bluuebunny/crossref_metadata_2025 huggingface dataset:
Coupled Thermal and Chemical Activation of Graphite Felt, to be Used As Positive Half-Cell Electrode in the Vanadium Redox Flow Batteries.
Authors: Hassan Ali , Tzedakis Theo
Published: February 2020

The graphite felt (GF) is widely used as electrode material in vanadium redox flow batteries (VRFB). The reversibility of positive half-cell redox couple (VO2+/VO2
+) on the GF is low and induce high overpotential in the battery. Coupled thermal and chemical treatment was applied to activate the graphite felt, to use it as positive half-cell electrode. GF was thermally treated at 400oC for 5 h, followed by boiling with saturated potassium dichromate (K2Cr2O7) solution in 5 M H2SO4 at 140oC for 2h. The cyclic voltammetry(CV) and linear sweep voltammetry(LSV) was used to characterize the electrochemical activity of the graphite felt at transient and steady state conditions, respectively. The changes occurred in the surface functionality and morphology of electrode was analyzed by Fourier-transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). High magnification digital camera was used to evaluate the wettability of the electrode. The treatment successfully modified the electrode by incorporating roughness and different oxygen groups (-COOH, -OH, C=O) on the surface of fibers, resulted in high performance electrode. The surface oxygen groups act as catalytic sites for VO2+ ⇌ VO2
+ reaction and responsible for the improvement of the wettability of the electrode. The charge-discharge cycles in classical half-cell exhibit improved electrocatalytic activity of the treated electrode. In galvanostatic conditions, the enhancement of 6.8% and 10% was observed in the conversion of charge and discharge reactions, respectively. In addition to that, average charge voltage lowered from 1.2V to 1.07 V and average discharge voltage increased from 0.43 V to 0.74 V, indicating improved reversibility of VO2+/VO2
+ redox reaction on activated GF. The prescribed treatment is novel, effective and operational easy.
(Invited) Development of Porous Structures for Electrochemical Energy Storage
Authors: Chan Kwong-Yu , Qin Bin , Zhou Ming , Li Chi-Ying Vanessa , Ho Ching-Kit , Voskanyan Albert A
Published: February 2020

We discuss the development of porous structures for the storage of electrochemical energy. Challenges in designing gas-diffusion electrodes for aqueous fuel cells are well known. Extending the use of oxygen electrode to a reversible metal-oxygen battery operating in aprotic media faces further difficulties. They include sluggish kinetics, components degradation, and formation of insulating solid oxide with irreversible structural changes. We synthesize carbon electrodes with controlled hierarchical porosity to investigate the impact of pore structure on performance. Using hierarchical porous carbon electrodes, investigations are carried out for electrocapacitance [1], the oxygen reduction reaction(ORR) in aqueous fuel cells,[2] and the cathode of an aprotic Li-O2 battery[3]. Results observed for Li-O2 has a capacity reaching 1/3 the theoretical energy density. The good performance of a Fe-N-doped hierarchical mesoporous carbon electrode are attributed to: i) A well-defined core-shell mesoporous structure for mass transport and dispersion of Li2O solid; ii) the Fe-N doping of carbon for corrosion resistance and improved conductivity; and iii) small and amorphous RuO2 for effective decomposition of Li2O. Challenges in electrodes for the sodium-oxygen battery technology are different and also discussed. The economic production of mesoporous materials is important for deployment of energy storage technologies in large scale. We also discuss the use of combustion techniques for the synthesis of porous metal oxides.[4,5]

Li, M. Morris and K.Y. Chan, J. Mater. Chem. 21 (2011) 8880-8886.

M. Zhou, C. Yang, K.Y Chan, Adv. Energy Mater., 4 (18), (2014) 1400840.

M. Zhou, C.Y.V. Li, and K.Y. Chan, Energy Technology, 5 (2017) 732-739.

A. Voskanyan, K.Y. Chan, and C.Y.V. Li, Chem. Mater.
28(8), (2016) 2768-2775.

A.A. Voskanyan and K.Y. Chan, ACS Applied Nano Materials 1(2) (2018) 556-563.
Nanoparticle Surface Charge Alters Membrane Ionic Permeability
Authors: Zhang Yunzhu , Sankarasubramanian Shrihari , Li Xue , Xie Xiaofeng , Ramani Vijay
Published: February 2020

Redox flow batteries (RFBs)are promising devices for medium- to large-scale energy storage owing to their decoupled power and energy, safety, reliability, and portability.[1] Active ion crossover through the (dense) separator membrane between the electrolyte solutions reduces RFB cell efficiency. Embedding highly charged metal oxide nanoparticles (NPs) into the separator membranecan electrostatically repel cations and inhibit the active ion crossover, thereby enabling high membrane selectivity during long-term RFB operation. To better understand how to modulate (lower) membranepermeability, we investigated the effect of NP surface charge on cation permeability through the separator membrane.

We selected quaternary ammonium functionalized cardo-polyether ketone (QPEK TMA+Cl-) as the model separator membrane due to its demonstrated performance in all vanadium redox flow batteries[2], and tested three NPs (TiO2, SiO2and Al2O3) based on their zeta potential (ζ), which is a function of their surface charge. Under the typical acidic conditions that prevail in an RFB, membranes containing NPs exhibiting high positive zeta potentials (ζ>40 mV) exhibited lower Fe3+/Cr3+permeability coefficients than pristine membranes, while membranes with weakly charged NPs (ζ:0~10 mV) exhibited higher Fe3+/Cr3+permeability coefficients than pristine membranes. This result indicated that the cation permeability through the separator membrane could be tuned by using metal oxide NPs with modulated surface charge. We note that the surface charge of NPs also affects their aggregation behavior during membrane casting. In a neutral pH environment typical of the casting process, highly charged NPs demonstrated less aggregation and distributed more uniformly through the membrane cross-section.

[1] G. L. Soloveichik, Chemical Reviews
2015, 115, 11533-11558.

[2] S. Yun, J. Parrondo, V. Ramani, J. Mater. Chem. A
2014, 2, 6605-6615.
(Invited) Capacity Fade and Cross-over in Redox Flow Batteries
Authors: Zawodzinski Thomas A. , Lou Kun , Wittman Reed M , Goenaga Gabriel A. , Cantillo Nelly M. , Peng Jing
Published: February 2020

In redox flow batteries, capacity fade upon cycling is often attributed to the effects of cross-over through membranes. However, capacity fade is sometimes observed in situations in which flow is stopped. Also, one common measure of cross-over that is described in the literature is the decline in open circuit voltage in a cell. There is a need for a more complete and coherent description of these phenomena and their interrelationship. In this talk, we will build for our extensive data base of measurements of transport properties of membranes, interactions underlying these properties, cell data and some new approaches to begin to build this picture.

Acknowledgement

We gratefully acknowledge the support of this work by the U.S. Department of Energy, Office of Electricity Delivery and Energy Reliability (Dr. Imre Gyuk). We also thank 3M for providing membranes.
The Effect of Channel Tapering on the Performance of Vanadium Redox Flow Batteries
Authors: García-Salaberri Pablo A. , Moreno-Carrero Carlos , Gokoglan Tugba Ceren , Vera Marcos , Agar Ertan
Published: February 2020

The recent growth of intermittent renewable energy sources, such as wind and solar, requires a simultaneous growth of grid-scale energy storage facilities to provide energy resilience and reliability. Redox flow batteries (RFBs) are electrochemical devices that stand out as potential candidates for the storage of large amounts of energy in an economical and flexible way due to their ability to decouple power and energy capacity. However, one of the main drawbacks that hinders the widespread adoption of RFBs is their relatively low power density, which results in large stack size and high system cost. In recent years, the optimization of engineering aspects, such as electrode materials and cell architectures, has become a key element on the roadmap towards high-performance and cost-effective RFBs. For example, flow fields are critical components for the transport of active species to/from the electrochemically active area of the electrode (i.e., the surface area of the fibers) and, therefore, their design significantly affects the power output and efficiency of the system.

In this work, the effects of interdigitated channel tapering on the performance of aqueous vanadium RFBs are examined experimentally, theoretically and numerically. Critical performance metrics, such as peak power density, limiting current density, round-trip efficiencies and pressure drop are obtained experimentally using flow cells with the tapered flow fields and compared to the ones obtained with the conventional (i.e., non-tapered) flow fields. To establish a fundamental understanding, the experimental results are further examined by means of a macroscopic multiphysics model. The initial results show that the use of novel flow-field designs can be an effective way to develop RFBs with superior performance, while maintaining pumping losses in acceptable levels. A mechanistic understanding on the transport behaviors and their coupling to the electrochemical performance will be provided.
Sodium Thiophosphate Cathodes and Polymeric Membranes for High Energy Density Redox Flow Batteries
Authors: Self Ethan Craig , Delnick Frank M. , Yang Guang , Lehmann Michelle , Gilmer Dustin B. , Ruther Rose E. , Saito Tomonori , Nanda Jagjit
Published: February 2020

Redox flow batteries (RFBs) are promising energy storage devices for grid-level applications due to their long cycle life and the ability to independently scale their energy and power densities. The energy density of conventional RFBs is dictated by their capacity (which is directly related to the solubility of the redox species in the electrolyte) and operating potential. Aqueous RFBs generally have low operating potentials ca. 1.5 V, resulting in poor energy densities (25 – 30 Wh/kg for an all vanadium RFB), whereas systems containing organic electrolytes with wider electrochemical windows have moderately higher energy densities.

Our team recently demonstrated proof-of-concept for a revolutionary approach which uses mediated electrochemical reactions in a RFB configuration to drive reversible Na storage in a red P anode. Extremely high capacities ~1,000 mAh/gP have been demonstrated using this method. In this configuration, the anion radical mediators are recycled several times throughout the cell stack during a single charge/discharge cycle, effectively decoupling the RFB’s energy density from the redox species’ solubility in the electrolyte. By pairing this mediated red P anode with a sulfide-based cathode, energy densities up to 200 Wh/kg (~10x that of conventional RFBs) can potentially be achieved.

This presentation will describe our recent progress developing polymer membranes and high energy density cathodes/catholytes for RFBs. The preparation and characterization of ionically conductive, mechanically robust poly(ethylene oxide) (PEO)-based membranes which are chemically resistant to and prevent crossover of the radical mediators will be discussed. The synthesis and electrochemical properties of a new class of high energy density sodium thiophosphate cathodes for RFBs will also be provided.

Acknowledgements

This research is supported by Dr. Imre Gyuk, Manager, Energy Storage Program, Office of Electricity Delivery and Reliability, U.S. Department of Energy and the Laboratory Directed Research and Development Program of Oak Ridge National Laboratory, managed by UT-Battelle, LLC, for the U.S. Department of Energy.
Low Temperature Molten Sodium-Based Batteries for Large Scale Electrical Energy Storage
Authors: Spoerke Erik D. , Percival Stephen , Small Leo J. , Peretti Amanda , Lamb Joshua , Chalamala Babu R.
Published: February 2020

Despite the tremendous advances in batteries for portable electronics and vehicle electrification, truly effective battery technologies for large scale energy storage remain relatively underdeveloped. These systems have distinct requirements as safe, low-cost, reliable systems, critical to robust and agile energy distribution, integration of renewable energy, effective emergency response, and even emerging national defense initiatives. Here, we describe a promising new class of molten sodium-halide batteries that show exciting potential as safe, cost-effective, long-lived batteries for large-scale applications. These Na-NaI batteries comprise a molten sodium anode and a molten NaI-based halide salt catholyte, separated by highly conductive solid-state sodium-ion conducting membrane. This NaI-based system offers a higher voltage (>3V) than traditional molten sodium batteries and enables the use of fully molten catholytes desired for long cycle life. By engineering the materials chemistry of these batteries, we have driven down operating temperature to near 100°C, utilizing chemistries that avoid potential problems with thermal runaway or flammable organic electrolytes that often plague other battery technologies. This dramatic reduction of operating temperature (compared to ~300°C typical of traditional molten sodium batteries) opens the door to valuable reduction in costs and extension of battery life. This presentation will discuss specific advances in molten catholyte composition and electrochemistry, the performance of the solid-state separators at these reduced temperatures, and the efficient cycling behavior of laboratory-scale prototypes. The encouraging performance of these innovative “low” temperature molten salt batteries promises new opportunities to address the widespread need for safe, reliable, and cost-effective large scale energy storage solutions.

Sandia National Laboratories is a multi-mission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC., a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525.
Real-Time Reservoir Balancing and Leak-Free Nonaqueous Cell Design for Flow Batteries
Authors: Smith Kirk P , Howey David Alastair , Ascencio Pedro , Monroe Charles W.
Published: February 2020

Benchtop-scale testing of redox flow batteries presents numerous operational challenges related to electrolyte imbalance, leakage, and chemical compatibility. Electrolyte imbalance creates a capacity-limiting reservoir and necessitates manual or automatic transfer of electrolyte between reservoirs to rebalance. Leakage of electrolyte in the cell, often at tubing connections or interfaces between the graphite plates, gaskets, and membrane, also reduces capacity and experimental repeatability. The testing of increasingly common nonaqueous electrolytes requires not only strict wetted material compatibility across a range of solvents but also greater resistance to leaks – the lower surface tensions of many organic solvents (vs. water) makes them more prone to leakage.

The above issues are more easily dealt with in large-scale, permanent installations that do not have the benchtop-scale requirements of manual assembly/disassembly, modularity, and configurational simplicity. Additionally, benchtop flow batteries often use peristaltic pumps, a type of positive displacement pump which create large pressure and flowrate pulsations compared to the continuous output of centrifugal pumps commonly used in large scale systems. The use of individual peristaltic pumps for each side of the flow battery can create an electrolyte imbalance when an asymmetric pressure drop occurs across the cell, causing a Darcy flow of electrolyte through the membrane separator. Other aspects of the flow battery can exacerbate this imbalance, such as using porous separators which are more permissive to electrolyte crossover, or more viscous electrolytes which create higher pressure differentials in the hydraulic circuit at a given flowrate.

A new pump control strategy for flow batteries is designed and implemented which controls the speed and flowrate of the pumps in real time in response to the reservoir levels, as shown in Figure 1. This control scheme maintains balanced electrolyte reservoirs by minimizing the average differential pressure across the membrane. Minimal pressure drops are achieved by effectively matching the pressures in each half-cell of the battery by adjusting each pump’s speed and flowrate independently, so that both pumps are operating at the same pressure on their respective fluid mechanical system curves. Additionally, a more leak-resistant cell gasket design shown in Figure 2 is developed, while maintaining chemical compatibility for nonaqueous systems. These two developments are employed in a long-term cycling experiment using a nonaqueous disproportionation electrolyte.

Figure 1
Investigating Anionic Chemistry of Na-Metal Halide Batteries for Large Scale Energy Storage Applications
Authors: Zhan Xiaowen , Lu Xiaochuan , Bonnett Jeff F , Canfield Nathan L , Chang Hee Jung , Sepulveda Jonathan , Sprenkle Vincent , Li Guosheng
Published: February 2020

Battery technologies continue gaining interests for large scale energy storage applications, because it is becoming more critical to couple renewable resources to the grid and yet to maintain the grid reliability and sustainability. In particular, sodium (Na) based battery technologies are suitable for this application due to its potential low materials cost from using earth abundant Na as the charge carrier and the prolonged cycle life. Among various Na based batteries, Na-sulfur (Na-S) and Na-metal halide (Na-MH, Na-NiCl2 or ZEBRA) have been extensively studied and deployed for practical applications. Although Na-S and Na-NiCl2 batteries share some common features such as molten sodium and beta-alumina solid electrolyte, Na-NiCl2 batteries can provide several advantages over Na-S batteries, including superior battery safety, high open-circuit voltage, lower operating temperature, and ease of assembly in the discharged state without using metallic sodium in the anode.

In here, we extend our studies of cathode materials to other nickel (Ni) halide compounds beside NiCl2, which has been extensively investigated in the past. It is found that using different types of halide anions can alter the anion diffusion process and the overall charge transfer reaction. We will present detailed electrochemical characterizations, battery testing, and spectroscopic characterizations to reveal the anionic chemistry of Na-MH batteries, which is important to further improve battery performances at lower operating temperatures.
Ni/Ni-Cr-P and Ni/Ni-Mo-Cr-P Electrodeposited Coatings As Bipolar Plate in Polymer Electrolyte Membrane Fuel Cell Environment
Authors: Chanda Uttam Kumar , Pati Soobhankar
Published: February 2020

Polymer electrolyte membrane (PEM) fuel cells are expected to play a major role in transporting humans and goods. However, one of major bottlenecks is the high materials and manufacturing cost. One way to lower the cost to a great extent is by replacing conventional graphitic bipolar plates with metallic bipolar plates (BPPs), as they costs around 30% of the total cost of stack1. That said, metallic BPPs have durability issues. Over time, they corrode and show higher interfacial contact resistance (ICR). In this work we attempt to engineer the surface of metallic BPPs, so that they perform for longer duration without degrading. To keep the process economical and commercially attractive, a bilayer coating of Ni followed by Ni-Cr-P alloy is pulsed electrodeposited on AISI 1020 low carbon steel. The electrodeposition process is optimized varying the process parameters, such as electrolyte composition, temperature and deposition current.

Field emission scanning electron microscopy and energy dispersive x-ray spectroscopy are used to study the surface morphology and compositional analysis of coating, respectively. Variation in microstructure and composition the Ni/Ni-Cr-P coating is observed with change in process parameter such as pH and temperature. Corrosion studies were carried out on Ni/Ni-Cr-P coated samples using potentiodynamic technique in accelerated (0.5 M H2SO4 + 2 ppm HF) solution at 80ºC. Ni/Ni-Cr-P coated samples with higher Cr content exhibited better corrosion resistance behaviour in both cathodic (air-purging) as well as anodic (H2-purging) environment compared to the bare substrate. Long term durability of Ni/Ni-Cr-P coated samples and AISI 1020 low carbon steel samples were studied using potentiostatic polarization technique. Both coated and bare samples are placed in the accelerated electrolyte solution. Ni/Ni-Cr-P coated samples showed better durability with less change in current density, while bare samples completely disintegrate and precipitate into the solution within 2–3 hours in potentiostatic mode in both the environments. Ni/Ni-Cr-P coated sample show lower interfacial contact resistance (ICR) value than that of bare AISI 1020 steel samples.

For better corrosion resistance and improvement in surface electrical property, Mo was included in the coating composition2. Ni/Ni-Mo-Cr-P coated samples show improved corrosion resistance than Ni/Ni-Cr-P coated samples and AISI 1020 low carbon steel bare samples in both anodic and cathodic PEM fuel cell environment.

Reference:

R. Taherian, J. Power Sources, 265, 370–390 (2014) http://dx.doi.org/10.1016/j.jpowsour.2014.04.081.

H. Rashtchi et al., Fuel Cells, 16, 784–800 (2016) http://dx.doi.org/10.1002/fuce.201600062
Development of Large-Scale Proton-Conducting Fuel Cells for Next Generation SOFC
Authors: Wee Seokeun , Lee Sewook , Park Sangho , Shin Dongwook
Published: February 2020

Solid oxide fuel cells (SOFCs) are known to exhibit an exceptional energy conversion efficiency over 80 % of the various fuel cell types and have environmentally friendly systems with fuel flexibility. Unfortunately, the SOFC based on yttria-stabilized zirconia (YSZ) electrolytes has a major obstacle to commercialization due to its high cost and low durability at high operating temperature range (800~1000 oC). To overcome this issue, many researchers have made efforts in studying materials with performance comparable to conventional SOFCs at intermediate temperature range (500~700 oC). Among these efforts, to use a proton conductive material with a perovskite structure (ABO3) is regarded as an attractive solution. A lot of previous literatures have already proved the potential of proton-conducting oxide fuel cells (PCFCs) as a next generation of SOFCs. However, most of the results are based on laboratory-scale, so the reliability and feasibility have not been confirmed yet. In the attempt of entering the market with the PCFCs, several issues that must be faced are related to large-scale production. Firstly, when it comes to large-scale cell, the difference in the thermal expansion coefficient (TEC) between the electrode and the electrolyte dominantly affects the overall mechanical property of cells. So, the shrinkage rate after sintering should be elaborately controlled to inhibit several problems such as cracking, lifting and warping. Secondly, the low sinterability of BaCeO3 based proton conductors requires a high sintering temperature, which is more serious problem particularly in large-scale cells. That is, the possibility of Ba evaporation during the heat treatment increase, involving in formation of a secondary phase, which eventually causes performance deterioration. To our knowledge, few literatures are reported on this topic, large-scale PCFCs fabrication.

In this work, we attempt to establish large-scale anode-supported PCFCs with BaCe0.6Zr0.2Y0.1Yb0.1 produced by citric-nitrate synthesis method. The electrostatic slurry spray deposition (ESSD) technology was used for each layer fabrication of large-scale cells. An anode functional layer (AFL) was adopted to adjust the TEC and shrinkage rate between the anode and the electrolyte. The quantitative shrinkage rates depending on temperature were analyzed by Dilatometer (Linseis Co.). A scanning electron microscope (SEM, JEOL Co.) was used for microstructural analysis. To examine Ba evaporation and interlayer diffusion, energy dispersive X-Ray spectroscopy (EDX) was used, and the phase development of the synthesized BCZYYb was analyzed by X-ray diffractometer (XRD, Rigaku Co.). The I-V curves and impedance spectra of the single cell were measured in the range of 500 ℃~700 ℃ with humidified hydrogen (~3 % water vapor). Finally, a short-term stability test (100 hours) was performed to confirm the electrochemical durability.
Elucidating the Electrode/Electrolyte Interface of Anionic Exchange Membrane Electrolyzers
Authors: Kendrick Ian , Mukerjee Sanjeev , Weber Adam Z. , Gerhardt Michael R. , Doan Huong
Published: February 2020

Anion exchange membrane electrolyzers (AEMEs) have the potential to dramatically decrease the cost of hydrogen production by enabling the use of non-platinum group metal (non-PGM) catalysts. While optimum performance is achieved using hydroxide electrolyte solution, corrosion issues require corrosion resistant system components. Recently, it has been demonstrated that using a carbonate solution as an electrolyte feed for the OER electrode has the potential of significantly lowering the overvoltage. Using carbonate in an AEM interface is however counterintuitive from the point of view of its lowering ionic conductivity, electrode poisoning and mass transport.

Initial results from a multiphase, multiphysics computational model of the electrode/electrolyte interface reveal advantages and disadvantages of using a carbonate feed. In terms of the former, the presence of carbonate results in a 1000x increase of the active surface area relative to water. However, the hydroxide flux at the anode causes an accumulation of carbonate ions at the anode resulting in a localized pH shift and Nerstian voltage loss. In addition, carbonate adsorption at the exchange site of the ionomer membrane restricts the use of a carbonate solution to solely the anode.

The computational model developed in the course of this research will be used to further characterize the AEME electrode/electrolyte interface. Observations gleaned from the model will be reconciled with performance data obtained from an AEME using non-PGM using various electrolyte feeds across each electrode.
Effect of Varying Co Content in PtCo Nanoparticles on the Performance of PEM Fuel Cells
Authors: Yarlagadda Venkata , Padgett Elliot , Moylan Thomas E , Gu Wenbin , Kukreja Ratandeep , Cai Yun , Thompson Levi T , Muller David A. , Kongkanand Anusorn
Published: February 2020

PtCo alloy catalysts are leading cathode candidates for PEMFC because of their relatively high activity and durability. Although it is known that during fuel cell operation the dissolution of Co results in loss of oxygen reduction reaction activity and that the migration of Co2+ into the membrane can have a negative impact on fuel cell high-current-density performance, the detailed mechanisms are unclear. Thus there are opportunities for PtCo alloy optimization to minimize these losses.

Here, we focused on dealloyed PtCo catalysts with varying degrees of acid leaching in an attempt to vary the Pt-rich shell content while maintaining the Pt-to-Co core composition. While the specific activity of the catalyst decreased with reducing Co content, as expected, the high current fuel cell performance improved. Post-mortem analyses were done to quantify the amount of Co2+ in the membrane. Mathematical modelling was used to help interpret the voltage losses at high current density. We also employed newly developed nanobeam electron diffraction techniques to measure local crystal structure across the PtCo core-shell nanoparticles at subnanometer resolution. This allows us to correlate lattice strain relaxation and defect sites to the apparent catalyst kinetic activity.

This work was partially supported by the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy under grant DE-EE0007271.
(Invited) Tailoring Metal Nanostructures for Energy-Efficient Electroreduction of CO2 and O2
Authors: Wang Chao
Published: February 2020

Electrocatalysts play a vital role in the development of renewable energy technologies based on electrical-chemical energy conversions, such as fuel cells, electrolyzers, photoelectrochemical solar cells and metal-air batteries. Many metallic nanostructures have emerged as promising candidates for such electrocatalytic applications, but the performances are yet to be improved to meet the technical and cost-effectiveness standards for practical implementations. On the other hand, it traditionally relies on the model-catalyst studies of well-defined extended surfaces for mechanistic understanding of electrocatalysis, but discrepancies in catalytic performance and knowledge gaps are also realized to be present between the extended surfaces and nanomaterials. The latter is probably not only due to the intrinsically different bulk and surface structures of materials at these two extremes of size, but also caused by the challenges in probing the active sites and reaction pathways on nanostructured materials.

This presentation aims to discuss two examples of our efforts on tailoring metallic nanostructures for electrocatalytic applications: i)
highly dense Cu nanowires for the electroreduction of CO2 and CO, and ii) Co/Pt core/shell nanoparticles as sustainable electrocatalysts for the oxygen reduction reaction (ORR). These nanostructures are characterized by combining electron-based microscopic imaging, diffraction and elemental mapping, while the surface structures are probed by using surface-specific adsorption/desorption of small molecules (e.g., COad and OHad). The gained structural information is correlated to the measured catalytic activity, durability and/or selectivity, based on which computational simulations are further performed to understand the established structure-property relationships, depict the active sites and reveal the catalytic enhancement mechanisms. Our work highlights the great potential of tailoring nanostructured materials to improve the energy conversion and chemical transformation efficiencies of electrochemical systems.
Probing the Nanoscale Morphology and Conductance of Anion Exchange Membrane Fuel Cells By Atomic Force Microscopy (AFM)
Authors: Barnes Austin , Buratto Steven K , Du Yifeng , Coughlin Bryan E
Published: February 2020

We have compared the morphology of a commercial quaternary ammonium (QA) AEM (FumaTech) and quaternary phosponium (QP) diblock copolymer AEM, synthesized by Coughlin et al., using AFM as a function of relative humidity, temperature, and CO2 exposure. The FumaTech AEM exhibits low phase separation between aqueous and hydrophobic domains and shows increased surface roughness above 60 °C providing a microscopic perspective of degradation. The QP block copolymers on the other hand offer improved stability at higher temperatures and self-assemble into well-ordered hexagonally packed cylinders and body-centered cubic spherical morphologies. Despite cross-sectional TEM suggesting perpendicularly aligned channels across the membrane thickness, we found channels lay parallel to the surface at lower IEC, which limits channel connectivity. At higher IEC, perpendicular alignment persists through the bulk and surface of the membrane thickness, enhancing connectivity. Using electrostatic force microscopy (EFM), we found a significant number of disconnected channels in parallel-oriented membranes compared to the perpendicular-oriented membranes.
Na2so4-Polyacrylamide Neutral pH Polymer Electrolytes for Electrochemical Capacitors
Authors: Virya Alvin , Abella Justin , Grindal Andrew , Lian Keryn
Published: February 2020

Polymer electrolytes are the key enablers for solid-state electrical double layer capacitors (EDLCs) that are thin, light-weight, and flexible. Neutral pH electrolytes are particularly interesting due to their wide operating voltage window for higher energy density and non-corrosive properties for enhanced safety [1-2]. To date, polymer electrolytes comprised of Li2SO4 and polyacrylamide (PAM) have exhibited promising results [3]. However, their ionic conductivity and industrial applications are still limited by the lower mobility of Li+ ions [4] and high cost of lithium salts. Among various sulfate salts, Na2SO4 is a promising candidate as ion conductors for its higher cation mobility, relatively high solubility in water, and low cost from its earth-abundance.

In this work, our objectives are to (a) develop a high-performance, low cost neutral pH polymer electrolyte using Na2SO4 and PAM, (b) understand the origin of the ionic conductivity and material properties of Na2SO4-PAM electrolytes, and (c) demonstrate its application in solid EDLC devices. Metallic cells were constructed to study the ionic conductivity, whereas cells with commercial activated carbon electrodes were fabricated to demonstrate the viability in solid EDLCs.

The ionic conductivities of the polymer electrolytes with different Na2SO4:PAM ratios were tracked over 30 days period in 45 %RH storage environment (Fig. 1). The optimized electrolyte with salt-to-polymer molar ratio of 10,000:1 demonstrated a high ionic conductivity >30 mS cm-1, considerably higher than previously developed neutral pH electrolytes. With activated carbon electrodes, the polymer electrolytes enabled a stable operating 1.8 V voltage window with good cycling performance >10,000x.

References:

[1] Q. Abbas et al., “Strategies to Improve the Performance of Carbon/Carbon Capacitors in Salt Aqueous Electrolytes,” J. Electrochem. Soc., 162, 2015

[2] D.P. Dubal, et al., “Towards flexible solid-state supercapacitors for smart and wearable electronics,” Chem. Soc. Rev., 47, 2018

[3] A. Virya and K. Lian, “Li2SO4-polyacrylamide polymer electrolytes for 2.0 V solid symmetric supercapacitors,” Electrochem. Comm., 81, 2017

[4] R.W. Impey, P.A. Madden, and I.R. McDonald, “Hydration and mobility of ions in solution,” J. Phys. Chem., 87, 1983

Figure caption: Ionic conductivity of Na2SO4-PAM with varying salt content over a 30-days period

Figure 1
Platinum-Iridium Modified Gold Nanoparticles Catalysts for Electrooxidation of Ethanol in Alkaline Media
Authors: Liang Zhixiu , Song Liang , Deng Shiqing , Zhu Yimei , Stavitski Eli , Adzic Radoslav R. , Chen Jingyi , Wang Jia X.
Published: February 2020

Ethanol is one of the most promising alternative fuels for fuel cells (FC). It is a renewable resource which can be produced on a large scale from biomass originating from agriculture, forestry and urban residues. The energy density of ethanol is as high as 8.01 kWh/kg, which is comparable to that of gasoline. Ethanol is easy to store, transfer and refuel owing to its non-toxicity and high boiling point in comparison with methanol and ammonia. [1] However, the sluggish kinetics and low energy efficiency for ethanol oxidation reaction (EOR) hinder the application of direct ethanol fuel cells (DEFCs). To address this issue, great effort has been made focusing on catalysts discovery as well as reaction mechanism understanding. [2]

Here we report a systematic study on Pt-Ir modified Au/C electrocatalysts for efficient ethanol oxidation in alkaline media. In-situ electrochemical Infrared reflection absorption spectra (EC-IRRAS) reveals a high selectivity toward full oxidization to carbonate at low potentials, resulting in a high energy conversion efficiency. EC-IRRAS also indicate that the C-C bond splits upon ethanol interaction with the surface of PtIrAu/C ternary catalyst. More detailed discussion on this topic will be presented at the meeting.

Acknowledgements

This manuscript has been authored by employees of Brookhaven Science Associates, LLC under Contract No. DE-SC0012704 with the U.S. Department of Energy. The publisher by accepting the manuscript for publication acknowledges that the United States Government retains a non-exclusive, paid-up, irrevocable, world-wide license to publish or reproduce the published form of this manuscript, or allow others to do so, for United States Government purposes.

[1] Liang An, Tianshou Zhao, Yinshi Li, Carbon-neutral sustainable energy technology: direct ethanol fuel cells. Renewable and Sustainable Energy Reviews 2015, 50: 1462- 1468

[2] Alexey Serov, Iryna V. Zenyuk, Christopher G Arges, Marian Chatenet. Hot topics in alkaline exchange membrane fuel cells. Journal of Power Sources 2018, 375: 149- 157
Direct Electro-Oxidation of Dimethyl Ether on Pt-Cu Nanoparticles
Authors: Elbaz Lior
Published: February 2020

As the use of portable devices such as mobile phones, laptops and tablets grows rapidly, efficient portable energy technologies are becoming more necessary than ever. In the past years, fuel cells made a great advancement in the field of power sources technology, and are currently referred to as the most promising alternative energy technology. The most popular type of fuel cells today is the polymer electrolyte membrane fuel cell (PEMFC), fueled with hydrogen. Although it offers very high power density, the lack of fueling infrastructure necessary for the handling of hydrogen is currently one of its biggest commercial impediments. In order to overcome this hurdle with portable devices, direct methanol fuel cells (DMFC) were proposed as an alternative. This is mainly due to the methanol’s high energy density and ease of handling. DMFC’s were studied thoroughly over the past decades, and the technology encountered some barriers such as slow anode kinetics, methanol crossover from the anode to the cathode and issues concerning methanol’s toxicity.

Dimethyl ether (DME) is an ether gas under ambient conditions that could be liquefied under low pressure, traditionally used for aerosol propulsion and as an alternative fuel for diesel combustion engines. It was also recently suggested as an alternative fuel for low-temperature fuel cells. This is mainly due to its higher energy density when compared to methanol, 8.2 vs. 6.1 kWh kg-1. There are no C-C bonds to break in the reaction and its theoretical open cell voltage (OCV) is relatively close to DMFC, 1.18 V compared to 1.21 V at 25°C. In addition, DME has a lower dipole moment than methanol and therefore, the fuel crossover in a fuel cell is expected to be much lower than methanol’s, decreasing the mixed potential impact on the cathode.

In this work, new catalyst for the direct electro-oxidation of dimethyl ether (DME) was synthesized and studied using an array of techniques. One of the most prominent catalysts for this reaction, platinum copper alloy (PtCu), was synthesized in an easy and low cost approach. Structural characterizations such as X-ray diffraction (XRD), scanning electron microscopy (SEM), high resolution transmission electron microscopy (HR-TEM) and elemental analysis revealed that the synthesized PtCu nanoparticles (3 nm on average), formed homogeneous alloy without aggregation of metallic platinum or copper. The catalyst’s activity towards electro-oxidation of DME was tested using rotating disk electrode (RDE) and in membrane-electrode assembly in a full cell. The catalyst performance was found to be promising. Direct DME fuel cell (DDMEFC) studied in this work has relatively high energy density as well as low “cross-over” tendency due to a low dipole moment and thus shows great potential as fuel for low power fuel cells. The electrocatalysis of the DME oxidation reaction (DOR) was compared between synthesized PtCu and commercial PtRu/C and exhibited an enhanced performance with the newly synthesized catalyst.
Intrinsic Strain Tuning of Electrocatalyst for Oxygen Reduction Reaction
Authors: Liu Guangdong , Zeng Zhenhua , Deng Huiqiu , Greeley Jeffrey
Published: February 2020

Surface strain is a powerful strategy to optimize the reactivity of electrocatalysts. Traditionally, surface strain in catalyst overlayer is imposed by external stress through the overlayer-substrate interfaces, which may lead to multiple stability and activity problems. In this presentation, we will introduce a way to generate and tune surface strain by utilizing intrinsic driving forces, i.e. intrinsic surface stress. For Pt(111) surface as an example, the tensile surface stress ( ~4.8 N/m) exerts a pressure on the order of 105 atmospheres on the surface atoms, which provides a strong driving force for surface contraction and reduction of the surface energy. While this surface pressure has little impact on the surface structure of symmetric Pt(111) surface, it can be released by introducing step type surface defects to break the surfaces symmetry constraint, which is accompanied with the contraction of surface lattice. Using well-defined Pt stepped surfaces, we demonstrate that the magnitude of surface strain is inversely proportional to the terrace width. Thus, the atomic-level control of terrace width enables generation and fine tuning of surface strain to optimize catalytic reactivity. Using oxygen reduction as an example, we show that the terrace-width dependent strain not only responses for the improved catalytic activity of a series of Pt-n(111)-(100) step surfaces, but also can be used to design electrocatalysts with simultaneously enhanced specific activity and mass activity.
High-Index Faceted Platinum Nanoflowers Catalysts for Proton Exchange Membrane Fuel Cell
Authors: Abdelhafiz Ali , Liu Meilin
Published: February 2020

Proton exchange membrane fuel cells (PEMFCs) have tremendous potential to be the preferred power sources for many emerging technologies, from electric vehicles to portable/mobile devices and smart grids, because of their numerous inherent advantages such as high efficiency, high energy density, low emissions, and fast start-up and shut-down capability. While PEMFCs are expected to use platinum group metal (PGM)-based catalysts in the near-term, the cost of the Pt-based catalyst alone constitutes over 40% of the fuel cell stack cost. Enormous efforts have been devoted to reducing the high cost of catalyst. To date, the catalysts can be classified into three groups according to the active component used: PGM-based catalyst (supported on carbon or other supports); PGM-based catalysts that are modified or alloyed with other metals such as Cu, Co, and Ru; and PGM-free catalysts such as non-noble metals and organometallic complexes. PGM-free catalysts are attractive for cost reduction of PEMFC technology, however, in reality is still a long way to go to before they can be used to run actual fuel cell application. Here in, we are proposing a facile, one-step, synthesis of Pt-based alloy nanoparticles for cost effective low temperature oxygen reduction reaction electrocatalysis at industrial scale.

Direct Pt nanoparticles synthesis is performed under room temperature to form a branched triple and quadruple-pods particles with an average size of ~3.5 nm, as confirmed by X-ray diffraction (XRD) and Scanning transmission electron microscope (STEM) analysis. Rotating disc electrode (RDE) setup is used to probe ORR. Results showed that synthesized Pt-nanoparticles superior catalytic activity for oxygen reduction reaction compared to state of the art Pt-XC/72R commercial catalyst. Pt-nanoparticles periphery are conformed of high index family crystallographic planes, as observed by STEM analysis. High index planes contain lower density of kinks, which optimize the adsorption/desorption energies to be neither too weak nor too strong. Pt-nanoparticles under accelerated durability testing (ADT) outperform their state of the art commercial catalyst counterparts, surviving 81% of electrochemical active surface area (ECSA) after 10,000 testing cycles.

Using a catalyst coated membrane (CCM) technique membrane electro assembly (MEA) was prepared to test Pt nanoparticles under actual PEMFC operation conditions (i.e. temperature and humidity). MEA prepared using the synthesized Pt-nanoparticles outperformed their counterparts prepared by Pt-XC/72R state of the art commercial catalyst with 27% enhancement factor. The reported Pt-based nanoparticles propose a competitive and more efficient synthesis route to prepare large scale commercial catalyst without the need of sophisticated apparatus or special heating conditions.
Super-Strong Nafion/PVA/Uhmwpe Membranes for Proton and Hydroxide Ion-Exchange Fuel Cells
Authors: Li Jin , Zhang Qinghua , Li Runlai , Gao Ping
Published: February 2020

Perfluorosulfonic acid (PFSA) ionomers have been used extensively in proton exchange membranes due to their high proton conductivity and strong electrochemical stability. However, proton and anion conductivity through the PFSA membranes are contingent upon water uptake, but high water content in the membrane causes loss of long-term durability of the fuel cell system because of the water swelling-induced reduction in membrane’s mechanical strengths. Large body of literatures are available to address these issues, for example, hydroscopic nanoparticulate fillers have been used for self-hydration of the membrane, and aligned polytetrafluoroethylene (PTFE) has been employed to reinforce the tensile strengths of the PFSA ionomer. Unfortunately, there is yet no report to date that can resolve pareto fronts issues, i.e., simultaneously having high proton conductivity and high tensile property. Besides, the cost of PFSA membranes, e.g., Nafion, is still prohibitively high. Here, we report a new and low-cost hierarchical membrane with high proton/anion conductivity, low moisture/methanol uptake and super-high tensile strengths. The new membrane is a hybridized composite structure consisting of biaxially oriented nanoporous ultrahigh molecular weight polyethylene (UHMWPE) film coated with Nafion and polyvinyl alcohol (PVA) blend. The tensile strength of the composite membrane is at least 10 times higher than that of the pure Nafion membrane when fully humidified, and the proton and alkaline conductivity is comparable to that of the Nafion/PVA blend. The nanoporous UHMWPE simultaneously acted to provide the high tensile strengths, ion-conductivity selectivity and nanoconfinement to limit the water and methanol uptake. Thus the new hierarchical Nafion/PVA/UHMWPE membrane is potentially an ideal ion-exchange membrane for low temperature hydrogen and direct methanol fuel cells.

The work is financially supported by the theme-based research project of the university grants committee of Hong Kong, Grant No. T23-601/17-R
Ultra-Stable Imidazolium-Based Anion Exchange Membranes for Alkaline Fuel Cell Applications
Authors: Lyu Hailong , Shih Jiun-Le , Jalarvo Niina H. , Nziko Vincent De Paul Nzuwah , Nawaz Kashif , Popovs Ilja , Custelcean Radu , Sun Xiao-Guang , Bryantsev Vyacheslav , Jansone-Popova Santa
Published: February 2020

The development of cationic polymers for anion-exchange membranes (AEMs) with high alkaline stability and conductivity is a considerable challenge in materials chemistry. However, the commonly employed organic cations have limited alkaline stability, especially at high temperatures, which restricts the commercialization of AEM alkaline fuel cell technology.

To address this problem, we have designed and synthesized a series of novel imidazolium-based AEMs for alkaline fuel cell applications. Degradation rates and mechanisms of small organic cations were analyzed by NMR spectroscopy and rationalized using density functional theory (DFT) calculations. The substituent selection at each position of the imidazolium ring has a dramatic effect on the overall cation stability, correlating to the stability profiles of corresponding AEMs. The most stable imidazoliums were chosen to polymerize robust AEMs, while their stability was examined by dynamic vapor sorption (DVS) technique, and conductivity was measured with the four-probe method. The results have shown the superior alkaline stability and conductivity of our imidazolium-based AEMs even at high temperature (80 °C), confirming they are promising AEM candidates for practical application in alkaline fuel cell.