bluuebunny/crossref_metadata_2025 huggingface dataset:
(Invited) Modeling at Multiple Scales for Development of Future Energy Storage Technologies
Authors: Stephens Ryan M. , Balachandran Janakiraman , Rudra Indranil , Maheshwari Shantanu , Thakkar Foram , Bonakala Satyanarayana , Verbist Guy , Ratnakar Ram
Published: February 2020

The energy sector is currently undergoing transition, driven by population growth, demand for more and cleaner energy, and increasing customer choice[1]. To facilitate the growth and uptake of renewable energy in a more electrified energy system, developing efficient and economical means of storing and distributing electricity is vital. Next-generation battery technologies and other electrochemical energy storage and conversion technologies have great promise to enable energy transition. Precise control and understanding of electrochemical and other phenomena over multiple length and time scales will play an important role as the energy transition unfolds.

Within Shell’s Advanced Energy Storage program, we utilize a framework referred to as Experimental-Modeling Powered Optimization Workflow for Energy StoRage Systems (EMPOWERS). The framework seeks to link phenomena observed at different length scales via experimental and computational means.

This talk will share some recent investigation of advanced lithium batteries, with use of DFT, molecular dynamics, and continuum models to investigate advanced battery systems over multiple length and time scales. We will share recent computational investigation into PEO-based polymer systems as electrolytes[2] for lithium metal batteries. We have used molecular dynamics to compute the effect of pressure on key electrolyte parameters, such as density, diffusivity, and transference number. We have also used DFT and ab initio molecular dynamics to study a particular class of cathode material for lithium sulfur batteries. In this case, DFT based on ultrasoft-pseudopotentials was used to calculate the XPS spectra for species present in the cathode in charged and discharged states, which was then validated by experimental XPS data[3]. To complement the electrolyte and electrode-specific component studies, continuum cell models have been used to combine measurements on individual cell components, with an eye towards development of reduced-order models.

[1] http://www.shell.com/investor

Royal Dutch Shell PLC, Shell: Energy transitions and portfolio resilience (2016)

Royal Dutch Shell PLC, 2016 North America Investor Day (2016)

Royal Dutch Shell PLC, Barclays CEO Energy Power Conference (2016)

[2] D. T. Hallinan Jr. and N. P. Balsara, Annual Review of Materials Research, 43, 503-525 (2013).

[3] Experimental work by Guy Verbist (Shell Global Solutions International B.V.), Alexey Deyko and Christina Christova (Polymer Technology Group Eindhoven (PTG/e) BV.)
Numerical Modeling of Anode-Supported Solid Oxide Fuel Cell Using Openfoam
Authors: Jeon Dong Hyup , Lee Seung-Bok , Hong Jong-Eun , Song Rak-Hyun
Published: February 2020

Three-dimensional comprehensive model of micro-scale transport in PEN (positive electrode/ electrolyte/negative electrode) and macro-scale transport in gas channel of anode supported SOFCs (solid oxide fuel cells) is developed in object-oriented CFD code Open Field Operation and Manipulation (OpenFOAM). The numerical procedure consists of calculations of complex phenomena which are fully coupled together with electrochemical reaction kinetics, mass balance, and energy balance, interacting between porous PEN structure and fluid gas channel. The Computational fluid dynamics (CFD) was performed in flow channels with calculations of mass balance and continuum micro-scale model were used to predict the electrochemical characteristics in PEN. The temperature distributions, temperature profiles, and standard deviations are investigated at different average current densities to evaluate the uniformity. The distributions of current density and mass fraction are employed to suggest a dependency. This study provides detailed information of heat and mass transport phenomena with electro-chemical characteristics for intermediate temperature SOFCs
(Invited) Intermediate Transport on Flexible Cascade Surfaces with Electrostatic Channeling
Authors: Liu Yuanchao , Calabrese Barton Scott
Published: February 2020

Biocatalytic cascades can potentially utilize the full bond energy stored in complex molecules using sequential active sites. This results in an enhanced electrocatalytic efficiency, enabling biofuel cells of high energy density and biosensors of high sensitivity. Mass transport of cascade intermediates is enhanced by electrostatic channeling, wherein where charged intermediate was transported along an oppositely charged pathway [1]. Natural cascade has be studied for decades and in 2017 we reported the first cascade with artificially introduced electrostatic channeling [2].

That finding highlighted a surface-channeled diffusing mechanism on a 1D bridge. However, intermediate hopping between an artificial bridge and an enzyme binding site is a flexible 2D surface with multiple pathways and increased potential for leakage [3]. This process is of great significance to design and optimization of electrostatic pathways. Here, we further map the channeling pathway between the bridge and intermediate active site for two different enzymes of varying overall electrostatic charge. Enhanced molecular dynamics sampling methods are used to elucidate the intermediate’s ergodicity in this process; the multiple pathways detected by MD are analyzed via a novel Markov State Model approach. Finally, the kinetic Monte Carlo method is used to quantify the overall kinetics, from which the leaking contribution from each channeling area can be evaluated.

I. Wheeldon, S. D. Minteer, S. Banta, S. C. Barton, P. Atanassov, and M. Sigman, Nat. Chem., 8, 299–309 (2016). doi:10.1038/nchem.2459

Y. Liu, D. P. Hickey, J.-Y. Guo, E. Earl, S. Abdellaoui, R. D. Milton, M. S. Sigman, S. D. Minteer, and S. Calabrese Barton, ACS Catal., 7, 2486–2493 (2017). doi:10.1021/acscatal.6b03440

Y. Liu, I. Matanovic, D. P. Hickey, S. D. Minteer, P. Atanassov, and S. C. Barton, ACS Catal., 8, 7719–7726 (2018). doi:10.1021/acscatal.8b01041

Figure 1
Open-Circuit Voltage Anomalies in Yttria-Stabilized Zirconia and Samaria-Doped Ceria Bilayered Electrolytes
Authors: Miyashita Tomofumi
Published: February 2020

The open-circuit voltage (OCV) in samaria-doped ceria (SDC) electrolytes has been explained by Wagner’s equation. According to this theory, even if there is no external current, two types of internal currents are created by electrons and oxygen ions. Due to the ohmic loss caused by the ionic internal short-circuit current, the OCV is 0.80 V, which is lower than the theoretical voltage of 1.15 V. Coating a thin electron-blocking layer of YSZ (yttria-stabilized zirconia) onto the SDC electrolyte is effective at stopping the electronic leakage current and improving the OCV. For cells with YSZ on the anode side, the OCV is 1.05 V-1.15 V. For cells with YSZ on the cathode side, the OCV is 0.81-0.87 V. Therefore, the electronic leakage currents have been thought to be not entirely stopped.

YSZ films deposited on the anode side are very effective, but YSZ films deposited on the cathode side are clearly less effective. Thus, we proposed experiments to confirm whether electronic leakage currents can be blocked by the YSZ films deposited on the cathode side. A polished YSZ film (500 mm thickness) on the cathode side and a polished SDC film (970 mm) on the anode side were physically contacted. The OCV was measured to be 819 mV at 1073 K, 825 mV at 973 K and 874 mV at 873 K. Then, we noticed that the large voltage loss was not due to electronic leakage currents.

However, there were objections in these experimental results. The surrounding air could enter the contact space between the YSZ film and the SDC film, which indicated that due to air entering the contact, an electronic leakage current could arise in SDC electrolytes.

By measuring the transient process, we showed that the electronic leakage currents were stopped entirely. After changing the anode gas from N2 gas to H2 gas including 3% H2O, the OCV was changed from 85 mV to 755 mV with a short time constant (12 seconds) and from 755 mV to 819 mV with a long time constant (100 seconds) at 1073 K. The equilibrium time based on the electron diffusion coefficient equation should be longer than 49 minutes. Thus, the voltage loss (0.35 V) in SDC could not be explained by the electronic leakage current. Furthermore, a higher OCV (819 mV) was not due to stop the electronic leakage current.

Figure 1
Ferroelectric Properties of Si Doped HfO2 Thin Films with NiSi2 As Bottom Electrode
Authors: Molina-Reyes Joel , Iwatsuka Haruki , Hoshii Takuya , Ohmi Shun-ichiro , Funakubo Hiroshi , Hori Atsushi , Fujiwara Ichiro , Wakabayashi Hitoshi , Tsutsui Kazuo , Kakushima Kuniyuki
Published: February 2020

It has been already demonstrated that the orthorhombic phase transformation of Zr or Si doped HfO2 (induced by annealing) is responsible for its ferroelectricity but the use of capping top electrodes is usually required [1-4]. Here, we show that by using NiSi2 as bottom electrode (suggesting an orthorhombic structure after annealing), moderate ferroelectric properties of Si-doped HfO2 thin films (8.7 nm in thickness) deposited on NiSi2 electrodes can be generated during post-deposition annealing (PDA). For this Si:HfO2/NiSi2 structure, the bottom and top metallic films are deposited by sputtering at room temperature while atomic-layer deposition is used for deposition of Si:HfO2 with a cycle ratio of 1:16 (SiO2:HfO2), see figs. 1-2. Annealing in argon, forming gas and oxygen atmospheres for temperatures ranging from 1000°C down to 400°C, was done on structures having NiSi2 or TiN (used as reference) as bottom electrodes in order to correlate the influence of these processing conditions to the electrical and ferroelectric properties of the resulting MIM devices. For this, leakage current, capacitance, remanent polarization and fatigue measurements with applied voltage were obtained. Moderate ferroelectric behavior was obtained for PDA samples having NiSi2 as bottom electrode in the temperature range of 750°C–500°C, see figs. 3-4. This result shows the advantage of the use of NiSi2 bottom electrode, broadening the processing window for CMOS-compatible ferroelectric materials.

Acknowledgement

This research is supported by the Center of Innovation Program from Japan Science and Technology Agency, JST.

References

[1] T. S. Boscke, IEDM, p.547 (2011). [2] T. Shimuzu et al., Jpn. J. Appl. Phys., 53, 09PA04 (2014). [3] S. Migita et al., SSDM2018, pp.195 (2018). [4] C. Richter et al., Adv. Electron. Mater. 3, 1700131 (2017).

Figure 1
Phenazine-Based Anolyte Materials and Their Application in Aqueous Redox Flow Batteries
Authors: Hollas Aaron , Wellala Nadeesha , Feng Ruozhu , Murugesan Vijayakumar , Li Bin , Nie Zimin , Thomsen Ed , Shao Yuyan , Reed David , Wang Wei
Published: February 2020

The redox flow battery has gained increased attention for grid-scale energy storage due to its safety, scalability, and decoupling of power and energy. The current state-of-the-art flow battery systems utilize vanadium, whose present high cost has prevented wide-scale deployment. Recently, organic molecules have emerged as a potential lower-cost replacement for vanadium. These systems offer candidates made from bulk commodity chemicals with tunable molecular properties, such as solubility, redox potential, and molecular size. Presented will be the development of water-soluble, phenazine-based molecules and their application as anolytes in redox flow batteries. The rational design, flow battery implementation, and long-term cyclability of select candidates will be detailed. Derivatives with solubilities greater than 1M and cell voltages >1V (coupled with ferricyanide as catholyte) will be presented.
Mechanistic Insights of Coupled Proton-Hydride Transfers on Pyridine Immobilized Metal Catalysts for Selective CO2-Electroreduction to Methanol
Authors: Kolla Praveen , Wang Wang , Sun Qiang , Mukerjee Sanjeev
Published: February 2020

The commercial implementation of CO2-electroreduction is driven by realization of electrocatalysts capable of achieving high-selectivity - Faradaic efficiency >80%, throughputs >200 mA/cm2 and durability >2000 hrs, to high-value products. Given the energy density advantages and existing transport-infrastructure, methanol is the most desirable liquid commodity among simple (C1-based) CO2-reduction products. The CO2 derived electrosynthesis of methanol follows through six elementary (electron-proton) charge transfers, involving many unstable and high energy transitions, thereby limiting its electrochemical selectivity. Pyridine and aromatic N-heterocycles (ANHs) have long been regarded as a homogenous mediator for promoting selectivity of electrocatalysts towards methanol. Musgrave et.al portrayed energy demands and catalytic mechanism of the pyridine-dihydropyridine (Py-PyH2) redox in sequential and coupled promotion of proton-hydride transfers (PT-HT) associated with electro-conversion of CO2 to methanol (1). Recently, Herbert et.al has provided experimental evidence of hydrogenation of benzannulated pyridine to dihydropyridine (2) and selective electrochemical promotion of 1,2-Dihydrophenanthridine (3) for sub-stoichiometric conversion of CO2 to methanol on glassy-carbon electrodes. However, when pyridine derivatives dissolved in the aqueous electrolyte, were mediated along heterogenous metal interface (Ex: Pt, Cu, Pd, etc.), the reaction selectivity improved considerably. In this context, our scalable synthesis of juxtaposed heterogenous catalyst, comprised of pyridine immobilized onto metal nanoparticles and its optimization strategies to improve commercialization aspects of electrochemical CO2 reduction selectivity, throughputs and durability will be presented. The presentation also highlights experimental insights that depict the role of metal catalysts and mechanistic aspects of pyridine mediated HT-PT transfers by characterization of reaction-intermediates via advanced electrochemical and spectroscopic methods.

References:

C.-H. Lim, A. M. Holder, J. T. Hynes and C. B. Musgrave, Journal of the American Chemical Society, 136, 16081 (2014).

P. K. Giesbrecht, D. B. Nemez and D. E. Herbert, Chemical Communications, 54, 338 (2018).

P. K. Giesbrecht and D. E. Herbert, ACS Energy Letters, 2, 549 (2017).
(Invited) Proton Pump for Solar Energy Transformation:from Nano- to Meso-Scale Architectures
Authors: Rozhkova Elena A.
Published: February 2020

Proton pumps are group of membrane proteins which carry out proton (H+) transfer across a biological membrane via energy-driven conformational changes in their structures. Light-driven proton pumps utilize sunlight energy to fuel ATP-synthase. Light is absorbed by the retinal cofactor that results in photoisomeriazation of the chromophore that leads to proton translocation through a membrane. Earlier we demonstrated that semiconductor nanoparticles can be self-assembled with membrane-proton pump complexes known as purple membranes (PM), wherein PM can be either isolated from microorganism as micron-scale patches [1,2] or synthesized cell-free as nano-sized particles [3]. These bio-inorganic constructs can be used for efficient water splitting systems in photocatalytic hydrogen production half-reaction. Catalytic activity of these assemblies can be boosted via variety of approaches, for example, control and scaling down of the soft material dimensions [3], introduction of a single atomic layer carbon material [2]. Further efforts are directed toward more complex meso-scale artificial systems for sunlight energy transformation to other fuels and useful products.

1.S. Balasubraanian, P. Wang, R. Schaller, T. Rajh, E.A. Rozhkova, NanoLetters 13, 3365−3371 (2013)

P. Wang, N.M. Dimitrijevic, A.Y. Chang, R.D. Schaller, Y. Liu, T. Rajh, E.A. Rozhkova, ACS Nano, 8(8), 7995-8002 (2014)

P. Wang, A. Y. Chang, V. Novosad, V. V. Chupin, R.D. Schaller, E. A. Rozhkova, ACS Nano, 11 (7), pp 6739–6745 (2017)
(Invited) Electrocatalytic Reduction of CO2in Gas-Phase Electrolyzers: Moving Towards a Relevant Use of CO2
Authors: Deutsch Todd G , Chen Yingying , Klein Ellis , Bender Guido , Neyerlin K C
Published: February 2020

Controlling product selectivity in electrocatalytic CO2 reduction is critical for achieving an economically viable process due to costly downstream separations of valuable products. Thermodynamically, several possible products of CO2 reduction, as well as the undesired (in this case) H+ reduction reaction, reside within a few tenths of a Volt. Thus, product selection cannot be manipulated by controlling the potential but rather must occur via engineering catalyst-intermediate kinetics. Because most CO2 reduction reactions utilize H+ as a reactant, the products are also a strong function of pH. As the local pH varies due to the consumption of protons, the local product changes at a fixed potential. The majority of CO2 electrocatalyst development occurs in a buffered, liquid electrolyte half-cell with a configuration that portrays a misleading parameter set. Aqueous-based cathode systems are limited by minimal water solubility limits of CO2, which at ~30 mM can only support current densities1 around 30 mA/cm2. Such current densities are at least an order of magnitude too low to be considered for an industrially-relevant device. The product selectivity and efficiency of any catalyst measured in aqueous half-cells will undoubtedly be different in high rate (current) devices. A new analytical solution is required for screening materials designed to utilize CO2 at a scale commensurate with which it is currently being produced. In this talk, we will present an overview of our approach for transforming the CO2 reduction reaction from an aqueous environment to an industry-relevant gas-phase environment, where high rates of conversion are possible.

Through a robust fuel cell and electrochemical engineering research program, the National Renewable Energy Laboratory has developed considerable expertise in transforming gas-phase reactions from utilizing material properties to a functioning device level. This expertise is leveraged to develop a CO2 electrolyzer utilizing a gas phase cathode, and alkaline oxidation anode assembly. The electrodes are separated by a bipolar membrane with an engineered 3-D interfacial layer. Accelerating the water dissociation reaction at the interface of the cation and anion exchange layers in the bipolar membrane is necessary for achieving and maintaining high current densities in our advanced CO2 electrolyzer assembly. Initial results of this endeavor will be presented. We will also describe our progress in designing and fabricating new automated test stands, with real-time online reduction product analysis, capable of performing in-situ electrochemical diagnostics on dynamic processes in these complex systems. The ultimate goal of this project is to establish a platform to evaluate and benchmark promising CO2 electrocatalysts subject to conditions relevant for incorporation into a viable solution for efficient industrial reduction of CO2.

Acc. Chem. Res. 2018, 51, 910−918
(Invited) Composition Dependent Performance of Au-Pd Core-Shell Nanocatalysts for CO2 Electrochemical Reduction
Authors: Zhu Shangqian , Qin Xueping , Shao Minhua
Published: February 2020

Electrochemical reduction of CO2 (CO2RR) to produce valuable chemicals is promising in simultaneously controlling the CO2 concentration and storing renewable energy. However, its wide adoption still needs highly selective and reactive catalysts.

In this study, Au-Pd core-shell (CS) nanoparticles consisting of a Au-rich core and Pd-rich shell were synthesized by wet methods. The nanoparticle composition and shell thickness were adjusted to evaluate their impacts on CO2-to-CO electrocatalytic conversion performance. The CS nanoparticles have a uniform morphology with an average size between 7 to 9 nm. As compared to pure Pd and Au nanoparticles with a similar size, all the synthesized CS nanoparticles exhibited a significantly increased CO selectivity (Figure 1). The CS nanoparticles also have superior mass and specific activities, which are highly dependent on the composition and structure. The best catalyst showed an ultrahigh mass activity of 99.8 mA mg-1 at -0.5 V along with a superior CO faradaic efficiency of 94.7%. In situ infrared spectroscopic studies with an attenuated total reflection configuration (ATR) and density functional theory calculations (DFT) were conducted to reveal the combined structure and composition impacts on the activity. It was found that the scaling relation between *COOH and *CO binding strength was broken on the core-shell nanoparticles and led to the high selectivity and activity toward CO production.

The authors acknowledge the support from Hong Kong Research Grant Council (26206115 and 16309418).

Figure 1. Faradaic efficiency of CO measured on synthesized Au-Pd core-shell, Pd and Au nanoparticles.

Figure 1
Biomineralization of Quantum Confined Nanocrystals and Heterostructures for Electrochemical Applications
Authors: Spangler Leah , Sadeghnejad Abdolhamid , Sakizadeh John , Cline Joseph , Kiely Christopher , McIntosh Steven
Published: February 2020

Functional nanomaterials are at the core of many innovations in renewable energy generation and catalysis. However, many of these materials are currently synthesized through high temperature, multi-step processes that utilize organic solvents and expensive precursors. These factors increase the complexity and economic and environmental costs of manufacturing scale-up. In contrast, biomineralization, the process by which biological systems produce structural nanomaterials, occurs under ambient conditions in aqueous media utilizing readily available precursors. We have developed a novel single enzyme route for the direct, scalable and controlled synthesis of a variety of pure and hetero-structured metal chalcogenide quantum dots. This approach represents perhaps the simplest biosynthesis system for these materials, consisting of only the single enzyme, a metal precursor, and amino acid sulfur source, and capping agent in an ambient temperature, buffered, aqueous solution. However, tight control of the growth parameters yields size and composition controlled crystalline materials and heterostructures with functional properties comparable to materials synthesized by traditional chemical routes. We demonstrate the application of this approach to direct biomineralization of quantum dots within solar cell photoanodes, and in fully biomineralized quantum dot/reduced graphene oxide photocatalysts.
Interface and Grain Boundary Degradation of Cathode from Commercial Cells Induced By Electrochemical Operation in Humidified Air
Authors: Chen Yun , Fan Yueying , Lee Shiwoo , Hackett Gregory A , Abernathy Harry , Gerdes Kirk , Song Xueyan
Published: February 2020

Electrode performance degradation is a major obstacle for the development of SOFC technologies. Among different causes of electrode performance degradation, variation of operating gas environment could impact durability of SOFCs and lead to degradation. For the cathode, certain degree of humidity is always present in ambient air. It has been consistently reported that the degradation rate is accelerated when the cell is operated in the humidified air. This work presents nanostructure analyses of operated commercial SOFCs with either LSM/YSZ cathode or with mixed conducting LSCF/SDC cathode exposed to humidified air. For the cell with LSM/YSZ cathode, three commercial button cells were operated in humidified air for various time at 800 °C. Microscopy work reveals nanostructure degradation occurred within the cathode active layer, and it is most pronounced in the region next to the electrolyte. Newly grown Mn-rich nano-precipitates accompanied with nano-voids and cracking propagate at the LSM/YSZ interface. Additionally, prolonged operation in humidified air promotes the formation of the Mn-enriched precipitates at the YSZ/YSZ grain boundaries. By contrast, for the cell with LSCF/SDC cathode, upon long term operation of 2600 hours, Co and Fe enriched Spinel nano-grains were found accumulated at the original pore region of the cathode. The formation mechanism of Mn-enriched nano-precipitates and Co-enriched nanograins for the LSM/YSZ and LSCF/SDC cathode are discussed.
Life Testing of Ni-YSZ Fuel Electrode Under Electrolysis and Fuel Cell Operation in High Reducing Environment
Authors: Liu Qinyuan , Zhang Qian , Voorhees Peter W , Barnett Scott A
Published: February 2020

An electrode supported Ni-YSZ/YSZ/Ni-YSZ symmetric cell was studied with direct-current operation, with one electrode operating in electrolysis mode, and another electrode in fuel cell mode. The 1000 h life tests were carried out at different current densities in 97% H2 / 3% H2O. At a current density ≤ 0.4 A/cm2, the cell total resistance value was reasonably constant, with a slight increase in ohmic resistance; no changes in microstructure were observed relative to the as-prepared cell. At current densities ≥ 0.6 A/cm2, there was a steady increase in ohmic resistance that was offset by a decrease in polarization resistance, resulting in a total resistance that was approximately stable. However, these higher current densities resulted in significant damage to the electrolyte microstructure. First, fracture was observed within the electrolyte near the electrolysis operation side. Second, fracture SEM images showed pronounced intergranular fracture that resulted because voids had formed at grain boundaries during the life tests. These changes presumably explain the observed ohmic resistance increase. In addition, nanoparticles formed in the electrode after electrolysis operation, probably explaining the decrease of polarization resistance.

The constant-current results are compared with those from similar cells life tested in reversing-current operation. The critical current density values for onset of signification degradation were similar: between 0.4 and 0.6 A/cm2. At the same values of current densities ≥ 0.6 A/cm2, the rate of increase in ohmic resistance were comparable during direct-current and reversing-current operation, while the rate of decrease in polarization resistance with direct-current operation were less than half of that with reversing-current operation. The microstructure changes after life tests at higher current densities were different: First, reversing-current operation resulted in damage to the electrode/electrolyte interface, but the electrolyte appeared to be intact. Second, highly concentrated Ni and YSZ nanoparticles were observed at both side of electrodes after reversing-current operation.

Numerical analysis was carried out to determine the effective oxygen partial pressure versus position within the electrolyte. The results show that the oxygen partial pressure near the electrolysis operation side decreased with increasing current density. The values may be low enough to reduce zirconia and form a Ni-Zr alloy. Subsequent oxidation of zirconium presumably causes the observed structural changes near the Ni-YSZ/YSZ interface.
The Examination and Characterisation of Water Transport in Metal Gas Diffusion Layers for PEMFC Via EIS and Neutron Imaging.
Authors: Fahy Kieran F. , Lee Chunghyuk , Lee Jason Keonhag , Zhao Benzhong , LaManna Jacob M , Baltic Elias , Hussey Daniel S , Jacobson David L , Bazylak Aimy
Published: February 2020

Novel materials for gas diffusion layers (GDLs) in polymer electrolyte membrane fuel cells (PEMFCs) are increasingly under investigation to improve high current performance. Metal gas diffusion layers are of interest as they provide high thermal and electrical conductivity as well as offering the possibility of integration of the flowfield and gas diffusion layer. These properties are all of importance to fuel cells as they should give increased volumetric power density and decrease resistive losses at higher current densities.

Some recent studies have shown that these metal GDLs can outperform commercial carbon GDLs in the high current region [1]–[3]. The water dynamics of these types of GDL are poorly understood however, and there has been little or no research on this topic.

We have performed a study using neutron imaging to study the movement of water in metal mesh GDLs and used EIS to study the consequent effect of mass-transport resistance at a number of current densities and humidities [4]. We have observed a number of interesting phenomena in the water transport in metal-mesh GDLs, which show quite different behavior to that of the normal carbon papers.

When metal mesh is used as the anode and cathode GDL, there appears to be water accumulation in the areas of the channel, which also promotes the back-diffusion of water from the cathode to the anode side of the cell. With a carbon-paper GDL, liquid water accumulates in the land, and there does not appear to be significant back-diffusion compared to the metal mesh GDL. These behaviors also have significant effects on mass-transport and the performance of the cell. The insights provided by the neutron imaging, along with the EIS data will allow us to inform novel and future fuel cell designs.

References

[1] T. Yoshida and K. Kojima, “Toyota MIRAI Fuel Cell Vehicle and Progress Toward a Future Hydrogen Society,” Interface Mag., vol. 24, no. 2, pp. 45–49, Jan. 2015.

[2] K. F. Fahy, J. Lapinski, and A. R. J. Kucernak, “Metal Mesh Gas Diffusion Layers for PEM Fuel Cells,” Meet. Abstr., vol. MA2016-02, no. 38, pp. 2569–2569, Sep. 2016.

[3] N. Hussain, E. Van Steen, S. Tanaka, and P. Levecque, “Metal based gas diffusion layers for enhanced fuel cell performance at high current densities,” J. Power Sources, vol. 337, pp. 18–24, Jan. 2017.

[4] R. S. Fu et al., “An Investigation of Thermally-Induced Water Transport in Polymer Electrolyte Fuel Cells with Neutron Radiography Imaging Technique,” in ECS Transactions, 2009, pp. 543–552.

Figure 1
(Invited) Perspective on Modeling in Proton Exchange Membrane Fuel Cells
Authors: Fuller Thomas F.
Published: February 2020

Following their use in the Gemini space program (1965-66), proton exchange membrane fuel cell (PEMFC) technology languished. Los Alamos National Laboratory (LANL), and more specifically Shimshon Gottesfeld’s group, was instrumental in the resurgence of PEMFCs. Polymer Electrolyte Fuel Cell Model,[i] has been cited more than 2000 times since 1991 and exemplifies the influence that Gottesfeld’s group had on the community during his roughly two decades at LANL. Remarkable advances have subsequently been made in modeling of PEMFCs, arguable greater than those seen in the lithium-ion battery field. The focus of this presentation is to connect the broader work of Gottesfeld’s group on PEMFCs to the field of modeling of fuel cells and to offer a perspective on the remaining barriers and opportunities, and specifically those for the catalyst layer, nearly 30 years after Springer et al.’s seminal paper.

[i] Springer, T. E., Zawodzinski, T. A. & Gottesfeld, S. Polymer Electrolyte Fuel-Cell Model. J Electrochem Soc
138, 2334-2342 (1991).
(Invited) Hydroxide Exchange Membrane Fuel Cells
Authors: Yan Yushan
Published: February 2020

In this presentation, I will share my interactions and collaborations with Shimshon Gottesfeld for the past several years in initiating a new course, CHEG632: Electrochemical Energy Engineering, at the University of Delaware, developing direct ammonia fuel cells, and optimizing hydrogen fuel cells.
(Invited) Fuel Cells Fueled By Sustainable Liquid Fuels
Authors: Soloveichik Grigorii L.
Published: February 2020

The Advanced Research Projects Agency (ARPA-E) funds high risk, high reward transformational research to reduce energy related emissions, reduce imports of energy from foreign sources, improve energy efficiency across all economic sectors, and ensure US technological lead in advanced energy technologies, including electrochemical technologies for energy transformation and storage for distributed, grid scale and automotive applications.

Recently hydrogen PEM fuel cells (FC) made great progress in performance, durability and cost that reflected in the emerging of multiple commercial vehicles powered by FCs. However their market penetration is hampered mostly by the absence of hydrogen infrastructure including transportation and storage, and high cost of its implementation. On the other side, carbon-neutral liquid fuels (CNLFs) have energy density higher than of liquid hydrogen, better safety, low footprint and cost of transportation and storage. Easily liquefied ammonia and dimethyl ether as well as more traditional lower alcohols are the most promising CNLFs. They can be used with or without internal reforming in direct liquid fuel cells (DLFCs) or as a hydrogen carrier for PEM fuel cells thus allowing the use of existing liquid fuels infrastructure. History of DLFCs started in 1960s from first GE attempts to use diesel fuel in a FC and continued with development of direct methanol fuel cells (DMFCs). In spite intensive research, the latter found very limited application because of low efficiency and power density. As conventional low temperature PEMs and AEMs content a lot of water to support high H+ or OH- conductivity, high crossover rate of most CNLFs is inevitable and leads to low cell voltage and energy efficiency. In addition, traditional platinum group metal catalysts are easily poisoned by CNLFs or by intermediate oxidation products. Therefore, to realize high energy density of CNLFs and provide high FC power density, it is necessary to increase operation temperature of DLFCs, develop more active and less expensive electrocatalysts, develop selective ion conducting membranes and design electrodes and cells for using liquid fuels.

Recent advances in the development of novel DLFCs that is being funded by ARPA-E via REFUEL and OPEN 2018 programs will be presented. Possible future ARPA-E program targeting the use of such fuel cells for transportation (in hybrids, range extenders, APUs for aviation and ground transportation) will be also discussed.
(Invited) Effects of an Alkyl Spacer and the Cationic Group on the Hydrated Morphology of Anion Exchange Membranes
Authors: Paddison Stephen J. , Luo Xubo , Zhu Zhenghao
Published: February 2020

Anion exchange membranes (AEMs) are increasingly of interest as the electrolyte in energy and conversion devices. Challenges for their use in these devices are the low chemical stability under alkali conditions and only meager ionic conductivity. A promising strategy to enhance the conductivity of these materials may be through tailoring of the phase segregation of the polymer. Hence, the hydrated morphology of an AEM polymer may be a strategy to achieving high performance. Recently, AEMs based on the triblock copolymer, polystyrene-b-poly(ethylene-co-butylene)-b-polystyrene (SEBS), and functionalized with various cationic groups have shown satisfactory chemical stability.

We have recently undertaken an extensive investigation to understand how various molecular features (placement of an alkyl spacer on the side chain, choice of the cationic group, and the associated anion) determine the hydrated morphology of functionalized SEBS systems. DPD, a meso-scale simulation technique, enables relatively large time and length scales to be examined and therefore permits the elucidation of the morphology of the polymer system in acceptable time and computational expenses. The optimized structure and the interaction parameters used in these DPD simulations were calculated using a recently developed methodology employing DFT based electronic structure calculations. The morphology was determined over a broad range of hydration and our results underscore the complexity of effects of these parameters.
(Invited) Ten Years on: Evolution, Status and Future of Alkaline Exchange Membrane Fuel Cell Systems
Authors: Page Miles , Amel Alina , Azra Charly , Kitayev Anna , Ben-Yehuda Chaya
Published: February 2020

In 2009, CellEra Technologies began work on an Alkaline Exchange Membrane Fuel Cell (AEMFC) stack. Shortly thereafter, at a time when there was relatively little interest in the technology, a stack with 100 cm2 active area, yielding slightly under 100 mW/cm2, running on H2 and O2 was achieved. This result was the first demonstration of an AEMFC stack in operation and generated significant market interest. The membrane-electrode assemblies (MEA’s) used therein yielded up to 200 mW/cm2 in single-cell tests, a comfortably world-leading AEMFC power density at the time. Nevertheless, critical and potentially insurmountable obstacles were also in sharp focus: Low performance vs PEM fuel cells, low durability arising from chemical instability of ionomer in alkaline conditions, sensitivity to atmospheric CO2 and more.

There exists in addition a special challenge of water management in the AEMFC. Though not traditionally assigned the same weight as the above obstacles in general AEMFC mythology, it was flagged as critical early on in our development program, and has since remained thematic, as it was determined to be a root cause in a large proportion, if not the majority, of identified device technology limitations. Active water consumption in the cathode electrode,

½O2 + H2O + 2e- → 2OH- (1)

balanced by double the overall water generation rate at the anode,

H2 + 2OH- → 2H2O + 2e- (2)

leads to a wide variety of mutually reinforcing detrimental phenomena that must be mitigated holistically to achieve sustained high performance and durability.

The existence of the additional reactant – water – in the cathode (Eq 1) is especially significant, with strong multi-scaled implications, from requirements for the chemistry of the component materials, to the design of catalyst layers, structural aspects of the MEA, optimization of operating conditions, design of flow fields and stack engineering. Even today, ten years on, this remains the core engineering and materials science challenge of the technology in spite of impressive progress made in the research field as a whole.

In this talk we review the developments in, and understanding of, the PO-CellTech (formerly CellEra) MEA, stack and fuel cell system that have by now resolved all the fundamental questions of AEMFC viability as a technology, and allow us to target the nascent consumer automotive “FCEV” market: Ultra-low Platinum Group Metal (PGM) loadings, next-generation membrane technology, high areal (MEA) and volumetric (stack) power density, CO2 tolerance, and significant room for continued improvement. We will analyze the status and limitations of AEMFC power density, as well as the major outstanding challenge of device durability, with special reference to the ever-present water management imperative as well as increasingly stringent demands that need to be met, in order successfully to address a rapidly maturing exchange membrane fuel cell market.
The Role of H-Bonding in Non-Concerted Proton-Coupled Electron Transfer: Explaining the Voltammetry of Phenylenediamines in the Presence of Weak Bases in Acetonitrile
Authors: Clare Laurie A , Pham Tammy Dung , Rafou Lily , Buenaventura Ayla , Mikhaylova Veronika , Smith Diane K
Published: February 2020

The kinetics of many proton-coupled electron transfer (PCET) reactions cannot be adequately described by step-wise proton and electron transfer. Concerted electron-proton transfer (CPET) is another possibility, but examples exist where step-wise mechanisms are not viable yet there is no compelling evidence for CPET. This study investigates such a reaction, the oxidation of an NH-containing phenylenediamine radical cation, H2PD+, in the presence of pyridines in acetonitrile. H2PD+ is formed by a net one electron oxidation of 2,3,5,6-tetramethylphenylenediamine in acetonitrile via a rather complicated mechanism that likely proceeds through a H-bonded dimer. Once formed, it can be further oxidized at more positive potentials to the quinoidal dication, H2PD2+, which will be considerably more acidic than the radical cation. Indeed, the E1/2 for the radical oxidation jumps to a considerably more negative potential upon addition of 1 equivalent of the weak base pyridine. The CV wave broadens but stays chemically reversible. Further addition of pyridine leads to smaller E1/2 shifts with continued reversibility. This behavior could possibly be explained by stabilization of H2PD2+ through H-bonding or proton transfer to pyridine, however, UV-vis spectroelectrochemical experiments provide definitive evidence for proton transfer. Furthermore, CV studies with 4-substituted pyridine derivatives of weaker basicity show that the observed E1/2 with 1 equivalent of the pyridine depends in a Nernstian fashion on the pKa of the conjugate acid of the pyridine, indicating that all the pyridines studied deprotonate H2PD2+ to give the quinoidal cation, HPD+. The continued E1/2 shift observed upon further addition of the pyridines can then be completely explained by application of the Nernst equation to the overall reaction H2PD+ + pyr → HPD+
+ Hpyr+ + e−. However, while this explains the thermodynamics, the classic step-wise proton-electron transfer mechanism for this reaction cannot explain the observed reversibility at high base concentration. In contrast, the reversibility can be explained by a “wedge” scheme mechanism in which electron and proton transfer occur within the H-bond complex formed as an intermediate in proton transfer. In this case, the electron-proton transfer could be concerted, however, the kinetics for the second oxidation in the presence of pyridine show no significant isotope effect. Furthermore, a new reduction peak that appears at faster scan rates suggests the presence of an intermediate in the electron-proton transfer. Both results strongly suggest that the electron-proton transfer is step-wise, not concerted, within the H-bond complex. This result points to the important role H-bonding may play in PCET even without CPET.
The Study of Electron Transfer at the Interface of Cytochromes and Iron Oxide Minerals
Authors: Wang Hanyu , Johs Alexander , Browning James F , Liang Liyuan , Tennant Alan
Published: February 2020

Molecular-scale protein-mineral interactions are central to understanding electron transfer mechanisms and microbial processes in subsurface environments. Although, the electron transfer between c-type cytochrome and hematite has been investigated many factors impacting the electron transfer rate have not been determined. We investigated the interactions of horse heart cytochrome c (cyt c) with hematite nanowire array electrodes by cyclic voltammetry to study the electron transfer between redox active proteins and mineral surfaces. Using this model system, specific interactions of cyt c with hematite as a function of electrical potential and pH were examined. We observed direct electron transfer between cyt c and hematite with an interfacial electron transfer rate of kº
ET = 0.6 s-1. show buffer pH has an apparent effect on the conformational and adsorption-induced change on the cyt c. Moreover, in the presence of the electron shuttling compound, anthraquinone-2,6-disulfonate (AQDS), electron transfer rate between cyt c and hematite increased to kº
ET = 2 s-1, which is more than three times of the rate determined in absence of AQDS. This study provides into biomolecular factors controlling the complex interactions and electron transfer processes between redox-active proteins and minerals, which has broader implications for describing chemical transformations at biological-mineral interfaces at the molecular scale.
Selectively Modified Odorant Molecules for Odor Mitigation
Authors: Vasquez Mariana Madelen , Ngaboyamahina Edgard , De March Claire A , Matsunami Hiroaki , Glass Jeffrey T.
Published: February 2020

There is an urgent human and environmental need to increase access to improved sanitation in developing countries. Effective sanitation systems and technologies need to be accessible, sustainable, and affordable. However, even when they are present, malodor nuisance remains a major risk factor in user adoption. Currently activated carbon or air fresheners are used to address the issue. These approaches have limited effectiveness as they try to mask or hide the smell and they do not apply to all malodor molecules. Here, we introduce ElectrosmellTM, an alternative solution using electrochemistry. ElectrosmellTM focuses on the mitigation of the most common and prevalent odorant molecules in human waste. These molecules consist mainly of volatile, small carbon chains ending with functional groups such as carboxylic acids, aldehydes, alcohols, or ketones. A change in the molecular structure can significantly modify olfactory perception. Butyric acid, which has a rancid cheesy smell, and p-cresol, which has a phenolic tar smell, were used as case studies. For both molecules their corresponding more pleasant-smelling homologs were identified: butanal, and 4-hydroxybenzaldehyde. Electrochemical characterization and treatment results suggest that butyric acid, p-cresol solutions could be modified to more pleasant odorous compositions.
Protein Film, and Diffusion–Controlled Voltammetry of Hemeproteins on a Single Surface
Authors: Gerroll Benjamin , Peters Dennis G
Published: February 2020

Protein film voltammetry has made possible electrochemical studies of complex protein reactions, such as redox-induced conformational dynamics1 and enzyme kinetics.2 However, without diffusion-controlled experiments as a reference, one cannot be sure of the extent to which the protein–electrode interaction affects conformational dynamics or enzyme kinetics. Diffusion-controlled voltammetric experiments can provide an alternate view into these processes. Previously, semiconductor electrodes have been successfully employed for diffusion-controlled experiments.3

Herein, we report novel application of electrochemically deposited cadmium oxide (CdO) as a working electrode for both diffusion-controlled voltammetry as well as protein-film voltammetry (PFV). The hydrophilic CdO surface allows transient protein interactions for diffusion-controlled measurements, as well as a suitable surface for drop casting protein films. Polycrystalline CdO electrodes were electrodeposited onto a fluorine-doped tin oxide (FTO) working electrode held at –0.7 V vs. SCE for 15 min in aqueous solutions of CdCl2, then annealed at 450 °C for 2 h. CdO surfaces were characterized by means of x-ray photoelectron spectroscopy (XPS), x-ray diffraction (XRD), and scanning electron microscopy (SEM). XPS and XRD confirm formation of polycrystalline CdO. Electron micrographs confirm complete coverage of the FTO by CdO. To generate protein films, 10 mg/mL solutions of either cytochrome c or hemoglobin were drop cast onto CdO electrodes and left for 2 h. Cyclic voltammograms recorded for both hemoglobin and cytochrome c display nearly reversible electron transfer, with redox potentials similar to those previously reported.4

1 A. El Kasmi, M. C. Leopold, R. Galligan, R. T. Robertson, S. S. Saavedra, K. El Kacemi, E. F. Bowden, Electrochem. Commun. 2002, 4, 177–181.

2 H. Liu, G. Zou, J. Biochem. Biophys. Methods.
2006, 68, 87–99.

3 G. Valincius, V. Reipa, M. P. Mayhew, V. L. Walker, Electrochem. Commun.
2002, 4, 314–317.

4 G. Battistuzzi, M. Bosari, M. Sola, F. Francia, Biochemistry, 1997, 36, 16247–16258.