bluuebunny/crossref_metadata_2025 huggingface dataset:
Hexacyanometalate-Based Redox Couple for High-Efficiency Iron-Chromium Flow Battery
Authors: Jang Ji-Eun , Kim Ryeong-ah , Lee Hyun-Wook
Published: December 2020

As increasing the importance of electrical grids and utilizing renewable energy sources, large-scale energy storage systems that can effectively store and supply electrical energy have attracted great research attention in recent times. Aqueous based redox flow batteries (RFBs) are promising candidates for large-scale energy storage due to their long cycle life, high safety, and high solubility of a catholyte and anolyte. Also, unlike other battery systems such as lithium-ion batteries, the energy density and power capabilities of RFBs can be decoupled, enabling flexibility for controlling capacity and power, and scalability as an industrial perspective. Iron-chromium (Fe-Cr) RFB is a good candidate for cost-effective systems comparing to all-vanadium RFB, which is well-known as the most developed RFB. However, sluggish Cr3+/2+ redox kinetics and hydrolysis of ferrous ion have become formidable obstacles to achieving high efficiency and stability. In particular, the poor kinetics of chromium ions make the hydrogen evolution reaction more dominant and cause the state of charge of the positive and negative side to being imbalanced.

Herein, we have demonstrated a new RFB system based on hexacyanometalate materials ([M(CN)6]3-/4-, M = transition metal). The cyanide ligands linked through transition metal ions play a role in mitigating the hydrolysis in the aqueous environment and enhance the electrochemical kinetics. We have investigated the stability and electrochemical kinetic information of our redox couples comparing to conventional active materials. The superior kinetics of hexacyanometalate based-redox couples contributed to improving voltage efficiency. Besides, by use of a transition metal oxide type-catalyst on a carbon-felt current collector, this RFB system can achieve higher energy efficiency than that of the pristine carbon-felt electrode, suggesting that the employing catalyst can enhance the electrochemical kinetics of the active materials.
Identification of Life Models for Li-Ion Batteries Using Penalized Regression and Bilevel Optimization
Authors: Gasper Paul , Smith Kandler
Published: December 2020

Reduced-order physics-based life models are extremely useful for rapidly predicting battery state-of-health and for simulating battery lifetime in arbitrary aging conditions. However, identification of well-parameterized models is difficult. This is because, for maximum usefulness in predicting lifetime under a variety of conditions, aging test data exhibits many degradation mechanisms, which all need to be accurately modeled. However, because aging tests are time-consuming and expensive, especially for large-format batteries, a minimum of tests are conducted while probing many stress factors. Building a well-parameterized model is then very challenging: an under-parameterized model will neglect critical degradation modes, and an over-parameterized model will extrapolate poorly to new testing conditions. To complicate this matter, the functional form of the model for any individual degradation rate can be very difficult to identify. In this work, the statistical tools of penalized regression and bilevel optimization are used to help identify both the functional forms of and optimize the parameters of reduced-order life models, accelerating identification of robust models. Model robustness is demonstrated through traditional statistics methods of cross-validation and sensitivity analysis, uncertainty quantification through bootstrap resampling and Monte-Carlo simulation, and simulation of real-world use cases.
A Pure Titania Photocatalyst: Preparation, Characterization and Photocatalytic Activity of Octahedral-Shaped Anatase Particles
Authors: Ohtani Bunsho , Li Yumin , Koike Sayaka , Takashima Mai
Published: December 2020

Different from organic molecules and metal complexes, which can be identified by chemical composition and structural characteristics such as NMR spectra, inorganic solid materials especially metal oxides cannot be identified, i.e., their purity cannot be evaluated in a strict scientific sense, because at least three structural parameters, bulk structure, surface structure and bulk/surface size, must be determined. However, in the other words, solid metal-oxide samples can be assigned to be "pure", if their three parameters are determined, by macroscopic measurements, to be uniform. Here, attempts to prepare octahedral-shaped anatase titanium(IV) oxide (titania) particles (OAPs) of uniform bulk structure (anatase with negligible non-crystalline components), surface structure (only exposing {101} facets) and particle size are reported as the first and sole example of a "pure" metal-oxide powder. In this study, OAP samples were prepared by sonication-hydrothermal (HT) reaction of potassium-titanate nanowires. Characterization of the samples by Rietveld analysis of XRD patterns, reversed double-beam photoacoustic spectroscopy and SEM observations revealed the homogeneousness of crystalline bulk, surface and particle size, respectively, to indicate the samples "pure".
(Invited) Effective Engineering of Copper-Cobalt Oxide Nanostructures for Water Splitting
Authors: Nath Narayan Chandra Deb , Lee Jae-Joon , Park Hyunwoong
Published: December 2020

The low-cost and low-toxic copper-cobalt oxide, CuCo2O4 have attracted a great deal of research interest owing to their wide range of applications such as oxygen evolution reaction, oxygen reduction reaction, hydrogen evolution reaction, alcohols oxidation, H2O2 decomposition, urea oxidation, and energy storage. Their controllable composition, electronic structure, valence states or redox characteristics, morphology, and high catalytic property have made them suitable as universal catalysts. However, their low intrinsic electrical conductivity still overshadows their practical application to some degree. In addition, The conventional preparation procedures of copper-cobalt oxide result in relatively low catalytic activity or large OER overpotential for catalytic reactions. In the present report, we have grown a series of surface functionalized Cu
x
Co3

-

x
O4 nanostructures directly on a charge-collecting substrate (e.g., Ni Foam) using a straightforward electrochemical deposition process and investigated the effects of its surface functionalization, morphology, content of oxygen vacancies, electrochemically active surface area (ECSA), and electrical conductivity on the performance of water splitting.
(Invited) Enhancement of Plasmon-Induced Charge Separation through Plasmon Coupling
Authors: Tatsuma Tetsu , Nishi Hiroyasu , Ishida Takuya
Published: December 2020

Plasmon-induced charge separation (PICS)1,2 involves electron transfer from plasmonic noble metal nanoparticles or compound nanoparticles to an n-type semiconductor such as TiO2. Oxidation reactions involved in PICS are based on a charge accumulation mechanism (Figure a) or a hole ejection mechanism (Figure b).3 The latter enables nanoscale local oxidation at relatively positive potentials.4-7 This can be applied to photoinduced nanofabrication beyond the diffraction limit of light. For instance, chiral plasmonic nanostructures can be prepared by PICS under right or left circularly polarized light (Figure c).8,9 Some other applications of the plasmonic hole ejection will also be mentioned. Enhancement of PICS with hole ejection through plasmon coupling10 and its application to photocatalysis will also be described.

References

Y. Tian and T. Tatsuma, J. Am. Chem. Soc., 127, 7632 (2005).

T. Tatsuma, H. Nishi, and T. Ishida, Chem. Sci., 8, 3325 (2017) [review].

T. Tatsuma and H. Nishi, Nanoscale Horiz., 5, 597-606 (2020) [review].

E. Kazuma, N. Sakai, and T. Tatsuma, Chem. Commun., 47, 5777 (2011).

I. Tanabe and T. Tatsuma, Nano Lett., 12, 5418 (2012).

K. Saito, I. Tanabe, and T. Tatsuma, J. Phys. Chem. Lett., 7, 4363 (2016).

H. Nishi, M. Sakamoto, and T. Tatsuma, Chem. Commun., 54, 11741 (2018).

K. Saito and T. Tatsuma, Nano Lett., 18, 3209 (2018).

K. Morisawa, T. Ishida, and T. Tatsuma, ACS Nano, 14, 3603 (2020).

T. Ishida and T. Tatsuma, J. Phys. Chem. C, 122, 26153 (2018).

Figure 1
Plasmonic Hydrogen Evolution at p-Type Semiconductor Electorode
Authors: Minamimoto Hiro , Sato Daiki , Murakoshi Kei
Published: December 2020

The efficient control of the visible light driven hydrogen evolution reaction can be recognized as the one of the promising challenge for the sustainable society. It can be said that the wide-band semiconductor electrode is the promising material for the photo-energy conversion system. However, various semiconductor electrodes have the limitation to the ultraviolet region because of their wide band gap energy. Recently, plasmoic photoelectric conversion system, which is the combination of the plasmon active metal nano-structures with the semiconductor substrate, has been received much attention because the system shows the visible light response characters beyond the limitation of the limitation. In this system, the electrons excited in the metal structures injected into the conduction band of the n-type semiconductor and the remained holes are consumed through the oxidation reaction. Up to now, various plasmon-induced chemical reactions, even the water splitting, have been proposed. As our previous study, we have not only visualized the reaction active sites but also determined the reaction active species through the polymerization reactions of the conductive polymer. Although well-established systems have been reported, the direct control of the reduction reaction at the metal-semiconductor interface by the excited electrons has not been well examined. This is because the almost plasmonic photoconversion systems consist of the n-type semiconductor electrode and applied the generated holes to the reactions. In this study, we have tried to establish the plasmon-induced hydrogen evolution system by the introduction of the plasmon-active metal nano-structures into the p-type semiconductor substrate. By supporting the plasmonic structures, we have confirmed the photo-current generation under the visible light illumination.[1] Through the photocurrent measurements and the incident photon to current conversion efficiency obtained under different pH conditions, we have confirmed the unique pH dependence. In addition to these, we have also investigated the isotopic effect on the hydrogen evolution reaction to clarify the unique surface molecular process. Through the various photoelectrochemical measurements, we are sure that our plasmonic hydrogen evolution system could be one of the good candidate for future light energy conversion system. [1] D. Sato, H. Minamimoto, and K. Murakoshi, Chem. Lett., in press.
Gold-Palladium Bimetallic Nanoparticles for Inducing Surface Plasmon Resonance to Catalyze Ethanol Oxidation
Authors: Boltersdorf Jonathan , Leff Asher C , Forcherio Gregory T.
Published: December 2020

Gold-palladium (Au-Pd) bimetallic nanoparticles were prepared as a series of alloy and core-shell nanostructures to synergistically couple plasmonic (Au) and catalytic (Pd) metals to tailor the optical and catalytic properties. Catalysts utilizing plasmonic metals that exhibit a localized surface plasmon resonance (SPR) can be harnessed for light-driven enhancement via augmented carrier generation/separation and photothermal conversion. Titania-supported Au-Pd bimetallic nanoparticles were used as catalysts to study the ethanol (EtOH) oxidation reaction, with an emphasis towards driving carbon-carbon (C-C) bond cleavage at low temperatures. Plasmonically-assisted photocatalytic oxidation of EtOH to CO2 under solar simulated-light irradiation was studied by monitoring the yield of gaseous products via suspended particle photocatalysis and electrochemical methods. Results are correlated with Au-Pd composition and homogeneity to maintain SPR-induced charge separation and mitigate the carbon monoxide poisoning effects on Pd. Under solar simulated conditions, carrier generation/separation and photothermal conversion was achieved, resulting in the photogenerated “hot” holes driving the photo-oxidation of EtOH primarily on the AuPd, providing a method to selectively cleave C-C bonds. Bimetallics provide a pathway for driving desired photocatalytic and photoelectrochemical reactions with superior catalytic activity and selectivity.
Characterization of Cuprous Oxide Thin Films Grown By Electrochemical Deposition with Sb-Incorporated
Authors: Choi Ji Hoon , Kim Dong Su , Cho Hyungkoun
Published: December 2020

Cu2O thin film is a p-type oxide semiconductor which has a high absorption system, eco-friendly, resource-friendly material. So it can be used in various fields of optoelectronic devices such as solar cell absorption layers, water splitting device and photocathode materials of photovoltaic cells. The electrochemical deposition process of the Cu2O thin film that can be used as an optoelectronic device has advantages such as large-area deposition, precursor recycling function, low-cost process, and low-temperature deposition. This has industrial and economic competitiveness, which has a great advantage over conventional vacuum processing equipment. However, Cu2O thin films grown by using an electrochemical deposition method based on normal pressure and low temperature have lower conductivity than thin films grown by using a vacuum process. The efficiency of the device is inevitably lower than that of thin films based on vacuum process equipment because the electrons and holes cannot be effectively separated. In order to solve the conductivity problem of the thin film, various methods such as optimizing the deposition method and applying a post-deposition treatment process were conducted. The research team improved the mobility of the thin film in the (111) direction by dramatically inducing the preferential growth of the Cu2O thin film by adding Sb, which acts as a metal surfactant that can control the growth behavior. The charge separation was effectively confirmed by light in the Cu2O thin film. This study relates to the process of optimizing the conductivity of the Cu2O thin film by effectively controlling the molar concentration of Sb actually added in the Cu2O thin film. In the process of growing the Cu2O thin film by electrochemical deposition, Cu2O thin films were grown by adding Sb ions at concentrations of 1 mM, 2 mM, 3 mM, 4 mM, and 5 mM. In order to clearly confirm the effect of improving the Cu ion consumption rate due to the addition of Sb at the electrode, linear sweep voltammetry for each molar concentration of Sb was measured and compared. Then, the structural and electrical properties of the Cu2O thin film added with Sb were analyzed using X-ray diffraction, current-voltage, etc. After that, thin films according to the Sb molar concentration were analyzed by capacitance-voltage method and impedance spectroscopy as an electrochemical analysis method. By analyzing the carrier concentration and properties of the optimum conditions for Cu2O thin film growth were confirmed.
Visible Light Hydrogen Production By CdZnS Photocatalysts Prepared in Ethylenediamine Aqueous Solution
Authors: Katsumata Hideyuki , Koguchi Kyosuke , Tateishi Ikki , Furukawa Mai , Kaneco Satoshi
Published: December 2020

Recently, semiconductor photocatalysts are expected to be a strategy to solve the energy demand and environmental pollution. Many researchers have attention, and have been developed photocatalysts for hydrogen production. Among them, metal sulfides (i.e. CdS, ZnS, MoS2, etc.), metal oxides (i.e. TiO2, Fe2O3, NiOx, RuO2) are regarded as good candidates for the photocatalytic H2 production. CdS is highly important as a photocatalyst because of the low band gap energy (~2.4 eV) and high activity under visible light irradiation for the photocatalytic hydrogen evolution reaction (HER) [1]. However, pure CdS tends to form particle aggregation and inherent photocorrosion, resulting in a higher recombination rate of charge carrier limited its application. One of the effective ways is by combing CdS with ZnS to form CdZnS (cadmium zinc sulfide) [2]. CdZnS has been regarded as a promising photocatalyst, but it has fast recombination of photogenerated electron-hole pairs. Therefore, the photocatalytic hydrogen evolution activity of sulﬁde semiconductor can be signiﬁcantly improved by loading noble metals as cocatalysts to provide active sites for proton reduction.

In this work, we report excellent H2 production performance when PdS, Pt are used as cocatalyst for CdxZn1-xS, which was synthesized via a simple solvothermal synthesis method. The resulting photocatalysts exhibit enhanced hydrogen production from water in 0.25 M Na2SO3 + 0.35 M Na2S as a sacrificial agent.

The crystalline structures of as-prepared CdxZn1-xS were analyzed by XRD. The XRD peaks of Cd0.5Zn0.5S are weaker and broader than those of one prepared in the absence of ethylenediamine during the solvothermal synthesis. These results indicate that the addition of ethylenediamine has a certain inhibitory effect on the growth of the grain of Cd0.5Zn0.5S.

Cd0.5Zn0.5S photocatalyst was selected as optimal one in this photocatalytic activity test. The photocatalytic H2 production over PdS deposited Cd0.5Zn0.5S was enhanced comparing that of pristine Cd0.5Zn0.5S, showing greater about two times. Further, in the presence of dual cocatalysts, namely PdS and Pt, the photocatalytic H2 production was about 2.4 times higher than that of pristine Cd0.5Zn0.5S.

In summary, this work showed that CdxZn1-xS photocatalysts were synthesized successfully by a simple solvothermal method. With ethylenediamine in the solvothermal process, the crystallinity of CdxZn1-xS photocatalysts was lower than that of one prepared by the hydrothermal method. The use of dual co-catalysts, namely PdS and Pt, were effective for the photocatalytic H2 production under visible light.
Design of a Reference Model for Fast Optimization of Photo-Electrochemical Cells
Authors: Tenholt Carmen , Klassen Thomas , Schieda Mauricio
Published: December 2020

The photo-electrochemical (PEC) cell, which combines the technology of electrolyzers and photovoltaics, is a promising candidate for the electrolysis of hydrogen with reduced external energy supply. Multiple parameters of such cells have to be adjusted to achieve the most efficient assembly for given requirements. These parameters include the choice of photoactive material, type and kinetics of electrolyte and the cell geometry, which finally determine the photocurrent. As the dependency between these parameters and the cell performance is complex, numerical simulations are an indispensable tool for the optimization process. To guarantee a reliable reference model that applies for all possible parameter changes, iterative verification with experiments is necessary. Especially the precise modelling of the interfaces between photoactive substrate and electrolyte poses a significant challenge for the numerical simulations. Nevertheless, precise modelling of this region is crucial, as it largely determines the cell efficiency by controlling the reaction rate, gas saturation, electrode corrosion and thus the photocurrent. In this work we present results of numerical modelling of PEC cells with COMSOL Multiphysics, their benchmarking with experimental data measured with varying 3D-printed geometries, electrode substrates and electrolyte compositions as well as new approaches for optimizing the efficiency of PEC cells.
Unexpected Facet-Selective TiO2 Surface Modification and Photoelectrochemical Property
Authors: Seo Junhyeok
Published: December 2020

Interface of the Group X metal oxides and TiO2 nanostructure has been examined regarding the photoelectrochemical water splitting reaction. Deposition of NiO-only nanoparticles covered the rutile (110) side of TiO2 nanostructure. However, application of the Group X hetero-metal oxides somewhat opened the rutile (110) side. Thermal post-treatment of the hetero-metal oxides at medium temperature readily generated mixed valence states of a metallic site and the high oxidation states on the TiO2-Group X hetero-metal oxides interface. The thermal post-treatment simultaneously generated the both catalytic sites for water splitting reactions, of which surface successfully facilitated the photoelectrochemical water splitting in the absence of a redox mediator. In addition to the formation of p-n heterojunction, the co-existing catalytic sites surely promoted the overall water splitting. The TiO2 surface decoration with the Group X hetero-metal oxides modulates band structure, as well provides an effective method to control the surface charge recombination. The size controlled TiO2 nanostructure and its surface decoration by the Group X hetero-metal oxides provided beneficial pathways for both of the photo-generated electrons and holes. In this talk, I will discuss the synthetic methods and analytical data for the photoelectrode materials.
Reorganization of Interfacial Water By an Amphiphilic Cationic Surfactant Promotes CO2 Reduction
Authors: Hall Shoji
Published: December 2020

The presence of cetyltrimethylammonium bromide (CTAB) near the surface of a Cu electrode promotes the electrochemical reduction of CO2-to-fuels. The presence of CTAB increases the CO2 reduction rate by as much as 10x and decreased the HER rate by 4x, leading to ~75% selectivity towards the reduction of CO2. We utilized Surface Enhanced Infrared Absorption Spectroscopy (SEIRAS) to probe the dynamics of CTAB adsorption on the structure of interfacial water and CO2 reduction intermediates. HER suppression was found to arise from the displacement of interfacial water molecules from the presence of CTAB in the double layer. The enhanced CO2 reduction rate can be correlated to an increased population of atop bound CO and the emergence of a low frequency atop CO band. These results unravel the role of additives in improving CO2-to-fuels electrocatalysis and establishing this as a powerful methodology for directing product selectivity.
Lithium-Ion Battery Degradation Mode Diagnostics Using Heat Generation Profiles
Authors: Prosser Ryan , Patel Yatish , Offer Gregory James
Published: December 2020

As lithium ion cells are used, internal chemical and physical degradation processes occur which negatively impact cell performance. A key issue for battery systems engineers is extending the life of their battery pack which amounts to slowing down the rate of these degradation processes.

The first step in addressing this problem is being able to frequently and accurately diagnose cell degradation. With this knowledge of cell state, it is possible to make better decisions on how to adjust the operating conditions of the battery pack to optimise cell longevity and performance.

Current methods which are capable of accurate quantitative diagnostics employ thermodynamic models parameterised by different degradation modes. These models require very slow discharge rates or galvanic intermittent titration tests (GITT) to obtain the cell open circuit voltage (OCV) and therefore cannot be used in most commercial applications. Other methods which do not require OCV conditions involve an impedance model coupled to the thermodynamic model. This adds computational complexity of the methods as well as incurring an accuracy penalty compared to the thermodynamic models.

We present a novel technique which uses cell instantaneous heat generation rate obtained in operando to quantify the extent of cell degradation. The proposed method provides results comparable to those obtained from thermodynamic models using a model which is no more computationally intense. The method also decouples the thermodynamic and kinetic effects of degradation allowing for a full diagnosis to be obtained more accurately and in a fraction of the time compared to alternative methods.

With this powerful and simple method, a battery management system would be able to make better and more frequent adjustments to its cell’s operating conditions for optimizing both longevity and performance.
Insights into the Reversible Redox Pathways in Lithium-Sulfur Batteries By in Situ AFM-SECM Coupled Raman Spectroscopy
Authors: Thangavel Naresh kumar , Mahankali Kiran , Arava Leela Mohana Reddy
Published: December 2020

Among many emerging energy storage systems, lithium-sulfur (Li-S) is the most sought-after technology due to its high energy density (2600 Wh/kg) and low cost.(1) However, its performance is guided by highly complex and non-equilibrium conversion reactions of several sulfur intermediates, known as lithium polysulfides (LiPS), along with solid-liquid-solid phase transformations at the cathode surface. Such Li-S batteries often face formidable challenges like rapid capacity fade, sluggish reaction kinetics, short cycle life, and poor coulombic efficiency(2). In spite of some success in mitigating these issues by employing a variety of cathode surface modifications(3, 4), the fundamental understanding of LiPS reaction pathways towards discharge end-products and their relation to the cathode surface are still not well established.

It is commonly believed that the morphology, composition and physio-chemical characteristics of the discharge products can be closely correlated to the deteriorating performance issues like internal resistance buildup and capacity fade in Li-S cell(5-7). Herein, we provide mechanistic perspectives of the substrate guided reaction pathways of LiPS and their correlation to redox activity of discharge end products using in situ atomic force microscopy-based scanning electrochemical microscopy (AFM-SECM) coupled Raman spectroscopy at a high spatiotemporal resolution. With a detailed spectro-electrochemical and morphological mapping, we decipher the substrate-dependent charge/discharge end product’s formation and their effect on redox processes in the subsequent cycles.

References:

1. G. Bruce, S. A. Freunberger, L. J. Hardwick and J. M. Tarascon, Nature materials, 11, 19 (2012)

2. Manthiram, Y. Fu and Y. S. Su, Accounts of chemical research, 46, 1125 (2012).

3. Babu, N. Masurkar, H. Al Salem and L. M. Arava, J Am Chem Soc, 139, 171 (2017)

4. Pang, D. Kundu, M. Cuisinier and L. Nazar, Nature communications, 5, 4759 (2014)

5. Yan, X. Liu and B. Li, Advanced Science, 3, 1600101 (2016)

6. Diao, K. Xie, S. Xiong and X. Hong, Journal of The Electrochemical Society, 159, A1816 (2012)

7. Y. Lang, Y. Shi, Y. G. Guo, D. Wang, R. Wen and L. J. Wan, Angewandte Chemie International Edition, 55, 15835 (2016).
Probing Electrode Electro-Chemo-Mechanical Coupling Behaviors through Mechanical Cyclic Voltammetry (mCV)
Authors: Tsai Wan-Yu , Balke Nina
Published: December 2020

Electrode deformations during charging and discharge process are directly related to the power performance and cyclability of the energy storage devices. Understanding the electrode deformation and changes in mechanical responses during electrochemical events and their impact on devices’ performance is crucial for achieving high power and high energy storage devices. In-situ atomic force microscopy (AFM) is well suited to tackle this task as it allows tracking local sub-nanometer volume changes and other mechanical responses. With a spatial resolution of tens of nanometer, this approach is capable of mapping the electro-chemo-mechanical behavior under the conditions close to the device operation and access information about local redox mechanisms.

In this work, the electro-chemo-mechanical coupling behaviors of different pseudocapacitive materials was studied via in-situ AFM. The concept of mechanical cyclic voltammetry (mCV) curves was developed, and the relationship between electrochemical current and strain were investigated with simplified models. The results revealed that multiple ion-intercalation processes with different mechanical responses are involved during electrode cycling. The mechanical CV mapping highlighted the local heterogeneity and showed that the charging mechanisms varied across the electrode. These local variations could be further corelated to local morphology, crystal orientations or chemical compositions. Besides providing information of redox heterogeneity, the mechanical CV methodology allows us to circumvent the common issues that are often encountered in the global electrochemical characterizations, for example cell resistance and unwanted parasitic reaction.

The work was supported by the Fluid Interface Reactions, Structures and Transport (FIRST), an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences. Measurements were performed at the Center for Nanophase Materials Sciences (CNMS), which is sponsored at Oak Ridge National Laboratory by the Scientific User Facilities Division, Office of Basic Energy Sciences.
Towards Quantifying Capacity Losses Due to Solid Electrolyte Interphase Evolution in Silicon Thin Film Batteries
Authors: Steinrück Hans-Georg , Cao Chuntian , Veith Gabriel M. , Toney Michael F
Published: December 2020

To better understand failure mechanisms in lithium-ion batteries (LIBs), it is imperative to quantify the capacity fading contributions from active material loss and solid electrolyte interphase (SEI) growth. However, these two contributions are indistinguishable in traditional electrochemical measurements. In this study, we used a model system in combination with (1) precision measurements of the overall Coulombic efficiency via electrochemical experiments and (2) X-ray reflectivity (XRR) measurements of the active material losses. The model system consisted of a 515 Å thick amorphous silicon (a-Si) thin film on silicon carbide in a half-cell geometry using a carbonate electrolyte with LiPF6 salt. Schematics of the cells used in operando XRR and precision electrochemistry measurements are shown in Fig. (a) and (b) respectively.

Specifically, we used surface/interface sensitive operando XRR to monitor the a-Si/LixSi thickness during (de)lithiation in order to quantify the capacity fading due to active material loss. Combined with electrochemical analysis, we quantified the capacity loss originating in SEI growth during each cycle (Fig. (c)). We have found that SEI continues to grow with cycling, and the SEI thickness is dependent on the time spent at low potentials (Fig. (d)). The continued SEI growth results in increasing overpotentials due to increased SEI resistance, which leads to a lower extent of lithiation when the cut-off voltage is reached. Finally, we extracted a proportionality constant for SEI growth following a parabolic growth law. Our results are in fair agreement with the capacity losses observed in full cell systems.

We envision that the proposed methodology can be used as a qualitative measure of the ion transport properties of the SEI. The model-based approach allows for quantitative determination of lithium ion loss mechanisms in LIBs by separately tracking lithium ions within the active materials and will aid in developing ways to reduce parasitic losses.

Figure 1
Suppressing High Current Induced Local Compositional Heterogeneity in LiNi0.6Co0.2Mn0.2O2 By Controlling the Kinetic Parameters
Authors: Hyun Hyejeong , Jeong Kyeongjae , Cho Hoon-Hwe , Han Heung Nam , Shin Taejoo , Lim Jongwoo
Published: December 2020

Understanding the cycling rate-dependent kinetics is crucial for engineering batteries with better performance in high power applications. Although high cycling rate induces phase heterogeneity which is responsible for life-time and rate capability, such dynamics are poorly understood and uncontrollable. In this study, operando X-ray diffraction analysis with high temporal resolution was utilized to investigate phase transition kinetics of LiNi0.6Co0.2Mn0.2O2 at a high cycling rate. Due to the sluggish Li diffusion at high lithiation levels, highly asymmetric phase transition was observed in charge and discharge. While relatively homogeneous phase transition took place during discharging, strong phase separation was observed during charging. By taking advantage of the dependence of diffusion and redox kinetics on Li composition and tuning the initial lithiation distribution, we were able to manipulate the overall phase transformation kinetics and further induce solid-solution phase transformation at the high C-rate charging. The finite element analysis elucidated the effect of Li content-dependent diffusion kinetics on the phase transition pathway. Our findings suggest a new direction of optimizing fast cycling protocols based on the fundamental understanding of the material properties.
(Keynote) Tuning the Selectivity of CO2 Electroreduction through Dynamic Catalyst Transformations Under Reaction Conditions
Authors: Roldan Cuenya Beatriz
Published: December 2020

The utilization of fossil fuels as the main energy source gives rise to serious environmental issues, including global warming caused by the continuously increasing level of atmospheric CO2. Recently, the electrochemical conversion of CO2 (CO2RR) to chemicals and fuels driven by electricity derived from renewable energy has been recognized as a promising strategy towards sustainable energy.

In my talk I will provide examples of recent advances in the development of highly active size- and shape-controlled nanoparticle (NP) electrocatalysts (Cu, Cu-Zn, Cu-Ag) and how their structure (crystal orientation, atomic arrangement, size, shape, defects), oxidation state and composition influence their selectivity in CO2RR. I will also discuss how important morphological motives and chemical sites can be created and regenerated in pulsed electrochemistry experiments. Additionally, the determining role of the electrolyte in the surface restructuring, reaction activity and selectivity will be illustrated. Finally, the importance of in situ and operando characterization methods (e.g. EC-AFM, Liquid-TEM, XAS, XPS, XRD, LEEM/XPEEM) to gain in depth understanding on the structure- and electrolyte-sensitivity of real CO2RR catalysts under working conditions will be demonstrated. Our results are expected to open up new routes for the reutilization of CO2 through its direct selective conversion into higher value products such as ethylene and ethanol.
(Invited) Tracking CO2 Reduction Products in Real Time
Authors: Katsounaros Ioannis
Published: December 2020

Time-resolved characterization methods provide fundamental insights into electrode processes by capturing events that occur at short time scales. We recently developed the electrochemical real-time mass spectrometry (EC-RTMS) to determine gaseous and liquid products of electrochemical reactions shortly after their formation, with resolution in the order of few seconds. After describing its basic components, I will present some representative examples of using EC-RTMS to monitor the products of CO2 reduction under dynamic conditions, on various copper electrodes.
(Invited) Electrodeposition of Manganese Oxides Utilizing Hydrothermal Electrochemical Technique
Authors: Yamaguchi Akira , Otsubo Yoshiki , Kitadai Norio , Nakamura Ryuhei , Miyauchi Masahiro
Published: December 2020

Hydrothermal electrochemistry can conduct electrochemical experiments under high temperature and pressure conditions and is one of the useful methods to fabricate size-controllable and highly crystalline materials. Although this technique has been applied to electrodeposition of metal oxides like BaTiO3 (Yoshimura et al., Jpn. J. Appl. Phys., 28, L2007, 1989), precise control and examination of electrochemical process was hard to be achieved in previous reactors because they adopted two-electrode systems. Moreover, reaction pressure was determined by temperature, so it is difficult to discuss their specific contribution to the electrochemical process.

Recently, we have developed hydrothermal electrochemical reactor in which three-electrode system was adopted in order to control and monitor the electrochemical process precisely. This system also achieves independent control of temperature and pressure so that we can discuss their contributions to the final products. Here in this work, we attempted to fabricate Manganese oxide thin film with electrodeposition technique under different temperature and pressure, and examined their electrochemical water oxidation activity. Manganese oxides are prepared in industry with electrodeposition technique, so they are good candidates as model compounds to examine the property of our home-made hydrothermal electrochemical reactor.

MnO2 was deposited on Ti substrate with galvanostatic condition of 10 mA /cm2 for 20 min utilizing 0.5 M MnSO4 / 0.2 M H2SO4 aqueous solution as a precursor. Based on XRD analysis, all deposited samples were ε-MnO2. When we increase deposition temperature, XRD peaks got sharpen, indicating the crystallinity increased. SEM observation clarified their morphological difference. Namely, MnO2 deposited at 160℃ possessed needle-like structure, while spherical structure was observed for sample deposited at 100℃. To examine the effect of pressure on deposition products, we conducted electrodeposition under different pressure from 0.1 to 4 MPa while maintaining temperature at 100℃. As a result, XRD peaks were slightly shifted depending on pressure. This means lattice constant is controllable by regulating deposition pressure.

Their electrochemical water oxidation activity also demonstrated the advantage of hydrothermal electrodeposition compared with conventional technique. After annealing at 200℃, 160℃-electrodeposited sample exhibited superior activity to 100℃-deposited sample. Although the elucidation of the reason for higher catalytic activity is future work, those results indicate our hydrothermal electrochemical technique is widely applicable to material synthesis such as metal oxides, metal sulfides, and so on.

Figure 1
Assessing pH and Voltage Effects on the Binding of CO to Model Copper Catalyst Surfaces Via a DFT-Continuum Theory
Authors: Weitzner Stephen Eric , Akhade Sneha A , Varley Joel Basile , Wood Brandon C. , Baker Sarah E , Duoss Eric B , Otani Minoru
Published: December 2020

The electrochemical conversion of CO2 to commodity products such as hydrocarbons and oxygenates is an attractive approach for generating non-fossil derived chemical and fuel stocks and for the storage of energy in chemical bonds. To date, a number of studies have shown that the activity and selectivity of copper-based catalysts for the CO2 reduction reaction towards valuable higher order carbon products are highly sensitive to the local reaction environment. Furthermore, the local electrolyte concentration and local pH is intimately tied to the applied voltage and the mass transport of reactants and products within the interfacial region. In recognition of this, several recent efforts focused on engineering the design of electrochemical reactors to reduce mass transport limitations indicate a pronounced effect on the apparent selectivity of the copper catalyst. While these efforts have highlighted a new direction for improving the efficiency of the CO2 reduction reaction, the rational design of these reactors remains challenging due to the need to optimize features of the reactor across multiple time and length scales. In this talk, we will discuss recent efforts within our laboratory to address the influence of the local pH on the CO2 reduction reaction at the atomistic level. We focus the discussion on the binding of CO, a key reaction intermediate in the CO2 reduction pathway, whose preferential hydrogenation or dimerization leads to the production of C1 and C2 products, respectively. We additionally demonstrate how the use of hybrid approaches employing density functional theory (DFT) and continuum models can help bridge time and length scales within the context of atomistic CO2 electroreduction modeling.

This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.
Development of Stable CO2 Electro-Reduction Catalyst in Real Water Matrix
Authors: Won Da Hye , Min Byoung Koun , Hwang Yun Jeong , Oh Hyung-Suk
Published: December 2020

Artificial photosynthesis refers to the conversion of water and CO2 into value-added chemicals powered by sunlight, and is the holy grail of a sustainable carbon cycle of chemicals. Since a big challenge facing this system is the conversion of stable CO2 into the desired chemicals, most studies have focused on the development of high-performing catalysts within well-refined and restricted test environments. However, such superior performances cannot guarantee their feasibilities in realistic conditions for future commercialization or practical application unless their durability issues are secured. Here we report a one-step ahead approach to develop a more practical and advanced CO2 electro-reduction catalyst with essential clues to overcome the obstacles from realistic conditions, based on the understanding of CO2 reduction reaction deactivation phenomena. Our investigation firstly deals with the performance profile of an Ag electrode, selected as a standard catalyst for CO production, in real-life used tap water which is representative general purpose water. Screening and accompanying thorough analyses on various components in tap water ranging from alkali earth metals to transition/post-transition metals elucidated the types of impurities that can impede the catalytic activity by surface deposition, and consequentially cause the deactivation. Based on the findings involving Ag, a design strategy for a catalyst having excellent tolerance to the deactivation factors was suggested using a carbon-based material with heteroatom-doped active sites. A metal-free nitrogen-doped short carbon nanotube was prepared by a simple three-step process, and was denoted as ball mill N-CNT. As expected, the ball mill N-CNT showed a competitive and tolerant performance to the metal impurities regardless of the nature of the water sources, deionized water and tap water.
Effects of Gas Diffusion Layers on a CO2 electrolysis Cell with an Anion Exchange Membrane for Ethylene Production
Authors: Kudo Yuki , Tamura Jun , Yamagiwa Masakazu , Kitagawa Ryota
Published: December 2020

The concept of an electrolysis system, where CO2 is converted into hydrocarbons using renewable electricity, has been attracting much attention because it is expected to be one solution to achieve a decarbonized society. In order to realize an economical electrolysis system, it is important to produce high-value products such as ethylene with high reaction rate (i.e. the operating current density of CO2 electrolysis), and high efficiency (low operation voltage).

The anion exchange membrane (AEM) CO2 electrolysis cells using gas diffusion electrodes (GDEs) are more advantageous than the traditional flow cell using a solution purged with CO2, both in terms of higher current density and lower voltage operation. This is because of the efficient CO2 reduction occurring at the three-phase interface of a GDE (i.e. CO2 is directly fed to the vicinity of the electrocatalysts though a gas diffusion layer (GDL)), increasing the current density, and of the cell electrodes being closely spaced, lowering the voltage. However, there are only several studies of the AEM CO2 electrolysis cells for high rate of ethylene production [1].

Here, we investigate ethylene production performance of an AEM CO2 electrolysis cell consisting of copper and copper oxide nanoparticles coated on GDL as a cathode, iridium oxide-coated titanium support as an anode, and an AEM. Among these components, the GDL can play a crucial role in the efficient transport of CO2 and water management, therefore we focus on understanding the effects of GDL properties such as thickness, porosity and density on ethylene production. We evaluated the electroreduction characteristics of the cells under ambient condition by a constant current method in which a constant current is supplied for a period of time. The faradaic efficiency (FE) and partial current density (PCD) of gas products such as ethylene, carbon monoxide, methane and hydrogen are examined as a function of the total current densities (TCD). We found that the FEs and PCDs depended on the density and the thickness of the GDLs. The low density and thick GDL showed high FE and PCD of ethylene due to high gas diffusibility. The FE and the PCD of ethylene at the TCD of 600 mA/cm2 reached a maximum of 50 % and 300 mA/cm2, respectively.

References

[1] Christine M. Gabardo, Colin P. O’Brien, Jonathan P. Edwards, Christopher McCallum, Yi Xu, Cao-Thang Dinh, Jun Li, Edward H. Sargent, and David Sinton, Joule 3, 1–15, November 20, 2019
Interplay between Mesoscale Architecture and Catalytic Output in CO2 Gas-Diffusion Electrolyzers
Authors: Raciti David , Braun Trevor Michael , Xu Heng , Cruz Mutya A. , Wiley Benjamin J. , Moffat Thomas P.
Published: December 2020

With the anticipated effects of global climate change upon us, induced by egregious CO2 emissions, it is imperative to implement technologies to close the carbon cycle. One potential technique to do this is storing the energy from intermittent sources (e.g. solar, wind, hydro) in the form of chemical bonds, such as the electrochemical reduction of CO2. By reducing CO2 to energetically and chemically useful products of CO2 (i.e. CO and C2H4) we can both reduce reliance on fossil fuels and mitigate atmospheric CO2 levels. However, controlling the selectivity towards which particular product is formed and preventing the parasitic hydrogen evolution reaction (HER) is a crucial challenge that must be overcome.1 Exploring fundamental mechanisms and new catalyst materials to overcome this challenge, can be skewed due to the low diffusivity (≈2x10-9 m2/s)2 of CO2 in the liquid phase causing inefficient utilization of catalyst active sites. Unlike the oxygen reduction reaction, use of a rotating disc electrode does not resolve the issue due to the competitive HER reaction. Therefore, it becomes imperative to study physical structure-function relations (e.g. catalyst layer thickness) in a cell that provides ample flux of solely CO2, such as a gas-diffusion electrolyzer (GDE) which greatly increases the diffusivity of CO2 and gas products by enabling transport through gas channels (≈1.6x10-5 m2/s). By filtering nanowires through a gas-diffusion electrode (Figure 1 a-b) we fabricated electrodes of varying thicknesses that were then applied as catalysts in a gas-diffusion electrolyzer (Figure 1c). Results show that even under high CO2 flux conditions there is an interplay between selectivity (Figure 1d), activity (Figure 1e) and catalyst layer thickness. Further exploration of this interplay in commercially relevant electrolyzers can expedite optimized implementation of catalysts in the industrial sector and hopefully aid in solving the global climate crisis at hand.

(1) Verma, S.; Kim, B.; Jhong, H.-R. “Molly”; Ma, S.; Kenis, P. J. A. A Gross-Margin Model for Defining Technoeconomic Benchmarks in the Electroreduction of CO2. ChemSusChem
2016, 9 (15), 1972–1979. https://doi.org/10.1002/cssc.201600394.

(2) Raciti, D.; Mao, M.; Ha Park, J.; Wang, C. Mass Transfer Effects in CO 2 Reduction on Cu Nanowire Electrocatalysts. Catalysis Science & Technology
2018, 8 (9), 2364–2369. https://doi.org/10.1039/C8CY00372F.

Figure 1: Electron microscopy images of Ag nanowires (a) top-down and (b) cross-section, on a gas-diffusion electrode. This electrode is than applied as a CO2 reduction catalyst in a (c) gas-diffusion electrolyzer. The thickness of the Ag nanowire catalyst layer influences both the (d) selectivity and (e) mass activity of the reaction.

Figure 1