bluuebunny/crossref_metadata_2025_split huggingface dataset:
Low-Platinum Electrocatalysts for the Oxygen Reduction Reaction at Fuel Cell Cathodes
Authors: Yusuf Maha 
Published: February 2020

Low-Platinum electrocatalysts for the Oxygen Reduction Reaction at fuel cell cathodes

Maha Yusuf+, Drew Christopher Higgins+, John Xu++, Yongmin Kim++, Tanja Graf+++, Thomas D. Schladt+++, Thomas F. Jaramillo+, Friedich B. Prinz++

+

Department of Chemical Engineering, Stanford University, Stanford, California, 94305, USA

++

Department of Mechanical Engineering, Stanford University, Stanford, California, 94305, USA

+++

Volkswagen Group Research, Wolfsburg, 38436, Germany

Low-temperature fuel cells are a promising technology that converts clean and sustainable carbon-free fuels to electrical power. They are suitable for a wide-range of applications including in the transportation sector to grid-scale power generation. One of the major limitations in fuel cell technologies is the efficiency loss at the cathode due to the kinetically sluggish oxygen reduction reaction (ORR).[1] Currently, Pt-based electrocatalysts are the most commonly used catalysts at the fuel cell cathode. However, the scarcity, high cost, and the sluggish ORR kinetics on Pt catalysts drive the need to develop alternative catalytic Pt-based electrocatalysts with better mass activity, and durability to improve the performance and lower the cost of fuel cells.[2-3]

We have developed sputter deposition techniques to fabricate Pt and Pt-alloy based electrocatalysts with reduced precious metal contents. We particularly aim to engineer the structure, surface chemistry, and catalyst-support interactions to achieve high Pt-based mass activities and catalyst durability. In this study, we focus on leveraging the ability of sputter deposition to achieve low-loadings of Pt, with the ability to achieve control over their thicknesses and compositions [4-5]. The sputter deposited Pt-based catalysts are characterized by various techniques such as X-ray photoelectron spectroscopy, X-ray diffraction, scanning electron microscopy, transmission electron microscopy and inductively coupled plasma mass spectrometry. The catalysts are rigorously evaluated for both electrochemical oxygen reduction reaction activity, and durability using the rotating-disk electrode (RDE) technique. Our initial electrochemical testing results are promising, and show mass activities that already exceed the DOE’s 2020 target criteria of 0.44 A/mgPt
6.

References:

Adina Morozan, Bruno Jousselme, Serge Palacin, Energy Environ. Sci., 2011
, 4 (1238-1254).

2. A. Brouzgou, S.Q. Song, P. Tsiakaras, Appl. Catal., B, 2012, 127 (371-388).

Haifeng Lv, Dongguo Li, Dusan Strmcnik, Arvydas P. Paulikas, Nenad M. Markovic, Vojislav R. Stamenkovic, Nano Energy, 2016
, 29 (149-165).

Ryan O’Hayre, Sang-Joon Lee , Suk-Won Cha , Fritz.B Prinz, J. Power Sources,
2002
, 109 (483-493).

Ikwhang Chang, Seunghee Woo, Min Hwan Lee, Joon Hyung Shim, Yuanzhe Piao, Suk Won Cha, Appl. Surf. Sci.,
2013
, 282 (463-466).

U.S. Department of Energy’s Multi-Year Research, Development, and Demonstration Plan 2016. Source: https://energy.gov/sites/prod/files/2016/10/f33/fcto_myrdd_fuel_cells.pdf
Electrochemical Oxidation of Methane on Metal Catalysts
Authors: Ataee-Esfahani Hamed , Chen Dejun , Tong YuYe 
Published: February 2020

Methane is the major component of natural gas and it is considered as an important feedstock in petrochemical industry for producing value-added chemicals. The current industrial processes have low selectivity and require conditions of high temperature and pressure for production of synthesis gas. Therefore, developing new methods for direct conversion of methane to methanol or higher hydrocarbons is necessary. Among the possible game-changing new chemistries, the electrochemical approach has its own advantages for both practical applications and fundamental studies and therefore represents emerging alternative opportunities to the conventional steam reforming and combustion of methane. This is because as electrochemical reactions are driven by either potential or current, they can most likely take place at room or mildly high temperature (<100 °C). Moreover, as the potential or current can be precisely controlled, so can be the electrochemical reactions, which is ideal for in situ mechanistic studies.
Here, we examined several metal-based materials as electrocatalysts for methane electro-oxidation in CH4-saturated aqueous solution using Cyclic Voltammetry and Chronoamperometry methods. The in situ SEIRAS (Surface Enhanced IR Reflection Absorption Spectroscopy) spectra recorded during the Chronoamperometry measurement of CH4 oxidation was used to investigate the intermediates and products on catalyst surface. Our findings confirms that redox chemistry of metals with more than one oxidation state can be utilized to generate active oxygen species (e.g. O2
-, O-, O2
2-) on the surface and facilitate efficient oxidation of methane. We will also compare the electrochemical oxidation of methane on these metal-based catalysts.

References

1. J. Baltrusaitis, I. Jansenc, J. D. Schuttlefield Christus, Catal. Sci. Technol., 2014, 4, 2397-2411.
2. K. Ogura and K. Takamagari, Nature, 1986, 319, 308–308.
3. B. Lee, Y. Sakamoto, D. Hirabayashi, K. Suzuki, T. Hibino, Journal of Catalysis, 2010, 271, 195–200.
(Invited) New Photoanode Materials for Photoelectrochemical Water Splitting
Authors: Yan Yanfa 
Published: February 2020

The direct photoelectrochemical (PEC) splitting of water into hydrogen and oxygen remains a promising route for producing sustainable and renewable hydrogen fuel. PEC devices use both photocathodes for the hydrogen generation (p-type semiconductors) and photoanodes for the oxygen evolution (n-type semiconductors), respectively. From chemical stability concerns, n-type metal oxides and p-type non-metal oxides are the desirable photoelectrodes. Unfortunately, none of the current existing metal oxides have demonstrated high solar-to-hydrogen conversion efficiencies under visible light irradiation, due largely to the fact that most metal oxides have too large bandgaps to effectively absorb the main portion of the sunlight spectrum, i.e., visible light. It is essential to engineer the bandgaps of metal oxides for the applications of PEC water splitting. For p-type photocathodes, most considered materials such as CuInS2, Cu(In,Ga)Se2, CuZnSnS4 (CZTS) and WSe2 have bandgap not wide enough or have poor performance when their bandgaps are widened. In this talk, I will present our recent results on two new PEC materials, one metal oxide (barium bismuth niobate) and one non-metal oxide (copper barium tin sulfide). Through density-functional theory (DFT) and experimental synthesis, we demonstrate a new approach to effectively engineer the bandgap of barium bismuth niobate double perovskites (Ba2Bi1+xNb1-xO6), i.e, varying the composition. We find that the film with the composition of Ba2Bi1.4Nb0.6O6 forms single pure phase and exhibits a nearly direct bandgap of about 1.64 eV, which is small enough to absorb visible light at wavelengths below 756 nm. For copper barium tin sulfide (CBTS), our DFT calculations indicate that it exhibits much better defect tolerance than CZTS. Our preliminary results show a saturated photocurrent of ~11 mA cm-2 were reached at -0.55 V vs RHE in a neutral electrolyte.
(Europe Section Heinz Gerischer Award Address) TiO2-Based Visible Light Photocatalysts Based on Interfacial Charge Transfer Process
Authors: Hashimoto Kazuhito 
Published: February 2020

TiO2 is known as an efficient photocatalyst and is well studied aiming for environmental and energy application. However, TiO2 absorbs only UV light and thus its application had been limited. We recently demonstrated that the surface modification of TiO2 with Cu(II) or Fe(III) nanoclusters produced a new optical absorption in the visible light region. We also found that those surface modified TiO2s show an efficient visible-light-sensitivity in photocatalysis under ambient conditions. Its reaction mechanism can be explained as follows. In the case of Cu(II) nanocluster-grafted TiO2 (Cu(II)-TiO2) for example, electrons in the valence band (VB) of TiO2 are excited to the Cu(II) nanoclusters under visible-light irradiation through an interfacial charge transfer (IFCT) process. The introduction of excited electrons into the Cu(II) nanoclusters leads to the formation of Cu(I) species, which efficiently reduce oxygen molecule through two-electron process. In other words, Cu(II) nanocluster serves as a multi-electron catalyst for molecular oxygen reduction reaction. In addition, during the IFCT process, holes are generated in the deep VB of TiO2 and are used for the decomposition of organic compounds. Thus, these nanocluster-modified TiO2s show very strong oxidation power even under visible light excitation and are promising materials for visible-light-sensitive photocatalytic applications under ambient conditions.
In this lecture, I will review our studies on these IFCT-based TiO2 visible light sensitive photocatalysts, and also show the results of their demonstration tests obtained in some public spaces such as airports and hospitals towards anti-bacterial and anti-virus building material application..
References
1. J. Am. Chem. Soc. 2007, 129, 9596. 2. Chem. Phys. Lett., 2008, 457, 202. 3. J. Phys. Chem. C., 2009, 113, 10761. 4. J. Am. Chem. Soc. 2010, 132, 6899. 5. J. Am. Chem. Soc. 2010, 132, 15259. 6. Chem. Mater. 2011, 23, 5282. 7. J. Phys. Chem. C 2009, 113, 10761. 8. J. Hazard. Mater. 2012, 235-236, 265. 9. ACS Nano 2012, 6, 1609. 10. J. Am. Chem. Soc. 2013, 135, 10064. 11. J. Mater. Chem. A 2014, 2, 13571. 12. ACS Nano 2014, 8, 7229. 13. J. Mater. Chem. A 2015, 3, 17312. 14. J. Phys. Chem. Lett. 2016, 7, 75.
Free Carrier Absorption Assisted Photoelectrochemistry of Silicon
Authors: Lee Benjamin T. -H. , Chiang C. -C. , Hwang Yean-Ren 
Published: February 2020

Free-carrier absorption (FCA) in semiconductor is a process which carriers within conduction or valence band absorbs near-bandgap photon energies to transfer themselves into a higher energy state without generating electron-hole pairs. The energy absorption activates phonon scattering and is generally considered to have undesirable impact on the performance of electronic or optical devices. Here we find, in an electrochemical processing of silicon, the FCA not only has a significate impact on chemical reaction but also contributed to the formation of nanocrystals. By the effect of FCA, nanocrystals form directly on the bulk surface via a rate-limited photo-electrochemistry processing. The formation mechanism of silicon quantum dots as follows: phonon scattering is generated at the photo-absorption site with its nearby atoms from absorbing laser as an hole-countercurrent to reduce redox reaction for dissolving silicon and caused amphoteric defects around the point. To proving the concept, we employed a 0.9 W/cm2, 1310 nm laser that can penetrate through silicon but be absorbed by free-carriers. After anodizing, a brilliant non-etching spot irradiated by the laser appeared on the black surface of P++
silicon substrate. Under He-Cd laser photoexcitation, we found the photoluminescence in the spot was enhanced to 450% than the around porous silicon forming in dark in the vicinity of the spot.
A Highly Sensitive Scanning Electrochemical Microscope Based Method for Studying Enzymatic Proton-Coupled Electron Transfer
Authors: Penhallurick Ryan , Chen Dejun , Tong YuYe 
Published: February 2020

Proton-coupled electron transfer (PCET) reactions, such as those used in the electron transport chain in mitochondria for adenosine triphosphate production, photosynthesis or nucleic acid repair, are often important to proper cellular functioning and survival. Despite this, many of the mechanisms and energetics that govern PCET in proteins are not fully understood and call for further examination. One of the limitations to understanding enzymatic PCET reactions includes the limited availability of sensitive bioelectroanalytical techniques for studying this class of biological redox chemistry. In this presentation, we report a new, highly sensitive approach to probe PCET in biochemical systems through the use of a scanning electrochemical microscope (SECM) based chronoamperometric method.
The proof-of-concept and feasibility measurements were carried out on surface-immobilized cytochrome c oxidase (CcO) and coenzyme Q10 / cytochrome c reductase (bc
1). The proteins were embedded into unilamellar liposomes and then immobilized onto the surface of a gold-coated silicon wafer electrode through integration of the membrane with various gold-bonded tethers or supported lipid membranes, such as long-chain alkanethiol or thiolated-PEG-cholesterol, while in HEPES-Na buffer (at various pH). Upon contact with the surface of the lipid membrane, the platinum ultramicroelectrode SECM tip (~600 nm) was held at a potential (–0.8 V vs. Ag/AgCl) so that diffusion-controlled hydrogen evolution can take place. This reaction current is proportional to the near-tip proton concentration. Upon application of a potential via the gold-coated silicon wafer, or injection of the protein’s native electron donor, such as reduced cytochrome c, a change in the localized proton concentration was measured (shown in Figure 1). The density of immobilized protein on the surface of the electrode was analyzed by AFM in order to normalize current responses. The technique proved to be successful in detecting sub-picoampere current changes in response to proton-pumping of the transmembrane proteins towards the platinum ultramicroelectrode, which could be used for further investigations in the kinetics of other proton-coupled electron transfer proteins.

Figure 1
(Invited) Structure-Activity Relationships for CO and CO2 Electroreduction to C2 Species on Copper
Authors: Calle-Vallejo Federico 
Published: February 2020

The electrochemical reduction of CO2 and CO has been extensively studied in the past few years, as it can convert such harmful oxides into useful compounds such as CH4, C2H4 and CH3CH2OH, using copper-based catalysts (1, 2). However, large overpotentials and low selectivities currently make CO2 electrolyzers commercially inviable, in spite of the low price and relatively high abundance of copper.
Therefore, it is vital to determine the structure-activity relationships that control the product selectivity as well as the reasons for the high overpotentials, so that enhanced catalysts can be rationally designed. In this talk, I will show a reaction mechanism obtained with DFT calculations for CO electroreduction to C2H4, CH3CHO, and CH3CH2OH on Cu(100) electrodes (3, 4). The mechanism proceeds via a (hydrogenated) CO dimer intermediate which can be observed experimentally (5). Based on the structure-activity relationships for Cu catalysts, I will explain the conspicuous preference of (100) terraces towards the production of C2 species such as C2H4 and CH3CH2OH. Importantly, such preference stems from the breaking of adsorption-energy scaling relations on Cu(100) (6).
Furthermore, the proposed mechanism predicts that the late stages of the electroreduction of CO to CH3CH2OH correspond to CH3CHO reduction (3, 4). Evaluating experimentally and theoretically the structure-activity relationships of CH3CHO reduction on various single-crystal Cu electrodes suggests that the selectivity of Cu catalysts towards CH3CH2OH or C2H4 can be tweaked by introducing certain undercoordinated sites (7).

References

1. M. Gattrell, N. Gupta and A. Co, Journal of Electroanalytical Chemistry, 594, 1 (2006).
2. R. Kortlever, J. Shen, K. J. P. Schouten, F. Calle-Vallejo and M. T. M. Koper, The Journal of Physical Chemistry Letters, 6, 4073 (2015).
3. F. Calle-Vallejo and M. T. M. Koper, Angewandte Chemie International Edition, 52, 7282 (2013).
4. K. J. P. Schouten, F. Calle-Vallejo and M. T. M. Koper, Angewandte Chemie International Edition, 53, 10858 (2014).
5. E. Pérez-Gallent, M. C. Figueiredo, F. Calle-Vallejo and M. T. M. Koper, Angewandte Chemie, 129, 3675 (2017).
6. H. Li, Y. Li, M. T. M. Koper and F. Calle-Vallejo, Journal of the American Chemical Society, 136, 15694 (2014).
7. I. Ledezma-Yanez, E. P. Gallent, M. T. M. Koper and F. Calle-Vallejo, Catalysis Today, 262, 90 (2016).
Photoelectrochemical Reduction of Carbon Dioxide at Copper(I) Oxide Modified with Ultra-Thin Polymer Layers
Authors: Szaniawska Ewelina , Bienkowski Krzysztof , Solarska Renata , Rutkowska Iwona Agnieszka , Rajeshwar Krishnan , Kulesza Pawel J 
Published: February 2020

There has been growing recent interest in the development of electrochemical and photoelectrochemical approaches toward effective fixation (reduction) of carbon dioxide. Having in mind a fact that the linear O=C=O molecule is very stable, the CO2 electroreduction requires large overpotentials. In other words, utilization of renewable energy to convert carbon dioxide and water into fuels would require selective CO2-reduction catalysts or efficient and robust semiconductors. There is a need to design unique nano-architectures consisting of the CO2 photocatalyst/semiconductor stabilized with the outer protective layer.
Our study utilizes copper(I) oxide either stabilized with nanostructured titania or ultra-thin films of certain, conducting or redox, polymers (e.g. polyaniline, polypyrrole, PEDOT, poly(4-vinylpyridine)). While in a case of the mixed oxide semiconductor, we have explored formation the p-n heterojunction favoring increase of density of the electron population within the conduction band following deposition of TiO2 over the electrodeposited large crystals of Cu2O, in the latter case we tailor light absorption properties and affect the system’s stability. Upon illumination (from the copper(I) oxide side), charge transport to the reaction sites should be enhanced and the overall electric conductivity (at the catalytic interface) increases. Having in mind both hydrophilic and hydrophobic properties of Nafion over-coating, the outer-most ultra-thin film of Nafion, having properties of both robust (protective) layer and wetting (favoring proton mobility) medium, has been applied. Moreover, the outer-most over-layer of Nafion is expected to facilitate attraction of CO2 (dissolved in the sodium sulfate electrolyte) at the photoelectrochemically active mixed-metal-oxides interfaceSpecial attention has been paid to synthesis, characterization and optimization of the hybrid photocathode, namely the Nafion-protected mixed-oxides (Cu2O-TiO2) and polymer modified copper(I) oxide systems (deposited on fluorine-doped tin oxide covered glass, FTO) toward photoelectrochemical reduction of carbon dioxide.
Theoretical Investigations of Electrochemical CO2 Reduction
Authors: Chan Karen 
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 chemicals[1]. 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 solution[2]. 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 CO2reduction: the determination of reaction pathways on transition metals field and solvation effects[9, 10], the resultant kinetics, and the implications for catalyst design.
1. Whipple, D.T. and P.J.A. Kenis, Prospects of CO2 Utilization via Direct Heterogeneous Electrochemical Reduction. The Journal of Physical Chemistry Letters, 2010. 1(24): p. 3451-3458.
2. Nørskov, J.K., et al., Origin of the Overpotential for Oxygen Reduction at a Fuel-Cell Cathode. J. Phys. Chem. B, 2004. 108(46): p. 17886--17892.
3. Shi, C., et al., Chan, K., Yoo, J., Nørskov, J.K. Trends in electrochemical CO2 reduction activity for open and close-packed metal surfaces. Physical Chemistry Chemical Physics, 2014. 16(10): p. 4720-4727.
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, 2014.
5. Chan, K., et al., Molybdenum Sulfides and Selenides as Possible Electrocatalysts for CO2 Reduction. ChemCatChem, 2014. 6(7): p. 1899-1905.
6. Asadi, M., et al., Robust carbon dioxide reduction on molybdenum disulphide edges. Nature communications, 2014. 5.
7. Chan, K. and J.K. Nørskov, Electrochemical Barriers Made Simple.J. Phys. Chem. Lett., 2015: p. 2663--2668.
8. Chan, K. and J.K. Nørskov, Potential Dependence of Electrochemical Barriers from ab Initio Calculations.The Journal of Physical Chemistry Letters, 2016: p. 1686-1690.
9. Montoya, J.H., et al., Theoretical Insights into a CO Dimerization Mechanism in CO2 Electroreduction. The journal of physical chemistry letters, 2015. 6(11): p. 2032--2037.
10. Chen, L.D., Urushihara, M., Chan, K., Nørskov, J.K. Electric Field Effects in Electrochemical CO2 Reduction.ACS Catalysis, 2016.
11. Liu, X., Xiao, J., Peng, H., Hong, X., Chan, K., Nørskov, J.K. Understanding trends in CO2 reduction on transition metals. Nature Communications, 2017.
Atomistic Simulations of Lithium Ion Mobility in Battery Electrolytes
Authors: Sanders Jeffrey M , Kwak Shaun H , Krauter Caroline M , Gavartin Jacob , Pandiyan Sudharsan , Morisato Tsuguo , Browning Andrea R , Halls Mathew D 
Published: February 2020

Li-ion battery electrolytes are complex solutions composed of solvents, functional additives, and lithium salts. Lithium ion mobility is a central property affecting battery performance. The chemical and physical factors impacting charge transport in complex solutions are not fully understood. Molecular dynamics (MD) simulation is a powerful technique that can provide insight into the critical details impacting ion transport in complex electrolyte solutions. Although several studies have been reported in the literature examining lithium diffusion using MD, limited computational power has restricted simulation time scales to only tens of nanoseconds. Additionally, the simulation results have been hampered due to lack of accurate force-field parameters. In this work, the enhanced predictive reliability for battery electrolytes provided by GPU-accelerated MD using the highly efficient Desmond MD engine [1], along with the quantitative OPLS3 force-field [2] is demonstrated. Using GPU-Desmond/OPLS3, hundreds of simulations can be performed in a production environment with simulation duration in excess of 1 µs. We discuss the impact that simulation duration and force-field has on the accuracy of Li-ion electrolyte simulations.
[1] K.J. Bowers, E. Chow, H. Xu, R.O. Dror, M.P. Eastwood, B.A. Gregersen, J.L. Klepeis, I. Kolossvary, M.A. Moraes, F.D. Sacerdoti, J.K.Salmon, Y. Shan and D.E. Shaw, Proceedings of ACM/IEEE Conference on Supercomputing (SC06), Tampa, Florida November 11-17, 2006.
[2] E. Harder, W. Damm, J. Maple, C. Wu, M. Reboul, J.Y. Xiang, L. Wang, D. Lupyan, M.K. Dahlgren, J.L. Knight, J.W. Kaus, D.S. Cerutti, G. Krilov, W.L. Jorgensen, R. Abel, R.A. Friesner, J. Chem. Theory Comput., 2016, 12 (1), pp 281; DOI: 10.1021/acs.jctc.5b00864