bluuebunny/crossref_metadata_2025 huggingface dataset:
(Invited) Enhancing Fuel Electrode Reliability of Solid Oxide Electrolyzers
Authors: Elangovan S , Hafen Tyler , Rane Taylor , Pike Jenna , Larsen Dennis , Hartvigsen Joseph
Published: November 2022

Solid oxide electrolysis (SOXE) provides a high efficiency pathway to electrolyze steam, carbon dioxide, or a mixture of the two to produce hydrogen, carbon monoxide, or synthesis gas respectively. Irrespective of the cell design, instability of fuel electrode is a source of performance degradation.

Traditionally, solid oxide electrolysis stacks use nickel–zirconia or nickel–ceria composite cathode to reduce the oxidized species. Nickel based electrodes are susceptible to oxidation by the feed gas (CO2 or steam) at the inlet conditions and are often irreversibly damaged unless reducing gas (carbon monoxide or hydrogen) is also present. This necessitates a complex, recycle loop that introduces a fraction of the product gas to the inlet. The gas recycle approach was successfully implemented for OxEon’s SOXE stack that is operating on Mars to produce high purity oxygen using atmospheric carbon dioxide. Under a NASA SBIR program, OxEon investigated a combination of materials and engineering solutions to improve redox tolerance of the nickel based cathode so that 100% dry CO2could be fed directly into a stack without damaging the electrode. The redox tolerance through the use of a modified nickel based cathode composition has been demonstrated. Button cells and stacks have been shown to tolerate complete oxidation of Ni to NiO, with performance recovery occurring in a matter of minutes using only the CO generated by the electrolysis reaction to re-reduce the cathode. The redox tolerant stack was also demonstrated to show improved coking tolerance over the traditional cathode material. This feature allows higher conversion of CO2enabling increased O2 production. Tests are ongoing to evaluate redox tolerance for steam electrolysis.
(Invited) Novel Air Electrode and Catalyst Materials for High-Performance and Durable Regenerative Proton-Conducting Solid Oxide Cells
Authors: Zhou Yucun , Zhang Weilin , Luo Zheyu , Kane Nicholas , Liu Meilin
Published: November 2022

Regenerative solid oxide cells can operate in either a fuel cell mode or an electrolysis mode as needed. Recently, regenerative proton-conducting solid oxide cells (R-PSOCs) have attracted considerable attention due to their potential for efficient and low-cost power and fuel co-generation.1, 2 However, the performance and durability of R-PSOCs are still limited by the lack of highly active and robust air electrode/catalyst materials for dual-mode operation. In this presentation, we will highlight the critical scientific challenges facing the development of efficient and durable air electrode/catalyst materials for R-PSOCs as well as the strategies for dramatically enhancing electrode activity and durability. We will then present our recent progress in the development of new air electrodes 3, 4 as well as the mechanism of electrode reactions and degradation, as revealed by a combination of modeling, simulation, and in situ/operando characterization of electrode processes 5, 6. Catalytic activity, evolution of the surface chemistry, and contaminant (e.g., water and chromium) tolerance of both the conventional La0.6Sr0.4Co0.2Fe0.8O3−δ (LSCF) electrode and the newly developed PrBa0.8Ca0.2Co2O5+δ–BaCoO3−δ (PBCC–BCO) electrode will be discussed. Performance, long-term stability, and degradation mechanism of R-PSOCs using LSCF and PBCC–BCO air electrodes will be reported. We will further introduce our recent progress in the development of highly active and durable catalyst coatings for the air electrodes with significantly enhanced performance and durability under typical operating conditions with the presence of contaminants.

Reference:

L. Yang, S. Wang, K. Blinn, M. Liu, Z. Liu, Z. Cheng and M. Liu, Science, 2009, 326, 126-129.

C. Duan, J. Huang, N. Sullivan and R. O'Hayre, Appl. Phys. Rev., 2020, 7, 011314.

Y. Zhou, E. Liu, Y. Chen, Y. Liu, L. Zhang, W. Zhang, Z. Luo, N. Kane, B. Zhao and L. Soule, ACS Energy Lett., 2021, 6, 1511-1520.

Y. Zhou, W. Zhang, N. Kane, Z. Luo, K. Pei, K. Sasaki, Y. Choi, Y. Chen, D. Ding and M. Liu, Adv. Funct. Mater., 2021, 2105386.

J. H. Kim, S. Yoo, R. Murphy, Y. Chen, Y. Ding, K. Pei, B. Zhao, G. Kim, Y. Choi and M. Liu, Energy Environ. Sci., 2021, 14, 1506-1516.

Y. Niu, Y. Zhou, W. Zhang, Y. Zhang, C. Evans, Z. Luo, N. Kane, Y. Ding, Y. Chen and X. Guo, Adv. Energy Mater., 2022, 2103783.
Design Optimization of Highly Efficient SOEC Co-Electrolysis Processes
Authors: Nakashima Yuhei , Tachikawa Yuya , Sasaki Kanzunari
Published: November 2022

Introduction

Research is underway to produce synthetic fuels such as hydrocarbon fuels by reacting hydrogen derived from renewable energy with carbon dioxide and other substances, and their use towards a decarbonized society is being considered.1 In this study, we focus on high-temperature co-electrolysis of CO2 and H2O using a solid oxide electrolysis cell (SOEC), which is one of the promising CO2 conversion technologies. The objective of this study is to evaluate the influence of the electrolysis process and operating conditions on the fuel synthesis process based on heat and mass balance analysis and to propose designs for a new fuel production system.

Experimental

A commercial chemical process simulation software Aspen Plus was used to simulate a fuel synthesis process using SOEC high-temperature co-electrolysis. In this simulation, H2O and CO2 were considered to be supplied to the SOEC for co-electrolysis, and a fuel synthesis process such as a CH4 production reactor was connected to the outlet of the SOEC to calculate the overall system efficiency. Figure 1 describes an SOEC and a fuel synthesis reactor of the SOEC high-temperature co-electrolysis process created by Aspen Plus.

Results and discussion

Figure 2 shows one of the simulation results calculated using the process model shown in Figure 1, where the operating temperature of the SOEC is 800 ℃ and the reaction pressure is 1 bar. Figure 2 shows the change in gas composition after the co-electrolysis process in the SOEC by varying H2O flow rate from 1 to 5 mol min-1 relative to CO2 flow rate of 1 mol min-1. As shown in Figure 2, the conversion rate of CO2 to CO increases with increasing H2O flow rate due to the reverse water-gas shift reaction, and the ratio of H2O to CO peaked at H2O/CO2=2, and then gradually decreased. Since the ratio of these gases affects the efficiency of fuel synthesis to CH4 and other downstream gases, we have studied the appropriate fuel synthesis ratio based on the simulation results. In this presentation, we report on the results of the performance evaluation of co-electrolysis and fuel synthesis process based on the obtained simulation results, by conducting electrolysis tests using SOEC cells and evaluating cell performance and downstream gas composition under different operating conditions, based on actual experimental results.

Acknowledgements

This work was partially supported by JSPS KAKENHI Grant Number JP21K04981.

Figure 1
Methanol Fueled Low Temperature Solid Oxide Fuel Cell with Pt-SDC Anodes
Authors: Yang Byung Chan , Jo Sung Eun , Kim Taeyoung , Park Geonwoo , GO Dohyun , Gur Turgut M. , An Jihwan
Published: November 2022

A low-temperature solid oxide fuel cell (LT-SOFC) is a next-generation energy conversion device and has advantages of high energy efficiency, fast start up and shut down and eco-friendliness. In addition, since it has the advantage of being able to use various fuels such as hydrogen, alcohol, and methane gas, research is being actively conducted in recent years. However, LT-SOFC using hydrogen as a fuel has difficulties in storing and transporting fuel, making it difficult to apply as a portable device. On the other hand, methanol fuel is an attractive alternative fuel because it is easier to transport and store than hydrogen fuel and has a high volumetric energy density. However, when methanol is applied to LT-SOFC, there is a disadvantage in performance due to the complicated oxidation process and CO poisoning. Complex methanol oxidation reaction (MOR) and CO poisoning reduce the performance and durability of fuel cells. Therefore, it is important to use a catalyst that can prevent CO poisoning and improve the oxidation reaction of methanol. Pt is an effective catalyst for methanol decomposition and is one of the materials widely used in direct methanol fuel cell (DMFC). However, there is a problem in that it is vulnerable to CO generated during the methanol oxidation process. It is known that CO is adsorbed on the Pt surface, blocks the active site, and reduces catalytic activity. Therefore, alloying Pt with samaria-doped ceria (SDC) with high oxygen storage capacity (OSC) and good OH generation capacity can be effective to reduce CO poisoning and coking.

In this study, we prepared the cells with Pt-SDC cermet anodes with the Pt volume percent of 69 (Pt 0.69), 83 (Pt 0.83), 92 (Pt 0.92), and 95 (Pt 0.95) volume% by varying Pt and SDC powers in the co-sputtering process. In the electrochemical impedance spectroscopy (EIS), ohmic resistance was similar between all samples; on the other hand, activation resistance was measured to be 24.0, 19.5, 31.8, 30.8, and 53.0 Ω∙cm2 at Pt 0.69, Pt 0.83, Pt 0.92, Pt 0.95, and Pt 1 samples, respectively, confirming the lowest activation resistance at Pt 0.83. We speculate that the MOR is improved by the increase of triple phase boundary (TPB) sites and the facilitation of bifunctional CO oxidation mechanisms with higher content of SDC up to 17 mol% (Pt 0.83). However, in the anode with excessive SDC content (31 mol%, Pt 0.69), the Pt is oxidized to form PtO2, lowering the catalytic activity.
Highly Durable Solid Oxide Fuel Cells: Prevention of Chemical Inter-Diffusion By Introducing a 4-Layered Structure
Authors: Hussain Amjad , Song Rak-Hyun , KIM TAE-Hun , Kwon Beom-Su , Ali Muhammad Measam , Joh Dong Woo , Hong Jong-Eun , Lee Seung-Bok , Lim Tak-Hyoung
Published: November 2022

Solid oxide fuel cell (SOFC) poses great potential for stationary power generation. Nevertheless, its full-scale commercialization has lagged due to the inadequacy of long-term durability. Along with diverse background of performance deterioration, the inter-diffusion between the cathode and electrolyte have been identified as a leading fatal factor. Herein, we introduced a robust GDC layer by sequential lamination approach that completely suppresses the detrimental phase of SrZrO3 at electrolyte interface during high temperature operation. This buffer layer is fabricated via green film sequential lamination, in which the anode support, anode functional layer, electrolyte and GDC layers were sequentially co-laminated by iso-static pressing and co-sintered at 1300-1400°C. The enhanced interfacial connectivity and desired packing density of electrolyte and buffer layer were attained by controlling the shrinkages behaviors of each component. Thus, the formation of detrimental secondary phases (SrZrO3) at interface of electrolyte and decomposition of cathode are successfully restrained during fabrication and operation at critical current density. The scale-able and mass production are also confirmed through the fabrication of large area cells (144cm2) having active area 100cm2. The sequentially co-laminated GDC layer exhibited extreme low degradation rate of 0.2%/khr, which fulfils the critical longevity benchmark for commercialization of technology. This work features a cost-effective, scalable, and reproducible method for larger scale production of robust multi-layer anode supported SOFC.

Keywords: Durability, Sequential lamination, life expectancy, Detrimental phases, iso-static pressing
Doped Barium Niobate Perovskite Based Materials for High-Temperature Electrolyzer Application and Efficient Methane Conversion
Authors: Ramaiyan Kannan , Denoyer Luke H , Benavidez Angelica , Garzon Fernando H.
Published: November 2022

Perovskite materials have helped make notable advances in many applications over the last few decades. Specifically, in high temperature electrochemical technologies such as solid oxide fuel cells (SOFC) and electrolyzers where perovskite-based electrolyte and electrode materials are playing pivotal roles. However, high temperature operation poses significant challenges in both fabrication and durable operation that is further complicated by the operating environment. For example, an electrolyte in a SOFC faces a highly oxidizing environment on the cathode while highly reducing environment on the anode and hence should possess chemical stability under these operating conditions and lifetime requirements for energy conversion technologies often times exceed 10 years of usage with no more than 20% degradation.[1]. Electrochemical oxidative coupling of methane (E-OCM) to ethylene process faces further problems associated with coke and carbonate formation along with the over oxidation of CH4 that invariably leads to CO and CO2. Here we present exciting class of barium niobate perovskites where different cations such as Mg, Ca, Y, and Fe on the niobium site was used for doping and evaluated for E-OCM application. The results are compared with another perovskite material Sr2Fe1.5Mo0.5O6-
d (SFMO) that showed good catalytic activity but poor chemical stability. [2][3] Prepared perovskite material was analyzed by XPS, TGA, TPR, SEM, and TEM methodologies towards their chemical stability. Electrochemical properties were evaluated in a home-made setup using different electrolyte materials in the temperature range of 700°C to 900°C by methods such as cyclic voltammetry, impedance spectroscopy, and chronoamperometry. Electrochemical measurements coupled with continuous mass spectra analysis provided valuable insights between product distribution and applied potential. Our results demonstrate doped barium niobates as a promising candidate for stable operation in high temperature electrochemical applications.

References

[1] A. Hauch, S. D. Ebbesen, S. H. Jensen, and M. Mogensen, “Highly efficient high temperature electrolysis,” J. Mater. Chem., vol. 18, no. 20, pp. 2331–2340, 2008, doi: 10.1039/B718822F.

[2] K. P. Ramaiyan, L. H. Denoyer, A. Benavidez, and F. H. Garzon, “Selective electrochemical oxidative coupling of methane mediated by Sr2Fe1.5Mo0.5O6-δ and its chemical stability,” Commun. Chem., vol. 4, no. 1, p. 139, 2021, doi: 10.1038/s42004-021-00568-1.

[3] C. Zhu, S. Hou, X. Hu, J. Lu, F. Chen, and K. Xie, “Electrochemical conversion of methane to ethylene in a solid oxide electrolyzer,” Nat. Commun., vol. 10, no. 1, p. 1173, 2019, doi: 10.1038/s41467-019-09083-3.
Characteristics of (Sr0.92Y0.08)0.85Ti1-XNixO3-
Authors: Kim Jun Ho , Mo Su In , Jung Hong-Ryun , Kim Hee Su , Kim Hyung Soon , Yun Jeong Woo
Published: November 2022

Perovskite with A-site deficiency(A1-xBO3) is promising candidate due to introduction of oxygen vacancy for ionic conductivity and nano-sized exsolution of B component with metal phase for catalytic activity. In this study, Ni-doped Sr0.92Y0.08TiO3 perovskite has been investigated to improve the catalytic activity for CO2 dry internal reforming of methane in solid oxide fuel cells. (Sr0.92Y0.08)0.85Ti1-xNixO3-
𝛿 (x=0.05, 0.10, 0.15, 0.20) perovskite with A-site deficiency is prepared by pechini method and compared to stoichiometric Sr0.92Y0.08Ti1-xNixO3-
𝛿 (SYTN15) perovskite. The physical and physicochemical characteristics of the synthesized powders are analyzed by GC, XRD, BET, TEM, XPS, and TPO. (Sr0.92Y0.08)0.85Ti0.85Ni0.15O3-
𝛿 (SYTN(+)15) shows the highest methane conversion with 93% and carbon dioxide conversion with 86%. In addition, the SYTN(+)15 results to the lowest decreasing rate of the methane conversion with 1.86% drop for 50h. The SYTN(+)15 shows better catalytic performance by 10% for dry reforming of methane (DRM) comparing to the SYTN15. The cell performances of the SYTN(+)15 and the SYTN15 are 60.05mW/cm2 and 28.50mW/cm2, respectively. Consequently, A-site deficiency catalyst, SYTN(+)15 exhibits excellent catalytic activity for DRM and sufficient electrochemical property for SOFC anode materials.
(Invited) Reducing the Operating Temperature of Protonic Ceramic Fuel Cells to <400 °C
Authors: Duan Chuancheng , Liu Fan
Published: November 2022

Protonic ceramic fuel cells (PCFCs) show significant promise for highly efficient and durable power generation. Intermediate-temperature PCFC operation (500–650 °C) enables significantly higher efficiency than low temperature (50–100 °C) polymer electrolyte membrane-based fuel cells and can approach that of high-temperature (700–900 °C) and intermediate-temperature (600 °C) oxygen-ion solid oxide fuel cells (SOFCs). Reduced operating temperatures (versus SOFCs) relax stack and balance-of-plant constraints, potentially lowering the fuel cell manufacturing cost while also improving the reliability, thermal cycling tolerance, and dynamic response. In the last decade, there have been several astonishing demonstrations of high-performance PCFCs. A peak power density of >1.5 W/cm2 has been demonstrated at 600-650 °C. However, PCFCs that operate at 500-650 °C haven’t led to revolutionary changes to the scaleup and commercialization of PCFCs yet, which is due to the operating temperatures are still too high to allow using low-cost interconnects, cheap endplates, and gasket sealant. Although reduced operating temperatures improve the fuel cell durability, PCFCs that operate at 500-650 °C require similar components to HT-SOFCs to build the stacks. Therefore, the operating temperature of PCFCs should be further reduced to <400 °C and the corresponding performance needs to be significantly enhanced to create a new scenario of power generation. At Kansas State University, we have made significant achievements on reducing the operating temperature of PCFCs. Herein, we will present how we rationally design and manufacture PCFCs that achieve remarkable performance and durability at <400 °C.
Bimetal-Doped BaCoO3-δ Materials As Oxygen Electrodes for High-Performance Protonic Ceramic Electrochemical Cells
Authors: Kim Dongyeon , Jang Seungsoo , Oh Seeun , Lee Kang Taek
Published: November 2022

Protonic ceramic electrochemical cells (PCECs) have received considerable attention owing to their ability to reversibly convert chemical fuels into electricity and vice versa on demand at low temperatures below 600 °C. Unfortunately, the sluggish kinetics at the oxygen electrode induces the poor reaction activity and stability of cells. Hence, the development of a highly active oxygen electrode is greatly needed for the realization of high-performance PCECs. One effective strategy is to bimetal doping high-valence cations in the SrCoO3-
𝛿 lattice to improve the oxygen permeability and stability of the oxygen electrode. However, Sr-containing perovskites still have durability issues related to Sr segregation under water vapor conditions. In this regard, BaCoO3-
𝛿 based perovskite oxides have attracted attention as Sr-free oxygen electrodes for many reasons such as large ionic radii, low electronegativity, and cost-effective of Ba compared to that of Sr. Inspired by recent studies, we present bimetal-doped BaCoO3-
𝛿 based perovskite oxides as a highly active and durable oxygen electrode. The bimetal doping strategy of high valence cations in BaCoO3-
𝛿 lattice can be expected to effectively stabilize the structure to form a cubic perovskite phase as well as a higher oxygen vacancy concentration. Through this work, we showcase the bimetal-doping strategy for BaCoO3-
𝛿 perovskite oxides as an oxygen electrode for high-performance PCECs.
(Invited) Electrical, Thermal, and H2o and CO2 Poisoning Behaviors of PrNi0.5Co0.5O3-δ Cathode for Proton Conducting Intermediate Temperature Solid Oxide Fuel Cell
Authors: Sozal Md Shariful , Tang Wei , Das Suprabha , Li Wenhao , Durygin Andriy , Drozd Vadym , Zhang Cheng , Jafarizadeh Borzooye , Wang Chunlei , Agarwal Arvind , Ding Dong , Cheng Zhe
Published: November 2022

PrNi0.5Co0.5O3-δ (PNC) cathode material demonstrates total electrical conductivity on the order of ~300 S/cm at 400-600oC in air, and the conductivity shows a slight increase as temperature increases with an activation energy (from ln(σT) vs 1/T plot) of 10.9 kJ/mol. The introduction of water vapor (H2O) leads to a small (~0.16%) increase in total resistivity, which is reversible upon water removal and explained, tentatively, by the defect reaction of H2O + 2Oo
x + 2h• = 2(OH)O
• + 0.5O2. The thermal expansion coefficient (TEC) of PNC is measured to be 17.6×10-6/K by dilatometry and 18.43×10-6/K by in situ XRD up to 800oC. On the other hand, despite bulk chemical stability for both PNC and BZCYYb4411 powders against low percentage H2O and CO2, a PNC cathode symmetrical cell over proton conducting BaZr0.4Ce0.4Y0.1Yb0.1O3-δ (BZCYYb4411) electrolyte shows degradation (or increase) in interfacial resistance upon introduction of 3% moisture or 5% CO2 into simulated air at temperature in the range of 650 to 450oC. In comparison, oxygen ion conducting symmetrical cells with PNC cathode and Ce0.9Gd0.1O2-δ (GDC) electrolyte show no change upon H2O and CO2 introduction. The observed sensitivity of the PNC cathode proton conducting symmetrical cell to H2O and CO2 is attributed to the preferred adsorption of H2O and CO2 molecules onto the BZCYYb4411 proton conducting electrolyte surface than on the PNC cathode, and such an explanation is supported by temperature programmed desorption (TPD) measurements for H2O and CO2 on both PNC and BZCYYb4411 powders.
(Invited) Selenium as a Top-Cell Absorber Candidate for Tandem Photoelectrochemical Stacks
Authors: Nielsen Rasmus , Youngman Tomas , Crovetto Andrea , Seger Brian , Hansen Ole , Mustafa Hadeel , Levcenco Sergiu , Hempel Hannes , Olsen Thomas , Chorkendorff Ib , Unold Thomas , Vesborg Peter
Published: November 2022

The ideal high-bandgap partner for a tandem solar absorber using c-Si as the low-bandgap bottom cell must have a bandgap of around 1.9 eV and excellent optoelectronic properties.

Selenium, perhaps the very first material to be studied for its photovoltaic properties, is emerging as an interesting candidate for this application. Indeed Se has a bandgap of around 1.95 eV [1] and a steep increase in absorption above this photon energy. Todorov et al showed [2] in 2017 that single-junction Se solar cells could reach 6.5% efficiency using a new cell architecture with a very thin absorber layer. Recently we have increased the OCV to a new record of 991 mV [2]. Simultaneously, we are also starting to identify the main shortfalls of state-of-the-art Se films which so far have prevented Se-cells from approaching their theoretical potential OCV, which is of course much higher than 991 mV. The talk will introduce Se as a solar absorber and discuss we know about its properties and use in solar devices such as PEC stacks.

[1] T. K. Todorov, S. Singh, D. M. Bishop, O. Gunawan, Y. S. Lee, T. S. Gershon, K. W. Brew, P. D. Antunez and R. Haight, Nature Communications, 2017, 8, 682

[2] R. Nielsen, T. Youngman, H. Moustafa, S. Levcenco, H. Hempel, A. Crovetto, T. Olsen, O. Hansen, I. Chorkendorff, T. Unold, P. C. K. Vesborg, (in preparation), 2022
(Invited) Hydrogen Atom Transfer Coupled Dye-Sensitized Photoelectrochemical Cell for Lignin Decomposition
Authors: Kang Hyeong Cheol , Kim Saerona , Yoo Kicheon , Leem Gyu , Lee Jae-Joon
Published: November 2022

For the decomposition process of lignin, there have been several processes reported. However, low selectivity of oxidative cleavage is one of prime issues because of reaction under harsh condition such as high temperature and high pressure. To overcome these problems, especially, dye-sensitized photo-electrochemical cells (HAT-DSPEC), which used photocatalyst (RuC) and homogeneous catalysts incorporated system was suggested. it represents conversion efficiencies over 90% under 24 h light illumination (AM 1.5G). However, metal complex sensitizer has disadvantages like low stability, high cost and low absorption coefficient.

In this study, for highly stable HAT-DSPEC process, metal based sensitizer was replaced by organic dye(5-[4-(diphenylamino)phenyl]thiophene-2-cyanoacrylic acid, L1) which has high stability and molar absorption coefficient. For regenerating dye molecules and oxidating lignin model compounds(LMCs), bicyclic nitroxyl derivates, such as 2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO), and 9-azabicyclo[3,3,1]nonan-3-one-9-oxyl (Keto-ABNO) was used. In HAT-ODSPEC (organic dye-sesitized photo-electrochemical cell), Keto-ABNO exhibits higher photo-electrocatalytic activity than TEMPO for the oxidation and decomposition of LMC. The superior activity of L1 sensitizer with Keto-ABNO mediator is especially noteworthy of Caryl-Cα bond cleavage and with keto-ABNO exhibits 100% conversion yield of for 24hrs at room temperature while 86% with TEMPO. This HAT-ODSPEC process provides a unique foundation to perform selective C−C bond cleavage for real lignin conversion technologies.
(Invited) Efficient and Selective Electrocatalytic and Photoelectrochemical Conversion of Energy and Chemicals
Authors: Jin Song
Published: November 2022

Due to the intermittent nature of most renewable energy sources (such as solar and wind), practical large scale renewable energy utilization demands both efficient energy conversion and large scale energy storage or alternative usage. Earth-abundant but highly active and selective electrocatalysts are needed to enable efficient and sustainable production of fuels and chemicals using electrocatalytic and photoelectrochemical (PEC) energy conversion. We developed earth-abundant electrocatalysts for highly efficient hydrogen evolution reaction (HER) and oxygen evolution (OER). We recently combined computations and experiments to develop metal compounds as selective catalysts for two-electron oxygen reduction reaction (2e- ORR) to produce hydrogen peroxide (H2O2) and the subsequent electro-Fenton process for upgrading biomass molecules. We have integrated these earth-abundant electrocatalysts with efficient semiconductor materials to demonstrate efficient photoelectrochemical hydrogen generation systems. We also developed high performance hybrid solar-charged storage devices that integrate photoelectrochemical solar cells and redox flow batteries (RFBs). In these integrated solar flow batteries (SFBs), solar energy is absorbed by semiconductor electrodes to directly charge up the redox couples without external electric bias. Such charged redox molecules can then be either discharged to generate the electricity when needed or used to produce fuels and chemicals.
(Invited) Ferroelectric Effect in SrTiO3 Promotes Photoelectrochemical Water Oxidation
Authors: Assavachin Samutr , Xiao Chengcan , Mamani Tatiana , Donadio Davide , Osterloh Frank E
Published: November 2022

Ferroelectric materials, such as BaTiO3 or BiFeO3, retain an electric polarization after exposure to an external electric field. In semiconductor photoelectrodes, such a ferroelectric effect (FE) could be potentially used to enhance the carrier separation and photoelectrochemical activity under photoexcitation. However, to date, examples of FE-enhanced photoelectrochemistry are rare. Here, we report the discovery of a FE effect in oxygen vacancy rich SrTiO3 nanoparticles and single crystals, and their application for improved photoelectrochemical water oxidation. Single crystals terminated by [111] facets were subjected to hydrogen annealing at 1000 C to induce oxygen vacancies, as confirmed with optical absorption and X-ray photoelectron spectroscopy. In 0.5 M aqueous Na2SO4 solution 1.0 cm2 large crystals produce a 2.1 mA photocurrent at 0.6 V RHE and under 55 mW cm-2 UV illumination. Prior exposure to 10 kV cm-1 electric field increases the photocurrent to 4.5 mA or decreases it to 0.05 mA, depending on the orientation of the polarization. The effect of the electric polarization on the carrier separation direction is confirmed with surface photovoltage spectra. At room temperature, the FE in SrTiO3 is relatively short lived; samples stored in argon retain 85% of the FE effect after 24h, but samples stored in air loose 100% of the FE, likely due to oxygen uptake and disappearance of the vacancies. To obtain a microscopic interpretation of the observed FE effect we investigated ferroelectricity in oxygen-deficient SrTiO3 by density functional theory with effective many-body corrections. These calculations applied to SrTiO3 bulk and surfaces provide a rationale to interpret the experimental results. The finding of an FE in oxygen vacancy rich SrTiO3 is significant because it may be applicable to other metal oxides in the cubic perovskite structure type.

Figure 1
(Invited) Local and Macroscopic Probes of Semiconductor/Electrocatalyst Photochemical Interfaces
Authors: Boettcher Shannon W. , Kaufman Aaron James , Shen Meikun
Published: November 2022

Charge-carrier-selective interfaces between electrocatalyst particles and semiconductor light absorbers are critical for solar photochemistry but controlling their properties is challenging. In this talk I will show that the nanoelectrode tip of an atomic-force-microscope cantilever can sense the surface electrochemical potential of thin-film and nanoscale electrocatalysts coating semiconductor photoelectrodes during operation. This technique allowed us to unambiguously show that metal (oxy)hydroxide layers act as both hole collectors and oxygen-evolution catalysts on metal-oxide photoanodes such as Fe2O3 and BiVO4. We also discovered the critical role that heterogeneous interfacial barrier heights, and a related nanoscale pinch-off effect, play in building carrier-selective interfaces in semiconductor photoelectrodes for generating fuel from sunlight. As specific example, thin films and nanoparticle of Pt hydrogen-evolution catalysts on p-InP, a high-performance photocathode material, along with macroscopic and nanoscopic electrical and chemical analysis, are used to show how hydrogen alloying, the pinch-off effect for nanoscale contacts, and the formation of a native surface oxides all play different roles in creating charge-carrier-selective junctions. These measurements are compared and contrasted to a new approach to “wirelessly” measure interfacial for different contact materials by analyzing shifts in element-specific shifts in x-ray photoelectron emission energies. The sum of these new insights can be broadly applied to photocathodes, photoanodes, and overall water-splitting systems to control charge-carrier selectivity and improve performance.
(Invited, Digital Presentation) Methane Conversion to High Value Chemicals By Photocatalysis
Authors: Tang Junwang
Published: November 2022

As underlined in the COP26, methane as a greenhouse gas is nearly 80 time more potent than CO2 while its reserve is much more than the sum of coal, oil and natural gas. Thus methane conversion not only involves the environmental issue but also is related to high-value chemical production /clean energy supply, which has been attracting substantial interest over the last decades. However CH4 activation is energy intensive and kinetically very challenging so that methane activation is regarded as the “holy grail” in the catalytically chemical process. [1] Photocatalysis provides a cost efficient potential to activation of such small molecule under very mild conditions, while to achieve the potential is a huge challenge.[2]

Stimulated by our research outcomes on the charge dynamics in inorganic semiconductor photocatalysis, which reveal that the low reaction efficiency is due to both fast charge recombination and large bandgap of an inorganic semiconductor [3,4], together with the recent findings on atomic catalysis [5], we developed novel material strategies for photocatalytic methane conversion to methanol.

Highly dispersed atomic level iron species immobilised on a TiO2 photocatalyst show an excellent activity for methane conversion, resulting into ~97% selectivity towards alcohols operated under ambient conditions by a one-step chemical process [6]. Such photocatalyst is also very stable, promising an attractive industrial process of methane upgrade. The dominating function of the iron species has also been investigated in detail. Furthermore, we designed a flow system for relatively efficient methane to C2, achieving the benchmark results in this area.[7] In addition, C1 oxygenates can be produced with nearly 100% by photocatalytic methane conversion due to the synergy between Au and Cu cocatalysts loaded on ZnO.[8]

References
：

Li, X. Wang, C., Tang, J.
Nature Reviews Materials
, 2022, Doi: 1038/s41578-022-00422-3.

Wang Y., Suzuki H., Xie, J., Tomita, O., Martin, D. J., Higashi, M., Kong, D., Abe R. Tang, J.,
Chem. Rev., 2018, 118: 5201-5241.

Tang, J. Durrant J. R., Klug, R .,
J. Am. Chem. Soc

., 2008, 130(42) : 13885-13891.

Miao, T., Wang, C., Xiong, L., Li, X., Xie, X., Tang, J.,
ACS Catalysis
, 2021, 11, 8226-8238.

Wang, A. Li J., Zhang. T.,
Nat
.
Rev. Chem

., 2018, 2; 65-81.

Xie, J., Jin, R. ,Li, A., Bi, Y., Sankar, G. , Ma , Tang, J.
Nature Catalysis

, 2018, 1: 889-896.

Li, X., Xie J.,Rao, H., Wang, , Tang, J.,
Angewandte Chemie International Edition

, 2020, 132: 19870-19875.

Luo, L., Gong, Z., Xu, Y., Ma, J., Liu, H., Xing, J., Tang, J.,
Journal of the American Chemical Society
, 2022, 144, 2, 740–750.
(Invited, Digital Presentation) X-Ray Spectroscopic Observations at the PEC Electrode-Electrolyte Interface
Authors: Braun Artur
Published: November 2022

Photoelectrochemical cells (PEC) can be used for the absorption of solar light as energy source for the production of solar fuels such as hydrogen, and for the conversion of other species into chemical products. The principles of semiconductor photoelectrochemistry are at the heart of a future PEC technology and economy. There it is important to realize and understand that the conversion of the light energy takes place predominantly in the bulk of the photoeletrode, whereas the chemical conversion takes place at the surface of the electrode, when in contact with the electrolyte. We are dealing therefore with a complex interplay of physical and chemical processes between photovoltaics and electrocatalysis. I will present a suite of ex situ, in situ and operando studies with synchrotron x-rays which helped to elucidate these processes and how they impact on the electronic structure and molecular structure of the photoelectrode, exemplified with iron oxide and tungsten oxide. It is not surprising that we find that the photoelectrode itself participates in chemical reactions which can constitute parasitic reactions which are recorded as photocurrents, but which do not contribute to hydrogen production, for example.
(Invited) Photochemical Energy Conversion with Integrated Plasmonics
Authors: Naldoni Alberto
Published: November 2022

Plasmonic nanostructures can dramatically increase the chemical reaction rates by providing more efficient solar-to-chemical energy conversion. Upon light excitation, metallic nanostructures sustain the collective oscillation of surface electrons, i.e. surface plasmons, producing local field enhancement and after one hundred femtoseconds decaying by generating a non-thermal distribution of hot carriers. Their consequent thermalization results in intense local heating of the nanostructures and their surrounding. All these effects can alter the reaction pathways and boost the reaction kinetics. Such discoveries have boosted the field of plasmonic photocatalysis, which aims at driving industrially-relevant chemical reactions using solar illumination. In this talk, I will present our recent progress in the fabrication of large-area plasmonic metasurfaces exhibiting a rich set of electromagnetic resonances and their integration in photoelectrochemical water splitting cells, direct alcohol fuel cells, and photochemical devices for hydrogen evolution. I will discuss the complex relationship between the optical resonances of the plasmonic metasurfaces with their chemical reactivity by distinguishing the various effects enhancing their photochemical performance. Finally, a new scanning photoelectrochemical method that provide the two-dimensional mapping of the chemical reactivity of plasmonic nanostructures on planar substrates with sub-micron resolution will be introduced.
(Invited) Chemical Interface Damping in Single Plasmonic Nanostructures
Authors: Link Stephan
Published: November 2022

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) Isotropic Hydrogen Evolution Reactions Induced By Plasmon Excitation
Authors: Sato Daiki , Minamimoto Hiro , Murakoshi Kei
Published: November 2022

The efficient visible light energy conversion to the electrochemical reaction system is an important challenge in the field of photoelectrochemistry. The visible light driven hydrogen evolution reaction can be recognized as one of the important targets. Recently, the introduction of the plasmonic metal nanostructures into the semiconductor electrodes has been received much attention because the system which is recognized as the plasmonic photoconversion electrode realizes the visible light response characters. Although various systems have been achieved both the cathodic and anodic reactions through the selection of the materials, the molecular process or charge transfer process have not been fully understood yet. In this study, we have proposed the plasmonic cathode system by combining the p-type semiconductor electrode with the plasmonic nanostructures and examined the both the electron transfer process.We have confirmed the unique isotope effects which cannot be observed the conventional cathode system, reflecting novel characteristics of molecular process at the plasmonic cathodes.
(Invited) Ultrafast Spectroscopy Measurements of Lead-Halide Hybrid Semiconductor Nanocrystals for Photocatalysis
Authors: Beard Matt C
Published: November 2022

We are exploring the use of metal-halide perovskite semiconductor nanocrystals (PNCs) as efficient photocatalysis. Heterogeneous photocatalysis are less common than homogeneous but can provide unique avenues for inducing novel chemical transformations and can also be utilized for energy transductions, i.e., the energy in the photons can be captured in chemical bonds. Additional, earth abundant nanocrystal based photocatalyst are highly sought after as they can potentially eliminate expensive noble metal catalyst. A detailed understand of the underlying reaction mechanism could provide guidance in designing new systems that can activate a larger class of small molecules. Here, we discuss transient absorption spectroscopy to study a model C-C bond formation reaction, i.e., alkylation of aldehydes catalyzed by colloidal CsPbBr3 NCs. We find that both electrons and holes undergo ultrafast charge transfer from photoexcited PNCs. After charge transfer the charge separated state lives ~ 1 ns enabling radical mechanism to form C-C bonds.

I will also discuss the use of PNCs to host a transition metal Cu-site incorporated at the surface of the PNCs to induce a to induce a N-N heterocyclization reaction. The reaction starts from surface coordinated diamine substrates and requires to subsequent photo-oxidation events. We established a photocatalytic cycle where photo-excited holes are funneled to the coordinated substrates.
(Invited) Light-Induced Structural Deformations in BiVO4 Photoanodes
Authors: Sharp Ian D.
Published: November 2022

Monoclinic scheelite bismuth vandate (BiVO4) stands as one of the best performing thin film metal oxide photoanodes investigated to date. However, these desirable photoelectrochemical performance characteristics are surprising given the driving force for free charge carriers to self-trap as polarons. For the case of electrons, localization at vanadium sites leads to formation of small electron polarons with a large, thermally activated hopping barrier of several hundred meV. For the case of holes, several experimental and theoretical studies have indicated polaron formation. However, despite the importance of photogenerated hole extraction for photoanode function, significant uncertainties remain regarding the degree of hole localization, the associated structural configurations, and the transport barriers. In this work, we apply time resolved optical pump/X-ray diffraction probe experiments to investigate light excitation-induced structural transformations of BiVO4. At low pump fluences, we observe a distinct, non-thermal response that indicates increased symmetry and a partial relaxation of the monoclinic distortion within the BiO8 dodecahedra. We rationalize this finding in terms of the underlying electronic structure of BiVO4, photo-induced depopulation of valence band states, and the nature of the monoclinic-to-tetragonal phase transformation. The resulting structural change is expected to increase hole localization and play a key role in the formation and structure of photo-induced hole polarons within the material. Complimentary electronic transport and optical pump-probe spectroscopies provide additional support for this interpretation and shed light on the underlying mechanisms of polaron formation, transport, and recombination in this promising photoanode material.
(Invited, Digital Presentation) Application of in Situ X-Ray Spectroscopy Techniques for Studying CO2 Reduction Reaction
Authors: Yano Junko , Li Xiang , Kaminsky Corey , Sokaras Dimosthenis , Crumlin Ethan J.
Published: November 2022

Artificial photosynthesis capable of the CO2 reduction reaction (CO2RR), with solar energy as external excitation energy and water (H2O) as the electron and proton source, has been considered an attractive method to achieve a sustainable energy cycle, since it allows direct solar-to-chemical energy conversion. To design such systems, X-ray techniques play an important role for gaining the fundamental understanding needed to tailor its components and assemblies, by providing their chemical and structural information [1-3]. We have utilized surface-sensitive soft and hard X-ray techniques to investigate the interaction of metal catalytic surfaces with electrolytes and/or gases (H2O and/or CO2) under in situ/operando conditions. Among those, Ambient Pressure X-ray Photoelectron Spectroscopy (AP-XPS) probes CO2 adsorption on catalyst surfaces, providing the information of the initial atomic level events for CO2 electroreduction on the metal catalysts. In situ X-ray absorption spectroscopy, on the other hand, can complement the study by providing metal catalytic surface sensitive information. We discuss in situ studies of the CO2 reduction reaction, with Cu and related oxides and alloys.

Reference

[1] Lee, S.H.; Lin, J.C.; Farmand, M.; Landers, A.T.; Feaster, J.T.; Avilés Acosta, J.E.; Beeman, J.W.; Ye, Y.; Yano, J.; Mehta, A.; Davis, R.C.; Jaramillo, T.F.; Hahn, C.; Drisdell, W.S., J. Am. Chem. Soc.
143, 588–592 (2020).

[2] Ye, Y.; Su, J.; Lee, K.-J.; Larson, D.; Valero-Vidal, C.; Blum, M.; Yano, J.; Crumlin, E.J., J. Phys. D: Appl. Phys.
54, 234002 (2021).

[3] Ye, Y.; Qian, J.; Yang, H.; Su, H.; Lee, K. -J.; Etxebarria, A.; Cheng, T.; Xiao, H.; Yano, J.; Goddard, W. A.; Crumlin, E. J., ACS Appl. Mater. Interfaces,
12, 25374–25382 (2020).
(Invited) Ultrafast Charge Recombination and Localisation in Transition Metal Oxides with Extended Visible Light Absorption
Authors: Sachs Michael , Harnett-Caulfield Liam , Pastor Ernest , Nelson Jenny , Walsh Aron , Durrant James
Published: November 2022

The development of materials with high activity for photocatalytic water splitting is a central challenge for the production of renewable hydrogen using sunlight. Owing to advantages such as low cost, elemental abundance, and chemical stability, transition metal oxides (TMOs) are some of the most widely used materials for this purpose. The most efficient systems developed to date reach solar-to-hydrogen conversion efficiencies (STH) of around 1%1 and are based on wide bandgap TMOs such as SrTiO3.2 Because such wide bandgap materials often absorb UV light only, TMOs with extended visible light absorption are key to bridge the activity gap towards the target for commercial applications,3 often considered to be 10% STH.

While large research efforts have been devoted to TMOs with smaller bandgaps, efficiencies for such materials have typically remained relatively far from their theoretical limit. For example, Fe2O3 is one of the most studied TMOs in the field of solar fuel production, but it has so far reached only 1/3 of its theoretical maximum activity for water oxidation,4 raising the question of limitations of more fundamental nature.

In this talk, I will discuss the links between ultrafast charge recombination and polaron formation in TMOs – two of the main processes considered to impose efficiency limitations. Firstly, Fe2O3, Cr2O3, and Co3O4, which have absorption onsets of around 2.1 eV, 1.9 eV, and 1.6 eV, respectively, are studied using time-resolved optical spectroscopic techniques to probe their excited state dynamics on a timescale of femtoseconds to seconds following light absorption. I will demonstrate how common photophysical features and dynamics suggest a shared pathway for the recombination and localisation of photogenerated charges in these materials, but with different branching ratios. Secondly, a comparison to wide bandgap metal oxides reveals a different relative importance of these recombination and localisation pathways compared to TMOs with smaller bandgaps. Taken together, a more general photophysical model emerges, providing insights into the performance limiting factors in TMOs, including those with extended visible light absorption.

References:

Wang, Q. et al. Scalable water splitting on particulate photocatalyst sheets with a solar-to-hydrogen energy conversion efficiency exceeding 1%. Nat. Mater. 1–3 (2016).

Takata, T. et al. Photocatalytic water splitting with a quantum efficiency of almost unity. Nature
581, 411–414 (2020).

Chen, S., Takata, T. & Domen, K. Particulate photocatalysts for overall water splitting. Nat. Rev. Mater.
2, 17050 (2017).

Kim, J. Y. et al. Single-crystalline, wormlike hematite photoanodes for efficient solar water splitting. Sci. Rep.
3, 2681 (2013).