bluuebunny/crossref_metadata_2025 huggingface dataset:
Supported Transition Metal Phosphides: Activity Survey for HER, ORR, OER, and Corrosion Resistance in Acid and Alkaline Electrolytes
Authors: Parra-Puerto Andres , NG Kai Ling , Fahy Kieran F. , Goode Angela E , Ryan Mary P. , Kucernak Anthony
Published: December 2020

One of the main bottle necks for the introduction of fuel cell technology in the market, is their dependency on precious metals as catalyst. Focusing on the electrochemical reactions involved, the most sluggish is the Oxygen Reduction Reaction (ORR). Significant research has been performed to optimize for the amount of the precious metal used, whilst keeping the same activity. On the other hand, many investigations have been carried out to find non-precious metal catalysts with the same performance for ORR, Oxygen Evolution Reaction (OER), Hydrogen Evolution Reaction (HER) and Hydrogen Oxidation Reaction (HOR) [1]. One of those candidates are the metal phosphides [2], however, these catalysts nowadays only are active for ORR, HER, OER and they have very poor activity towards the HOR [3]. Here we present the work done related to the simple synthesis of different MP catalysts (M = Ni, Co, W, Cr and Mo) [4]; their catalytic activity towards H2 and O2 reactions; and their corrosion resistance in acidic and alkaline electrolytes. Co2P was found to have a very interesting ORR catalytic behaviour and peroxide generation under alkaline and acidic conditions respectively. To understand the activity of Co2P, an HRTEM analysis was done to understand the changes in the morphology before and after the ORR reaction.

References

[1] M. S. Faber and S. Jin, “Earth-abundant inorganic electrocatalysts and their nanostructures for energy conversion applications,” Energy Environ. Sci., vol. 7, no. 11, pp. 3519–3542, Oct. 2014, doi: 10.1039/C4EE01760A.

[2] A.-M. Alexander et al., “Alternative catalytic materials: carbides, nitrides, phosphides and amorphous boron alloys,” Chem. Soc. Rev., vol. 39, no. 11, pp. 4388–4401, Oct. 2010, doi: 10.1039/b916787k.

[3] R. Prins and M. E. Bussell, “Metal Phosphides: Preparation, Characterization and Catalytic Reactivity,” Catal. Letters, vol. 142, no. 12, pp. 1413–1436, Dec. 2012, doi: 10.1007/s10562-012-0929-7.

[4] A. Parra-Puerto, K. L. Ng, K. Fahy, A. E. Goode, M. P. Ryan, and A. Kucernak, “Supported Transition Metal Phosphides: Activity Survey for HER, ORR, OER, and Corrosion Resistance in Acid and Alkaline Electrolytes,” ACS Catal., vol. 9, pp. 11515–11529, Nov. 2019, doi: 10.1021/acscatal.9b03359.

Figure 1
Highly Active Fe-N/C Oxygen Electrocatalysts Based on Silicon Carbide Derived Carbon
Authors: Teppor Patrick , Jäger Rutha , Hints Johanna , Volobujeva Olga , Valk Peeter , Koppel Miriam , Lust Enn
Published: December 2020

Extensive research is currently being conducted in the field of non-platinum group metal oxygen reduction catalysts for low-temperature fuel cells1,2. Many of the synthesis methods used to produce these novel materials involve grinding the precursors in a planetary ball mill3,4. Consequently, more information is needed to understand how this procedure affects the physical properties of the resulting carbon-based materials. Additionally, it is crucially important to investigate the influence of the physical properties on the electrochemical performance of the electrocatalysts.

In this work, several Fe-N/C type electrocatalysts were synthesized from silicon carbide derived carbon via ball milling. A number of parameters, such as grinding mode and ball diameter, were changed in order to study their effect on both the physical and electrochemical properties of the Fe-N/C catalysts. The main characterization methods used in this study were N2-sorption and laser diffraction, which provide insight into the pore and particle size distributions of the materials, respectively.

From the rotating disc electrode measurements it is clear that highly active Fe-N/C catalysts can be successfully synthesized using a facile two-step process involving ball milling and pyrolyzing. Changing the ball milling parameters has a considerable effect on both the surface morphology as well as particle size distributions of the studied Fe-N/C catalysts. As a final step, the importance of these changes in the physical properties was studied in a single cell experimental setup.

B.-Y. Song, M.-J. Li, Y.-W. Yang, and Y.-L. He, J. Clean. Prod., 249, 119314 (2020) http://www.sciencedirect.com/science/article/pii/S0959652619341848.

D. Banham, J.-Y. Choi, T. Kishimoto, and S. Ye, Adv. Mater., 31, 1804846 (2019) https://onlinelibrary.wiley.com/doi/abs/10.1002/adma.201804846.

S. Ratso et al., ACS Appl. Energy Mater., 2, 7952–7962 (2019) https://doi.org/10.1021/acsaem.9b01430.

M. J. Workman et al., J. Power Sources, 348, 30–39 (2017) http://www.sciencedirect.com/science/article/pii/S0378775317302410.

Figure 1
Rationalizing Effect of Metal Substitution in Ruthenium Pyrochlores on the Lattice Oxygen Binding and Oxygen Evolution Activity
Authors: Kuznetsov Denis A. , Naeem Muhammad A. , Kumar Priyank V. , Abdala Paula M. , Fedorov Alexey , Müller Christoph R.
Published: December 2020

Ruthenium pyrochlores, i.e. oxides of composition A2Ru2O7
−
δ, are known as advanced catalysts for the oxygen evolution reaction (OER) in acidic conditions.1 In this work, we discuss a direct correlation between the OER activity of Y1.8M0.2Ru2O7
−
δ pyrochlores (M = Y, Fe, Co, Ni, Cu), the lattice oxygen binding strength/lability and the formation enthalpy of the binary MOx oxide, i.e. metals M with highter enthalpies of formation for the respective oxide weaken the oxygen binding on the surface of Y1.8M0.2Ru2O7
−
δ pyrochlores that results in enhanced OER activity. DFT studies captured changes in the electronic structure of the Y1.8M0.2Ru2O7
−
δ oxides induced by M substitution and revealed trends in the electronic band structure that govern the OER performance of the Y1.8M0.2Ru2O7
−
δ catalysts. Specifically, an increase in the density of oxygen vacancy (VO) sites and the OER activity in Y1.8M0.2Ru2O7
−
δ is attributed to the shift of the O 2p band center closer to the Fermi level. Our work introduces Y1.8Cu0.2Ru2O7
−
δ as a novel OER catalyst with enhanced OER activity and, more fundamentally, emphasizes the underexplored role that substituents can play in regulating the OER activity of complex oxides, i.e. by influencing the surface oxygen binding strength. Our results can be utilized for the rational design of new compositions for oxygen electrocatalysis and other applications that involve lattice oxygen sites.

(1) Kim, J.; Shih, P.-C.; Tsao, K.-C.; Pan, Y.-T.; Yin, X.; Sun, C.-J.; Yang, H., J. Am. Chem. Soc.
2017,
139, 12076-12083.
Investigation of Anodic Porous Transport Electrode for Anion Exchange Membrane Electrolyzers
Authors: Wang Ruixiang , Ishida Masayoshi , Ohashi Masato , Ito Hiroshi
Published: December 2020

As global warming and the exhaustion of fossil fuels deepen, major countries are trying to promote the spread of renewable energy such as solar and wind power. Hydrogen with high energy density, no harmful emissions and various transportation, storage methods is regarded as the optimal energy carrier for renewable energy. Water electrolysis technology is usually used for the transformation of renewable resources to hydrogen. In the development of water electrolysis technology, proton exchange membrane (PEM) water electrolysis used a PEM with high mechanical/chemical stability and a membrane electrode assembly (MEA) with a zero-gap structure of electrodes has excellent variability to power fluctuation and a better electrolysis efficiency. However, due to the acidic electrolyte, cell components materials of PEM water electrolysis are limited to precious metal such as iridium (Ir) based catalysts on anode and platinum-group metals (PGMs) catalyst on cathode.

In contrast, in the anion exchange membrane (AEM) water electrolysis, alkaline membrane can be used as electrolyte which means, compared with PEM water electrolysis, widely available non-precious metal catalysts and stainless components can be used. However, different from proton exchange ionomer (PEI), typical models of anion exchange ionomer (AEI) tend to lack mechanical and chemical stabilities and are difficult to apply to the binder for anode catalyst layer [1]. Therefore, we have adopted a different electrode structure for each of the two electrodes in the MEA, that is, catalyst-coated-membrane (CCM) for the cathode and porous transport electrode (PTE) for the anode.

In this study, various types of PTE were fabricated and applied for the anode. The effect of each property of PTE (catalyst lading, porosity, thickness, and pore diameter) on the electrolysis performance was examined experimentally.

Acknowledgement

Part of the experiments reported here are supported by the New Energy and Industrial Technology Development Organization (NEDO).

Reference

[1] H. Ito et al. J. Appl. Electrochem., 48, 305 (2018)
High Performance and Durable Membrane Electrode Assemblies with Free-Standing Binder-Free Plasma Sprayed Electrodes and Nanocomposite Membranes for Anion Exchange Membrane Electrolyzer
Authors: Razmjooei Fatemeh , Kaur Jasneet , Zarrin Hadis , Gago Aldo Saul , Ansar Syed Asif , Friedrich Kaspar Andreas
Published: December 2020

Hydrogen production via water electrolysis using electricity from renewable power sources is a promising method for storing energy in a large scale. Anion exchange membrane (AEM) electrolyzers have the potential for decreasing the hydrogen cost produced by renewables due to use of non-noble materials and inexpensive components for the membrane electrode assembly (MEA). This work demonstrates a highly active and durable MEA for AEM electrolysis using binder-free atmospheric plasma sprayed (APS) RANEY-type nickel and RANEY-type nickel-molybdenum electrodes,[1,2] as anode and cathode, respectively, in combination with robust boron nitride (BN)-based anion exchange membranes, nanocomposed with either polyvinylidene fluoride (PVDF) or polyvinyl alcohol (PVA). In this present work, various AEMs with different ionic conductivity and thickness, M1: High-loaded BN nanocomposite with PVDF or HL-BN-PVDF (0.23 Scm-1 and 125 mμ), M2: low-loaded BN nanocomposite with PVDF or LL-BN-PVDF (0.19 Scm-1 and 80 mμ) and M3: high-loaded BN nanocomposite with PVA or HL-BN-PVA (0.36 Scm-1 and 45 mμ) have been used. Three MEAs were fabricated using three membranes of HL-BN-PVDF, LL-BN-PVDF and HL-BN-PVA sandwiched between two APS-based electrodes denoted as The MEA1, MEA2 and MEA3, respectively, and tested in single AEM electrolyzer cells. The tests are carried out in 1M KOH at 60 0C. As expected, the highest current, 2.6 Acm-2 at 2 V is achieved with MEA3, while MEA2 and MEA1 reached 2.95 and 3 A cm-2, respectively. The performance of AEM water electrolysis with the MEA3 is found to be slightly better than the MEA with the same electrode package but commercial membrane from Fumasep (2.71 Acm-2 at 2.0 V). The stability of the cell with MEA3 is tested under the constant load of 0.5 A cm-2 for 250 h showing negligible degradation. This can be attributed to the high mechanical and chemical stability of the membrane and low dissolution of anodic electrode. Furthermore, the lack of binders or ionomers in the APS electrodes avoids irreversible oxidation reactions of the polymer that can lead to voltage loss over time [3]. Thus APS electrodes combined with stable nanocomposed (BN)-based membranes can potentially lower the cost of the hydrogen produced by water electrolysis.

Razmjooei, R. Reißner, A. S. Gago, and A. Ansar, ECS Transactions, 92 (8) 689-702 (2019).

Wang, T. Weissbach, R. Reißner, A. Ansar, A. S. Gago, S. Holdcroft, K. A. Friedrich, ACS
Appl. Energy Mater. DOI: 10.1021/acsaem.9b01392 (2019).

Li, I. Matanovic, A. S. Lee, E. J. Park, C. Fujimoto, H. T. Chung, and Y. S. Kim, ACS Appl. Mater. Interfaces, 11 (10) 9696-9701 (2019).
Using Ion Exchange Capacity to Control Water Uptake in Electrodes of Low-Temperature Anion Exchange Membrane Electrolyzers
Authors: Huang Garrett , Mandal Mrinmay , Dobbs Alexandra , Groenhout Katelyn , Kohl Paul A
Published: December 2020

Hydrogen today is mainly produced by steam reforming natural gas or other fossil fuels. However, this method produces low purity hydrogen with a high concentration of carbonaceous species and ultimately does not relieve dependencies on fossil fuels or reduce harmful greenhouse gasses. Hydrogen production from water electrolysis is a low-carbon or carbon-free alternative to steam reforming and can be utilized as a chemical means of storing excess energy from intermittent sources such as wind and solar.

Solid polymer electrolyte electrolysis based on anion exchange membranes (AEM) seeks to combine the benefits of more established water electrolysis technologies such as alkaline electrolysis (AEL) and proton exchange membrane electrolysis (PEMEL). The high pH environment in AEM electrolysis (AEMEL) promotes facile oxygen evolution reaction kinetics and enables the use of electrodes with little to no platinum group metals. AEMEL systems also have the advantage of a compact design without the need for constant circulation of a concentrated KOH electrolyte.

The polymer membranes used in AEM devices have seen significant advances in recent years, with the development of highly conductive, stable and low-cost membranes for AEM fuel cells (AEMFC). Less attention has been paid to the ionomers in the gas diffusion electrodes. Proper water management has been a key factor in obtaining maximum performance in AEMFCs and it is reasonable to infer that water management will also play an important role in achieving high performance in AEMEL.

In this study, a series of high performance polynorbornene tetrablock copolymer ionomers were synthesized and used to understand the effects of hydrophobicity and ionic conductivity on the performance of low-temperature AEMEL. The ion exchange capacity (IEC) of the ionomers was used to control the amount of swelling and water uptake within the catalyst layer. Teflon was also used to add hydrophobicity to the catalyst layer without sacrificing ionic conductivity. It was found that low IEC at the oxygen evolving electrode and high IEC at the hydrogen evolving electrode enables more efficient water electrolysis.

Financial support for the authors provided by the EERE H2@Scale program (U.S. Department of Energy) is gratefully acknowledged.
Theory Driven Catalysts Design for Hydrogenation Reactions in Solid Oxide Electrolyzer
Authors: Li Meng , Hua Bin , Wang Lu-Cun , Ding Dong
Published: December 2020

Hydrogenation reactions are essential processes in the chemical industry, giving access to a variety of valuable compounds. CO2 and N2 can be transformed into carbonates and NH3 through hydrogenation reactions. Metal oxides supported metals/alloys are the most investigated catalytic materials in heterogeneous electrochemical catalysis. The strong metal-support interaction (SMSI), which determines the catalytic activity, largely depends on chemical conditions of the support and particle size of dispersed metal nanoparticles (NPs). In this work, we studied the SMSI in doped CeO2 supported noble metal NPs systems and their activities for CO2 and N2 hydrogenation reactions in solid oxide electrolyzer. By using a combination of high-throughput density functional theory (DFT) calculations and electrochemical measurements in solid oxide electrolyzer, we developed highly active catalysts for CO2 and N2 hydrogenation reactions.

The reactions of CO2 and N2 hydrogenation normally require large energy input because both CO2 and N2 are quite stable and inert molecules with strong chemical bonds and low polarizability. The adsorption of CO2 and N2 molecules on metal-oxide composite surfaces is normally quite weak, which results in large energy barriers for their activation processes. We performed DFT calculations to determine the key properties for selected doped CeO2 supported noble metal NPs systems to achieving high performance under solid oxide electrolyzer operating conditions. The predictions were further confirmed by the experiments. The highly predictive DFT calculations played a great role in determining the development of electrochemical catalysts for hydrogenation and reactions. Atomic-level materials properties and reaction pathways based on different reaction mechanisms from DFT paved the way for searching for highly active catalysts. The experimental evidence indicated that it is applicable to several hydrogenation reactions.
(Invited) Ruthenium/Samaria-Doped Ceria Cermet Anode through Plasma Enhanced Atomic Layer Deposition
Authors: Kim Hyong June , Kye Seunghyeon , An Jihwan
Published: December 2020

Direct methane-fueled solid oxide fuel cells (DM-SOFCs) operating at low temperature range (<450 C) are promising next-generation energy conversion devices, in which, however, anode reactions should be facilitated for high performance even at low temperatures. Obtaining catalyst with high activity, thermal stability and carbon coking resistance is essential for high-performance SOFC operating with hydrocarbon fuel. Noble metal catalyst, e.g., Ru, can be effective for direct methane oxidation in DM-SOFC anode. However, their high costs prevent them from being extensively applied to such devices as SOFCs, and, therefore, significant efforts have been made to lower the noble metal loading in designing fuel cell electrodes.

Herein, we report the design and fabrication of heterogeneous catalyst with ultra-low-loading Ru nanostructures via plasma enhanced atomic layer deposition (PEALD) on SDC backbone anode. We confirmed the presence of highly dispersed PEALD Ru particles over the SDC backbone compared to sputtered Ru deposited on only porous sputtered SDC surface. We found out that PEALD Ru of 100 ALD cycles, or approximately 5nm in thickness with Ru loading of only 0.004 mg/cm2, was sufficient for the use of anode catalyst with methane fuel. Furthermore, compared to the cell with 100 nm-thick sputtered Ru/sputtered SDC anode, the cell with PEALD Ru/sputtered SDC anode showed 45 % higher peak power density with only 1/20 of Ru loading. Moreover, after 4 hours operation with dry methane at 450 C, the activation resistance of the cell with the sputtered Ru composite anode increased by 7 times, while that of the cell with the PEALD Ru composite anode increased by only 2 times. This result suggests that, using PEALD, one can simultaneously reduce Ru loading, thereby reducing cost, and improve the performance and the thermal stability of the anode for DM-SOFC.
(Invited) Engineering the Charged Defects at the Perovskite Oxide Surfaces for the Stable Operations at the Elevated Temperatures
Authors: Choi Mingi , Lee Wonyoung
Published: December 2020

Perovskite oxide is one of the most promising materials for the energy conversion devices including the solid oxide cells (SOFC/SOEC), photovoltaics, and others. However, operations at the elevated temperatures induce the considerable cation re-arrangement at the perovskite oxide surfaces, resulting in the chemical heterogeneities. Since re-arranged cations typically form the undesired secondary phases, destroying the ideal stoichiometry of the perovskite oxides near the outermost surface, the surface exchange reaction rates are significantly retarded. Therefore, the underlying mechanisms of cation re-arrangements should be systematically conducted based on in-depth fundamentals.

Here, we present the relationship between the re-arrangements of the charged defects such as oxygen vacancy and doped-Sr in the perovskite oxides and the chemical and electrochemical stability at the elevated temperatures. Sr-doped perovskite oxides were employed as model electrodes, and doped ceria was additionally deposited onto the perovskite oxides to make the hetero-interface for controlling the distribution of charged defects. The hetero-structured electrodes maintained the initial surface exchange reactivity at 650 °C with substantially suppressed cation rearrangements. Systematic characterizations revealed that the space charge layers established near the hetero-interfaces with re-arranged charged defects reduce the electrostatic interactions for cation rearrangements. The experimental evidences for the charge transfer near the hetero-interfaces and the chemical and electrochemical stability at the elevated temperatures will be discussed.
(Invited) Studies on Fabrication Process Cost Reduction for LT-/IT-SOFCs
Authors: Lim Yonghyun , Park Jun-Sik , Kim Young-Beom
Published: December 2020

Solid oxide fuel cells (SOFCs) have attracted many attentions as a next-generation energy conversion device because of their high efficiency and the ability to use a variety of fuels. However, conventional manufacturing processes cause high manufacturing cost and therefore impedes commercialization of SOFCs. SOFC components are mainly produced by non-vacuum powder based process to improve productivity. To achieve desired material properties high-temperature post-heat treatment process usually above 1400oC is required for a long time for ceramic electrolyte and electrode fabrication. This long and high temperature sintering process significantly increases production costs and becomes a hurdle for widespread usage. Therefore, in order to reduce the manufacturing cost of the SOFCs, it is essential to improve the fabrication process especially the high temperature sintering process. Accordingly, to lower the high sintering temperature, a bilayer sintering process using a sintering aid was designed, and it successfully lower the sintering temperature while maintaining the material properties. The fabricated YSZ electrolyte by the developed low temperature sintering process showed a relatively high performance. In addition, through the applying an innovative flash light sintering process, the rapid sintering process of powder based ceramic electrolyte and electrode are successfully demonstrated for the first time. Therefore, a long process time of several tens of hours in thermal sintering process can be significantly reduced within tens of seconds through the development of flash light sintering process.
(Invited) Ultra-Low-Cost Long-Duration Energy Storage Using Solid Oxide Batteries
Authors: Graves Christopher , Jensen Søren Højgaard
Published: December 2020

Solar and wind power are now the lowest cost electricity sources, making an urgent need for low-cost long-duration energy storage technologies to turn these intermittent renewables into on-demand power. Long-duration energy storage is defined as an energy to power ratio of more than 10 h. For some applications, hundreds of hours storage capacity will be needed to balance supply and demand. Available storage systems are inadequate: conventional batteries are too expensive, water electrolysis with fuel-cell re-oxidation is too inefficient, and pumped hydro and compressed air are geographically constrained. Reversible solid oxide electrochemical cells operated like flow batteries have the potential to meet the needs of long-duration storage by using ultra-low-cost storage media. This presentation will include: (1) the advantages of such solid oxide batteries using different storage media than the classical H2/O2/H2O chemistry, (2) experimental demonstration and system design, (3) analysis of the storage requirements for reversible electricity storage applications, and (4) techno-economic analysis of novel solid oxide battery systems compared with conventional batteries and flow batteries.

Figure 1
(Invited) HT-PEM Fuel Cell Development for Product Definition and Scaleup
Authors: Primdahl Soeren , Alfaro Silvia M. , García Héctor R. , Terkelsen Carina , Steenberg Thomas , Hjuler Hans Aage
Published: December 2020

“High Temperature” Proton conducting Electrolyte Membrane (HT-PEM) fuel cells offer an attractive method of converting renewable energy carriers (e.g. methanol) to electricity, especially remotely and in transportation. A particular advantage is their ability to digest reformates containing a few % CO, thus not requiring high purity hydrogen.

Membranes of polybenzimidazole (PBI) allow for operation in the 150-200 °C range, as they do not require liquid water for continuous moisturizing as do fluorinated polymer membranes. This temperature range is advantageous for the typically used Pt catalyst, as the passivation by CO is limited.

A central challenge is cost reduction, with particular focus on Pt loading of electrodes. The critical trade-off is against lifetime and electrode performance while maintaining adequate tolerance to CO and fuel trace impurities. These limitations are sensitive to system and customer parameters via selection of fuel, reformer characteristics and operation mode.

Results will be presented and discussed on single cell lifetime in the 10.000 h range; objectives and results in electrode development and Pt loading, as well as results on methanol slip testing, start-stop testing and testing at elevated pressure. Lessons from early upscaling will be shared.
High Performance Commercial SOFC Cathodes Achieved with YSZ Nanoparticles
Authors: Gross Michael D. , Muhoza Sixbert P. , Lee Shiwoo , Song Xueyan , Guan Bo , Yang Tao
Published: December 2020

The electrochemical performance of solid oxide fuel cell (SOFC) cathodes was improved via integration of ultra-high surface area ceramic nanoparticles, up to 115 m2·g-1, generated with a novel processing method herein introduced. The processing method generates the high surface area nanoparticles at traditional SOFC sintering temperatures in two steps. In the first step, a hybrid inorganic-organic material comprising the ceramic precursors is sintered in an inert atmosphere at any temperature between 850°C-1350°C. During this step, an amorphous carbon template is generated in situ, preventing coarsening of the ceramic nanoparticles. The carbon template is then removed during the second step by a mild calcination in air at 700°C. Yttria-stabilized zirconia (YSZ), lanthanum strontium cobalt ferrite (LSCF), gadolinium-doped ceria (GDC), and strontium titanate (STO) have all been successfully prepared by this method. YSZ nanoparticles (nYSZ) were incorporated into a lanthanum strontium manganite-YSZ (LSM-YSZ) cathode of a commercial cell, resulting in a 90% increase in maximum power density. Impedance spectroscopy indicates the large improvement in power density was attributed to a combination of significant improvement in polarization resistance, a 45% decrease, and ohmic resistance, a 35% decrease. Remarkably, the performance of the cell modified with nYSZ was higher than cells modified with two mixed ionic electronic conductors (MIEC): PrxBa1-xCo3-δ (PBC) and LaxSr1-xCoyFe1-yO3-δ (LSCF). Both MIECs enhanced the density of active sites, but, unlike nYSZ, did not significantly improve ohmic resistance. The results demonstrate a novel pathway to achieve high performance in commercial SOFCs.
Comparative Investigation of Electronic Leakage in Proton-Conducting Ceramics for High-Temperature Water Electrolysis
Authors: Regalado Vera Clarita Yosune , Ding Hanping , Zhou Meng , Ding Dong
Published: December 2020

The electronic conduction within proton-conducting ceramics represents a significant problem for the efficiency of hydrogen production through water electrolysis at high or intermediate temperatures. The doped barium-cerium-zirconate oxides, which have been successfully used for fuel cell applications, however, show electronic leakage when used in water electrolysis that ultimately lowers the Faradaic efficiency of hydrogen production. In this work, the defect chemistry of proton-conducting ceramics was used to evaluate the proton, hole, and electron conductivity from the total conductivity of BaCe0.7Zr0.1Y0.1Yb0.1O3-δ, BaCe0.4Zr0.4Y0.1Yb0.1O3-δ and BaZr0.8Y0.2O3-δ ceramics studied under different steam and oxygen partial pressures. The intrinsic electronic leakage was then related to the Ohmic potential, steam and oxygen partial pressures and temperature. The proton and electronic current densities were calculated from transport equations and then used to estimate the electronic leakage at the specified electrolysis conditions. The comparison of these three materials revealed that the rational material design and optimization of operating conditions can mitigate electronic leakage in electrolytes, which promotes the fast and efficient hydrogen production by proton-conducting solid oxide electrolysis cells.
Performance and Durability of Kw Class Reversible Solid Oxide Cell Stacks
Authors: Kim Sun-Dong , Kim Tae Woo , Byun Segi , Choi Yoonseok , Seo Doo-Won , Woo Sang-Kuk , Hwang Hyojung
Published: December 2020

Mass production of hydrogen by water electrolysis has attracted great attention because it is sustainable without emitting CO2 and there is no problem of resource depletion when combined with renewable energy technologies such as solar and wind power. In particular, solid oxide cells can provide high conversion efficiency assisted by thermodynamically advantageous water splitting at high operating temperatures typically over 700 oC. In this work, as can be seen in Figure below, we fabricated 1kW class stacks consisting of 30 flat-tubular solid oxide cells with an active area of 100cm2 for mass production of hydrogen. The performance and durability of the stacks are investigated while operating in both electrolysis cell (EC) and fuel cell (FC) modes. The effect of the operating conditions, e.g. temperature, mass flow rate, steam-to-hydrogen ratio, etc., will be mainly discussed.

Figure 1
Ultra-Thin GDC Buffer Layer Fabricated By Vacuum Slurry Coating Method for High Performance Intermediate-Temperature SOFC
Authors: Joh Dong Woo , Shin Sang-Woo , Song Rak-Hyun
Published: December 2020

The Vacuum Slurry Coating (VSC) method has the advantage of being able to produce thin films with a simple device and is cost effective over other thin film coating methods. In solid oxide fuel cells (SOFCs), gadolinium doped ceria (GDC) buffer layer should be thin and dense to minimize ohmic resistance as well as prevent the undesirable reactions between scandia-stabilized zirconia (ScSZ) electrolyte and cobaltite perovskite cathodes. In this study, GDC buffer layer was coated on pre-sintered anode-supported half-cell comprising an ScSZ electrolyte layer on the NiO-YSZ anode using vacuum slurry coating process. Then GDC coated cells were sintered at 1400oC. The GDC buffer layer coated on the pre-sintered cell at 1200oC was thin and dense regardless of the immersion time. The maximum power density of the SOFC using VSC was 400 mW/cm2 (@ 700oC), which is 38 % higher than that using screen printing method (290 mW/cm2). The microstructure of the coated GDC buffer layer using the VSC method was much denser than using the screen printing method.
A Zero-Dimensional Electrochemical Model for Organic Flow Cells
Authors: Modak Sanat Vibhas , Kwabi David G.
Published: December 2020

We develop and experimentally validate a zero-dimensional model of the electrochemical performance of a flow cell. The model takes into account voltage losses due to Faradaic charge transfer, ohmic and mass transport resistance, as well as the effect of spatial variations in state-of-charge between the cell and electrolyte reservoir. We validate the model by comparing voltage-current data during cycling to equivalent electrochemical measurements from a symmetric cell with organic reactants. With the exception of the mass transfer coefficient, all relevant model parameters are determined independently prior to the experiment using electrochemical impedance spectroscopy and cyclic voltammetry measurements. We find excellent agreement between the model and experiment for constant-current and constant-voltage cycling, across a wide range of current densities (40 – 200 mA/cm2) and volumetric flow rates (~ 10 – 140 mL/min). The relationship between the fitted mass transport coefficient and flow rate conforms to expectations from the literature [1-3], and reasonably approximates the analogous relationship from single-reservoir cell measurements. This work supports the notion that zero-dimensional electrochemical models can yield simple but predictive frameworks for optimizing organic flow battery performance and understanding how reactant decomposition and crossover contribute to capacity fade.

References

[1] M. Pugach, M. Kondratenko, S. Briola, and A. Bischi, "Zero dimensional dynamic model of vanadium redox flow battery cell incorporating all modes of vanadium ions crossover," Applied Energy, vol. 226, pp. 560-569, 2018/09/15/ 2018, doi: https://doi.org/10.1016/j.apenergy.2018.05.124.

[2] J. L. Barton, J. D. Milshtein, J. J. Hinricher, and F. R. Brushett, "Quantifying the impact of viscosity on mass-transfer coefficients in redox flow batteries," Journal of Power Sources, vol. 399, pp. 133-143, 2018/09/30/ 2018, doi: https://doi.org/10.1016/j.jpowsour.2018.07.046.

[3] J. D. Milshtein, K. M. Tenny, J. L. Barton, J. Drake, R. M. Darling, and F. R. Brushett, "Quantifying Mass Transfer Rates in Redox Flow Batteries," Journal of The Electrochemical Society, vol. 164, no. 11, pp. E3265-E3275, 2017, doi: 10.1149/2.0201711jes.
An Electrolyte-Decoupled Ammonia Battery for Enhancing Electricity Production from Low-Grade Waste Heat
Authors: Wang Weiguang , Shu Gequn , Huo Dongxing , Yang Shuang , Zhu Xiuping , Tian Hua
Published: December 2020

Tremendous amount of fossil fuel is consumed in the form of low-grade waste heat (< 130 °C) due to inefficient energy utilization, and harvesting this waste heat as useful electricity contributes to mitigating the increasing energy crisis and the global greenhouse effect. Recently, compared with the past technologies (e.g. solid-state thermoelectric generator (s-TEG) and organic Rankine cycle (ORC)), liquid-based thermo-electrochemical batteries or systems feature more efficient and low cost for heat-to-electricity conversion. Among them, bimetallic thermally regenerative ammonia batteries (B-TRABs) based on redox reactions and ammonia thermal distillation that output the highest power density. However, all the existing ammonia batteries exhibit a common phenomenon that their discharge voltage curve basically has no stable platform and gradually decreases after peaking early, which is mainly due to the large pH difference between catholyte and anolyte, leading to self-discharge and severe energy decay. Here, an electrolyte decoupled strategy is proposed for a Cu/Zn-TRAB to restrain the self-discharge and enhance energy density as well as power generation at high temperatures. The self-discharge by ions cross contamination is observed visually as a colour evolution of the interlayer solution, and a transition of principal cathodic reactant from Cu(NH3)4
2+ to Cu2+ exists during discharging, which signals the beginning of performance degradation. The results demonstrate that the decoupled Cu/Zn-TRABs with double and triple-membrane designs improve the energy density by 45-50%, mainly due to the delay of transition region. With an energy density of 1034 W h m-3 obtained by a decoupled Cu/Zn-TRAB with double-membrane design, a thermoelectric conversion efficiency of 1.86% (15.6% relative to the Carnot efficiency) is achieved at a condenser temperature of 16 °C.
Highly Stable and Efficient Lead Halide Perovskite Nanocrystals for Light-Emitting Diodes Displays
Authors: Xuan Tongtong , Zhou Tianliang , Wang Jing , Xie Rong-Jun
Published: December 2020

All inorganic lead halide perovskite nanocrystals (NCs), CsPbX3 (X=Cl, Br, I), have been attracting increasing attention because of their excellent optical properties, such as tunable emission wavelength, high photoluminescence quantum yield (PLQY), narrow full width at half maximum (fwhm), and high defect tolerance. Therefore, the NCs have great potential application in light-emitting diodes for display. However, the NCs suffer from poor stability due to the hydrolytic degradation and fluorescence quenching in the solid agglomerations state. To improve the photoluminescence (PL) stability of the NCs, the ammonium bromide, alkyl phosphate, microscale Cs4PbX6, and super hydrophobic porous organic polymers (SHOP) were used as frameworks to from the composites with NCs. Specially, the CsPbBr3-super hydrophobic polymers composites not only preserve a high PLQY (60%) and narrow band emission (fwhm~16nm) but also inherit the outstanding water-resistant property of SHOP to protect the NCs from hydrolytic degradation. The PLQY of the composites was maintained at 91% of the initial one after being immersed in water for 31 days. Even after being immersed in water for six months, the composites still retain bright green emission. A white light-emitting diode (WLEDs) device was prepared by combining green-emitting composites and red-emitting K2SiF6:Mn4+ phosphors with a blue LED chip. The device exhibits a high luminous efficiency of 50 lm/W and a wide color gamut (127% of the National Television System Committee and 95% Rec. 2020). This work provides an alternative approach to solve the challenging stability issue of perovskite QDs; therefore, it has a positive implication for their practical application in liquid crystal display backlights.
Quenching and Reliability in Mn4+-Based Fluoride Phosphors
Authors: Setlur Anant A
Published: December 2020

Over the past seven years, Mn4+-based fluoride phosphors have become one of the standard red phosphors, especially for LCD backlighting. The development of these materials has come with some synthesis and compositional challenges, especially with respect to the phosphor reliability under various accelerated testing and operating conditions. In this presentation, we will primarily discuss some of the steps and modifications that has led to high reliability. In addition, while the mainstay phosphor in this family, K2SiF6:Mn4+, has excellent quantum efficiency at high temperature, other phosphors within the Mn4+-based fluoride phosphor family have much stronger quenching. We also discuss potential reasons for this difference and implications for practical use in LCD backlighting and general illumination LEDs.
High-Efficiency Moisture-Resistant Narrowband Emitting Perovskite Nanocrystals for Wide Color Gamut Display
Authors: Wang Jing , Xuan Tongtong , Lou Sunqi , Huang Junjian
Published: December 2020

All inorganic perovskite nano-crystals are promising materials in advanced display devices. Unfortunately, they have poor moisture resistance, which is one of the main technical bottlenecks that greatly limit their actual application in the future. Here we introduce several strategies for improving moisture resistance proposed by our group in recent years, including the organic compound coating or organic framework compound nesting and homogenous inorganic compound core-shell coating. Multi-color high-efficiency perovskite nanocrystals with excellent moisture resistance properties were succefully prepared based on the above strategies. Also, we successfully demonstrate the fabrication of the white LEDs with wide color gamut using the as-synthesized perovskite nanocrystals with improved moisture resistance.
Multidimensional Perovskite Cesium Lead Halide Nanocrystal for Light Conversion Applications
Authors: Im Won Bin
Published: December 2020

Zero-dimensional (0D) inorganic perovskites have recently emerged as a new class of material for optoelectronics owing to their outstanding excitonic properties, strong photoluminescence (PL), and high exciton binding energy. These materials have a unique quantum-confined structure, which originates from the presence of fully isolated octahedra exhibiting single-molecule behavior. In this work, we probed the optical behavior of single molecule-like isolated octahedra in 0D Cs4PbX6 (X = Cl, Br/Cl) perovskite through isovalent (Mn2+) doping at Pb sites. The incorporation of Mn2+ stabilizes the Cs4PbX6 phase by lowering the symmetry of PbX6 via enhanced octahedral distortion (preventing the high-symmetry cubic CsPbX3 impurity) and controlling the compositional variation of Cs-Pb salts. This strategy enabled the synthesis of CsPbX3 free Cs4PbX6 nanocrystals. A high PL quantum yield (QY) of Mn2+ emission was obtained in the colloidal (29%) and solid (21%, powder) forms. These performances can be attributed to structure-induced confinement effects, which enhance the energy transfer from localized host exciton states to Mn2+ dopant within the isolated octahedra of 0D perovskite. The present findings could lead to designing of low-dimensional perovskites as efficient light emitters with photo and chemical stability for high-performance optoelectronic devices.
Stable and Efficient Transfer-Printing of GaN-Based Microscale Light-Emitting Diode Array for Deformable Displays
Authors: Park Jun-Beom , Ha Jun-Seok , Jeong Tak
Published: December 2020

GaN-based microscale light-emitting diodes (μLEDs) are reported for assembly into deformable displays and repair systems. A stamp-imprinting method that enables large area assembly without spatial limitation is involved in the system, and a selective pick-up method is presented that includes a method for removing detected defective chips through micro-pulsed laser scanning. The photosensitive functional material, which is an accepted layer for the stable imprinting of chips, is determined by controlling the adhesion. In addition, selective pick-up and adhesion-controlled functional materials allow the implementation of defect-free displays through two pick-and-place cycles. Displays and related systems fabricated with this method can offer interesting optical and electrical properties.

Figure 1
Optimized SrVOx/Ag/SrVOx Multilayers As High Transparency Electrodes for UV Optoelectronic Devices
Authors: Kim Su-Kyung , Seong Tae-Yeon
Published: December 2020

GaN-based ultraviolet LEDs are important for their use in various applications such as space-to-space communications, curing, sterilization, etc. For these applications, the development of high-efficiency UV LEDs is needed. However, UV LEDs show relatively lower external quantum efficiencies than visible LEDs. To enhance the performance of UV optoelectronic devices by increasing light extraction, it is essential to develop p-type transparent conducting electrodes (TCEs) with high transparency in the UV region. Sn-doped indium oxide (ITO) is typical material for transparent conducting electrodes (TCEs) because of its low resistivity (< 10-4 Ω·cm) and high transmittance (> 85%) in the visible range. However, ITO has large light absorption below 400 nm wavelength and the poor electrical properties when it is thinner than 50 nm. Thus, there is a need for alternative TCEs that have high transmittance in the UV light region (200 – 400 nm). Extensive studies have been conducted to develop TCEs such as graphene, CNT, metal nanowire, and oxide/metal/oxide (OMO) multilayer. Among them, the OMO structure can be a good candidate for TCEs, because the mid-metal layer acts as a conduction path and the oxide layers can lead to zero reflection conditions.

In this study, we used SrVOx (SVO) films to develop UV-transparent multilayer and investigated their structural, optical, and electrical properties as functions of SVO and Ag thickness by means of UV-VIS spectrometer, Hall-measurement, and transmission electron microscopy. Unlike ITO film, SVO film exhibited high transmittance (> 80%) up to 320 nm. It was shown that the SVO film showed larger optical bandgap (4.3 eV) than that of ITO (3.7 eV). For the OMO structures with Ag thickness of 15 nm, the sheet resistance was in the range 2.76 – 3.15 Ω/sq, depending on the SVO thickness. In particular, SVO (25 nm)/Ag (15 nm)/SVO (25 nm) sample exhibited the highest Haacke’s figure of merit (FOM) of 144.5 x 10-3 Ω-1 where the average transmittance of the OMO was 91.5% over the 360 – 400 nm wavelength. For the 25 nm-thick SVO-based OMO films, the transmittance and sheet resistance gradually decreased with increasing Ag thickness from 9 nm to 21 nm. For example, the sheet resistance of SVO/Ag/SVO samples was in the range 1.97 – 6.48 Ω/sq and the transmittance varied from 82.6 to 95.5%. Among these samples, SVO/Ag (15 nm)/SVO sample showed the highest FOM value. Rigorous coupled-wave analysis (RCWA) simulations were performed to understand the measured transmittance behavior and zero reflection condition in the SVO/Ag/SVO structure. These results imply that SVO-based OMO structure could be a potentially important TCEs for the fabrication of high-efficiency UV optoelectronic devices.

Figure 1
Electroreduction of Substituted Chlorobenzenes: Understanding Silver Catalysis
Authors: Scherschel Nicholas Franklin , McKenzie Eric C.R. , Couto Petro Ana G. , Peters Dennis G
Published: December 2020

It has been well established that silver electrodes are remarkable catalysts for the reduction of carbon–halogen bonds. The mechanism of electron-transfer (concerted vs. stepwise) seems to be an important aspect for silver electrocatalysis, as catalysis is only observed for concerted electron-transfer processes.1,2 For several years, it has been understood that aliphatic halides prefer concerted transfer, whereas aromatic halides prefer stepwise transfer as a result of their low-lying π* orbitals.3 However, the effect of adding various substituents to the aromatic ring on silver catalysis has not been widely studied. Indeed, preliminary studies performed in our laboratory indicate a deviation from this standard behavior; reduction of 1,2- and 1,3-dichlorobenzene at carbon and silver cathodes display remarkable catalysis at a silver surface. Moreover, these results suggest that silver is only catalytic for the first cathodic process, not the second. As a result, we propose a change in the electron transfer mechanism after the first reduction event, which is believed to be cleavage of a carbon–chlorine bond.

To gain a deeper understanding of factors that influence catalysis at silver cathodes, more specifically for the reduction of substituted aromatic chlorides, the catalytic activity of silver for substituted chlorobenzenes was assessed by means of cyclic voltammetry. Voltammograms of chlorobenzene, 1,2-, 1,3-, 1,4-dichlorobenzene, and 1,2,3-, 1,2,4-, 1,3,5-trichlorobenzene were obtained at both glassy carbon and silver cathodes in dimethylformamide containing 0.10 M tetramethylammonium tetrafluoroborate. Analysis of reduction potentials reveals a moderate to significant positive potential shift, 50–200 mV, for these aromatic halides, which is indicative of electrocatalysis.

References

Isse, A.; Gottardello, S.; Durante, C. Dissociative electron transfer to organic chlorides: Electrocatalysis at metal cathodes. Phys. Chem. Chem. Phys. 2008, 10, 2409–2416.

Isse, A.; Mussini P.; Gennaro, A. New Insights into Electrocatalysis and Dissociative Electron Transfer Mechanisms: The case of Aromatic Bromides. J. Phys. Chem. C 2009, 113, 14983–14992.

Isse, A.A.; Falciola, L.; Mussini, P.R.; Gennaro, A. Relevance of electron transfer mechanism in electrocatalysis: the reduction of organic halides at silver electrodes. Chem. Commun. 2006, 334–346.