bluuebunny/crossref_metadata_2025 huggingface dataset:
Understanding the Mechanisms for Recoverable Vs. Unrecoverable AEMFC Degradation
Authors: Ul Hassan Noor , Adabi Firouzjaie Horie , Mustain William E.
Published: May 2020

In recent years there has been significant improvement in the achievable current and peak power densities [1 - 3] as well as the longevity of operating AEMFCs [4]. However, cell performance degradation remains an area of concern for the technology and a key to reducing performance decline is understanding mechanisms at work – which includes both recoverable and irrecoverable (irreversible) losses. To date, very few studies have been done that aim to understand and counter performance degradation mechanisms, while those that have generally focused only on irrecoverable performance degradation [5,6] The present study highlights recoverable (mainly associated with water management) and unrecoverable degradation mechanisms (AEM and Ionomer degradation, catalyst loss etc.) and propose solutions for these problems. Rigorous experiments have been performed to understand the degradation processes and fundamental factors have been explored responsible for AEMFC in-situ degradation.

References

[1] Huang et al., “Composite Poly (norbornene) Anion Conducting Membranes for Achieving Durability, Water Management and High Power (3.4 W/cm2) in Hydrogen/Oxygen Alkaline Fuel Cells”, J. Electrochem. Soc. 2019 volume 166, issue 10, F637-F644.

[2] Mandal et al., “The Importance of Water Transport in High Conductivity and High-Power Alkaline Fuel Cells”, J. Electrochem. Soc. 2020 volume 167, issue 5, 054501.

[3] Kohl et al., “High Conductivity, Stable Anion Conducting Membranes Based on Poly(norbornene)”. 235th ECS Meeting.

[4] Peng et al., “Improving the Long-Term Operational Stability (>1000h) of AEMFCS By Understanding Water Dynamics through in-Situ Neutron Imaging and X-Ray Computed Tomography”, 236th ECS Meeting.

[5] Dekel et al., “Predicting performance stability of anion exchange membrane fuel cells”, Journal of Power Sources, Volume 420, 30 April 2019, Pages 118-123.

[6] Charles E.Diesendruck and Dario R.Dekel, “Water – A key parameter in the stability of anion exchange membrane fuel cells”, Current Opinion in Electrochemistry, Volume 9, June 2018, Pages 173-178.
Using Impedance to Quantify Transport Losses in Alkaline Water Electrolysis Electrode Catalyst Layers
Authors: Reumert Alexander Kappel
Published: May 2020

Anthropogenic climate change has brought on a global climate crisis and emergency. Increased levels of atmospheric carbon dioxide levels has brought with it undesirable changes to the world’s climate. To halt and eventually stop this trend the world needs to move to zero-carbon sources of electricity, transport and chemical production.

To offset the variability in zero-carbon electricity sources storage or usage of the excess energy is necessary. One of several technologies to achieve this is water electrolysis. A promising candidate of this field of study is Alkaline Water Electrolysis

The field of alkaline electrolysis have recently moved from a gap-based macro-material approach to a nanomaterials based membrane cell architecture.

Due to recent advances in membrane technology both ion-conduction and electrolyte solvating membranes allow for a zero-gap architecture. With this approach comes new engineering challenges. Bubble formation, -diffusion, -suppresion, and –transport are all phenomena that are recently unexplored in the context of nanopowder-based electrode in flooded KOH systems.

One of the ways of exploring this is the use of Galvanostactic Electrochemical Impedance Spectroscopy (GEIS)..

Through GEIS investigations and Distribution of Relaxation Times of the electrochemical response of nano-powder based cathodes a Gerischer-like response indicating transport issues and a way of quantifying this.
Spray Pyrolysis Strategy for Preparation of Cathode-Supported Protonic Ceramic Fuel Cells
Authors: Tsimekas Georgios , Irvine John T. S.
Published: May 2020

Since the discovery of proton conducting ceramic materials many research efforts have been focused into overcoming processing difficulties that hinder long-term stability and high performance of protonic ceramic fuel cells (PCFCs). Notably, high processing temperatures exceeding 1600 °C are often required to meet the microstructural demand of a dense proton conducting electrolyte membrane [1-2]. At this temperature range most potential electrode materials are chemically incompatible and therefore preclude the fabrication of electrode supported structures. In addition, for barium-based electrolytes (e.g. BaZr1-xYxO3-d) barium loss is anticipated resulting in lower conductivities and formation of structural defects. To overcome this major challenge thin film deposition techniques can be employed[3-4].

Spray pyrolysis is a cost effective and simple deposition technique for preparation of ultra-thin films (i.e.<5μm) enabling the reduction of operating and processing temperatures of fuel cells [5]. Microstructures and electrochemical performance of multi-layered thin film PCFCs fabricated at exceptional low temperatures of 950 °C, are investigated. Large area 5x5cm2 cathode substrates of (La0.8Sr0.2)0.95MnO3-d prepared by tape casting were used for mechanical support of the cells. To modify and reduce the surface porosity of the substrate Ce0.9Gd0.1O3-d was coated to facilitate the deposition of the BaZr0.9Y0.1O3-d (BZY) thin electrolyte. Subsequently, the anode electrode was sprayed in two stages comprised by a nano-porous layer of BZY and infiltrated Ni particles. Characterization of the cathode-supported PCFCs was performed by electrical measurements operating up to 600°C and scanning electron microscopy (SEM), X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDX) techniques.

[1] Shanwen Tao and John T.S. Irvine, Adv. Mater., 18, 1581-1584, (2006).

[2] Peter Babilo and Sossina M. Haile, J. Am. Ceram. Soc., 88 2362-2368, (2005).

[3] Kiho Bae et al., Adv. Energy Mater., 8, 1801315, (2018).

[4] Georgios Tsimekas et al., ECS J. Solid State Sci. Technol.,6(8), P553-P560, (2017).

[5] Georgios Tsimekas et al., ECS Trans., 70(1), 205-212, (2015).
Designing the Ideal Catalyst Layer in PEMFCs
Authors: Lamb James , Andrei Petru
Published: May 2020

Many design parameters affect the performance of PEMFCs, including catalyst density, porosity, nafion distribution, agglomerate size, etc. The ideal values of these parameters vary not only from layer to layer (for instance from catalyst layer to gas diffusion layer or from anode catalyst layer to cathode catalyst layer) but also from location to location inside the same layer, resulting in non-uniform 3-dimensional spatial distributions of the platinum, nafion, and pore and agglomerate sizes. Furthermore, the optimal values of these parameters also depends on the operating conditions, such as electrical current density, pressure, and temperature, which increases the complexity of the problem even more. To design the ideal catalyst layer, the designer must determine the optimum distributions of the above parameters within each layer. In this work, we focus on estimating the ideal structure of the catalyst layer in PEMFCs, in particular on determining the optimum spatial distributions of the platinum, porosity, nafion, and agglomerate size.

To solve the above problem, we apply the adjoint method to compute the optimum parameters for the microstructure of the catalyst layer. We start by computing the sensitivity functions (which are related to the Gâteaux derivatives) of the cell voltage or current in the direction of the design parameter variation. The sensitivity functions are then applied to adjust the parameters of the entire catalyst layer in a point-by-point fashion. The process is repeated until convergence is obtained.

Numerical results will be presented showing the non-optimized and optimized distributions at different values of the operating current density, temperature, and pressure for a 25 μm membrane PEMFC, as well as the polarization curves for non-optimized and optimized configurations.

References

[1] M. Secanell, K. Karan, A. Suleman and N. Djilali, Jour of the Electrochemical Society, 155, B125 (2008).

[2] F. C. Cetinbas, S. G. Advani and A. K. Prasad, Jour of Power Sources, 250, 110 (2014).

[3] J. Lamb, G. Mixon and P. Andrei, Jour of the ECS, 164, E3232 (2017).

[4] P. Andrei and L. Oniciuc, Jour of Appl. Physics, 104, Art. No. 104508 (2008).

[5] P. Andrei and L. Oniciuc, Jour of Comp. Elec., 7, 111 (2008).
Enhancing the Stability and Performance of Mo-Doped Titanium Suboxide Fuel Cell Catalyst Supports
Authors: Alipour Moghadam Esfahani Reza , Easton E. Bradley
Published: May 2020

Polymer electrolyte membrane fuel cells (PEMFCs) are a near-commercial clean energy technology with potential application in automotive and station power systems. However, the high cost of Pt catalyst and long-term durability of electrode materials still represents barriers towards that hinder market gains for the technology. The catalyst support material greatly influences electrocatalytic activity and durability of the catalytic Pt nanoparticles. Carbon black has been the primary catalyst support in fuel cells over the last 30 years due to its high surface area and electrical conductivity. However, carbon corrosion occurs readily during start-up/shutdown conditions. Therefore, more advanced support materials are need in order to overcome these problems.

Metal oxides supports have improved corrosion resistance over carbon black supports, but they typically lack the required electrical conductivity for high performance. Titanium suboxides, specifically those doped with Mo (TOM) and other metals, have been shown to have acceptable electronic conductivity and strong affinity for Pt nanoparticles, to enhance their activity and stability in fuel cells. However, doping with only Mo still creates materials with a sizable band bandgap of 2.6 eV. Furthermore, the long term stability of the Mo dopant is a potential concern.

Our group has taken a two-pronged approach to improving TOM materials. The first approach has been to add a second dopant. Specifically, we have a new material doped with both Mo and Si, Ti3O5-Mo-Si (hereafter referred to as TOMS) support. Remarkably, this support has a band gap of only 0.31 eV, approaching the conductivity of a metal. Furthermore, the TOMS material are highly durable and corrosion resistant, showing no signs of dopant loss under extremely corrosive conditions.

Our second approach to improving TOM has been to convert it into a nanotube structure (TNTS-Mo) and from there covalently attach a monolayer of a nitrogen-rich terpyridine (tpy) ligand to the surface of the support (hereafter referred to as TPY/TNTS-Mo). The tpy ligand serves as a protective barrier that stabilizes the TNTS-Mo support. Furthermore, the nitrogen groups also have an electronic interaction with Pt catalyst nanoparticles that enhances their stability under harsh operating conditions.

In this presentation, we will give an overview of support modification methods as well as detailed discussion of catalyst durability.

Figure 1
Synthesis of Au Nanoparticles Attached to Large-Area Cu-Oxide Nanowires By Thermal Treatment for Artificial Photosynthesis Process
Authors: Canto-Olvera Jose Fernando , Cigarroa-Mayorga Oscar E. , Guillen-Cervantes Angel
Published: May 2020

Developing materials for fuels based on solar utilization is a current need to solve the energy problem in the world society [1]. The proposal of heterostructures conformed by nanowires and nanoparticles has been suggested for solar energy recovery application [2] focused on the artificial photosynthesis process.

In this work, heterostructures of copper oxide nanowires (CuO-Nw) and Gold nanoparticles (Au-Np) were achieved by thermal treatment. To grow the nanowires array, a Cu foil (99.99 % in purity) of 1 cm x 1 cm was chemically etched with 1 M nitric acid solution for 10 seconds, then it was isothermally heated in a horizontal furnace. The Oxygen atmosphere inside the furnace was controlled within 21 wt. % ± 1 wt. % content and a 20 L/min flux rate was used. The effect of temperature and time on density, diameter, and length of CuO-Nw was studied. The experiments were carried out at 400, 500 and 600 °C for 1h, 3h, and 5h. Afterward, Cu-O Nw were Au-coated by sputtering. Au films with 10 nm and 60 nm in thickness were deposited. In order to synthetize the Au-Np a thermal treatment was isothermally performed under Nitrogen atmosphere at 450 °C for 15 min. To guaranty reproducibility, the experiments were performed by triplicate in separated experiments.

Field emission scanning electron microscopy images proved the achievement of heterostructures consisting of Au-Np attached to CuO-Nw walls. The average diameter of Au-Np was obtained about 60 nm and 80 nm. No organic contaminants were identified by Raman spectroscopy, thus, the proposed methodology is a clean and environment friendly process. Cyclovoltammetry curves were recorded by potentiometer chamber in alkaline medium to characterize the electrochemical response of samples. It was found that Au-coated heterostructures exhibit an enhancement in efficiency for oxygen evolution reaction against those containing CuO-Nw array alone.

Acknowledgments

The authors acknowledge the Secretaría de Investigación y Posgrado of the IPN for the economic support to this work. The authors have no conflict of interest to disclosure.

References

[1] Beck, Fiona J., ACS Applied Energy Materials (2019), doi: 10.1021/acsaem.9b01030

[2] Cigarroa-Mayorga, O., Neri, E., Calderon, H., & Kisielowski, C. Microscopy and Microanalysis (2017), doi:10.1017/S143192761701100X

Figure 1
Cerium-Mediated Hydrogen Production and Energy Storage System
Authors: Frey Daniel , Modestino Miguel Antonio
Published: May 2020

The implementation of electrolysis systems for electrochemical hydrogen production has continued to grow as the paradigm shift towards renewable energy and fuels progresses. However, some issues regarding conventional polymer electrolyte membrane (PEM) electrolysis systems still remain; the performance of PEM electrolyzers degrade if operated with intermittent energy sources, while the cost of electricity continues to be the highest cost contributor (over 70% of hydrogen production cost). In order to make electrochemical hydrogen production more feasible and compete with methane reforming on a large scale, renewable energy sources and new strategies are needed to reduce the electricity cost. Decoupled electrolysis systems have been studied to temporally and spatially separate the evolution of hydrogen and oxygen, making the electrolysis system safer, but these systems only add an additional electricity burden. In this presentation, I will describe a cerium-mediated decoupled water electrolysis system that can produce hydrogen and store energy through a redox cycle that bridges the hydrogen evolution and oxygen evolution reactions. Cerium (III/IV) was chosen as a redox couple given that it exhibits a higher oxidation potential (~1.6V) than water. This high redox potential of Ce allows for the design of a dual function (i.e., energy storage and hydrogen generation) system consisting of a hydrogen evolution cell which requires an energy input to oxidize Ce(III) and reduce protons, and an oxygen evolution cell which outputs energy by reducing Ce(IV) and oxidizing water. This dual function design can reduce the costs of electrochemical hydrogen production in renewable-rich electricity grids by operating the hydrogen evolution cell when the electricity prices are low and the oxygen evolution cell when they are high. In this talk, I will discuss the electrochemical performance of this system with regards to operational factors such as temperature, flow rate, and concentrations of reactants. In addition, I will discuss the technoeconomic factors that drive the hydrogen production cost in the redox-mediated system and compare them to PEM electrolysis under grid scenarios with various degrees of renewable energy penetration. Finally, I will discuss on-going research into the improvement of the electrochemical performance and efficiency of this system, focusing on enhancing mass transport and faradaic efficiencies in Ce redox processes.

Figure 1
Electrochemical CH4 Oxidation on Spinel NiCo2O4-Based Composite Catalysts
Authors: Al-Attas Tareq Ali , Kibria Md Golam
Published: May 2020

CH4 is the main component of natural gas, which represents 21.4 % of the total primary sources of energy in the world; it is an essential fuel for both daily human life and chemical industry. The increasing emissions of methane is considered as a crucial issue because its effect as a greenhouse gas is more than 30 times potent than that of CO2. One attractive solution to cut-off the impact of methane emission is performed by oxidizing methane into liquid high-value fuels, such as methanol. For decades, the conversion of methane into liquid fuels has been a significant challenge for heterogeneous catalysis. Nevertheless, to yield higher efficiencies, complicated multistage processes should be utilized, which require higher pressures and temperatures and consequently extended infrastructure. On the contrary, the electrochemical oxidation of methane could be a far more promising approach. The challenge of producing liquid intermediate products at elevated rates and selectivity lies in activating CH4 while suppressing the competing oxygen evolution reaction (OER) and its complete oxidation into carbon dioxide, which is the most thermodynamically favorable product. It is worth mentioning that the direct electrochemical oxidation of CH4 at mild conditions is extremely sluggish. Alternatively, the CH4 oxidation could be achieved via exploiting the partial OER. The reaction would take place purely through a thermal catalytic step, whereby coupling the adsorbed oxygen atom (*O) on the active sites governed by the first two elementary reactions in OER with CH4 in the vicinity to it. Here, nickel-cobalt oxide (NiCo2O4)-based nanowire electrodes for partial oxidation of CH4 are reported. The NiCo2O4-based materials could achieve elevated electrochemical performance by its resilience in terms of controlling the pore properties and morphology. Nanowire catalysts with porous structures are attained by the facile decomposition of the adsorbed cetrimonium bromide during the calcination process. The spinel NiCo2O4 is further improved by incorporating metal oxides, i.e., RuO2 and V2O5, oxygen delivery sources. Moreover, the synergistic effects of the NiCo2O4 and metal oxides would enhance the conductivity and its bi-functional catalytic activity towards favoring CH4 and O* coupling. The electrocatalysts are investigated at room temperature in a liquid-phase electrolyzer, where the CH4 gas and anolyte flows are separated by a carbon-based gas diffusion layer that sandwiches the reaction interface between separate conductive and hydrophobic supports.

Keywords
: methane oxidation; NiCo2O4; synergistic effects; oxygen evolution reaction; gas diffusion electrode; spinel.
(Invited) In Depth Analysis of the Promotion of Ni on Mg:SrTiO3 By CrOx
Authors: Mul Guido , Han Kai , Haiber Diane , Cherevko Serhiy , Crozier Peter A , Mei Bastian Timo
Published: May 2020

Ni/NiO-Mg:SrTiO3 is a promising formulation for the overall splitting of water to H2 and O2 when illuminated with light of 365 nm. The preparation prescribes various steps, including solid state synthesis of MgO/TiO2, followed by mixing with SrCO3 and calcination at 1100 C for 10 h. Ni@NiO is deposited by impregnation, calcination, reduction in H2, and passivation with O2. When CrOx is finally photodeposited on such composite, a significant enhancement of the performance is observed, both in activity and stability. A steady state apparent quantum yield at 365 nm of no less than 38% is obtained. The composition of the photo-active material was investigated using state-of-the-art electron microscopy and elemental analysis, which demonstrates that CrOx is photodeposited in the vicinity of several, but not all Ni/NiO particles. This is explained by the inhomogeneity in interfacial contact between the Ni/NiO particles and the Mg:SrTiO3 substrate, affecting the probability of reduction of Cr(VI)-species during the photodeposition process. In situ ICP shows various elements of the composite catalyst leach into solution, including Sr, Mg and Ni. CrOx reduces leaching of Ni/NiO from Ni/NiO-Mg:SrTiO3, which might explain the enhanced stability of CrOx containing composites. The mechanism of activation of the catalyst by photodeposition of CrOx and suggestions for further improvement in the preparation cycle of the composite catalyst, are discussed.
(Invited) Engineering Hematite Interfaces By Dual Modification for Sunlight Driven Water Oxidation Reaction
Authors: Freitas Andre L. M , Souza Flavio L
Published: May 2020

The present study describes the role of different modifiers on the overall hematite photocurrent response, which allowed a dual material insertion increasing the charge separation without compromise the surface catalysis. The pristine and Sn-hematite electrodes were obtained with two different morphologies (columnar, CN, and ellipsoid (EN) nanostructure) by low-cost aqueous chemical method. The following step was the addition at the Sn-hematite surface of a spinel cocatalyst that was also synthesized via chemical method. Sn-hematite-cocatalyst (Ni2FeOx) electrodes were submitted to additional thermal treatment under nitrogen atmosphere to activate the material surface. The pristine hematite electrode showed considerable enhancement on photocurrent density J, in comparison with previous work in our group for both method from a range of ~ 30 µA.cm-2 up to 0.2 mA.cm-2 and 1.0 mA.cm-2 to 2.0 mA.cm-2 at 1.23 VRHE, for CN and EN photoelectrodes respectively. Sn-addition onto hematite electrodes clearly increased flat band potential promoting a good charge separation and shifts the onset to a higher potential, attributed to the surface state created by this modification. Notoriously, Sn-hematite electrode loaded with FeNiOx exhibited the highest photocurrent density suggesting a partially passivation of surface states created during the electrode designing. The well-known co-catalyst acted majoritypassivating the surface states instead of improving surface for catalysis. The dual modification contributes to understand the role of different modifiers that is possible to satisfactorily improve charge separation maintaining the conductivity attributed to intermetallic ions. In summary, the synergy of Sn+4 and Ni2FeOX addition enables us to promote a shift on the onset towards a lower potential and enhancing the photocurrent density.

The authors gratefully acknowledge support from FAPESP (Grant 2017/11986-5) and Shell and the strategic importance of the support given by ANP (Brazil’s National Oil, Natural Gas and Biofuels Agency) through the R&D levy regulation.
Identifying Structural Defects in Hematite Photoanodes through Structure-Property Analysis
Authors: Smith Rodney D. L. , Liu Yutong
Published: May 2020

Hematite photoanodes continue to exhibit highly variable photoelectrocatalytic water oxidation performance across the literature despite over two decades of intensive research. Studies have advanced the understanding of fundamental photophysical behavior of key electron transfer and enriched material design in hematite photoanodes, but poor photoelectrocatalytic performance and high variability in reported behavior indicate missing information. We believe that a lack of the chemical nature of structural defects in hematite and their specific impacts on material properties and photoelectrocatalytic water oxidation is a key problem. We target this issue with a structure-property analysis using photoelectrochemical, X-ray diffraction, Raman and UV-visible spectroscopic data on a series of hematite photoanodes. The analysis reveals a formally Raman inactive vibrational mode in hematite films prepared by annealing lepidocrocite films whose intensity varies with annealing protocols. Correlations between the intensity of this feature in the Raman spectrum with photocurrent density, semiconductor band structure, and the onset of photoelectrocatalysis signifies systematic changes in the magnitude of a crystal lattice distortion. Analysis of the nature of these key Raman vibrations and the synthetic conditions lead us to conclude that the observed defects are iron vacancies induced by trapped protons within the crystal lattice. This finding provides a means to rapidly diagnose a specific structural defect and will aid in the optimization of fabrication protocols for hematite photoanodes.

Figure 1
(Invited) Quantitative Analysis of Si/Liquid Interfaces with Semiconductor Ultramicroelectrodes (SUMEs)
Authors: Liu Zhihui , Lancaster Mitchell , Maldonado Stephen
Published: May 2020

This presentation will describe the use and advantages of semiconductor ultramicroelectrodes (SUMEs) for the quantitative study of Si/electrolyte interfaces. Specifically, recessed Si SUMEs have been prepared by coating single crystal substrates with a patterned dielectric film. These SUME platforms have been used to obtain steady-state voltammograms both in the dark and under illumination while immersed in three separate solvents: water, methanol, and acetonitrile. This presentation will show that raw SUME voltammetry, in conjunction with a comprehensive model of the semiconductor/solution interfaces, can be deconvoluted to provide the same or superior information that is traditionally obtained by impedance methods. The resultant data has been fit comprehensively to identify the nature of the semiconductor band bending (inversion, depletion, accumulation), the band edge energetics, and the extent of surface states that populate the interface. Further, the dynamics of surface degradation (oxidation) have been followed through the voltammetric responses. Time permitting, data will be presented that further illustrates size scaling effects and the prospects of using SUMEs as analogs of discrete semiconductor nanoparticles.
(Invited) Thermoplasmonic Generation of Carbon Nanohydrids for the Oxygen Reduction Reaction
Authors: Zhang Yu , Kment Štěpán , Zbořil Radek , Naldoni Alberto
Published: May 2020

Local heating from plasmonic nanostructures has shown great potential in photothermal therapy, optical trapping, heterogeneous catalysis, and synthesis of nanostructures. Titanium nitride (TiN) is one the most promising plasmonic materials for thermal applications (thermoplasmonics) due to its high thermostability (i.e. refractory), CMOS compatibility, and resistance in chemically harsh environments. On the other hand, hydrogen peroxide (H2O2) has a large annual production approaching 4 ×106 tons worldwide and the selective reduction of O2 via electrochemical oxygen reduction reaction (ORR) using renewable electricity is a promising way for H2O2 production. Carbon-based materials have shown great potential for the two-electron ORR to hydrogen peroxide. In this contribution, I will show a general approach to use the highly intense local temperature generated from plasmonic TiN nanocrystals for generating TiN/carbon nanohybrids that show enhanced efficiency and selectivity toward the ORR. The general applicability of plasmon-driven synthesis of nanocarbons to electrocatalysis will be discussed.
Piezocatalyst Assisted Plasmon-Induced Hot-Electron Generation for Highly Effective Piezo-Photo Catalytic Hydrogen Evolution Via Au@MoS2 Nanoflowers
Authors: Tu Chia-Yu , Wu Jyh-Ming
Published: May 2020

This work, Au nanoparticles@MoS2 heterostructure sonicated with visible light has been confirmed it can enhance piezo-photo catalytic activity for hydrogen evolution reaction. MoS2 displays prominent photocatalytic properties due to its narrow bandgap and obsesses unique piezoelectricity at its edge sites. However, the high rate of electrons and holes recombination and lack of active sites limit efficiency for hydrogen evolution. Herein introduction of gold nanoparticles into MoS2 nanoflowers has been synthesized by a facile hydrothermal process and forms heterojunction structure. The transmission electron microscopy (TEM) images evidence the as-synthesized Au@MoS2 heterostructure exhibits a high surface to volume with abundant nanopetals. As compared to Au NPs decorated MoS2, utilizing Au NPs burying beneath MoS2 nanoflowers eliminates the shielding effect of MoS2 active edge sites. Based on the photoluminescence (PL) spectrum, Au@MoS2 achieved to reduce the recombination possibility of electrons and holes. Through gas chromatography (GC) analysis, the hydrogen evolution of Au@MoS2 shows better than pristine MoS2. The significant improvement arises from piezoelectricity inducing hot electron of localized surface plasmon resonance (LSPR) effect as observed by the absorption spectrum of ultraviolet-visible (UV-Vis) spectrophotometer. The COMSOL software was employed to simulate the charge distribution. The mechanism on LSPR enhanced piezo-photo catalytic hydrogen evolution will be investigated.
Plasmonic Hydrogen Evolution Reactions Driven By Visible Light Illumination at p-Type Semiconductor Electrodes
Authors: Minamimoto Hiro , Sato Daiki , Murakoshi Kei
Published: May 2020

The efficient control of the visible light driven hydrogen evolution reaction can be recognized as the one of the promising challenge for the sustainable society. It can be said that the wide-band semiconductor electrode is the good material for the photo-energy conversion system. However, various semiconductor electrodes have the limitation to the ultraviolet region because of their wide band gap energy. Recently, plasmoic photoelectric conversion system, which is the combination of the plasmon active metal nano-structures with the semiconductor electrodes, has been received much attention because the system shows the visible light response characters beyond its limitation. In this system, the electrons excited in the metal structures injected into the conduction band of the n-type semiconductor and the remained holes are consumed through the oxidation reaction. Up to now, various plasmon-induced chemical reactions, even the water splitting, have been proposed. As our previous study, we have not only visualized the reaction active sites but also determined the absolute electrochemical potential of the reaction active species through the polymerization reactions of the conductive polymer.1 Although well-established systems have been reported, the direct control of the reduction reaction at the metal-semiconductor interface by the excited electrons has not been well examined. This is because the almost plasmonic photoconversion systems consist of the n-type semiconductor electrode and applied the generated holes to the reactions. In this study, we have tried to establish the plasmon-induced hydrogen evolution system by the introduction of the plasmon-active metal nano-structures into the p-type semiconductor electrodes. By supporting the plasmonic structures, we have confirmed the photo-current generations under the visible light illumination. Through the photocurrent measurements and the incident photon to current conversion efficiency obtained under different pH conditions, we have confirmed the unique pH dependence. In addition to these, we have also investigated the isotopic effect on the hydrogen evolution reaction to clarify the unique surface molecular process.2 Through the various photoelectrochemical measurements, we are sure that our plasmonic hydrogen evolution system could be considered as one of the good candidate for future light energy conversion system.

Reference

1. Minamimoto and K. Murakoshi et al., J. Phys. Chem. C., 120(29), 16051 (2016).

2. Minamimoto, R. Osaka, and K. Murakoshi, Electrochimica Acta, 304(1), 87 (2019).
(Invited) Defect Engineering and Surface Probing of Few-Layer MoS2 As Photocatalyst for CO2 Reduction to Solar Fuels
Authors: Chen Li-Chyong , Huang Yi-Fan , Lien Hsiang-Ting , Du He-Yun , Chang Yu-Chung , Chen Kuei-Hsien
Published: May 2020

Photocatalytic CO2 conversion to hydrocarbon fuels, which makes solar energy harvesting and CO2 reduction reaction (CO2RR) simultaneously, is a killing two birds with one stone approach to solving the energy and environmental problems. However, challenges are the low photon-to-fuel conversion efficiency of the photocatalysts and lack of the product selectivity. Recently, 2D-layered nanomaterials with defect engineering, e.g. the carbon interstitial-doped SnS2 nanosheets [Nature Comm. 9, 169 (2018)], have shown promise for CO2RR. Here, I will present a different case, MoS2 with vacancies controlled by plasma. Productivity and selectivity of CO2RR were found to be dependent strongly with the different Mo/S ratios of the MoS2 of single to few layers. Orders of magnitude enhancement in productivity and selectivity of C2 product over 97% have been obtained. The role and interplay of the defects and the hosting materials, and their effects on the adsorption of CO2 and subsequent CO2RR, studied by the near-ambient pressure X-ray photoemission spectroscopy, along with density functional theory will be discussed.
(Invited) Nanostructured Layered Double Hydroxide Based Photocatalysts for Solar Fuels and High-Value Chemicals
Authors: Zhang Tierui
Published: May 2020

In this presentation, some very recent research progress in my group will be reported on the rational design of nanostructured layered double hydroxides (LDHs) based photocatalysts with heterointerface active sites for photoreduction of CO2 or CO into high value-added hydrocarbons with high selectivity, originating from the adjusted reaction pathway of intermediates. For instance, by constructing heterogeneous interface structure, NiO/Ni nanocatalysts exhibited an unexpectedly high selectivity of 60% for C2-C7 hydrocarbons in the CO hydrogenation reaction under visible-light irradiation.[1-8]

References

1. T. Zhang, et al., Adv. Mater. 2018, 30 (3), 1704663.

2. T. Zhang, et al., Adv. Mater. 2017, 29 (42), 1703828.

3. T. Zhang, et al., Adv. Mater. 2017, 29 (27), 1700803.

4. T. Zhang, et al., Adv. Mater. 2017, 29 (16), 1605148.

5. T. Zhang, et al., Adv. Mater. 2016, 28 (43), 9454-9477.

6. T. Zhang, et al., Angew. Chem. Int. Ed. 2016, 55 (13), 4215-4219.

7. T. Zhang, et al., Adv. Energy Mater. 2016, 6 (3), 1501241.

8. T. Zhang, et al., Adv. Mater. 2015, 27 (47), 7824-7831.
(Invited) Ligands in Electroreduction of CO2: N-Heterocyclic Carbene-Capped Polymers to Promote Catalytic Efficiency
Authors: He Jie
Published: May 2020

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. Compared with other conventional ligands including thiols and amines, metal-carbene bonds that are stable under reductive potentials prevent the nanoclustering of nanoparticles, that 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, carbene-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) Local Electrolyte-Driven Redox Cycling within a Nanoporous Photoanode
Authors: Houle Frances A , Cheshire Thomas , Boodry Jeb
Published: May 2020

Nanoporous photoanodes used in dye-sensitized solar energy conversion systems such as solar cells and solar hydrogen generators have been carefully studied to understand factors that influence their performance, as measured by photocurrents and open-circuit photovoltages. We have developed a chemically detailed, multiscale reaction-diffusion model that seeks to connect these observables to the detailed dye redox and electrolyte chemistry for the simpler dye-sensitized solar cell (DSC) system, incorporating dyes bound within a TiO2 nanoparticle-based anode, and an I-/I3
- redox shuttle connecting the anode to the cathode [1]. The model framework permits nanoscale characteristics of the interfacial and solution-phase redox processes, including charge trapping, to be connected to photocurrents and electron densities under various dye excitation scenarios, and is extendable to the more complex interactions occurring in hydrogen generators. In DSCs, it is generally assumed that the redox shuttle needs to make a full round trip between anode and cathode to convert I3
- to 3 I- at the cathode after dye reduction reactions in the anode. It is also thought that electron trapping by electrolyte components, in particular I2, is deleterious, and degrades performance. Detailed simulations assess these mechanistic elements. The results show that during operation, I- is deeply depleted in the photoanode pores, leading to significant populations of oxidized dyes and a shift in the I-/I3
- equilibrium with formation of I2. Electron trapping by I2, which forms I2
- at the photoanode-electrolyte interface, does not invariably affect photocurrent or photoanode charging. This is because the increased rate of I2
- disproportionation in the electrolyte enables local regeneration of I- within the pores and efficient dye reduction after photoexcitation, without requiring I3
- diffusion to the cathode. The possibility of local cycling, which results in photoanode redox activity without net current flow, has not been reported previously and suggest that causes of less-than-ideal performance may lie elsewhere. The simulations provide nanoscopic predictions for interfacial processes that control dye cycling. The timing of electrolyte anion diffusion toward the anode-dye interface within the pores, relative to charge injection and to dye neutralization, will be discussed.

[1] F. A. Houle, J. Phys. Chem. C 123, 14459-14467 (2019).
Influence of Film Coverage on CrOx Protective Layers for Pt-Based Water-Splitting Catalysts
Authors: Worsley Myles Peter , Smulders Vera , Mei Bastian Timo , Mul Guido
Published: May 2020

The generation of hydrogen from renewable sources is of great interest in sustainable fuel production and storage. Emerging technologies such as photocatalytic water splitting are being considered as cost effective solutions for the production of hydrogen. In these applications Pt is commonly employed as it is highly effective for the hydrogen evolution reaction (HER), however loss of efficiency can be a problem due to back-reactions (for example the oxygen reduction reaction (ORR)) and to a lesser extent poisoning from contaminants (e.g. CO). CrOx-based protective layers have been shown to improve selectivity towards hydrogen for Pt catalysts, for which lower concentrations of the chromate precursor are preferred due to toxicity issues. Still, there is a lack of fundamental understanding of coating procedures and the levels required. In this study cyclic voltammetry and eQCM have been used to systematically investigate the dependence of concentration and deposition time on the extent of film growth and activity in the relevant reactions for photocatalytic water splitting. Specifically we highlight trends in the HER and ORR activity on the buried Pt surface and evaluate stability as a function of CrOx coverage. It has been shown by the experimental results that an optimum can be found between minimising the overpotential required for HER whilst fully protecting against the oxygen reduction back-reaction. Thus, these results reveal the lowest Cr precursor concentrations that can be effectively applied in photocatalysis.
Controllable Vacancy Redistributions in Embedded Thin Films Under Concentrated Electric Fields
Authors: Nonnenmann Stephen S.
Published: May 2020

The redistribution and accumulation of oxygen vacancies under electric field underpins both the functionality and degradation of electrical and electrochemical devices comprising oxide layers. Interfacial accumulations of oxygen vacancies form defect dipoles, significantly reduce the breakdown strength, increase the breakdown path area, yet facilitates charge transfer reactions. Confinement of both oxygen vacancy redistributions and their mobility remains critical to preserving function in oxide systems.

Here we study one of the most important, yet random transport processes: the redistribution of oxygen vacancies in binary oxides under high local electric fields. The ability to identify or predefine the shape, size, and location of vacancy distributions is critical to controlling interfacial properties of functional oxides. We achieved superior uniformity in HfO2 films by embedding highly-ordered metal nanoisland (NI) arrays to act as electric field concentrators. Embedded films exhibit significant reduction in operating voltages while displaying enhanced uniformity of resistance states. This behavior is attributed to the concentration of electric fields along Pt and Ti NIs and their interactions with the surrounding oxide film matrix environment, which induce separate and distinct filamentary formation mechanisms that affect the stability. A comparison of the density and distribution of the oxygen vacancies responsible driving filament dynamics is made via combined electrostatic force microscopy (EFM) and conductive atomic force microscopy (c-AFM) studies. Finally, the morphological evolution of conducting vacancy filaments is enabled by three-dimensional (3-D) c-AFM nanotomography and cross-sectional scanning transmission electron microscopy – energy dispersive spectroscopy (STEM-EDS) to provide direct correlations of nanoisland-oxide interactions with overall switching performance. The application of these exciting results to other vacancy-mediated electronic and electrochemical processes will also be discussed.
(Invited) of the Interfacial Electrochemo-Mechanical Effects in All-Solid-State Li-Ion Batteries
Authors: Qi Yue , Tian Hong Kang
Published: May 2020

Maintaining the physical contact at the electrolyte/electrode interface and preventing mechanical failure are critical to the performance of all-solid-state batteries (ASSB). The ceramics based solid electrolyte and electrode interface tends to have imperfect contact, which can be worsened due to cycling and improved due to cell stack pressure. The solid electrolyte is also subject to electrochemical decomposition at the interface, causing volume change, in addition to the well-known volume change in the electrodes during lithiation-and-delithiation. These chemical strains generate mechanical stress, which leads to fracture in the highly compliant all-solid-state batteries, especially in 3D ASSBs. In this presentation, new continuum models were developed to capture the highly coupled electrochemical-mechanical phenomena. First, we will present a 1D Newman battery model for a film-type Li|LiPON|LiCoO2 ASSB that incorporated the effect of imperfect contact area with battery performance by assuming the current and Li concentration will be localized at the contacted area. To establish the relationship between the applied pressure and the contact area, we applied Persson’s contact mechanics theory as it uses self-affined surfaces to simplify the multi-length scale contacts in ASSLBs. The model is then used to suggest how much pressures should be applied to recover the capacity drop due to contact area loss. Furthermore, we will introduce a 3D Newman battery model for the experimentally-made 3D Si|LiPON|LiCoO2 ASSB to incorporate the chemo-mechanical strains due to interfacial decomposition of LiPON and the lithium concentration gradient while cycling. This electrochemo-mechanical model could be used for predicting whether and where the fractures would be produced in order to guide the architecture design of 3D ASSB with balanced energy density and mechanical integrity.
Mechanistic Understanding of OER Degradation of SOEC through Computational Modeling
Authors: Jin Xinfang , Huang Kevin
Published: May 2020

One of the major barriers to the commercialization of solid oxide electrolysis cells (SOECs) for hydrogen production through electrochemical water splitting is the short cell/stack life caused by chemical-expansion-mismatch induced mechanical delamination of oxygen electrode. To address SOEC’s degradation problem, we have been developing an isostructural bilayer oxygen evolution reaction (OER) electrode that is electrocatalytically active and Cr-tolerant. The bilayer OER electrode structure consists of a commercial LSCF (La0.6Sr0.4Co0.4Fe0.6O3-
d)-GDC (Ce0.8Gd0.2O1.9 porous backbone on a thin SrCo0.9Ta0.1O3-
d (SCT10) film. The new oxygen electrode has an inherently fast OER electrokinetics (or high oxygen evolution rate) to mitigate the delamination problem by minimizing the accumulation of oxygen in OER electrode lattice and thus chemical stresses. To understand the fundamental Electro-Chemical-Mechanical coupling mechanism and its contribution to SOEC degradation, we propose a rigorous Multiphysics model to explore the interplays between reaction rates and transport properties in delamination probability of the pristine and bilayer OER electrodes.

Figure 1 shows a schematic of model domain to be constructed with details at the interface. The model will address how the dimensional change of oxygen lattice incurred in the electrode during OER-operation affects its bonding strength with the electrolyte and how electronic/ionic conductivity in the oxygen electrode as well as electrolyte will alter the change. We will apply classical charge transport conservation, Ohm’s law and multi-species Maxwell-Stefan’s equation to simulate electronic/ionic transport and gas diffusion in the porous electrode. The distribution of oxygen vacancy concentrations in the electrode and across the electrode/electrolyte interface will be considered a key descriptor for the chemically-induced lattice dimensional change. The displacement associated with the lattice dimensional change is governed by Navier’s equation. Different criteria will be used to evaluate the failure modes at the O2-electrode/electrolyte interface, such as elastic energy and Weibull approach. The research work will lead to a better understanding of the delamination mechanisms and effective mitigation plan, and provide guidelines to the experimental optimization of bilayer OER electrode processing with improved electrochemical and mechanical performance.

Figure 1 (a) Illustration of a SOEC cell; (b) Microscale electrode/electrolyte Interface Model; (c) Elastic energy in the particles and interfaces under chemical expansion.

Figure 1
Aluminum-sulfur Composites for Li-S Batteries with a High-rate Performance
Authors: Zhou Sophia P. , Lu Yan-Qiu , Shen Shou-Yu , Zhang Shao-Jian , Li Jun-Tao , Huang Ling , Sun Shi-Gang
Published: May 2020

Over the past few years, lithium sulfur (Li-S) batteries have attracted growing attention as an enabling technology because of their high energy density. The limitations to commercialize Li-S batteries originate from the intrinsic properties of sulfur: its poor electronic conductivity and the polysulfide shuttling effect. The aim of this research is to address these challenges by developing an additive for Li-S batteries. Aluminum (Al) powders prepared from soda cans were mixed with sulfur to form a composite with a sulfur mass loading up to 90 wt%. The electrochemical performance shows that the Al-S composite in Li-S cells exhibits a stable retention after 200 cycles and an ability to stabilize quickly (<10 cycles). Moreover, the rate performance of the Al-S composite is improved over conventional carbon additives. Post analysis suggests that Al-S surface interaction is a possible origin for this improvement.