bluuebunny/crossref_metadata_2025 huggingface dataset:
(High-Temperature Energy, Materials, & Processes Division Outstanding Achievement Award Address) Mechanisms of Oxide Exsolution and Electrode Applications in Solid Oxide Cells
Authors: Barnett Scott A
Published: November 2022

Solid oxide cell fuel electrodes based on perovskite oxides are desirable to avoid problems with Ni-based anodes, including coking in hydrocarbon fuels and degradation due to fuel impurities or redox cycling. However, oxide anode electrochemical performance is often lacking, limited by surface processes such as the dissociative adsorption of hydrogen. One way to improve such anodes is by the addition of a reducible cation in the oxide formulation, resulting in cation exsolution and nucleation of metallic nanoparticles on oxide surfaces during cell startup and operation. For example, substitution of small amounts of Ni or Ru on the B-site of Sr(Ti,Fe)O3 results in the formation of Ni-Fe or Ru-Fe nanoparticles, respectively, during exposure of the electrode to fuel during cell operation. This talk will examine the microstructural evolution of these exsolution anodes, making use of in situ x-ray diffraction measurements to detect formation of exsolved metal alloys and oxide phase changes. Exsolved metal nanoparticles enhance electrochemical performance, usually by promoting hydrogen dissociation on electrode surfaces. Changes in perovskite stoichiometry resulting from B-site exsolution can also impact the phase stability of the oxide, in some cases resulting in the formation of Ruddlesden-Popper phases that deleteriously affect electrochemical performance. The application of exsolution in fuel electrodes in novel thin-electrolyte oxygen-electrode-supported cells is discussed; the results indicate that performance in H2/H2O fuel is superior to Ni-YSZ in both electrolysis and fuel cell modes. Electrochemical characteristics of the exsolution electrodes are especially superior to Ni-YSZ when operated in CO/CO2 fuel.
Effect of Manganese Concentration in Cerium Oxide Dispersed Ferritic Stainless Steels on Oxidation Behavior for Metallic Interconnect Material of Solid Oxide Fuel Cell
Authors: KIM TAE-Hun , Hussain Amjad , Kwon Beom-Su , Joh Dong Woo , Lee Seung-Bok , Lim Tak-Hyoung , Hong Jong-Eun , Song Rak-Hyun
Published: November 2022

The ferritic stainless steel is used as interconnect materials of planar solid oxide fuel cell (SOFC) stack designs. However, the formation of a Cr2O3 oxide layer on the metallic interconnect is inevitable in the SOFC cathodic environment, and the formed layer decreases its electrical conductivity. In this study, we have investigated the effect of manganese (Mn) concentration in the cerium oxide (CeO2) dispersed ferritic stainless steels on oxidation behavior of SOFC metallic interconnect. The mixed powders with various Mn concentrations of 0.5 to 2wt.% were prepared by high-energy ball milling (HEBM), and subsequently were pelletized and sintered at 1400oC in reduction atmosphere. The area specific resistance (ASR) tests were carried out for 1,000 hrs. in air at 800 oC. The material characterization and morphology analysis of the tested samples were performed. After oxidation test, the oxide scale formed on the surface of the sample with Mn was confirmed as a Mn-Cr spinel structure. The thickness of the oxide scales increased with Mn concentration of the samples. Among the various Mn compositions, the sample with 1wt.% Mn had the lowest area specific resistance. The results show that the Mn in the ferritic stainless steel has great influence on the oxidation behavior. In this talk, we will discuss these results as related the requirements of the SOFC metallic interconnect.
A-Site Doping Effect on the Performance of Sr2Fe1.4 Ni0.1Mo0.5O6-Δ Anodes for SOFCs
Authors: Li Haixia , Wang Wanhua , Park Ka-Young , Lee Taehee , Chen Fanglin (Frank)
Published: November 2022

A site doped Sr2Fe1.4 Ni0.1Mo0.5O6-
δ (SFNM), i.e., La0.1Sr1.9Fe1.4Ni0.1Mo0.5O6-δ
(LSFNM) and Pr0.1Sr1.9Fe1.4Ni0.1Mo0.5O6-δ
(PSFNM) materials have been synthesized by sol-gel method in air and investigated as anode catalysts for intermediate temperature solid oxide fuel cells. Metallic nanoparticle-decorated ceramic anodes were prepared by in situ reduction of the LSFNM and PSFNM in H2 at 850 °C, forming Ruddlesden−Popper structure and FeNi3 bimetallic alloy nanoparticle catalyst. The electrochemical performance of the doped SFNM ceramic anode is greatly enhanced by A site La or Pr doping due to the ~50% decrease of the polarization resistance. The maximum power densities of the LSGM (320μm) electrolyte supported single cells with LSFNM and PSFNM as the anode reached 1.142 and 1.084 W cm−
2 in wet H2 at 850 °C, respectively. LSFNM and PSFNM are promising high-performance anodes for solid oxide fuel cells.

Acknowledgements: Financial support from the U.S. National Science Foundation (DMR–1832809) is greatly appreciated.
Metal Supported Solid Oxide Fuel Cells for Ethanol Fueled Vehicles
Authors: Hu Boxun , Tucker Mike C , Lau Grace Y. , Shen Fengyu
Published: November 2022

Porous metal supported solid oxide fuel cells (MS-SOFCs) have been engineered with micro-pores and nano-sized catalysts for directly converting chemical energy in ethanol to electricity. The MS-SOFCs developed at Lawrence Berkeley National Laboratory offer advantages of rapid start-up, mechanical ruggedness, high performance, and low-cost materials. A symmetric metal/ceramic scaffold with micro-pore range of 1 to 25 μm has been fabricated using tape-casting and lamination. Select catalysts were infiltrated in the porous electrodes and metal supports by fast infiltration. Continuous cell performance improvement has been achieved by optimization of cell structure, processing temperature and catalyst compositions. The stability of MS-SOFCs has been evaluated during continuous operation for >300 hours. The degradation mechanisms revealed by electrochemical impedance spectroscopy and high-resolution scanning electron microscopy techniques will be presented. The effect of impurities such as Cr on the cathode stability has been evaluated at an intermediate operating temperature range of 600 to 700°C. The phase change of praseodymium-oxide oxygen reduction catalysts has been identified at low oxygen pressure (such as nitrogen environment) by in situ high temperature X-ray diffraction.
Surface-State-Controlled Fluence-Dependent Apce Behavior of p-GaAs-TiO2-Pt Water Reduction Photocathode
Authors: Suo Sa , Zhao Fengyi , Xu Zihao , Shi Haotian , Cai Zhi , Zhao Bofan , Hill Craig L , Musaev Djamaladdin G , Lian Tianquan
Published: November 2022

The demand for reform in energy production and reduction in carbon dioxide emission lays emphasis on the development and mechanistic study of photocatalytic water splitting photoelectrodes. Understanding the bottlenecks of the photoelectrochemical (PEC) conversion efficiency in photocatalytic water splitting systems is essential to impart guidance to material selection and photoelectrode design. Absorbed photon-to-current conversion efficiency (APCE), which represents the fraction of absorbed photons converted into electrons in photocurrents, is the key metric in the evaluation of PEC performance. A large portion of studies have reported an illumination fluence-independent APCE under continuous wave (CW) illumination with power densities around 10~100 mW/cm2, whereas few cases have reported the fluence-dependent APCE performance. In the present work, we observe a rarely reported fluence-dependent APCE performance in the p-GaAs/5 nm TiO2/2 nm Pt photocathode under a low-excitation intensity regime. The APCE reaches close to unity at 0.005 mW/cm2 and gradually decreases to 60% at 1 mW/cm2. However, a theoretical explanation for this fluence-dependent APCE reduction is not established.

We develop a steady-state kinetic model with the least parameters to decipher such a phenomenon. In this model, the surface electrons in the GaAs/TiO2/Pt photocathode are consumed by three pathways: 1) transferred to redox active species in solution via the conduction band, 2) trapped into surface states that serve as the reaction sites, which competes with the electron-hole recombination at such surface states, and 3) directly recombining with the surface holes. The APCE decrease at higher illumination intensity is attributed to the increasing recombination between the GaAs holes and the TiO2 electrons caused by the saturation of surface sites. A detailed parametric survey shows that the interfacial electron transfer rate, ks, from the trap states to solution redox species is the only parameter that tunes the extent of the APCE reduction. With higher ks, APCE displays a smaller reduction in response to increasing fluences. Thus, the fluence-dependent feature of the APCE is an indicator that the surface reaction is the efficiency-determining step.

Through this work, we establish a kinetic model for the semiconductor photoelectrode with catalyst layer and successfully explain the cause to the fluence-dependent APCE performance. These significant findings can be universally applied to address the function of catalytic layer (nanoparticle or molecular) and surface modifier in hybrid photoelectrode systems that exhibit fluence-dependent APCE.
Intermetallic Water Splitting (Pre)Catalysts
Authors: Menezes Prashanth W. , Hausmann Jan Niklas , Driess Matthias
Published: November 2022

The continuous increase in the population and industrial development has led to an increase in global energy demand. Most of the current primary energy consumption is obtained from the burning of fossil fuels that releases an enormous amount of greenhouse gases. Notably, hydrogen (H2) is a clean and eco-friendly fuel and has already shown its ability to be a promising substitute for fossil energy. One of the cleanest ways to produce H2 is by splitting of water by electrolysis.1 Recently, numerous inexpensive and robust catalysts based on transition metals (oxides, chalcogenides, pnictides, carbides, or alloys, etc.) have been developed for water splitting with reasonable activity.2 Despite the massive development of electrocatalysts for water splitting, huge challenges still exist for their use in practical application. Our current goals are to uncover new classes of suitable unconventional catalysts based on non-noble metals that can offer better overall catalytic efficiency for practical applications; to study their structural transformation, active sites, surface, and bulk structures; and to investigate the influence of precatalysts on the properties of the final catalyst.

In this context, intermetallic compounds have numerous advantages owing to their intriguing structural, chemical and physical properties, especially being catalytically active and electrically conductive at the same time and thus, making them an ideal class of materials for electrocatalytic applications.3 Using different approaches, we synthesized various classes of intermetallic materials (e.g., stannides, gallides, germanides, indates, silicides, etc.) with interesting structural and electronic features.4-5 Most of these materials exhibited remarkable electrocatalytic activity for water splitting, yielding considerably low overpotentials with enhanced long-term durability for both O2 and H2 generation in alkaline media. The active catalyst structure during each half-reaction (H2 and O2) and the correlation of the structure with the activity of the catalysts were revealed by a profound understanding of the system using in-situ and ex-situ techniques. This talk will provide a brief summary of the ongoing water splitting research as well as delve into selected examples of our recent work to pave the way to a concept-guided design system beyond water electrolysis (e.g., paired electrolysis).

References

[1] H Yang, M Driess, P. W. Menezes, Adv. Energy Mater. 2021, 11, 2102074.

[2] Z Chen, H Yang, Z Kang, M Driess, P. W. Menezes, Adv. Mater. 2022, 2108432.

[3] C. Walter, P. W. Menezes, M. Driess, Chem. Sci. 2021, 12, 8603.

[4] N. Hausmann, R. Beltrán-Suito, S. Mebs, V. Hlukhyy, T. F. Fässler, H. Dau, M. Driess, P. W. Menezes, Adv. Mater. 2021, 33, 2008823.

[5] B. Chakraborty, R. Beltrán-Suito, S. Garai, J. N. Hausmann, M. Driess, P. W. Menezes, Adv. Energy Mater. 2020, 10, 2001377.
(Invited) Computational Modeling of Photoelectrochemical Processes for Hydrogen Production
Authors: Ogitsu Tadashi
Published: November 2022

Recent progresses in predictive modeling methods together with high-fidelity experimental characterization techniques that take device operation condition into consideration led to significant advancements in understanding how microscopic interfacial processes propagate to macroscopic device behavior. In this talk, we will overview our computational modeling efforts within HydroGEN consortium based on various method such as ab-initio atomistic modeling and continuum model, wherein the state-of-art characterization techniques are fully leveraged for the reliability of our interpretation. As examples, we will present our recent activities to improve understanding about the mechanisms that dictate performance and durability of hydrogen production devices, where considering operating conditions and integration with experimental characterization often played critical roles [1-6]. More specifically, we will discuss how computational models have helped to elucidate mechanisms of interface chemistry, formation of new phases, and the impact of interfaces on key reaction pathways that are intimately related to the device performance and durability, wherein experimental characterization data was used as the constraint for our models and obtain new understanding of interfacial phenomena relevant for the performance of hydrogen production techniques. Finally, we will discuss how the obtained knowledge can be used to develop strategies for improving materials used in hydrogen production technologies. This work was supported by the U.S. Department of Energy, Energy Efficiencies and Renewable Energies Office, Hydrogen and Fuel Cells Technologies Office, and was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under contract DE-AC52-07NA27344.
(Invited) Ultrafast Reducing Power of a Plasmonic Photocatalyst
Authors: Frontiera Renee
Published: November 2022

Plasmonic nanomaterials are promising catalysts for selective, green, and efficient photo-driven processes, however currently the mechanisms involved in plasmon-driven catalysis are under debate. Contributions from processes such as vibrational and electronic energy transfer, electron transfer, or electromagnetic field enhancement could all lead to modified potential energy landscapes in the plasmon-molecule system. We have developed ultrafast and electrochemical surface-enhanced Raman spectroscopic (SERS) techniques to probe the contribution of these processes on the nanometer length scale and femtosecond timescale. This talk will highlight the use of these approaches in quantifying the rate, yield, and lifetime of plasmon-to-molecule charge transfer. We monitor changes in the vibrational spectra of adsorbed molecular species following plasmon excitation with picosecond time resolution, and quantify how many molecules are reduced and how quickly they undergo back electron transfer. Overall, these methods allow for quantification of the ultrafast reducing power of a plasmonic surface, and suggest routes for optimizing plasmonic systems for efficient and selective photochemistry.
(Invited) Non-Equilibrium Electroconversion Using Plasmons
Authors: Jain Prashant K
Published: November 2022

Electroconversion is seeing a resurgence due to its utility for the manufacturing of chemicals and fuels powered by renewable energy. While catalyst design and engineering has been the key strategy for optimizing electroconversions, we have found that light excitation can instead be used to modulate the electrochemical activity in cases where the electrocatalyst is comprised of noble metal nanoparticles. The localized surface plasmon resonances of these nanoparticles allow strong absorption of light and the generation of non-equilibrium conditions at the electrode–electrolyte interface. As an outcome, the electrosynthetic activity is boosted beyond the equilibrium limit. I will describe several examples of such phenomena, including electrocatalytic ammonia oxidation, ammonia synthesis, methanol oxidation, and hydrogen evolution. I will also discuss the various non-equilibrium interfacial processes induced by plasmonic excitation and their mechanistic role in the electroconversion.
(Invited) Ultrafast Symmetry-Breaking Charge Separation in Organic Semiconductors
Authors: Wasielewski Michael R , Lin Chenjian , Kim Taeyeon , Schultz Jonathan D , Young Ryan M
Published: November 2022

Understanding the photophysics and photochemistry of molecular π-stacked chromophores is important for utilizing them as functional photonic materials. However, these investigations have been mostly limited to covalent molecular dimers, which can only approximate the electronic and vibronic interactions present in higher oligomers typical of functional organic materials. In this work, we show that a comparison of the excited-state dynamics of a covalent slip-stacked perylenediimide (PDI) dimer(1)and trimer (2) provides fundamental insights into electronic state mixing and symmetry-breaking charge separation (SB-CS) beyond the dimer limit. We find that coherent vibronic coupling to high-frequency modes facilitates ultrafast state mixing between the Frenkel exciton (FE) and charge transfer (CT) states. Subsequently, solvent fluctuations and interchromophore low-frequency vibrations promote CT character in the coherent FE/CT mixed state. The coherent FE/CT mixed state persists in 1, while in 2, low-frequency vibronic coupling collapses the coherence resulting in ultrafast SB-CS between the distal PDI units.

Figure 1
(Invited) Non-Metal P Doping for Efficient Water Splitting
Authors: Jang Ji-Hyun
Published: November 2022

Here, we investigate how a simple in-situ phosphorus (P) doping strategy improves the overall PEC performance of hematite. By introducing enriched FePO4 regions on the Ti-doped FeOOH surface and subsequent high-temperature annealing, P,Ti co-doped Fe2O3 (P,Ti-Fe2O3) nanorods were fabricated. P,Ti-Fe2O3 not only increased the conductivity by creating oxygen vacancies but also generated a porous structure inside the hematite. Benefiting from the efficient P doping effects, the resulting P,Ti-Fe2O3 photoanode exhibited 94% improved photocurrent density compared to that of Ti-Fe2O3 (@ 1.23 VRHE) under 1 sun illumination. After applying the co-catalyst, NiFeOx/P,Ti-Fe2O3 showed significantly enhanced photocurrent density (3.54 mA cm-2 at 1.23 VRHE) with a 108 mV cathodic shift. Our study suggests a new approach for achieving porous hematite and a highly efficient PEC system by a simple and cost-effective nonmetal P-doping method.
(Invited) Understanding Water Oxidation Mechanisms on Heterogeneous Catalyst Surfaces
Authors: Wang Dunwei
Published: November 2022

Water oxidation is an important first step in photosynthesis. It provides electrons and protons for reduction reactions such as hydrogen generation or carbon dioxide reduction. From a technological development perspective, it is critically important to carry out water oxidation on heterogeneous catalyst surfaces. However, this reaction is exceedingly difficult to study. Part of the reason for the challenge lies in the lack of clarity of the catalytically active centers for water oxidation. Another reason for the difficulty comes from the fact that the structures of the active center often evolve under reaction conditions. These issues have made water oxidation by heterogeneous catalysts poorly understood. In this talk, we present our recent efforts in addressing this challenge. Using cobalt oxide-based catalysts as a model system, we introduced a new approach of varying water activities. This was achieved through a "water-in-salt" electrolyte system. It was observed that such an electrolyte allows for discerning two competing mechanisms of water oxidation, namely water nucleophilic attack and intramolecular oxygen coupling. Moreover, it was found that the mechanisms are sensitive to the driving forces, demonstrating a preferences to water nucleophilic attack at high applied potentials and intramolecular oxygen coupling at low applied potentials. The results have major implications to the catalyst design for water oxidation reactions.
(Invited, Digital Presentation) Photocatalytic C-C/C-O Bond Cleavage in Lignin Using a Dye-Sensitized Photoelectrochemical Cell
Authors: Leem Gyu , Li Shuya , Zheng Weiwei , Sherman Benjamin , Lee Jae Joon , Yoo Chang Geun
Published: November 2022

Molecular-based dye-sensitized photoelectrochemical cells (DSPECs) have traditionally targeted solar-driven water splitting for the conversion of solar energy into fuels in aqueous media. Here we describe a novel approach to develop the DSPECs by combining hydrogen atom transfer mediator (HAT) with nanostructured semiconductors and photocatalysts for photocatalytic C−C/C−O bonds cleavage in lignin. This work reports the application of the DSPEC specifically designed to carry out photocatalytic oxidative cleavage of C−C/C−O σ-bonds in lignin model compounds at the photoanode. Current studies targeting the development of photocatalysts via HAT process for biomass conversion especially lignin depolymerization will be described, with the novel finding that a DSPEC utilizes a solar-driven catalytic conversion of woody biomass into value-added fuels and chemicals under aerobic mild conditions. The efficient photocatalytic bond cleavage in DSPECs is important to the development of sustainable approaches for lignin depolymerization and biomass conversion.
(Invited) Crystal Engineering of Bismuth Vanadate for Enhanced Light-Driven Water Oxidation
Authors: Ng Yun Hau
Published: November 2022

Photocatalytic and photoelectrochemical processes employing photoactive semiconductors are two key systems in harvesting sunlight for energy and environmental applications. Strategies have been formulated to improve the properties of the semiconductor for better performances. However, requirements to yield excellent performances are different in these two distinctive systems. Understanding of the underlying mechanism for the photoexcited charge transportation in relation to their photoactivities is of fundamental importance for rational design of high-performing photoactive materials, which may serve as a useful guideline for the fabrication of good photocatalysts or photoelectrodes toward sustainable solar fuels generation. Many photoactive semiconductors, including bismuth vanadate, are having inadequate charge transport properties such as low charge mobility, short lifetime, and slow surface kinetics. Standalone single photoactive semiconductors also faces the challenge of meeting the needs for large redox potentials with a sufficiently narrow bandgap for visible light absorption. Coupling two or more components into a photoactive composite may address some of these drawbacks by utilizing the strengths of the individual semiconductors. In this presentation, the charge transportation behavior of single component photoactive semiconductor based on bismuth vanadate, and the composite materials forming heterojunction with bismuth vanadate, will be examined and discussed (example of modulation of BiVO4 photocatalyst in
Figure 1
).1

Typically, crystal facet engineering, interfacing with non-photoactive secondary component, and narrowing the crystal size into quantum-confinement region, will be the three strategies to be shared with audience during the presentation. Preferential charge migration depending on the crystal facet has been reported in various photocatalysts. These promoted charge migration can be further boosted with spatially deposited cocatalysts on the selective redox sites. The manipulation of crystal facet allows the controlled electron transfer to induce 4-electron process (oxygen evolution) or 2-electron process (hydrogen peroxide evolution) in water oxidation. Nanosizing the bismuth vanadate into <10 nm region with distinctive yet interconnected crystal domains leads to the expansion of band structure. Conduction band of bismuth vanadate was expanded to energetic level capable of reducing proton into H2. The traditional O2-evolving bismuth vanadate is now demonstrating H2-producing properties.

Figure 1:
Time-resolved microwave conductivity (TRMC) spectroscopy signals measured for BiVO4 and its Power-law decay fittings.

Reference

1. H. Wu, R. Irani, K. Zhang, L. Jing, H. Dai, H. Y. Chung, F. F. Abdi, Y. H. Ng*, Unveiling Carrier Dynamics in Periodic Porous BiVO4 Photocatalyst for Enhanced Solar Water Splitting. ACS Energy Lett. 2021, 6, 3400-3407.

Figure 1
Metal Oxide Photocatalyst for Artificial Nitrogen Fixation
Authors: Moore James , Wu Nianqiang
Published: November 2022

The industrial generation of ammonia feedstock through the reduction of dinitrogen is a cornerstone of modern chemical industry. Current methods to produce ammonia using the Haber-Bosch process generate a very large carbon footprint due to sourcing hydrogen gas from fossil fuels as well as from the large energy input required to pressurize and heat the reactant gases. An alternative approach that can source hydrogen from sustainable sources such as water while reducing the overall energy burden by proceeding under milder conditions is direly needed. A possible approach to improve efficiency and utilize alternate hydrogen sources is to use a photocatalyst that can split water and dinitrogen, but currently studied photocatalysts cannot compete with the Haber and Bosch process at scale. To realize the potential photocatalysts can have on the future of industrial ammonia production, much more work will need to be done to understand the fundamental underlying physics to improve design rationale. A polaron, the interaction between holes or electrons with phonons, is a newly studied phenomenon that is known to reduce charge carrier mobility and therefore the photocurrent of a photocatalyst. Herein lies a study on the effect small polarons, which are polarons confined to a single unit cell, have on the photocurrent of a Bi3FeMo2O12 thin film. The polaron phenomenon was characterized using UV-Vis as well as IPCE. A DFT study is also included investigating the lattice sites a polaron will likely form in order to guide future material design.
Influence of Fermi-Level Engineering in Multi-Interface CuO/Cu2o||Rgo||H-WO3||Rgo|| Photoelectrodes on Photoelectrochemical CO2 Reduction
Authors: Bienkowski Krzysztof , Solarska Renata
Published: November 2022

Novel materials, architectures, geometries are crucial for achieving the progress in science in general. Therefore, heterojunction engineering, which enables more versatile and higher performance systems than single components, has emerged as a means of tailoring the optoelectronic properties of photoelectrodes. However, constructing effective and stable hybrid semiconductor heterojunctions is a challenging task under the strict requirements of band alignment, vacancy characteristics, and interface properties. In this presentation, we will demonstrate the enhancement of photoelectrochemical (PEC) reduction of CO2 to methanol, by a novel approach relying on modeling the Fermi level in a multi-interface architecture. The excellent PEC CO2 reduction activity has been attributed to the formation of a high-performance, energetically aligned multi-interface system of CuO/Cu2O||rGO|h-WO3|rGO (rGO = reduced graphene oxide layer). The overall performance of this hybrid system strongly depended on the number of oxygen groups in rGO and the structural properties of rGO. Furthermore, to construct an effective PEC system, numerous postsynthetic treatments were explored for their practicality and usefulness. The results presented herein clearly showed that the best performance toward the CO2 photoreduction currents of 3 mA/cm2 at 0.00.1 V versus RHE (more than double that of the CuO/Cu2O system) had been reached for the semiconductor architecture containing two inter-layers of rGO. The role of those layers in the overall system performance will be an objective of the presentation.
(Invited) Ligand Effect in Electroreduction of CO2: N-Heterocyclic Carbene-Capped Polymers to Promote Catalytic Efficiency
Authors: He Jie
Published: November 2022

N-heterocyclic carbenes (NHCs) are excellent ligands that bind to a variety of transition metals with extremely high binding strength via σ donation. In my talk, I will highlight the use of two polymeric N-heretocyclic carbenes (NHC) (polydentate and monodentate) to stabilize metal nanocatalysts (Au and Pd) for efficient CO2 electroreduction in aqueous solution. Compared with other conventional ligands including thiols and amines, metal-NHC bonds are stable under reductive potentials prevent the nanoclustering of nanoparticles, which is of key importance for any practical application. In particular, Au nanocatalysts modified by polymeric NHC ligands show an activity retention of 86% after CO2 reduction at -0.9 V for 11 h, while it is less than 10% for unmodified Au. We demonstrate that the hydrophobicity of polymer ligands and the enriched surface electron density of metal NPs through σ-donation of NHCs substantially improve the selectivity for CO2 reduction over proton reduction. As a passive coating on the surface of metal nanocatalysts, NHC-terminated polymers can control the accessibility of substrates, i.e., CO2 vs. H2O, as a means to improve the Faradic efficiency toward CO2 reduction. Our results provide guideline to improve catalytic efficiency and stability of metal nanocatalysts for CO2 electroreduction and, more generally, as cathodic materials for other electroreduction reactions.
(Invited, Digital Presentation) Interface Rich Catalyst Design for Enhanced CO2 Conversion
Authors: Kwon Youngkook
Published: November 2022

The efficient electrochemical conversion of CO2 to fuels or stock chemicals with high-energy density would be a major step forward in the introduction of a carbon neutral energy cycle. Especially, understanding the role of electrocatalysts, supports, and electrolytes that can efficiently reduce CO2 to fuels with high selectivity is a subject of significant interest. Copper is the only known catalyst for producing a reasonable quantity of hydrocarbons, which means that designing proper electrode interfaces would modulate the catalytic reactivity and product selectivity. One of the observations on copper catalyst interface is that copper catalyst with a specific atomic-scale gap accelerates the reaction kinetics and selectivity to C2+ products, by confining CO2 and reaction intermediates within a sub-nanoscale reactor in which the reaction energy for CO formation and subsequent C-C coupling can be accelerated. However, the selectivity control toward a target product such as ethylene or ethanol is a remaining issue to be resolved. Recently, we have designed interface rich CuO-Al2CuO4 catalyst and were able to reach about 80% FE of ethylene. In-situ ATR-FTIR and DFT calculation supported that CO2 was selectively converted to CO on CuO and subsequently CO was coupling on Al2CuO4 to ethylene. Therefore, designing interface rich catalysts offers efficient, yet cheap electrochemical CO2 reduction systems.
Modelling the Electrochemical Reduction of CO2 Under Gas-Liquid Channel Flow
Authors: Bagemihl Isabell , van Steijn Volkert , van Ommen J.
Published: November 2022

Electrochemical reduction of CO2 using renewable energy sources is a promising avenue for sustainable production of bulk chemicals. The feasibility of electrochemical CO2 conversion has been demonstrated at lab scale, leading researchers to propose several reactor designs. However, CO2 electrolysis in aqueous systems is severely limited by mass transfer leading to performance parameters insufficient for industrial application. A strategy to enhance mass transfer is to actively introduce CO2 as a gas flow, while keeping diffusion paths between reactants and catalyst short, by separating the gas flow from the liquid electrolyte through a gas diffusion electrode. However, flooding, salt formation, or drying out of the gas diffusion electrode are common problems and present a major obstacle towards commercialisation. A promising reactor concept that enhances mass transfer without the complexity of a gas diffusion electrode is a structured reactor operated under gas-liquid Taylor flow: gas–liquid flow consisting of elongated bubbles in micro- or milli-channels. While this is a proven concept to enhance mass transfer for heterogeneous catalysis in flow cells, literature on this approach for electrochemical processes is scarce and the effect of process conditions on the reactor performance are poorly understood.

In this work, we propose a tubular cell design, inspired from the field of fuel cells, for CO2 electrolysis with a zero-gap membrane electrode assembly. We further, develop a simple analytical model revealing how reactor performance in terms of faradaic efficiency and current density is governed by the key features of Taylor flow. These features film thickness, bubble velocity, and volume fraction of CO2 bubbles over aqueous electrolyte, for a given cathode potential.

We find that the film thickness and the volume ratio of CO2/electrolyte fed to the reactor significantly affect the limiting current density and the faradaic efficiency. Additionally, we find industrially relevant performance with faradaic efficiencies (> 90 %) at current densities of up to 500 mA cm-2, when operating the reactor at elevated pressure beyond 5 bar. This demonstrates the general potential of this reactor concept to overcome mass transfer limitations in the field of electrolysis. We compare our predictions with numerical simulations, showing good agreement for a large window of operation conditions, illustrating when the simple predictive expressions for the current density and faradaic efficiency can be applied. We will discuss the importance of including interdependencies on the reactor scale to assess the economic viability of a reactor design and presents a tool to evaluate reactor design choices. We expect that the simple predictive expressions are instrumental in guiding experimental studies and reactor design choices, taking into account both technical and economic considerations.
(Invited) Recent Progress in the Development of Highly Durable and Conductive Proton Conductors for High-Performance Reversible Solid Oxide Cells
Authors: Luo Zheyu , Zhou Yucun , Hu Xueyu , Liu Meilin
Published: November 2022

Proton conductor-based solid oxide fuel cells (SOFCs) and electrolysis cells (SOECs) are receiving increasing attention because of their potential for operation at intermediate temperatures (400 - 600 oC) with high energy efficiency at low cost. In addition, water is formed/provided on the air electrode side of proton-conducting cells, effectively avoiding fuel dilution and nickel oxidation problems associated with oxide-ion conductor-based cells. To date, doped barium cerates-based perovskite oxides are the most widely adopted proton conducting electrolytes due to their desired electrochemical properties. To achieve high proton conductivity, acceptor doping with rare earth elements is a commonly used strategy, which is critical to the formation of protonic defects. Although many trivalent elements have been studied as dopants in the barium cerate family and reasonable electrochemical performance has been demonstrated, the effect of acceptor dopants on other properties of electrolyte materials, especially in single cells under operating conditions, is yet to be studied in detail. In this presentation, we will report our recent progress in the development of a series of acceptor-doped proton-conducting electrolytes. The results reveal that conductivity, transference number, chemical stability, and compatibility with NiO are all closely correlated with dopant size. In particular, the reactivity with NiO is found to strongly affect the properties of the electrolytes and hence cell performance. Among all tested compositions, an optimized electrolyte shows excellent chemical stability and minimal reactivity towards NiO, as predicted from density functional theory (DFT)-based calculations and confirmed by experimental results. In addition, reversible protonic ceramic electrochemical cells (R-PCECs) based on the optimized electrolyte demonstrate exceptional performance and stability, achieving a remarkable peak power density of 1.2 W cm-2 at 600 oC in the fuel cell mode and a high current density of 2.0 A cm-2 at 1.3 V and 600 oC in the steam electrolysis mode while maintaining long-term durability for over 1000 h without obvious degradation.
Metal-Supported Solid Oxide Electrolysis Cells with Coatings to Suppress Chromium Migration
Authors: Tucker Mike C , Shen Fengyu , Welander Martha M
Published: November 2022

High-temperature electrolysis (HTE) is an efficient technology for converting steam to hydrogen. The performance, durability, and applications of metal-supported solid oxide electrolysis cell technology developed at Lawrence Berkeley National Laboratory (LBNL) will be discussed. The unique LBNL symmetric cell architecture design, with thin zirconia ceramic backbones and electrolyte sandwiched between porous metal supports, offers a number of advantages over conventional all-ceramic cells, including low-cost structural materials (e.g. stainless steel), mechanical ruggedness, excellent tolerance to redox cycling, and extremely fast start-up capability.

An inherent limitation of this design is the intimate contact between the electrode and the porous stainless steel, which is a source of chromium (Cr). Cr migrates from the support to the electrode during cell fabrication and operation, and reacts with the oxygen evolution electrocatalyst (LSCF). This Cr poisoning reduces performance and durability. To overcome this limitation, Cr-blocking coatings have been applied to the porous stainless steel. A variety of coating compositions and deposition techniques have been evaluated. The best coating dramatically reduces the amount of Cr detected in the electrode both after catalyst infiltration at 800°C and after 1000 h continuous operation at 700°C, Fig 1.

Other aspects of the MS-SOEC design and operation have been optimized for performance and durability. These include the infiltrated catalyst composition and processing, metal support structure, and operating temperature.

Figure 1
Intermediate-Temperature Alkane Electrochemical Activation
Authors: Nason Abigail K. , Reese Austin Jerad , Suntivich Jin
Published: November 2022

Electrochemical activation of alkanes plays an enabling role for applications ranging from fuel cells to electro-production of materials and chemicals. Intermediate-temperature (>200 oC) electrochemical devices have improved diffusions, reaction kinetics, and feedstock flexibility. In this contribution, we present the electrochemical activation of alkanes using intermediate-temperature electrochemical devices. Our work is inspired by Duan et al. whose work showed that alkanes can be oxidized as fuel in protonic ceramic fuel cells1. We extend this concept and evaluate whether this electrochemical activation can activate longer-chain hydrocarbons to form industrial gases. We present a comparison of the electrochemical approach to pyrolysis, and in particular, its selectivity. Different electrocatalysts will be evaluated to test both electrochemical and thermal oxidation. Finally, we use small-molecule oxidation experiments to probe how the thermochemical reactions occur in parallel with the electrochemical conversion. We identify the products from these processes and propose the alkane activation mechanism.

Duan, C.; Kee, R. J.; Zhu, H.; Karakaya, C.; Chen, Y.; Ricote, S.; Jarry, A.; Crumlin, E. J.; Hook, D.; Braun, R.; Sullivan, N. P.; O’Hayre, R., Highly durable, coking and sulfur tolerant, fuel-flexible protonic ceramic fuel cells. Nature
2018,
557 (7704), 217-222.
(Invited) Electrochemical Conversion of Nitrogen to Ammonia Using 2D Transition Metal Dichalcogenides
Authors: Miller-Link Elisa
Published: November 2022

We use 2D transition metal dichalcogenide (TMDC) catalysts to facilitate the nitrogen (N2) reduction to ammonia (NH3) via dark electrocatalysis. TMDCs are an important class of materials because they can be reduced to 2D, where their quantum confined properties are easily manipulated for various applications. Transition metal-based catalysts offer a unique opportunity to exploit the d electrons and orbitals for N2 activation, where we specifically compare theoretically and experimentally MoS2, TiS2, and VS2. In addition, the 2D TMDC catalysts are highly tunable 2D catalysts, where the band energetics, surface functionalization, defects, and phase can be tuned to control the N2 reactivity. We use indophenol and 1H NMR with isotope labeling to identify and quantify NH3 from the catalytic reaction and not from setup/system contaminants; moreover, we use density functional theory to add insight into the 2D TMDC active site and reaction pathway. Through various attempts and iterations, we have many lessons learned about experimental and theoretical setup that will be communicated.
Highly Efficient and Cost-Effective Electrocatalysts Using Nickel-Based Metal-Organic Frameworks for Water Splitting
Authors: Bhardwaj Shiva , Gupta Ram K.
Published: November 2022

The low-cost nickel compound is one of the most effective electrocatalysts among the transition metals-based electrocatalysts. Therefore, understanding the electroactivity of nickel-based metal-organic frameworks (MOFs) plays a vital role in green energy production via hydrogen and oxygen evolution reactions. The demand for green and efficient energy devices is increasing rapidly and fuels cells could be one of the solutions for such requirements. This work introduces the use of MOF-derived nickel hydroxide and oxide as highly efficient electrocatalysts. The electrocatalysts were synthesized using a hydrothermal method at different growth temperatures (140, 160, and 180 °C). Glutaric acid was used as an organic ligand. The MOF-based nickel hydroxide was converted to nickel oxide via a facile calcination process at 350 °C. The best sample of MOF-derived nickel oxide (160 °C) showed an oxygen evolution overpotential of 394 mV at 10 mA/cm2 with a Tafel slope of 73 mV/dec. The unique structure of MOF-derived nickel hydroxide provides more electroactive sites. The shorter pathway for ion transference reduces the overpotential to 330 mV at 10 mA/cm2 with the lowest Tafel slope of 107 mV/dec. The best MOF-based nickel oxide electrocatalyst for hydrogen evolution reaction required 103 mV to deliver 10 mA/cm2. On the other hand, MOF-based nickel hydroxide needed 189 mV of overpotential to reach 10 mA/cm2. The stability of the prepared electrocatalysts was tested using cyclic linear voltammetry and chronoamperometry. Both measurements showed high electrocatalytic stability of the prepared samples for over 1,000 cycles of linear voltammetry and 24 hrs of chronoamperometry test. Our research provides cost-effective and highly efficient electrocatalysts for green energy production.
Improved Stability of Nickel-Iron Based Oxygen Evolution Electrocatalyst By the Immobilization of Tetraphenylporphyrin
Authors: Kang Sinwoo , Im Changbin , Spanos Ioannis , Ham Kahyun , Lim Ahyoun , Schlögl Robert , Jacob Timo , Lee Jaeyoung
Published: November 2022

Anion exchange membrane water electrolysis (AEMWE) is an attractive technology for the production of green hydrogen and has advantages in terms of cost owing to the use of non-precious catalyst materials. NiFe-based materials are the best-in-class electrocatalysts for the alkaline oxygen evolution reaction. Defining the active sites of NiFe-based materials has been a controversial issue over the past decades. Previously, Ni was regarded as an active site; however, active sites, such as Fe or Ni–Fe dual active sites have been considered in recent studies. Despite the complexity of heterogeneous catalysis, with the aid of in situ/operando measurements and density functional theory (DFT) calculations, Fe was selected as the ultimate active site in state-of-the-art materials. However, the electrocatalyst suffers from rapid degradation in Fe-purified KOH. Herein, we report a catalyst/electrolyte interface engineering strategy using tetraphenylporphyrin (TPP) to alleviate the destabilization of NiFe-based catalysts. The online electrochemical flow cell inductively coupled plasma-optical emission spectroscopy proved that thermodynamically unstable Fe liberation was the primary cause of deactivation. TPP acts as a protective layer and suppresses hydrated metal dissolution at the catalyst/electrolyte interface. The stable TPP layer on NiFe elongates the lifetime near the electrode, enhancing the redeposition kinetics of the active site, Fe. As a proof of concept, the role of TPP was validated at the half-cell and 2.4 times suppression of degradation rate in AEMWE scale at a constant current density of 500 mA cm-2. This strategy of using a TPP as a protective layer may serve as a new platform for stable oxygen evolution electrocatalysts.
Influence of Exchange Correlation Functional on Electrochemically Relevant Properties for Protonic Ceramic Fuel Cells
Authors: Sjølin Benjamin Heckscher , Castelli Ivano Eligio , Vegge Tejs
Published: November 2022

Conductivity plays a crucial role in devices for the green transition: solid-state electrolytes in all-solid-state batteries need to be ionically conductive but electronically insulating, electrodes for protonic ceramic fuel cell need to be simultaneously ionic (O2- and H+) and electron conducting. We benchmark different Density Functional Theory (DFT) methods on the accuracy of descriptors to estimate electronic and ionic conductivity as well as thermodynamic and electrochemical stability. Calculation of these using density functional theory requires relaxations, high k-point calculations and nudged elastic band calculations, which can all benefit from cheap functionals. The result of this work is to be used in a high-throughput screening for perovskite materials for protonic ceramic fuel cell cathodes.
Unrevealing the Correlation between Temperature and Electrocatalytic Activities of Cobalt Sulfide for Oxygen Evolution and Glycerol Oxidation Reactions
Authors: He Rong , Luo Hongmei , Zhou Xiao-Dong , Zhou Meng
Published: November 2022

The drastic depletion of carbon-based conventional fossil fuels with significant release of greenhouse gases have stimulated research interest towards the development of renewable energy resources. The electrochemical water splitting is considered a promising approach for the sustainable production of clean hydrogen. However, it is severely restricted by oxygen evolution reaction (OER) due to the sluggish kinetics of its complicated oxidation process. Hence, the electrocatalytic performance of OER has a significant impact on the overall water splitting rate and energy efficiency. In this work, we reported two efficient strategies to accelerate OER by adding glycerol as chemical mediator and increasing temperature. The cobalt sulfide nanosheets directly grown on nickel foam (Co-S/Ni3S2@NF) were prepared by hydrothermal method and demonstrated an outstanding OER performance with an overpotential of ~ 340 mV (1.57 V) to achieve a current density of 20 mA cm-2 in alkaline solution, favorably comparing the performance of the noble metal-based catalyst IrO2@NF. This electrocatalyst only requires a potential of ~ 1.35 V to reach the same current density by adding glycerol to the alkaline electrolyte, indicating that glycerol oxidation reaction (GOR) has great potential to replace the sluggish OER. In addition, we found that the OER/GOR electrocatalytic activity increased with increasing temperature. Double current densities for both OER and GOR can be obtained at a potential of 1.60 V when the temperature increased to ~55 oC. This study provides two efficient approaches to overcome the sluggish kinetics of OER and offers new perspectives to improve the energy efficiency for clean hydrogen production.