bluuebunny/crossref_metadata_2025 huggingface dataset:
Electrochemical Atomic Layer Growth of a n-p Junction
Authors: Innocenti Massimo , Giaccherini Andrea , Guerri Annalisa , Vizza Martina , Berretti Enrico , Lavacchi Alessandro , Passaponti Maurizio , Caporali Stefano , Di Benedetto Francesco
Published: February 2020

The increasing in worldwide energy consumption, moved the interest of governments and scientist towards research on renewable energy. Among all the renewables, photovoltaic energy (PV) is one of the most researched technology, because of the availability of its primary energy source (the sun) and the possibility of a direct conversion of solar energy into electric energy. However, the growth of a p-n junction involving non-abundant elements (e.g. CIGS), could have an important drawback in its full life cycle assessment when considering the shortage of the elements and the energy required to assemble the device. Electrodeposition is known for its low energy requirements and facile growth of thin-films of semiconducting materials. In this context, compounds such as Kesterites (CZTS, ternary and quaternary copper and zinc sulfides) could be used in virtue of their semiconducting behavior in conjunction with electrodeposition from aqueous media methodologies to overcome the energy and materials constraints impairing the full exploitation of the actual generation of semiconducting devices. It is important to stress that for the conversion of solar energy in electric energy the charge separation and the bending of the electronic bands occurring at a p-n junction is necessary. Moreover, enhanced transport proprieties (e.g. low concentration of defect) ensure a slow recombination kinetics leading to higher current. Hence, a high quality growth of the p-n junction is crucial to maximize the efficiency and power density of a photovoltaic device. In this context, E-ALD (Electrochemical Atomic Layer Deposition) proven to very suitable for the growth of ordered (even pseudo single crystal) ultra-thin films. Thus, such method seems a legitimate alternative to the high pressure and temperature methods used since today. In recent years we tried to make a proof of concept for the E-ALD growth of a p-n junction. To confirm this proof of concept, in this communication we explore the feasibility of the E-ALD growth for an n-p composite ultra-thin film composed by 60 cycle of Cu2S (p semiconductor and Kesterite precursor) on top of 60 cycle of CdS (with n electronic proprieties). Preliminary electrochemical studies revealed the complex nature of this composite ultra-thin film, impairing the anodic stripping of metals due to a stabilization of the CdS substrate. However, the stability of the substrate and the voltammetric study of a Cu solution in ammonia buffer pointed to the surface limited nature of the Cu deposition step. In order to confirm that the Cu electrodeposition is surface limited several electrochemical and spectroscopical measurements on a composite ultra-thin film Cu2S(60cycle)/CdS(60cycle)/Ag(111) are reported, leading to the confirmation of the layered (p-n) structure of the thin film.
(Invited) Novel in-Situ Operando X-Ray Absorption Spectroscopy Techniques for the Characterization of the Electrochemical Growth of Metal Oxides
Authors: Di Benedetto Francesco , Berretti Enrico , Giaccherini Andrea , Giurlani Walter , Innocenti Massimo , Lavacchi Alessandro , Montegrossi Giordano
Published: February 2020

In-situ Operando X-ray Absorption Spectroscopy (XAS) has been widely adopted to understand materials modification under working conditions. Under appropriate conditions, In-situ operando XAS provides surface information, being a tool of primary importance to study electrochemical growth.

In the present talk we will describe the application of a recently developed XAS technique to the electrochemical growth of metal oxides. This technique, known as FEXRAV (Fixed Energy X-ray Absorption Voltammetry), is an experimental method that couples cyclic voltammetry (CV) with the acquisition of the XAS signal at a fixed energy diagnostic of a chemical and/or structural modification of the material. This approach is extraordinary powerful and we propose it as a new tool to understand the formation of oxide thin films on metals relevant to electrochemical energy conversion and storage.

This contribution reviews the fundamental principles, the electrochemical cell design, and the synchrotron beamline set-up that enable the collection of FEXRAV data. As a case study, we report the investigation of the formation of palladium oxides on palladium nanoparticles in alkaline media, a subject of extreme importance for alkaline fuel cells. With our investigation we have discovered that palladium oxidation occurs at potential larger than 0.65 V (RHE) and that the passivation layer blocks out the capability of palladium to oxidize alcohols. Remarkably, these conditions happen in real systems and are responsible of the loss of efficiency of direct alcohol fuel cells. We have also found that the presence of promoting metal oxide in contact with Pd accelerate the oxidation and, ultimately are detrimental for the stability of the devices.

Finally, the description of a novel experimental set-up with enanched surface sensitivity based on grazing incidence FEXRAV experiments will be given, together with preliminary results on the in-situ electro-oxidation of palladium thin films thae have been obtained at the LISA BM08 beamline of the European Synchrotron Radiation Facility.
Morphological and Compositional Study of Cu2s Grown By Means of E-ALD on Ag(111)
Authors: Giaccherini Andrea , Innocenti Massimo , Russo Francesca , Salvietti Emanuele , Berretti Enrico , Passaponti Maurizio , Lavacchi Alessandro , Montegrossi Giordano , Di Benedetto Francesco
Published: February 2020

CIGS are very promising semiconducting materials for solar energy conversion due to their high efficiency. However, when analyzing the full life cycle assessment the toxicity and shortage of the involved elements along with the EROEI (Energy Return Over Energy Investment) needed to assemble the devices are considered unfavorable for the large scale exploitation of the CIGS. To overcome this issues, scientific community is focusing attention on new compounds based on economic and low-environmental impact elements such as Cu, Sn, Fe and Zn. In particular, quaternary semiconducting materials based on the kesterite (Cu2ZnSnS4) mineral structure are the most promising candidates to overtake the current generation of light-absorbing materials for thin-film solar cells. Electrodeposition is known as a low-cost semiconductor technique for the growth of semiconducting materials in electronic devices. Surface limited electrodeposition of atomic layers, can be performed by means of Electrochemical Atomic Layer Deposition (E-ALD) technique to obtain ultra-thin films of copper sulphides on a Ag(111) single crystal. Although its band gap it is not optimal for solar energy conversion, this materials can have interesting electronic proprieties, for instance Cu2S is a superionic conductor. However, from the E-ALD scheme one would expect a CuS hexagonal structure (covellite) with no any important electronic proprieties. Still, recently reported operando SXRD on this material allowed to assign a crystallographic cell corresponding to a cell directly derived from chalcocite’s (Cu2S). These unexpected results are confirmed by the analysis of the growth mechanism performed by means of operando SXRD and XRR. In this communication we reports a morphological and compositional study, confirming the composition and morphology expected from the results of the SXRD operando measurements pointing to the growth of Cu2S by means of E-ALD.
Superconformal Bottom-up Gold Deposition in High Aspect Ratio through Silicon Vias
Authors: Josell Daniel , Moffat Thomas P.
Published: February 2020

This work demonstrates gold filling of 56 mm tall, annular Through Silicon Vias (TSVs) using a mechanism that couples suppression breakdown and surface topography to achieve controlled bottom-up deposition. The chemistry, a sulfite electrolyte containing a dilute suppressing additive, and processes are fully detailed. The impact of deposition potential and additive concentration on the filling of the patterned features is presented. Voltammetric measurements on planar substrates, including the impact of rotation rate and suppressor concentration on the rate of metal deposition and potential of suppression breakdown, are used to quantify the interplay between metal deposition and suppressor adsorption. The derived kinetics are then used with the S-shaped negative differential resistance (S-NDR) mechanism for superconformal deposition to quantitatively predict the observed bottom-up filling in the TSVs as well as understand the spatial variation of deposit microstructure. The predictions capture the experimental observations. This work extends understanding and application of the additive-derived S-NDR mechanism, including previous demonstrations of superconformal filling of TSVs with nickel, cobalt, zinc and copper.
Hybrid Electrolytes for Lithium Batteries
Authors: Balsara Nitash P
Published: February 2020

Lithium-ion batteries, developed for powering consumer electronics, are being reconfigured for use in electric vehicles, and for backing-up home solar installations. The adoption of batteries in large-scale applications will accelerate if some of the key limitations of current lithium-ion technology can be addressed: cost, energy density, cycle-life, and safety. The limited cycle-life of current lithium-ion batteries is mainly due to the instability of the liquid electrolytes used therein. In this talk we will discuss solid electrolytes. No one solid has the properties needed for practical applications. Glass electrolytes (e.g. lithium-phosphorous-sulfur glasses) exhibit excellent ion transport properties but they are brittle and processes for their incorporation into large format batteries have not yet been established. One may add non-brittle components, but this reduces the conductivity of the electrolyte. Polymer electrolytes (e.g. mixtures of amorphous poly(ethylene oxide) and lithium salts) are soft and non-brittle, but have poor mechanical properties due to the coupling between segmental and ion motion. In this case, incorporating a stiff non-conducting block may be introduced to improve mechanical properties but this results in decreased conductivity. I will first discuss the general properties of hybrid electrolytes. This will be followed by a description of attempts to commercialize these materials.
Electrodeposition of Iron Group Metals from Ethylene Glycol Solution: From Thin Films to Nanowires
Authors: Panzeri Gabriele , Accogli Alessandra , Gibertini Eugenio , Magagnin Luca
Published: February 2020

Iron group metals (Fe, Ni, Co) electrodeposition has been studied extensively from aqueous solutions, especially because of the great practical interest of such elements and their alloys. However, there are cases where non-aqueous solvents show advantages over the traditional baths and for some systems they may represents the only solution to carry out successfully electrodeposition [1, 2]. Nowadays, particular attention is paid to deep eutectic solvents (DESs) because of their easy preparation method and working conditions [2]. In this work we tried to simplify further this kind of solutions by studying the electrodeposition of Fe, Ni and Co from ethylene glycol solvent without the employment of quaternary ammonium salt; it has to be noted that only a few studies on this system are reported in literature [3, 4, 5]. Fundamental electrochemical characterization was firstly carried out highlighting analogies and differences among the three systems considered. Microstructural, morphological and magnetic characterization were performed on metallic deposits obtained by means of potentiostatic electrodeposition. In addition, commercially available aluminium membranes ware employed for the synthesis of nanowires with enhanced magnetic properties with respect to the film. Finally, considerations on the results obtained are given with respect to deposits properties typically obtained from aqueous solutions.

References

[1] Welton T. Room-temperature ionic liquids. Solvents for synthesis and catalysis. Chemical reviews. 1999 Aug 11;99(8):2071-84.

[2] Abbott AP, Boothby D, Capper G, Davies DL, Rasheed RK. Deep eutectic solvents formed between choline chloride and carboxylic acids: versatile alternatives to ionic liquids. Journal of the American Chemical Society. 2004 Jul 28;126(29):9142-7.

[3] Vorobyova TN, Vrublevskaya ON. Electrochemical deposition of gold–tin alloy from ethylene glycol electrolyte. Surface and Coatings Technology. 2010 Jan 15;204(8):1314-8. 

[4] Nguyen HP, Wu M, Su J, Vullers RJ, Vereecken PM, Fransaer J. Electrodeposition of bismuth telluride thermoelectric films from a nonaqueous electrolyte using ethylene glycol. Electrochimica Acta. 2012 Apr 30;68:9-17.

[5] Neuróhr K, Pogány L, Tóth BG, Révész Á, Bakonyi I, Péter L. Electrodeposition of Ni from various non-aqueous media: the case of alcoholic solutions. Journal of The Electrochemical Society. 2015 Jan 1;162(7):D256-64.
(Invited) Conductive Polymer/Metal Composite for Filling of TSV
Authors: Kawakita Jin , Chikyow Toyohiro
Published: February 2020

Fast formation of through-silicon via (TSV) is an essential issue to fabricate the 3D-IC with respect to production efficiency. Currently, TSV is formed by opening a hole in silicon wafer, followed by stacking of an insulation layer and a diffusion barrier on the wall inside the hole and by filling of a conductive material such as metal copper by electroplating often after preparing a seed layer. Since it takes more than one hour to complete all these steps, the efficiency of formation process of TSV should be improved.

The purpose of this research was to shorten the time of the filling step less than 10 minutes. In order to realize that, solution chemistry was used in this research. Photo chemical reaction enabled conducting polymer/metal composites to be synthesized and took advantage of fast deposition of the composite ten times larger than electroplating metal in terms of growth rate. The composite obtained showed conductivity two orders of magnitude higher than commercial conducting polymer. Furthermore, reaction solution was penetrated deeply into narrow hole in silicon wafer because of its high wettability to silicon and silicon oxide.

Filling of polypyrrole/silver as conducting polymer/metal composite was carried out in two ways; 1) injection of reaction solution to silicon holes followed by UV irradiation for photo chemical reaction to form the composite and 2) injection of dispersion solution containing the composite prepared by photo chemical reaction. Filling of the composite was confirmed with laser microscopy and cross sectioning, and time of filling was within 10 minutes. The electrical characteristics such as an I-V curve were obtained with a measurement device in which the electric signal was applied between any two electrodes formed by filling of holes silicon wafer. In addition, the structure at the interface between the composite and silicon wafer was revealed and new diffusion barrier was found to attain both silver anti-diffusion and interfacial adhesion.

These results summarized that the solution chemistry of conducive polymer/metal composite could decrease the time and step for filling to narrow vertical hole of silicon wafer, indicating fast formation of TSV.
(Invited) Silicon Nanopillars Coated with Earth-Abundant Electrocatalysts for Enhanced Photoelectrochemical Hydrogen Production
Authors: Zhang Xingwang , Yu Chunlin , Jia Qing
Published: February 2020

Solar-driven photoelectrochemical (PEC) water splitting for hydrogen production promises to solve the impending energy and environmental crisis. The key to increase the efficiency of PEC hydrogen generation is developing high-performance catalysts and photocathodes. 3D p-type silicon (p-Si) nanopillar (NP) arrays are promising architectures due to the high light harvesting and the large interfacial areas. We demonstrate its enhanced PEC performance with a photocurrent density of -37.5 mA/cm2 at 0 V (vs. RHE) under simulated 100 mW/cm2 (1 Sun) with an AM 1.5 G filter, which is the highest value reported for p-type Si photocathodes. The synergic effects of the excellent light harvesting of Si NP array core and the good optical transparency, as well as excellent electrocatalytic activity of NiCoSex shell boost the production and utilization of photogenerated electrons. The Faradaic efficiency of H2 and O2 on p-Si/NiCoSex was approximately 100%, which confirmed that the photocurrent during PEC reaction was attributed to hydrogen generation. The completely enclosed core-shell structure isolated the Si NP from air and aqueous electrolyte and minimized the oxidation of silicon, leading to good stability. The design of p-Si/NiCoSex core/shell NP arrays offers a new strategy for preparing highly efficient photoelectrochemical solar energy conversion devices.
Kinematically Driven Triboelectric Nanogenerator As a Practical Power Source
Authors: Bhatia Divij , Choi Dukhyun
Published: February 2020

Triboelectric nanogenerators (TENG) can convert various forms of wasted mechanical energy in our environment into useful electrical energy that can power wireless sensor nodes constituting an internet of things (IoT) application. The TENG usually generates at high voltage and low current. This is a problem when trying to power portable devices which commonly require low voltage and high current. Our goal in this work was to address this common problem and demonstrate how any TENG can be used as a practical power source. For this purpose we designed a kinematic system that can reliably drive a transformer based power circuit. Our TENG system utilizes mundane rotation energy to power a IoT sensor node. A windup spring based mechanism was used to store the input rotation energy. Then using a custom gear-train and four-nose cam, the TENG was driven at a high frequency. A power converter constituting a transformer and charge pump circuit was used to reliably power a temperature and humidity sensor node that periodically transmitted data wirelessly via bluetooth to any smart device like a laptop or mobile phone. Such a system is applicable in self-powered environment monitoring as well as in industrial control systems where maintaining specific temperature and humidity is critical.
(Invited) Band Gap Engineering and Heterostructures of Low Dimensional Semiconductors
Authors: Yang Tiefeng , Zhang Xuehong , Pan Anlian
Published: February 2020

Band gaps are one of the most important parameters of semiconductor materials for their optoelectronic applications since they determine the spectral features of absorptions and emission processes [1,2]. Due to the limited band gaps of natural semiconductors, alloying and heterostructured semiconductors with different band gaps have long been the standard methods of achieving semiconductor structures with new band gaps and functions [3,4]. In this talk, I will report our recent progress on the band gap engineering of 1D semiconductor nanowires and 2D atomically thin layered materials through controlled vapor growth. Using some examples, I will show how to realize composition graded and interface sharped low dimensional semiconductor heterostructures through composition controlled band gap modulation. The achieved band gap engineered nanostructures can give continuously tuned or white light emission, and can be used to realize multi-color nanolasers, wavelength splitter, asymmetric waveguiding and high-performance photodetectors etc [5-7].

References

[1] Hong Zhou, Shuangping Yuan, Anlian Pan et al., Vapor Growth and Tunable Lasing of Band Gap Engineered Cesium Lead Halide Perovskite Micro/Nanorods with Triangular Cross Section. ACS Nano, 2017, 11 (2), pp 1189-1195.

[2] Honglai Li, Xueping Wu, Anlian Pan et al., Composition-Modulated Two-Dimensional Semiconductor Lateral Heterostructures via Layer-Selected Atomic Substitution, ACS Nano, 2017, 11, 961-967.

[3] Xidong Duan, Anlian Pan, Xiangfeng Duan et al., Synthesis of WS2xSe2–2x Alloy Nanosheets with Composition-Tunable Electronic Properties, Nano Lett. 2016, 16 (1), pp 264-269.

[4] Xidong Duan, Anlian Pan, Xiangfeng Duan et al.. Two-dimensional transition metal dichalcogenides as atomically thin semiconductors: opportunities and challenges, Chem. Soc. Rev., 2015, 44, 8859-8876.

[5] Honglai Li, Anlian Pan, Xiangfeng Duan et al., Lateral growth of composition graded atomic layer MoS2(1-x)Se2x nanosheets, J. Am. Chem. Soc., 2015, 137, 5284-5287.

[6] Xidong Duan, Anlian Pan, Xiangfeng Duan et al., Lateral epitaxial growth of two-dimensional layered semiconductor heterojunctions, Nature Nanotechnology, 2014, 9,1024-1030.

[7] Pengfei Guo, Xiujuang Zhuang, Anlian Pan et al., Semiconductor Alloy Nanoribbon Lateral Heterostructures for High-performance Photodetectors, Adv. Mater., 2014, 26, 2844-2849.
Ionomer Binder-Dependent Degradation Behavior of Cathode Catalyst Layers in PEFCs
Authors: Cho Seonghun , Yim Sung-Dae , Park Seok-Hee
Published: February 2020

Recently, short-side chain (SSC) ionomer binders have been reported to improve the initial performance of polymer electrolyte fuel cells (PEFCs) by giving more uniform ionomer coats on the catalyst surface, particularly in a highly graphitized carbon support, compared with the long-side chain (LSC) ionomer binders in catalyst layers. The uniform coating property of the SSC ionomer binder improves the performance of the PEFCs by increasing the proton conductivity of the catalyst layer, particularly under low humidification conditions. The study on the SSC ionomer binder has been actively carried out from the perspective of the improvement of initial performance of PEFCs. However, the study on the SSC ionomer binder from the perspective of the durability of PEFCs has hardly been performed. In this study, the effect of structural characteristics of ionomer binders on the durability of PEFCs was investigated. In particular, the degradation behavior of different ionomer-based catalyst layers was observed with different humidification conditions. The cathode catalyst layers were fabricated by using three types of ionomer binders with the side chain length and ion exchange capacity (IEC) value as variables. The durability behavior of the PEFC MEA was studied using the catalyst and catalyst support accelerated degradation test (ADT) protocols with different humidification conditions. The catalyst used for the preparation of the MEA was Pt/C (TEC10E50E) and the ionomer binder was LSC (IEC 1.00), SCC (IEC 1.02, 1.39). The ADT was conducted according to the DOE protocol (catalyst ADT: between 0.6 and 1.0 V, 50 mV/s, catalyst support ADT: between 1.0 and 1.5 V, 500 mV/s). The degradation phenomena of the cathode catalyst layer were measured by electrochemical analysis. The change of the electrochemically active surface area (ECSA) of Pt and that of the proton conductivity of the catalyst layer were measured. The corrosion of the catalyst support was measured by measuring the catalyst layer thickness change by SEM. The detailed analysis of degradation behavior of MEAs depending on the ionomer binders and RH conditions will be discussed.
Controlling the Polymer/Gas Interfacial Property of the Ionic Polymer Phase of a PEM Fuel Cell Catalyst Layer during Membrane Electrode Assembly Fabrication
Authors: Dowd Regis Paul , Nguyen Trung Van
Published: February 2020

Water management in a PEM fuel cell is vital during high current density operation. Water production in the cathode catalyst layer can negatively impact performance by lowering mass transport of oxygen into the cathode. Various advances have been developed to overcome water management issues related to PEMFCs. A few of these discoveries include the development of the interdigitated flow field [1], integration of hydrophobic PTFE nanoparticles into the catalyst layer [2, 3], and gas diffusion layer fabrication from various types of non-wetting materials [4, 5]. Each of these advances led to improved mass transport performance during high current density operations.

In this presentation, a novel heat treatment process for controlling the ionic polymer phase surface properties in the fuel cell catalyst layer is incorporated into the fabrication process of the membrane electrode assembly (MEA). XPS is used to characterize the catalyst layer ionomer-gas interface in order to verify specific heat treatment conditions lead to a hydrophobic or hydrophilic ionomer surface. The MEA fabrication procedure is modified to ensure the catalyst layer is subjected to suitable heat treatment exposure conditions in order to create a hydrophobic ionomer-gas interface inside the cathode catalyst layer. Fuel cell performance results will be presented using the new MEAs under different operating temperatures, flow field types, and air humidification conditions.

Acknowledgement

The work presented was partially funded by the National Science Foundation under Grant No. EFRI-1038234 and CBET-1518755.

References

T.V. Nguyen, J. Electrochem. Soc., 143, L103 (1996).

R. Friedmann and T.V. Nguyen, J. Electrochem. Soc., 157, B260 (2010).

M. Uchida, Y. Aoyama, N. Eda and A. Ohta, J. Electrochem. Soc., 142, 4143 (1995).

J. Benziger, J. Nehlsen, D. Blackwell, T. Brennan and J. Itescu, J. Membrane Science, 261, 98 (2005).

T.V. Nguyen, A. Ahosseini, X. Wang, V. Yarlagadda, A. Kwong, A.Z. Weber, P. Deevanhxay, S. Tsushima and S. Hirai, J. Electrochem. Soc., 162, F1451 (2015).
(Invited) Formed Metal Fuel Cell Bipolar Plates
Authors: Nelissen Gert
Published: February 2020

Formed and welded metal PEM fuel cell bipolar plates are the most prominent strategy to reach low cost and high performance in a high volume production environment. Using the proprietary coil-based Hydrogate proces, Borit is able to achieve world class thin sheet metal forming with excellent repeatability and reproducibility. An overview of the typical process flow for metal bipolar plate production, process capabilities and yields will be shown. Implementing the appropriate process controls overcomes the challenges related to laser welding of thin metal foils with constraints regarding plate flatness, leak tightness and weld strength. An update on the latest developments will be presented, together with the related QC and traceability efforts.
PtMo Sponge-like Nanoporous Structure Wrapped with Ultrathin N,S-Co-Doped Carbon Dots Exhibiting Enhanced Electrocatalytic Activity for Hydrogen Evolution Reaction and Oxygen Reduction Reaction
Authors: Choi Ho-Suk , Nguyen Van-Toan
Published: February 2020

A simple one-pot aqueous method is proposed to synthesize PtMo sponge-like nanoporous structure wrapped with ultrathin nitrogen and sulfur co-doped carbon dots by using NaBH4 as the reductant without any surfactants. The materials are carefully investigated by microscopic (SEM, TEM), spectroscopic (high resolution photoemission, Raman spectroscopy) techniques, evidencing that N,S-co-doped Cdot wraps PtMo sponge-like nanoporous structure. The electrocatalytic activity of the material is tested toward the electrochemical evolution of hydrogen and the electrochemical reduction of oxygen. The obtained N,S-co-doped Cdot/PtMo nanohybrids display enlarged electrochemically active surface area and superior electrocatalytic performances toward hydrogen evolution reaction (HER) and oxygen reduction reaction (ORR) in comparison with single PtMo and c-Pt/C catalysts, exhibiting promising applications in energy storage and conversion.
Oxygen Electrocatalysis on Transition Metal Spinel Oxides
Authors: Xu ZhiChuan, Jason
Published: February 2020

Exploring efficient and low cost oxygen electrocatalysts for ORR and OER is critical for developing renewable energy technologies like fuel cells, metal-air batteries, and water electrolyzers. This presentation will presents a systematic study on oxygen electrocatalysis (ORR and OER) of transition metal spinel oxides.[1] Starting with a model system of Mn-Co spinel, the presentation will introduce the correlation of oxygen catalytic activities of these oxides and their intrinsic chemical properties. The catalytic activity was measured by rotating disk technique and the intrinsic chemical properties were probed by synchrotron X-ray absorption techniques. It was found that molecular orbital theory is able to well-explain their activities.[2,3] The attention was further extended from cubic Mn-Co spinels to tetragonal Mn-Co spinels and it was found that the molecular theory is again dominant in determining the catalytic activies. This mechanistic principle is further applied to explain the ORR/OER activities of other spinels containing other transition metals (Fe, Ni, Zn, Li, and etc.).

References

[1] Wei C, Feng Z, Scherer G, Barber J, Shao-Horn Y, Xu Z, Adv. Mater. 2017, DOI: 10.1002/adma.201606800.

[2] Suntivich J, Gasteiger, HA, Yabuuchi, N, Nakanishi H, Goodenough, JB, Shao-Horn, Y. Nat. Chem. 3 (2011) 546.

[3] Suntivich J, May KJ, Gasteiger HA, Goodenough JB, Shao-Horn Y, Science 334 (2011) 1383.

[4] Wei C, Feng Z, Baisariyev M, Yu L, Zeng L, Wu T, Zhao H, Huang Y, Bedzyk M, Sritharan T, Xu Z, Chemistry of Materials, 2016, 28, 4129–4133.
Understanding the Trilemma in Electric Vehicle Batteries: Energy Density, Fast Charging, and Cycle Life
Authors: Yang Xiao-Guang , Wang Chao-Yang
Published: February 2020

Range anxiety is one of the most significant barriers to mainstream adoption of electric vehicles (EVs). An effective solution to range anxiety is increasing energy density of EV batteries combined with fast charging. Energy density of EV batteries has advanced significantly over the past few years, from 150 Wh/kg in 2012 to ~220 Wh/kg of state-of-the-art cells, and is targeting >300 Wh/kg by 2020. A practical approach to higher energy density of Li-ion cells is to increase areal loading of electrode active materials. Two critical challenges, however, arise. One is that cycle life of Li-ion cells drops significantly with increasing loading amount. The other is that the ability of fast charging is drastically limited with increasing electrode loading. Gallagher et al. (1) tested a sets of graphite/NMC622 cells with different areal loadings, and found that cells with higher areal loadings have much poorer cycle life. Furthermore, though the cells were cycled at room temperature with only 1C charge rate, a significant amount of lithium deposit was observed in cells with higher anode loading, indicating serious lithium plating in these high energy cells. These results differ greatly from those in the literature based on high power cells. Aging of high power cells is typically believed to be dominated by growth of solid-electrolyte interphase (SEI), and lithium plating is expected to occur only at harsh charge conditions (e.g. low temperature, high charge rate). To date, research on aging behavior of high energy Li-ion cells is still rather limited (2).

In this talk, we will give a comprehensive discussion on the aging characteristics of high energy Li-ion batteries for next generation EVs, with special focus on fast charging conditions @2-3C rate. An aging model will be introduced which incorporates both SEI growth and lithium plating. As such, cell aging associated with SEI growth and with lithium plating can be distinguished. The model is applied to predict the cycle life of Li-ion cells at various operating conditions. Specially, we will focus on the effects of a) areal loading density, b) operating temperature, and c) charge rate on the cycle life of Li-ion cells.

References:

1. K. G. Gallagher, S. E. Trask, C. Bauer, T. Woehrle, S. F. Lux, M. Tschech, P. Lamp, B. J. Polzin, S. Ha, B. Long, Q. Wu, W. Lu, D. W. Dees and A. N. Jansen, J. Electrochem. Soc., 163, A138 (2016).

2. Y. Leng, S. Ge, D. Marple, X.G. Yang, C. Bauer, P. Lamp and C.Y. Wang, J. Electrochem. Soc., 164, A1037 (2017).
Capillary-Based Micro-Battery Cells for Operando X-Ray Diffraction Studies of Electrode Materials in Working Li-Ion Batteries
Authors: Johnsen Rune E. , Norby Poul
Published: February 2020

Lithium-ion battery technology remains to be the heart in operating the majority of new commercial mobile devices and electrical vehicles. Thus, even though it is more than 25 years ago Sony introduced the world's first commercial Li-ion battery, there is still today a demand for cheaper and safer battery materials with higher energy density. In order to meet this demand, an increased fundamental understanding of the detailed structural and microstructural transformations and electrochemical reactions taking place in Li-ion batteries is needed. For this purpose we have developed special capillary-based micro-battery cells allowing diffraction information to be obtained from only the active electrode material during battery operation. We have used the cell to study structural and microstructural changes during battery operation by in situ / operando synchrotron X-ray powder diffraction (XRPD). Operando XRPD studies of both cathode and anode materials will be presented as examples of the applicability of the micro-battery cell design, e.g. the initial intercalation and deintercalation of lithium into graphite. The study revealed remarkable changes in the stacking order and disorder in the graphitic electrode material during charging and discharging. Another example will be an operando XRPD study of a high-capacity lithium-vanadium oxyfluoride cathode material.
Investigation of Polyanion Materials with Multiple Intercalation Cations
Authors: Paharik Ethan , Koenig Gary
Published: February 2020

As the market for secondary batteries increases to include electric vehicles, load-leveling systems, and storage for intermittent energy generation, significant battery research has been directed towards improving battery safety, reliability, robustness, and cost. Replacing the LiCoO2 cathode with less expensive and more environmentally friendly manganese or iron based materials has been one research direction aimed at meeting some of these goals. In addition, alternative earth abundant cations such as Na+ or Mg++ as the intercalation species would also be an attractive battery option. Phosphate polyanion materials are promising low cost active materials due to their high thermal stability and reasonable gravimetric capacities, and are suitable for use in both aqueous and organic electrolytes and with a variety of intercalation ions due in part to their open framework structures. Herein, we examine the electrochemical behavior of a variety of phosphate polyanion batteries within a suite of different electrolytes for systematic investigations of the electrochemical behavior of the polyanion compounds with different intercalation cations. Electrochemical characterization will be described for phosphate polyanion structures, particularly Ti and Fe based NASICON structured materials, within electrolytes containing a variety of cation species.
(Invited) Investigation of Thermal Quenching Process for 5d-4f and 3d-3d Luminescence
Authors: Ueda Jumpei , Tanabe Setsuhisa
Published: February 2020

White light LEDs (light-emitting diodes) are rapidly replacing incandescent lamps and (compact) fluorescent tubes in all lighting markets (consumer, automotive, and professional). The most widely used type of white LEDs (w-LEDs) is a phosphor-converted w-LED (PC-LED), which is composed of an InGaN-based blue LED and visible light emitting inorganic phosphors, such as oxides and nitrides doped with Ce3+, Eu2+ , Mn4+ as an active center. These phosphors are required to have excellent thermal quenching behavior because the LED chip reaches temperatures up to ∼200 °C in recent high-power w-LED. In these phosphors, two processes of thermal quenching are considered generally. One is the thermally activated cross over from the excited state to the next lower state. The other is the thermal ionization from the excited state to the bottom of the conduction band (CB). In this study, we investigated the thermal quenching mechanism for the 5d-4f and 3d-3d luminescence in w-LED phosphors doped with Ce3+ or Mn4+.

Ce3+-doped Y3Al5O12 garnet (yttrium aluminum garnet,YAG) is the most prominent phosphor in w-LEDs. The excellent thermal quenching behavior of the Ce3+ luminescence in YAG:Ce3+ is well established, but the mechanism for thermal quenching remains unclear. To elucidate the mechanism of thermal quenching of YAG:Ce3+, thermoluminescence excitation (TLE) spectra were recorded at room temperature and 300 °C. At room temperature, the lowest 5d1 band at 450 nm does not contribute to the charging process for TL while at 300 °C, a temperature corresponding to the onset of thermal quenching of the Ce3+ luminescence, the excitation in 5d1 band gives rise to a TL signal. This result indicates that thermal ionization is responsible for thermal quenching of the Ce3+luminescence.

We also investigated the thermal quenching process for calcium aluminum magnetoplumbite, CaAl12O19, doped with Mn4+ (CAO:Mn4+), which is narrow red luminescence phosphor. We tried to understand the quenching mechanism of Mn4+ compared with the luminescence quenching properties of Mn2+. From the temperature dependence of Mn4+: 2E-4A2 red luminescence and Mn2+:4T1-
6A1 green luminescence intensities in CaAl12O19, the quenching temperatures of Mn4+ and Mn2+ are 330K and 800K, respectively. There is a big difference between the quenching temperatures of Mn4+ and Mn2+ in spite of the same host material and the similar luminescence transtion energy. The Mn4+:2E-4A2 red luminescence is quenched by the thermally activated crossover through the 4T2 excited state whose potential curve possesses a large configurational offset in a configurational coordinate diagram. Mn2+ green luminescence is also quenched by the thermally activated crossover, but the activation energy for non-radiative process is much larger than that for Mn4+ because there are no other excited states related with the quenching process.
CO2 reduction on Cu2O(110) Surface: A Combined Theoretical and Experimental Study
Authors: Li Liang , Zhang Rui , Wu Yimin , Liu Yuzi , McNulty Ian , Vinson John , Shirley Eric , Guest Jeffrey R , Chan Maria K. Y.
Published: February 2020

The rational design of novel catalysts for CO2 reduction has attracted considerable attention, owing to the increasing global fuel demand and greenhouse gas emission. Cu2O has been suggested to be thermodynamically capable of photocatalytically reducing CO2 to methanol.1 However, due to the inertness of CO2 molecules, it is relatively hard for CO2 to draw electrons from the catalyst and become reactive. Earlier studies have shown that the CO2 conversion rate is quite limited on stoichiometric, defect-free oxide surfaces due to the low catalytic activity; on the other hand, defected surfaces generally have higher activity and may provide better catalytic performance.2

In this work, we performed density functional theory (DFT) calculations to investigate the catalytic activity of Cu2O(110) surface, with a primary focus on the surface affinity of CO2 molecules. The preferred CO2 adsorption sites and configurations on both pristine and defected Cu2O(110) surfaces are determined, and the surface stoichiometry that favors CO2 adsorption is thus identified. Scanning tunneling microscopy (STM) images and X-ray Absorption Near-Edge Structures (XANES) of various adsorption configurations are also simulated within the first-principles framework. The results from this study demonstrate the importance of rational surface engineering of catalysts for effective CO2 conversion, and provide important insight into experiment design.

(1) Bendavid, L. I.; Carter, E. a. First-Principles Predictions of the Structure, Stability, and Photocatalytic Potential of Cu2O Surfaces. J. Phys. Chem. B
2013, 117 (49), 15750–15760.

(2) Liu, L.; Zhao, H.; Andino, J. M.; Li, Y. Photocatalytic CO2 Reduction with H2O on TiO2Nanocrystals: Comparison of Anatase, Rutile, and Brookite Polymorphs and Exploration of Surface Chemistry. ACS Catal.
2012, 2 (8), 1817–1828.
Progress in Electrochemical CO2 Reduction in Gas Phase – Design of Efficient Co-Electrolyser Systems
Authors: Patru Alexandra , Binninger Tobias , Schmidt Thomas J.
Published: February 2020

The electrochemical CO2 reduction reaction (CO2RR) is a complex reaction which must be carried out in a highly selective and efficient manner. Many efforts are being taken to develop catalysts with improved reaction selectivity and efficiency and significant progress has been made in this area of research [1]. However, CO2RR kinetics, product identification and quantification are mostly carried out in half-cell configurations using liquid electrolytes. This fundamental approach of studying CO2RR is limited by the low solubility of CO2 in water, the maximum CO2 reduction current reported in the literature is in the range of 0.01- 0.02 A/cm2 [2]. In order to overcome the solubility problem and to reach higher operating current densities, CO2 reduction can be carried out in a co-electrolysis system where pure or diluted gaseous CO2 is used. Our research efforts were focused on the design of an electrochemical cell for co-elecrolysis operating at high-current densities with good product selectivity.

The most promising results were obtained when a bipolar membrane was used as the electrolyte. The experiments were conducted in a membrane electrolyzer-like configuration setup. Various gold type cathode electrode materials were tested. IrTiO2 was used as an anode material to catalyse the oxygen evolution reaction. The reaction products were analysed by on-line mass spectroscopy. The co-electrolyser performance and the selectivities of the various MEAs are examined in detail.

 

References

[1] J. Herranz, J. Durst, E. Fabbri, A. Patru, X. Cheng, A.A. Permyakova, T.J. Schmidt, Nano Energy
2016, 29, 4.

[2] J. Durst, A. Rudnev, A. Dutta, Y. Fu, J. Herranz, V. Kaliginedi, A. Kuzume, A.A. Permyakova, Y. Paratcha, P. Broekmann, T.J. Schmidt, Chimia
2015, 12, 69.

 

Acknowledgements

Financial support of this work by the Commission of Technology and Innovation Switzerland (CTI) and the Swiss Competence Center for Energy Research Heat and Electricity Storage are greatly acknowledged.
Theoretical Characterization of the Electronic and Optical Properties of Beryllium and Nitrogen Co-Doped Graphene: A Proposed P-Type Semiconductor for Nanoelectronic and Optoelectronic Applications
Authors: Olaniyan Okikiola , Mapasha Edwin R , Khaleed Abubakar Abubakar , Emmanuel Igumbor , Manyala Ncholu
Published: February 2020

Ab-initio calculations within the framework of density functional (DFT) have been performed to study the electronic and optical properties of Be and N co-doped graphene. The results have been compared with that of Be-doped, N-doped, and pristine graphene. The effect of doping and isomerization on the electronic and the optical properties of these systems have been studied by varying the impurity concentrations of Be-doped and N-doped graphene systems from 3.13% through 12.5%, whereas for Be and N co-doped graphene, the concentration has been varied from 6.25% through 25.0 % impurity concentration.

The formation energies of the systems with different impurity configurations were calculated to examine their relative stabilities. It was found that for Be-N co-doped graphene, the configuration of which N and Be coexisting as the nearest neighbors is energetically the most favorable configuration. Moreover, at the same impurities concentration, Be-N co-doped graphene was observed to be more stable than Be-doped graphene due to its lower formation energy. Thus these results reveal that it is much easier to synthesize Be-N co-doped graphene than to synthesize Be-doped graphene. Hence, the relatively high formation energy of Be-doped graphene could be the reason why the system is yet to be synthesis experimentally despite a recent theoretical report on it.

The results of the electronic structure calculations reveal that Be-N co-doped and Be-doped graphene are p-type semiconductors while N-doped graphene has been verified to be an n-type semiconductor. For all the doped systems considered in this study, it was observed that the size of the band gap increases with impurity concentration with respect to the aforementioned energetically most favorable isomer. At impurity concentration of 3.13%, a minimum band gap of 0.44 eV and 0.21eV was realized for Be-doped and N-doped graphene respectively while at 12.5 % corresponding maximum gap of 1.41 eV and 0.6 eV were observed. Besides, Be-N co-doped graphene was found to have a minimum band gap of 0.43 eV at 6.25% and a maximum gap of 1.54 eV at 25.0% impurities concentration.

The dielectric matrices of the doped systems were calculated using first-order time-dependent perturbation theory in the simple dipole approximation. It was found that all the systems investigated were transparent within the frequency interval of 7.0eV-10eV for parallel EM polarization. In general, we observed that the optical properties of the doped systems investigated respond to doping concentration differently across the EM spectrum with respect to the anisotropic signature of the host system.

The results of our study demonstrate that the band gap of graphene can be tailored to meet the requirements of specific applications in nanoelectronic and optoelectronic devices.
Broadband Sum-frequency Generation Spectroscopy Study of Electrochemical Surface Processes
Authors: Huang-Fu Zhi-Chao , He Yu-Han , Zhou Zhi-You , Wang Zhao-Hui , Sun Shi-Gang
Published: February 2020

As a second order nonlinear technique, sum-frequency generation (SFG) spectroscopy is forbidden, under the electric-dipole approximation, in the bulk of a medium with inversion symmetry and then generate only at the surface of such media where the symmetry is broken and appear to be highly surface-specific for interfaces between the centrosymmetric media. So far, many studies of electrochemical processes at various interfaces have been performed by using SFG, and molecular level insight like the molecular adsorption, orientation, packing, and dynamics has been obtained.

We have developed broadband sum-frequency generation (BB-SFG) spectroscopy. It enables us to obtain information on in situ electrochemical systems. One of the electrochemical processes is the CO2 reduction on a polycrystalline copper and polycrystalline gold electrode. The antisymmetric C−H stretching modes of methyl group and antisymmetric C−H stretching modes of methylene group were observed on copper electrode surface, no adsorbed CO intermediate was observed. As for the process on gold electrode surface, the adsorbed CO was the main intermediate detected, and CO was observed at a relative high potential (-0.5V vs SCE). In addition, we present some other examples that investigate the electrochemical interface with SFG techniques, such as the potential-dependent nonresonant (NR) SFG.

Figure 1 (a)(b) Potential-dependent BB-SFG spectra of 0.1M CO2-saturated NaHCO3 solution at poly-Cu electrode (C-H region) and poly-Au electrode (CO region). (c) Variations of the wavenumbers (black) and intensities (red) of the CO peak in (b) from the fitting data.

Acknowledgement: This work was financially supported by NSFC (21327901 and 21621091).

Figure 1