bluuebunny/crossref_metadata_2025_split huggingface dataset:
Investigation on Nitridation Process of SrNbO2N Particles from SrNbO3 for Photoelectrochemical Water Splitting
Authors: Kodera Masanori , Seo Jeongsuk , Katayama Masao , Hisatomi Takashi , Minegishi Tsutomu , Domen Kazunari 
Published: February 2020

Hydrogen produced from water using renewable energy has been investigated as a next-generation energy carrier. Photoelectrochemical (PEC) water splitting is a potential candidate for clean hydrogen production with reasonable cost. Considering utilization of sunlight as an energy source, photocatalysts need to absorb a wide range of visible light. SrNbO2N is an attractive material with an absorption edge of 690 nm and works as a photoanode in a PEC system.1 Photoelectrochemical properties of SrNbO2N particles are greatly affected by their oxide precursors and nitridation conditions. Therefore it is thought that understanding nitridation mechanism is a critical issue to activate PEC properties of oxynitrides. In this study, a novel oxide precursor SrNbO3 and subsequently nitrided SrNbO2N was investigated.
SrNbO3 oxide precursor was synthesized by a solid state reaction under an Ar flow.2 A mixture of Nb and Sr5Nb4O15 which was synthesized by calcining a stoichiometric mixture of SrCO3 and Nb2O5 in advance was heated under an Ar flow at 1773 K for 20 h. Obtained oxide precursors were nitrided under an ammonia flow at 1173 K for different time. Photoelectrodes of synthesized particles were fabricated by particle transfer method.3Nitridation process of oxide precursors were investigated based on X-ray diffraction, diffuse reflectance spectra and elemental analysis as which were combined oxygen-nitrogen analysis with inductively coupled plasma atomic emission spectroscopy (ICP-AES) as well as PEC properties.
SrNbO3 and SrNbO2N nitrided for more than 20 h both had a perovskite-type structure. At the initial stage of nitridation, however, SrNbO3 was separated to Sr5Nb4O15 and SrNbO3-x
N
y
then gradually nitrided to SrNbO2N as shown in Fig. 1. This phase separation appeared due to introduction of N atoms to oxidize Nb4+ to Nb5+. According to progression of nitridation, photocurrent densities improved. This study shows the effect of oxide precursor on the PEC performance of resulting oxynitrides. Nitridation mechanism affected by the crystal structure of oxide precursors is also discussed.
1) M. Kodera, H. Urabe, M. Katayama, T. Hisatomi, T. Minegishi and K. Domen, J. Mater. Chem. A, 2016, 4, 7658–7664.
2) X. Xu, C. Randorn, P. Efstathiou and J. T. Irvine, Nat. Mater., 2012, 11, 595–598.
3) T. Minegishi, N. Nishimura, J. Kubota and K. Domen, Chem. Sci., 2013, 4, 1120–1124.

Figure 1
Investigating the Plasmonic Hot-Carrier Injection Mechanism for CO2 Reduction Using Nanostructured Ag Catalysts
Authors: Kim Youngsang , Creel Erin , Corson Elizabeth , Qiu Fen , Urban Jeffrey J , McCloskey Bryan D , Kostecki Robert 
Published: February 2020

Converting CO2 into hydrocarbons or other liquid fuels and leveraging solar energy to do so are of great importance as an alternative energy source and as a potential pathway to slow climate change. However, CO2 reduction reactions suffer from high overpotentials and poor selectivity. Recently, localized surface plasmon resonance (LSPR) was suggested as a way to overcome these challenging barriers [1-3]. Nanostructured catalysts absorbing visible light at their plasmon frequency can excite hot carriers which can be transferred directly or indirectly into the molecular orbitals of adsorbates. This unique charge injection mechanism along with the ability to tune the plasmon frequency over a wide range of energies may allow plasmonic photocatalysts to unlock a new, unexplored CO2 reduction pathway resulting in increased selectivity and lower overpotentials. Silver (Ag) is a strong plasmonic material and well-known for selectively producing CO [4,5]. In the hopes of taking advantage of the plasmonic properties to make more reduced products on Ag, we have developed Ag nanopyramid arrays, resulting in strong plasmonic and catalytic behaviors. Photocurrent measurements were performed on the plasmonic nanopyramid catalysts in aqueousNaClO4 saturated with either CO2 or Ar. The photocurrent is greatly enhanced in the presence of CO2, and shows ‘resonant-like’ behavior at a specific potential (-1.1 V vs. RHE). In Ar-saturated electrolyte, the photocurrent was drastically reduced and no characteristic feature of photocurrent was observed. This result indicates that the hot carriers created by LSPR react specifically with CO2 molecules or other CO2 reduction intermediates. By measuring incident photon to current efficiency (IPCE), we find that the hot-carrier transfer mechanism can be modulated as a function of applied potentials. Further, we discuss the differences in product distributions measured with a gas chromatograph (GC) and high performance liquid chromatography (HPLC) under light illumination and in the dark.
References
[1] A. O. Govorov, et. al., Nano Today 9, 85 (2014). [2] R. Sundararaman, et.al., Nature Comm. 5, 5788 (2014). [3] S. Mukherjee, et.al., J. Am. Chem. Soc. 136, 64 (2014). [4] R. Kostecki, et. al., J. Appl. Electrochem. 23, 567 (1993). [5] T. Hatsukade, et. al., Phys. Chem. Chem. Phys. 16, 13814 (2014).
(Invited) Mathematical Modeling of Novel Artificial-Photosynthesis Devices
Authors: Bala Chandran Rohini , Weng Lien-Chun , Ardo Shane , Bell Alexis T. , Weber Adam Z 
Published: February 2020

An artificial-photosynthesis device is a multicomponent system composed of various components including perhaps light absorbers, electrocatalysts, membranes or separators, and electrolytes in a specific system geometry. The overall solar-to-fuel conversion efficiency of such a system depends on the performance and materials properties of the individual components as well as the design of the system. In this talk, we will cover recent modeling of various motifs of such artificial-synthesis systems. In particular, we will examine modeling and experimental results for particle-based devices for solar-hydrogen production as well as vapor-feed devices for solar water splitting and electrochemical carbon-dioxide reduction. Mathematical modeling is ideally suited to examine the various tradeoffs and determine design targets and feasibility.
Z-scheme particle-suspension reactor designs consisting of freely suspended semiconductor particles in an electrolyte to drive solar water splitting could be cost-effective alternatives to produce renewable hydrogen. In this work, we develop a device-scale model to evaluate the effects of coupled light absorption, electrolyte species transport, and reaction kinetics on overall reactor performance and ability to sustain rector operation via diffusion. We also extend this work by numerically investigating particle-scale and -size effects on colloidal stability, light absorption and scattering, and charge-carrier transport across the semiconductor/cocatalyst/electrolyte interface.
Within the Joint Center for Artificial Photosynthesis (JCAP), we utilize continuum-scale modeling of the various components in order to determine design tradeoffs of vapor-feed or gas-diffusion electrode systems. Such systems can provide routes towards optimizing local reaction conditions and overcoming inherent liquid-phase transport limitations for carbon-dioxide reduction as well as solar water splitting to produce hydrogen. For the latter, integrated architectures can be used that are more stable than those in liquid environments. Overall, the functioning of both vapor feed and particle systems will be explored.
(Invited) Recent Advances in III-V Multijunction Semiconductor Photo-Electrochemical Water Splitting
Authors: Deutsch Todd G , Young James L. , Steiner Myles , Döscher Henning , Turner John A 
Published: February 2020

In order to economically generate renewable hydrogen fuel from solar energy using semiconductor-based devices, the U.S. Department of Energy Fuel Cells Technology Office has established technical targets of over 20% solar-to-hydrogen (STH) efficiency with several thousand hours of stability under operating conditions [1]. We have modeled attainable efficiencies of tandem absorbers that, for the first time, considered the absorption of sunlight by water [2]. We used this modeling to identify top and bottom semiconductor bandgap combinations that should be targeted to achieve maximal STH efficiency.
We had to employ several key solid-state technological advances to achieve STH efficiencies exceeding 16%. The first improvement was to increase the device current via a non-lattice-matched 1.2 eV InGaAs grown using the inverted metamorphic multijunction technique developed by NREL’s III-V photovoltaics group. The second modification was to add a thin n-GaInP2 layer to p-GaInP2 to generate a "buried junction", which increased the photocurrent onset or Voc of the device by several hundred mV and enabled 14% STH efficiency. Finally, we increased the top junction photon conversion efficiency by adding an AlInP "window layer", which is commonly used in solid-state PV devices to reduce surface recombination. Through the use of a collimating tube, we measured our devices outdoors under direct solar illumination and verified over 16% STH conversion efficiency. I will also briefly introduce pitfalls of common experimental procedures that can influence the accuracy of measured STH efficiencies, which can be exaggerated for mulitjunction absorbers.
The largest loss in our current system is reflection at the semiconductor/electrolyte interface, so I will address the photon management strategies we use to achieve greater parity between measured efficiency and the theoretical limit. Capturing a significant portion of the ~25% of photons lost to reflection at this interface should allow the realization of devices that exceed 20% STH efficiency.
[1] http://energy.gov/sites/prod/files/2015/06/f23/fcto_myrdd_production.pdf
[2] H. Döscher et al., Energy Environ. Sci. 7, 2951 (2016).
Theoretical Investigations of Electrochemical CO2 Reduction
Authors: Chan Karen , Liu Xin-Yan , Xiao Jianping , Nørskov Jens 
Published: February 2020

The electrochemical reduction of CO2 has the potential to store energy from intermittent renewable sources and to produce carbon-neutral fuels and chemicals1. In recent years, theoretical studies of CO2 reduction have usually applied the computational hydrogen electrode model, which allows for the determination of the energies of reaction intermediates without explicitly treating the potential and the ions in solution2. This thermochemical approach has been shown to correlate well with experimental onset potentials 3,4 and applied to computational screening of new catalysts 5,6. However, an understanding of charge transfer barriers, kinetics, selectivity, and pH effects all require explicit consideration of solvent and charge. In this talk, I will discuss new developments in the explicit treatment of the electrochemical interface, which is based on a simple capacitor model that uses the interfacial charge to obtain barriers at constant potential 7,8. I will then discuss the application of such a scheme to CO2 reduction: the determination of reaction pathways on transition metals, field and solvation effects9,10, the resultant kinetics, and catalyst design criteria.
1 Whipple, D. T. & Kenis, P. J. A. Prospects of CO2 Utilization via Direct Heterogeneous Electrochemical Reduction. The Journal of Physical Chemistry Letters
1, 3451-3458, doi:10.1021/jz1012627 (2010).
2 Nørskov, J. K. et al. Origin of the Overpotential for Oxygen Reduction at a Fuel-Cell Cathode. J. Phys. Chem. B
108, 17886--17892 (2004).
3 Shi, C., Hansen, H. A., Lausche, A. C. & Nørskov, J. K. Trends in electrochemical CO2 reduction activity for open and close-packed metal surfaces. Physical Chemistry Chemical Physics
16, 4720-4727, doi:10.1039/C3CP54822H (2014).
4 Kuhl, K. P. et al. Electrocatalytic Conversion of Carbon Dioxide to Methane and Methanol on Transition Metal Surfaces. Journal of the American Chemical Society, doi:10.1021/ja505791r (2014).
5 Chan, K., Tsai, C., Hansen, H. A. & Nørskov, J. K. Molybdenum Sulfides and Selenides as Possible Electrocatalysts for CO2 Reduction. ChemCatChem
6, 1899-1905, doi:10.1002/cctc.201402128 (2014).
6 Asadi, M. et al. Robust carbon dioxide reduction on molybdenum disulphide edges. Nature communications
5 (2014).
7 Chan, K. & Nørskov, J. K. Electrochemical Barriers Made Simple. J. Phys. Chem. Lett., 2663--2668 (2015).
8 Chan, K. & Nørskov, J. K. Potential Dependence of Electrochemical Barriers from ab Initio Calculations. The Journal of Physical Chemistry Letters, 1686-1690, doi:10.1021/acs.jpclett.6b00382 (2016).
9 Montoya, J. H., Shi, C., Chan, K. & Norskov, J. K. Theoretical Insights into a CO Dimerization Mechanism in CO2 Electroreduction. The journal of physical chemistry letters
6, 2032--2037 (2015).
10 Chen, L. D., Urushihara, M., Chan, K. & Nørskov, J. Electric Field Effects in Electrochemical CO2 Reduction. ACS Catalysis (2016).
11 Liu, X. et al. Understanding trends in CO2 reductin on transition metals. (2016).
Electrochemical Carbon Dioxide Reduction on Cu-Zn Bimetallic Catalysts with Enhanced Ethanol Selectivity
Authors: Ren Dan , Yeo Boon Siang 
Published: February 2020

The electrochemical carbon dioxide (CO2) reduction to ethylene (C2H4) and ethanol (C2H5OH) using renewable energy is a viable method for the production of these commercially vital chemicals. Copper (Cu) based materials are by far the most promising electrocatalysts for this purpose. However, the formation of ethanol using Cu and its oxides is generally less favored as compared to that of ethylene. Here, we demonstrate that the selectivity of CO2 reduction towards ethanol could be systematically tuned by introducing a co-catalyst to generate an in situ source of mobile CO reactant. Cu-based oxides with different amount of Zn dopants (Cu, Cu10Zn, Cu4Zn and Cu2Zn) were prepared via electrodeposition and used as catalysts under ambient pressure in aqueous 0.1 M KHCO3 electrolyte. By varying the concentration of Zn in the bimetallic catalysts, we found that the selectivity of ethanol versus ethylene formation, defined by the ratio of their faradaic efficiencies (FEethanol/FEethylene), could be tuned by a factor of up to ~12.5. Ethanol selectivity was maximized on Cu4Zn at -1.05 V vs. RHE, with a remarkable faradaic efficiency and current density of 29.1% and -8.2 mA/cm2 respectively. The Cu4Zn catalyst was also catalytically stable towards ethanol formation for at least 5 hrs.

Operando Raman spectroscopy revealed that the as-deposited oxides were reduced to the metallic Cu/Zn during CO2 reduction, after which only signals belonging to CO adsorbed on Cu sites were recorded. This indicated that the reduction of CO2 might preferably occur on metallic sites rather than on metal oxides. The importance of Zn as a CO producing site was also demonstrated by performing CO2 reduction on Cu-Ni and Cu-Ag bimetallic catalysts. Thus, the mechanism of ethanol formation was proposed as following: Incoming CO2 molecules could first bind to either Cu or Zn sites, and be reduced to CO. On the Cu sites, CO could be reduced further to CHO or CHx (x=1,2,3) intermediates, while CO adsorbs weakly on Zn sites and is likely to desorb. The desorbed CO could diffuse and spill over onto the Cu sites. The spilled-over CO may then insert itself into the bond between the Cu surface and *CH2, to form *COCH2. Further reduction of *COCH2 will produce acetaldehyde and finally ethanol.
1) Ren, D.; Ang, B. S. H.; Yeo, B. S. ACS Catal.
2016, 8239-8247.
2) Ren, D.; Deng, Y.; Handoko, A. D.; Chen, C. S.; Malkhandi, S.; Yeo, B. S. ACS Catal.
2015, 5, 2814-2821.
3) Hori, Y.; Murata, A.; Takahashi, R. J. Chem. Soc., Faraday Trans. 1
1989, 85, 2309-2326.
4) Calle-Vallejo, F.; Koper, M. T. M. Angew. Chem. Int. Ed.
2013, 52, 7282-7285.
(Invited) From in-Situ to in-Operando Evaluation of SOFC Cathodes for Enhanced ORR Activity and Durability
Authors: Wachsman Eric D. , Cohn Gil , Huang Yi-Lin , Pellegrinelli Christopher 
Published: February 2020

To study the SOFC cathode oxygen reduction reaction (ORR) mechanism and the effects of ambient gas composition on ORR, we used in-situ
18O isotope exchange techniques to probe the exchange of H2O and CO2 with two of the most common SOFC cathode materials, (La0.8Sr0.2)0.95MnO3-x (LSM) and La0.6Sr0.4Co0.2Fe0.8O3-x (LSCF). A series of temperature programmed isotope exchange measurements were performed to comprehensively study the interaction of H2O and CO2 with the cathode surface as a function of temperature, oxygen partial pressure, and contaminant gas concentration. The experimental data are summarized in a Temperature-PO2 diagram to visualize the dominant reactions at each temperature and PO2 for the two cathode materials.
We further report on the development of a novel in-operando
18O isotope exchange technique by modifying our heterogeneous catalysis system for operation and measurement under electrochemical polarization. The system allows ORR investigations under real time, real life, operating conditions. We will present our studies on the effect of cathodic polarization on LSM and LSCF. The studies show the effects of operating voltage, temperature, and oxygen partial pressure on the oxygen exchange coefficient. We will also present our model for the understanding and analysis of the isotope oxygen exchange profiles under in-operando conditions.
(Invited) The Effect of (La,Sr)MnO3 Cathode Surface Termination on Its Electronic Structure
Authors: Kotomin Eugene , Merkle Rotraut , Mastrikov Yuri , Kuklja Maija , Maier Joachim 
Published: February 2020

La1-xSrxMnO3 (LSM) was one of the first perovskites employed as SOFC cathode material and is still used in the form of porous composites with the respective electrolyte [1]. In our previous study [2], we analyzed oxygen adsorption, dissociation and migration on the (001) MnO2-terminated LM surface. In pure LaMnO3, the MnO2 (001) termination was found to be the energetically most stable, however with an increase of Sr doping, the (La,Sr)O termination is predicted to become even more favorable thermodynamically [3].
In this talk, we discuss and compare the results of first principles calculations on the elementary steps (oxygen vacancy formation, O2 molecule and O atom adsorption) of the oxygen reduction reaction on (La,Sr)MnO3 on the two (001) polar terminations – (La,Sr)O and MnO2. The LSM slab calculations were performed using the plane wave VASP computer code with GGA exchange correlation functionals. Properties of oxygen vacancies in different planes from the surface were analyzed. The vacancy formation energy on the MnO2 terminated surface is smaller than that in bulk. In contrast, the vacancy energy on the (La,Sr)O termination is larger, thus strongly reducing the surface vacancy concentration.
Our approach allows for a clear separation of the two distinct effects -- different surface terminations and slab cation stoichiometry (ratio of a number of (La,Sr) ions to Mn that affects the average Mn oxidation state). It is found that oxygen vacancy formation energy in the bulk (slab center) is almost independent of the Mn oxidation state in the region +2.6 to +3.25, whereas it is monotonically decreasing on both surfaces. This surface-to-bulk discrepancy will be discussed. The oxygen atom adsorption energy on the (La,Sr)O termination considerably exceeds that on the MnO2 termination.
As a result, the equilibrium oxygen adsorbate concentration was found to be about two orders of magnitude larger for the (La,Sr)O termination, but on the other hand, the surface oxygen vacancy concentration is smaller by nearly six orders of magnitude. Therefore, the oxygen reduction rate on (La,Sr)O termination is expected to be significantly lower than on the MnO2 termination.
[1]. M. Kuklja, E.A. Kotomin, R. Merkle, Yu.A. Mastrikov, J. Maier, PCCP 15, 5443 (2013).
[2]. Yu.A. Mastrikov, R. Merkle, E. Heifets, E. A. Kotomin, J. Maier, J. Phys. Chem. C 114, 3017 (2010).
[3]. S. Piskunov, E. Heifets, T. Jacob, E. A. Kotomin, E. Spohr, Phys. Rev.B 78, 121406 (2008).
Operando Investigation of the Chemical Interaction of Water Vapor with Ceramic Proton Conductors
Authors: Braun Artur 
Published: February 2020

The protons are the key players in ceramic proton conductors. But they are very elusive and had to detect. I will shows a suite of experiments, ex situ, in situ and operando, where the protons are shown as structural elements at low temperatures where they do not yet constitute charge carriers. They actually constitute OH groups in the crystal lattice. With increasing temperature, the protons participate with the lattice vibrations while and OH-bond breaking takes place at some transition temeprature where the protons become charge carriers. We have observed this on the Y-doped BaZrO3 and BaCeO3 model proton conductors with quasi elastic neutron scattering under ambient and under high temperature high pressure conditions. The phonon modes as determined from high presssure Raman spectroscopy propel the protons and cause a net protonic charge transfer via phonons. The changes in the chemical bond environment were observed with ambient pressre x-ray spectroscopy, particular changes in the oxygen core lecvel spectra and the Ce, Y and Zr resonant valence band spectra under humidified high temperature conditions. We are able to sketch the changes in bond breaking at exactly the temperature where the ptoton conductivty sets on.
[1] Q. Chen, F. El Gabaly, F. Aksoy Akgul, Z. Liu, B.S. Mun, S. Yamaguchi, A. Braun, Observation of 8.238 oxygen vacancy filling under water vapor in ceramic proton conductors in-situ with ambient pressure XPS; Chem. Mater., 2013, 25 (23), pp 4690–4696.
[2] Q. Chen, J. Banyte, X. Zhang, J. P. Embs, A. Braun; Proton Diffusivity in Spark Plasma Sintered BaCe0.8Y0.2O3-δ: in-situ combination of quasi-elastic neutron scattering and impedance spectroscopy; Solid State Ionics 252 (2013) 2–6.
[3] Q. Chen, T.-W. Huang, M. Baldini, A. Hushur, A. Pomjakushin, S. Clark, W. Mao, M. Manghnani, A. Braun, T. Graule, The Effect of Compressive Strain on the Raman Modes of the Dry and Hydrated BaCe0.8Y0.2O3 Proton Conductor, J. Phys. Chem. C, 2011, 115 (48), pp 24021–24027.
Understanding the Cathode Reaction Process for Proton Conducting Intermediate Temperature Solid Oxide Fuel Cells Using Comparison Between BSCF and Other Cathode Materials
Authors: Sun Shichen , Cheng Zhe 
Published: February 2020

Intermediate temperature (~400-600oC) solid oxide fuel cells (IT-SOFC) have drawn growing attention due to the possibility to use cheaper sealing and interconnect materials and the potential to improve system stability and reliability comparing with conventional SOFC that operate at ≥~750oC. For IT-SOFC, proton conducting oxides such as acceptor-doped Ba(Ce, Zr)O3 are often preferred over oxide ion conductors as the electrolyte materials due to their high ionic conductivities and low electronic leakage at intermediate temperature. In this study, the electrochemical behaviors of Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF), which is one of the most active cathode materials for SOFC and shows significant hydration to become proton conductive in humidified atmosphere, is studied in comparison with other oxide (e.g., Pr2NiO4+δ) as well as metal (e.g., Ag) cathode materials at intermediate temperatures of ~350-650oC. In particular, the influences of different testing conditions including cell configuration (cathode symmetrical cells versus full cells), proton conducting electrolyte thickness, cathodic bias voltage, oxygen concentration, and the presence of air impurities such as water vapor (H2O) and carbon dioxide (CO2) on the electrochemical performance are systematically investigated. The implication of the experimental observations especially in terms of the similarity and differences in electrochemical behaviors between different electrode materials to the overall cathode reaction mechanism for proton conducting IT-SOFC is discussed. Finally, the directions for further improving the cathode performance for proton conducting IT-SOFC will be pointed out.