The time-resolved character of this method allows to get dynamic information about the processes leading to a SERS active substrate and correlate them with the microscopic electrode structure at various stages of the substrate preparation. Results show a good linearity between the SERS signals and low concentrations of several species with a good precision between measurements.
Probing Photoelectrochemical Performance and Corrosion at the Nanoscale with Electrochemical Scanning Probe Techniques
Authors: Simpson Burton H. , Mazza Michael , Yu Weilai , Lewis Nathan S
Published: February 2020

Materials of nanoscale thickness are widely being explored as strategies for enhancing the performance and stability of photoelectrochemical cells for solar energy conversion. 2D materials such as graphene and transition metal dichalcogenides have shown promise as protecting layers and catalysts for photoelectrochemical cells. Atomic layer deposition techniques can be used to deposit metal oxides that function as ultrathin catalysts or protecting layers. While approaches using 2D materials or ALD often show improved performance, the challenge of analyzing nanoscale materials in operando often means that there is little direct evidence of why ultrathin layers can profoundly differ in catalytic performance or why protecting layers suddenly and catastrophically fail. Here, we present ongoing examples from our lab in which we are using recently developed techniques based on scanning electrochemical microscopy to mechanistically explore mechanisms of catalysis and corrosion on operating photocatalysts. Using microscale anodic stripping voltammetry, scanning electrochemical cell microscopy, and surface interrogations alongside traditional scanning electrochemical microscopy, we are elucidating the structure̶ function relationships governing the performance of both 2D materials and ALD layers at the semiconductor/electrolyte interface. By understanding how ultrathin materials behave differently from bulk materials, our conclusions can facilitate their integration into photoelectrochemical cells.
Shedding Light on Single Nanoparticle Electrochemistry: Combined Optical and Electroanalytical Methods for Correlating Structure and Reactivity
Authors: Hill Caleb M. , Saha Partha , Walmsley Joshua
Published: February 2020

The inherently heterogeneous nature of nanoparticles (NPs) presents a significant challenge for fundamental studies into relationships between structure and reactivity. Utilizing analytical methodologies which probe individual NPs is a promising approach to overcoming this challenge. To this end, analytical methods which utilize correlated electroanalytical and optical measurements have been developed which enable detailed studies into the electrochemical reactivity of individual NPs. Scanning electrochemical cell microscopy (SECCM) is employed to directly measure the rate of electrochemical reactions at individual NPs, while optical spectroscopy is used to probe the structure of these particles in situ. This enables the correlation of electrochemical kinetic data with particular NP structures, providing valuable insights into structure-function relationships for a given electrochemical process. Additionally, in situ spectroscopic measurements facilitate investigations into the mechanisms responsible for transient changes in electrochemical reactivity (e.g., catalyst deactivation). Initial studies applying the described methods to model electrocatalytic systems will be presented.
Rotating Ring-Disk Electrode Study of the Electrochemical Dehalogenation of Iodinated Contrast Media
Authors: Korshin Gregory V , Yan Mingquan , Zhang Chenyang
Published: February 2020

Iodinated contrast media (ICM) occur widely in the environment and are difficult to remove by conventional water treatment methods because of ICMs’ hydrophilicity and resistance to biodegradation. ICMs have also been shown to be precursors of toxic reaction products, notably iodine-containing trihalomethanes and haloacetic acids. This study examined the performance of an alternative method of ICM degradation, notably their electrochemical (EC) reduction. ICMs used in this study were exemplified by iopamidol and diatrizoate. The method of rotating ring-disc electrode (RRDE) was used to elucidate rates and mechanisms of the EC reactions of the selected ICMs. Experiments were carried at varying hydrodynamic conditions, concentrations of iopamidol, diatrizoate, natural organic matter (NOM) and model compounds (resorcinol, catechol, guaiacol) which were used to examine interactions between products of the EC reduction of ICMs and halogenation-active species. The data showed that iopamidol and diatrizoate were EC-reduced at potentials < -0.45 V vs. s.c.e. In the range of potentials -0.65 to -0.85 V their reduction was mass transfer-controlled. The presence of NOM and model compounds did not affect the EC reduction of iopamidol and diatrizoate but active iodine species formed as a result of the EC-induced transformations of these ICMs reacted readily with NOM and model compounds. These data provide more insight into the nature of generation of iodine-containing by-products in the case of reductive degradation of ICMs.
Low-Voltage Reversibly Switchable Wettability through Electrochemical Manipulation of Oxidation State
Authors: Kung Chun Haow , Zahiri Beniamin , Sow Pradeep Kumar , Mérida Walter
Published: February 2020

Various biological organisms in nature exhibit unique surface wettability in order to adapt to their living environment. Diverse range of wettability can be observed, ranging from the low-adhesion superhydrophobic lotus leaf with self-cleaning property, high-adhesion superhydrophobic gecko foot, to the in-air superhydrophilic and underwater superoleophobic fish scale. Inspired by these natural systems with superwetting/antiwetting properties, significant efforts have been devoted to fabricate artificial surfaces with different wettabilities by engineering the surface morphology and chemical composition. Of particular interest is the stimuli-responsive surface which integrates two extreme wetting states of water-attracting and water-repelling properties. External stimuli such as temperature, light, pH, and electrical potential could induce reversible changes in the wetting behavior of the smart surface through transformation in the topological structure and/or surface chemistry. Here we present a novel approach for reversible wettability cycling on dendritic core-shell copper nanostructure surface through electrochemical modulation of the oxidation state. Application of low voltage in the range of regular alkaline battery (<1.5 V) converts the as-prepared copper-based surface from roll-off superhydrophobic, to sticky superhydrophobic, and superhydrophilic wetting state. Precise control over the rate and extent of the wetting switching is achieved by tuning the magnitude and period of the applied voltage. Air drying at room temperature for 1 hour or mild heat drying at 100°C for 30 min reverses the wettability transition to initial superhydrophobic state with low adhesion easy roll-off property. We describe the underlying mechanism for the reversible adhesion and wettability switching from the physical and electrochemical perspectives, as well as practical applicability of this method with specific demonstration for on-demand oil-water separation. The in-situ adhesion and wettability control reported in this work provide a platform for design of oxidation state-mediated wetting transition on different metal oxides for application in remote water filtration, atmospheric water harvesting, droplet manipulation, and microfluidic lab-on-a-chip application.
Experimental Validation of the Transmission Line Model Via Impedance Spectroscopy of an Ordered Array on Porous Carbon Electrode
Authors: Sharma Trishank , Díaz-Real Jesús Adrián , Zahiri Beniamin , Mérida Walter
Published: February 2020

In this paper, the interface of a porous substrate with an arranged and well-defined geometry is investigated for the impedance response with different electrolytes by using the well known electrochemical technique of Electrochemical Impedance Spectroscopy (EIS). Based on De Levie's Transmission Line Model (TLM) for porous electrodes a modification has been done in the model by incorporating the CPE behavior to reflect the non-ideal behaviour for real electrodes at low frequencies. The geometry used to validate the proposed model was fabricated from a smooth Glassy carbon electrode (GCE) surface to correlate the EIS response to that obtained by the model. The desired array was obtained by using laser micromachining tool on a glassy carbon substrate with a goal to study the influence of different electrolytes, varying electrolyte concentrations, the morphological features of pore- depth and radii of pore as well as different pore shapes.

The outcomes of the experiments carried out on the in-house setup are compared with the MATLAB simulated results of the impedance. The transition from resistive to capacitive behavior is found to be shifted to lower frequency side and TLM behavior at high frequencies is more apparent as the concentration is increased. For the same concentration, different electrolytes are found to behave differently due to varying conductivity and ion sizes. In all the experiments carried out the impedance response showed CPE (constant phase element) behavior at the low frequency end while for high frequencies the nature/appearance of TLM behavior is found to be dependent on the pore depth to radius ratio. In addition the concept of time constant is also dealt with which exhibits differences for different geometries of the pores on glassy carbon. The results suggest that the GC electrode engaged here could provide a tractable model for studying electrochemical impedance behavior of porous electrodes without using any surface area analysis or pore volume analysis technique.

Keywords: Transmission Line Model, Glassy carbon, EIS, MATLAB
(Invited) Platinum Nanotubes and Platinum Thin Layers on Nanowires As Electrocatalysts
Authors: Yan Yushan
Published: February 2020

PEMFCs are attractive for powering cars because of their high efficiency, high power density, and zero emission. The biggest barrier to the widespread deployment of PEMFC cars has been the cost and durability of the Pt catalysts. Early Pt catalysts were large Pt particles that had high specific activity and durability, but were clearly not economical due to the very low specific surface area. To develop an economical Pt catalyst the effort has been focused on Pt nanoparticles (PtNP). To increase mass activity, the ultimate measure of cost, the prevailing wisdom for a long period of time was to increase specific surface area by reducing the diameter of the PtNP. However as the diameter of PtNP decreases the specific activity also reduces, leading to unchanged or even lower mass activity. Small PtNPs are also not durable due to dissolution, aggregation and Oswald ripening15. To overcome this difficult tradeoff between high specific activity-low specific area (as in Pt macrowires and macroparticles) and low specific activity -high specific area (as in PtNP of 2-3 nm diameter), we have been working on the concept of Pt nanotubes (PtNTs) and their derivatives that can exhibit the favorable features of the Pt macrowires/macroparticles (high specific activity and durability) and the PtNPs (high specific activity) in the same structure15. We later made porous PtNTs to increase the Pt utilization17; replaced the Ag nanowire (AgNW) template15 with CuNWs to reduce cost18
,
19; and synthesized Pt thin layer on CuNWs (Pt/CuNWs) to improve mass activity further.18
,
19
(Invited) Fabrication and Operation Under the Same Conditions: Oxygen Reduction on Cathodically Deposited Manganese Oxide
Authors: Pugolovkin Leonid V. , Levin Eduard E. , Savinova Elena R. , Tsirlina Galina A.
Published: February 2020

We present the data on the oxygen reduction (ORR) and oxygen evolution (OER) in an alkaline solution for manganese oxide electrocatalysts fabricated by means of cathodic electrocrystallization. The catalysts are deposited from a permanganate alkaline bath, and later operate in the same 1 M NaOH medium. The effect of the deposition potential is addressed. The goal of the study is to obtain carbon-free oxide electrocatalysts with satisfactory activitiy and stability.

A qualitative difference of the electrochemical behavior is observed for oxides deposited at low (potentials above ~0.75 V RHE, region 1) and at higher overvoltage (potentials below ~0.75 V (RHE) region 2). Current efficiency is close to 40% in region 1, and increases up to 60% in region 2. All the samples consist of delta-MnO2 (birnessite), but their microstructure is essentially different for electrodeposition from regions 1 and 2. For the deposits fabricated in region 2 the birnessite structure is slightly distorted, while for the deposits prepared in region 1 a complete disordering along the layer stacking direction is observed.

The voltammograms of oxides in supporting electrolyte solution undergo fast evolution under potential cycling, accompanied by a decrease of the total charge. Stabilized voltammograms for the samples fabricated in region 2 are featureless and demonstrate a pronounced Ohmic contribution, while for the samples deposited in region 1 a reversible redox behavior is observed, with broad current peaks and formal potential of ~ 0.85 V RHE. The total charge is proportional to the oxide loading in the interval under study (~ 10 – 90 mkg/cm2). Both types of samples do not exhibit reductive degradation at potentials above 0.7 V (RHE).

ORR activities are estimated from the rotating disc electrode data in an O2-saturated solution. For oxides fabricated in region 1 the kinetic currents at 0.85 V RHE approach 40-50 A/g (for intermediate loadings), making them promising binder-free ORR catalysts. The ORR activity of oxides electrodeposited at higher overvoltages is an order of magnitude lower corroborating the influence of structure on the electrocatalytic activity. Even though the OER activities of electrodeposited oxides at 1.63 V RHE do not exceed 3 A/g, their remarkable stabilities both in the ORR and in the OER potential interval allows one to hope that these materials may be of interest as a component of hybrid bi-functional catalytic compositions together with other oxides more active in the OER.

The authors are grateful to Yu.A. Velikodnyi and A.Ye. Baranchikov for their help with structural characterization of the samples. The work is supported by EraNetRus program, project (#270 NANO-Morf).
Adsorption of Methane at Platinum Electrodes Under Potentiodynamic Control at Ambient Conditions, and Characterization of Adsorbed Intermediates Via ATR-FTIR Spectroscopy
Authors: Boyd Michael James , Jaramillo Thomas F
Published: February 2020

Electrochemical oxidation of methane is a promising route towards the direct production of high value oxygenates such as methanol, formaldehyde, and formic acid. Compared to traditional catalytic processes such as methane steam reforming and Fischer-Tropsch reactions that operate at high temperatures and pressures, electrochemical oxidation of methane has the benefit of operating at ambient temperatures and pressures. However, there are still many challenges associated with electrochemical methane oxidation including catalyst activity and selectivity. Previous work has established platinum as one of the few catalysts able to oxidize methane to CO2 at room temperature and pressure. By applying a constant potential within the capacitance region of platinum in methane saturated aqueous electrolytes an ad layer can be built up on the platinum surface. The adsorbed intermediates can then be stripped from the platinum surface by sweeping to more anodic potentials. In this work, the aforementioned electrochemical methods are coupled with in-situ infrared spectroscopy to identify reaction intermediates and determine their dependence on applied potential, pH, and time. Improving our understanding of the mechanism of methane oxidation on platinum is necessary for the design of more active and selective catalysts. With better catalysts, fuel cell technologies could allow for the utilization of stranded natural gas for the production of electricity and oxygenates.
An Investigation of the Adverse Effect of TiO2 on Pt-Catalyst for the Oxygen Reduction Reaction
Authors: Miller Todd , Mukerjee Sanjeev , Jia Qingying
Published: February 2020

Northeastern University Center for Renewable Energy Technology (NUCRET), 317 Egan Center, Northeastern University, 360 Huntington Avenue, Boston, MA 02115

Metal oxides have long been used to protect carbon supports from corrosion on the anode side of a fuel cell during fuel starvation, when the metal oxides serve as a catalyst for water hydrolysis it protects the carbon supports from corrosion. Titanium dioxide (TiO2) is commonly used on the anode, and known to be effective at protecting the carbon from corrosion. However, we recently found that mechanically mixing Pt/C with some TiO2 as the anode catalyst of a PEMFC leads to a significant drop of the cell performance at a very early stage of operation. Subsequent efforts to understand the phenomenon led to the finding that the even a small amount of TiO2 seriously poison the Pt/C catalyst for the oxygen reduction reaction (ORR) by reducing the half wave potential by more than 150 mV (Figure 1), whereas the HOR rate was not significantly affected. By combing ex situ and in situ characterizations and detailed electrochemical testing, we provide solid experimental evidence for the unexpected TiOx–induced poisoning effect, which largely accounts for the activity loss. The new findings of the interactions between the Pt/C and the metal oxide help to pursue metal oxides that are better at protecting the carbon from corrosion while minimizing the poisoning effects.

Acknowledgement:

The authors gratefully acknowledge the financial support of Automotive Fuel Cell Corporation (AFCC), Canada and Ford Motor Co., Detroit, MI (under a URIP program). The authors also acknowledge instrumental support from Thermo Fisher Corp., and access to synchrotron based facility for x-ray absorption spectroscopy at National Synchrotron Light Source-II (NSLS-II) situated in Brookhaven National Laboratory (BNL), Upton, NY, under grant # DE-SC0012704

Figure 1
The Structural Effect of Pd-H Catalysts on Synthesizing Temperature for Direct Alkaline Formate Fuel Cell
Authors: Hong Sujik , Hwang Hongsun , Lee Jae Kwang , Lee Jaeyoung
Published: February 2020

Direct liquid fuel cells (DLFCs) have been received much attention due to its safety, transportation, storage and utilization. Among them, the formate (HCOO-) as a fuel have more attracted due to its faster oxidation kinetics compared with formic acid (HCOOH) in optimal pH and higher theoretical voltage compared with the methanol and the ethanol.[1-3] Furthermore, the HCOO- has being predominant form in alkaline media and there has been no poisoning effect on palladium (Pd) catalyst on the oxidation of HCOO- such as carbon monoxide which is the inevitable species as the oxidation of formic acid and HCOO- on platinum (Pt). In the point of view of mechanistic study, decreasing the chemisorption strength of the adsorbed hydrogen (Hads) plays a key role in determining the enhanced catalytic activity of the oxidation of HCOO- on Pd, since the desorption of Hads is rate-determining step (RDS) of the oxidation of HCOO- on Pd so that it blocks an active site of the adsorption of HCOO-.[4] By alloying Pd and other transition metal such as copper (Cu) or gold (Au), the adsorption strength on Pd has been weakened through the d-band of Pd has been more filled due to the electron transfer from other transition metal to Pd.[5] In addition, the adsorption strength on Pd can be also weakened by the electronic effect that the d-band of Pd is more filled by electrons of heteroatoms such as hydrogen (H) and boron (B) entered to Pd lattice.[4,6]

In previous study [4], we had synthesized Pd-H catalyst on the carbon powder via sodium borohydride as a reducing agent and observed enhanced catalytic activity of the oxidation of HCOO- despite of the large particle size compared with that of commercial Pd/C. Because the morphology is also deeply related to the catalytic activity, we have investigated the correlation between structural changes such as dispersity or particle size and catalytic activity of the oxidation of HCOO- by controlling synthesizing temperature. In this study, we have synthesized Pd-H catalyst using a characteristic of lattice on the carbon powder of in accordance with temperatures and comparing their surface, particle size, crystal structure and catalytic activity of the oxidation of HCOO- using electrochemical method and physicochemical analysis.

Refrerences

J. Joo et al., ACS catalysis, 2015, 5, 6848.

S. Uhm et al., Angewandte Chemie, 2008, 120, 10317.

S. Uhm et al., Physical Chemistry Chemical Physics, 2009, 11, 9326.

M. Choun et al., Catalysis Today, 2017, 295, 26.

O. Yepez et al., International Journal of Hydrogen Energy, 2002, 27, 99.

C.W.A. Chan et al., Nature Communication, 2014, 5, 5787.

Figure 1
(Invited) Developing Electrocatalysts for Ethanol Oxidation Reaction in Alkaline Media
Authors: Cai Wen-Bin
Published: February 2020

The ethanol oxidation reaction (EOR) has drawn increasing interest in electrocatalysis and fuel cells by considering that ethanol as a biomass fuel has advantages of low toxicity, renewability, and a high theoretical energy density compared to methanol. Alternatively, the ethanol electroreforming is a low energy cost technology that may produce valuable chemicals in the anode and clean hydrogen in the cathode at low temperature and atmospheric pressure. In both of the above energy conversion and storage technologies, the efficient oxidation of the ethanol in the anode by means of electrocatalysis is essential and the efficiency is largely determined by the chosen catalysts. Notably, in alkaline media both Pt and Pd show enhanced EOR activities.

The mechanistic investigation as well as the rational design of electrocatalysts are challenging yet essential for the desired complete oxidation to CO2, in considering that EOR is a complex multiple-electron process involving various intermediates and products. This talk starts with discussion on the mechanistic understanding of EOR on Pt and Pd surfaces using selected publications as examples. Consensuses from the mechanistic studies are that sufficient active surface sites to facilitate the cleavage of the C–C bond and the adsorption of water or its residue are critical for obtaining a higher electro-oxidation activity. I will then show by cases how this understanding has been applied to achieve improved performance on Pt- and Pd-based catalysts for EOR in alkaline media through optimizing electronic and bifunctional effects, as well as by tuning their surface composition and structure.

Acknowledgements
：Financial support from the NSFC (grant No. 21733004 and 21473039）and the 973 Program (No. 2015CB932303) of MOST is highly appreciated

References

[1] Y. Wang, S.Z. Zou, and W. B. Cai, Catalysts, 5, 1507 (2015).

[2] Y. Y. Yang, J. Ren, Q. X. Li, Z. Y. Zhou, S. G. Sun and W. B. Cai, ACS Catal., 4, 798(2014).

[3] H. Wang, K. Jiang, Q.L. Chen, Z.X. Xie, W.B. Cai, Chem. Commun., 52, 374(2016).

[4] T. T. Zhao, H. Wang, X. Han, K. Jiang, H. X. Lin, Z. X. Xie and W. B. Cai, J. Mater. Chem. A, 4, 15845 (2016).

[5] W. J. Huang, X. Y. Ma, H. Wang, R. F. Feng, J. G. Zhou, P. N. Duchesne, P. Zhang, F. J. Chen, N. Han, F.P. Zhao, J.H. Zhou, W.B. Cai and Y.G. Li, Adv. Mater. 29 (2017). DOI: 10.1002/adma.201703057.

[6] X.Y. Ma, Y.F. Chen, Q.X. Li, W.F. Lin, W.B. Cai, to be submitted.
Metal Ion Cycling of Cu Foil for Selective C-C Coupling in Electrochemical CO2 Reduction
Authors: Jiang Kun , Sandberg Robert , Chan Karen , Wang Haotian
Published: February 2020

Electrocatalytic CO2 reduction to higher value hydrocarbons beyond C1 products is desirable for applications in energy storage, transportation, and the chemical industry. Cu catalysts have shown the potential to catalyze C-C coupling for C2+ products, but still suffer from low selectivity in water.1 Here we use density functional theory to determine the energetics of the initial C-C coupling steps on different Cu facets in CO2 reduction, and suggest that the Cu(100) and stepped (211) facets favor C2+ product formation over Cu(111). To demonstrate this we report the tuning of facet exposure on Cu foil through the metal ion battery cycling method. Compared to the polished Cu foil, our 100-cycled Cu nanocube catalyst with (100) facets exposed presents a 6-fold improvement in C2+ to C1 product ratio, with a highest C2+ Faradaic efficiency of over 60 % and H2 below 20 %, and a corresponding C2+ current of more than 40 mA/cm2.2

References:

(1) Hori, Y., Takahashi, I., Koga, O. & Hoshi, N. J. Mol. Catal. A Chem.
199, 39-47 (2003).

(2) Jiang, K., Sandberg, R.B., Akey, A.J., Liu, X., Bell, D.C., Nørskov, J.K., Chan, K. & Wang, H. Nat. Catal. in press (2018).
Understanding the Mechanisms of Photosynthetic Electron Transport for Energy Conversion Applications
Authors: Ramasamy Ramaraja P.
Published: February 2020

Light energy can be harnessed using photosynthesis for either direct generation of electricity or production of energy rich fuels such as ethanol, propanol, butanol of hydrogen in photo-bioelectrochemical cells (1). A photo-bioelectrochemical cell (PBEC) based on natural photosynthesis is composed of an anode containing a photo-biocatalyst such as photosystem II, thylakoid membrane, or whole cell microorganism such as cyanobacteria coupled with an enzymatic cathode. With the help of light, the photo-biocatalyst on the anode oxidizes water to generate electrons and protons. On the cathode, enzymes such as laccase or bilirubin oxidase are employed to catalyze the reduction of oxygen and protons to water. When such anodes are coupled with cathodes containing enzymes such as hydrogenase or nitrogenase, the system generates hydrogen. In either case, water and light are the only raw materials used to generate electricity or hydrogen. The photo-biocatalysts on the anode utilize the photosynthetic light reactions to generate electrons and deliver them to the anode via either direct or mediated electron transfer. The electron transfer mechanisms of the light reactions determine the pathways for electron delivery to the anode, which in turn determines the photocurrent density, stability and overall conversion efficiency of the process. This talk will overview our research over the years on the understanding of the photosynthetic light reactions and the underlying pathways through which the electrons are channeled to the anode.
Stainless Steel-Based Bioanodes for Applications in Bioelectrochemical Systems
Authors: Fontmorin Jean-Marie , Hou Junxian , Head Ian , Scott Keith , Yu Eileen
Published: February 2020

The majority of studies focusing on bioelectrochemical systems (BES) report the utilization of carbon-based electrodes. However, in order to overcome the limitations related to the scale-up of Microbial Fuel Cells (MFC) and Microbial Electro Synthesis (MES) cells technologies, the utilization of metal-based electrodes need to be considered due to their conductivity, cost and robustness. Stainless steel fiber felts (SSFF) as bioanode material for BES applications was investigated in this study. The unmodified SSFF was tested alongside with electrodes modified with reduced graphene oxide (rGO), magnetite nanoparticles (Fe3O4), manganese oxide (MnO2) and flame-oxidation (FO). The performance of the metal-based electrodes as bioanodes were investigated in half-cells in terms of stability and current densities. In addition, the impact of the capacitance of the abiotic electrode materials on the performance of the bioanodes and MFCs was evaluated (Fig. a), especially to assess how these materials can increase the energy harvested compared to non-capacitive bioanodes. The results showed that the stainless steel- based electrodes studied are competitive alternatives to the carbon-based electrodes. Current densities recorded in half-cells were 1.96, 1.95 and 2.26 mA/cm2 for FO-MnO2-SS, rGO-SS and carbon cloth, respectively. In addition, charge/discharge experiments carried out with the bioanodes developed (Fig. c) showed that the modified SSFF electrodes allow the storage of electrical charge from the biofilm to the capacitive layers of the electrodes when cells are left at open circuit potential (OCP). These results demonstrate the potential of these materials for energy generation and storage applications from waste in BES.

Figure 1
On-Chip Enzymatic Microbiofuel Cell-Powered Integrated Circuits
Authors: Mano Nicolas
Published: February 2020

In situ energy harvesting is a major limitation for the development of implantable biomedical digital devices. Considerable efforts have been made to improve Glucose/O2 Enzymatic Biofuel Cells (EBFCs), able to generate electrical power in the physiological environment, in order to match the demands of biomedical electronics [1]. A key advance was the development of redox hydrogels. They permit efficient connection of high amounts of oxidoreductases to electrodes, leading to easily miniaturizable BFCs with power densities in the range of 100 μW.cm-2 suitable for application [2]. However, their open circuit potentials still fall below the requirements of conventional electronics. On the other hand, the power and voltage demands have decreased thanks to tremendous progress in low-power electronics [3], rendering devices compatible with the performance of EBFCs.

Here we demonstrate that common data processing functions such as binary counting can be powered by a glucose/O2 micro-EBFC directly integrated on an Application Specific Integrated Circuit (ASIC) at the die level. An EBFC based on Glucose Oxidase and Bilirubin Oxidase hydrogels immobilized on 400 μm diameter electrodes was designed on the Si chip of the 4-bit ripple-counter. The system could be continuously powered during several hours from a single 50 μL droplet of aerated 5mM glucose solution.

1] S. Cosnier, A. Le Goff, M. Holzinger, Electrochem. Comm., 2014, 38, 19-23.

[2] N. Mano, F. Mao, A. Heller, JACS, 2003, 125, 6588-6594.

[3] A. Chandrakasan, N. Verma, D.C. Daly, Annual Rev. Biomed. Eng., 2008, 10, 247-274.
Hybrid Non-Enzymatic and Enzymatic Cascade Bioanode for Glycerol/O2 Biofuel Cell Applications
Authors: Arugula Mary , Pinchon Erica , Lindstrom Ulf , Juzang Patria , Pant Kapil , Minteer Shelley D. , Singhal Sameer
Published: February 2020

Enzymatic biofuel cell technology has demonstrated the possibility of producing electrical power from chemical energy using biological catalysts for powering portable and implanted electronic devices. However, this technology has been limited by insufficient power and shell life compared to existing commercial, non-biological fuel cells. During the last 20 years, significant advancements have been made in improving the overall performance of the biofuel cells with incorporation of hybrid nanostructures including carbon and metal based nanomaterials and combination thereof with enzymes. Typically, biofuel cell cathodes utilize a single enzyme system, while a cascade of reactions for deeper and more complete oxidation of fuel is frequently necessary at the anodes. Here, we present the feasibility of using glycerol for the development of alcohol based biofuel cell. For the first time, the biofuel cells were extended via the assembly of hybrid enzymatic anode and bilirubin oxidase (BOx) biocathode. The hybrid anode was integrated with non-enzymatic oxidation of glycerol by inorganic nanoparticles and enzymatic nanocomposite conversion of final byproduct to achieve a cascade of efficient energy conversion from glycerol. The constructed mediator-less and membrane-less biofuel cell demonstrated maximum open circuit potential (OCV) greater than 600mV, power output of 0.7mW/cm2 and maximum current density of 3.0mA/cm2 with 0.1M glycerol at neutral pH. The fuel cell demonstrated remarkable discharge capacity of 600mAh/g under 0.25mA constant current load. The enzymatic/non enzymatic hybrid strategy can be further extended to develop other alcohol based biofuel cells.
(Invited) First-Principles Design of Mixed Proton-Electron Conductors for Solid-Oxide Fuel Cell Electrodes
Authors: Pavone Michele
Published: February 2020

Electrolyzer and fuel cells based on proton-conducting solid oxides (PC-SOEC/FC) are gaining ground in the energy conversion scenario, thanks to fast proton diffusion rates at convenient operating temperatures. However, current performances are curbed by severe limitations of common electrodes [1]. Within this context, here we outline the latest work of our group on the rational design of innovative electrode materials for PC-SOEC/FC applications. With first-principles methods we aimed at providing unbiased explanations and predictions of materials properties and functions, so to assess new design principles based on quantum mechanics.

The desired electrode materials for PC-SOEC/FCs should pair mixed proton/electron conductive (MPEC) features to good catalytic activity. We followed two design strategies: induction of proton conduction to mixed ion-electron conductors to obtain triple conducting oxides [2] or induction of electronic conduction on well-known proton conductor materials [3]. To this end, in bulk solids we evaluated oxygen vacancy formation and water uptake enthalpies, and we characterized the minimum-energy path for proton migration and the corresponding barrier heights. Then, we investigated the catalysis associated to the four proton-coupled electron transfer processes for the oxygen evolution reaction (OER) and reverse oxygen reduction reaction (ORR) at the electrode surfaces. Our calculations revealed the structural and electronic features than are needed for an effective bifunctionality towards the OER and ORR.

Our findings can trigger the targeted experimental synthesis and testing of new single-phase electrodes and can enable the deployment of reversible proton-conducting SOEC/FC devices. Moreover, our analysis can be exploited for the rational design of bifunctional electrocatalytic systems with similar key characteristics.

[1] L. Bi, S. Boulfrad, and E. Traversa, Chem. Soc. Rev. 43 (2014) 8255.

[2] A. B. Muñoz-García and M. Pavone, Chem. Mater. 28 (2016) 490

[3] A. B. Muñoz-García, M. Tuccillo, and M. Pavone, J. Mater. Chem. A 5 (2017) 11825
The Ionic and Water Transport Properties Studies of Univalent Ion Exchanged Perfluorosulfonate Membrane
Authors: Peng Jing , Goenaga Gabriel A. , Zawodzinski Thomas A
Published: February 2020

Perfluorosulfonic acid (PFSA) polymer membranes have been widely studied in the context of their applications as ion exchange medium/solid electrolytes in proton exchange membrane (PEM) fuel cells and other redox applications since 1970s(1). Water management plays a significant role in the performance of polymer membrane electrolytes, especially in fuel cells, because the ionic conductance dramatically decreases at low relative humidity, while excess water may flood the flow channels and hinder the transport of reagents such as gases (2). The conductivity and water diffusion coefficient of membranes therefore are always of concern because of their function in electrochemical devices.

In this work, Li+, Na+, NH4
+ and TEA+ form PFSA membranes were prepared based on H-form 3M PFSA membrane. The water uptake, density and conductivity of these membranes were investigated at various hydration levels. It’s found that the hydrophilicity of cations determines the water uptake of membranes with different cations, showing a series of water uptake in the order of: H+ > Li+ > Na+ > NH4
+ > TEA+. As expected, H+ form membranes show the highest conductivity among all membrane forms due to the smallest charge carrier size and proton hopping transport mechanism. This mechanism may also contribute for NH4
+ transport, resulting in a comparably high conductivity of NH4
+ form membranes even though the latter take up much less water. Pulsed field gradient (PFG) Nuclear Magnetic Resonance (NMR) was exploited to observe the diffusion coefficient of water in the membranes. It was observed that hydrophilicity of cations and the hydrogen bonding interactions affect the water transport in the membranes. Based on density measurements, a partial molar volume analysis is carried out in this study. This parameter provides insight into the water and polymer interactions in various univalent PFSA membranes.

Acknowledgement.

We gretefully acknowledge the support of this work by the Office of Naval Research. We also appreciate the assistance of 3M company in providing 3M PFSA membrane samples.

References:

K. A. Mauritz and R. B. Moore, Chemical Reviews, 104, 4535 (2004).

T. A. Zawodzinski, C. Derouin, S. Radzinski, R. J. Sherman, V. T. Smith, T. E. Springer and S. Gottesfeld, J Electrochem Soc, 140, 1041 (1993).

Figure 1
(Invited) Ionic Charge Separation at the Electrode Interface
Authors: Kattirtzi John , Limmer David , Willard Adam Phillip
Published: February 2020

In aqueous solution, the association or dissociation of oppositely charged ions requires the collective rearrangement of surrounding water molecules, which solvate bound ion pairs differently than individual ions. The solvent fluctuations that enable these collective rearrangements drive the dynamics of ion pairing and unpairing and therefore play a fundamental role in many chemical reactions. Near the surface of an electrode these collective solvent fluctuations can differ significantly from that of the bulk liquid and these differences can affect the rates and mechanisms of aqueous electrochemical reactions. Here, I present the results of molecular simulations that are aimed at investigate the microscopic processes of aqueous ion pairing when it takes place near but not in direct contact with an extended metallic electrode. These results show that the presence of an electrode has little effect on the mechanistic details of ionic charge separation, but can significantly influence the thermodynamics and kinetics of the process.
Functionalizable Nanoporous Two-Dimensional Covalent Organic Frameworks
Authors: Parkinson Bruce A
Published: February 2020

We have synthsized new two dimensional nitrogen containing covalent organic framework (COF) materials with conductive backbones that may be ideal candidates for many electrochemical applications. The materials are "bottom up" synthesized rather than top down as in modifification of graphene or graphene oxide. We can produce materials with various sized ordered nanopores that can be functionalized with virtually any functional group. For electrochemical membrane applications we focus on lining the pores with charged carboxylate, quaternary nitrogens and sulfonate groups. Prelimary studies indicate that, depending on the dimension of the COF backbone, we can put as many as 6 to 12 carboxylate groups in each nanopore and have demonstrated selective ion conductivity to both size and charge with membranes fabricated with these materials.
Biomass Activated Carbon for Solid Supercapacitors
Authors: Lian Keryn , Genovese Matthew , Wu Haoran , Virya Alvin , Li Jak
Published: February 2020

Biomass activated carbon (AC), produced from the pyrolysis of biomass waste feedstock (wood, agricultural residues, etc.) has been studied as low cost Electrochemical Double Layer Capacitor (EDLC) electrodes. Their parent biomass materials also lead biomass ACs with different natural porous templates which can be further tuned or modified via chemical activation techniques. We have investigated several waste biomass ACs ranging from corn cobs, pine cones, to chitosan and found that, while all inherited porous structures from nature, they displayed quite different surface chemical compositions and pore structures. For example, the surfaces area of these biomass AC were in around 570 m2/g, 2400 m2/g and 3300 m2/g, respectively. These differences, especially in surface area, morphology and pore size distribution, have direct impact on the electrochemical performance of these biomass ACs in both liquid and solid electrolytes. Among the three biomass materials, chitosan-based carbon has demonstrated a high level of hierarchical meso-pore structure and the highest specific energy density.

Solid-state supercapacitors, enabled by polymer electrolytes, are ideal solutions for future energy storage applications that require high performance, safe operation, light-weight, thin and flexible form factors. We have developed a series of aqueous-based polymer electrolytes that are proton-conducting, hydroxide ion-conducting or neutral salt ion-conducting to match various cell chemistries. Many electrolytes exhibited ionic conductivities >10-2mS/cm and maintained stable performance under ambient conditions (i.e. room temperature and 45% relative humidity).

In this talk, we will present the development of solid EDLC devices leveraging biomass ACs and aqueous based polymer electrolytes. The performance of solid EDLC devices using chitosan AC carbon and polymer electrolyte containing Li2SO4 will be compared with their liquid counterpart (Fig. 1) as well as with the commercial baselines.

Figure 1
Influence of Oxygen and Chlorine on the Electrical Performance of ZnO Field-Effect Transistors
Authors: von Seggern Heinz , Mundt Paul
Published: February 2020

The effect of different atmospheres and differently composed dispersions on spin-casted nanoporous ZnO field-effect transistors has been investigated. Devices were fabricated by multiple spin-casting of ZnO nanoparticle dispersions with MeOH, water and chlorine containing solvents onto bottom-gate/ bottom-contact Si/SiO2 substrates with gold electrodes commercially available through Fraunhofer IPMS, Dresden. This was possible by a synthesis route which allowed for an easy exchange of the solvents by dialysis. In all cases transistors exhibit a nanoporous ZnO channel resulting from the globular shape of the individual nanoparticles. These transistors allow for an easy access of gases and liquids to the transistor channel. For a single spin-coating process it will be shown that the coverage of the transistor channel is insufficient for a reasonable transistor performance which is why multiple coatings (at least two) have been utilized successfully. In addition, for all solvents an annealing step at temperatures between 50°C to 250°C for 15 min was found to be necessary to activate charge transport through the removal of remainders of acetate groups from the nanoparticle surface. Such acetate groups are leftovers of nanoparticle synthesis and hinder the neck-forming between particles, latter being a prerequisite for charge transport. With increasing temperature the charge carrier mobility improves up to values of 9 x10-3 cm2/(Vs) and the threshold voltage or equivalently the trap density at the ZnO/SiO2 interface diminishes. The reason for the decrease of the threshold voltage is shown to be due to the removal of adsorbed oxygen molecules from the surface with increasing temperature or with decreasing pressure of the surrounding oxygen atmosphere. When prepared in a water-based dispersion a two orders of magnitude larger on-current and a 3 order of magnitude higher off-current compared to the MeOH based dispersion is observed. The higher on-current can be explained by the better filtration of the acetate groups during dialysis performed for the substitution of MeOH by water. This reduction of spacer groups leads to an easier neck formation between particles, which also explains the higher off-currents. An amazing performance change is obtained when chlorine-based dispersions are employed such as chloroform and dichloromethane. Apparently the transistor characteristics seem to be destroyed and a highly conducting device is obtained within the experimentally possible voltage windows. The function of the chlorine was unraveled by adding different concentrations of HCl or KCl to a MeOH based dispersion. A concentration dependent shift of the threshold voltage has been observed indicating increased n-doping with increasing chlorine concentration allowing for a potential adjustment of the threshold voltage. A phenomenological model will be presented.
All-Solid-State Potentiometric Sensors for Potassium Ion Detection with Enhanced Stability By Interlayer Incorporation
Authors: Tran Wendy , Qiu Shide , Chung Hyun-Joong
Published: February 2020

Solid state potassium ion selective electrode (K+ ISE) has been the epitome of the most studied chemical sensors in recent years due to its practical importance in biomedical applications. In fact, potassium monitoring in food and serum, urine, and potentially in brain has been carried out in the clinical and medical fields to reveal physical conditions of the patients such as renal diseases, hypopotassemia, alkalosis, cirrhosis of liver, etc. In this report, we developed an electrochemical sensing unit which working, counter and reference electrodes are integrated in a single plane as all-solid-state form. Here, a polyaniline intermediate layer and salt-saturated polyvinylebutyral top coating are introduced in the working and reference electrodes, respectively, in order to mitigate the output potential drift problem that prevented widespread use of solid-state K+ ISE. Morphological and electrochemical properties of K+ ISE are studied by using a scanning electron microscope (SEM) and a potentiostat, respectively. Various measurement modes of electrochemical measurements, including cyclic voltammetry (CV), chronopotentiometry (CP), and electrochemical impedance spectroscopy (EIS), are implemented. The K+ ISE show desirable properties including high sensitivity (60.5 mV/decade), low concentration for the limit of detection (10-5.8 M), and large range of linear detection (10-5 – 1 M). Selectivity of our of K+ ISE against NH4
+ , Na+ , Mg2+ , Ca2+ , and Fe3+ was studied. With its high potential to be miniaturized, we foresee that our solid-state K+ ISE will find future applications in microdevices for clinical analysis, agricultural and, environmental applications.