bluuebunny/crossref_metadata_2025 huggingface dataset:
(Invited) Emerging Chalcopyrite Photo-absorbers for Renewable Hydrogen Production
Authors: Gaillard Nicolas
Published: February 2020

Photoelectrochemical (PEC) water splitting is an attractive method for efficient renewable hydrogen production. However, the cost, efficiency and durability of lab-scale systems are not yet at the level required to make this technology economically attractive. Amongst all materials studied to date, the chalcopyrite class is arguably one of the most promising classes for PEC water splitting, as it has already demonstrated low-cost and high photoconversion capabilities as a photovoltaic material. In the context of PEC, our group has shown that co-evaporated 1.65 eV bandgap (EG) CuGaSe2 is capable of evolving hydrogen with Faradaic efficiency greater than 85% and generate photocurrent densities over 15 mA.cm-­2, as measured in a 3-electrode configuration in 0.5M H2SO4 under simulated AM1.5G illumination. Unfortunately, CuGaSe2’s narrow EG limits its integration as top absorber into a dual junction stacked PEC device (also known as hybrid photoelectrode, HPE). In the present communication, we report on our latest efforts to synthesize wide-EG (1.8-2.0 eV) chalcopyrites, compatible with the HPE integration scheme, and capable of generating saturated photocurrent densities greater than 10 mA/cm2. We present specifically results on EG tunable Cu(In,Ga)S2, CuGa(S,Se)2 and CuGa3Se5. We also discuss some of the strategies developed to improve their surface energetics for the hydrogen evolution reaction, including the use of non toxic n-type buffer layers. We also include recent durability testing of chalcopyrite photocathodes coated with metal oxide protection layers. Finally, we present solid-state techniques and theoretical modeling used by our team to identify possible pitfalls in these material systems and discuss potential paths for improvement.
Charge Separation Enhancement Mechanism By p-n Junction in Water Reduction Electrode
Authors: Xu Zihao , Hou Bingya , Zhao Fengyi , Cronin Stephen B. , Lian Tianquan
Published: February 2020

Solar water splitting overall efficiency largely depends on the photoanode/photocathode charge carrier separation efficiency. Understanding the competition between charge separation and charge recombination is crucial to improve the device efficiency. In this study first we discussed the challenges in studying such process with femtosecond transient spectroscopy. Then we demonstrated a feasible method by combining transient reflectance (TR) spectroscopy and in situ electrochemical measurement to provide critical information on charge carrier separation efficiency and IPCE on a water/CO2 reduction photoanode, p-type gallium phosphate with protective titanium dioxide (TiO2) layer. Enhanced charge separation at the interface of gallium phosphate (GaP, 100) single crystal and TiO2 layer is observed by TR. The separated charge carrier concentration obtained by reflectance change shows strong correlation to the IPCE measured in situ under same condition. Through this correlation we provided direct evidence that the IPCE is heavily determined by the transiently separated charge carriers. This study also provides an applicable and powerful method to study similar HER and OER semiconductor electrode photogenerated charge carrier dynamics at ultrafast time scale.
(Invited) Chalcopyrites for Solar Water Splitting: Soft X-Ray and Electron Spectroscopy of the Chemical and Electronic Surface Structure
Authors: Heske Clemens
Published: February 2020

In this presentation, it will be demonstrated that the combination of soft x-ray and electron spectroscopies (using lab-based surface characterization and high-brilliance synchrotron radiation) can be used to gain insights into the electronic and chemical surface properties of Cu(In,Ga)(S,Se)2-based chalcopyrite devices for solar water splitting. It will be shown that x-ray and UV photoelectron spectroscopy (XPS and UPS), x-ray-excited Auger electron spectroscopy (XAES), inverse photoemission (IPES), x-ray emission spectroscopy (XES), and x-ray absorption spectroscopy (XAS) can be suitably combined to derive band edge positions, band gaps, work functions, and electronic level alignments. Furthermore, insights into chemical stability can be gained, both with experiments in ultra-high vacuum, as well as under in situ and operando conditions.
(Invited) Electronic Structures of Metal Centers in OER Catalyst Models and Electron/Energy Relays in the Excited State Supramolecular Dinuclear Transition Metal Complexes
Authors: Chen Lin X
Published: February 2020

Electronic Structures of Metal Centers in an OER Catalyst Model. One of the challenges in solar fuels generation is generating multiple redox equivalents for the oxygen evolution reaction (OER) (i.e., 2H2O→O2+4H++4e-) that is a four-electron, four-proton coupled process. Earth-abundant first-row transition metal oxides of cobalt, nickel, and their mixed-metal forms can drive this half-reaction at relatively low overpotentials. In collaboration with Nocera Group, we used a combination of in situ and ex situ X-ray absorption and emission spectroscopies as well as quantum mechanical calculations on OER thin films and their molecular and heterogeneous inorganic analogs. These studies provided insights into the electronic structures of the high-valent states involved in the mechanisms of O-O bond formation and for the high-valent states to drive the bond-forming and bond-breaking steps of OER reactions. Using a Co4O4 cluster as a model for the Co-based OER anode, CoPi, which has a similar topology and can host a stable, but electronically delocalized, mixed-valent Co(IV) state, we employed complementary X-ray spectroscopies, X-ray absorption (XAS) and 1s3p resonant inelastic X-ray scattering (Kβ RIXS), to effectively extract Co(IV) contributions within a spectroscopically active background (Figure 1). Co K- and L-edge X-ray absorption directly probe the 3d-manifold of effectively localized Co(IV), providing a handle on the covalency of the dπ-based redox active molecular orbital (MO) of Co4O4. Kβ RIXS is shown to be highly sensitive to metal cluster oxidation state and oxo-mediated metal-metal coupling in high-valent, delocalized mixed-valent species. We also probed the doubly oxidized Co(III)2(IV)2 state of the Co4O4 cluster, which features a cofacial Co(IV)2 site and is thus a molecular model of the active site in Co-OEC.

Electron and Energy Relays in the Excited State Supramolecular Dinuclear Transition Metal Complexes. The rational design of multinuclear transition metal complexes (TMCs) for photochemical catalysis of homogeneous and/or heterogeneous multi-electron reactions (e.g. for producing solar fuels) requires a detailed understanding of the often unique and convoluted excited state charge and energy transfer dynamics in this class of compounds. Using combined optical and X-ray transient spectroscopic measurements, excited state electron electron relays in tetrapyridophenazine-bridged heteroleptic dinuclear Cu(I) bis(phenanthroline) complexes have been investigated as an exemplary system.
(Invited) Colloidal Semiconductor Nanocrystal Photocatalysts: Teaching an Old Dot New Tricks
Authors: Burke Rebeckah , Chakraborty Saikat , Cogan Nicole , Sowers Kelly , Frenette Leah , Caputo Jill , Weix Daniel , Bren Kara , Krauss Todd D
Published: February 2020

Colloidal semiconductor nanocrystal quantum dots (QDs) have shown great promise as photocatalysts for a variety of chemical transformations including oxidations, reductions, and most recently carbon-carbon bond forming reactions. QDs inherently possess several desirable properties for photocatalysis including oxidation and reduction potentials that are size tunable, and also that are largely independent of their surface chemistry. Due to their size, QDs can also interact with several substrates at once, enhancing charge-transfer rates. We recently found that CdSe QDs and simple aqueous Ni2+salts in the presence of a sacrificial electron donor form a highly efficient, active, and robust system for photochemical reduction of protons to molecular hydrogen. Under appropriate conditions, the nanocrystal-based system has undiminished activity for at least 360 hours with about a million turnovers. Ultrafast optical spectroscopy studies of electron transfer from the nanoparticles to a Ni-catalyst reveals the optimal nanoparticle size and shape for photochemical proton reduction, which was confirmed with photocatalytic experiments. We will also discuss recent measurements of carbon-carbon bond formation driven photochemically using CdSe QDs. A single-sized CdSe QD can replace several different dye catalysts needed for five different photoredox reactions (beta-alkylation, beta-aminoalkylation, dehalogenation, amine arylation, and decarboxylative radical formation).Even without optimization of the QDs or the reaction conditions, efficiencies rivaling the best available metal dyes were obtained. The facile customization afforded by QDs for photoredox catalysis suggests they could have important applications in future syntheses of novel pharmaceuticals.
Photocatalysis Using Earth-Abundant Copper-Based Plasmonic and High-Dielectric Nanostructures to Produce High-Value Chemicals
Authors: Addanki Tirumala Ravi Teja , Mohammadparast Farshid , Ramakrishnan Sundaram Bharadwaj , Andiappan Marimuthu
Published: February 2020

Over the years plasmonic materials have received wide attention for their ability to convert solar into chemical energy. Plasmonic nanoparticles (NPs) exhibit strong electromagnetic-field (EMF) enhancement for the incident light because of the Localized Surface Plasmon Resonance (LSPR). This property has been shown to enhance the photocatalytic performance of nearby semiconductors in the composite, and hybrid photocatalysts build on plasmonic metal nanoparticle and semiconductor. In this presentation, we will focus on copper based hybrid plasmonic nanostructures and optically resonant high dielectric nanostructures for efficient conversion of solar into chemical energy.

Our FDTD simulation results predict that the EMF enhancement observed over high dielectric NPs are 2-3 orders of magnitude higher than the plasmonic NPs. This new family of non-plasmonic metal oxide nanostructures is dielectric in nature with high refractive index (> 2). Our simulation results predict that the Mie resonance over these high-dielectric nanostructures can be tuned anywhere from UV-Vis to the near-IR region by controlling the geometry of the nanostructures. We will also show experimental results that validate the simulation results. We utilized size and shape-controlled synthesis techniques to design optically resonant nanostructures with tunable Mie resonance. The optoelectronic properties of these nanostructures are confirmed using a number of spectroscopic techniques.

Also, we will show the visible-light enhanced photocatalytic performance of the high dielectric nanostructures for carbon-carbon (C-C) coupling reactions. The design rules developed for the optically resonant nanostructures in our study will potentially have a wide range of applications including the use of these nanostructures for solar-light driven photocatalysis and thin-film solar cell applications.
(Invited) Semiconductor Device Modeling for Photoelectrochemical Cells: Band Diagrams and Kroemer’s Lemma
Authors: Bevan Kirk H , Iqbal Asif , Miao Botong
Published: February 2020

The rising global need for green carbon neutral fuels has driven a resurgence of intense research into photoelectrochemical cells. This talk presents an overview of the role that semiconductor modeling can play in understanding and engineering the operation of photoelectrochemical cells. Focusing on the photo-anode, we begin by exploring how the operation of semiconductor/oxide based photocatalytic devices performing water splitting can be understood in a similar framework to solid-state Schottky diodes. From this it is then demonstrated how key properties such as the photovoltage, the photocurrent and carrier trapping can be modeled. Overall, we will discuss the importance of sound semiconductor band diagrams (often referred to as “Kroemer’s Lemma”) to interpreting the experimental operation of photoelectrochemical systems. The aim of this methodology is to accelerate the development of practical photoelectrochemical systems through closer coupling between modeling and experimentation.
Computational Quest for High-Performance Electrocatalysts for Nitrogen Fixation
Authors: Chen Zhongfang , Zhao Jingxiang
Published: February 2020

The nitrogen electroreduction reaction (NRR) in aqueous solutions at ambient conditions represents an attractive prospect to produce ammonia, but the development of long-term stable and low-cost catalysts with high-efficiency and high-selectivity remains a great challenge. Single-atom catalysts have emerged as a new frontier in heterogeneous catalysis, and demonstrated distinguishing performances for various reactions due to their high catalytic activity with a significantly reduced amount of metals used. The emerging metal-free catalysts for NRR have attracted increasing attention due to their intrinsic advantages, such as low cost, high reliability, good biocompatibility, and excellent sustainability

In this talk, we will present our recent efforts in designing single-atom and metal-free electrocatalysts to realize nitrogen reduction reaction (NRR) at ambient conditions. Besidesidentifying promising catalysts for N2fixation, we will emphasize the designing principles and the procedure in screening effective NRR catalysts based on the mechanism understanding.
(Invited) Chemical Interface Damping in Single Plasmonic Nanostructures
Authors: Link Stephan
Published: February 2020

A surface plasmon in a metal nanoparticle is the coherent oscillation of the conduction band electrons leading to both absorption and scattering as well as strong local electromagnetic fields. These fundamental properties have been exploited in many different ways, including surface enhanced spectroscopy and sensing, photothermal cancer therapy, and color display generation. Chemical synthesis and assembly of nanostructures are able to tailor plasmonic properties that are, however, typically broadened by ensemble averaging. Single particle spectroscopy together with correlated imaging is capable of removing heterogeneity in size, shape, and assembly geometry and furthermore allows one to separate absorption and scattering contributions. In this talk I will discuss our recent work on distinguishing the different contributions that cause plasmon decay, and especially plasmon damping due to energy and charge transfer from the metal to molecular, semiconducting, and metallic acceptors.
(Invited) Ultrafast Exciton, Bi-Exciton and Trion Dissociation Dynamics in Metal@Semiconductor Hetero-Structure Interface
Authors: Ghosh Hirendra Nath
Published: February 2020

Multiexciton harvesting from semiconductor quantum dot has been a new approach for improving the semiconductor device efficiency which include quantum dot sensitized solar cells (QDSC) and photodetectors. Till date, not many reports are available where relation between exciton/multiexciton dissociation in metal−semiconductor nanohybrid system and boosting the power conversion efficiency (PCE) of QDSC are discussed. Herein we report a detailed spectroscopic investigation on the dissociation dynamics of i) exciton in Au@CdSe, ii) biexciton in Au@CIS (CuInS2) and, iii) trion in Au@2D-MoS2 utilizing both time-resolved PL and ultrafast transient absorption (TA) techniques. Ultrafast transient absorption studies suggest that in all the above three systems the ultrafast formation of exciton/bi-exciton/trion, which efficiently dissociates in Au-semiconductor nano-hybrid structures. Prior to the dissociation electrons are captured by Au NP in the nanohybrid from the conduction band of CdSe/CIS/2D-MoS2 nano-structures which is energetically higher than Fermi level of Au. Here we demonstrate the proof-of-concept in multi-electron dissociation which may provide a new approach for improving the efficiency in QDSSCs. These findings can be an efficient approaches towards the design and development of efficient solar cell and optoelectronic devices using the principles of multiexciton/trion generation and extracting them in metal-semiconductor nanohybrid system.
(Invited) Element-Specific Measurement of Hole Transport in a Photoanode By Transient Extreme Ultraviolet Spectroscopy
Authors: Cushing Scott Kevin
Published: February 2020

A passivating oxide layer is critical for the performance and stability of solar-fuel photoelectrodes. While the semiconductor surface can be passivated by a few nanometer oxide film, the best performance often correlates with a thicker and defect-rich amorphous TiO2 layer. The defect states are suggested to facilitate hole transport between the semiconductor and metal catalyst. In this presentation, transient extreme ultraviolet (XUV) absorption spectroscopy is used to measure the electron and hole transport between each element of a photoexcited Ni-TiO2-Si junction. The transient changes in the Ni M2,3 edge, Si L2,3­ edge, and Ti M2,3 edge are quantified using a broad-band, high harmonic XUV continuum that spans 30 to 120 eV. Hole tunneling from the p-type Si to the Ni metal is measured immediately following 800 nm optical excitation. The measured transport time and electric field indicate a ballistic tunneling through the TiO2 that originates from a Si hole with a mobility of ~400 cm2/Vs. An appreciable transfer of photoexcited electrons is not measured. The quantum yield of the hole tunneling is calculated to be ~50% percent by using the photoexcited carrier density in Si and the measured shift in the Ni M2,3 edge Fermi energy. On a picoseconds time scale, the holes are measured to back-transfer from the Ni to the Si through the mid-gap states in the TiO2. The extracted kinetics suggest a hole diffusion constant of ~1 cm2/s. The surface recombination velocity of electrons and holes at the Si-TiO2 interface is also quantified as ~200 cm/s. These results suggest that transient XUV spectroscopy can be used to quantitatively measure electron and hole transport in solar-fuel relevant nanoscale junctions.
Charge Carrier Dynamic Study on Different Catalyst-Modified BiVO4 Photoanodes
Authors: Zhao Fengyi
Published: February 2020

Transient absorption measurement is developed to investigate the charge carrier dynamic of different catalyst-modified BiVO4 and the origin of photocurrent performance enhancement. In-situ IPCE under conditions of transient absorption measurement showed the IPCE enhancement and cathodic shift of onset potential on both Co9POM and CoPi modified of BiVO4 compared to bare BiVO4. The normalized transient absorption kinetics averaged from 500-530 nm exhibited similar slower kinetic decay on both catalysts treated BiVO4 compared to bare BiVO4. The power law decay feature of kinetic decay from 10 ns – 500 ns indicates a trap-limited recombination process occurs in all investigated BiVO4. The slower bulk recombination kinetic decay observed on Co9POM/BiVO4 and CoPi/BiVO4 suggests that both co-catalyst treatments on BiVO4 enhance the PEC performance by suppressing the bulk recombination process.
(Invited) Solar Energy Conversion Enhanced By the Structure and Surface Improvements of Quaternary Semiconductors
Authors: Solarska Renata , Bienkowski Krzysztof , Jadwiszczak Michal , Dubiel Adrian
Published: February 2020

Solar energy conversion with high yield and cost-effective ratio requires use of materials which are easily available, stable within the time and flexible in structure in order to allow improvements in their intrinsic and surface properties. A class of such materials are perovskites with ABO3 structure or kesterites. The basic structure of ABO3, has a high structural tolerance factor and can be maintained with a wide variety of constituent elements. As a result, the composition-property relationship can be systematically investigated while keeping the same crystal structure. Also, due to the exceptional stability of the structure, the valency, stoichiometry, and vacancy of perovskite compounds can be varied widely in order to tune optical, electrical and catalytic properties. Therefore, the challenge is to couple the synthetic approach with an expected outcome resulting from the theoretical calculations.

In this presentation we will show the study on quaternary Ln1-xNixTiO3 that revealed the optical and electronic properties might be affected by varying La content in the matrix under employment of a reductive atmosphere of H2. This constitutes a unique and advantageous feature for its use in solar energy conversion. Understanding the effect of La doping and Ni segregation occurring under the reductive atmosphere on the photoelectrochemical properties of the La1-xNixTiO3 will generate new set of knowledge while providing a facile route to tune photon absorption and charge transport properties. A similar study will be presented for kesterite Cu2ZnSnS4. The questions which will be undertaken are: does La doping favourably affect the electron-hole separation in addition to the enhancement of photon absorption?; how do oxygen vacancies created by ion doping and reduction in hydrogen affect the charge transport properties?; can Ni segregation affect the catalytic property of the Ln1-xNixTiO3 surface?. The same questions will be applied to kesterite based PEC system upon ion doping and applied atmosphere. We will try to answer these questions through use transient absorption spectroscopy approach allowing to follow changes in charge carrier dynamics from the sub nanoseconds up to seconds timescales upon introduction of any variable to the system.
Exploration of Vapor Electrolysis for Chemical Transformations
Authors: Fornaciari Julie C. , Zhou Jie , Bell Alexis T. , Weber Adam Z.
Published: February 2020

Electrolytic devices provide a carbon-free option to producing hydrogen, with many advantages such as modular, scalable design and flexibility of operating parameters (temperature, pressure, etc.).1 Typically, electrolyzers are run under conditions that require a significant amount of clean, liquid water and are run at several A/cm2. However, the solar flux limits achievable current densities to ~100 mA/cm2 and furthermore the strong solar resources are oftentimes located in regions away from a ready supply of clean water. Finally, multiphase flow in electrolyzers also complicate the transport physics and reaction kinetics. These above challenges can be surmounted through the use of vapor electrolyzer, where water vapor is split to oxygen and hydrogen directly. Vapor electrolysis has not been extensively studied due to a limitation in how much water can be supplied to the system – water electrolysis is never mass-transport limited. Some studies have shown such a device2,3 but are more proof of concept. In this talk, we discuss an experimental diagnostic study of various parameters to increase the performance of such cells that can reach 1 A/cm2. In addition, using mathematical modeling we explore the various losses endemic to this system as well as its natural advantages to utilize impure water in arid or possibly marine climates. Finally, we will discuss how the understanding gained on vapor electrolysis and gas-diffusion electrodes can be transferred to the electrochemical conversion of other gases (e.g., methane, carbon dioxide, etc.). Preliminary findings of fuel electrochemical oxidation to partial oxidation products will be discussed.

Acknowledgements:

J.C.F. would like to thank Dr. Michael Gerhardt, Dr. Nemanja Danilovic, and Dr. Yagya Regmi for the helpful discussions. J.C.F. also acknowledges support from National Science Foundation Graduate Research Fellowship under Grant No. DGE 1106400. This work was partially funded by the Energy & Biosciences Institute through the EBI-Shell program.

References:

Carmo M., et. al. International Journal of Hydrogen Energy,Volume 38, Issue 12, 2013 .

Kistler T.A., et. al. Electrochem. Soc.volume 166, issue 5, 2019

Spurgeon J.M. , et. al. Energy Environ. Sci., 2011, 4, 2993-2998
Effect of Bias and Aerobic Conditions on Photocatalytic Nitrogen Fixation By Titania
Authors: Liu Yu-Hsuan (Carol) , Chen Sarah , Hatzell Marta C.
Published: February 2020

Photo-catalytic nitrogen fixation on titania (TiO2) was discovered for decades ago by an Indian Soil Scientist (N Dhar) [1]. Dhar’s early work suggested that titania in soil produces fixed nitrogen (ammonia) from air. Despite these findings, a clear understanding regarding how nitrogen fixation occurs on titania remain unclear. Previous studies has demonstrated nitrogen photofixation in both gas and liquid phase and in various environmental conditions (temperature, pressure, relative humidity) [2]. Investigation have also centered on the use of various proton source (hydrogen, water) and hole scavengers. Under all conditions, the prevailing consensus is that ammonia is formed photo-catalytically. However, very few investigations have detailed the impact of oxygen, as a competing reactant. Most investigations used nitrogen that is separated from air. Separation nitrogen from air is energy intensive and expensive. If photocatalytic technologies are to be developed for ammonia production, omitting the air separation process and operating with air is necessary to drive down the cost. Therefore, it is important to understand the impact of oxygen plays in suppressing photo(electro)catalytic nitrogen fixation. Here we will present data from a series of photocatalytic experiments conducted in aerobic conditions (Air) and anerobic conditions (N2). We demonstrate the production rates and efficiencies as applied bias and light intensity varies. Results show that ammonia production in air flow nearly in all cases are 30% lower than nitrogen flow. Literature also indicated that oxygen will suppress the ammonia formation because oxygen will be easier to reduce in conductive band on titania than nitrogen due to more long pair ions on oxygen [3]. Therefore, we also investigate the potential for both nitrogen and oxygen reduction through a series of rotating ring disk experiments. Through biasing the ring potential, we evaluate the product of nitrogen reduction (ammonia) and oxygen reduction (hydrogen peroxide).

Reference

[1] N. Dhar, E. Seshacharyulu and N. Biswas, Proc. Natl. Acad. Sci., India, 1941,7, 115-131.

[2] G. Schrauzer and T. Guth, J, Am. Chem. Soc., 1977, 99, 7189-7193.

[3] H. Hirakawa, M. Hashimoto, Y. Shiraishi, T. Hirai, J, Am. Chem. Soc., 2017, 139(31), 10929-10936.
Radical Redox Mediator Free Photoelectrochemical Biomass Valorization
Authors: Lhermitte Charles Roger , Canjura Pamela , Plainpan Nukorn , Sivula Kevin
Published: February 2020

Over the past decade, researchers have begun to re-explore the idea of replacing water oxidation with more kinetically facile oxidation reactions for photoelectrochemical solar H2 production.1–3 Alternate photo-oxidation reactions can be employed as a means of chemical valorization, in addition to providing electrons for H2 production from water while reducing the losses associated with water oxidation. In particular, the oxidation of 5-hydroxymethylfurfural (HMF)—which is a key intermediate derived from the acid catalyzed poly-dehydration of 6 carbon monosaccharides—has gained significant attention. This is because a number of its oxidation products, such as 2,5-Furandicarboxylic acid (FDCA), may be employed as monomers in the synthesis of renewable polyesters, and FDCA in particular, has also been identified by the US Department of Energy as one of 12 priority chemicals for establishing the green chemistry industry of the future.4

As a result, solar powered chemical transformations of HMF have recently gained attention. However, to date, the selective oxidation of HMF using either photo-, or electrochemical means, has been limited by the need to employ the radical redox mediator (2,2,6,6-Tetramethylpiperidin-1-yl)oxyl (TEMPO). This additional redox-mediating reagent poses a problem by increasing system complexity, and by behaving as a competitive light absorber in photoelectrochemical (PEC) systems —which reduces the solar conversion efficiency.

Recently, our group has investigated TEMPO free, direct PEC oxidation of HMF using metal oxide photoelectrodes. In this presentation, we show that the direct oxidation of HMF can be carried out on sol-gel processed WO3 electrodes without the need to use an additional redox shuttle such as TEMPO. Figure 1 depicts a linear sweep voltammogram under 1 sun illumination of a sol-gel processed WO3 electrode in the presence and absence of HMF. We observe that the addition of HMF to an aqueous buffered solution improves photocurrent densities by 33%, and the onset potential is favorably shifted by -50 mV. These properties highlight this reaction’s promise as a replacement for water oxidation in an H2 producing PEC cell. In addition, we report the oxidation product distribution as well as efforts to control product selectivity via solution processed heterogeneous catalysts and the optimization of the electrolyte solution.

Figure 1: Linear sweep voltammograms of a WO3 electrode in a pH 4 0.1M KPi buffered solution with (red), and without (black), 5mM HMF in solution. The illumination intensity was 1 sun AM1.5G. Dotted lines represent the linear sweep voltammograms in the absence of illumination.

References:

C. R. Lhermitte and K. Sivula, ACS Catal., 9, 2007–2017 (2019).

H. G. Cha and K.-S. Choi, Nature Chemistry, 7, 328–333 (2015).

M. F. Kuehnel and E. Reisner, Angewandte Chemie International Edition, 57, 3290–3296 (2018).

J. J. Bozell and G. R. Petersen, Green Chem., 12, 539–554 (2010).

Figure 1
Photo-Rechargeable Perovskite Cell for Direct Solar Energy Conversion and Storage
Authors: Almakrami Husain , Lin Guanzhou , Liu Fuqiang
Published: February 2020

Perovskite solar cells (PSCs) are remarkably efficient. Recent years have witnessed a surge in PSC researches in both material development and structure optimization. In a PSC, a lead halide perovskite absorber is typically sandwiched between layers of hole and electron transport materials (i.e., HTM and ETM, respectively) to facilitate the extraction of photoexcited charges, but this may also create issues of energy level mismatch and interfacial degradation. A critical challenge for both HTM and ETM materials is the ineffective charge collection because of their incompatible work functions with the perovskite, which causes significant efficiency loss. In addition, the electron mobility of an ETM doesn’t typically match with the hole mobility in an HTM, leading to interfacial charge accumulation, hysteresis and degradation. There have been extensive efforts in developing materials via work-function modulation and interfacial treatment; however, they are expensive and challenging, and may not be compatible with the solution processing of the perovskite. In this work, we demonstrated replacing HTM and ETM with two pairs of nonaqueous redox couples to extract charges from the perovskite-electrolyte interfaces through photoelectrochemical or electrochemical reactions. These redox couples, dissolved in a low dielectric constant solvent, are not only to fully encapsulate and stabilize the perovskite, but also offer easy fine-tuning of their electrochemical properties to match with the perovskite. Most importantly, the nonaqueous redox couples serve as efficient energy media and solar energy can be directly converted/stored into chemical energy at the point of solar energy generation without the intermediate step such as electricity. Recent progress will be discussed and the intricate interplay between the perovskite layer morphology and redox couples will be presented.
(Invited) Materials Discovery and Development for the Sustainable Production of Fuels and Chemicals
Authors: Jaramillo Thomas F.
Published: February 2020

There is a strong motivation to develop new chemical processes for the sustainable production of fuels and chemicals. Key to these chemical transformations are catalysts that can operate with the necessary activity, selectivity, and stability. This talk will focus on materials discovery and development efforts to design, synthesize, and investigate new classes of materials that show promise in catalyzing electrochemical and photo-electrochemical (PEC) reactions of interest. Topics include H2 production from water-splitting, the production of C-based products from the conversion of CO2, and H2O2 production from O2.
(Invited) Accelerated Materials Design and Discovery: Novel Approaches for Accelerating Synthesis, Characterization, and Screening of Materials
Authors: Suram Santosh K
Published: February 2020

High-throughput computations have provided access to multiple properties of several inorganic materials. High-throughput experiments have enabled generation of materials properties under operating conditions. Both these approaches have accelerated discovery of materials. Further acceleration of materials discovery requires integration of these approaches that have different scopes and underlying assumptions.

In this talk, I will present novel approaches based on network theory to predict synthesizability and hence reduce the "synthesis gap" between theory and experiments. Another significant gap between theory and experiment is the "characterization gap" which is due to the need for laborious characterization methods to capture an experimentally synthesized material's fingerprint. In this talk, I will present the use of machine learning methods to address this gap to capture structural, chemical, and electronic fingerprints of materials.

High-throughput experiments have played a significant role in accessing high-dimensional chemical and screening space for materials discovery. However, practical implementations of high-throughput experimentation focuses on a specific region of the large chemical and screening space due to the exponential increase in number of experiments needed as dictated by the curse of dimensionality. I will present further acceleration of high-throughput experimentation by using machine learning approaches. Particularly, approaches that utilize information obtained from high-throughput computations will be discussed.
(Invited) High Throughput Synthesis As an Enabling Capability for Materials and Interface Discovery
Authors: Gregoire John M.
Published: February 2020

The proliferation of computational materials science has resulted in rapid prediction of energy materials, resulting in materials synthesis being a primary bottleneck in materials R&D. High throughput synthesis techniques can help address this bottleneck in certain settings, in particular where automation and parallelization can utilized in a manner that yields materials of sufficient quality and appropriate format for the target technology. Appropriate coupling to characterization and data science are also necessary to take advantage of the large material sets resulting from high throughput synthesis. Challenges in quality control and characterization of fundamental properties will be highlighted. The differences in synthesis design for bulk, surface and interface properties will be described using high throughput screening examples in the areas of light absorber, catalyst, and catalyst-absorber integration, respectively. The needs for continued development and increased utilization of data science will also be discussed.
(Invited) HydroGEN PEC Supernode: Emergent Degradation Mechanisms with Integration and Scale up of PEC Devices
Authors: Danilovic Nemanja , Young James L. , Kistler Tobias , Steiner Myles A , Zeng Guosong , Weng Lien-Chun , Deutsch Todd G , Toma Francesca M. , Houle Frances A , Weber Adam Z.
Published: February 2020

This talk will give an overview of the HydroGEN Photoelectrochemistry (PEC) Supernode and present recent progress. This Supernode project is a collaboration of nine PEC capability nodes that are part of the HydroGEN Advanced Water Splitting Materials (AWSM) consortium. These nodes are contributing to a common objective of developing an understanding of integration issues and emergent degradation mechanisms of PEC devices upon scale up above 1cm2 active areas. Larger devices are expected to introduce new component integration challenges and pathways for degradation that this PEC Supernode project will identify and propose pathways for future progress.

The objective of this Supernode includes: 1) Photoreactor chassis fabrication and baselining, 2) development, fabrication, and testing of larger area PEC devices, 3) development of in-situ morphology and corrosion analysis techniques and characterization, and 4) analysis of durability mechanisms and impacts using modeling LCA and TEA. A new photoreactor chassis will be presented that has been designed to facilitate indoor and on-sun efficiency and durability benchmarking measurements. The design will be validated in a preliminary set of multi-institution round robin measurements toward understanding and harmonizing measurement conditions and protocol. Furthermore, we will present initial STH, durability and degradation characterization results upon scale up to 8 cm2 active area of integrated vapor fed PEC cell.
(Invited) Research Progress of High Temperature Electrolysis (HTE) Supernode
Authors: Ding Dong , Boardman Richard , O'brien James , Ding Hanping , Ginley David , Dinh Huyen N. , Tucker Mike , Sugar Joshua D , Wood Brandon C. , Barnett Scott A , Voorhees Peter W
Published: February 2020

A deeper understanding of high temperature electrolysis (HTE) electrode microstructure evolution as a function of local solid-oxide composition and operating conditions is needed to develop more active, longer-life electrodes. A supernode that advances and orchestrates four HydroGEN node capabilities to provide a unique capability to characterize and predict microstructure evolution of solid oxide electrode materials as a function of electrode materials selection, synthesis methods, and operating conditions and identify the degradation mechanisms. More importantly, the mitigation solutions will be proposed and validated through the Supernode effort. The HTE supernode will support fundamental research and cell development being conducted by HydroGEN projects and commercial developers of HTE stacks. The goal is to help HTE cell developers achieve higher performance and lower degradation rates to reduce the costs of hydrogen production by HTE. In this work, we present the progress on how five national laboratories and one university work together and move forward on the HTE Supernode.
(Invited) Hydrogen Storage Measurements; Protocols and Reproducibility
Authors: Hurst Katherine E. , Parilla Philip A. , Gennett Thomas
Published: February 2020

The transport and storage of hydrogen remains one of the critical challenges for hydrogen-based technologies. Specifically, the U.S. Department of Energy (DOE) has set forth hydrogen storage system targets for gravimetric and volumetric capacities in order to make light-duty polymer electrolyte membrane fuel cell vehicles viable alternatives to the current vehicle driving ranges. Hydrogen storage sorbent materials have shown continuous improvement in the past decade and many DOE targets have been met singularly, however, further advancements in materials development are needed to meet all of the performance targets simultaneously.

The accuracy of hydrogen storage measurements is fundamental to identifying the potential of novel materials. Previous reports have called into question the reproducibility of hydrogen storage measurements. A round-robin report in 2009,[1] discovered large discrepancies among the different participating laboratories for H2 gravimetric capacity measurements on a standard material. This study brought attention to the challenges of H2 capacity measurements, provided recommendations, and discussed possible sources of errors. In a later study, we demonstrated an improved reproducibility amongst a smaller set of laboratories for the excess gravimetric capacity of standard sorption samples.[2] Both of these studies emphasized H2
gravimetric excess capacity. The volumetric capacity, however, is often not reported in the literature as determining volumetric capacities is not as straight-forward, especially for amorphous materials.

Research efforts at the National Renewable Energy Laboratory, as a part of HyMARC, include characterization of thermodynamic and kinetic energetics, and hydrogen adsorption capacity measurements. In this talk, we will discuss the recommended measurement protocols and show the results from a recent comparative study of reproducibility of both volumetric
and
gravimetric H2 capacities. Common analysis protocols and figure of merits for reporting data[3] allow the materials to be compared on an equal basis, and provide insight into the uncertainty of measurements amongst the research community. We will also discuss the issues of approximating absolute capacities and calculating isosteric heats of adsorption at super critical conditions.

[1] C. Zlotea, et.al. Int. J. Hydrog. Energy 34, 3044 (2009), [2] K.E. Hurst et.al. Appl. Phys. A2016, 122, 42.[3] P. Parilla, et.alAppl. Phys. A. 2016, 122, 201.
UV-Stable Inorganic Perovskite Quantum Dots/Cellulose Nanocrystals Hybrid Structures
Authors: Chiang Chih-Hao , Tsai Meng-Lin
Published: February 2020

In recent year, colloidal lead halide perovskite quantum dots (PQDs) play a vital role in the development of various optoelectronic devices including solar cells, light emitting diodes, or displays due to their intriguing properties such as narrow emission peaks, tunable bandgap, and ultrahigh (>90%) photoluminescence quantum yield. However, the poor stability of PQDs either under ambient condition or under ultraviolet (UV) illumination significantly limits PQDs for practical applications. Herein, we developed a novel oleylamine and oleic acid-free strategy to effectively stabilize inorganic CsPbX3 (X = Cl, Br, or I) PQDs by synthesizing PQDs with cellulose nanocrystals (CNC) at room temperature. The as-prepared PQDs/CNC hybrid structures are highly stable and the photoluminescence (PL) intensity can be maintained at 88% of its original value under ambient environment for 2 months, at 90% of its original value under UV light illumination for 600 hours and at 86% of its original value under high temperature (100 °C) for a week, respectively. In addition, by controlling the halide concentration, the hybrid structure can be successfully tuned for light emission throughout the visible spectrum. The high stability, narrow emission peaks, and wavelength tunable characteristics reported here for PQDs/CNC hybrid structures can provide the possibility for practical applications in the future development of PQDs related devices.
(Invited) On Dilemmas of Band Gap Engineering in Luminescence Thermometers
Authors: Sójka Małgorzata , Ramalho João Filipe Candeias Baptista , Brites Carlos Delgado Sousa , Fiaczyk Karolina , Carlos Luís D , Zych Eugeniusz
Published: February 2020

Luminescence thermometry and 2D imaging by means of luminescence thermometric phosphors are of growing interest as these non-contact and almost non-invasive techniques may possibly offer important advantages in some areas of applications. The requirements such thermometers have to fulfill are quite dependent on considered application. It is obvious that bio and medical applications points on different parameters than measurements in cryo range and measuring high temperatures point on yet different needs. Nevertheless, high-sensitivity and low inaccuracy are always appreciated, as well as chemical stability in conditions the thermometers are used.

One of the limitations of luminescence thermometers proposed up to data is the limited range of temperatures they may measure. Clearly, some applications do not need a broad range of a thermometer usability. On the other hand, presenting a good performance over a wide range of temperatures luminescence thermometer could be considered a versatile “all-purpose” device. This might open a door for truly broad usage of such phosphors.

Trying to deliberately manage the performance of luminescence thermometers for broad-range temperature measuring we paid attention into the band gap engineering as a tool to achieve the goal. In this presentation we shall focus on Sr2(Ge,Si)O4:0.05%Pr powders with different Ge:Si ratio to adjust the host lattice band gap and consequently to manage the thermometer performance, see the figure attached. Basing on the lesson learned from Sr2(Ge,Si)O4:0.05%Pr we shell try to draw more general conclusions too.

This research was supported by Polish National Science Centre upon the grant #UMO-2017/25/B/ST5/00824 and by the Portuguese project CICECO-Aveiro Institute of Materials, FCT Ref. UID/CTM/50011/2019.

Figure 1
On-Line Monitoring of the Stability of Electrodes in Non-Aqueous Media
Authors: Ranninger Johanna , Wachs Susanne J. , Möller Jonas , Mayrhofer Karl J. J. , Berkes Balázs B.
Published: February 2020

Stability of electrochemical systems is particularly important in applications. No matter if it is a fuel cell, a battery, a supercapacitor, a construction subject to corrosion or an electrode used for synthesis, economic considerations require a certain lifetime of these systems. Depending on the systems, instability can have several causes, like changes in the mechanical or crystal structure of electrodes, oxidation of materials, decomposition of electrolytes, loss of percolation and electrical conductivity, or material loss due dissolution. Many of these processes happen slowly, causing only minimal performance loss within laboratory timescales. Their studies involve therefore usually long-term measurements with ex situ analysis. In situ, real-time analysis requires very sophisticated and usually coupled analysis methods. In this work we show a powerful approach to study dissolution phenomena in non-aqueous electrochemical systems.

A scanning electrochemical flow cell (SFC) combined with on-line inductively coupled plasma mass spectrometric (ICP-MS) analysis has proven to be a very valuable tool for the study of stability of electrocatalysts in aqueous solutions. This coupled technique is mainly connected to the works of Dr. Mayrhofer and Dr. Cherevko. It was very appealing to develop this method further and make it useable in organic systems too. This task might seem for the first glance to be almost trivial, however, the harsh conditions caused by the organic electrolytes limit the usability of materials to contrive these systems to a huge extent. Furthermore, the ICP-MS is standardized mainly for aqueous media and a lot of experimental work has to be devoted for the optimization of the device for each individual organic solvent. Most of the chemicals used are sensitive to atmospheric components, like O2, H2O, CO2 or even N2. Therefore, the experiments have to be carried out in a glovebox that ensures a controlled and very clean atmosphere.

Platinum is often considered to be a model electrode and catalyst material. This metal is probably the most thoroughly studied one in electrochemistry, however, it still shows many interesting yet not well understood features. This is also true for the stability of the metal during potential cycling. The electrochemical stability window of organic electrolytes is usually much higher than that of water enabling the simultaneous cycling and downstream analysis of dissolution in a higher potential range. As a result, even the electrochemistry of platinum shows hitherto unveiled phenomena regarding its dissolution mechanism. In this work, we focus on the effect of water contamination, anions, cations and organic solvent molecules on the anodic and cathodic dissolution behavior of platinum. To demonstrate the benefits of this novel method on the field of non-aqueous electrochemistry the stability of other non-aqueous systems will be discussed shortly, too.