bluuebunny/crossref_metadata_2025_split huggingface dataset:
(Keynote) Oxide Semiconductors, Solid-State Chemistry, and Photoelectrochemistry: A Nexus
Authors: Rajeshwar Krishnan 
Published: February 2020

Solid-state chemistry languished as an esoteric discipline till interest exploded on the so-called high-Tc superconductor materials; oxides were discovered to have unique properties in this regard. Paralleling this was the gradual realization that solid-state chemistry principles underpinned many technologically-important areas such as batteries, supercapacitors, and even solar cells. The culmination of this trend was in the application of solid-state chemistry to the preparation and characterization of electrode materials in photoelectrochemical (PEC) cells.
This perspective talk will examine how solid-state chemistry principles have contributed both to the design and synthesis of photoelectrode materials for PEC applications related to water splitting, CO2 reduction, and environmental remediation. The design of new-generation oxide semiconductors with the correct optoelectronic and bulk/interfacial chemistry characteristics needed to efficiently drive the above reactions will be addressed. The list of material pre-requisites for efficient solar fuels generation or photocatalytic degradation is daunting and it is hardly surprising that a “magic bullet” material has not emerged even after 4 decades of R&D effort. However, these same challenges have attracted researchers drawn from diverse communities including solid-state/device physics, photophysics/photochemistry, colloid chemistry, ultra-fast spectroscopy, classical inorganic chemistry, environmental chemistry and organometallics.
To keep the discussion coherent, only a very limited subset of topics will be addressed in this talk. The progression from binary to ternary, and even quaternary oxides will be examined from the perspective of “band-gap engineering” (a much-maligned word!) and tuning of the interfacial semiconductor surface/fluid energetics. Examples will be drawn from recent research in the speaker’s laboratory and with collaborators.1-4

Acknowledgements

The author thanks his collaborators, particularly, Prof. Csaba Janaky (University of Szeged, Hungary) and the National Science Foundation (CHE- 1303803) for partial funding support.

References

1. K. Rajeshwar, C. Janaky, W-Y. Lin, D. A. Roberts and W. A. Wampler, “Photocatalytically Prepared Metal Nanocluster-Oxide Semiconductor-Carbon Nanocomposite Electrodes for Driving Multielectron Transfer,” J. Phys. Chem. Lett.
4. 3468-3478 (2013) (Perspective).
2. K. Rajeshwar, C. Janaky and A. Thomas, “Photocatalytic Activity of Inorganic Semiconductor Surfaces: Myths, Hype, and Reality,” J. Phys. Chem. Lett.
6, 139-147 (2015) (Viewpoint).
3. C. Janaky and K. Rajeshwar, “The Role of (Photo)Electrochemistry in the Rational Design of Hybrid Conducting Polymer/Semiconductor Assemblies: From Fundamental Concepts to Practical Applications,” Prog. Poly. Sci.
43, 96-135 (2015).
4. K. Rajeshwar, C. Janaky and E. Kescenovity, “Electrodeposition of Inorganic Oxide/Nanocarbon Composites: Opportunities and Challenges,” ChemElectroChem
3, 181-192 (2016).
Interplay of Mass Transfer and Local pH Effects in CO2 Reduction Electrocatalysis
Authors: Raciti David , Wang Chao 
Published: February 2020

Here we report on the study of mass transfer and local pH effects on CO2 reduction by using Cu nanowires as the electrocatalysts. Highly dense Cu nanowires were synthesized by first thermal oxidation of Cu mesh in air, and then reduction by applying a cathodic electrochemical potential or thermal annealing in a reducing atmosphere (see the Methods). Our previous report has shown that the electrochemically reduced (ECR) Cu nanowires are highly active for CO2 reduction, with favorable production of CO and formate at potentials more positive than ‒0.5 V (versus reversible hydrogen electrode; the same potential scale is used in the following discussion) and C2 species (ethanol, ethylene, and ethane) at more negative potentials. In this work, we performed more systematic studies in the high-overpotential region, i.e., potentials more negative than ‒0.5 V, where the mass transport of CO2 and high local pH near the electrode surface are believed to play a significant role in determining the electrocatalytic performance. We aimed to examine the interplay between the mass transfer and local pH effects in the electrocatalysis for CO2 reduction and elucidate their roles in the structure-performance relationships of the high-surface-area nanowire catalysts. The ultimate goal is to explore the optimal electrochemical conditions for CO2 reduction to produce valuable C2 products.
Nanoporous Cu Thin Films for Electrochemical CO2 Reduction
Authors: Pounds Tyler D. , Benn Ellen , Wang Chao , Erlebacher Jonah 
Published: February 2020

Copper catalysts have been extensively researched as catalysts for electrochemical reduction of CO2 (CO2RR) due to their capability to catalyze production of hydrocarbons. The selectivity and activity of Cu catalysts for CO2RR are greatly dependent on the surface structure of the catalysts, and due to this dependence, many forms of Cu (ranging from high quality single crystals to densely populated arrays of supported nanostructures) have been investigated as CO2RR catalysts.
Nanoporous (np) metals, which are produced through selective dissolution of an element from a parent alloy or compound, have inherent properties not typically present in other nanostructured materials that can strongly affect their catalytic properties, including concave surfaces with unique surface structures and open porosity that can cause mass transport effects during catalysis. Nanoporous Au and Ag, have been demonstrated as efficient and selective catalysts for oxidation of CO and reduction of CO2 to CO relative to their bulk metals. However, np-Cu has yet to be comprehensively studied as a CO2RR catalyst. To date, np-Cu has been primarily produced from homogeneous bulk materials which are not well suited for practical use as a potential CO2RR catalyst due to long dealloying treatments required to produce np-Cu that remains stable, without continued dealloying of the non-noble metal, at low CO2RR overpotentials.
In this work, we demonstrate new electrochemical methods for producing fully dealloyed thin films of high-quality, crack-free np-Cu on inert substrates in significantly shorter processing times compared to bulk samples. We examine the activity and selectivity of np-Cu film catalysts produced by several dealloying methods for CO2RR. These results are presented in relation to other Cu catalysts with focus on the catalytic effects of the unique structural properties of np-Cu and the effects of post dealloying treatments to tune pore and ligament sizes of the np-Cu films. In addition to np-Cu films, we discuss how the presented techniques offer a path for production of stable thin films of other nanoporous metals on complex geometries.
This work is supported by the Department of Energy award number DE-SC0008686.
Oxygen Reduction Reaction Catalytic Sites on Carbon-Coated Fe3C Catalyst
Authors: Reda Mateusz , Hansen Heine A. , Vegge Tejs 
Published: February 2020

Proton-exchange membrane fuel cells (PEMFC) are promising chemical-to-electrical energy conversion devices which can potentially replace combustion engine in automobiles. Their commercialization is currently suppressed primarily due to the price of the platinum catalyst for the cathodic oxygen reduction reaction (ORR). Required platinum loading per fuel-cell car is about 10 times higher than for the conventional one [1], which results in a significant contribution to the car price. Therefore, either the platinum loading needs to be drastically decreased, or a stable and active non-precious metal catalyst has to be developed.
Recently, a new type of ORR catalyst composed of carbon-coated iron carbide nanoparticles has been synthesized [2]. It exhibits only slightly lower activity than, and comparable durability to platinum in acidic solutions. It has been suggested that a new ORR catalytic site may have been discovered [3]. In this work we study the catalyst by means of the Density Functional Theory to identify its active sites.
Spin-polarized DFT calculations are performed using the Vienna Ab Initio Simulation Package (VASP) with PAW potentials, BEEF-vdW exchange-correlation functional [4], plane wave cutoff of 400 eV and vacuum layer of 14 Å. The model system consists of Fe3C/carbon interface and a few explicit water molecules to model the liquid environment. The following factors influencing the activity are taken into account: (i) thickness of the carbon layer (single- or multilayer graphene), (ii) defects in the carbon structure, (iii) nitrogen doping, (iv) adsorbate coverage, (v) presence of spectator adsorbates. A few other catalyst structures, which are independent of the presence of iron carbide, but still may exist in the real system, are also studied. These include catalysts with porphyrin-iron moiety embedded in the graphene structure and defective graphene with or without nitrogen doping. As a result, a few possible structures of catalytic sites in the carbon-coated Fe3C catalyst are proposed.
[1] H.A. Gasteiger, D.R. Baker, R.N. Carter, W. Gu, Y. Liu, F.T. Wagner, P.T. Yu, in Hydrogen and Fuel Cells: Fundamentals, Technologies and Applications (D. Stolten, Ed.) Ch. 1 p. 3, Wiley-VCH, Weinheim, 2010.
[2] Y. Hu, J. O. Jensen, W. Zhang, L. N. Cleemann, W. Xing, N. J. Bjerrum, Q. Li, Angew. Chem. Int. Ed., 2014, 53, 3675.
[3] J.-P. Dodelet, R. Chenitz, L. Yang, M. Lefèvre, ChemCatChem, 2014, 6, 1866.
[4] J. Wellendorff, K.T. Lundgaard, A. Møgelhøj, V. Petzold, D.D. Landis, J.K. Nørskov, T. Bligaard, K.W. Jacobsen, Phys. Rev. B, 2012, 85, 235149.
(Invited) Fick's II Law and Deploying Spatially Varying Diffusion Coefficients on Electrodes
Authors: Knoche Krysti L. , Landgren Jeffrey , Leddy Johna 
Published: February 2020

In typical applications of electrochemistry, Fick's second law for diffusion is established with spatially invariant diffusion coefficients. However, when the diffusion coefficient is spatially dependent, D(x), Fick's second law in one dimension, as shown below, introduces opportunities to control transport.
When the diffusion coefficient varies spatially and the solution is quiescent, steady state flux of the diffusant is possible. Films of nonuniform density and viscosity on electrodes provide a matrix to establish domains with spatially varying diffusion coefficients. To explore impacts of D(x) on probe transport through films under voltammetric perturbation, several inquiries were undertaken.
The impact of spatially varying diffusion coefficients is simulated by explicit finite difference for a redox probe moving through a graded film on an electrode. Voltammetric morphologies vary with the structucture of the gradient. Sigmoidal voltammograms result as cyclic voltammetric scan rate slows.
Graded diffusion coefficients are established on electrodes by modification of density gradient polymers such as Ficoll^{®}. Sigmoidal voltammograms with limiting currents independent of scan rate are observed at slow scan rates, consistent with steady state transport in a domain where the diffusion coefficient is spatially varying.
Ion exchange polymer Nafion cocast with a graded density polymer similarly impacts transport of a probe through the graded Nafion film and sigmoidal voltammograms are observed.
The interplay between Fick's second law with spatially varying diffusion coefficients; simulation of voltammetry with D(x); and implementation of graded diffusion coefficients on electrode modification by Ficoll and by Ficoll-Nafion composites will be presented.

Figure 1
(Invited) In Situ FTIR Reflection Spectroscopy and Its Applications
Authors: Zhou Zhi-You , Li Jun-Tao , Jiang Yan-Xia , Sun Shi-Gang 
Published: February 2020

In situ FTIR reflection spectroscopy (in situ FTIRS) can probe both surface and solution species involved in electrochemical reactions, and is powerful in characterization of interfaces and studies of electrode reaction mechanism at a molecule level. This communication reviews our recent progresses in developing in situ FTIR reflection spectroscopy, including microscope FTIR reflection spectroscopy (MFTIRS), step-scan fast time-resolved FTIR reflection spectroscopy (SSTRFTIRS) and the surface combinatorial analysis method by combining the MFTIRS with an individually addressable array of microelectrodes. Selected examples of using these advanced techniques in studies of electrochemical reactions such as electroadsorption of different molecules, electrocatalytic reactions of different fuels and amino acids, as well as interfacial reactions involved in a lithium ion battery will be demonstrated. In addition, the first infrared free electron laser and spectroscopic facilities for energy chemistry studies built up in China will be briefly introduced.

Acknowledgement: The study was supported by NSFC (21621091, 21327901)

References:

Ye, J.Y., Jiang, Y.X., Sheng, T., Sun, S.G. Nano Energy, 2016, 29, 414.

Huang, L., Sun, J.Y., Cao, S.H., Zhan, M., Ni, Z.R., Sun, H.J., Chen, Z., Zhou, Z.Y., Sorte, E.G., Tong, Y.Y.J., Sun, S.G. ACS Catal., 2016, 6, 7686.

Liu, H.X., Tian, N., Ye, J.Y., Lu, B.A., Ren, J., Huangfu, Z.C., Zhou, Z.Y., Sun, S.G. Faraday Discus. 2014, 176, 409.

Lin, J.L., Ren, J., Tian, N., Zhou, Z.Y., Sun, S.G. J. Electroanal. Chem. 2013, 688, 165.

Li, J.T, Zhou, Z.Y.; Broadwell I., Sun, S.G. ACR, 2012, 45, 485.

Zhou, Z.Y., Huang, Z.Z., Chen, D.J., Wang, Q., Tian, N. and Sun, S.G. Angew
.
Chem
.
Int
.
Ed
., 2010, 49, 411.

Cheng, Q., Jiang, Y.X., Tian, N., Zhou, Z.Y. and Sun, S.G. Electrochim Acta, 2010, 55 , 8273.

Li, J.T., Chen, S.R., Ke, F.S., Wei, G.Z., Huang, L. and Sun, S.G. J Electroanal Chem, 2010, 649, 171.

Zhou, Z.Y., Chen, D.J., Li, H., Wang, Q., and Sun, S.G. J. Phys. Chem. C, 2008, 112: 19012.

Chen, Q. S., Sun, S.G., Zhou, Z.Y., Chen, Y.X., Deng, S.B. Phys. Chem. Chem. Phys., 2008, 10, 3645.

11. Li, J.T., Chen, S.R., Fan, X.Y., Huang, L., Sun, S.G. Langmuir, 2007, 23: 13174.
In-Situ Gracing Incidence X-Ray Diffraction Cell for Electrochemically Formed Thin Films
Authors: Reither Sabine , Artner Werner , Eder Andreas , Larisegger Silvia , Nelhiebel Michael , Eisenmenger-Sittner Christoph , Fafilek Günter 
Published: February 2020

Grazing incidence X-ray diffraction allows surface sensitive measurements of structural and phase properties of thin solid films. For the characterization of layers formed during electrochemical processes ex-situ techniques are usually employed which has the requirement of a stable structure and composition of the formed films even at atmospheric conditions. For cases where this requirement is not met, in-situ techniques have been developed. Existing designs of in-situ electrochemical cells normally have the disadvantage of high absorption of the beam in the setup and/or brittle window materials. The problem of high absorption of the X-ray in the setup is normally compensated by either using very thin electrolyte films or high intensity radiation as is provided by a synchrotron.
This work presents a novel solution for a grazing incidence X-ray diffraction setup. Backside-illumination of a thin film working electrode applied on a Mylar® foil by magnetron sputtering as support is used to eliminate the problem of high absorption of the X-ray in the setup. It can be used in a three electrode setup and tackles the common problems of gas evolution, voltage drop and non-constant electrolyte bulk solution in in-situ X-ray setups. The setup is tested on the anodic and cathodic formation of Cu2O on copper as an example for X-ray irradiation from a Lab-scale (not synchrotron) source.
Acknowledgement:

This work was jointly funded by the Austrian Research Promotion Agency (FFG, Project No. 854247) and the Carinthian Economic Promotion Fund (KWF, contract KWF-1521/28101/40388).
(Invited) Benefits of Borohydride- and Glyme-Containing Electrolytes for Improved Magnesium Anode Behavior
Authors: Buttry Daniel A , Kumar Ashok 
Published: February 2020

Our group has been involved in studies of the complexation and speciation of Mg2+ in ionic liquids as a means to understand the influence of coordination environment on Mg anode electrochemical behavior.1,2 As part of those efforts, we showed the beneficial effects of borohydride and glyme electrolytes for improved magnesium anode behavior. In this presentation we will focus on the complexation of Mg2+ by glyme components in electrolytes and chemical reactivity of borohydride anion on the reversibility of Mg electrodeposition/dissolution. We show that the lessons learned from such studies of Mg2+ complexation allow the design of new chelating ionic liquids that show markedly improved Mg2+/Mg0 electrochemical behavior compared to the parent TFSI-based ionic liquids. Specifically, we describe reasonable coulombic efficiency and current densities that are achievable through judicious choice of the complexation environment and other chemical features of the electrolyte system.
We also discuss more generally the factors that act to suppress facile Mg electrodeposition/dissolution. We provide experimental verification of some of the means by which these various factors influence both chemical and electrochemical reversibility of Mg anode behavior.

Acknowledgment We acknowledge support from the Army Research Office grant number W911NF-11-1-0432.
References:

“Determination of Mg2+ Speciation in a TFSI--Based Ionic Liquid With and Without Chelating Ethers Using Raman Spectroscopy”, Watkins, T., Buttry, D. A.; J. Phys. Chem. B, 2015, 119(23), 7003-7014. (DOI: 10.1021/acs.jpcb.5b00339)

“Designer Ionic Liquids for Reversible Electrochemical Deposition/Dissolution of Magnesium”, Watkins, T.; Kumar, A.; Buttry, D.A.; J. Am. Chem. Soc.,
2016, 138(2), 641-650 (DOI: 10.1021/jacs.5b11031)
(Invited) Electrodeposition and Development of Mg and Ca Metal Anodes
Authors: Ponrouch Alexandre 
Published: February 2020

Various metals have been used as battery anodes in electrochemical cells ever since the birth of batteries with Volta’s pile and also in the first commercialized primary (Zn/MnO2, Leclanché 1866) and secondary (Pb/acid, Planté 1859) batteries. The idea and prospects of building a technology based on lithium are much more recent, as it required moving away from aqueous electrolytes. However, the first Li-MoS2 cells with specific energy two or three times higher than the current Ni/Cd or Pb/acid cells were withdrawn from the market after safety difficulties were experienced with overheating on recharge related to dendrite growth. As an alternative, secondary Li-ion batteries avoiding the use of lithium metal anodes were commercialized by Sony in 1991. In contrast with Li metal anode, electrodeposition of Mg and Ca does not seem to be plagued with dendrite formation.1,2 In addition to the low cost of the raw materials ($5000/ton, $100/ton and $265/ton for Li2CO3, CaCO3 and MgO2, respectively), such alternative technologies would benefit from high standard reduction potentials (ca. -2.87 V and -2.37 V vs NHE for Ca and Mg, respectively, as compared to -3 V for Li) and high theoretical electrochemical capacities (both gravimetric and volumetric) for the metal electrode, while relying on the 5th (Ca) and 8th (Mg) most abundant elements on the Earth’s crust, respectively, whereas Li is the 25th. These metals are thus interesting candidates as anodes in rechargeable batteries.
Pioneering research work by Aurbach et al.3,4 allowed to conclude that the electrochemical behavior of Ca and Mg metal anodes in conventional organic electrolytes is surface-film controlled, as is the case for Li, but Ca and Mg plating is virtually impossible, which was attributed to the lack of divalent cation transport through the passivation layer (solid electrolyte interphase or SEI). Therefore, research has been focusing on electrolyte formulation in which no SEI is formed. Recently Ca plating and stripping through a stable SEI layer has been demonstrated, setting out the basis for the development of new electrolytes for divalent cation based batteries with high resilience upon oxidation.2 The effect of several factors influencing the Ca deposition/stripping will be presented. Also, the reliability of the so called half-cell configuration in which Mg or Ca pseudo reference and counterelectrodes are used will be discussed and a systematic evaluation of the non-polarizability and stability in the electrolytic environment will be presented for these metal electrodes.

Fig
ure 1. Theoretical gravimetric and volumetric capacities for different anodes: metals and Li-ion.
References:
[1] M. Matsui, J. Power Sources 196 (2011) 7048.
[2] A. Ponrouch, C. Frontera, F. Bardé, M.R. Palacín, Nat. Mater. 15 (2016) 169.
[3]. D. Aurbach, R. Skaletsky, Y. Gofer, J. Electrochem. Soc. 138 (1991) 3536.
[4]. Z. Lu, A. Schechter, M. Moshkovich, D. Aurbach, J. Electroanal. Chem. 466 (1999) 203.

Figure 1
(Invited) Effect of Ni:Fe Stoichiometry and Architectural Expression on the Bifunctional Activity of Nanoscale Ni
y
Fe1–Y
ox
Authors: Ko Jesse S. , Chervin Christopher N. , Vila Mallory , DeSario Paul A. , Parker Joseph F. , Long Jeffrey W. , Rolison Debra R. 
Published: February 2020

The efficient electrocatalysis of reactions involving molecular oxygen determines the performance of many electrochemical energy-storage and -conversion systems. Electrocatalysis of the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) was assessed for a series of Ni-substituted ferrites (Ni
y
Fe1–y
Ox, where y=0.1–0.9) prepared as high surface area nanoarchitectures using epoxide-based sol–gel chemistry. Wet gels were processed using either ambient-pressure or supercritical-fluid drying to render ambigel or aerogel nanoarchitectures, respectively. For this series of Ni
y
Fe1–y
Ox materials, we correlate electrocatalytic activity with Ni:Fe stoichiometry and nanoarchitecture. In order to ensure in-series comparisons, calcining at 350°C in air was necessary to crystallize the respective Ni
y
Fe1–y
Ox nanoarchitectures, which index to the inverse spinel structure for Fe-rich materials (y ≤ 0.33), biphasic for intermediate stoichiometries (0.5 ≤ y ≤ 0.67), and rock-salt for the most Ni-rich material (y = 0.9). For the OER, Ni-rich nanoarchitectures (y > 0.5) exhibit high activity (low overpotential, η), while both the ambigel and aerogel series in the intermediate Ni:Fe stoichiometry range (0.33 ≤ y ≤ 0.67) exhibit a monotonic increase in current density with progressively higher specific surface area. The commensurate OER activity obtained for ambigel and aerogel expressions across a given Ni:Fe stoichiometry highlights the fact that competitive electrocatalytic performance can be achieved without the additional complexity of supercritical-fluid extraction. We also find improved OER performance (η decreases from 390 to 373 mV) for Ni0.67Fe0.33Ox aerogel when heated at 300°C under flowing Ar, owing to an increase in crystallite size (2.7 to 4.1 nm). For the ORR, electrocatalytic activity favors Fe-rich Ni
y
Fe1–y
Ox (y < 0.5) materials. As the Ni-content increases beyond y = 0.5, a two-electron reduction pathway is still exhibited, demonstrating that bifunctional OER and ORR activity may be possible by choosing a Ni
y
Fe1–y
Ox nanoarchitecture that provides high OER activity with decent ORR activity. We find that assessing catalytic activity requires an appreciation of the multivariate interplay between Ni:Fe stoichiometry, surface area, crystallographic phase, and crystallite size rather than basing electrocatalyst selection on Ni:Fe stoichiometry alone.