bluuebunny/crossref_metadata_2025 huggingface dataset:
(Invited) A Spontaneously Generated Electrical Charge of an Aqueous Droplet by Pipetting and Its Use of a Self-Powered Sensor
Authors: Choi Dongwhi , Kim Dong Sung
Published: February 2020

Recently, we reported that pipetting always dispenses an electrically charged aqueous droplet by spontaneous electrical charging process between the pipet tip inner surface and the aqueous droplet. The amount of an electrical charge depends on the constituents of the droplet, on coating material of a pipet tip, and on atmospheric humidity. It is clarified that this spontaneous electrical charging of an aqueous droplet is originated from the electrical charge separation between the droplet and the pipet tip inner surface through performing consecutive measurement of the electrical charge amount of the pipet tip and the droplet during a pipetting process. Since this unexpected electrification phenomenon could influence the localization and combination of charged bio-molecules inside the aqueous solution, controlling and suppressing the spontaneous electrification phenomenon are important. To suggest the way to suppress the electrification phenomenon, a graphene-based nanocomposite coated pipet tip, which we called a zeta-pipet tip, is fabricated, as a proof-of-concept example to reduce the zeta potential of the pipet tip inner surface. Since the electrical charge is always spontaneously generated in the case of solid-water contact, it could be potentially utilized with a self-powered sensor.
Durability Improvements in PBI Membranes
Authors: Qian Guoqing , Fishel Kayley , Chen Xiaoming , Mao Yating , Ploehn Harry , Benicewicz Brian C
Published: February 2020

Phosphoric acid (PA) doped polybenzimidazole membranes made by the PPA process have been the main focus of our research efforts for more than a decade.1 These membranes exhibit an excellent combination of properties including high proton conductivities, excellent fuel cell performance, and long-term durability. For both fuel cell and hydrogen pump devices, the improvement in membrane mechanical properties at high temperatures could lead to further increases in durability and lifetimes of the membranes and resulting devices. We have been particularly interested in membrane compressive creep properties and have developed test protocols which are being used to understand the compressive creep properties and develop structure-property relationships for PPA processed membranes. In this work, we have investigated PBI copolymer membranes that showed higher mechanical properties (in particular, creep resistance) than homo-para-PBI membranes, and still possessed good proton conductivities at 180˚C under anhydrous conditions. Membrane electrode assemblies were prepared and tested in single cells to demonstrate long-term durability at different current densities and low phosphoric acid leaching rates. We will also discuss recent investigations in terms of hydrogen pumping applications, which may have broad applications in both emerging energy applications and current industrial gas markets.

1. L. Xiao; H. Zhang; E. Scanlon; L.S.Ramanathan; E.-W. Choe; D. Rogers; T. Apple; B.C. Benicewicz. Chem. Materials, 2005, 17, 5328-5333.
Organic/Inorganic Composite Membrane Using a Proton-Conducting SnP2O7 Electrolyte and PFSA Polymers for Intermediate Temperature PEMFC
Authors: Lee Kwan-Soo , Kim Yu Seung , Kreller Cortney R , Wilson Mahlon S. , Mukundan Rangachary
Published: February 2020

Current fuel cells for transportation and residential applications use polymer electrolyte membrane fuel cells (PEMFCs) which require platinum catalysts and operate below 80 °C due to water management issues. However, PEMFCs operating at 100 °C or higher temperatures in anhydrous conditions do not need a humidifier, and do not suffer from water management issues created by the presence of liquid water. Excessive amount of liquid water in the electrode can flood the backing and catalysts layers at lower temperatures leading to poorer fuel cell performance. Furthermore, such intermediate temperature PEMFCs can solve the problem of carbon monoxide (CO) poisoning of the anode electrocatalyst leading to relaxation of the hydrogen fuel quality standards, thus lowering infrastructure costs. Finally, higher operating temperatures allow for simpler cooling systems in transportation applications, which results in smaller and lighter radiators. These advantages mean that a paradigm shift in fuel cells for transportation and residential applications can be achieved with an intermediate temperature proton conducting solid-electrolyte that can operate above 150 °C.

Unfortunately, electrolyte membranes and ionomers developed so far do not have satisfactory conductivity and performance in the above temperature ranges, at low-humidity, or in non-humidified conditions. The further advancement of higher temperature PEMFCs this relies on the development of membranes that process the desired electrochemical and mechanical properties in dry (< 30% RH) hot (> 100 oC) conditions.

In this study, we have developed an organic/inorganic composite membrane using a SnP2O7 (TPP) inorganic conductor and evaluated the fuel cell performance under various condition. Figure 1 illustrates the conductivity of this membrane under anhydrous conditions at various temperatures. The conductivity is a strong function of the % of TPP in the composite and reach as high as 0.1 S/cm at T ≥ 250oC using ≈ 90wt % TPP.

Membrane electrode assemblies (MEA) were prepared from these membranes using either standard PEMFC Gas diffusion electrodes or Pt/C/TPP based electrodes painted into to the membrane. The performance of one of these MEAs is shown in Figure 2. A maximum power density of 300mW/cm2 (not shown) has been obtained for fuel cell operation at ≈ 250 oC and < 5 % relative humidity. While these preliminary results are promising, there are still challenges with low open circuit voltage (OCV) due to membrane porosity and high kinetic losses due to insufficient electrode morphology optimization. In this talk we will address these issues and discuss the progress made towards better performing intermediate temperature fuel cells.

[1]    Nagao et al., J Electrochem Soc, 2006

[2]    Nagao et al. Electrochem Solid State Lett, 2006.

Figure 1
Tomographic Analysis of Polymer Electrolyte Fuel Cell Catalyst Layers: Methods, Validity and Challenges
Authors: Thiele Simon , Vierrath Severin , Klingele Matthias , Zengerle Roland
Published: February 2020

The catalyst layer (CLs) are the central part of Polymer Electrolyte Fuel Cells. Consisting of catalyst particles, ionomer, carbon black plus numerous gases and liquid water during operation, the CL contains not less than five different phases with a plethora of mutual physical interactions. Further, all these phases have characteristic length scales in the nanometer range. Due to its nanoscale, multi-phase nature the CL bears complex physical phenomena that are very challenging to describe and understand.

The precise morphology of all phases within a CL plays a key role for reactant transport and thus  performance: Platinum catalyst particles with poor connection to ion conducting, electron conducting or gas transporting phases cannot contribute to the fuel cell reaction. Also, the precise shape of the pathways of the reaction species determines their effective transport properties. Wetting or non-wetting pore wall areas influence water precipitation and therefore the generation of liquid water networks. Such networks both improve ionic transport and adulterate gas transport. 

Facing the tremendous influence morphology has on PEMFC performance, cost and durability, tools to image morphology are an obvious necessity. While there is a variety of imaging methods that allow three-dimensional reconstructions, only few are able to resolve the nanostructure of CLs: x-ray tomography (Xt), focused ion beam / scanning electron microscopy tomography (FIB-SEMt) and transmission electron microscopy tomography (TEMt) [1].

Both Xt and FIB-SEMt have been proven to enable differentiating porous and solid phase within PEMFC CLs [2,3]. TEMt allows imaging with resolutions below 1 nm and can be directly used to image Platinum particles [4]. To image all important phases multiple tomographic techniques must be used. In this talk we give an overview on the latest tomographic analysis techniques for PEMFC CL reconstruction with a particular emphasis on FIB-SEMt, multi-scale imaging approaches and validity of the existing reconstruction methods.

References

[1]   G. Möbus, B.J. Inkson, Materials Today 10 (2007) 18–25.

[2]   C. Ziegler, S. Thiele, R. Zengerle, J. Power Sources 196 (2011) 2094–2097.

[3]   W.K. Epting, J. Gelb, S. Litster, Advanced Functional Materials (2012).

[4]   H. Uchida, J.M. Song, S. Suzuki, E. Nakazawa, N. Baba, M. Watanabe, The Journal of Physical Chemistry B 110 (2006) 13319–13321.

[5]   S. Thiele, T. Fürstenhaupt, D. Banham, T. Hutzenlaub, V. Birss, C. Ziegler, R. Zengerle, J. Power Sources 228 (2013) 185–192.
Preparation Procedures of Pt-Decorated SnO2 Electrocatalysts on Conductive Fillers
Authors: Horiguchi Dai , Noda Zhiyun , Hayashi Akari , Sasaki Kazunari
Published: February 2020

For polymer electrolyte fuel cells (PEFCs), the electrocatalysts with Pt nano-particles homogeneously dispersed on carbon black (Pt/C) are widely used. However, during the fuel cell start-stop cycles, the potential of the cathode can reach up to ca. 1.5V, resulting in a severe carbon corrosion. Tin oxide (SnO2) has been studied as an alternative support material because of its thermochemical stability. Takasaki et al. [1] have demonstrated negligible degradation within 60,000 cycles in a half-cell test, indicating that Pt/SnO2 electrocatalyst can exhibit an excellent voltage cycle durability. However, relatively low electrical conductivity in such semiconducting oxides often leads to poor cell performance. In the previous PEFC Symposium in Cancun, we reported higher activity of Pt/SnO2 electrocatalysts on conductive fillers acting as the backbones of the electrocatalysts [2]. We selected vapor grown carbon fibers (VGCF) and acetylene black (AB) as possible conductive fillers, and Pt/SnO2/VGCF and Pt/SnO2/AB were synthesized. Their electrochemical surface area (ECSA) was about three times as large as that of Pt/SnO2. However, they are slightly inferior to the ECSA of Pt/C. Here, we aim to improve the electrochemical activity of Pt/SnO2electrocatalysts on conductive fillers approaching that of the state-of-the-art Pt/C electrocatalyst.

First, we have reexamined the procedure for the preparation of SnO2. Previously, SnO2/VGCF and SnO2/AB were synthesized via the ammonia co-precipitation. In this process, due to heat treatment required at a high temperature (e.g. 600oC), the particles of SnO2 were agglomerated. We thus introduced a homogeneous precipitation procedure using microwaves which requires no heat treatment at a high temperature. Consequently, the BET specific surface area of SnO2becomes one order of magnitude larger.

Second, we have adjusted the loading of SnO2 for the conductive fillers. The BET specific surface area of SnO2/VGCF becomes larger with increasing SnO2 loading. However, their electrochemical activity decreased for too high SnO2 loading, due to its lower electrical conductivity. In addition, the catalytic activity was improved by heat treatment to 200 or 400oC. The details on the catalytic activity increase by optimizing SnO2loading and heat treatment temperature will be presented at the meeting.

 [1] F. Takasaki et al., J. Electrochem. Soc.,
158(10) B1270 (2011).

 [2] D. Horiguchi et al., ECS Trans., 64(3) 215 (2014).

Figure 1
Facile Synthesis of Three-Dimensional Graphene Nanomaterials via Supercritical Fluid for Oxygen Reduction Reaction
Authors: Zhu Chengzhou , Zhou Yazhou , Fu Shaofang , Du Dan , Lin Yuehe
Published: February 2020

The considerable interest in polymer electrolyte membrane fuel cells (PEMFCs) has sparked a sustained research effort on more active and reliable oxygen reduction reaction (ORR) electrocatalyst. Although great progress has been made on ORR catalysts in recent decades, the further development of PEMFCs is severely restrained by high-priced Pt in the cathode catalysts and the slow kinetics of the ORR. Control of nanostructures at the atomic level can precisely and effectively tune catalytic properties of materials, optimizing the structural and compositional effect and further enabling enhancement in both activity and durability. Besides, most electrochemical systems consist of porous electrode materials. These 3D porous architectures are able to provide higher specific surface areas and larger pore volumes, not only maximizing the availability of electron transfer within nanosized electrocatalyst surface area but also providing better mass transport of reactants to the electrocatalyst. Fabricating interconnected mesoporous arrays/superstructures is critical to achieve both high surface area and fast mass transfer. Under the circumstances, constructing novel 3D porous nanostructures with non- and low Pt group metal (PGM) nanocatalysts have received significant attention to further enhance ORR electrocatalytic performance.

Supercritical CO2 (sc-CO2) process offers an elegant and efficient route for the synthesis and processing of novel nanocomposite materials, consisting of active nanocarbon and nanocrystals. Herein, we developed the sc-CO2 technique to synthesize boron-doped 3D graphene and low PGM-based graphene/PtFe with 3D porous nanostructures. Significantly, these 3D nanocomposites show excellent electrocatalytic activity and high stability toward the ORR, holding great promise for the development of PEMFCs.
Imaging Phosphoric Acid Migration in High Temperature Polymer Electrolyte Fuel Cells by X-Ray Tomographic Microscopy
Authors: Eberhardt Sebastian H. , Marone Federica , Stampanoni Marco , Büchi Felix N , Schmidt Thomas J.
Published: February 2020

High temperature polymer electrolyte fuel cells (HT-PEFC) use phosphoric acid (PA) as the proton conducting electrolyte, which is imbibed in a polybenzimidazole (PBI) membrane. The low vapour pressure of PA allows for increased operating temperatures of up to 200°C. At the higher operating temperatures, the tolerance to fuel gas impurities increases significantly and operation with CO levels up to 3% and H2S up to 10 ppm can be achieved.1 Phosphoric acid doped PBI membranes are therefore ideal candidates for cost-efficient combined heat and power (CHP) as well as hydrogen separation, purification and pumping applications. Unlike low temperature sulfonic acid based PEFC, the electrolyte is not covalently bound to the polymer backbone of the membrane and migration of anions in the electric field can occur similar to what has been observed in phosphoric acid fuel cells (PAFC).2,3 We have recently demonstrated how X-ray tomographic microscopy (XTM) can be applied for imaging electrolyte migration in HT-PEFC under dynamic operation.4 It was shown, for the first time, that PBI based membrane systems exhibit extensive PA migration from cathode to anode under high current operation. PA flooding of the anode gas diffusion layer (GLD) and flow field channel was observed.

In this contribution, the application of synchrotron based XTM for in-operando imaging and quantification of migrated phosphoric acid in HT-PEFC will be presented. The influence of current density, temperature, membrane material (conventional m-PBI film casted5 and sol-gel based6 membranes) and phosphoric acid loading will be discussed.

[1]       T. J. Schmidt and J. Baurmeister, ECS Trans., 3, 861–869 (2006).

[2]       H. R. Kunz, ECS Trans., 11, 1447–1460 (2007).

[3]       H. R. Kunz, Electrochem. Soc. Proc., 99-14, 191–207 (1999).

[4]       S. H. Eberhardt, M. Toulec, F. Marone, M. Stampanoni, F. N. Büchi, and T. J. Schmidt, J. Electrochem. Soc., 162, F310–F316 (2015).

[5]       R. Savinell, E. Yeager, D. Tryk, U. Landau, J. Wainright, D. Weng, K. Lux, M. Litt, and C. Rogers, J. Elelectrochemical Soc., 141, L46–L48 (1994).

[6]       L. Xiao, H. Zhang, T. Jana, E. Scanlon, R. Chen, E.-W. Choe, L. S. Ramanathan, S. Yu, and B. C. Benicewicz, Fuel Cells, 5, 287–295 (2005).
Enhanced Ir-Ru-Ox Electro-Catalysts for Oxygen Evolution in Proton Exchange Membrane Water Electrolysis
Authors: Monforte Giuseppe , Siracusano Stefania , Baglio Vincenzo , Aricò Antonino S.
Published: February 2020

Interest in water electrolysis has recently increased with the large diffusion of renewable energy sources and the perspective to produce hydrogen with a very low environmental impact [1-2].  In this regard, hydrogen appears a promising energy carrier that can be produced by cost-effective electrolysis of water using renewable energy sources and it can be used to store energy in grid-balancing services.  A challenging problem to the development of such process is the substantial energy loss associated with the oxygen evolution during electrochemical water splitting. High surface area nanostructured (2-10 nm) IrRu-oxide electro-catalysts can substantially reduce this loss allowing to achieve efficient  hydrogen production. IrOx and Ir0.7Ru0.3Ox nanosized materials of similar crystallite size (mean size 5 nm) were prepared for application as oxygen evolution electro-catalysts in solid polymer membrane water electrolysers (PEMWEs). The physico-chemical properties of the catalysts were characterized by X-ray diffraction (XRD), Transmission Electron Microscopy (TEM), Scanning Electron Microscopy (SEM) with Energy Dispersive X-ray (EDX) and X-ray-Photoelectron Spectroscopy (XPS). Particular efforts were addressed to tailor the crystallographic characteristics and the surface properties. The electrochemical properties were investigated in an electrolysis cell, based on Nafion 115 and 30% Pt/C as cathode catalyst, by using linear sweep voltammetry, electrochemical impedance spectroscopy and Tafel curves. The Ir0.7Ru0.3Ox-based electro-catalyst showed a performance of 3.2 A cm-2 at 1.85 V at 90°C which corresponds to a voltage gain of 0.1 V as compared to the IrOx catalyst at the same current density.  A similar Tafel slope with a decrease of charge transfer resistance for IrRuOx compared to IrOx would indicate the same mechanism for these materials and higher intrinsic activity for the mixed oxide. The present study indicates that Ir0.7Ru0.3Oxcan be an excellent electro-catalyst for the oxygen evolution in PEM-based water electrolysis provided that structure, morphology and surface characteristics are properly tailored.

 

Acknowledgements

The authors acknowledge the financial support of the EU through the FCH JU Electrohypem Project. ‘‘The research leading to these results has received funding from the European Community’s Seventh Framework Programme (FP7/2010-2013) for the Fuel Cells and Hydrogen Joint Technology Initiative under grant agreement Electrohypem n 300081.’’

References

 

 Siracusano, S.; Van Dijk, N.; Payne-Johnson, E.; Baglio, V.; Aricò, A.S.; Applied Catalysis B: Environmental,
2015, 164:488. DOI:10.1016/j.apcatb.2014.09.005

 

Aricò, A.S., Siracusano, S., Briguglio, N., Baglio, V., Di Blasi, A., Antonucci, V. Journal of Applied Electrochemistry,
2013, 43:107.  DOI:
 10.1007/s10800-012-0490-5
A CFD Simulation for an Air Breathing PEMFC for Power Source Portable Applications
Authors: Carcadea Elena , Varlam Mihai , Stefanescu Ioan , Ingham Derek , Marinoiu Adriana , Patularu Laurentiu , Raceanu Mircea , Schitea Dorin
Published: February 2020

Air breathing PEM fuel cells are a promising and a potential power source for portable applications. The challenges that air breathing fuel cells has to overcome in order to be used in portable applications and to be cost competitive are related to the ability to use logistic fuels, to the prevention of cathode contamination with impurities from the used air (supplied by active or passive methods), to the reduction of the size and weight.

In this context, the development of a mathematical model for a better understanding of the fundamental processes and characteristics associated with air breathing cathode operation is required. The three-dimensional model developed in this paper based on the ANSYS Multiphysics software was used to analyse the influence of the factors that influence the PEM fuel cell performance (flow field configuration, operating conditions). Regarding the flow field configuration a 3 step-serpentine was used for the anode channel and parallel channels were used in the cathode side for the forced air supply. In this respect, for the cathode side channels, the width, depth and the space between two adjacent channels was varied (1 mm, 1.5 mm, and 2 mm) in order to see their influence on the uniformity of the reactant distribution (particularly water) and on heat management. Regarding the operating parameters that can have a significant influence on the performance, our numerical analysis took into consideration the air flow rate, the humidity and temperature and the results are discussed in the paper. The analysis was intended to identify critical parameters and give an insight into physical mechanisms that can influence this type of air breathing PEM fuel cell.
Impact of Membrane Properties and Membrane Degradation on Cathode Catalyst Layer Degradation
Authors: Dutta Monica , Ghassemzadeh Lida , Lauritzen Mike , Harvey David , Wessel Silvia , Young Alan P , Knights Shanna
Published: February 2020

Understanding the effect of material properties and the structure of MEA components is critical to understanding MEA performance and degradation. Previous studies have shown that cathode catalyst layer degradation was observed to be influenced by water content within the MEA.  Both relative humidity and membrane type were shown to have a substantial effect on the degradation rates1.  As the membrane / ionomer plays a key role in the water management within an MEA, affecting water sorption, water crossover and phase changes, an improved understanding of the effects of membrane properties on cathode catalyst degradation is required. This study examines the effect of membrane properties, as well as the effects of membrane degradation on cathode catalyst layer degradation.

In this work, six membranes, including dense membranes Nafion®211 and Nafion®212, experimental reinforced PFSA  membranes with low and high equivalent weights (EW), and experimental reinforced partially fluorinated hydrocarbon membranes of high and low equivalent weights, were chosen for investigations of membrane property impacts on beginning of test (BOT) performance and cathode accelerated stress test (AST) durability.  These membranes had EW values ranging from ~ 600 to 1100, while the dry thickness ranged from 13 to 50 microns.  

Performance variations at BOT for the different membranes may be due to a combination of membrane thickness, resistance, and hydrogen and water cross-over effects.  After cathode AST cycling, ECSA loss and performance loss were increased for the thinner, lower EW membranes of each membrane family suggesting that membrane water content was the contributing factor.   The effects of membrane degradation on cathode catalyst layer degradation for three down-selected membranes will also be discussed.

Acknowledgements

Funding was provided by Department of Energy EERE Hydrogen and Fuel Cell Technology Program (Project DE-EE0006375).

References

[1] Silvia Wessel, David Harvey, “Development of Micro-Structural Mitigation Strategies for PEM Fuel Cells: Morphological Simulations and Experimental Approaches”, 2013 Annual Merit Review Proceedings: Fuel Cells, 16 May 2013, Project ID# FC049.
FEM Modelling of Diffusional Electrochemical Impedance Spectroscopy at a Channel Electrode
Authors: Holm Thomas , Ingdal Mats , Seland Frode , Harrington David A.
Published: February 2020

Calculation of the electrochemical impedance spectroscopy for a diffusional process at a channel electrode with laminar flow necessitates the solution of the diffusion-convection equation with appropriate boundary conditions.

Although the full equation has not been solved analytically, two sets of assumptions have been used previously, and the resulting equations were solved analytically:

i)     The axial diffusion is neglected and the Poiseuille flow is simplified as a Lévêque flow1,2.

ii)    Convection is neglected and it is solved as a simple diffusion process3.

However, although the assumptions intuitively allow for solving the problem in a large parameter space, parameters for which these approximations are valid have not been determined.

We demonstrate by using FEM software (Comsol Multiphysics™), that the full problem can be solved numerically. The solution obtained by FEM software is compared to experimental results and the two analytical solutions. The method shows good correspondence with the experimental results and a large flexibility, making it possible to solve more complex problems such as different diffusion coefficients4 and unconventional geometries. An example of a comparison between experimental results, numerical results using FEM software, and an analytical solution is shown in Fig. 1. The parameter space of the analytical solutions is investigated using two non-dimensional parameters, A and B, and a validity area is found where the analytical solutions are well-suited. The parameter A is a version of the Péclet number, A = 6vavh/D, and B is the ratio of electrode width and channel height, B = w/h.

References:

[1] B. A. Coles, R. G. Compton, J. Electroanal. Chem.
127,37 (1981).

[2] R. G. Compton, G. R. Sealy, J. Electroanal. Chem.
145,35 (1983).

[3] R. G. Compton, J. Winkler, J. Phys. Chem.
99,5029 (1995).

[4] Y. Wang, J. G. Limon-Petersen, R. G. Compton J. Electroanal. Chem.
652,13 (2011).

Fig 1: Nyquist plot of impedance spectroscopy at a channel electrode showing experimental values (blue boxes), values modelled in Comsol (blue line), values calculated analytically by neglecting axial diffusion and simplifying the flow (upward pointing black triangles), and values calculated by neglecting convection (downward pointing black triangles). Impedance values are dimensionless.

Figure 1
Thin TiO2 Overlayers As Catalysts for Oxygen Reduction and Evolution Reactions
Authors: Tavassol Hadi , Haile Sossina M
Published: February 2020

We report on the electrochemical activity of thin TiO2 overlayers on titanium micro-particles toward oxygen reduction and evolution reactions in a CsH2PO4 solid acid electrochemical system. The electrocatalysis at the interface of the super-protonic (at 245 °C) CsH2PO4 solid acid with the electrodes occurs at active sites which are also accessible to the humidified gases. Pt remains the best catalyst for the O2 reduction reaction in the cathodes of the solid acid fuel cells. Because of the strong O=O bond, oxygen reduction is a slow reaction even on a Pt surface at 245 °C, requiring high loadings of the precious Pt catalyst.  Solid state TiO2 catalysts are an attractive alternative. TiO2 catalysts show a range of activity depending on the relative ratio of the rutile to anatase polymorphs. Rutile phase exhibits a lower overpotential for the ORR. TiO2 films are grown on Ti metal micro-particles under slightly oxidizing environment at elevated temperature (600-900 °C). The thickness and relative ratio of the rutile to anatase phase is controlled by the growth temperature and holding time. X-ray diffraction analysis of the films reveals that the amount of the oxide increases with increasing the growth temperature. At higher growth temperatures, the oxide layer formed is mostly rutile.  The activity of the TiO2 films is controlled by both the phase and thickness of the films. Between 700-900 °C, the activity of the TiO2 overlayers for oxygen reduction reaction increases with increasing the growth temperature. Interestingly, thin oxide overlayers with mostly rutile phase grown at 600 °C show higher activity. We will discuss the origin of the improved activities of thin TiO2 overlayers.
Electrochemical Characterisation of Cobalt-Oxide Catalysts with Different Cobalt Loading for Oxygen Reduction Reaction in Alkaline Media
Authors: Uhlig Lisa Maria , Dyck Alexander , Sievers Gustav Wilhelm , Brüser Volker , Wittstock Gunther
Published: February 2020

Alkaline fuel cells are very promising because of their high efficiencies (1). In fuel cells the reduction of oxygen on cathode side is the performance-limiting step (2, 3). Catalysts, e.g. platinum, are used to enhance the oxygen reduction reaction (ORR) rate and also the performance. Due to the high costs of the fuel cell components, especially for the platinum catalyst (4), the fuel cell is not common for various applications up to now. The alkaline media enables the use of non-precious metals, e.g. cobalt or manganese oxides (5-8), to enhance the kinetic on the cathode side.

The electroactivities of different non-precious metal catalysts like cobalt oxide are promising to achieve a similarly high activity as platinum. A cobalt acetate precursor is plasma-treated and resulting cobalt oxide catalysts with different cobalt loading were investigated in different alkaline media and at temperatures between 25 and 75 °C using a rotating ring disk electrode (RRDE) analysis. The advantage of plasma treatment is the better distribution of particles, they are less agglomerated compared due to the common heat treatment (9-11). This leads to a higher activity of the catalyst material (9). Different characterisation methods are used to identify the catalyst material like XRD, TEM and SEM. A custom-built Teflon cell is used for the RRDE analysis to avoid glass corrosion in alkaline media. Glass corrosion affects the electrochemical measurements (12), therefore it is necessary to replace glass components for the experiments.

References:

1.            E. Gülzow, Fuel Cells, 4, 251 (2004).

2.            K. Kordesch, V. Hacker, J. Gsellmann, M. Cifrain, G. Faleschini, P. Enzinger, M. Ortner, M. Muhr and R. R. Aronson, Jounal of Power Sources, 5 (1999).

3.            B. Viswanathan, C. V. Rao and U. V. Varadaraju, in Photo/Electrochemistry & Photobiology in the Environment, Energy and Fuel, p. 43 (2006).

4.            G. Wu, K. L. More, C. M. Johnston and P. Zelenay, Science, 332, 443 (2011).

5.            S. Lu, J. Pan, A. Huang, L. Zhuang and J. Lu, Proc. Natl. Acad. Sci. U. S. A., 105, 20611 (2008).

6.            H. Meng and P. K. Shen, Electrochem. Commun., 8, 588 (2006).

7.            F. Cheng, J. Shen, W. Ji, Z. tao and J. Chen, Applied Materials & Interfaces, 1, 460 (2009).

8.            M. Mamlouk, S. M. S. Kumar, P. Gouerec and K. Scott, J. Power Sources, 196, 7594 (2011).

9.            V. Brüser, N. Savastenko, A. Schmuhl, H. Junge, I. Herrmann, P. Bogdanoff and K. Schröder, Plasma. Process. Polym., 4, S94 (2007).

10.          N. A. Savastenko, K. Anklam, A. Quade, M. Brüser, A. Schmuhl and V. Brüser, Energy Environ. Sci., 4, 3461 (2011).

11.          I. Herrmann, U. I. Kramm, S. Fiechter, V. Brüser, H. Kersten and P. Bogdanoff, Plasma.
Process. Polym., 7, 515 (2010).

12.          K. J. J. Mayrhofer, G. K. H. Wiberg and M. Arenz, J. Electrochem. Soc., 155, P1 (2007).
Electroreduction of Oxygen on Carbon Supported Palladium Nanocubes
Authors: Erikson Heiki , Sarapuu Ave , Tammeveski Kaido , Solla-Gullón José , Feliu Juan
Published: February 2020

In recent years palladium has proven to be a good alternative to platinum in low-temperature fuel cell cathode catalysts.1 The electrocatalytic activity of Pd catalysts toward the oxygen reduction reaction (ORR) can be improved by preparing shape-controlled nanoparticles.2

The aim of this study was to investigate the electrocatalytic activity of carbon-supported Pd nanocubes of different size and varied metal loading toward the ORR. CTAB or PVP were used as capping agents to prepare the Pd nanocubes of different sizes.

The morphology of Pd/C catalyst was evaluated using transmission electron microscopy, which showed that the particles are cube shaped and their size depends on the synthesis method. The thermogravimetric method was used to determine the Pd loading on carbon. The nominal Pd contents of the prepared catalysts were 5, 20 and 50 wt% and the measured content deviated only slightly.

Electrochemical experiments were carried out in acid and alkaline solutions. The catalysts were electrochemically characterized by cyclic voltammetry and by oxidation of pre-adsorbed CO. Both electrochemical methods showed characteristics that can be attributed to Pd(100) facets that are predominant on cubic Pd nanoparticles. From cyclic voltammograms the electrochemically active surface area was found, expectedly it increased with increasing Pd content in the catalyst and also with decreasing the particle size.

The ORR studies in 0.5 M H2SO4 showed that the half-wave potentials increase with palladium content and with decreasing the particle size, following the changes in the electrochemical surface area. The mass-activity of the catalysts did not depend on the Pd loading, but increased with decreasing the particle size.  From the rotating disk electrode studies the number of electrons transferred per O2molecule was found to be near 3.5, showing that some hydrogen peroxide is formed. The Tafel analysis revealed that the ORR mechanism on carbon-supported Pd nanocubes was the same as on bulk Pd.

In alkaline media the half-wave potentials were in the same order as in acid solution, but more subtle differences were evident. The Koutecky-Levich analysis of the RDE data showed that the number of electrons transferred per oxygen molecule was 4 in the whole range of potentials studied. The Tafel analysis showed that the rate limiting step is the sluggish transfer of first electron to O2molecule.

References

1. E. Antolini, Energy Environ. Sci., 2, 915 (2009).

2. H. Erikson, A. Sarapuu, N. Alexeyeva, K. Tammeveski, J. Solla-Gullon, and J. M. Feliu, Electrochim. Acta, 59, 329 (2012).

Figure 1
Extensive Studies of the Electrochemical Behavior of Pt Ni/MWCNT Catalysts in Alkaline Media
Authors: Valenzuela-Muñiz Ana Maria , Rosado Gabriel , Verde Gomez Ysmael
Published: February 2020

Multi-walled carbon nanotubes (MWCNT) enclose properties and characteristics that are interesting and suitable for electrochemical applications. In this way, the deposition of metallic particle in the surface of MWCNT has been a topic of intense study. It is well know that bimetallic systems of Pt with other metal are of great interest due to the possibility of reduce the costs by decreasing the metal loading, and at the same time increase the properties of the electrocatalyst. In specific, PtNi/MCNT systems have proven to have high activity in different electrochemical reactions in acid media, along with good tolerance to CO poisoning. However, the main drawback is the poor stability in acidic environments. Thus, the electrochemical evaluation of these materials in alkaline media becomes an interesting field of study. Previous investigations of the research group performed in alkaline media showed that the system PtNi/MWCNT exhibited activity towards the hydrogen oxidation reaction as well as the oxidation of methanol. As a continuation, in this work a more detailed study was performed including the evaluation of different materials PtNi/MWCNT in the oxygen reduction reaction. The experimental matrix was designed to evaluate the influence of PtNi structure on the electrochemical behavior, interesting results were found.  The materials were characterized by microscopy as well as x-ray diffraction. The electrochemical tests were done in a conventional three electrodes cell, using a glassy carbon rod as working electrode, a Pt wire as counter electrode, a Ag/AgCl (KCl Sat) electrode as reference, and 1M NaOH solution as electrolyte. The results as well as the discussion will be presented at the conference.

Authors acknowledge the support to CONACyT under grant No. 213373
Field-Dipole Interactions at p-GaAs (100) Electrode in Sodium Dodecyl Sulfate Acid Solution
Authors: Lazarescu Valentina , Enache Mirela , Dobrescu Gianina , Anastasescu Mihai , Negrila Catalin , Lazarescu Mihail Florin
Published: February 2020

Electrochemical impedance spectroscopy (EIS), X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) have been used to investigate the effects of the sodium dodecyl sulfate (SDS) at the electrified p-GaAs(100) / H2SO4 interface. The analysis of the EIS data revealed that the surfactant adsorption brings about a pronounced decrease of the capacitive contributions of the semiconductor surface state (Fig. 1 B) accompanied by a shift to more positive potentials of the Mott-Schottky plot (Fig. 1 A). According to the XPS (Fig 1 C) and AFM data, SDS forms a well-ordered protective overlayer on p-GaAs(100) which prevents the surface oxidation in air. However, the field-dipole interactions acting under the applied potential control become preponderant at the electrified GaAs / solution interface yielding distinct effects at the end of the direct and forward potential scans as seen in Fig 1 C. These results suggest that SDS interaction with GaAs substrate might be an efficient tool to improve both the electronic properties of the semiconductor and its protection against the surface oxidation in air.

Acknowledgements

This work was supported by a grant of the Romanian National Authority for Scientific Research, CNCS – UEFISCDI, project number PN-II-ID-PCE-2011-3-0304

Figure 1
The Importance of Testing and Designing Lithium-Ion Batteries in the Relevant Environment
Authors: Jeevarajan Judith A
Published: February 2020

Lithium-ion batteries have the highest energy density and cycle life of the rechargeable battery chemistries in the commercial battery market today.  However, associated with that high energy density is its tendency to go into thermal runaway when the battery is not designed or used appropriately.  Although the size of the lithium-ion batteries in various applications are growing in energy and power, the nature of tests carried out to characterize their safety has not grown to adequately understand the hazards associated with the battery designs.  Typical hazards associated with these batteries are overcharge, external and internal short circuites and high temperatures.  Thermal runaway can occur in these batteries in many ways including the failure of internal cell protective devices.  One needs to characterize not only a cell design but also the appropriate module and battery design especially if the cell level controls are used as one of the first two levels of control. The thermal dissipation characteristics and the propensity of any cell going into thermal runaway to propagate to other cells should also be considered for faults that are not fully understood at the battery level for the environment it is to be used in.  Stringent certification and qualification tests of the battery design in the relevant environment with post-test destructive and non-destructive analysis will help in defining the safety as well as provide insight on the robustness of the safety controls.  This paper will discuss the various aspects of the li-ion battery design that needs to be characterized and provide some insight into recommended design solutions.
Development of an on-Demand Internal Short Circuit (NREL/NASA)
Authors: Keyser Matthew , Pesaran Ahmad , Darcy Eric
Published: February 2020

NREL, in conjunction with NASA, has developed an internal short circuit (ISC) device that can be placed anywhere within the battery and may be used with both spirally wound and flat-plate cells.  The internal short device is small compared to other shorting techniques being developed by industry and does not rely on mechanical pressure deforming the battery to activate the short as do most of the other “internal shorts” being developed.  The battery can be used and cycled within normal operating conditions without activating the internal short device.  This allows for the battery to be aged prior to activation of the internal short.  Another unique feature of NREL’s internal short device is that the resistance of the short can be tuned to simulate a hard (more energetic) or soft (less energetic) short. Once the short is activated, the positive and negative components of the battery are internally connected within the cell and internal short circuit begins.  NREL’s ISC can simulate all four types of shorts within a cell – collector to collector, collector to anode, collector to cathode and collector to collector.

NREL uses the internal short circuit device to better understand the failure modes of Li-ion cells and to validate NREL’s abuse models.  The internal short produced by NREL’s device is consistent and is being developed as an analysis tool for battery manufacturers and other national laboratories as well as OEMs. This has broad-reaching applications as automakers bring electrified vehicles to market in larger

Over the past three years, NREL has implanted their ISC into cylindrical 18650 LiCoO2 cells to determine the effectiveness of a shutdown separator with regards to ISC type – in particular, we compared a collector to collector ISC versus a collector to aluminum ISC.  NREL has also been using the ISC to determine the effectiveness of a non-flammable electrolyte in LiMnO4 pouch cells.  During our presentation, we will update the battery community on the effectiveness of the ISC in understanding the behavior of these safety devices incorporated into these two cell types and chemistries.  We will also show how the ISC can be used for propogation testing in modules and packs.
Measurement of Energy Distributed Between Cell Mass and Hot Ejecta during Thermal Runaway of Lithium Ion Cells at Varying State of Charge
Authors: Yayathi Sandeep , Doughty D. H. , Walker William Q.
Published: February 2020

Thermal runaway propagation is a major concern in battery packs constructed with large numbers of small lithium ion cells. This is especially true for battery applications involving manned space flight.

This work by NASA presents a scientific study that evaluates the thermal energy release of these cells during thermal runaway.  Specifically, these experiments compare, as function of state of charge, the energy retained in the cell mass versus energy released in ejected materials and hot gasses. In addition, this study evaluates the effect of state of charge on thermal stability, including onset of self-heating and thermal runaway temperature for three types of commercial cells.

Tests are conducted utilizing accelerating rate calorimeter (ARC) equipment using a heat wait seek heating algorithm combined with unique cell containment fixtures and properly placed thermal sensors to allow the aforementioned energy calculations. This work seeks to inform the development of thermal abuse models and aid the engineering design and development of non-propagating battery pack designs utilizing small lithium ion cells.
Low-Cost Synthetic Routes for Fabricating Tandem/Multi-Junction Photoelectrochemical Devices
Authors: Cheng Wei , Rassoolkhani Alan M , Mubeen Syed
Published: February 2020

Using sunlight to convert widely available and inexpensive feed stocks such as water, CO2, and industrial wastes (including halogenides) reliably to fuels and value added chemicals, efficiently and cost-effectively, has been, and continues to be a major goal. Most such reactions require a minimum of 1eV or more photon energies. For example, the minimum free energy required to split water reversibly is 1.23 eV. However, kinetic limitations and other sources of inefficiencies (for example, water oxidation on photoanodes is kinetically sluggish, and CO2 reduction at photocathodes needs high overpotentials) make the practical energy needed to carry such reactions even considerably higher. A single-junction photosynthetic device would therefore need to base on a semiconductor with a band gap (Eg) > 2.5 eV for it to carry out water splitting or CO2 reduction, precluding the exploitation of a substantial portion of the solar spectrum. Using tandem/multi-junction photovoltaic architectures is an attractive strategy to overcome these limitations. Such strategies have been estimated to be capable of achieving ~18% solar-to-hydrogen conversion efficiencies.  John Turner and his colleagues [1] demonstrated a solar-to-H2 conversion efficiency of 12.4% using multi-junction III-V semiconductors in 1990’s. However, the high cost and complexity associated with device fabrication using Si  and III-V semiconductors to produce triple junction devices have impeded commercialization. Here, we report a novel and low-cost wet chemical synthesis route to fabricate a tandem junction PEC device through direct deposition of inexpensive and efficient metal oxide/sulfide based photoanodes on single junction Si solar cells which act as photocathodes. The above structures were able to generate sufficiently high cell voltages to drive valuable, and, at times, challenging photoelectrochemical processes sustainably.

Reference:

Khaselev, O. & Turner, J. A monolithic photovoltaic-photoelectrochemical device for hydrogen production via water splitting. Science (New York, N.Y.) 280, 425–7 (1998).
Silica-Coated Magnetostrictive Biosensors for Real-Time Detection of Campylobacter Jejuni in Washing Water
Authors: Zhang Lin , Wang Ou , Cheng Z.-Y. , Huang Tung-Shi
Published: February 2020

It is known that foodborne pathogens have been found to cause food contamination at every stage of food production, processing, and distribution.
Campylobacter jejuni (C. jejuni) is one of the most common genera of foodborne pathogens. There is a critical need for developing a simple and affordable device that allows the poultry industry to monitor the dynamic population changes of C. jejuni rapidly and frequently. In this work, biosensors using magnetostrictive particle (MSP) are developed to detect C. jejuni
in washing water directly got from chicken factory/company. The MSPs in different sizes are fabricated and coated with three layers of silica. The coatings are highly stable according to the resonance frequency response in pure water and poultry rinse water. Anti-C. jejuni antibodies are well immobilized on silica-coated sensors by covalent bonding to form a biosensor and the immobilization efficiency was tested by ELISA. SEM images and resonance frequencies show that the MSP based biosensors can capture C. jejuni in washing water. The responses of the biosensor in C. jejuni suspension with different concentrations were studied, which were used to determine the detection limit of the biosensor. The detection limits of silica-coated MSP biosensor in bacterial detection is around 102 CFU/mL. However, the silica coated MSP biosensors may have better performance in more complex food systems due to its strong covalent binding antibody attachment. The silica coated MSP biosensors have higher potential application in the food industry for onsite monitoring of microbial populations.