bluuebunny/crossref_metadata_2025_split huggingface dataset:
Improvements of CoPx Stability By Cathodic Protection in Discontinuous and Interrupted Operations of Alkaline Water Electrolysis
Authors: Kim Ik-Sun , Cho Hyun-Seok , Cho Won-Chul , Kim Sang-Kyung , Joo Jong Hoon , Kim Chang Hee 
Published: February 2020

This paper presents a study of the degradation phenomena of Cobalt phosphides (CoPx), which is attracted as the hydrogen evolution reaction (HER) electrode for alkaline water electrolysis cells(AWEs).1-9 Although the HER activity of CoPx showed 100-fold HER activity enhancements over a nickel catalyst, the kinetic current for the HER after discontinuous and interrupted operations was observed to decrease as shown in Figure 1. During the shut-down of the AWEs, the cathode potential changed from -1.03V to -0.8V (vs. Hg/HgO), which is close to the equilibrium potential of Co oxidation reaction to Co(OH)2. Once Co(OH)2 was formed on CoPx electrode, the kinetic degradation was not recovered even though voltage sweep was applied. We employed cathodic protection to mitigate degradation of the CoPx electrode by shifting the potential of the electrode below the open circuit voltage of Co(OH)2. For the cathodic protection case, Mn was co-deposited with the CoPx electrode as a sacrificial species, which reduces the electrode degradation rate by negative polarization of the electrode. The results showed that by the co-depositing even small amount of Mn into the CoPx electrode could restrain HER performance loss during the repeat of discontinuous operation of the AWEs. That is, controlling the performance loss with the cathodic protection is applicable to ensure the stability of the CoPx electrodes of the AWE system for the integration with renewable powers.
Figure 1. Stability improvements for CoPx HER electrodes in 5 h discontinuous operation by the cathodic protection

Acknowledgements

The authors gratefully acknowledge financial support for this work by the Technology Development Program to Solve Climate Changes of the National Research Foundation (NRF) funded by the Ministry of Science and ICT (NRF-2015M1A2A2074657).

R
eferences

[1] A. Goryachev L. Gao, Y. Zhang, R. Y. Rohling, René. H. J. Vervuurt, A. A. Bol, J. P. Hofmann, E. J. M. Hense, ChemElectroChem 2018, 5, 1230-1239
[2] Q. Liu, J. Tian, W. Cui, P. Jiang, N. Cheng, A. M. Asiri, X. Sun, Angew., Chem. Int. Ed. 2014, 53, 6710–6714.
[3] E. J. Popczun, C. G. Read, C. W. Roske, N. S. Lewis, R. E. Schaak, Angew. Chem. Int. Ed. 2014, 53, 5427–5430.
[4] N. Jiang, B. You, M. Sheng, Y. Sun, Angew. Chem. Int. Ed. 2015, 54, 6251–6254.
[5] Z. Huang, Z. Chen, Z. Chen, C. Lv, M. G. Humphrey, C. Zhang, Nano Energy 2014, 9, 373–382.
[6] F. H. Saadi, A. I. Carim, E. Verlage, J. C. Hemminger, N. S. Lewis, M. P. Soriaga, J. Phys. Chem. C 2014, 118, 29294–29300.
[7] F. H. Saadi, A. I. Carim, W. S. Drisdell, S. Gul, J. H. Baricuatro, J. Yano, M. P. Soriaga, N. S. Lewis, J. Am. Chem. Soc. 2017, 139, 12927–12930
[8] S. Oh, H. Kim, Y. Kwon, M. Kim, E. Cho and H. Kwon, J. Mater. Chem. A, 2016, 4, 18272-18277
[9] J. F. Callejas, C. G. Read, E. J. Popczun, J. M. McEnaney and R. E. Schaak, Chem. Mater., 2015, 27, 3769–3774.

Figure 1
New Avenues to MOF-Derived Cobalt Chalgogenides for Efficient Electrocatalysis
Authors: Das Debanjan , Nanda Karuna Kar 
Published: February 2020

Metal–organic frameworks (MOFs) are a class of porous hybrid solids consisting of metal-containing nodes coordinated with multitopic organic linkers. Recently there has been tremendous interest in the exploration of MOFs and their derivatives for electrocatalysis, however slow charge-transport kinetics often limit the performance. Therefore, making suitable carbon composites would greatly improve their electronic conductivity and subsequently the electrocatalytic activity.
Herein, we have developed two different routes using cobalt imidazolate frameworks (ZIF-67) to design cobalt selenide (CoSe) hybridized with nitrogen doped carbon. The solid-state strategy involves direct conversion of ZIF-67 into CoSe nanoparticles with an average size of ~20 nm encapsulated within N-doped graphitic carbon shells with an average size of 300 nm. Interestingly, this method can easily be extended to similarly synthesize CoTe encapsulated N-doped graphitic carbon cages by simply changing the precursor.
The other method involved the self-templated conversion of ZIF-67 into Co nanoparticles encapsulated N-doped carbon polyhedral and their subsequent transformation into vertically aligned CoSe grafted N-doped carbon sheets via a hydrothermal selenization method. Both, these class of materials so synthesized were found to exhibit excellent electrocatalytic activity towards HER and OER in alkaline medium. It is believed that the methods being developed here may be extended to other transition metal chalcogenides for various applications.
Transient Gas Saturation in Porous Transport Layers of Polymer Electrolyte Membrane Electrolyzers
Authors: Lee ChungHyuk , Lee Jason Keonhag , Zhao Benzhong , Fahy Kieran F. , Bazylak Aimy 
Published: February 2020

Intermittency of renewable energy sources, such as wind and solar, remains as a major barrier to the establishment of a sustainable energy infrastructure (1). Balancing the supply of intermittent energy with demand requires an energy storage technology capable of operating under dynamic conditions. Over the last decade, polymer electrolyte membrane (PEM) electrolyzers attracted much attention as the ideal energy storage technology for renewable energy generators (2). PEM electrolyzers are favorable due to their wide operating current density range (0.6 – 2.0 A/cm2) and rapid response to dynamic changes (3). However, PEM electrolyzers need to become significantly more efficient to become commercially-viable energy storage technology (4).
A major source of inefficiency stems from the undesired accumulation of oxygen gas in the anode porous transport layers (PTLs), which leads to blockage of reaction sites and water transport pathways in the PTL (5). The overpotential associated with this effect is termed mass transport overpotential, and it can contribute up to 25% of the total overpotential (6). Furthermore, mass transport overpotential could increase exponentially at higher current densities (7). Despite the extensive studies on gas transport in the PTL over the last decade, the effect of dynamic operating condition on the transient gas distribution in the PTL remains unknown. Understanding the transient gas transport through the PTL is an important first step for coupling PEM electrolyzer systems with intermittent renewable energy sources.
In this work, we studied gas transport through the PTL under dynamic operating conditions via in operando synchrotron X-ray imaging. Specifically, we used synchrotron X-ray imaging with high spatial (6.5 µm/pixel) and temporal (2.5 frames per second) resolution to quantify the change in gas volume in the PTL under changing current densities. We observed that the gas volume oscillated at a constant amplitude with a similar frequency over a series of repeating step currents (Fig. 1). We also operated the electrolyzer using a real output power profile acquired from a wind turbine. The results provide insights on the transient behaviour of gas distribution in the PTL of PEM electrolyzers coupled with renewable energy sources.
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Figure 1
(Invited) Understanding the Solid-Electrolyte and Electrode Interface via First-Principles Prediction of Potentials and Space-Charge Layers in All-Solid-State Batteries
Authors: Qi Yue , Swift Michael 
Published: February 2020

Solid-state electronic heterojunctions at the solid-electrolyte and electrode interfaces play a critical role in determining ionic transport, and therefore the performance of solid-state batteries and fuel cells. The formation of a “space-charge layer” at the solid electrolyte and electrode interface is often cited as a barrier for ion transport, but a comprehensive first-principles modeling approach is still missing. For solid-state-batteries (SSB), predicting the space-charge-layer formation at the solid-electrolyte-and-electrode interface is even more challenging, as ion insertion and/or reaction with the electrode alters the material and thus band alignments at the interfaces.
In this talk, we established a theoretical framework to predict the interface potential profiles from thermodynamic driving forces [1]. We first assumed the electrochemical potential for Li+ ions reached a constant at the open circuit equilibrium condition, then derived the relationship among the electrostatic potential, the lithium chemical potential, Fermi level, ionization potential, and the work function. This relationship yielded quantitative profiles of the electrostatic potential and electronic energy level alignments across the entire battery. This model complemented direct microscopic and macroscopic simulations by rigorously and simultaneously determining the potential drop, electrostatic dipole, and space-charge layer at the interface.
The application of this model to the Li/LiPON/LixCoO2 system led to the important discovery that the space-charge layer varies with the state of charge (SOC, i.e. Li concentration in LixCoO2). More specifically we predicted that Li+ transferred from LIPON to Li0.5CoO2, but transferred from Li1.0CoO2 to LiPON, this result unified the seemingly contradictory experimental observations. We also predicted that electron transfer caused the interface dipole that can accelerate or impede Li+ flow during the discharge process at the in LixCoO2/LiPON interface, depending on the SOC. This will have a profound impact on the overpotentials and the overall cycling efficiency. An important design rule was suggested that increasing solid electrolytes’ valence band or engineering the interlayer at the interface can overcome the additional barrier caused by the interface dipole.
This modeling framework is general for other solid-state energy storage devices with ionic and mixed conductor interfaces.
[1] Michael W. Swift and Yue Qi, Phys. Rev. Lett. 122, 167701 (2019)
Investigating Phase and Electrical Properties of Calcium-Doped Yttrium Iron Garnet
Authors: Zhang Zheyu , Singh Kalpana , Thangadurai Venkataraman 
Published: February 2020

Literature studies have shown that Ca0.5Y2.5Fe5O12-δ can be a promising cathode material for intermediate temperature solid oxide fuel cell (IT-SOFC) 1. As it exhibits higher electrical and ionic conductivity compared to several other kinds of rare-earth garnets 2. However, given the high resistivity (> 1012 Ω cm at room temperature) and less-explored oxide ion conductivity of its parent phase yttrium iron garnet (Y3Fe5O12, YIG), the effect of calcium doping on the electronic and ionic properties has not been fully studied yet 3. In this work, polycrystalline samples of Ca-doped YIG, with general chemical formula CaxY3-xFe5O12-δ (x=0, 0.1, 0.3, 0.5 and 0.7), were prepared and phase characterized by powder X-ray diffractometer. The oxygen non-stoichiometry was determined by iodometric titration at room temperature and thermogravimetric analysis (TG) at elevated temperatures. Total electrical conductivity was measured by four-probe DC method, and ionic conductivity was calculated by using a modified Hebb-Wagner polarization method. As a result, the ionic transference number was calculated and discussed in relation to its potential applications.
Reference:

Zhong, W., Ling, Y., Rao, Y., Peng, R. & Lu, Y. Calcium doped Y3Fe5O12 as a new cathode material for intermediate temperature solid oxide fuel cells. J. Power Sources
213, 140–144 (2012).

Kharton, V. V. et al. Ionic Transport in Gd3Fe5O12- and Y3Fe5O12-Based Garnets. J. Electrochem. Soc.
150, J33 (2003).

Lehmann-Szweykowska, A., Wojciechowski, R. J., Gehring, G. A. & Tobijaszewski, I. Quasiparticles in Calcium Doped Yttrium-Iron Garnets. Acta Phys. Pol. A
91, 423–426 (1997).
New Electrochemical Synthesis of Fe2TiO5 Photoanode from Metal-Catechol Complexes
Authors: Lee Dongho , Choi Kyoung-Shin 
Published: February 2020

Solar water splitting in a photoelectrochemical cell (PEC) is an attractive approach to generate hydrogen fuel from the abundant solar energy source in a benign and environmentally friendly manner. In this field, TiO2 and Fe2O3 are some of the most extensively studied candidates for use as photoanodes. This is because they consist of naturally abundant elements and are photostable in a wide pH range. However, the major drawback of TiO2 for water splitting is its wide bandgap (3.2 eV). Though Fe2O3 has a narrow bandgap (2.0–2.1 eV), its conduction band minimum (CBM) is still ~200 mV below the water reduction potential. Recently, Fe2TiO5, one of the Fe-Ti-O ternary oxide compounds, has received a considerable interest as a new candidate material to overcome the intrinsic limitations of TiO2 and Fe2O3 while maintaining their strengths. That is, Fe2TiO5 has a favorable bandgap (2.1 eV), chemical robustness, and band edges that straddle the water oxidation and reduction potentials. These properties make Fe2TiO5 a promising photoanode candidate for solar water splitting.
In this presentation, we report a new electrochemical method to prepare a high quality Fe2TiO5 film to systematically investigate its photoelectrochemical properties. The synthesis is based on the interaction between metals and catechol where catechol acts as a chelating agent to solubilize metal ions in a plating solution. When the catechol ligands are removed by applying electrochemical bias, the resulting insoluble metal ions or metal-catechol complexes are deposited onto the FTO surface. Using this method, we deposit a film that contains atomically well mixed Fe and Ti, which are then converted to crystalline Fe2TiO5 after annealing at a moderate temperature. This method also allows facile doping of the Fe2TiO5 film, enabling us to investigate the effect of both bulk and surface composition tuning on its photoelectrochemical properties.
The Role of MnOx and Ni:MnOx Co-Catalysts on the Photoelectrochemical Properties of Ta-O-N Photoanodes
Authors: Irani Rowshanak , Plate Paul , Harbauer Karsten , Bogdanoff Peter , Abdi Fatwa Firdaus , van de Krol Roel 
Published: February 2020

The ever-increasing energy demand and environmental concerns associated with fossil-based fuels have driven the urgent need for sustainable methods to produce chemical fuels. One approach is to perform solar water splitting to produce hydrogen and oxygen. For this purpose, metal oxide-based semiconductor are promising photoelectrode materials due to their relatively high abundance and stability in aqueous solutions. However, metal oxides typically have only slow surface reaction kinetics for water oxidation [1]. To overcome this, water oxidation co-catalysts, such as CoPi, FeOOH, NiFeOx, and MnOx, have been deposited on the surface of numerous metal oxide semiconductors resulting in an improved performance [2-6]. However, the processes at the semiconductor/co-catalyst interface are not yet well understood. Here, we investigate the role of MnOx and Ni:MnOx co-catalysts (thickness < 10 nm) deposited by atomic layer deposition (ALD) on Ta-O-N thin films as a model system. By systematically controlling the partial pressure of NH3, H2 and H2O during post-annealing of Ta thin films, different phases (e.g. Ta2O5, TaOxNy, Ta3N5) with varying valence band maximum positions were successfully prepared. The valence band position of the co-catalyst was also varied by modifying the Ni content. Photoelectrochemical studies with and without hole scavenger reveal that MnOx and Ni:MnOx enhances the photocurrent of Ta-O-N films by a factor of ~ 4, but they do not affect the charge injection efficiency. Instead, the photocurrent increase is likely a result of higher charge separation efficiency. We attribute this to the formation of a band bending at the Ta-O-N/MnOx and Ta-O-N/Ni:MnOx interface, as suggested by the open circuit potential (OCP) and in-line X-ray photoelectron spectroscopy (XPS) data. This is further supported by analyzing Ta-O-N films with varying thickness of the co-catalysts; thicker co-catalysts result in increasing band bending, which correlates with the photocurrent trend as well as the effective carrier diffusion length measured by time-resolved microwave conductivity (TRMC). Finally, the influence of the band offsets between the different photoanode in the Ta-O-N systems and the co-catalysts is discussed.

References

[1] M. De Respinis, Chem. Mater. 2015, 27, 7091.
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[3] W. D. Chemelewski, J. Am. Chem. Soc. 2014, 136, 2843.
[4] J.-W. Jang, Nat. Commun. 2015, 6, 7447.
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[6] A. Ramirez, J. Phys. Chem. C. 2014, 118, 14073.
(Invited) Quantum-Sized Metal Nanoparticles: Bridging Photons and Chemical Transformations
Authors: Sun Yugang 
Published: February 2020

The incompatibility of the energy of a solar photon and the absorption band of a chemical bond prevents the use of light to activate the chemical bond for interesting chemical reactions directly. This presentation will focus on a strategy that enables the efficient coupling of photon energy into chemical bonds to selectively promote the desired chemical reactions. The strategy relies on the generation of hot electrons in quantum-sized metal nanoparticles (QSMNPs, with size < 10 nm) upon photo-illumination and the next efficient injection of the hot electrons into specific chemical bonds. The redistribution of hot electrons in the chemical bonds dissipates the kinetic energy of hot electrons to the chemical bonds, activating the chemical bonds to promote the target chemical reactions. These sequential processes occur in a confined space, representing a series of quantum transitions, i) optical-to-electronic transition in quantum-sized metal nanoparticles (i.e., hot electron generation), ii) electronic-to-electrical transition at the nanoparticle/adsorbate interface (i.e., hot electron injection), and iii) electrical-to-electronic transition in adsorbate molecules (i.e., chemical bond activation).
Selective oxidation of alcohols to aldehydes rather than ketones/acids, a class of important chemical reactions for many industrial processes (e.g., esterification), will be used as an example to highlight the use of QSMNPs for photo-driven selective chemical transformation on platinum group metal (PMG) nanoparticle catalysts, which do not exhibit strong optical absorption. Current practices primarily rely on the use of strong oxidants (e.g., permanganate and dichromate), which are too strong in oxidizing power to prevent over-oxidation of alcohols to ketones. These strong oxidants are usually toxic and have to be removed from the products. In contrast, using ambient oxygen as oxidant is promising to develop an environmentally friendly synthesis strategy that does not require additional separation. However, ambient oxygen is lack of the power to oxidize alcohols at mild temperatures. Therefore, precisely controlling the oxidizing power of the oxidants becomes crucial to promote the selective oxidation of alcohols to aldehydes. The PMG QSMNPs are used to improve the selective oxidation with ambient oxygen by converting the molecular oxygen adsorbed on the catalyst to more active species when the QSMNPs absorb visible light.
(Invited) Benchmarking and Round Robin Testing for Proton Exchange Membrane Water Electrolyzers
Authors: Bender Guido , Carmo Marcelo , Lickert Thomas , Fischer Stefanie , Kadam Pankajkumar , Kang Zhenye , Young James L. , Smolinka Tom 
Published: February 2020

Hydrogen generation via proton exchange membrane water electrolysis is one technology that offers a pathway to store large amounts of electrical energy in the form of hydrogen and enables the integration of renewables into the grid. In order to realize a large market penetration of carbon free hydrogen, produced through PEM water electrolyzers, high capital and operating costs need to be reduced via rapid and successful research and development. This is only possible if a meaningful comparison of performance across laboratories can be achieved and demonstrated. As shown in Figure 1, performance data in the literature of nominally identical systems vary significantly. For example, up to 200 mV deviation was reported at current densities of 1 A/cm2for cells that employed Nafion 117 membranes (Figure 1) [1]. These deviations may originate from using different materials, hardware, test equipment, and operating conditions and procedures. The data confirm an obvious need for standardization of materials and testing protocols to enable such a comparison in the low temperature electrolysis field. Herein, we address this need by reporting on the latest results of a round robin test effort conducted by contributors to the IEA Electrolysis Annex 30. Building upon a method and equipment framework developed and verified in an iterative process, the work recently expanded to include titanium based porous transport layer materials and pressure capable hardware. As shown in Figure 2, initial results with these material sets between laboratories (Figure 2, right) indicate a similar if not reduced deviation between laboratories when compared to the results of the first study (Figure 2, left). The presentation will address the method and thought process selected for harmonizing low temperature electrolysis performance experiments and defining equipment requirements. Latest results and progress of the round robin phase II effort will be reported and discussed and further action summarized.
References:

Bender, M. Carmo, T. Smolinka, A. Gago, N. Danilovic, M. Mueller, F. Ganci, A. Fallisch, P. Lettenmeier, K.A. Friedrich, K. Ayers, B. Pivovar, J. Mergel, D. Stolten, „Initial approaches in benchmarking and round robin testing for proton exchange membrane water electrolyzers”, International Journal of Hydrogen Energy, Vol. 44, Issue 18, 2019, P. 9174-9187, https://doi.org/10.1016/j.ijhydene.2019.02.074

Lickert, M. Carmo, G. Bender, B. Pivovar, T. Smolinka, S. Fischer, J. Young, A. Kang, P. Kadam, A. Fallisch, „Round Robin Testing Activities – Phase 2”, IEA Annex 30 Workshop, Hannover, March 2019

Figure 1