bluuebunny/crossref_metadata_2025 huggingface dataset:
(Keynote) Photoelectrochemistry - Looking Back to the Future
Authors: Uosaki Kohei
Published: February 2020

Photoelectrochemistry and/or semiconductor electrochemistry are of active research fields and thousands of papers in these fields are published annually. They attract many research groups because their potential importance in achieving low carbon society based on renewable energy, i.e., solar energy. Research on photoelectrochemistry was very active in late 1970's and 1980's after the 1st oil crisis following the suggestion by Fujishima and Honda that solar energy may be directly converted to a chemical energy, hydrogen, by using semiconductor/aqueous electrolyte solution/metal cells,1 although semiconductor electrochemistry was studied systematically since 1950's and many reviews and books were published by early 1970's.2-8 ECS organized symposia on photoelectrochemistry/semiconductor electrochemistry in the annual meetings and many proceeding volumes were published.9-14 Major target of the research changed from solar energy conversion to environmental issues and activity declined due to the lack of funding, particularly in the US. There must be reasons why photoelectrochemistry lost supports as solar energy conversion process in 1990's and it is a good time to look back what had been achieved, what were the problems, and are these problems solved.

In this talk, I will try to sum up the results achieved by 1990's and compare them with current activities.

References

1. A.Fujishima and K. Honda, Nature, 238 (1972) 37.

2. M. Green, in Modem Aspects of Electrochemistry, No. 2. Ed. by J. O’M. Bockris, Butterworths, London, 343-407 (1959).

3. J. F. Dewald. in Semiconductors. ACS Monograph, No. 140, Ed . by N. B. Hannay, Reinhold, New York, 727-752 (1959).

4. H. Gerischer. in Adv. Electrochem. Electrochem. Eng., Vol. 1, Ed . by P. Delahay, Interscience, New York, 139-232 (1961).

5. P. J. Holmes. Ed.. The Electrochemistry of Semiconductors, Academic. London, 1962.

6. V. A. Myamlin and Yu. V. Pleskov，Electrochemistry of Semiconductors. Plenum, New York. 1967.

7. H. Gerischer, in Physical Chemistry: An Advanced Treatise, Vol. IXA. Ed. by H. Eyring. Academic. New York. 1970, Chap. 5.

8. S. R. Morrison, Prog. Surf. Sci., 1(1971) 105.

9. PV 77-3 "Semiconductor Liquid-Junction Solar Cells", Ed. A. Heller.

10. PV 82-3 "Photoelectrochemistry: Fundamental Processes and Measurement Techniques", Ed. W. L. Wallace, A. J. Nojik, and S. K. Deb.

11. PV 88-14 "Photoelectrochemistry and Electrosynthesis on Semiconducting Materials", D. S. Ginley, A. Nojik, N. Armstrong, K. Honda, A. Fujishima, T. Sakata, and T. Kawai.

12. PV 93-18 Environmental Aspects of Electrochemistry and Photoelectrochemistry", M. Tomkiewicz, H. Yoneyama, R. Haynes, and Y. Hori.

13. PV 94-19 "Water Purification by Photocatalytic, Photoelectrochemical, and Electrochemical Processes", T. L. Rose, E. Rudd, O. Murphy, and B. E. Conway.

14. PV 97-20 "Photoelectrochemistry", .K. Rajeshwar, L. M. Peter, A. Fujishima, D. Meissner, and M. Tomkiewicz.
(Invited) Solar Fuels and the Important Role of Hydrogen
Authors: Miller Eric L. , Randolph Katie , Peterson David , Stetson Ned T
Published: February 2020

Harnessing the power of the sun to produce energy-rich chemicals from abundant resources offers the promise of providing a plentiful supply of sustainable solar fuels to meet future U.S. energy needs. Opportunities for producing strategically-important solar fuels include hydrogen from water, hydrocarbon fuels from carbon dioxide and hydrogen/water, and ammonia from di-nitrogen and hydrogen/water. Most fuels are currently produced from fossil resources using energy-intense high temperature processes, but advanced processes for fuel synthesis utilizing sunlight in conjunction with air and water can provide critical supplements to help meet near- and longer-term energy demands. Most pathways for solar fuels rely heavily on the availability of an abundant and sustainable hydrogen supply. More generally, synthetic fuels production is an important end-use sector supported by the U.S. Department of Energy’s (DOE) H2@scale initiative. Specific challenges and opportunities for a new generation of solar fuels production will be discussed in the context of H2@Scale as well as other DOE efforts including the Fuels from Sunlight Energy Innovation Hub and the HydroGEN Energy Materials Network Consortium on Advanced Water Splitting Materials.
(Invited) Transient Absorption Spectroscopy of Au/CeO2 Powder
Authors: Ziani Ahmed , Nadeem Amtiaz , Idriss Hicham
Published: February 2020

CeO2 is one of the most studied metal oxide catalysts due to its redox and oxygen transport properties. Transitions occur between the O2p - Ce5d (ca. 6 eV) and the O2p - Ce4f (ca. 3.5 eV) in addition to defect states that can be present between the O2p and Ce4f levels [1],[2]. Very few studies have been conducted by transient absorption spectroscopy (TAS) to probe into the generated charge carrier dynamics[3],[4] to date. The system Au (nanoparticles) / CeO2 has been studied extensively in catalysis because of many reactions such as CO oxidation and ethanol reforming [5],[6]. Because of the plasmonic nature of Au nanoparticles, the interface Au/CeO2 and consequently the charge carriers lifetime and concentration are poised to be affected. In this work, we have studied by pump-probe TAS the lifetime of excited electrons for a series of Au/CeO2 particles (1-4 Au wt. %). Upon excitation with a 480 nm light (2.55 eV), TAS signal in the 700-900 nm range (1.75-1.35 eV) was observed for both CeO2 alone and Au/CeO2. This signal is tentatively attributed to defects states between Ce4f and O2p. Excitation with a 300nm light (4.2 eV) resulted in the appearance of a strong signal in the 400-500 nm (3.1-2.5) in addition to the 700-900 nm. The 3.1-2.5 eV signal might be originating from the Ce4f-O2p recombination process. The presence of gold nanoparticle was found to increase the lifetime of this signal, and this might be linked to an electric field effect. Work in progress in order to extract kinetic information related to the charge lifetime in both regions and further probe into gold plasmon-CeO2 effects.

[1] El Khalifi, M.; Picaud, F.; Bizia, M.; Anal. Methods, 2016, 8, 5045–5052.

[2] Castletona, C.W.M.; Kullgren, J.; Hermansson, K.; J. Chem. Phys., 2007, 127, 244704, 1-11.

[3] Singh, P.; Srivatsa, K.M.K.; Jewariya, M.; Optical Mater., 2016, 58, 1-4.

[4] Pettinger, N. W.; Williams, R.E.A.; Chen, J.; Kohler, B.; Phys. Chem. Chem. Phys., 2017, 19, 3523-3531.

[5] Zhang, S.; Li, X.-S.;Chen, B., Zhu, X.; Shi, C.; Ai-Min Zhu, A.-M.; ACS Catal., 2014, 4, 3481–3489.

[6] Sheng, P.-Y.; Bowmaker, G.A.; Idriss, H.; Appl. Catal. A, 2004, 261, 171-181.
(Invited) In Situ x-Ray Spectroscopies Gear up for Energy Science
Authors: Dong Chung-Li
Published: February 2020

To reduce global greenhouse gas emissions in response to globalization and increasingly strict carbon emission policies, green energy technologies must be developed. Improving the energy conversion/generation/storage efficiency of energy materials has always been a great challenge. Monitoring the atomic/electronic structures close the interface in many important energy materials, such as nanostructured catalysts, artificially photosynthesizing materials, smart materials, and energy storage devices, is of great importance. Understanding and controlling the interfacial electronic structures of energy conversion/storage materials require in-situ/operando characterization tools, of which synchrotron x-ray spectroscopy is one with many unique features. The last decade has witnessed a golden age of operando and in situ synchrotron x-ray spectroscopy for energy materials. X-ray absorption spectroscopy can be used to determine local unoccupied electronic structures while X-ray emission spectroscopy can be utilized to examine the occupied electronic structure. The additional use of resonant inelastic X-ray scattering reveals inter- or intra-electric transitions (d-d or f-f excitation or charge transfer excitation). An emerging scanning transmission x-ray microscopy is a spatial-resolved x-ray absorption spectroscopy which allows us to study the regional electronic structures. The in situ/operando approach enables modifications of atomic/electronic structures of an energy material in an operational environment to be tracked. This presentation will report recent studies and perspectives of the application of in situ/operando synchrotron x-ray spectroscopy to energy materials. It will also introduce Tamkang University (TKU) end-station constructed at the Taiwan Photon Source (TPS) 45A and 27A beamlines for the in situ/operando x-ray spectroscopic investigation of energy materials.
(Invited) Hafnium Oxynitride-Derived Electrocatalyst with High Activity and Stability in Strong Acid for Both Hydrogen Evolution and Oxidation Reactions
Authors: Koel Bruce E.
Published: February 2020

There is a need to decrease our dependence on fossil fuels for producing energy and chemicals, and there is a great interest in using sunlight to drive fuel-forming reactions to produce solar fuels. Solar fuels are important future energy carriers and provide a way to store solar energy, and this makes for a theme that is continuing to move up the global research agenda. Alternatively, with solar and wind power creating increasingly large amounts of electricity, an important question is how can we take advantage of the expanding increase of renewable electricity for catalysis? By applying a voltage in electrocatalysis, we can harness the flow of electrons to form and break chemical bonds, with the remaining challenge to carry out this catalysis with high selectivity and energy efficiency utilizing sustainable electrocatalyst materials.

Renewable H2 technologies could provide alternatives to fossil fuels, and this could be enabled by H2 production from water electrolysis and generation of electricity using H2 fuel cells. However, lack of highly active, stable, earth-abundant electrocatalysts for carrying out the hydrogen evolution reaction (HER) in water electrolyzers and the hydrogen oxidation reaction (HOR) in fuel cells, is a major technical challenge for developing economical polymer electrolyte membrane (PEM)-based electrolyzers and fuel cells. Carrying out these reactions in strongly acidic conditions is desirable because of the advantages of using proton exchange membranes, including compact system design, lack of liquid electrolyte, high current density and energy efficiency, and high gas purity. Recently, we have found a material that demonstrates excellent HER and HOR activities in acids using non-platinum group metal (PGM) catalysts [1]. Processing hafnium oxide with an atmospheric nitrogen plasma forms an acid-insoluble hafnium oxynitride material. We propose that under electrochemical environments this material is transformed into an active oxynitride hydroxide that demonstrates unprecedented high catalytic activity and stability for both HER and HOR in strong acidic media for earth-abundant materials. The zero onset potentials and high current densities demonstrate that this material is a promising alternative to Pt. This opens up new opportunities to develop technologically and economically viable PEM-fuel cells, regenerative fuel cells, and electrolyzers. Furthermore, these results have broad implications for using nitrogen incorporation (e.g. by nitrogen plasma treatment) to activate other non-conductive compounds and films to form new active electrocatalysts.

1. X. Yang, F. Zhao, R.S. Selinsky, Z. Chen, Y.-W. Yeh, N. Yao, C.G. Tully, and B.E. Koel, Nature Communications, 10, 1543−1−8 (2019).
Plasmonic Hot-Carrier-Mediated Solar Energy Conversion and Tunablephotochemical Reactions
Authors: Zhang Yu , Nelson Tammie , Tretiak Sergei , Guo Hua , Schatz George
Published: February 2020

The detailed balance between photon-absorption and energy loss constrains the efficiency of conventional solar cells to the Shockley-Queisser limit. Recent developments of hot-carrier science and technology have stimulated the design of solar cells utilizing hot-carriers, but the efficiency is limited. In this presentation, a theoretical model for hot-carrier solar cells is discussed. Our theoretical model indicates that this cell can significantly improve the absorption of solar radiation without reducing open-circuit voltage. However, a significant fraction of the hot-carriers have energies below the Schottky barrier, which makes the cell suffer low internal quantum efficiency. Despite the limitation in solar energy conversion, the plasmonic hot-carrier can be applied to drive the photochemistry which is impossible in previous thought. Examples of hot-carrier mediated photochemical reaction and how the plasmonic hot-carriers can be employed to tune the chemical reactions will also be introduced. Our non-adiabatic molecular dynamics simulations and time-dependent density functional calculations found the hot-carriers generated from the nanoparticle can transfer to the anti-bonding state of the attached molecule and drive the photochemical reaction. We also found chemical reaction is tunable if the molecule is placed in the center of the plasmonic dimer. The reaction rate can be either suppressed or enhanced depending on the geometry. Thus, our work demonstrates the possibility of tunable photochemistry via plasmonic hot-carriers.
(Invited) Energetic Hole Ejection Involved in Plasmon-Induced Charge Separation: Local Oxidation and an Application to Near IR Photovoltaics
Authors: Tatsuma Tetsu , Nishi Hiroyasu , Ogata Rui , Lee Seung Hyuk
Published: February 2020

Plasmon-induced charge separation (PICS)1-3 involves electron transfer from plasmonic nanoparticles of Au, Ag, or Cu to a semiconductor such as TiO2.1-4 PICS of Ag-TiO2 systems often involve oxidation of Ag to Ag+,5 and that this reaction occurs preferentially at resonance sites, at which optical near fields are localized.6-8 This cannot be ascribed to thermal acceleration of reaction,9 but can be explained in terms of ejection of energetic holes from the nanoparticles as Ag+ ions.

This hole ejection has been investigated further for Au nanocubes on TiO2 by using other reactions; Pb2+ oxidation to PbO2 and pyrrole oxidation to polypyrrole. Au nanocubes on TiO2 show distal mode, in which electron oscillation is localized at the top face of the nanocube, and proximal mode, in which electron oscillation is localized at the bottom face. In the case of Pb2+ oxidation, PICS for the distal mode and proximal mode resulted in PbO2 deposition at around the top face and the bottom face, respectively.10 However, in the case of pyrrole oxidation, both of the distal mode PICS and proximal mode PICS resulted in polypyrrole deposition at the whole surface of the nanocube.

On the basis of those results, we conclude that the localized oxidation and the delocalized oxidation are ascribed to energetic hole ejection mechanism and positive charge accumulation mechanism, respectively. We have applied energetic hole ejection to fabrication of chiral plasmonic nanostructures11 and near IR photovoltaics.12

Y. Tian and T. Tatsuma, J. Am. Chem. Soc., 127, 7632 (2005).

Y. Tian and T. Tatsuma, Chem. Commun., 2004, 1810.

T. Tatsuma, H. Nishi, and T. Ishida, Chem. Sci., 8, 3325 (2017) [review].

E. Kazuma and T. Tatsuma, Adv. Mater. Interfaces, 1, 1400066 (2014).

Y. Ohko, T. Tatsuma, T. Fujii, K. Naoi, C. Niwa, Y. Kubota, and A. Fujishima, Nat. Mater.,
2, 29 (2003).

E. Kazuma, N. Sakai, and T. Tatsuma, Chem. Commun., 47, 5777 (2011).

I. Tanabe and T. Tatsuma, Nano Lett., 12, 5418 (2012).

K. Saito, I. Tanabe, and T. Tatsuma, J. Phys. Chem. Lett., 7, 4363 (2016).

K. Saito, K. Setoura, S. Ito, H. Miyasaka, Y. Mitsuda, and T. Tatsuma, ACS Appl. Mater. Interfaces, 9, 11064 (2017).

H. Nishi, M. Sakamoto, and T. Tatsuma, Chem. Commun., 54, 11741 (2018).

K. Saito and T. Tatsuma, Nano Lett., 18, 3209 (2018).

S. H. Lee, H. Nishi, and T. Tatsuma, Nanoscale, 10, 2841 (2018).
(Invited) Plasmonic Photosynthesis
Authors: Jain Prashant K
Published: February 2020

The photochemical conversion of CO2 into fuels has promise as a strategy for storage of intermittent solar energy in the form of chemical bonds. However, higher-energy-value hydrocarbons are rarely produced by this strategy, because of the kinetic challenges associated with multi-electron, multi-proton, and C–C coupling reactions required for hydrocarbon generation. My talk will make the case that catalysts comprised of plasmonic metal nanostructures may be well-suited to this challenge. With Au, Ag, and Cu nanostructures, it is possible to pair strong light-matter interactions with the ability of these metals to activate CO2. Using Au nanoparticle-based photocatalysts, we have realized green-light-driven synthesis of hydrocarbons from CO2 and H2O, with no applied potential or high temperatures. In this scheme, plasmonic excitation of Au nanoparticles produces a charge-rich environment at the nanoparticle/solution interface conducive for CO2 activation. Alongside, we employ an ionic liquid to stabilize charged intermediates formed at this interface. The outcome is a rich cocktail of C1-C3 hydrocarbon products. Thus, unlike electrochemical CO2 reduction on Au, C-C coupling appears to be prevalent in this light-driven scheme, which suggests that unique reaction pathways are possible under plasmonic excitation. The product selectivity is dependent on the attributes of the exciting light, which opens up avenues for mechanistic understanding and light-mediated control of reactivity.
(Invited) What Did the Metals Know, and When Did They Know It? Femtosecond M-Edge XANES Reveals Short-Lived States in Transition Metal Catalysts
Authors: Vura-Weis Josh
Published: February 2020

X-ray absorption near edge spectroscopy (XANES or NEXAFS) is a powerful technique for electronic structure determination. However, widespread use of femtosecond XANES is limited by the need for scare free-electron laser beamtime. We have developed M2,3-edge XANES, corresponding to 3p→3d transitions, as a reliable technique for measuring the electronic structure of first-row transition metal coordination complexes. The tabletop high-harmonic source provides femtosecond time resolution and 24/7 acessiblility. This talk present the photophysics of three transition metal complexes relevant to photocatalysis: Iron(III) tetraphenyl porphyrin chloride, which relaxes through a ligand-to-metal charge transfer state; Nickel (II) octaethylporphyrin, which relaxes through a 3(d,d) state; and a Co4O4 cubane that catalyzes water oxidation through one of two proposed pathways. We demonstrate M-edge XANES as a powerful new tool for identification of catalytic intermediates.
(Invited) Observing Ultrafast Charge and Spin Dynamics at Photochemical Interfaces
Authors: Baker L. Robert
Published: February 2020

The ability to follow charge and spin dynamics at surfaces is necessary to understand the material properties, which mediate carrier lifetime and determine energy conversion efficiency. To realize this goal, we have constructed an ultrafast tabletop extreme ultraviolet (XUV) light source. Reflection–absorption (RA) spectroscopy using this light source combines the benefits of x-ray absorption, such as element, oxidation, and spin state specificity, with surface sensitivity and ultrafast time resolution, having a probe depth of less than 3 nm and a time resolution faster than 100 fs. This technique is applied to the study of electron trapping and defect-mediated recombination at the surface of NiO. Direct observation of ultrafast electron trapping and subsequent recombination shows that grain boundaries rather than oxygen vacancies are primarily responsible for fast electron-hole pair recombination. This result clarifies the design parameters for NiO water oxidation catalysts by showing that oxygen vacancies, which enhance catalytic activity, have no detrimental effect on carrier lifetime. Rather, carrier lifetime can be dramatically extended by the elimination of near-surface grain boundaries even in the presence of chemically active oxygen vacancies. Finally, we explore several examples where ultrafast spin crossover in semiconductor photocatalysts may play an important role in the material’s photochemical performance.
(Invited) Ultrafast X-Ray Studies of Interfacial Energy- and Charge-Transfer Dynamics
Authors: Gessner Oliver
Published: February 2020

The success of many emerging molecular electronics concepts hinges on an atomistic understanding of the underlying electronic dynamics. Processes evolving on spatial and temporal scales spanning orders of magnitude have to be connected in order to gain a comprehensive understanding of the fundamental dynamics and scaling laws that enable molecular, interfacial, and macroscopic charge and energy transport. Time-domain X-ray spectroscopy techniques have the potential to provide a deeper understanding of electronic dynamics in complex, heterogeneous systems owing to their elemental site specificity and sensitivity to local valence electron configurations.

We present femtosecond to picosecond time-resolved X-ray photoelectron spectroscopy (TRXPS) studies of photoinduced charge transfer dynamics in nanoporous films of N3 dye-sensitized ZnO and bilayer heterojunctions consisting of copper phthalocyanine (CuPc) electron donors and C60 acceptors. For the N3/ZnO system, differential TRXPS line shifts provide site-specific access to the locations of intermittently trapped electrons, interfacial dipoles, as well as charge delocalization and recombination dynamics. For the CuPc/C60 heterojunction, a deeper understanding of the predominant energy transport and charge generation mechanisms is achieved. Contrary to common belief, fast intersystem crossing from initially excited singlet excitons to triplet excitons within the bulk of the donor domain is not a loss channel but the triplet excitons contribute to a significantly larger extent to the time-integrated interfacial charge generation than the initially excited interfacial singlet excitons. The TRXPS data provide direct access to the diffusivity of the triplet excitons in the CuPc donor domain DCuPc = (1.8 ±1.2) × 10−5 cm2/s and their diffusion length Ldiff = (8 ± 3) nm.

Preliminary TRXPS results will be presented for a model system for plasmon-enabled photocatalytic nano-assemblies consisting of a nanoporous TiO2 layer sensitized with gold nanoparticles (Au NPs). Clear differences between the temporal responses of the Au4f and Ti2p photolines are observed, indicating both the interfacial site-specificity of photoinduced electronic dynamics and the capacity of TRXPS to distinguish them.

Figure 1
(Invited) Interfacial Charge Transfer from Si Wafer to Pt
Authors: Yang Ye
Published: February 2020

Interfacial charge transfer from silicon to metal contact plays a key role in silicon-based electronics and optoelectronics. Surprisingly, a direct probe of this interfacial charge transfer process has not been investigated. Here we exploit the transient reflection spectroscopy to interrogate the charge transfer from silicon to platinum. We find that the charge transfer from silicon to Pt is extremely fast, which can also be drastically reduced and eventually shut by inserting silica spacing layers with increasing thickness between silicon and Pt. Our result suggests the possibility to extract carriers from silicon without losing their kinetic energy.
Photoelectrochemical and Surface Analysis of CdSe-Poma Composites on Highly Oriented Pyrolytic Graphite
Authors: Casto Sophia Maria , Dulovic Stephanie , Widera Justyna , Maranowski Bartosz , Strawski Marcin , Szklarczyk Marek
Published: February 2020

Abstract

Over the past decade, semiconductors have been of great interest and are currently found in numerous devices such as: computers, cell phones, and medical equipment. Semiconductors are the integral component of solar cells, converting solar energy into electricity.

This research studies the photoactivity and stability of semiconductors cadmium selenide (CdSe) and poly(o-methoxyaniline) (POMA) deposited on highly oriented pyrrolic graphite (HOPG). The CdSe-POMA deposits were electrochemically deposited on HOPG using cyclic voltammetry. The composites were deposited in the following order: (1) CdSe before POMA (CdSe/POMA), (2) POMA before CdSe (POMA/CdSe), and (3) CdSe and POMA simultaneously (CdSe+POMA). For the sequential depositions, the deposition of CdSe and POMA were performed sequentially so that the surface consisted of the desired hybrid. The CdSe layer was deposited for 20 cycles from a solution of 5 mM CdSO4 and 1 mM SeO2 in 0.1 M HClO4. The polymerization of POMA was accomplished by electrochemical cycling for 5 cycles from a 0.06 M o-anisidine solution in 0.1 M HClO4. The deposition of CdSe+POMA was performed by electrochemical cycling for 20 cycles in a solution of 5 mM CdSO4, 1 mM SeO2, and 0.06 M o-anisidine in 0.1 M HClO4.

The photoactivity and stability of the deposits were studied using open circuit potentiometry (OCP), cyclic voltammetry (CV), and chronoamperometry (i/t) in 0.1 M Na2SO3. The CdSe/POMA deposit had the greatest photopotential at around 200 mV while POMA/CdSe and CdSe+POMA presented lower photopotentials at 30 mV and 14 mV respectively. Chronoamperometric studies found that CdSe/POMA had the greatest photocurrent density of 17 µA/cm2 compared to 0.05 µA/cm2 for POMA/CdSe and 0.42 µA/cm2 for CdSe+POMA. Photoelectrochemical measurements suggest that POMA/CdSe and CdSe+POMA deposits were less stable than CdSe/POMA. X-ray photoelectron spectroscopy (XPS), Scanning Electron Microscopy (SEM), and Atomic Force Microscopy (AFM) were used to analyze the surface. The surface morphology and chemical composition of the deposits were studied before and after photo-studies to observe the degree of degradation after the sample was exposed to light. Measurements found that the POMA/CdSe and CdSe+POMA deposits degraded more than CdSe/POMA, suggesting that depositing the polymer over the CdSe film might be necessary in reducing the degree of degradation when the sample is exposed to light.
PVDF/SiO2-TiO2 Photocatalytic Membranes for Water Treatment
Authors: Zhang Xinrong
Published: February 2020

Polymeric membranes have been widely used for many kinds of wastewater treatment. However, the fouling of membranes decreases their permeability. TiO2 is widely used for water treatment because its photocatalytic properties, stability, availability and desirable hydrophilicity properties. In the recent years, many researchers have investigated the possibility of coupling polymeric membrane filtration technology and TiO2 photocatalysis to improve membrane performance by reducing fouling and increasing hydrophilicity. Because TiO2 particles on the membrane surface not only increase membrane hydrophilicity, but also create a photocatalytic property, formation of cake layer and blocking of membrane pores are prevented. So, the polymeric membranes with TiO2-based photocatalysts provide an opportunity for wastewater treatment.

In previous studies, our group revealed that PVDF/TiO2 hybrid hollow fiber membrane through a phase inversion method to improve filtration efficiencies and antifouling properties.

In the present work, SiO2 as inorganic material into PVDF membrane matrix increases the membrane permeability. SiO2 modified PVDF/TiO2 hybrid hollow fiber membrane is prepared by similar strategy. The membranes performances are evaluated based on the water permeability, humic acid (HA) rejection and antifouling properties. And this work focuses on the long-term stability and antifouling performance, especially under visible light.
(Invited) Aqueous Thermal-Electrochemical Catalysis for Light Alkane Upgrading
Authors: Kronawitter Coleman X
Published: February 2020

The recent dramatic increase in supply of natural gas in the United States, largely enabled by rises in shale gas production, presents a unique opportunity to develop new catalytic processes that utilize abundant light alkanes for chemical manufacturing and transportation fuel synthesis. Alkenes as well as alcohols and other oxygenates are attractive target product molecules because they are either commodity chemicals or serve as precursors for production of commodity synthetic materials. This presentation will describe several approaches for designing new catalysts and reaction schemes for light alkane upgrading. These approaches include thermal catalytic, electrocatalytic, and hybrid thermal-electrocatalytic reactions in both batch and flow conditions.

The presented work shows that oxidative functionalization of C-H bonds is possible using only air, water, and electricity as inputs when suitable catalysts and reaction conditions are utilized. Results demonstrate conversion of methane and ethane into a number of oxygenates and hydrocarbons at temperatures below 60 ºC in aqueous conditions, and quantify the associated catalytic performance. These efforts are supplemented by ex situ materials characterization and operando FTIR spectroscopy measurements, which provide new insights into the nature of these aqueous thermal and thermal-electrocatalytic reactions. The use of reactive oxidizing species generated from air and water for low temperature hydrocarbon catalysis has enormous potential to open new avenues of research. Additionally, the fundamental insights gained on the role of water in driving product selectivity in these reactions will be of interest to the broader catalysis community, which often encounter water in the gas phase as a side reactant.
Strongly Coupled Ni-Molybdenum Carbide Grafted N-Doped Carbon Architectures for Efficient Electrocatalysis
Authors: Das Debanjan
Published: February 2020

Despite the recent promise of transition metal carbides as non-precious catalysts for hydrogen evolution reaction (HER), their extension to oxygen evolution reaction (OER) in order to achieve the goal of overall water splitting remains a significant challenge. Herein, a new Ni/MoxC (MoC, Mo2C) nanoparticles supported N-doped graphene/CNT hybrid (NC) catalyst is developed via a facile, one-step integrated strategy which can catalyze both the HER and OER in an efficient and robust manner. The catalyst affords low overpotentials of 162 and 328 mV to achieve a current density of 10 mA/cm2 for HER and OER, respectively, in an alkaline medium which either compares favourably or exceeds most of the Mo-based catalysts documented in the literature. The electronic synergistic effect between MoxC, Ni and NC are responsible for the higher electrocatalytic activity wherein, a tandem electron transfer process yields both excellent HER and OER activity. [1] Unfortunately, however, the synergy among the components was curtailed on account of large spatial separation. To mitigate this problem, we pyrolyzed a PANI/NiMoO4 nanowire@rGO hybrid which brought the individual components closer as compared to the previously adopted method resulting in improved catalytic activity. To further enhance the intimacy in these multi-component catalysts, a MOF-confined synthesis method was developed which resulted in the best activity among all the catalysts developed in the series. Moreover, we further extended this strategy to other MOFs resulting in Co/Mo2C/NC architecture which points to the versatility of this method.

[1] D.Das, S.Santra and K.K Nanda, ACS Appl. Mater. Interfaces, 2018, 10, 35025−35038
(Invited) Materials Discovery for Energy Applications
Authors: Tumas William
Published: February 2020

New materials are critical for meeting our future global energy needs and to create the needed disruptive technologies for energy conversion, delivery, storage, and use. Materials discovery is being accelerated by significant advances in theory and high-throughput materials synthesis and characterization to a point where theory and computation can directly guide experimental materials discovery and development. We will present an overview and highlights from the Next Generation for Materials Design (CNGMD) Energy Frontier Research Center (EFRC), a multi-institution center funded by DOE including results from partners at NREL, Lawrence-Berkeley National Laboratory, SLAC National Laboratory, Harvard University, Oregon State University, Colorado School of Mines, and CU-Boulder. Our EFRC team integrates theory and experiment, including high-throughput methods and in-situ characterization, to discover new functional semiconductor materials, particularly metal oxides and nitrides, relevant to energy applications. Our main goal is to develop a systematic methodology to incorporate and actively design for functional metastability. We focus not only on ground-state materials discovery but also on incorporating metastability (i.e. non-equilibrium structures and compositions) into materials design. We are establishing ranges for accessible metastable materials as a function of the chemistry, energetics, and structure by investigating three classes of metastable systems: defects, polymorphs, and solid solutions (alloys). Another aim is to guide the synthesis of new materials. By coupling theory with state-of-the-art in-situ characterization to probe materials growth pathways, we are developing a systematic theory-driven approach to guide the synthesis of new materials—including metastable systems. An overview of NREL’s extensive R&D program in photovoltaics will also be presented along with challenges to address the development of the needed terawatts of global solar energy.
(Invited) Designing and Discovering Transformational Materials for Energy Applications
Authors: Ingram Brian J.
Published: February 2020

Imagine if solid state materials could be designed over multiple length scales and created with precise control over their various forms of complexity. An integrated approach is being used to efficiently combines theory, synthesis, and operando characterization to control, assemble, and stabilize solid state materials and with various forms of complexity for enhancement of ion and/or electron transport. While computational materials design is a well-established with many known successes in the field of Li-ion chemistry, compounds are usually not designed with defects in mind or an understanding of what synthetic pathway can be utilized to achieve them. By understanding how materials complexity influences electrochemical performance, we are advancing comprehensive rational materials design beyond the level of defect-free design. Furthermore, the science of synthesis needs to consider extrinsically controlled complexity. A large-scale effort has been established which combines extensive and state of the art in situ and ex situ characterization tools. This talk will provide an overview of the results and approaches being taken as they relate to energy storage and conversion applications.
(Invited) Machine Learning in Materials Discovery
Authors: Meredig Bryce
Published: February 2020

Machine learning (ML) is rapidly emerging as an important tool for materials discovery. In this talk, we will address key considerations involved in applying ML to materials design problems, including: using sequential learning for inverse design of materials with target properties; quantifying model performance when extrapolating to new chemistries (rather than interpolating among well-known chemistries); and optimizing the design space (i.e., the set of candidates to search with ML).
(Invited) Combined Ab Initio and Machine Learning Approaches to Discover Materials for Hydrogen Generation
Authors: Musgrave Charles Bruce
Published: February 2020

In this talk we will present our results using ab initio and machine learned models to discover candidate perovskite STWS materials. This includes predicting the stability of these materials at the operating temperature, whether these materials form as perovskites and in what specific phase, the energy of oxygen vacancies and other defects that mediate the redox process, and finally the viability of these metal oxides as STWS redox materials. The Gibbs energy, G, determines the equilibrium conditions of chemical reactions and materials stability. Unfortunately, G has been tabulated for only a small fraction of known inorganic compounds, thus impeding an analysis of whether materials are stable and synthesizable at operating conditions. We used a statistical learning approach to identify a simple and accurate descriptor to predict G(T) for stoichiometric inorganic compounds with ~40 meV/atom resolution, and minimal computational cost, for temperatures between 300 K and 1800 K. We then applied this descriptor to screen various compositions for their stability at STWS temperatures. Candidate materials that form as perovskites were then analyzed using a machine learned one-dimensional tolerance factor, τ, that we developed that correctly predicts 92% of compounds as perovskite or non-perovskite to predict which of the predicted stable compounds form perovskites. Finally, we applied DFT on the remaining viable candidates to predict the thermodynamics of STWS reactions. This requires predicting the correct perovskite phase, symmetry breaking distortions and modeling the correct defect, spin and charge state of the defect mediating the oxidation and reduction processes at the operating conditions.
(Invited) The U.S. Department of Energy’s Energy Materials Network
Authors: Miller Eric L. , Randolph Katie , Peterson David , Stetson Ned T
Published: February 2020

Accelerating the discovery and development of novel materials is essential for the U.S. to compete globally in key energy sectors throughout the 21st century and beyond. In support of its priorities in energy-materials innovation, the U.S. Department of Energy (DOE) established the Energy Materials Network (EMN) as a network of application-specific consortia that facilitate industry and academia access to the unique and world-class resources at the national laboratories in materials theory, computation, experimentation, analysis, and data informatics. EMN consortia have been established to address a broad range of materials challenges in specific energy-related applications such as platinum-group-free catalysts for fuel cells, advanced water-splitting materials, breakthrough materials for hydrogen storage materials and carriers, next-generation catalysts for bio-fuels and products, light-weight materials to revolutionize the transportation sector, and new module materials to support and enable the large-scale deployment of photovoltaics. The EMN model along with recent scientific accomplishments from individual EMN consortia will be discussed.
(Invited) H-Mat: Enhancing the Durability and Affordability of Metals and Polymers in Hydrogen Service
Authors: Rustagi Neha , San Marchi Chris , Simmons Kevin L , Hill Laura , Stetson Ned T
Published: February 2020

The H-Mat national laboratory consortium is conducting cross-cutting, foundational R&D to enhance the durability of key polymers and metals in hydrogen service. Technologies utilized in hydrogen service commonly face stresses that influence materials compatibility, such as cryogenic temperatures, fatigue loading, and corrosive environments. Industries in which hydrogen compatibility can heavily influence materials selection are diverse, and include fuel cell electric vehicles (FCEVs), nuclear energy technologies, oil & gas sectors, and vehicle lightweighting applications. H-Mat R&D aims to enhance fundamental understanding of materials’ behavior in hydrogen, with a current focus on materials used onboard FCEVs and at fueling stations. Key research thrusts include: 1) development of novel experimental polymers with enhanced durability in hydrogen pressure cycles, 2) microstructural engineering to enhance the fracture toughness of high-strength steels in hydrogen, 3) development of higher-fidelity predictions of crack initiation in steels in hydrogen service, and 4) evaluation of the effects of moisture on hydrogen induced degradation in aluminum alloys. These R&D thrusts are targeted to enhance durability of hydrogen seals by 50%, fracture resistance of pressure vessel steels by 50%, and life of pressure vessels by 50%. H-Mat is led by Sandia National Laboratories and Pacific Northwest National Laboratory, with participation from Oak Ridge National Laboratory, Savannah River National Laboratory, and Argonne National Laboratory. Members of industry and academia are encouraged to engage with the consortium through cooperative research and development agreements (CRADAs) and funding opportunity announcement (FOA) awards. For more information, please see: https://www.energy.gov/eere/fuelcells/h-mat-hydrogen-materials-consortium
High Efficiency PEM Water Electrolysis Enabled By Advanced Catalysts, Membranes and Processes
Authors: Capuano Christopher B , Ayers Kathy , Manco Judith , Wiles Luke , Zenyuk Iryna V. , Leonard Emily , Kusoglu Ahmet , Weber Adam Z. , Danilovic Nemanja , Alia Shaun M , Ulsh Michael , Mauger Scott A , Pfeilsticker Jason , More Karren L.
Published: February 2020

Commercial water electrolysis technologies, including proton exchange membrane electrolysis (PEMWE), are the only renewable hydrogen generation technologies that can achieve the U.S. Department of Energy (DOE) cost targets within the next ten years at the required scale, based on the supply chain maturity and materials performance. In particular, membrane and electrode modifications have enabled the use of advanced electrolysis membranes to achieve the efficiency targets, while nanoengineered alloy catalyst layers (CLs) have been pursued to meet the cost and efficiency targets. These advancements have been achieved by building the basic understanding to allow the successful technical development and include: (1) Mechanical and chemical understanding of membranes in liquid water below 90oC; (2) Characterization of as-deposited electrodes and MEAs after operation; (3) Water management in the anode catalyst layer, dependence on catalyst loading and porous transport layer form factor; and (4) Long-term degradation rate and stability of engineered alloy Ru-Ir alloy nanocatalysts in well-defined anode catalyst layers.

Nel Hydrogen’s pathway to meet these DOE goals is through the i) use of 50-75% thinner membranes that operate at 80-90 oC, while controlling mechanical creep and gas crossover; ii) reducing the catalyst loading to 1/10th the current value on both electrodes, while controlling water distribution and the porous transport layer/catalyst layer (PTL/CL) electrochemical interface; iii) incorporation of a less stable but more active Ru containing catalyst managed on the anode side of the cell, which is achievable with lower voltage operation (accomplished via low ohmic drop in the anode catalyst layer, thinner membranes, and higher temperature operation); and iv) fabricating a membrane electrode assembly (MEA) integrating all of these characteristics.

In this talk, some of the advancements achieved and how these have impacted the cost of hydrogen will be discussed, as well as the longer-term targets that need to be reached to provide the robustness required for commercial applications. Additionally, cost models will be compared along with sensitivity analysis to show how the impact of operating parameters, with regard to the capital and operational expense for the PEM electrolysis technology cost, show the critical areas to focus on to provide the largest impact towards meeting cost target goals and what is required to go beyond.

Figure 1
Designing Catalysts for Water Splitting Based on Electronic Structure Considerations
Authors: Andrews Justin , Suwandaratne Nuwanthi , Watson David , Piper Louis F.J. , Guo Jinghua , Prendergast David , Banerjee Sarbajit
Published: February 2020

Water splitting involves the synergistic operation of water oxidation and hydrogen evolution half-reactions and remains a considerable challenge since it requires the concerted transfer of four electrons and four protons. Catalysts that can facilitate both of the half-reactions at low overpotentials are imperative to avoid squandering free energy harvested using a semiconductor in a photoelectrochemical cell, or provided directly in the form of current in a water electrolyzer. Photocatalytic water splitting requires the operation of light harvesting, charge separation, charge transport, and redox catalytic steps that must outcompete charge recombination. As such, it requires the precise tunability of energetic offsets to establish optimal thermodynamic driving forces for charge transfer and control of interfaces to mediate kinetics of charge transfer. The talk will focus on the design of compounds with the composition M
x
V2O5 where M is a post-transition metal cation with lone-pairs characterized by intercalative mid-gap states that can accept holes from photoexcited semiconductor quantum dots. Such compounds, accessible through topochemical intercalation of metastable polymorphs of V2O5, have facilitated the design of heterostructures with energetic offsets primed to facilitate effective hole transfer upon photoexcitation of the heterostructures, thereby mitigating the longstanding challenge of the anodic photocorrosion of quantum dots. Interfacial design further provides a means of modulating the dynamics of hole transfer, which occurs at <1 ps timescales. The second half of the talk will focus on discussing the specific electronic structure characteristics of edge sites of MoS2 that enable them to function as catalysts for the hydrogen evolution reaction. Interfacial hybridization of MoS2 with nC60 provides a means to modulate the electronic structure and enhance catalytic activity. Interfacing MoS­2 with semiconductor quantum dots further yields effective photocatalysts for hydrogen evolution that have been examined using operando X-ray absorption spectroscopy. The two examples illustrate the potential of computationally driven materials design to unravel new physical insights and provide practical solutions to challenges in hydrogen generation. The authors acknowledge support from the NSF under DMREF-1627197, DMREF-1626967, and DMREF-1627583 as well as from the NSF DMREF/ DOE EERE EMN project.
Framework Materials As Porous Liquids
Authors: Mow Rachel E. , Braunecker Wade A. , Martinez Madison B. , Shulda Sarah M , Gennett Thomas
Published: February 2020

Porous liquids have recently been introduced as a new class of material with great potential for gas storage and purification. The permanent porosity and fluid properties of porous liquids provide an avenue for gas storage and transportation that avoids the processing restrictions of solid porous materials. Despite the promise of porous liquids, only a handful of these materials have been realized to date, including functionalized hollow-silica particles, cage-like organic materials, and metal organic frameworks or zeolites suspended in bulky ionic liquids. This work describes an approach to make porous liquids out of covalent organic frameworks (COFs) by functionalizing the outer shell with ionic liquids or liquid polymer chains. COF particle size can be controlled down to 60 nm by varying the solvent and reaction parameters. The injection of a capping agent during synthesis can further control particle size and prevent future aggregation during processing. Click chemistry is one effective synthetic route to functionalize the outer shell with ionic liquids. The functionalized COFs are then suspended in a bulky ionic liquid solvent that is size-excluded from entering the COF pore. Another synthetic route involves directly attaching a liquid polymer chain to the outer framework, thereby introducing stable, unoccupied pores into a liquid. A series of imine-based COFs with different pore and particle sizes are functionalized with liquid polymers and different sizes of ionic liquids. The uptake of various gasses into these materials is then evaluated. This work presents a new type of tunable organic porous liquid that can be used for gas storage and separation.