bluuebunny/crossref_metadata_2025_split huggingface dataset:
Bimetallic Au-Cu Nanocatalysts with Enhanced Electrochemical CO2 Conversion Activity
Authors: Kauffman Douglas R. , Alfonso Dominic R , Tafen DeNyago 
Published: February 2020

Converting waste CO2 emissions into value added chemicals and fuels is one approach to mitigating greenhouse gases and reducing the carbon footprint of fossil-fuel processes. The electrochemical CO2 reduction reaction (CO2RR) is a promising carbon mitigation strategy because it can operate at high reaction rates and excellent efficiency at ambient conditions using environmentally friendly aqueous electrolytes. Moreover, the ability to couple carbon-free electricity sources (wind, solar, etc.) enables "carbon neutral" or "carbon negative" technologies that convert CO2into value added products without producing additional emissions.
We’ve combined experimental and computational techniques to characterize the catalytic activity of 2-3 nm, bimetallic gold-copper nanoparticles (NPs) for CO2RR. The catalysts showed composition-dependent CO2RR activity that exceeded both the parent gold and copper metals. Interestingly, the bimetallic NPs produced only CO and H2, whereas bulk, polycrystalline copper also produced methane and ethylene. Electrocatalytic activity studies identified 21% Cu NPs as the most active composition with reaction turnover (TOF) frequencies exceeding 60 s-1 and Faradaic Efficiencies approaching 100% FE at -1.0V vs. RHE. The enhanced activity indicates a synergistic effect upon diluting gold atoms in copper. Laboratory and synchrotron-based X-ray spectroscopies were coupled with density functional theory (DFT) to confirm Au-Cu charge transfer within the NPs and identify mixing between near Fermi-level electronic states. We found a strong correlation between the experimentally-determined TOFs and the computationally-predicted binding energy of key reaction products. The superior performance of 21% Cu NPs stemmed from facile desorption of reaction products and extremely weak H binding. This study shows that atomic composition can be used to tune the electronic structure and chemical reactivity of small bimetallic NPs.
CO2 Conversion to Formic Acid in a Three Compartment Cell with Sustainion™ Membranes
Authors: Yang Hongzhou , Kaczur Jerry , Sajjad Syed D. , Masel Richard I 
Published: February 2020

Formic acid generated from CO2 has been proposed both as a key intermediate renewable chemical feedstock as well as a potential energy storage chemical media for hydrogen. In this paper, we describe a novel three compartment electrochemical cell configuration with the capability of directly producing a pure formic acid product in the concentration range of 5 – 20 wt% at high current densities and Faradaic yields. The electrochemical cell employs a Dioxide Materials Sustainion™ anion membrane, allowing for the improved CO2 electrochemical reduction performance. Stable electrochemical cell performance for more than 500 hours has been experimentally demonstrated.
Figure 1 shows the current produced as a function of the cell voltage in a cell with a tin cathode, and IrO2 anode, and deionized water in the middle compartment with no electrolyte added to the water. Notice that one can obtain up to 200 mA/cm² at reasonable cell voltages.
Figure 2 shows how the exit concentration and Faradaic efficiency varies with flowrate. Experimentally, as the Faradaic efficiency decreases as the formic acid concentration rises. Physically, the some of the formic acid is transported to the anode, where it is oxidized leading to formic acid loss. The use of thicker and/or higher MW PSA cation membranes significantly reduces these formate losses.
Figure 3 shows a steady state run. In this case, we are able to maintain an output concentration of 15% formic acid for 500 hours, with no significant change in cell voltage.

Figure 1
Insights in the Catalytic Product Selectivity Trends of Single Site Transition Metal-Nitrogen-Doped Carbons during the Electrochemical Reduction of CO2 to CO
Authors: Ju Wen , Bagger Alexander , Hao Guangping , Varela Ana Sofia , Sinev Ilya , Roldan Beatriz , Kaskel Stefan , Rossmeisl Jan , Strasser Peter 
Published: February 2020

The direct electrochemical reduction of CO2 to fuels and chemicals using renewable electricity has attracted much attention in part due to the fundamental surface catalytic challenges related to activity and selectivity, in part owing to its potential practical importance in CO2 valorization for energy and chemicals application.1 In particular, the selective 2-electron reduction to CO has captivated chemists’ and engineers’ minds for the design of technological CO2-consuming cathodes (CCCs) for use as counter electrodes in the polymer-chloralkaline industries, where fossil-based CO currently still serve as feedstock for production of e.g. polycarbonate and polyurethanes. Work on solid catalysts for the selective electrochemical reduction of CO2 to CO has been limited to the traditional noble metal catalysts such as Ag and Au.2 Here, we present new advances in our understanding of the CO2 reduction process on N-coordinated, non-noble metal-doped nano-porous carbons (M-N-C, M=Mn, Fe, Co, Ni, Cu). These materials are single site catalysts comprising active M-Nx moieties. We investigate the trends in their intrinsic electrochemical reactivity, CO turnover frequencies, and CO efficiencies and show that Fe-N-C and Ni-N-C catalysts outperform Au or Ag. We model the active site by Density Functional Theory (DFT) and arrive at a consistent atomic-scale understanding of their potential-dependent CO and hydrocarbon selectivity. Linking DFT predictions directly with experiments we explain why Fe-N-C and Ni-N-C represent the most cost-effective and energy-efficient carbon-based catalysts for future CO generation inside CCCs.
References:
1 Huei-Ru “Molly” Jhong, S. M., Paul JA Kenis. Electrochemical conversion of CO2 to useful chemicals: current status, remaining challenges, and future opportunities. Current Opinion in Chemical Engineering
2, 191-199 (2013).
2 AS Varela, N. S., J Steinberg, W Ju, HS Oh, P Strasser. Metal-Doped Nitrogenated Carbon as an Efficient Catalyst for Direct CO2 Electroreduction to CO and Hydrocarbons. Angew. Chem. Int. Ed.
54, 10758–10762 (2015).
Effect of a (La,Sr)2CoO4 Phase on the Oxygen Exchange Reaction of Dense and Porous (La,Sr)CoO3 Electrodes
Authors: Kawada Tatsuya , Yashiro Keiji , Hashimoto Shin-ichi , Amezawa Koji 
Published: February 2020

Oxygen reduction reactions on a mixed conducting lanthanum cobaltite, (La,Sr)CoO3: LSC, have been widely investigated both from scientific interest and from the technological importance as a cathode of a solid oxide fuel cell. Since the reaction pathway is not simple in a practical porous electrode, model electrode approaches have been adopted by many researchers. However, the reaction mechanism and rate determining processes may not be always identical between model and porous electrodes, which can mislead the research and development.
The authors have been making efforts to improve oxygen reduction activity of LSC by utilizing the promotion effect of a co-existing Ruddlesden-Popper phase, (La,Sr)2CoO4 : LSC214, which was first observed at the surface of a dense ceramic LSC(1). The concept worked for a dense film electrode but not for a practical porous electrode except when the initial performance of LSC was somehow poor(2). The difference between dense and porous LSC may account for the results. The followings are what we found in the course of the research:
1. The oxygen exchange rate around on LSC was faster around the thermally precipitated LSC214 particles. (1)
2.Application of a porous LSC214 layer on a dense film LSC electrode showed increased reaction rate and decreased activation energy. (3)
3. Application of a porous LSC214 layer on a porous LSC electrode appeared to improve the performance when the base LSC layer had somehow large electrochemical resistance. (2)
4. Well-prepared LSC electrode showed the electrochemical resistance of about 0.5 ohm cm2 in air at 600˚C, and no further improvement was achieved by application of LSC214 layer on the electrode ore mixing LSC214 particles in the electrode.
5. Effective utilization length of a porous LSC electrode evaluated by the electrochemical impedance was thinner than expected from the surface reaction and bulk diffusion constants of dense ceramic LSC.
6. Surface reaction rate of a dense LSC decreased significantly with Sr segregation in the surface/sub-surface layers.
7. Strontium on the surface of LSC film appeared to be removed when it was in contact with porous LSC214 layer. Based on the above observations, the difference of dense and porous LSC electrodes will be discussed in terms of Sr segregation and in the role of LSC214.
References
(1) M. Sase, K. Yashiro, K. Sato, J. Mizusaki, T. Kawada, N. Sakai, K. Yamaji, T. Horita, H. Yokokawa, Solid State Ionics 178(35), 1843 (2008).
(2) K. Yashiro, T. Nakamura, M. Sase, F. Hermes, K. Sato, T. Kawada, J. Mizusaki, Electrochem. Solid State Lett. 12(9), B135-B137 (2009).
(3) T. Kawada, T. Tairako, K. Nagao, A. Unemoto, M. Sase, K. Yashiro, S. Hashimoto, and K. Amezawa, Proc. 16th Intern. Conf. Nanotechnology, Sendai, Japan, August 22-25, 2016
Microstructure Degradation of Solid Oxide Fuel Cells Aged in Stack after Long Operation Time up to 20 000h Using 3D Reconstructions by FIB Tomography
Authors: Zekri Atef , Knipper Martin , Parisi Jürgen , Plaggenborg Thorsten 
Published: February 2020

Solid oxide fuel cells (SOFCs) are getting more importance with their promising future, due to their high-energy conversion efficiency, low-emissions and flexibility of usable fuel type. The performance and the lifetime of SOFCs are keenly dependent on electrode microstructure. In order to recognize the microstructural evolution and its degradation kinetics in SOFC cermet cathodes during long exposure time (up to 20 000 h) under realistic operating conditions ( T= 850 °C, J= 190-250 ), investigations on porous LSM/YSZ cathodes were conducted. The 3D-tomography technique (FIB/SEM) offers extensive data about the microstructures of various cathode aged during different operating times (2 500 h, 15 000 h and 20 000 h), which allows an exact quantification of particle size distribution, phase-connectivity, tortuosity factor and Triple Phase Boundary Length (TPBL). With the increasing operating time no significant 3D microstructural changes in the cathode were noticed in the obtained data. However, additional qualitative X-ray fluorescence measurement, indicate a clear presence of chrome contamination on aged cathodes, which may be the main degradation mechanism in the SOFC cathode.
Keywords: chrome poisoning, long operating time, particle size distribution, SOFC, triple phase boundary, SEM, XRF
Impact of Dislocations on Surface Reactivity of Ceria with Singe Atom Catalysts
Authors: Yildiz Bilge , Sun Lixin 
Published: February 2020

Single-atom catalysts, where atomically dispersed transition metals are anchored at solid surfaces, are a new type of low price, high efficiency and nonflammable catalysts for water gas shift and CO2 methanation, where selective oxidation or reduction is needed. Ceria is one of the most promising support materials for these single-atom catalysts, because of its large oxygen capacity and high ionic mobility. The large amount of available lattice oxygen or oxygen vacancies in ceria is beneficial for selective oxidation and reduction, though the performance of pure ceria is limited by its poor surface exchange properties. Mixing or doping transition metals to ceria can activate the surface of ceria. In particular, transition metals anchored as isolated single atoms are found to be highly active. However, it is challenging to enhance the density of these single atoms due to the strong tendency of metal agglomeration. Having understood how dislocations in oxides can serve as traps for charged point defects in our previous studies, we have aimed here to assess whether we can stabilize single metal atoms at dislocations in ceria.
To this end, first, a wide range of charge states and configurations of Cu defects in a dislocation free ceria model are calculated to elucidate the defect chemistry for Cu ions in bulk ceria. The formation energies of these defects as a function of chemical potential of oxygen and the Fermi energy indicate that the most preferred Cu defect is Cu1+ interstitial. This finding differs from previous calculations in the literature where only a copper vacancy complex is calculated, but is consistent with reported experimental observations. Moreover, the equilibrium Cu defect concentration in ceria is negligible, indicating a low solubility of Cu in bulk ceria.
Second, an edge dislocation model in ceria was constructed. We found that the Cu defect formation energy at the edge dislocation core is 2 eV lower than that in the bulk, indicating a tendency for Cu to enrich at the dislocation compared to the bulk ceria (which has a very low solubility of Cu). More interestingly, and importantly, Cu has a lower oxidation state in the dislocation core than in the bulk. This lower oxidation state is more active for catalytic activity. Both the enrichment of Cu at the dislocation core and the more active oxidation state indicate that dislocations in ceria are beneficial for increasing surface electro-catalytic reaction kinetics with single atom catalysts.
(Invited) Triple Phase Boundary Reaction in a Mixed-Conducting SOFC Cathode
Authors: Amezawa Koji , Fujimaki Yoshinobu , Mizuno Keita , Kimura Yuta , Nakamura Takashi , Nitta Kiyofumi , Terada Yasuko , Iguchi Fumitada , Yugami Hiroo , Yashiro Keiji , Kawada Tatsuya 
Published: February 2020

Solid oxide fuel cells (SOFCs) attract attentions as high-efficiency energy-conversion devices. In order to establish high-performance SOFCs, the slow electrode kinetics, which is often a main cause of the energy loss, should be improved. In present SOFCs, mixed ionic-electronic conducting (MIEC) oxides, such as (La,Sr)CoO3
-δ
and (La,Sr)(Co,Fe)O3
-δ
, are typically used as the cathode materials. In such an MIEC cathode, it is generally believed that electrochemical oxygen reduction reaction takes place mainly at the oxide surfaces (double phase boundary, DPB) and the contribution of the reaction at the electrode/electrolyte/gas interface (triple phase boundary, TPB) is insignificant. Therefore, researches on the kinetics of SOFC cathodic reaction have mostly concerned to investigate the surface reaction on the electrode oxides.
In our previous works, the reaction distributions in MIEC SOFC electrodes were experimentally evaluated by using operando micro X-ray absorption spectroscopy (operando μ-XAS) [1, 2]. For more quantitative and precise investigation of the reaction distribution, we proposed a patterned thin film electrode, which is a kind of the columnar electrode simplifying the microstructures of a porous electrode [2]. However, the patterned thin film electrode in our previous work did not have triple phase boundaries, and it was thus impossible to discuss the contribution of TPB reaction to the total reaction. In this work, a patterned thin film electrode having triple phase boundaries was fabricated. (La,Sr)CoO3-

d
(LSC) was chosen as the model MIEC oxide for SOFC cathodes. The reaction distribution in this new type of the patterned thin film electrode was experimentally determined by using operando μ-XAS, and the results were compared with ones obtained with the old type of the patterned thin film electrode without TPB. It was found the effective reaction area tended to shrink by the introduction of TPB to the patterned thin film electrode. This fact might suggest that the reaction at TPBs in SOFC cathodes is not negligible even when MIEC oxides are used as electrode materials.
References
[1] Y. Fujimaki, T. Nakamura, K. Nitta, Y. Terada, K. Yashiro, T. Kawada, K. Amezawa, to be sumitted.
[2] K. Amezawa, Y. Fujimaki, T. Nakamura, K. D. Bagarinao, K. Yamaji, K. Nitta, Y. Terada, F. Iguchi, K. Yashiro, H. Yugami, T. Kawada, Electrochem. Soc. Trans., 66(2), 129 (2015).
First-Principles Study on Oxygen Reduction Reaction over La1-xSrxCoO3-δ
Authors: Koyama Michihisa , Ishimoto Takayoshi 
Published: February 2020

Electrode kinetics in solid oxide fuel cells are intensively studied to realize the highly efficient system in small- and large-scale applications. As the understandings become deeper, it is important to understand the atomistic-level kinetics of the electrode catalysis as well as to understand the essential nature of catalyst properties. Thus the application of computational chemistry to this issue will be an effective and important option. The author’s research group has theoretically investigated the oxygen reduction reaction kinetics over La1-xSrxCoO3-δ cathode by using density functional theory method and the Ni-YSZ anode by using both density functional theory method [2] and a microkinetic simulation [3]
State-of-the-art results will be introduced in the presentation.
Acknowledgements
Activities of INAMORI Frontier Research Center is supported by Kyocera Co. Ltd. The part of the research is supported by CREST, Japan Science and Technology Agency.
References
[1] T. Ishimoto, K. Sato, T. Tada, K. Amezawa, M. Koyama, ECS Trans., 68(1) (2015) 651.
[2]S.-x. Liu, T. Ishimoto, D. Monder, M. Koyama, J. Phys. Chem. C, 119 (2015) 27603-27608.
[3] H. Kohno, S. Liu, T. Ogura, T. Ishimoto, D. S. Monder, K. Karan, M. Koyama, ECS Trans., 57(1) (2013) 2821-2830.
Promoted Cr-Poisoning Resistance of La2NiO4+
δ-Coated PrBa0.5Sr0.5Co1.5Fe0.5O5+
δ Cathode for Intermediate Temperature Solid Oxide Fuel Cells
Authors: Li Jun , Li Jin , Pu Jian 
Published: February 2020

Solid oxide fuel cell (SOFC) is considered a highly promising technology for clean power and heat generation.1 One critical component in SOFC stack is metallic interconnect, which works as an oxidant/fuel gases separator as well as an electricity conductor.2, 3 However, Fe-Cr based ferritic stainless steels, the most common interconnect alloys, have been reported to cause rapid performance degradation of SOFC cathodes.4 Cr species evaporating from chromia-forming alloys deposit on the cathode, which deteriorates the ORR activity of the cathode. In this study, Cr-poisoning effect on pure layered perovskite PrBa0.5Sr0.5Co1.5Fe0.5O5+
δ cathode and La2NiO4+
δ-coated PrBa0.5Sr0.5Co1.5Fe0.5O5+
δ cathode are investigated. After 20 h aged at 750°C in the presence of SUS430 interconnect and under cathodic current, the performance of pure PrBa0.5Sr0.5Co1.5Fe0.5O5+
δ cathode shows severe degradation, and BaCrO4 product is identified on the cathode surface. However, La2NiO4+
δ-coated PrBa0.5Sr0.5Co1.5Fe0.5O5+
δ cathode shows remarkable tolerance and resistance towards chromium, and the performance of cathode maintains stable during the test. The results indicate that the presence of La2NiO4+
δ coating not only improves the electrochemical performance, but also prevents the cathode from being poisoned by chromium.
References
1. Z. Shao and S. M. Haile, Nature, 431, 170 (2004).
2. J. W. Fergus, Materials Science and Engineering: A, 397, 271 (2005).
3. J. C. W. Mah, A. Muchtar, M. R. Somalu and M. J. Ghazali, Int. J. Hydrogen Energy (2016).
4. S. P. Jiang and X. Chen, Int. J. Hydrogen Energy, 39, 505 (2014).
Oxygen Reduction Reaction at Self-Assembled La-Sr-Co-O Composite PLD Films: Dependence on Temperature and pO2
Authors: Merkle Rotraut , Stämmler Sebastian , Maier Joachim 
Published: February 2020

Several recent investigations indicated that hetero grain boundaries between perovskite La1-xSrxCoO3-
d (P) and Ruddlesden-Popper phase (La1-xSrx)2CoO4+
d (R) may exhibit an accelerated oxygen exchange surface reaction ("TPB effect"), see e.g. [1,2,3]. In the present work, compact La-Sr-Co-O composite films with different fractions of P and R are formed by self assembly on single crystalline YSZ substrates during pulsed laser deposition from a single PLD target [4,5]. The lateral grain size is about 50 nm, and characteristic morphologies can be assigned to the different crystalline phases. In addition to P and R two metastable phases were found: a Co-deficient perovskite phase La0.7Sr0.3Co0.9O3-
d, and a higher order Ruddlesden-Popper phase.
During the self-organized phase separation, different Sr contents are established in P and R, leading for most sample compositions to a Sr accumulation in R and corresponding depletion in P [4,5]. However, during the PLD process the thermodynamic Sr distribution (as determined in [6] for powder samples annealed at 1200 °C) is not fully reached.
Since the oxygen exchange activity of P strongly depends on the Sr content, the knowledge of the actual Sr distribution is required to calculate the correct reference activity for the composite films, i.e. the hypothetical activity in absence of a "TPB effect". At 600 °C, the effective surface rate constant k
q measured by impedance spectroscopy of the self-assembled composite films with an overall La:Sr ratio of 7:3 exceed this reference activity by half to one order of magnitude [7]. This corresponds to a strength of the TPB effect normalized to the triple phase density of 2-9×10-13 cm2/s. Furthermore, the Co-deficient perovskite phase exhibits an increase of k
q by about two orders of magnitude relative to La0.7Sr0.3CoO3-
d(cf. related findings in [8]). The present results are compared to literature, and possible reasons for the increased oxygen exchange activity at hetero grain boundaries are discussed.
[1] T. Kawada, M. Sase, M. Kudo, K. Yashiro, K. Sato, J. Mizusaki, N. Sakai, T. Horita, K. Yamaji, H. Yokokawa, Solid State Ionics 177 (2006) 3081
[2] E. J. Crumlin, E. Mutoro, S.-J. Ahn, G. J. la O’, D. N. Leonard, A. Borisevich, M. D. Biegalski, H. M. Christen, Y. Shao-Horn, J. Phys. Chem. Lett. 1 (2010) 3149
[3] W. Ma, J. J. Kim, N. Tsvetkov, T. Daio, Y. Kuru, Z. Cai, Y. Chen, K. Sasaki, H. L. Tuller, B. Yildiz, J. Mater. Chem. A 3 (2015) 207
[4] S. Stämmler, R. Merkle, B. Stuhlhofer, G. Logvenov, J. Maier, poster at SSI-19 in Kyoto, June 2013
[5] S. Stämmler, R. Merkle, B. Stuhlhofer, G. Logvenov, K. Hahn, P. A. van Aken, J. Maier, submitted (2016)
[6] S. Stämmler, R. Merkle, B. Stuhlhofer, G. Logvenov, J. Maier, ECS Transact. 68(1) (2015) 579
[7] S. Stämmler, R. Merkle, J. Maier, submitted (2016)
[8] A. Takeshita, S. Miyoshi, S. Yamaguchi, T. Kudo, Y. Sato, Solid State Ionics 262 (2014) 378