bluuebunny/crossref_metadata_2025_split huggingface dataset:
Glucose Oxidation in Viologen-Mediated Fuel Cells Using a Non-Precious-Metal Anode
Authors: Bahari Meisam , Brown Daniel , Roberts Matt , Hawkins Adam , D. Watt Gerald , Lewis Randy , Harb John N. 
Published: February 2020

Glucose has a great potential as a renewable source of energy for fuel-cell applications. However, rapid and complete oxidation of glucose in fuel cells has been a challenge. To address these issues, this study examines the use of dimethyl viologen (MV) as an electron mediator. MV has the potential of oxidizing glucose to a large extent at a relatively fast rate. In a MV-mediated glucose fuel cell, MV homogeneously oxidizes glucose. Subsequently, MV oxidized at the anode of an electrochemical cell, generating current. Since the electrochemical reaction of MV does not require a catalyst, MV-mediated fuel cells also offer a potential cost advantage over precious-metal-based fuel cells. This study investigates the efficiency of MV-mediated glucose oxidation. The study also evaluates the rate capability of an MV-mediated glucose fuel cell in terms of current density and power density.
Glucose oxidation efficiency was experimentally investigated in an electrochemical cell. To do so, the impact of various factors including the initial molar ratio of MV to glucose and the rate of the electrochemical reaction were examined. In addition, 13C-NMR was used to identify reaction products in order to obtain insight into the oxidation mechanism. Our experimental results show that the oxidation efficiency depends on the rate of electrochemical reaction and, over a certain range, can be increased by increasing that rate. Moreover, the oxidation efficiency can also be increased by increasing the initial molar ratio of MV to glucose. The maximum oxidation efficiency observed was 22%, which is almost three times larger than that observed in precious-metal-based fuel cells. 13C-NMR results confirmed that the main oxidation product was glycolic acid, consistent with the measured oxidation efficiency.
To investigate the rate capability of a MV-mediated glucose fuel cell, a mathematical model was developed. A fuel cell device was also made and rate experiments were performed. In such a cell, the homogeneous reaction of glucose with the mediator and the electrochemical reaction of the mediator at the anode are coupled, so that both types of reactions contribute to and have the potential to limit the overall rate. The model helped us to better understand the influence of each type of reaction on the overall rate. Methods for enhancing the overall rate were also explored. Based on the model, system optimization has the potential to produce power densities about one order of magnitude larger than values reported to date in the literature.
Effects of Temperature on the Faradaic Efficiency of Hydrogenation and Hydrogenolysis of Furfural
Authors: May Andrew Scott , Biddinger Elizabeth J 
Published: February 2020

Alternative sustainable methods for chemical and fuel production are a growing area of interest. One alternative for biomass upgrading, which typically requires high operating temperatures and pressures, as well as externally-supplied hydrogen gas, is to use electrochemistry to undergo the reaction. Using electrochemical methods, the reaction can be run at ambient conditions. In addition, the external hydrogen which comes from energy intensive methods is not necessary because adsorbed hydrogen for biomass conversion can come from the electrolyte. Furfural (FF) reduction to furfuryl alcohol (FA) and 2-methylfuran (MF) is a promising case for the reaction to be performed electrochemically.
Furfural electroreduction requires high overpotentials for appreciable partial current densities to desired products which leads to significant hydrogen evolution (HER). In this work we show that the reactions rates to desired and non-desired products vary differently with temperature between 10 to 45 °C when studied over copper electrocatalysts in 0.5M sulfuric acid. This affects the overall Faradaic efficiency for all products and allows for the shift of Faradaic efficiency of products as a function of temperature. The Faradaic efficiency is shown to be a function of both temperature and overpotential allowing one to target higher FE of desired products by tuning both temperature and potential.
Pulse Reverse Current Surface Finishing of Additively Manufactured Impellers
Authors: Hall Timothy D. , Garich Holly , Liu Danny X. , Snyder Stephen , Taylor E. J. 
Published: February 2020

Powder bed methods of additive manufacturing (AM) use either an electron beam (Electron Beam Melting – EBM) or a laser (Selective Beam Melting – SLM) to sequentially melt powder, layer by layer, to build up a 3-dimensional object directly from a powder bed according to a computer aided design (CAD) file. Complexity is free with AM processes, so parts such as the impeller shown in the Figure Left, are natural candidates for AM.
With EBM. there are four steps to build each layer in a build. First, the beam is scanned to preheat the powder bed without melting, second, the contours (outer edge) of the area to be melted is traced and powder melted, third, the hatch (area within the contours) is melted and finally any supports that need to be built to support higher layers of the part being built are added. The side face of a part adjacent to powder after an EBM build is shown in the Figure Right.
With SLM, a similar strategy is used although powder bed preheating is not necessary (the powder bed remains at ambient temperature or is preheated to a low temperature – up to 200°C – with separate heaters). The result of this low temperature processing is that residual stresses are created. The supports which are added to the model to support higher level downward facing surfaces are structural in nature and used to prevent distortion (unlike those supports in the EBM process which are added for thermal management).
The major concerns for incorporation of AM into structural parts are (1) microstructural anisotropy/inhomogeneity, (2) porosity – open near the surface and closed internally and (3) surface finish that is strongly dependent on the orientation of the surface relative to the build direction. Improving the surface finish is critical for certain applications. While finish machining can be used where surfaces are accessible, one benefit of the complexity of part shape is the possibility of building parts with internal channels, inaccessible to machining.
Therefore, this paper will discuss recent developments toward the demonstration of electrochemical processing conditions and tooling that enable electrochemical finishing of complex components like shrouded impellers. Unlike conventional electrochemical surface finishing processes, the pulse reverse process does not require low conductivity/high viscosity electrolytes or the addition of chemical species (like HF) to remove the passive film associated with electropolishing of passive and strongly passive materials like Ti alloys. This paper will focuses on pulse/pulse reverse electrofinishing processes developed by Faraday Technology and the technique to scale this approach to functional parts of interest.

Acknowledgements: The financial support of USAF Contract No. FA8814-15-C-0007 is acknowledged.

Figure 1
Carbon Dioxide Electroreduction to Multi-Carbon Products Using a Large-Scale Membrane Electrode Assembly
Authors: O'Brien Colin P , Gabardo Christine M. , Edwards Jonathan P. , McCallum Christopher , Xu Yi , Dinh Cao-Thang , Li Jun , Sargent Edward H. , Sinton David 
Published: February 2020

Rising atmospheric carbon dioxide (CO2) concentrations has led to an increased focus on electrochemical CO2 reduction using low-cost renewable electricity to produce low-carbon-intensity fuels and chemical feedstocks. The electrosynthesis of multicarbon (C2+) hydrocarbons and oxygenates, such as ethylene and ethanol, from CO2 feedstocks is appealing due to the large global market demand of these high-value products.
Industrial-scale implementation of this technology requires operation at reaction rates above 100 mA/cm2 to minimize electrolyzer capital costs. Gas diffusion electrodes (GDEs) feed CO2 directly to the electrocatalyst surface, alleviating mass transport limitations faced in traditional aqueous environments and enabling operation at industrially relevant reaction rates. However, when implemented in conventional liquid flow cells with alkaline or neutral electrolytes, major challenges emerge in maintaining electrolyte stability with detrimental carbonate and bicarbonate formation, consequently having adverse effects on energy efficiency.
Here we introduce therefore a membrane electrode assembly (MEA) based CO2 electrolyzer for C2+ production. We investigate the extent to which it can overcome the electrolyte stability limitations by eliminating alkaline electrolyte degradation and neutral electrolyte salt precipitation typically observed in the conventional approach. The MEA design maintains its performance while operating at elevated temperatures and low partial pressures of CO2, important considerations for industrial reactors. We further design a copper catalyst that takes advantage of the high CO2 concentrations afforded by the MEA. This catalyst design strategy achieves more than 50% Faradaic efficiency towards ethylene and more than 80% Faradaic efficiency towards C2+ products while operating at more than 300 mA/cm2. We demonstrate the stability of the system design through the continuous generation of ethylene while operating at industrially-relevant currents for more than 100 hours. The outcome is an engineered system that provides the longest stable ethylene production amongst all CO2 electrolyzers at reaction rates greater than 100 mA/cm2. To reduce costs associated with gas product separation from dilute streams, maximizing CO2 utilization is important. We investigate alternative flow field designs for the MEA reactor to achieve uniform reactant distribution, leading to improved current densities and reduced hydrogen evolution by at least 25% each. Finally, we demonstrate the process and system scalability through C2+ production in a large-scale MEA electrolyzer as part of the NRG COSIA Carbon XPRIZE.
Numerical Study of Mass Transport and Electrochemical Kinetics inside Porous Structure Layers of PEMFC Using Direct Simulation Approach
Authors: Satjaritanun Pongsarun , Shimpalee Sirivatch , Weidner John W. , Hirano Shinichi , Zenyuk Iryna V. 
Published: February 2020

The enhancement of the mass transports in porous layers of a polymer electrolyte fuel cells (PEFCs) is essential for developing material and design system to improve the PEFC performance and durability. The oxygen transport resistance is a large fraction of the mass-transport overpotential at the cathode. Condensed water in the flow field and porous layers reduces oxygen transport to the oxygen reduction reaction (ORR) region. Experimental investigation of locally saturated porous media in the operating cell is difficult. The Computational Fluid Dynamics (CFD) is mathematical modeling tool, which can be considered the incorporation of theory and experimentation in the field of kinetics, heat, and mass transport of the PEFCs. The purpose of this work is to use direct modeling-based, Lattice Boltzmann Method (LBM) within the detailed structure of porous layers to understand the kinetics and multi-scalar/multi-physics transports in a polymer electrolyte fuel cells (PEFCs). The model geometries consist of gas diffusion layer (GDL), micro porous layer (MPL), and Catalyst layer (CL), as shown in Fig. 1. The studies include the understanding of water evolution, water saturation, breakthrough pressure, heat transfer, species transport, and electrochemical kinetics inside porous layers under different conditions and situations that could occur in fuel cells.
This work will show the enhancement of direct CFD simulation with LBM (CFD-LBM) approach [1-4], which incorporates with detailed structure of porous and catalyst layers from both micro- and nano- X-ray CT. This approach will consist of the kinetic model in the catalyst layer, which will involve coupling electrochemical kinetic to investigate the electrical potentials, electrical current, electron transfer, and exchange current in the catalyst layers, as shown in Fig. 2. The output of this work will be used for the optimization of catalyst layer thickness, with durability and water management improvement, for novel porous materials, particularly in the catalyst layer.
References:

P. Satjaritanun, S. Hirano, A. D. Shum, I. V. Zenyuk, A. Z. Weber, J. W. Weidner, and S. Shimpalee, Journal of the Electrochemical Society, 165 (13), (2018) F1115-F1126.

P. Satjaritanun, J.W. Weidner, S. Hirano, Z. Lu, Y. Khunatorn, S. Ogawa, S.E. Litster, A.D. Shum, I.V. Zenyuk, S. Shimpalee, Journal of the Electrochemical Society, 164 (11), (2017) E3359-E3371.

S. Shimpalee, S. Hirano, M. DeBolt, V. Lilavivat, J.W.Weidner, Y. Khunatorn, Journal of the Electrochemical Society, 164(11), (2017) E3073-E3080.

S. Shimpalee, V. Lilavivat, H. Xu, J. R. Rowlett, C. Mittelsteadt, and J. W. Van Zee, Journal of the Electrochemical Society, 165 (11), (2018) F1019-F1026.

Figure 1
Comparative Investigation of Polyphenylene Sulfide Polymer-Graphite Bipolar Plates for Fuel Cell Application
Authors: Dushina Anastasia , Satola Barbara , Dyck Alexander , Wagner Peter 
Published: February 2020

Bipolar plates (BPPs) are one of the key components of the polymer electrolyte membrane fuel cell (PEM FC) which play an important role in the development of fuel cell application. They should fulfil many functions in a fuel cell stack such as feeding H2 and O2 gases through the flow field upon operation, heat transfer, physical separation of individual fuel cells in series, collection and transport of electrons from anode to cathode of adjacent cells [1]. Among the BPPs used in PEM FC the polyphenylene sulfide (PPS) polymer-graphite BPP has a good electrical conductivity, lower cost, higher flexibility and chemical stability, in comparison to metallic and graphite plates. However, some challenges such as higher thickness and weight in comparison to metallic bipolar plates are limiting their use in automotive application [1]. In addition, it was reported that corrosion of carbon is taking place under operation conditions of fuel cells [2].
Therefore, in this work two compression molded commercial polyphenylene sulfide (PPS) polymer-graphite composite bipolar plates BPP-20 and BPP-15 from two different manufacturers with amount of PPS binder equal to 20 and 15 %, respectively, were employed for an analytical comparative investigation using physical and electrochemical analysis. Chemical stability of BPPs was investigated after storage in phosphoric acid. Corrosion resistance and electrochemical aging of the BPPs were studied by using linear sweep voltammetry, cyclic voltammetry and electrochemical impedance spectroscopy in phosphoric acid. In order to characterize the difference in physical properties water contact angle measurement and through-plane electrical conductivity experiments were performed. The morphology of the BPPs surfaces was determined by scanning electron and confocal microscopy. The chemical composition was investigated by X-ray diffraction and energy dispersive X-ray spectroscopy, respectively. Comparison of BPPs revealed that the surface roughness and electrical conductivity is lower while acid uptake and hydrophilicity is higher for BPP with higher amount of PPS. Moreover, there was a trend of reduced corrosion rate for BPP with increased PPS content. These properties could be explained based on structure and electrical characteristics of the materials.
[1] S. S. Araya, F. Zhou, V. Liso, S. L. Sahlin, J. R. Vang, S. Thomas, X. Gao, C. Jeppesen, S. K. Kær, International Journal of Hydrogen Energy 2016, 41, 21310-21344.
[2] T. Engl, L. Gubler, T. J. Schmidt, Journal of the Electrochemical Society 2015, 162, F291-F297.

Figure 1
Bypassing the Jam: How GDLs with Engineered Water Highways Can Re-Enable Interdigitated Flow Fields for PEFCs
Authors: Manzi-Orezzoli Victoria , Siegwart Muriel , Schmidt Thomas J. , Boillat Pierre 
Published: February 2020

The use of interdigitated flow fields in polymer electrolyte fuel cells (PEFCs) was originally proposed in the 90’s by Nguyen (1), and can lead to a significant reduction of mass transport losses due to the fact that oxygen is not transported by diffusion, but by convection under the flow field lands (2). However, the same authors reported a few years later (3) that this type of flow field introduces significant cell-to-cell flow distribution issues when placed in a stack arrangement. With the help of neutron imaging, several authors (4-6) have identified the accumulation of water at the end of the inlet channels and the related increase in pressure drop as a major contribution to this problem.
Here, we will present a novel solution to this problem on the basis of our previously developed gas diffusion layers featuring patterned wettability (7). Hydrophilic lines are used to create a bypass for water without altering the mechanical structure of the GDL – which would produce a bypass for gases in dry conditions. Experiments conducted on a 12 cm2 cell and with gas flow stoichiometries as low as 1.4 demonstrated an outstanding improvement in comparison with a standard, fully hydrophobized material. Besides the stable performance, the increase of pressure drop is moderate and nearly constant in comparison with the much larger and unpredictable pressure drop obtained with a conventional GDL. Neutron imaging confirmed that this difference is due to the water accumulation in the gas flow channels with a commercial material – which is fully avoided thanks to the hydrophilic highways in the patterned material (see Figure 1). The moderate and stable pressure drop of our proposed design is highly promising, as it will likely solve the cell-to-cell flow distribution issue in a stack configuration.

References

T. V. Nguyen, Journal of The Electrochemical Society, 143, L103 (1996).

K. Tajiri, J. Karani and U. N. Shrivastava, Journal of The Electrochemical Society, 165, F1385 (2018).

T. Van Nguyen and M. W. Knobbe, Journal of Power Sources, 114, 70 (2003).

N. J. Cooper, A. D. Santamaria, M. K. Becton and J. W. Park, Energy Conversion and Management, 136, 307 (2017).

D. Kramer, J. Zhang, R. Shimoi, E. Lehmann, A. Wokaun, K. Shinohara and G. G. Scherer, Electrochimica Acta, 50, 2603 (2005).

J. P. Owejan, T. A. Trabold, D. L. Jacobson, D. R. Baker, D. S. Hussey and M. Arif, International Journal of Heat and Mass Transfer, 49, 4721 (2006).

A. Forner-Cuenca, J. Biesdorf, L. Gubler, P. M. Kristiansen, T. J. Schmidt and P. Boillat, Advanced Materials, 27, 6317 (2015).

Figure 1
Degradation-Conscious Control for PEM Fuel Cell Systems
Authors: Goshtasbi Alireza , Ersal Tulga 
Published: February 2020

Cost and durability remain the main roadblocks to widespread commercialization of polymer electrolyte membrane (PEM) fuel cell technology for automotive applications. Significant research efforts over the past decade have resulted in considerable improvements on both fronts. Most of this research has focused on developing new materials for enhanced durability. Nevertheless, as demonstrated by the commercialized Toyota Mirai, system-level strategies designed to effectively utilize the full potential of a given fuel cell stack also hold a great promise in realizing the durability targets. Additionally, such system-level approaches can reduce the overall cost, for example by downsizing or eliminating the humidifier. Despite their potential, these system-level mitigation strategies are not commonly pursued in the literature.
As a starting step towards developing a system-level strategy to mitigate membrane degradation, in this talk we present a degradation-conscious control algorithm that aims to meet the requested power demand while respecting the degradation constraints to ensure safe operation of the fuel cell. This is achieved using the model-predictive-control (MPC) framework [1]. In particular, we present a coarsely discretized version of a two-phase and non-isothermal model for transport phenomena in the through-the-membrane direction [2], [3]. We then show how the model can be simplified for the purpose of the control design. To ensure feasibility of real-time control law generation, we further simplify the model by linearizing it about the current operating point. Having derived the linear model, we show how we can construct a degradation-conscious controller that respects the bounds on the membrane hydration and its temperature using the MPC framework. Our preliminary results indicate that the approach can be used to control the state of the membrane in order to ensure its safe operation [4].
[1] J. B. Rawlings and D. Q. Mayne, Model predictive control: Theory and design. Nob Hill Pub. Madison, Wisconsin, 2009.
[2] A. Goshtasbi, B. L. Pence, and T. Ersal, “Computationally efficient pseudo-2D non-isothermal modeling of polymer electrolyte membrane fuel cells with two-phase phenomena,” J. Electrochem. Soc., vol. 163, no. 13, pp. F1412–F1432, 2016.
[3] A. Goshtasbi, B. L. Pence, and T. Ersal, “A real-time pseudo-2D bi-domain model of PEM fuel cells for automotive applications,” in ASME 2017 Dynamic Systems and Control Conference, 2017, p. V001T25A001-V001T25A001.
[4] A. Goshtasbi and T. Ersal, “LQ-MPC Design for Degradation-Conscious Control of PEM Fuel Cells,” in Proceedings of the 2019 American Control Conference, 2019.