bluuebunny/crossref_metadata_2025 huggingface dataset:
(Invited) A Novel Optical Characterization of a-Si:H/c-Si Interface Microstructures Based on Data of Positron Annihilation Spectroscopy
Authors: Matsuki Nobuyuki , Matsui Takuya , Michishio Koji , O' Rourke Brian , Oshima Nagayasu , Uedono Akira
Published: February 2020

The power conversion efficiency of amorphous/crystalline silicon (a-Si:H/c-Si) heterojunction solar cells has exceeded 26% recently.1) Such high efficiency is essentially achievable thanks to the notable passivation capability of the several-nm-thick amorphous silicon layer deposited on the c-Si surfaces. For further improvement of the performance, it is necessary to understand and to control the structural properties of the a-Si:H/c-Si heterointerface.

Recently, we have found that there is a systematic correlation between the microvoid size determined by the positron annihilation spectroscopy (PAS) and the optical constant of a-Si:H by spectroscopic ellipsometry (SE).2) However, it has been still not clear that this correlation is universally consistent for any a-Si:H thin-films that are fabricated under various preparation conditions using any different apparatus.

In this study, we prepared undoped a-Si:H films on H-terminated FZ Si(111) substrates under various chemical vapor deposition conditions including different source gases (SiH4 or Si2H6) and deposition systems. The average diameter of microvoids (D
void) and the dielectric function (ε = ε
1 - iε
2) in these a-Si:H films were estimated via PAS and SE measurements, respectively. The peak values of ε
2,
ε
2
peak, were extracted from the dielectric function determined based on the Tauc-Lorentz dispersion model.3) It is notable that the D
void vs. plots are aligned on a straight line; this result indicates that D
void in undoped nm-thin a-Si:H can be estimated readily from SE measurement results using the found D
voidーε
2
peak　linear correlation. Details in this method and results will be discussed in the presentation.

References

1. Yoshikawa, H. Kawasaki, W. Yoshida, T. Irie, K. Konishi, K. Nakano, T. Uto, D. Adachi, M. Kanematsu, H. Uzu and K. Yamamoto, Nature Energy
2, 17032 (2017).

2. N. Matsuki, A. Uedono, B. E.O’Rourke and N. Oshima., 8th Intl. Conf. on Plasma-Nano Technol. and Sci., 3-O-03 (2015).

3. S. Kageyama, M. Akagawa, and H. Fujiwara, Phys Rev. B 83, 195205 (2011).

Figure 1
A Study of Factors Responsible for Cracking during Drying of Thick Aqueous-Processed NMC811 Cathodes
Authors: Sahore Ritu , Li Jianlin , Wood David L.
Published: February 2020

Replacing the widely used NMP solvent for processing of lithium-ion battery electrodes with water has both environmental and cost benefits. Compared to aqueous-processing of anodes, the aqueous-processing of cathodes is considerably more challenging. Issues such as damage of the NMC-type active material upon exposure to water, damage of the aluminum substrate due to highly basic aqueous-slurry, and cracking of the water-based cathode slurry coatings upon drying are known and are actively being researched. In this study, we focus on the cracking-issue which is more severe for relatively thick cathodes with loadings of >~11-12 mg/cm2. Our group has previously reported the role of high surface-tension of water compared to NMP on cracking and demonstrated that the addition of 20-30 wt% IPA as a co-solvent lead to crack-free thick (~25 mg/cm2) NMC532 cathodes. This finding was attributed to reduction of surface tension of water, which decreased the capillary forces during drying. Further investigations have resulted in identification of several other factors that are also responsible for the cracking-issue. These factors, which are not necessarily related to the surface tension, will be discussed.
Mechanofusion-Derived Si Alloy-Graphite Composite Electrode Material for Li-Ion Battery
Authors: Cao Yidan , Wang Jun , Hatchard Timothy , Wei Congxiao , Dunlap R. A. , Obrovac M. N.
Published: February 2020

Silicon-graphite composites are extremely promising negative electrode materials for Li-ion batteries. However, simple and effective methods to synthesize silicon-graphite composites with engineered structures are needed to realize this technology in practical applications. Here, we show that the environmentally friendly and low-cost dry mechanofusion (MF) process can effectively synthesize silicon alloy-graphite composites, in which silicon alloy particles can be well dispersed and embedded between flake graphite layers, as shown in Figure 1(a)-(b). This results in increased tap density and reduced surface area. The special structure provides a way to buffer volume expansion and contraction of the silicon alloy during lithiation and delithiation. As a result of this hierarchical arrangement, superior cyclability and rate capability are achieved compared to simple mixtures, with capacities of 950 mAh/g (i.e. 1473 Ah/L) and 900 mAh/g (i.e. 1432 Ah/L) at 2C and 4C, respectively (Figure 1(c)).

Moreover, using this process, micron-sized silicon alloy particles can be well embedded within spherical natural graphite particles, as shown in Figure 1(d)-(e). The specially engineered structure created by the MF dry process leaves room for expansion and contraction of the silicon alloy during lithiation and delithiation process. In addition, the silicon alloy particles are protected within the graphite particle, which could be helpful to avoid excessive electrolyte exposure and improve cycle life.

Figure 1
(Invited) Electrode/Battery Engineering to Increase the Energy Density of High-Ni NMC Cathode
Authors: Zhou Hui , Pei Ben , Xin Fengxia , Whittingham M. Stanley
Published: February 2020

High-nickel NMC cathode is becoming more and more popular, because with increased nickel content, the energy density is increased and at the same time the cost is reduced. Presently, NMC 622 has been commercialized. The higher nickel composition, NMC 811, has higher capacity and tolerates higher material loadings and even better rate performance, so it will become the material of choice if its increased instability can be controlled. However, the request on energy density is keeping going up due to the application requirement, which needs not only the materials optimization, but also the electrode/battery engineering to maximally reduce the irreversible capacity loss. Our initial studies have found that most capacity loss for NMC cathode is kinetically limited, especially the much slower diffusion at the end of relithiation (Figure 1). Through electrode/battery engineering, the kinetics limits can be reduced/eliminated and the capacity loss would be recovered. This work was supported by the Assistant Secretary for Energy Efficiency and Renewable Energy, Office of Vehicle Technologies of the U.S. Department of Energy, through the Advanced Battery Materials Research Program (Battery500 Consortium).

Figure 1
(Invited) Thin Film Processing for Innovative Solid State Lithium Batteries
Authors: Oukassi Sami , Porthault Helene , Salot Raphaël
Published: February 2020

With the emergence of novel multifunctional internet of things and wearable electronic devices, the development of high performance energy storage devices is becoming increasingly important. Thin film solid state lithium batteries (TFBs) are known to be one of the most promising candidates to meet these applications’ demands.

In this context, it is expected that the development of thick (20µm+) electrodes with active material only would provide opportunities to enhance the device performance and widen the scope of possible integration schemes. Several options have been explored at LETI, including key enabling technologies such as electrochemical, hydrothermal, physical vapor deposition as well as a combination thereof. Here we will discuss our efforts to develop advanced TFB electrodes based on the thick active material electrodes.
A Proton Conducting Solid Oxide Electrolysis Cell with Tri-Doping Electrolyte and Three-Phase Conducting Steam Electrode for Sustainable Hydrogen Production
Authors: Ding Hanping , Rajendran Sathish , Arava Leela , Ding Yi , Thangavel Naresh Kumar , Centeck Kevin , Ding Dong
Published: February 2020

Proton conducting solid oxide electrolysis cell (P-SOEC) is an emerging technology that enables sustainable hydrogen production at reduced operating temperatures (400~600 ○C). Economically competitive P-SOEC systems have distinct advantages over conventional oxygen-ion conducting counterpart (O-SOEC), but further technology development and widespread market acceptance will require continuous innovation of materials in order to improve cell performance, enhance system lifetime and reduce cost. In this work, a new type of tri-doping barium-zirconium-cerate electrolyte and a triple phase conducting steam electrode are explored as material candidates. The material synthesis, pellet sintering, and electrical conductivity are carried out to evaluate the feasibility as an electrolyte. For the triple phase conducting electrode, the conduction behavior and catalytic activity towards water splitting reaction are studied. In addition, these two materials are incorporated into P-SOEC button cells and the electrochemical performance is evaluated under different operating conditions (temperature, humidity, feed gas composition, etc). The long-term durability in high steam pressure is also carried out to examine the stability of the material system. Such an early-stage R&D showed feasibility of hydrogen production systems for field operations and the ability to cost effectively produce hydrogen at the scale needed to support military operations.
Performance Enhanced Solid Oxide Fuel Cell Cathodes By Electrocatalyst Surface Modification
Authors: Robinson Ian , Huang Yi-Lin , Horlick Sam , Wachsman Eric D.
Published: February 2020

Solid oxide fuel cells (SOFCs) are a promising energy conversion device due to their fuel flexibility and high efficiency. However, commercialization of SOFCs has been hindered by high operating costs due to high balance of plant and high degradation rates, mainly caused by the high operating temperature. However, the sluggish cathode activity limits the performance of low temperature SOFC operation. Here we show our recent results on cathode surface modification. Different modification techniques were used and different metal oxide electrocatalysts were introduced on the surface of common SOFC cathodes, La0.6Sr0.4Co0.2Fe0.8O3 (LSCF) and Sm0.5Sr0.5CoO3 (SSC). These nano-sized electrocatalysts significantly enhance the cathode performance by increasing oxygen activity and reaction sites due to the high intrinsic catalytic activity and the increase in triple phase boundary length. The overall activity of SOFC cathodes at lower temperatures is significantly enhanced, providing a cost effect route to enhancing cathode activity for low temperature SOFC operation. The effect of number of available valence states in a metal may play a role in the facilitating the cathode reaction. Specifically, higher valence state metals could accept and transport oxygen more rapidly than lower valence state metals. Correlating electrochemical performance with the available valence states of metal cations may help elucidate the mechanism of the cathode reaction in SOFCs. The most promising metal oxide candidates were also tested to investigate CO2 poisoning and strontium oxide segregation to increase durability of SOFC cathodes. Our results demonstrate surface modification to existing SOFC cathodes could potentially increase the activity at lower temperatures while limiting unwanted material interaction between cell components.
Enhancing the Electrochemical Performance of Metal-Supported Solid Oxide Fuel Cells
Authors: Shen Fengyu , Dogdibegovic Emir , Lau Grace Y , Tucker Mike
Published: February 2020

This paper will present the electrochemical performance and durability of metal-supported solid oxide fuel cells (MS-SOFCs) developed at LBNL. The cell is comprised of a thin ceramic electrolyte and porous electrode backbones sandwiched between stainless steel metal supports. Compared to conventional all-ceramic SOFCs, MS-SOFCs offer a number of advantages due to their low-cost structural materials (e.g. stainless steel), mechanical ruggedness, excellent tolerance to redox cycling, and extremely fast start-up capability. The sensitivity to MS-SOFCs is determined by the cell architecture, catalyst, and sintering process. Performance of the MS-SOFCs is characterized by voltage-current, impedance spectroscopy measurements at 0.7 V, and durability in 100 h. The impact of cell architecture, like thickness of the electrolyte and electrode backbone, pore microstructure of the backbone, will be reported. Catalyst is ascribed to play the major on the performance of MS-SOFCs. Here, the catalysts, such as Sm0.5Sr0.5CoO3, La0.37Sr0.38Co0.2Fe0.8O3, Pr2NiO4, Pr6O11, BaZr0.4Co0.4Y0.1Yb0.1O3, et al., will be presented with the performance obtained at 700 °C, with steam content of 3 vol.%. The initial peak power density is enhanced more than 50%. The ohmic and polarization resistances are reduced to less than 0.07 and 0.30 Ω cm-2 at 0.7 V, respectively. In addition, the sintering process of catalyst is optimized to obtain the desired crystal structure. The durability of MS-SOFCs is catalyst-dependent, which makes the selection of catalyst more significant. The primary degradation modes are currently being elucidated to the Cr poisoning on catalyst, oxidation of supported metal, and catalyst coarsening.
(Invited) Challenges of Solid State Electrolytes for High Energy Batteries
Authors: Liu Jun
Published: February 2020

The development of solid state electrolytes is very important for future high energy batteries. Among the different strategies, Li metal is a key electrode material for high energy batteries with a specific energy much higher than 300 Wh kg−1. Despite of intensive efforts, significant challenges remain in direct utilization of Li metal anode in realistic high energy cells. This talk will summarize our current understanding of the scientific and technological challenges, discuss recent progress and propose potential directions of solid state electrolytes based on a high-energy cell design, fabrication and testing. The fundamental relationship between the Li anode and other cell components, including all active and inactive materials, is explored at the cell level in order to inspire more new ideas to effectively address the grand challenges in high energy and low cost batteries.
(Invited) Design Consideration of an IGFC System with CO2 Capture
Authors: Liu Zhien , Li Pingping , Liu Changlei , Wang Hanlin , Li Chufu
Published: February 2020

Due to vast coal reserve and its lower cost, integrated Gasification Combined Cycle (IGCC) and Integrated Gasification Fuel Cell (IGFC) power generation system are being developed to use coal effectively and reduce air pollution. Compared to IGCC, the advantage of IGFC is higher efficiency and lower overall cost, especially pressurized system. An IGFC system is being developed using syngas as fuel with CO2 capture at National Institute of Clean Low-Carbon Energy (NICE). In the system, the high temperature solid oxide fuel cell (SOFC) stacks are used to convert fuel to electricity. The system design principles, syngas composition and SOFC stack performance effect on system efficiency, and the system cost will be discussed, estimated, and analyzed based on the model established. The method of CO2 capture will also be discussed and recommended based on experimental data.

There is variety of impurities in syngas, such as sulfur, PH3, Siloxane, chlorine, Arsine, etc, which may poison SOFC anode and significantly affect system performance. Syngas cleaning is needed before powering the stack using syngas. Besides, there is significant amount of CO2 in initial syngas which will dilute flammable H2 concentration which may affect both power generation and the efficiency of the system, which eventually resulted in higher cost. Two syngas cleaning methods were evaluated and recommendation was made based on experimental results.

Syngas composition may vary based on the cleaning method to be used. The CO in syngas has two potential negative effects on SOFC operation. First, the Boudouard reaction is of concern in the temperature range from 500 to 600oC when CO can dissociate into C and CO2 (equation 1), which is called carbon coking. The method to prevent carbon coking was discussed. Second, if dry syngas is used as fuel, the water-gas shift reaction (equation 2) may occur in SOFC stack with the accumulation of water steam formation from electrochemical reaction, which is exothermic. The heat release from water-gas shift reaction would increase temperature difference between stack inlet and outlet which make it difficult to manage stack temperature to achieve optimized performance. SOFC stack electrical efficiency was analyzed with different fuel compositions and under different designed operation conditions, such as anode recycle ratio, using the model established.

CO ↔ CO2 + C (1)

CO + H2O ↔ H2 + CO2 (2)

In order to capture CO2 from exhaust fuel gas, CO2 has to be concentrated higher than 98% first in the tail gas. Technical approaches were identified. Small scale matrix tests show promising results to meet expectation. Fabrication of scale-up testing equipment for technology verification is in process.
Fabrication and Characterization of Thin Film SrCo0.8Nb0.1Ta0.1O3-Δ By Pulsed Laser Deposition
Authors: Ryu Sangbong , Yu Wonjong , Lee Sanghoon , Jeong Wonyeop , P Arunkumar , Cho Gu Young , Cha Suk Won
Published: February 2020

High working temperature(≥800 °C) of solid oxide fuel cell(SOFC) causes high cost of balance of plant, long start up time, and low durability. To overcome these barriers, lowering the working temperature of SOFC is one of the most attractive ways and such strategy has been researched through the fabrication of thin electrolyte and developing new perovskite cathode material. Recently, mixed ionic electronic conducting(MIEC) cathode material, SrCo0.8Nb0.1Ta0.1O3-δ (SCNT), has been developed by Li et al. and the SOFC with the cathode showed high performance(1.22W/cm2) at low working temperature (500 °C) with 14µm thick gadolinia doped ceria(GDC) electrolyte[1]. To apply SCNT to SOFC with thin electrolyte(≤1µm), the cathode must be fabricated on the electrolyte without high temperature sintering process(≥1000 °C) because of the weak mechanical strength of thin electrolyte. In this work, pulsed laser deposition(PLD) method was employed for the fabrication of thin film SCNT. PLD has been used widely for perovskite material deposition because of its high preservability of stoichiometric ratio of its original target material. However, the deposition temperature of PLD has a great influence on both physical and chemical structure of the film which means oxygen reaction activity(ORR) of the film also varies as temperature changes. Therefore, thin film SCNT was deposited by PLD at various temperature condition in this work to see the diversity of thin film characteristic for understanding the feasibility of application of SCNT to thin film SOFC (TF-SOFC).

Powder and PLD target of SCNT were both prepared by the method Li et al. used, solid state reactive sintering(SSRS). The film was firstly deposited on Si wafer at various temperature (room temp, 500, 600, 700 °C) by PLD. Field emission scanning electron microscope (FE-SEM) and focused ion beam-SEM (FIB-SEM) were used to see the nano-structure of the film and deposition rate. 75mTorr of oxygen atmosphere was enough to make the structure of thin film deposited at room temperature very porous but dense film was observed at the temperature higher than 500 °C. The atomic ratio and crystallinity of each film were identified by X-ray spectroscopy(XPS) and X-ray diffraction(XRD) respectively. Through the understanding the physical and chemical variation of PLD deposited SCNT at different temperature condition, the best PLD deposition condition of SCNT for TF-SOFC was derived.

Acknowledgment

This work was supported by the Global Frontier R&D Program on Center for Multiscale Energy System funded by the National Research Foundation under the Ministry of Science, ICT & Future Planning, Korea (2012M3A6A7054855)

References

[1] M. Li et al., “A niobium and tantalum co-doped perovskite cathode for solid oxide fuel cells operating below 500 °c,” Nat. Commun., vol. 8, no. 5, pp. 1–9, 2017.
Dual-Phase Nanocomposite Cathode Materials for Low-Temperature Protonic Ceramic Fuel Cells
Authors: Zhao Zeyu , Tong Jianhua
Published: February 2020

Due to the relative low activation energy, protonic ceramic fuel cells (PCFCs) have attracted increasing attention in recent years because of the efficient low-temperature (LT, 300-600oC) operation. However, the insufficient LT activity of cathode materials for oxygen reduction reaction (ORR) is still one of the significant challenges to achieve excellent performance. It has been recognized that the triple conductivity (electron, oxygen ion, and proton) are prerequisite properties for a high-performance PCFC cathode. Many strategies on material selection have already been done to meet this requirement. BaCo0.4Fe0.4Zr0.1Y0.1O3-δ (BCFZY0.1) was reported as a single-phase triple conducting oxide cathode material which provides improvement of cell performance. However, the pure phase in return limits the further adjustment of the triple conductivities. The composite structures comprised proton conducting oxide and mixed ionic and electronic conducting can also introduce triple conductivity for cathode materials. Unfortunately, traditional fabrication methods for these composites are limited by mechanical mixing with two or more components, which significantly restricted contact sites/areas of different components and further obstacle ORR performance. Thus, the nanocomposite cathodes are demanded with high phase connection and flexible phase adjustment. Herein, the modified Pechini method was utilized to synthesize nanocomposite materials comprised of a mixed ionic and electronic conducting cubic perovskite phase and a protonic conducting orthorhombic perovskite phase from a nominal composition of BaCe0.4Fe0.4Co0.2O3-δ (BCFC). This one-pot method not only increased the density of the activated sites/areas for ORR by decreasing grain sizes for each phase but also provided excellent thermodynamic stability because the solid-state reaction thermodynamic equilibrium has arrived during synthesis. BCFC was confirmed to be a new promising nanocomposite cathode material for LT-PCFCs.
Phase-Field Simulation of Resistive Switching Behavior in Bipolar Metal-Oxide Based Resistive Random Access Memory
Authors: Zhang Kena , Wang Jianjun , Cao Ye
Published: February 2020

Metal-oxide based Resistive Random-Access-Memory (RRAM) exhibits multiple resistance states, due to the growth and retraction of a conductive filament between the electrodes of the device. The performance of RRAM relies on the fast switching speed, large current on/off ratio, and longer endurance reliability, which are critically dependent on the nonlinear resistive switching under electrical bias, temperature, interfacial chemical reaction and mechanical stress effects. In this work we developed a comprehensive phase-field model to simulate the resistive switching. The developed model enables us to separately study the aforementioned effects and understand their relative roles in the switching process. By choosing TaOx as an example, we find that voltage-driven ion transport is responsible for the resistance change between low and high states. It also induces a local stress that influences the endurance of the device. Our work helps shed light on understanding the microstructure dependent ion transport behaviors in RRAMs.
Influence of Electrode Distance on the Electrochemical Reduction of CO2 in Aqueous Solution
Authors: Liu Junyu , Peng Luwei , Zhou Yue , Qiao Jinli , Jung Joey
Published: February 2020

At present, the research on the electrochemical reduction of CO2 (ECR-CO2) mainly focuses on the electrode material and the catalyst. However few studies involved the reactor and reaction conditions. In this study, the commerical available nano-Sn catalyst was coated on a gas diffusion electrode to form a working electrode (Sn/GDE), the influeces of distance between the aonde and the cathode were systematically investigated in a reactor for ECR-CO2. The experiments show that for the electrode distance chnaged from 1.5 cm to 5.7 cm, both current density and Faradaic efficiency were decreased sharply from 34.6 to 10.4 mA cm-2 and 80% to 60%, respectively. However, the distance of 3.3 cm seems to be a critical point, at which the current density was no longer changed.
(Invited) Recent Developments in Intermediate-Temperature Reversible Fuel Cells
Authors: Chen Yu , Zhou Yucun , Kane Nick , Murphy Ryan , Zhang Weilin , Liu Meilin
Published: February 2020

Intermediate-temperature fuel cells have potential to be the cleanest and most efficient option for direct conversion to electricity of a wide variety of fuels, from hydrogen to hydrocarbons, coal gas, and bio-derived fuels. When operated in the reverse mode, on the other hand, they are very efficient for low-cost production of hydrogen from splitting water. Thus, a reversible fuel cell is ideally suited for large-scale energy storage and conversion, which is vital to the deployment of renewable energies. However, the commercialization of these systems hinges on rational design of novel materials of exceptional functionalities at lower temperatures to dramatically reduce the cost while enhancing performance and durability. A key challenge is the development of bifunctional catalysts, especially those for the oxygen electrode, for efficient dual-mode operation. Further, the reversible fuel cells must have high durability when cycled between the fuel cell and the electrolysis modes while maintaining high Faraday efficiency and roundtrip energy efficiency. The electrolyte materials must have high ionic transference number and excellent stability under the operating conditions. To accomplish these goals, it is imperative to gain a fundamental understanding of the mechanisms of charge and mass transport along surfaces, across interfaces, and through porous electrodes. Further, new protocols must be developed to control materials structure, composition, and morphology over multiple length scales. This presentation will highlight the critical scientific challenges facing the development of a new generation of reversible fuel cells based on oxygen ion- or proton- conducting electrolyte, the latest development of bifunctional electrodes and electrolyte materials, the strategies for enhancing electrode activity and durability of hydrogen evolution/oxidation, and oxygen reduction/evolution reactions in reversible fuel cells, the latest developments in modeling, simulation, and in situ characterization techniques for unraveling charge and mass transport mechanisms, and the outlook for future-generation energy storage systems that exploit nano-scale materials of significantly improved performance.
(Invited) Zirconia Doped Ceria As a Mixed Ion and Electron Conductor
Authors: Haile Sossina M , Yuan Weizi , Huang Ruiyun
Published: February 2020

Introduction of zirconia into ceria is known to increase the oxygen vacancy concentration in the host fluorite, despite the fixed tetravalent state of zirconium. Here we use 4-probe conductivity and electrical conductivity relaxation (ECR) methods over a wide range of oxygen partial pressures and several temperatures to explore the implications of this behavior on the transport of ionic and electronic species as a function of Zr content, up to ~ 45 mol %. All materials studied display predominantly n-type electronic conductivity, with a strongly increasing electronic conductivity with increasing Zr content. The ionic conductivity also increases with Zr concentration, but only moderately, and accordingly, the electronic transference number increases. Despite higher electronic and ionic conductivities, the bulk chemical diffusion of oxygen in ceria-zirconia is comparable to that in ceria. Furthermore, the surface reaction constant is dramatically decreased upon Zr doping. The connections between these and related observations are discussed.
(Invited) Synchrotron-Based Hard X-Ray Microscopy: Instruments for 3-D Spectroscopic Imaging at the Nanoscale
Authors: Chiu Wilson K. S.
Published: February 2020

Advances in materials increasingly rely on the 3-D characteristics of its microstructure and chemistry at the nanoscale. This presentation will review 3-D spectroscopic imaging techniques that measure microstructural and chemical properties, and discuss its influence on material function and performance. The presentation will then focus on two synchrotron-based 3-D spectroscopic imaging instruments: the Transmission X-ray Microscope (TXM) and the Hard X-ray Nanoprobe (HXN) to characterize the 3-D structural and chemical distribution of fuel cell, gas separation membrane and nuclear waste form materials. Challenges and opportunities for future work will then be discussed. The goal of this research will be to obtain a scientific and engineering understanding into how microstructure-induced transport mechanisms govern performance, with a long-term goal to improve current materials and create new materials that will enable improved device performance and increased long-term reliability for advanced engineering applications.
(Invited) Protonic Ceramic Electrochemical Cells for Energy Conversion and Storage
Authors: Duan Chuancheng , Kee Robert J. , Zhu Huayang , Sullivan Neal P , Zhu Liangzhu , O'Hayre Ryan
Published: February 2020

The rapid growth in solar and wind-based intermittent renewable electricity generation and the spectacular drop in renewable energy cost necessitates the development of highly efficient, long-term energy storage to levelize seasonal wind/PV generation output variations. While batteries are well suited for short-term (e.g. hourly or daily) energy storage, they are less suited for longer term (e.g. seasonal) energy storage due to self-discharge challenges and economic constraints caused by a linear cost/stored-energy scaling relationship. While significant progress has been made on developing reversible electrochemical cells based on proton exchange membrane fuel cells (PEMFCs) and solid oxide fuel cells (SOFCs), major challenges remain. In particular, high PGM catalyst cost and low energy efficiency due to sluggish kinetics still limit the commercialization of low-temperature reversible PEMFCs. Intermediate-temperature reversible electrochemical cells can potentially mitigate the challenges associated with both low-temperature reversible PEMFCs and high-temperature reversible SOFCs. Protonic ceramic electrochemical cells (PCECs) are an emerging and potentially promising energy storage technology which can electrochemically convert chemical energy to electricity in fuel cell mode and convert renewable electricity to fuel in electrolysis mode with high round-trip efficiency. In this presentation, we will discuss applications of PCECs for energy conversion and storage, how to achieve high round-trip efficiency, and efficient conversion of electrons to chemicals in PCECs.
(Invited) High Performing and Stable Proton-Conducting Solid Oxide Electrolysis Cells with Triple Conducting Anodes
Authors: Li Wenyuan , Guan Bo , Ma Liang , Li Zhongqiu , Tian Hanchen , LIU Xingbo
Published: February 2020

Proton-conductors BaZr0.1Ce0.7Y0.1Yb0.1O3-δ (BZCYYb) and La2Ce2O7 (LDC) are combined to create an interface active and steam-tolerant electrolyte for high-performance proton-conducting solid oxide electrolysis cells. LDC shows good chemical compatibility with BZCYYb. The readily fabricated LDC/BZCYYb bilayer electrolyte can be densified at a temperature as low as 1300oC vs. ~1600oC for the benchmark vapor-stable BaZr0.8Y0.2O3-δ electrolyte. With Pr2NiO4+δ as the anode and Ni as the cathode catalyst, this bilayer electrolyte cell yields a current density of 975 mA/cm2 and 300 mA/cm2 under a 1.3 V applied potential at 700oC and 600oC, respectively. This performance is among the best of all H-SOECs equipped with a chemically stable electrolyte so far. BZCYYb layer in the bilayer electrolyte promotes the hydrogen evaluation reaction at the cathode side, resulting in a 108% improvement over the cell without this layer. The LDC layer, on the other hand, effectively protects this functional BZCYYb layer from high concentration of vapor in a practical SOEC operation condition. The cell without LDC layer shows degradation in terms of increase in the electrolyzing potential from 1.07 V to 1.29 V during a 400 mA/cm2 operation at 700oC. In contrast, the bilayer electrolyte cell maintains the same electrolyzing potential of 1.13 V under the same conduction for a 102 h operation. These findings demonstrate that this synergic bilayer electrolyte design could be a vital strategy to overcome the dilemma between performance and stability faced by the current benchmark Zr- or Ce-rich Ba(CeZr)O3-δ electrolytes, achieving good performance and stability at the same time.
Electrochemical Ammonia Synthesis Using a BZCYYb4411 Proton Conductor
Authors: Hortance Nicholas Michael , Hatzell Kelsey B.
Published: February 2020

The Haber Bosch process is the dominant route to synthesizing ammonia. Ammonia is an important component in fertilizers, which are widely used across the agriculture community. Dependence on the Haber Bosch process is detrimental because: (1) this process operates at high temperatures (~450°C)1 and pressures (150-300 bar) and accounts for 2% of the worlds energy supply2, (2) contributes 1% of all CO2 emissions, and (3) is typically centralized which limits access in developing worlds. Electrochemical ammonia production has the potential to greatly reduce society’s carbon footprint and energy consumption, as well as increase ammonia production in developing worlds and rural communities. This type of ammonia synthesis method has been shown to operate with air and water sources as opposed to highly pure nitrogen and hydrogen reactants used in commercial plants. Solid state electrochemical systems are able to operate at elevated temperatures (300-600 °C) unlike ambient processes (low temperature fuel cells) and thus have the potential for higher yields. Solid state ceramic proton conductors show high ionic conductivities (1E-2 Scm-1 at 600°C)3 and are stable in this intermediate temperature range. Currently, the investigation of intermediate temperature ion conductors in solid state ammonia synthesis is nascent but growing in interest. Herein, we describe the synthesis and processing of a highly conductive proton conductor BaZr0.4Ce0.4Y0.1Yb0.1O3-
δ (BZCYYb4411) (Fig. 1a,b) is characterized and implemented in a solid state fuel cell arrangement. BZCYYb4411 is synthesized using a solid-state reaction route and Ag-Pd catalyst is used to make a symmetric cell. In this one chamber reactor employing 3% H2/N2, the faradaic efficiency and ammonia production rate is explored at different temperatures and operating voltages to elucidate the optimal conditions for ammonia synthesis.

(1) Kyriakou, V.; Skodra, A.; Stoukides, M.; Vasileiou, E.; Garagounis, I. Electrochemical Synthesis of Ammonia in Solid Electrolyte Cells. Front. Energy Res.
2014, 2 (January), 1–10.

(2) Martín, A. J.; Shinagawa, T.; Pérez-Ramírez, J. Electrocatalytic Reduction of Nitrogen: From Haber-Bosch to Ammonia Artificial Leaf. Chem
2019, 5 (2), 263–283.

(3) Choi, S.; Kucharczyk, C. J.; Liang, Y.; Zhang, X.; Takeuchi, I.; Ji, H. Il; Haile, S. M. Exceptional Power Density and Stability at Intermediate Temperatures in Protonic Ceramic Fuel Cells. Nat. Energy
2018, 3 (3), 202–210.

Figure 1
(Invited) Building Resilience into Ni-YSZ Anodes with Secondary Phases
Authors: Welander Märtha , Sofie Stephen , Zacharaisen Marley S. , Walker Robert A.
Published: February 2020

Solid oxide fuel cells anodes are typically composed of a porous nickel-yttria stabilized zirconia (Ni-YSZ) ceramic metallic (cermet) composite. The advantages of a Ni-YSZ anode are many: the materials are inexpensive, Ni is an exceptionally effective CH bond activation catalyst and these electrodes can operate with a wide variety of fuels. However, Ni-YSZ anodes are also susceptible to material degradation and deteriorating device performance, especially when subjected to repeated reduction/oxidation cycling and/or carbon accumulation and metal dusting. Recent work in our laboratory has sought to improve the durability and resilience of Ni-YSZ anodes by adding small amounts of secondary materials to the anode stock prior to fabrication and processing. One secondary material that has proven particularly effective is aluminum titanate (Al2TiO5or ALT) During anode processing, ALT (4% by mass) reacts with Ni-YSZ to form nickel aluminate (NiAl2O4) and zirconium titanate (Zr5Ti7O24). Upon anode reduction, NiAl2O4 forms Ni particles decorated with Al2O3 nanoparticles. These secondary phases improve device performance and appear to preserve anode microstructure even after 100 hours of continuous operation. Furthermore, these secondary phases enhance anode resilience to redox cycling. We have used a variety of electrochemical and operandooptical methods to test the resilience of ALT-enhanced anodes subject to both electrochemically-induced oxidative stress and environmentally driven anode oxidation. In both cases, ALT-enhanced anodes can withstand more than twice as many redox cycles as anodes that have not had ALT added. In addition, adding ALT to the anode reduces its susceptibility to carbon accumulation when operating with hydrocarbon fuels.
Integration of Layered Double Hydroxide to Enhance Charge Carrier Utilization of Hematite Photoanodes for Water Splitting
Authors: Sarma Satirtha Kumar , Mohan Ratan , Shukla Anupam
Published: February 2020

Photoelectrochemical (PEC) water splitting presents an effective approach to meet the ever increasing energy crisis by conversion of the inexhaustible solar energy to hydrogen. From practical application viewpoint, hematite is a promising candidate material due to its high theoretical solar to hydrogen (STH) efficiency of ~ 15%. However, it is still a challenge to increase the charge carrier utilization of hematite. Herein, we report the enhancement of carrier utilization of hematite by nanostructuring and addition of thin film of cocatalyst overlayer. Based on the characterizations and analysis of X-ray diffraction and SEM with EDX, it was found that a crystalline NiFe phase for composite electrodes was formed after treatment. Integrating NiFe layered double hydroxide (LDH) to doped hematite photoanodes resulted in an enhanced photocurrent density of 2.5 mA/cm2 at 0.8 V vs Ag/AgCl, due to the efficient hole transfer to the surface leading to better carrier utilization. Electrochemical Impedance Spectroscopy analysis further shows that addition of cocatalyst overlayer helps in improving the surface reaction kinetics and reducing the barrier of oxygen evolution reaction of the developed photoanode.
Atomic Layer Deposited Tungsten-Based Coatings for Durable Solar Hydrogen Production
Authors: Palm David W. , Muzzillo Christopher P. , Gaillard Nicolas , Jaramillo Thomas F.
Published: February 2020

Workers in the field of solar water splitting have had success in synthesizing devices that approach the 20% solar-to-hydrogen efficiency metric required for economically feasible hydrogen production. However, these devices rely upon expensive epitaxial synthetic techniques and have not yet achieved technologically-meaningful durability metrics. The focus of this work, building upon our recent efforts (Hellstern et al, ACS Applied Energy Materials, 2019) and those of others in the field, is to enhance the hydrogen production durability of scalable copper chalcopyrite (CuGaxSey) light-absorbing materials. In this work, we have developed an atomic layer deposition (ALD) synthesis of tungsten oxide (WOx) coatings as a conformal platform for extending the durability of these already promising absorbers (Muzzillo et al, ACS Applied Materials & Interfaces, 2018). We also explore the conversion of these oxide coatings to tungsten sulfide and tungsten carbide, as electrocatalytically active protective coatings. A CuGaxSey/WOx/Pt photocathode operating under external bias (an electrode architecture that initially yielded -8 mA cm-2 of photocurrent density) continuously produced hydrogen for 6 weeks with simulated sunlight conditions in acidic electrolyte. The amount of charge passed by this device (~21,500 C cm-2) demonstrates a durability that exceeds all others reported for a polycrystalline absorber device.
Mo Thio Molecular Complexes As Water-Soluble Catalysts for the Photocatalytic Hydrogen Evolution Reaction on 2D Materials
Authors: Barbosa Juliana Barros , Taberna Pierre-Louis , Chane Ching Jean-Yves , Gerber Iann , Poteau Romuald , Balocchi Andrea , Marie Xavier
Published: February 2020

Producing hydrogen fuel through solar-driven photoelectrochemical (PEC) water splitting represents an attractive approach for the development of sustainable energy. 2D semiconducting Transition Metal dichalcogenide (TMDC) nanosheets are attractive materials for solar energy conversion and have been applied as photocathodes for the Hydrogen Evolution Reaction (HER). To improve the performances of the photocathodes, optimized TMDC film microstructure was proposed involving a self-assembly at a liquid-liquid interface. In addition, in combination with a hexyl-tri-silane surfactant treatment, molecularly thin 2D WSe2 nanosheets films were coated by a Pt-Cu catalyst. In this process, the increase of photocurrent resulting from the surfactant treatment was attributed to edge site passivation of the 2D nanosheets drastically decreasing the charge carrier recombination site density. Indeed, for a large scale development of these photocathodes, replacement of Pt-Cu by a precious metal-free catalyst is highly desirable. In this talk, we will present our recent results concerning Mo thio complexes as catalysts anchored on WSe2 nanosheets for efficient water splitting under visible light irradiation. We used WSe2 films prepared by a simple film forming process, i.e. drop casting, and an aqueous environmentally friendly process for the catalyst preparation.

Active molecular Mo catalysts including (Mo2S12)2- were deposited via a selection process from a solution allowing the deposition of the most interactive Mo complexes towards the WSe2 nanosheets thus improving their anchorage and durability. Our ultrathin films showed a current density up to -2 mA/cm² at 0 V vs NHE without any passivation additive such as HTS surfactant. The respective contributions namely in electro-catalysis and site passivation observed experimentally for the various molecular Mo complexes involved were supported by DFT calculations of i) Adsorption energies of the Mo thio complexes on the WSe2 substrates and ii) Free energies changes for the hydrogen Evolution Reaction on the various adsorbed molecular Mo complexes. These results will greatly help to better design molecular photo-catalysts for photo-electrodes displaying high surface recombination site density.
Shedding Light on the Stability of Photoelectrochemical Water Splitting Cells
Authors: Nandjou Fredy , Haussener Sophia
Published: February 2020

The instability of the semiconductor-electrolyte interface is a major challenge for the development and implementation of long-lasting photoelectrochemical (PEC) solar fuel producing devices [1]. Kinetic studies, incorporating the competing photocorrosion and fuel producing reaction mechanisms at the photoelectrode of the PEC device, predicted that some thermodynamically unstable semiconductors could be kinetically stable as a result of their extremely low photocorrosion current and therefore enable acceptable lifetimes [2].

We developed a 1-D multi-physics model that coupled the reactions kinetics to photo-physical processes occurring in the PEC device. These processes include radiation absorption, charge carrier generation, charge transport, charge transfer from the semiconductor to the electrocatalyst, charge transport in the catalyst and photocorroded layers, and mass transport in the electrolyte phase. The model accounted for the impact of surface chemical properties, catalyst activity, charge carrier density in the semiconductor and in the electrocatalyst, and electrolyte acidity. In parallel, a bonding model was developed to predict the surface back-bond potential of the semiconductor, which is known in highly impact on the stability [2].

When applied to some promising semiconductors for photoelectrochemical water splitting, the model provided trends on the dependence of the stability of the semiconductor-electrolyte interface on irradiation intensity, semiconductor and electrocatalyst properties, and mass transport in the electrolyte.

[1] Fredy Nandjou and Sophia Haussener, Degradation in photoelectrochemical devices: review with an illustrative case study, Journal of Physics D: Applied Physics 50, 2017.

[2] Fredy Nandjou and Sophia Haussener, Kinetic Competition between Water‐Splitting and Photocorrosion Reactions in Photoelectrochemical Devices, ChemSusChem 12, 2019.
(Invited) Bi-Functional Electrocatalysts for Water Splitting and Metal-Ion Batteries
Authors: Fan Hong Jin
Published: February 2020

Water electrolysis, fuel cells, and metal-air batteries all require efficient and cheap electrocatalysts that can significantly lower the reaction overpotentials. Bimetallic alloys and their oxides or nitrides compounds are particularly interesting as non-precious metal electrocatalyst materials for HER and OER, because of their tailorable electronic structure, conductivity, and surface chemistry. Our group has been actively working on nanoarray materials directly grown on conductive substrates as electrodes for supercapacitor, batteries and electrocatalyst.

In this talk, I will present two main results about surface and interface engineering/functionalization of array-type electrocatalysts for water splitting and for meal-ion batteries.

(1) RF nitrogen and carbon plasma as a highly effective technique for conversion reaction and surface functionalization of nanostructured electrocatalysts. The N plasma treatment not only generates hierarchical nanostructure surface, but also induces N doping as well as hydrophilicity. Using C-plasma, we can partially reduce the metal oxide surface, and simultaneously deposit a thin and uniform carbon coating.

(2) We demonstrate that dual cation doping, or cation-anion co-doping can simultaneously modulate key parameters in water dissociation and hydrogen adsorption energies. As a result, the dopings lead to a significant enhancement in catalytic activities for both HER and OER. Recent result on atomic scale doping in 2D materials will also be presented.

(3) I will also present our achievements of effective bi-functional catalysts (ORR and OER) for cathode materials in Li-O2 and Zn air batteries.