bluuebunny/crossref_metadata_2025 huggingface dataset:
Microstructured Cathodes for Enhanced Transport in Unitized Reversible Fuel Cells
Authors: Komini Babu Siddharth , Brounstein Zachary Ryan , Uddin Md. Aman , Spendelow Jacob S
Published: February 2020

Large scale energy storage challenges are increasing with increasing energy demand. Unitized reversible fuel cells (URFCs) coupled with intermittent renewable power sources could be instrumental in enabling the transition away from non-renewable sources. URFCs operate as a fuel cell (FC) and electrolyzer (E) in a single cell/stack (1, 2). However, several technical barriers must be overcome to make URFCs competitive with other energy storage technologies. For low-temperature membrane-based systems, the optimal operation in E mode requires high liquid water saturation, while FC mode requires just enough water to maintain ionic conductivity. The conflicting saturation requirements prevent transport optimization for either mode, while also causing inefficiencies when switching between the operating modes.

In this work, we present a novel binary array structure that could lead to improved operation in both E and FC mode while avoiding any need for gas purging when switching between operating modes. This is achieved by patterning the electrodes and diffusion media to induce localized hydrophilic and hydrophobic domains. The hydrophobic domain enables improved gas transport during switching between the different operating modes. However, electrodes with only hydrophobic domains can provide an improvement in FC mode, but E mode performance suffers due to poor water transport as seen in Figure 1. Binary array electrode enhances water management and thereby increases performance in both the operating modes.

Acknowledgments

This research is supported by DOE Fuel Cell Technologies Office; Technology manager: Nancy Garland.

References

B. Paul and J. Andrews, Renewable and Sustainable Energy Reviews, 79, 585 (2017).

Y. Wang, D. Y. C. Leung, J. Xuan and H. Wang, Renewable and Sustainable Energy Reviews, 65, 961 (2016).

Figure 1
On the Role of the Porous Transport Layer Structure in Polymer Electrolyte Water Electrolysis
Authors: Schuler Tobias , Schmidt Thomas J. , Büchi Felix N.
Published: February 2020

In polymer electrolyte water electrolysis, the mass transport losses are the least understood overvoltage contribution. Underlying origin as well as correlation parameters with the structure of the porous transport layer (PTL) are not identified, because in the past the focus was set on the PTL bulk1,2and not on the PTL surface properties. The application of X-ray tomographic analysis of the interface3 (an example shown in Figure 1), in combination with electrochemical characterization leads to the identification of governing parameters. PTL interface properties (interfacial contact area, membrane deformation) seem to be key properties, as they correlate with cell performance. Based on these findings, novel two layer PTL materials were designed and characterized. Increased performance and reduced mechanical deformation were obtained in comparison to conventional PTL materials, also enabling the employment of ultra-thin membranes.

1. M. Suermann, K. Takanohashi, A. Lamibrac, T. J. Schmidt and F. N. Büchi, Journal of The Electrochemical Society, 2017, 164, F973-F980.

2. S. A. Grigoriev, P. Millet, S. A. Volobuev and V. N. Fateev, International Journal of Hydrogen Energy, 2009, 34, 4968-4973.

3. T. Schuler, R. De Bruycker, T. J. Schmidt and F. N. Büchi, Journal of The Electrochemical Society, 2019, 166, F270-F281.

Figure 1
Flexible Cu2znsn(S, Se)4 Solar Cells over 7% Power Conversion Efficiency
Authors: Yang Kee-Jeong
Published: February 2020

The development of flexible solar cells is necessary for achieving market competitiveness through the implementation of low cost solar cells and for applying customized business models, such as Building Integrated Photovoltaics (BIPV). Cu2ZnSn(S,Se)S4 (CZTSSe) thin films have attracted attention as low-cost absorber materials for solar cells; however, further studies are required to develop flexible solar cells from this material and to achieve a high power conversion efficiency. In this work, the carrier separation characteristics of flexible CZTSSe thin-film solar cells on Mo foil substrates were identified. The surface electrical characteristics of the CZTSSe absorber layer indicate that the topography, surface potential, and local current are proportional to one another, in contrast to the characteristics exhibited by CIGS cells. For the CZTSSe absorber layer, an upward band bending-like band structure formed at and near the GBs, and a current path formed along the IGs as holes collected toward the GBs, and electrons collected toward the IGs. In contrast to that in CIGS cells, the carrier separation induced by the formation of the upward band bending-like band structure at the GBs is crucial in CZTSSe thin-film solar cells. Furthermore, the positive potential distribution at the IGs and average potential difference showed a proportional relationship to the local current and PCE. Through the implementation of these carrier separation characteristics, a flexible CZTSSe thin-film solar cell on a Mo foil substrate achieved a PCE of over 7%.

Acknowledge: This work was supported by the Korea Institute of Energy Technology Evaluation and Planning (KETEP) and the Ministry of Trade, Industry & Energy (MOTIE) (No. 20173010012980) and by the DGIST R&D Programs of the Ministry of Science, ICT & Future Planning of Korea (19-BD-05).
(Invited) The Processing Science and Engineering Research Portfolio for Advanced Vehicle Batteries at the U.S. Department of Energy
Authors: Faguy Peter W.
Published: February 2020

The widespread adoption of electric vehicles using advanced battery technologies and the development of their manufacturing base in the United States are critically important for the US economy and therefor a major focus of research and development sponsored by DOE’s Office of Energy Efficiency and Renewable Energy. Materials development is often touted as the most important enabling activity, however in a rank of major cost items, manufacturing costs ranks just below the cathode components. In addition to the need to reduce costs, US R&D should also focus on new, yet-to-be-scaled processing technologies that, when developed and implemented in the US provide both a strong component of US energy security and US-based employment in the production of electric vehicle batteries. This presents a major economic opportunity to the USA, as the global electric vehicle market is expected to grow to over $100 billion in the next ten years. Advances in battery processing science and technology could lead directly to the displacement of the established non-US-based manufacturing base via creative destruction--new innovative technologies lead to new manufacturing facilities, facilities that could be built and run in the USA.

Processing science and engineering has traditionally been underrepresented in federally funded electrochemical energy storage R&D. Over the last nine years, the Vehicle Technologies Office (VTO) has been building an advanced processing R&D portfolio. This includes competitively funded research at universities, small businesses, and large corporations as well as programs supported across the national laboratory complex. Processing science and technology projects organize into two general activities: scaling-up materials production and developing innovative electrode fabrication approaches. This presentation will provide an overview of the sub-program’s history and several example successes. Future research directions and scenarios for possible funding opportunities will also be discussed.
Elevated Mixing and Coating Temperatures Yield Beneficial Processing Properties of Organic Solvent-Based Lithium-Ion Battery Cathode Slurries
Authors: Hawley William Blake , Li Jianlin
Published: February 2020

In traditional lithium-ion battery cathode manufacturing, the slurry mixing and coating stages bear tremendous influence on downstream processing steps and, consequently, the viability of the end product. Two avenues for improving these two stages include increasing the coating throughput to meet rising consumer demands and to make coatings with more consistent, homogeneous distributions of slurry components in order to create higher-performing devices. In state-of-the-art slot die coating operations, coating speed is maximized and imperfections (i.e. air bubbles and thickness variations) are minimized by reducing the viscosity of the material being coated. The active materials, which routinely form agglomerates with diameters on the order of 10 μm, must be prevented from settling under gravity to form a homogeneous active layer. In this work, heating the slurry during the mixing and coating stages is proposed as a scalable and effective solution to achieve faster and more reliable coating operations.

This study demonstrates that increasing the mixing and coating temperature from 25°C to 60°C can reduce the slurry viscosity by 21 percent at practical industrial coating speeds. At low shear rates, slurries mixed at 60°C are also 10 percent more viscous, providing the additional benefit of sharper edge contours and, thus, less cut-off waste during processing. Oscillatory shear probing revealed that the gel strength of heated slurries is also greater, meaning there is greater sedimentation resistance due to increased polymer bridging. The discharge capacity of the cathode mixed and coated at 60°C was about 4% greater than that of the cathode mixed and coated at 25°C for all C-rates between C/10 and 5C, which could be indicative of an improved distribution of components. The results indicate that mild heating of the slurry (1) does not irreversibly gel the slurry such that it is unable to be processed, (2) provides rheological properties that correlate to quicker and more consistent coating operations, and (3) yields slightly higher-performing cathodes at C-rates of practical interest. Heating the slurry also provides the manufacturer with the option to increase the solid loading to reduce drying times and solvent recovery.
Understanding the Silicon/Binder Interaction and Influence on Anode Properties
Authors: Burdette Mary Kathyrn , Rogers Alexander M , Armstrong Beth , Veith Gabriel M.
Published: February 2020

Polymeric binder interactions with silicon were investigated as a function of electrode processing and electrochemical behavior. Using ultra-small angle neutron scattering, the evolution of the dynamics between a poly(acrylic acid) and silicon slurry showed that, under shear conditions, the slurry aggregated heavily when compared to the no shear condition. This behavior is undesirable as silicon anode slurries must de-agglomerate under shear conditions for a uniform electrode cast, which facilitates even lithiation across the anode. Electrodes made from these slurries show the connection between the binder/silicon interaction and electrochemical behavior. Additionally, the role of the silicon surface chemistry on the rheology of the electrode slurry was elucidated and connected to electrode processing and electrochemical performance. Based on these results, the binder for the silicon anode materials may need to be re-evaluated in order to improve the viability of silicon anodes.

Acknowledgement: This work was supported by the US Department of Energy’s Office of Energy Efficiency and Renewable Energy through the Vehicle Technology Office (Brian Cunningham Program Manager).
Alignment of Conductive Additive in Li-Ion Battery Electrodes through Use of Electric Fields
Authors: Clemens Noah , Wheeler Dean , Mazzeo Brian
Published: February 2020

Currently, Li-ion battery electrodes are produced by coating onto the current collector a slurry composed of active particles, carbon black (CB), binder, and solvent. Coating is followed by drying, and calendering steps. This method creates a quasi-random distribution of CB particles throughout the battery electrode. The CB particles are intended to improve electronic pathways between active particles and the current collector.

By applying an electric field to the electrode slurry while it is drying, the carbon particles can be aligned or form chains in response to electric forces. These chains function as improved pathways for the electrons, reducing the impedance of the electrode. This has the potential to allow thicker electrodes, faster charging, or possibly a reduction in the required amount of CB additive.

In this talk, we discuss our use of flexible micro-probes [1] to both apply an electric field during drying and to assess the final conductivity of the dried film. Alternating electric current (AC) is used. The impedance of the samples dried with AC will be compared with of those of sample dried using conventional methods. We also explore the effects of different frequencies of AC on the resulting conductivity and discuss the plausibility of scaling this method of drying under electric fields to an industrially relevant process.

[1] Lanterman et al., J. Electrochem. Soc.
162, A2145-A2151 (2015).
A Tape-Casting/Freeze-Drying Approach to Prepare Low-Tortuous Graphite Electrodes
Authors: Dang Dingying , Wang Yikai , Gao Shuang , Cheng Yang-Tse
Published: February 2020

Lithium ion batteries (LIBs) with high energy density and fast charging capability are in high demand to satisfy the development of plug-in hybrid electric vehicle (PHEV) and full electric vehicle (EV). Limited ion transport in thick electrodes is one of the major challenges that impede the rate capability of a battery. Directional freeze-drying, with the aid of ice templating, is a feasible method to introduce low-tortuous pore structure in composite electrodes. In this study, we propose a traditional tape-casting process followed by the directional freeze-drying and calendering procedures to prepare graphite electrodes with low tortuosity. Compared with the traditional tape-casting method, the tortuosity of the graphite electrodes is effectively reduced by the subsequent freeze-drying process. Higher capacity retention and better rate capability are achieved due to enhanced ion transport capability in the low-tortuous microstructure. We confirmed that the concept of continuous tape-casting/freeze-drying is an effective and scalable approach for manufacturing high-performance thick battery electrodes.
(Invited) A Decade of Progress Under the U.S. Department of Energy Office of Fossil Energy’s Solid Oxide Fuel Cell Program
Authors: Stoffa Joseph
Published: February 2020

The U.S. Department of Energy Office of Fossil Energy (FE) National Energy Technology Laboratory (NETL) Solid Oxide Fuel Cell (SOFC) Program is committed to developing efficient, low-cost electricity from natural gas or coal with intrinsic carbon capture capabilities for cost-competitive distributed generation and central power generation applications. Advancements in the cost, durability, reliability, energy density, specific energy, and adoption of SOFC technology over the past decade will be chronicled to provide a picture of today’s state of the art SOFC technology. A discussion of current DOE funded research will provide an introduction to the next generation of SOFC technology and illustrate what advancements are expected in the near term. The status of these strategically oriented research projects will be presented in the context of the program’s integrated systems tests and the roadmap to deploy a MWe-class natural gas-fueled distributed generation system.
(Invited) High-Performance Thin-Film Solid Oxide Fuel Cells
Authors: Minh Nguyen , Lee Yoon Ho , Tran Tuyen Quang , Ren Haowen , Fullerton Eric , Wu Erik , Meng Ying Shirley
Published: February 2020

A process based on sputtering has been developed for fabricating thin-film solid oxide fuel cells (TF-SOFCs) that have a total thickness of ~3 µm and are based on the conventional configuration using common SOFC materials. Single cells (with dense electrolytes, dense interlayers, and porous electrode films) on various substrates were effectively fabricated through sputtering/co-sputtering of metal and/or ceramic targets and the electrodes exhibited a fine nanostructure consisting of very small columns of roughly 10 nm in diameter. Fabricated cells exhibit open circuit voltages of ~1.0 V and exceptional power densities at reduced temperatures (500o-650oC) on different fuels. Single cells (of the composition lanthanum strontium cobaltite-gadolinium doped ceria (LSC-GDC) cathode/GDC interlayer/yttria stabilized zirconia (YSZ) electrolyte/Ni-GDC anode) show record power densities of ~3.5 W/cm2 with hydrogen/air and ~1.5 W/cm2 with dry methane/air at 650oC.
Tri-Functional Catalysts Derived from MnO2/Carbon Nanotube Hybrids for Flexible Metal-Air Batteries and Supercapacitors
Authors: Su Tianshun , Liu Jiawen , Xu Nengneng , Zhou Xiao-Dong , Qiao Jinli
Published: February 2020

Metal-air batteries and supercapacitors have gained growing attention in wearable devices due to their high energy density, long shelf life, low cost and environmental compatibility. The suitable electrocatalysts for these metal-air batteries still remain a critical issue in order to achieve high energy density, large capacitance, and long stability. Recently, manganese oxides show some potentials, but require to be mixed with conductive additives to leap over the limitations of small current densities and large overpotential. In this work, we utilize a novel trifunctional catalyst consisting of intertwined MnO2/carbon nanotubes (MnO2/CNTs) hybrid with flexible morphology by a two-step hydrothermal method. The hybrid catalyst exhibits a high electrochemical activity (ΔE: 0.98 V), power density and charge-discharge (C-D) stability relative to the Pt/C catalyst. More importantly, the flexible MnO2/CNTs catalyst improves the flexibility and stability of wearable energy devices.
Solid Electrolyte for Li-Ion Batteries: Synthesis, Characterization and Solid-State Cell Integration
Authors: Botros Miriam , Clemens Oliver , Breitung Ben , Hahn Horst
Published: February 2020

Combining nebulized spray pyrolysis (NSP) with field assisted sintering technology (FAST) provides a novel strategy for the preparation of ceramic electrolytes, e.g., garnet-type Li7-3xLa3Zr2AlxO12, with a homogeneous elemental distribution and high density. Utilizing FAST for ceramic preparation shows major impact on the structure and microstructure of the material. By varying the pressure during sintering, for instance, strong straining of the lattice can be induced, providing a high conductivity of 0.42 mScm-1. Therefore, this phenomenon might open a new field of research for garnet type electrolytes examining an enhancement of the electrochemical performance by introducing lattice strain. In this contribution, a detailed mechanism for the lattice distortion and resulting microstrain during FAST treatment of the garnet-type electrolyte is proposed. Furthermore, the charge transfer resistance of Li-ions at the interface, between the solid electrolyte and Li electrodes (characterized using AC impedance spectroscopy) is in the order of 37 Ωcm-2 and is among the best reported values to date. The ceramic electrolyte is fully functional and is integrated into both, an all-solid-state battery cell as well as a hybrid cell, the latter providing a practical approach to combine the advantages of the solid electrolyte with the good wetting behaviour of a liquid electrolyte to the slurry-based cathode material.
Densification and Ionic-Conduction Improvement of Tantalum-Doped Garnet-Type Lithium Lanthanum Zirconate Solid Electrolytes
Authors: Zhang Xingxing , Fergus Jeffrey
Published: February 2020

Garnet-type Li7La3Zr2O12 (LLZO) is one promising solid electrolyte material for lithium batteries. Obtaining the desired high conductivity requires high density and formation of the cubic phase. Small amount of tantalum has been shown to stabilize the cubic crystal structure and increase the conductivity. In this work, LiOH additives were introduced into the cubic LLZO at the final sintering step of the co-precipitation method to densify LLZO. Results on the synthesis, material characterization, and electrochemical impedance spectroscopy of dense tantalum-doped LLZO are presented.
(Invited) Structure of NMC Family Cathodes from Monte Carlo Simulation and NMR Spectroscopy
Authors: Harris Kristopher J. , Hurst Chelsey , Goward Gillian R. , Foster Jamie M.
Published: February 2020

The cathode active material Li[Ni1/3Mn1/3Co1/3O2], NMC 111, is well known for its excellent cycling lifetime and capacity. It is also well known that varying the ratios of transition metals (TMs), Li atoms, and vacancies1 can provide capacity increases of up to 40 %, though at the expense of structural stability. Not only are these structural-breakdown pathways not understood, full models of even the pristine materials are not available because of the significant disorder. It seems apparent that better structural characterization tools are needed to understand these materials, and therefore may finally provide the key to unlocking their potential.

Here, we present a Monte-Carlo structure-solution method, using a Hamiltonian that is based on local electroneutrality [2]. The close-packed 2D TM sheet of the NMC family is partitioned according to valence-bonding principles and a state of local charge balance—for the TM atoms with respect to the neighboring (fixed) 2D oxygen sheet—is sought. This simple Hamiltonian allows rapid, yet realistic, sampling of the configuration space of the large sheets (up to 10,000 TM atoms) necessary to properly capture the (often) complex arrangements.

The predicted structural models are verified as accurate using 7Li NMR spectroscopy. The unpaired electrons of the TM atoms generate large paramagnetic chemical shifts in the neighboring Li atoms [3]. The 7Li spectra are therefore sensitive to the identity of the 12 TM atoms neighboring each Li: 6 in the TM sheet above, 6 in the sheet below [3]. Notably, the orientation dependence of this effect is not a hindrance when using 7Li MATPASS NMR spectroscopy under 60 kHz MAS [4].

A series of samples with compositions Li[Ni
x
Mn
x
Co1-2x
O2] are investigated, where x = 2%, 10%, and 33%. In each case, structures generated by the Monte Carlo calculations are verified through an extremely accurate matching between predicted and experimental 7Li NMR spectra. Additionally, accurate 3D simulations of electrochemically charged versions of these samples, where transition-metal oxidation and delithiation occur, are presented.

Reference
s
:

[1] R. Shunmugasundaram, S. Arumugam, J.R. Dahn Chem. Mater. 25 (2015) 989.

[2] K.J. Harris et al. Chem. Mater. 29 (2017) 5550. [3] D. Zeng et al. Chem. Mater. 19 (2007) 6277.

[4] I. Hung et al. J. Am. Chem. Soc. 134 (2012) 1898.

Figure 1
(Invited) Role of Mixed Conduction in Chromium Poisoning of Oxygen Electrodes of SOFCs and SOECs
Authors: Gopalan Srikanth
Published: February 2020

Oxygen electrodes in solid oxide fuel cells (SOFCs) and solid oxide electrochemical cells (SOECs) can either be predominantly electronic conductors like Sr-doped lanthanum manganite (LSM) or a mixed ionic and electronic conductor (MIEC) such as Sr-doped lanthanum ferrite (LSF) or lanthanum nickelate (LNO). Ferritic stainless steels are currently the preferred interconnection material in both SOFCs and SOECs. During cell operation, it is well known that chromium from the ferritic stainless steel volatilizes and transports into the oxygen electrode. However, it has been observed that the response to chromium exposure of electronic conductors like LSM is very different from mixed conductors like LSF and LNO. In this work we present recent experimental results of in operando response of predominantly electronic and mixed conducting electrodes to chromium exposure, and discuss thermodynamic and transport models that explain the differences in the observed responses.
(Invited) Progress in Metal-Supported Solid Oxide Cells with Infiltrated Electrodes
Authors: Tucker Michael C , Dogdibegovic Emir , Shen Fengyu , Wang Ruofan , Lau Grace Y
Published: February 2020

This talk will provide an overview of performance, durability, and applications of metal-supported solid oxide fuel cell and electrolysis cell technology developed at Lawrence Berkeley National Laboratory (LBNL). The unique LBNL symmetric cell architecture design, with thin zirconia ceramic backbones and electrolyte sandwiched between porous metal supports, offers a number of advantages over conventional all-ceramic cells, including low-cost structural materials (e.g. stainless steel), mechanical ruggedness, excellent tolerance to redox cycling, and extremely fast start-up capability. The metal-supported solid oxide cells achieve high performance at 700°C:

>1.5 W/cm2 with 3% humidified hydrogen fuel

>1.2 W/cm2 with internal reforming of ethanol fuel

>2.6 A/cm2 electrolysis current density at 1.3V and 50%steam/50% hydrogen

With infiltrated catalysts, there is a tradeoff between initial performance and long-term stability, as extremely high surface area promotes high electrochemical reaction rates, but also provides high surface energy leading to coarsening and facilitates Cr deposition. Recent approaches to mitigating catalyst coarsening and Cr deposition within the cathode include coatings to prevent Cr evaporation from the stainless steel components, and optimization of infiltrated catalyst processing to stabilize the microstructure during operation. The degradation rate has improved to 2.3% kh-1 in fuel cell mode, compatible with the requirements for electric vehicle range extenders. Electrolysis operation, however, results in higher degradation rate. Efforts to identify and mitigate the additional degradation mechanisms in electrolysis mode will be discussed. Scale-up from button cells to 50cm2 is ongoing, and highlights will be presented.

In addition to our long-standing development of zirconia-based metal-supported cells, recent exploratory effort has focused on compatibility between stainless steel metal supports and proton-conducting ceramics. Co-sintering of 400-series stainless steel and BZCY-type proton conductors presents a number of challenges, including: Ba evaporation in reducing atmosphere, over-densification of steel at the high temperatures (>1400°C) required for BZCY processing, and migration of Cr and Si from the steel support into the BZCY layers. Feasibility of new approaches to overcome these challenges will be discussed.
(Invited) Laser 3D Printing of Highly Compacted Protonic Ceramic Electrochemical Cells
Authors: Tong Jianhua "Joshua" , Mu Shenglong , Huang Hua , Meng Yuqing , Hong Yuzhe , Zou Minda , Lei Jincheng , Duffy Jack , Zhao Zeyu , Geng Xiao , Peng Fei , Brinkman Kyle S , Xiao Hai
Published: February 2020

Protonic ceramic electrochemical devices (PCEDs) such as fuel cells, electrolysis cells, membrane reactors, and electrochemical hydrogen compressors can operate at low temperatures (300-600oC) because of the low proton transport activation energy, which allows the significant improvement of durability, materials cost, and efficiency of PCEDs. The great effort has been devoted to discovering new component materials for achieving improved cell or stack performance. Parallelly, the manufacturing of the cells and stacks with the desired microstructures should also be paid more attention. In this work, the highly compacted multilayer protonic ceramic fuel cell and electrolysis cell stacks were designed for achieving significant improvement of volumetric power density and substantially decreased the device size, which will be fabricated by a novel laser 3D printing technique. The crack-free layers of dense protonic ceramic electrolyte, dense interconnect, porous hydrogen electrode and porous oxygen electrode were 3D printed and laser sintered, which showed desired microstructures and promising electrochemical properties. The five-layer single cells comprised of two porous electrodes, one dense electrolyte, and two interconnect layers were automatically manufactured through laser 3D printing. The single cells demonstrated promising fuel cell and water electrolysis performance at 600oC.
(Invited) Recent Progress in Low-Temperature Proton Conducting Ceramics for Hydrogen Isotope Processing
Authors: Brinkman Kyle S , Meng Yuqing , Gao Jun , Zhao Zeyu , Amoroso Jake , Tong Jianhua "Joshua"
Published: February 2020

Proton conducting ceramics (PCCs) are of considerable interest for use in energy conversion and storage applications, electrochemical sensors, and separation membranes. PCCs that combine performance, efficiency, stability, and the ability to operate at low temperatures are particularly attractive for these applications. This presentation summarizes the progress made towards developing low temperature proton conducting ceramics (LT-PCCs), which are defined as operating in the temperature range of 25-400°C. The structure of these ceramic materials, the characteristics of proton conducting mechanisms, and the potential applications for LT-PCCs will be summarized with particular emphasis paid to interfacial protonic conduction. Three temperature zones are defined in the LT-PCC operating regime based on the predominant proton transfer mechanism occurring in each zone. The variation of material properties such crystal structure, conductivity, microstructure, fabrication methods required to achieve the requisite grain size distribution, along with typical strategies pursued to enhance the proton conduction are addressed. Finally, a perspective regarding applications of these materials to low temperature (LT) solid oxide fuel cells, hydrogen separation membranes and emerging areas in the nuclear industry including off gas capture and isotopic separations are presented.

Figure 1
Distribution of Oxygen Partial Pressure in Multilayer Electrolytes: Explaining Degradation of Solid Oxide Electrolyzer Cells
Authors: Zhang Qian , Park Beom-Kyeong , Barnett Scott A , Voorhees Peter W
Published: February 2020

It is found experimentally that solid oxide electrolyzer cells (SOECs) with mixed ionically and electronically conducting oxygen electrodes such as Lanthanum Strontium Cobalt Ferrite (LSCF) show much-reduced electrode fracture and degradation compared to cells with Sr-doped LaMnO3 (LSM): Yttria-stabilized Zirconia (YSZ) electrodes. In the former case, the cells have a Gadolinium doped Ceria (GDC) barrier sandwiched between the electrode and the YSZ electrolyte, i.e., there is a multi-layer electrolyte.

In order to investigate how different electrodes and the GDC barrier layer affect degradation phenomena and optimize the design of SOECs to achieve the desired long-term stability, a diffused interface model is proposed to investigate the distribution of oxygen partial pressure in the SOEC multi-layer electrolyte. Influence of operating condition, structures and properties of the electrolyte on the distribution of oxygen partial pressure are studied.

The model quantitatively predicts the conditions under which oxygen electrode fracture/delamination occurs, largely determined by the electrode overpotential given by the electrode polarization resistance. In addition, it is found that when a GDC barrier layer is present, there is a maximum in the oxygen pressure at the interface of the YSZ and GDC that can result in degradation or fracture. An analytical estimation on the oxygen partial pressure at the YSZ/GDC interface is obtained and shown to provide good agreement with numerical results. The predictions are also in accord with experimental observations of fracture or void formation near the GDC/YSZ interface. The results indicate that this peak pressure can be reduced by reducing the GDC layer thickness, use of a lower polarization resistance oxygen electrode, and by altering the electrolyte materials in order to affect their transport properties, e.g. reducing the Y doping level of YSZ to reduce the oxygen vacancy diffusivity. Changes in operating conditions, i.e., lowering the current density and increasing operating temperature can also reduce the peak pressure, and should thereby suppress the formation of pores or cracks at the YSZ/GDC interface.

Finally, inter-diffusion between YSZ and GDC during the electrolyte firing process can yield a low oxygen ion diffusivity zone at their interface. Our numerical simulation results show that this low oxygen ion diffusivity layer increases the maximum oxygen partial pressure at the GDC/YSZ interface, thereby exacerbating degradation.
Generalized Electrical Conductivity Relaxation Approach to Determine Electrochemical Kinetic Properties for MIECs
Authors: He Fei , Ren Chunlei , Gan Yun , Yang Chunyang , Lee Myongjin , Green Robert , Xue Xingjian
Published: February 2020

Electrical conductivity relaxation (ECR) technique has been widely used to determine kinetic properties of mixed ionic and electronic conductors (MIECs). However, this technique is only applicable for reliable determination of kinetic parameters within a confined range of chemical Biot numbers. Since the kinetic properties of the materials are not known a priori, this imposes great difficulties on how to verify the obtained kinetic parameters from obtained ECR data. Further due to the ill-posed nature of ECR problem, the measurement noise could lead to significant uncertainties in the determined kinetic parameters. Herein a generalized ECR (g-ECR) approach is developed by coherently incorporating multiple ECR measurements simultaneously into an inverse algorithm. This new approach is able to improve the accuracy of calculated kinetic parameters and attenuate uncertainties induced by measurement noise over a wider range of chemical Biot numbers than the ECR approach with a single measurement. The capability of both reducing uncertainties and increasing the range of chemical Biot numbers for accurate parameter determination can be achieved by increasing the number of employed ECR measurement responses. A case study of ECR measurement for PrBa(Co0.75Fe0.25)2O5
+
δ is performed in a mixture gas of N2/Air at 600 °C. The kinetic parameters are determined and evaluated using this g-ECR approach. The rationality of using g-ECR approach instead of ECR approach is verified.
Photoelectrochemical Supercontinuum Solar Light Zero Bias Hydrogen Generation with Membrane-Based Cells Designed for Decreasing Overall Water Electrolysis Voltage and Water Dissociation (23)
Authors: Sakamaki Kenji , Watanabe Ayana , Matsuda Honoka , Usui Sayuri , Sakashita Wakana , Kato Ryoko , Endo Haruka , Sato Masataka
Published: February 2020

We have created a two-compartment cell (2CC) separated by a bipolar membrane (BPM1) sandwiched between through-holed electrodes (THEs) assembly (BPMTHEA-2CC) based on the Golden Role for sustainable water splitting derived from water dissociation (WD) with a dual chemical bias (CB).2 The BPMTHEA-2CC has distinguishing characteristics of integrated functionality of dualities, providing an infinite supply of active reaction species, H+ and OH-, from water with an opposite bidirectional charge separation under appropriate applied voltage conditions. We wish to suggest the feasibility of electrochemical water splitting (decomposition) with less than theoretical 1.23 V at RT using an anolyte (water or base)|OER active THE|BPM|HER active THE|catholyte (water or acid). We disprove the theory of water electrolysis established for hundreds of years with sustainable dual CBs. However, we still require external voltage for water electrolysis.

Instead of external voltage, we have harnessed solar energy by applying the TH n-type semiconductor photoanodes to BPMTHEA-2CC for a zero-bias photogalvanic cell. Anatase TH TiO2 was used for a model to demonstrate our concept. We succeeded in measuring photocurrent from distilled water with a response of optical shutter. The magnitude of the zero bias photocurrent is proportional to the magnitude of outer CB and illuminance intensity. TH Fe2O3 was prepared by the aqueous chemical growth method. Visible light zero bias photocurrent from distilled water was also observed in the TH Fe2O3 photogalvanic cell without any external voltage. Currently, our research efforts are focused on PEC zero bias hydrogen generation with harnessing supercontinuum solar light by designing optical tandem, wavelength multiplexing with BPMTHEA-2CC and Au plasmon-induced WD.

1) V. J. Frilette, J. Phys. Chem., 60, 435 (1956).

2) K. Sakamaki et al., 97th CSJ, 3A6-05 (2017), 68th ISE, Providence, USA, ise171503 (2017), The 22nd Top. Meeting of ISE, Tokyo, abs170627 (2018), 69th ISE, Bologna, Italy, ise183543 (2018).

Figure 1
Catalytic Water Oxidation Reaction at Nanostructured Titania Modified with Carbonized Metal Organic Framework
Authors: Li Xiao , Pan Shanlin
Published: February 2020

Solar energy can be used for direct water splitting to produce hydrogen through a photoelectrochemical (PEC) reaction at semiconducting electrodes. Thus, the overall efficiency of the PEC system is dependent on electrocatalytic or photoelectrocatalytic electrode materials for efficient light absorption, charge separation and transport, in proton reduction and water oxidation half reactions. Herein, a new hybrid catalytic electrode comprised of NH2-MIL-125, a titanium-based metal organic framework (MOF), derived nanostructured Titania electrode material. XRD, SEM and EDX characterizations suggest that nanostructured Titania-MOF electrode is comprised of an underlying layer of TiO2nanorods and the upper layer of distributed clusters of MOF derived disk-shaped nanoparticles (NPs) with an island morphology. The NH2-MIL-125 NPs are formed through a colloid seed-assisted solvothermal reaction and afterwards carbonized while clustering during a pyrolysis process. The resulting nanostructure proved to be composed of C, O, N, and Ti elements. The Titania was employed as the anode substrate of the MOF NPs because it exhibits significantly improved activity for water oxidation and this reaction is greatly enhanced upon coating with carbonized MOF structure. The surface interrogation mode of scanning electrochemical microscopy (SI-SECM) is applied in this study to investigate reactive surface states (RSSs) on the nanostructured electrodes, owing to its selectivity to surface species, capability to in situ quantify for both surface coverage and reactivity of adsorbed RSSs, and usefulness to obtain spatially and temporally-resolved information.
(Invited) Photocatalytic Conversion of Methane to Higher Valuable Compounds
Authors: Hu Yun Hang
Published: February 2020

The conversion of methane to higher valuable compounds at lower temperature has attracted much attention. In this invited talk, Prof. Hu will highlight the recent findings for photocatalytic conversion of methane at low temperature in his group, including (1)photocatalytic coupling of methane, (2) photocatalytic CO2 reforming of methane, and (3)photocatalytic steam reforming of methane.
(Invited) Engineering Hematite Photoelectrodes Interfaces for Sunlight Water Oxidation Reaction
Authors: Muche Dereck N. F. , Freitas Andre L. M , Souza Flavio L
Published: February 2020

Here, pristine and Sn-hematite electrodes were obtained with two different morphologies (columnar, CN, and ellipsoid (EN) nanostructure) by low-cost aqueous chemical method. The following step was the addition at the Sn-hematite surface of a spinel cocatalyst that was also synthesized via chemical method. Sn-hematite-cocatalyst (Ni2FeOx) electrodes were submitted to additional thermal treatment under nitrogen atmosphere to activate the material surface. The pristine hematite electrode showed considerable enhancement on photocurrent density J, in comparison with previous work in our group for both method from a range of ~ 30 µA.cm-2up to 0.2 mA.cm-2 and 1.0 mA.cm-2to 2.0 mA.cm-2at 1.23 VRHE, for CN and EN photoelectrodes respectively. Such improvement has been mainly attributed to a better uniformity of the films and an improved interfacial adherence of the hematite thin film to the TCO provoked primarily by the deposition layer control. Likewise, the addition of Sn+4during hematite photoelectrode prepared enhance the photocurrent response with a pronounced alteration on the onset of the photocurrent curve, moving towards anodic direction from ~0.8 VRHE for pristine photoelectrode to ~0.95 VRHE for Sn-hematite photoelectrode. The final step was the addition of a cocatalyst, such as Ni2FeOX, over the Sn-hematite that leads to a significant shift on the onset potential toward the cathodic direction without drop photocurrent performance as usually observed. In summary, the synergy of Sn+4and Ni2FeOXaddition enables us to promote a shift on the onset towards a lower potential and enhancing the photocurrent density. The authors gratefully acknowledge support from FAPESP (Grant 2017/11986-5) and Shell and the strategic importance of the support given by ANP (Brazil’s National Oil, Natural Gas and Biofuels Agency) through the R&D levy regulation
(Invited) Harvesting Solar Energy in Near Infrared
Authors: Ma Dongling
Published: February 2020

Broadening photon absorption into the near infrared (NIR) range represents a unique opportunity of improving the use of solar energy in various fields, including but not limited to solar fuel, solar cells and solar-enabled photo-degradation of pollutants. It is however challenging to realize this goal as most of traditional materials, such as dyes and semiconductors, do not absorb NIR lights efficiently. Recent advances of nanomaterials opens a new door in this research theme. In this talk, I will present some of our recent work on the design and synthesis of NIR absorbing materials, such as upconverting nanoparticles, plasmonic nanostructure with strong NIR plasmons, NIR absorbing quantum dots and two-dimensional black phosphorous, and on their combination with semiconductors for extending photon absorption into the NIR range for application in solar fuel and photocatalysis [1-8]. Rational design of hybrid nanomaterials, which is the key to maximize the benefits from respective nano-components, is highlighted.

References:

Am. Chem. Soc., 2013, 135, 9616; 2. Adv. Funct. Mater., 2019, under review; 3. Adv. Energy Mater. 2018, 1703658; 4. Adv. Funct. Mater. 2018, 1706235; 5. ACS Catalysis, 2017, 7, 6225; 6. Adv. Funct. Mater, 2015, 25, 2950; 7. Adv. Funct. Mater. 2015, 25, 6650; 8. Nanoscale Horizons, 2019, DOI: 10.1039/C8NH00373D
(Invited) Enhancement of Triplet-Triplet Annihilation-Based Upconversion Emission By Localized Surface Plasmon Resonance
Authors: Sugawa Kosuke , Takeshima Naoto , Jin Shota
Published: February 2020

The upconversion emission systems using triplet-triplet annihilation (TTA-UC emission) has attracted much attention because these systems can be driven by a noncoherent light with low intensity (e.g. sunlight). Namely, the achievement of efficient TTA-UC emission systems directly leads to the development of high-performance solar energy devices. On the other hand, since the Dexter energy transfer between the sensitizers and the emitters is contained in the process of TTA-UC emission, the emission efficiency is quite low in solid state. We have tried to enhance the emission in solid state TTA-UC systems by interacting with the localized surface plasmon (LSP) resonance of metal nanoparticles.

The anisotropic triangular silver nanoplates (silver nanoprisms: AgPRs) were employed as a plasmonic metal nanoparticle because of the generating wavelength tunability of their LSP resonance and the generation of strong local electromagnetic fields. The hybrids of AgPRs and TTA-UC systems were fabricated by spin-coating the polymer solution containing the sensitizer (palladium(II) tetraphenyltetrabenzoporphyrin: Pd-TPTBP) and the emitter (9,10-bis(phenylethynyl)anthracene: BPEA) onto the AgPRs-immobilized glass plates. When the LSP resonance band of AgPRs spectrally overlapped with both the photoexcitation wavelength of Pd-TPTBP and the fluorescence band of BPEA, the TTA-UC emission was efficiently enhanced. It is reasonable to consider that the former spectral overlap provides the enhancement of TTA-UC emission through the photoexcitation enhancement of Pd-TPTBP (Figure 1). In addition, the threshold excitation intensity (the figure-of-merit in TTA-UC systems) significantly decreased by overlapping the LSP resonance band with the photoexcitation wavelength. Also, it was suggested by the fluorescence lifetime measurements that the enhancement of TTA-UC emission caused by overlapping with the fluorescence band was induced by the efficient nonradiative energy transfer from the singlet excited BPEA to the LSP of AgPRs (Figure 1). On the other hand, when the LSP resonance band overlapped well with the phosphorescence band of Pd-TPTBP, the TTA-UC emission was rather quenched. These results suggest that the nonradiative energy transfer by the LSP resonance from the triplet excited Pd-TPTBP to the LSP became dominant, as compared with the triplet-triplet energy transfer from the Pd-TPTBP to the BPEA. Namely, it was demonstrated that the LSP resonance of AgPRs has both of the positive and negative effects on the solid state TTA-UC emission systems.[1] Furthermore, we investigated the optical interaction between the singlet excited palladium porphyrin and the LSP resonance of AgPRs. Consequently, we will discuss the detailed effects of LSP resonance of the AgPRs on the complicated TTA-UC emission processes.

[1] S. Jin, K. Sugawa et al., ACS Photon., 2018, 5, 5025-5037.

Figure 1
(Invited) Toward Unity Quantum Efficiency for Plasmon Induced Hot Electron Transfer at Metal/Semiconductor Junctions
Authors: Lian Tianquan
Published: February 2020

It has been well-established that excitation of plasmons in metal nanostructures can lead to the injection of hot electrons into semiconductors or adsorbed molecules, which can be used to enhance photocatalysis. This novel mechanism suggests that plasmonic nanostructures can potentially function as a new class of widely tunable and robust light harvesting and catalytic materials for solar energy conversion. More importantly, it provides a novel approach to access highly energetic and reactive states of metals that is difficult to access with thermal chemistry. However, plasmon-induced hot electron injections from metal to semiconductor or molecules are still inefficient because of unfavorable initial hot electron distribution and the competing ultrafast hot electron relaxation processes within the metallic domain.

In this talk, we discuss two approaches to enhance the efficiency of plasmon induced hot electron transfer. In the first approach, we explore the possibility of enhancing hot electron distribution by decreasing the size of plasmonic Au particles. Using CdS/Au nanorod heterostuctures, we show that the hot electron injection efficiency increases at smaller Au particle size. We attribute this size dependence to increasing contribution of surface assisted plasmon damping, which generates more hot electrons compared to damping by interband transition. In the second approach, we demonstrate that in CdSe/Au hetersostructureswith strong metal/semiconductor coupling, the plasmon decays by direct excitation of an electron from the metal to semiconductor, i.e. plasmon induced interfacial charge transfer transition (PICTT). The new plasmon damping pathway can be very efficient because it bypasses the competition with hot electron relaxation within the metal satisfies both the energy and momentum conservation. We will discuss whether PICTT is a general scheme for efficient hot electron transfer and present preliminary findings of highly efficient plasmon induced hot electron transfer at plasmonic metal/oxide semiconductor interfaces.