bluuebunny/crossref_metadata_2025 huggingface dataset:
A Wearable All-Solid Photovoltaic Textile
Authors: Zhang Nannan
Published: February 2020

Flexible solar cell has received a wide range of interests due to the development of wearable electronics. Herein, we have come up with the idea of wire-shaped solar cell, which has provided a new solution to get rid of expensive TCO substrates. We present a solution to power the portable electronics in a wearable manner by fabricating an all-solid photovoltaic textile. The photoanode is fabricated by assembling dye-sensitized ZnO nano-arrays on low-cost Mn-plated wire. And then, it was woven with Cu wires and colorful polymer fibers, for specially designed electrical connection and a colorful outlook. Colorful and flexible photovoltaic textile modules with arbitrary size and various knitting patterns were demonstrated as a wearable power source for portable and flexible electronics. As a result, a flexible photovoltaic textile with a Voc of 4.6 V was realized, which could directly power up a commercial calculator. With such features as low-cost, thinness, light-weight, being flexible and wearable, as well as colorful appearance, this work represents a significant step towards the development of large scale solar energy harvesting for wearable electronics and self-powered home technology.
(Invited) Printable Two-Dimensional Nanomaterial Inks for Flexible Electronics and Photonics
Authors: Hersam Mark C.
Published: February 2020

Layered two-dimensional nanomaterials interact primarily via van der Waals bonding, which has created new opportunities for heterostructures that are not constrained by epitaxial growth [1]. In order to efficiently explore the vast phase space for van der Waals heterostructures, our laboratory employs solution-based additive assembly [2]. In particular, constituent two-dimensional nanomaterials (e.g., graphene, boron nitride, transition metal dichalcogenides, and black phosphorus) are isolated in solution, and then deposited into thin films with scalable additive manufacturing methods (e.g., aerosol, inkjet, gravure, and screen printing) [3]. By achieving high levels of nanomaterial monodispersity and printing fidelity, a variety of electronic, electrochemical, and photonic applications can be enhanced including digital logic circuits [4], lithium-ion batteries [5], and photodetectors [6]. Furthermore, by integrating multiple nanomaterial inks into heterostructures, unprecedented device function is realized including anti-ambipolar transistors [7], gate-tunable photovoltaics [8], and neuromorphic memristors [9]. In addition to technological implications for electronic and photonic technologies, this talk will explore several fundamental issues including band alignment, doping, trap states, and charge/energy transfer across two-dimensional van der Waals heterointerfaces [10].

[1] D. Jariwala, et al., Nature Materials, 16, 170 (2017).

[2] J. Zhu, et al., Advanced Materials, 29, 1603895 (2017).

[3] J. Kang, et al., Accounts of Chemical Research, 50, 943 (2017).

[4] M. Geier, et al., Nature Nanotechnology, 10, 944 (2015).

[5] K.-S. Chen, et al., Nano Letters, 17, 2539 (2017).

[6] J. Kang, et al., Nano Letters, 16, 7216 (2016).

[7] D. Jariwala, et al., Nano Letters, 15, 416 (2015).

[8] D. Jariwala, et al., Nano Letters, 16, 497 (2016).

[9] V. K. Sangwan, et al., Nature Nanotechnology, 10, 403 (2015).

[10] S. B. Homan, et al., Nano Letters, 17, 164 (2017).
(Invited) Wafer-Scale Synthesis of Monolayer WS2 By Enhanced Chemical Vapor Deposition for High-Performance Flexible Photodetectors
Authors: Ho Johnny C.
Published: February 2020

In recent years, due to their exotic properties, wafer-scale synthesis of monolayer two-dimensional (2D) nanomaterials is vital for their practical utilizations in next-generation electronics and optoelectronics. Great efforts have been devoted in developing different synthesis techniques, such as various kinds of chemical vapor deposition (CVD), to obtain large-scale and uniform 2D nanomaterials. However, it is still a grand challenge to achieve the monolayer format with the large grain size and excellent uniformity across the entire wafer substrate. Herein, in contrast to other conventional growth methods, we demonstrate the wafer-scale synthesis (e.g. 2 inch in diameter) of highly crystalline, homogeneous and monolayer WS2 by an enhanced CVD technique, in which precise control of precursor vapor pressures can be effectively achieved in the multi-temperature zone horizontal furnace. Importantly, these monolayers exhibit impressive optoelectronic properties and mechanical flexibility. When configured into typical rigid photodetectors, the monolayer WS2 exhibits respectable photodetection performance with a responsivity of 0.52 mA/W, a detectivity of 4.9×109 Jones and a fast response speed shorter than 560 μs. Furthermore, once fabricated as flexible photodetectors on polyimide, the photodetectors yield the responsivity of up to 5 mA/W. Also, the photocurrent can maintain 89% of its initial value even after 3000 bending cycles. All these results indicate the versatility of this technique to extend for larger substrates as well as the excellent mechanical flexibility and robustness of our large-scale, CVD grown, homogenous monolayer WS2 for the advanced flexible optoelectronic devices.
Stretchable Intrinsically Conductive Polymers for Wearable Thermotherapy and Electromagnetic Interface Shielding
Authors: Ouyang Jianyong
Published: February 2020

Stretchable conductors can have important application in wearable electronics. We prepared stretchable conductors by blending poly(3,4-ethylenedioxythiophene):poly(styrene sulfonic acid) (PEDOT:PSS, a conductive polymer) and elastomeric waterborne polyurethane (WPU) and demonstrated the application of the blends for thermotherapy and electromagnetic interference (EMI) shielding. Wearable heaters were fabricated by using the stretchable PEDOT:PSS/WPU blends. rGO was mixed into the to improve the temperature uniformity because rGO has high thermal conductivity while the polymers have very low thermal conductivity. The heater shows stable heating behavior under repetitive voltage on/off cycles, and the temperature remains almost unchanged under a tensile strain of up to 30%. The devices can be comfortably attached to the skin of humans, for example on the wrist, and they exhibit a uniform and stable heating profile even under mechanical disturbance. In addition, the PEDOT:PSS/WPU blends can be investigated for EMI shielding. Flexible or even stretchable electromagnetic interference (EMI) shielding materials with high performance are needed for wearable electronic systems. The PEDOT:PSS/WPU blends can exhibit a high EMI shielding effectiveness (SE) of about 62 dB over the X-band frequency range at a film thickness of only 0.15 mm.
(Invited) Bio-Inspired Helical Coil Network for Soft, Wireless Electronics
Authors: Song Juwon , Jung Han Hee , Jung Han Na , Jang Kyung-In
Published: February 2020

Coils are made of elastic materials formed into the shape of helixes which return to their natural length when unloaded. With its unique geometry, the helix coil structure is one of the most stretchable forms among all kinds of shapes in man-made systems and nature. I employed the coil mechanics to modern stretchable electronics to archive an extreme level of elastic stretchability, which cannot be accomplished with existing technologies. Compared to typical 2D filamentary serpentines fully bonded onto soft planar elastomeric substrates, the proposed 3D helix structures are designed to be uniformly bent with compressive buckling with minimally defined bonding sites. The constructed helix coil interconnections can be naturally deformed along the coil direction under tensile stress with minimal stress concentration. As a result, these structures exhibit extreme elastic stretchability up to ~100%. Currently, I am building extremely stretchable biomedical devices as a system-level demo.
(Invited) Mechanical Design Strategies in Wearable/Flexible Electronics
Authors: Pharr Matt
Published: February 2020

Managing the mechanical mismatch between hard conductor/semiconductor device components and soft biological tissues represents a key challenge in the development of advanced forms of wearable electronic devices. In this talk, I will discuss two mechanical design strategies to address this issue. The first strategy consists of producing a structure in which a liquid surrounds the electronics and resides in a thin elastomeric shell to provide a strain-isolation effect that not only enhances the wearability but also the range of stretchability in suitably designed devices. Combined experimental and theoretical results establish the strain-isolating effects of this system, and the considerations that dictate mechanical collapse of the fluid-filled cavity. Examples in skin-mounted wearable include wireless sensors for measuring temperature and wired systems for recording mechano-acoustic responses. In the second strategy, we strive to increase the stretchability of metallic interconnects on stretchable substrates. Finite element analyses reveal a substantial increase in stretchability with reducing substrate thickness. Low-cycle fatigue tests confirm this trend by examining the stretch required to form fatigue cracks associated with plastic deformation. To elucidate the mechanics governing this phenomenon, we examine the buckling behavior of deformed serpentine interconnects on substrates of various thickness. Our experimental and theoretical studies suggest a change in the buckling mode from local wrinkling to global buckling below a critical thickness of the substrate. The global buckling found in thin substrates accommodates large stretching prior to plastic deformation of the serpentines, thereby drastically enhancing the overall stretchability of these systems.
A Highly Sensitive Flexible Pressure Sensor Based on Polystyrene@Graphene Core-Shell Nanoballs
Authors: Ai Yuanfei , Hsu Ting Heng , Wu Ding Chou , Lee Ling , Chen Jyun-Hong , Chen Yu-Ze , Wu Shu-Chi , Wang Kuangye , Wu Cuo , Wang Zhiming , Chueh Yu-Lun
Published: February 2020

Many novel building highly sensitive flexible pressure sensors have achieved high development in recent years, showing their potential applications in the field of electronic skin and wearable health monitors. In this work, we report a fabrication of flexible film-shaped resistive-type pressure sensor with high performance and versatile applications by sandwiching PS balls@rGO core-shell nanomaterials film layer between two thin flexible polydimethylsiloxane sheets. The preparation of materials and the fabrication process of the sensor devices is simple, efficient and economy. Our PS balls@rGO based pressure sensors are able to detect pressing forces as low as 3.1 Pa, and have a low energy consumption (~1 μW) at a low bias voltage of 1V, fast response time of 50 ms, high sensitivity (50.9 kPa-1) in 3.1 Pa ~ 20 kPa, and high stability during 20,000 loading–unloading cycles. In addition, our flexible sensor can detect pressing, blood pulse, swallowing, skin pulling and joint activities when attached on human bodies. By an efficient scalable fabrication process, large-area integrated pressure sensors array was manufactured, enabling patterning for mapping spatial pressure distribution to large-area monitoring of body pressure, pulses and human actions.
(Invited) Rational Design of Nanostructures and Materials for Flexible and High Performance Electronics and Optoelectronics
Authors: Fan Zhiyong
Published: February 2020

Wearable and flexible electronics requires energy efficient materials and devices with excellent flexibility for the active and passive components. Many nanostructured materials possess high surface-to-volume ratio, mechanical flexibility and low power consumption. These intriguing properties can be harnessed for a variety of applications in electronics and photonics. In the past, we have fabricated an assortment of arrayed nanostructures using a variety of materials from inorganic semiconductors to organometal perovskite materials. These nanomaterials can be fabricated with chemical vapor deposition method and/or printable method with scalability. Meanwhile, the materials have been fabricated into various flexible optoelectronic devices, including photodetectors and solar cells. The study has shown that three-dimensionally (3-D) arrayed nanostructures can help to improve solar cell device energy conversion efficiency, as well as the flexibility. However, rational design and proper structural optimization is not trivial. Using printable method and template guided growth method, semiconductor nanowires have been fabricated into planar arrays and 3-D arrays for photodetectors. Proof-of-concept flexible image sensor devices with high density 3-D nanowire arrays have been fabricated. Meanwhile, flexible energy storage devices have also been fabricated using nanostructured materials to enhance storage capacity for wearable devices. Overall, the nanostructure integration methodology that we developed may enable many applications on electronics and optoelectronics in the future.
Ionomer Thin Films for PEM Fuel Cells
Authors: Kusoglu Ahmet
Published: February 2020

Ion-conductive polymers (ionomers) such as perfluorosulfonic-acid (PFSA) have been widely adopted in polymer electrolyte fuel cells (PEFCs) as a polymer-electrolyte membrane (PEM) due to their ability to conduct ions in hydrated conditions without losing stability. The role of ionomers in PEFCs, however, is not limited to PEM as it also extends to the porous catalyst layers (CL) where ionomers exist as nanometer-thick electrolyte thin films binding the catalytic agglomerates and facilitating proton transport. Moreover, the ionomer’s properties differ from the bulk (PEM) when it is confined to these nanometer thicknesses where its behavior is influenced by its interfaces with the air and the catalytic sites, such as carbon/platinum. In particular, this phenomenon of confinement onto Pt sites could have important implications for the mass-transport limitations observed in fuel-cell catalyst layers, which have been related to the transport resistances at the ionomer thin-film. Thus, despite an ever-growing number of studies on ionomer membranes for PEM, for desired next-generation PEFCs, it is important to characterize catalyst ionomers and elucidate factors controlling their transport properties. In particular, if is of great interest to develop model systems for thin films that can mimic catalyst ionomer behavior and establish their structure/functionality to optimize ionomer interfaces and improve CL performance.

This tutorial talk will present an overview of PFSA ionomer thin films and their current state of understanding with a focus on recent developments in advanced diagnostics and the information they can provide to establish their structure/function relationship. In addition, applicability of the various diagnostics techniques in the thin-film regime (5 to 500 nm) will be discussed, including the use of state-of-the-art techniques, such as Grazing-Incidence X-ray scattering (GIXS). First, thin films of dispersion-cast ionomers on model substrates will be explained in relation to catalyst ionomers. Swelling and water uptake behavior as well as various transport properties of these thin films will be examined. Then, it will be discussed how an ionomer’s phase-separated nanostructure and properties are correlated and impacted by film thickness (i.e., confinement effect) and substrate interactions, especially below 50 nm. Lastly, it will be explored how EW and side-chain chemistry influence the nature of ionomer-substrate interactions and thus the structure and properties of PFSA thin films. The collected data set will be analyzed to illustrate the bulk-to-film transition of ionomers of various equivalent weights used in fuel-cells. The results will be elucidated to highlight the key aspects of ionomer thin films, provide insight into optimization of their structure and functionalities for fuel-cell catalysts, and discuss implications for PEFC performance.
(Invited) Electrochemical Fuels Production Using High Temperature Alkaline Electrolytes
Authors: Xu Hui
Published: February 2020

Anion exchange membranes (AEMs) have potential applications in a variety of energy conversion technologies (e.g. fuel cell, electrolyzer), due to enabled adoption of non-precious metal catalysts. However, these polymer-based AEMs generally have poor stability, particularly at elevated temperatures (> 80 ℃), limiting their viable applications. On the other hand, operating electrochemical cells at higher temperature can improve the electrode kinetics, simplify heat management, and increase the system efficiency. Here we report an alkaline system that utilizes molten alkaline (e.g., lithium, sodium, or potassium hydroxide) impregnated into a porous metal oxide (MO) matrix as the electrolyte. The operating temperature can vary from 250 to 500 °C, depending on the category and ratio of each individual electrolyte. A key factor that will influence the success of this technology is the microstructures of the porous oxide matrices. Their thickness, porosity, pore size and structure largely determine whether they can successfully retain molten hydroxides in their pores, particularly over extended period of time.

The single and binary hydroxide with 25 wt% (e.g., MO-LiOH-25 and MO-LiOH-NaOH-25) electrolyte showed OH- conductivity of 0. 15 S.cm-1 and 0.5 S.cm-1, respectively, at 500 ℃, demonstrating significant advantage of this alkaline electrolyte. As two applications, water electrolysis and electrochemical synthesis of ammonia using this composite electrolytes are being tested and will be reported. Cell components and process conditions will be optimized to maximize the performance of the electrochemical cells.

Acknowledgements

Financial support from DOE EERE Fuel Cell Technology Office under award # DE-EE0007644
Solid Oxide Electrolysis for Hydrogen Production: From Oxygen Ion to Proton Conducting Cells
Authors: Hu Boxun , Aphale Ashish N , Heo Su Jeong , Hong Junsung , Marina Olga A , Stevenson Jeffry W , Singh Prabhakar
Published: February 2020

Electrochemical splitting of water, using solid oxide electrolysis cells (SOEC), offers an economic and efficient pathway for large-scale hydrogen production that not only utilizes and integrates renewable energy but also allows for both distributed and centralized hydrogen production to accelerate and enable hydrogen infrastructure for mobility. In this technical contribution, two types of electrochemical systems using conventional oxygen ion conducting (O-SOEC) and newly developed proton conducting (P-SEOC) will be compared. The advantages and disadvantages of each technology in terms of hydrogen purity, electrochemical performance, and stability (structural and electrochemical) will be analyzed. Experimental results from initial 100-hour tests will be presented and discussed. The observations on dopant exsolution, solid-solid (electrode/electrolyte interface) and solid-gas (electrode-H2O, O2, and H2) interactions will be presented. Electrode composition, structure, and morphology changes and their roles on electrochemical performance and electrode stability in oxidizing (O2) and reducing (H2) atmospheres will be discussed
PBI-Blended Membrane Evaluated in High Temperature SO2 Electrolyser
Authors: Retha Peach , Krieg Henning , Kruger Andries , Bessarabov Dmitri , Kerres Jochen A.
Published: February 2020

It has been shown that hydrogen, which can be used for energy storage, can be produced efficiently by the membrane based Hybrid Sulfur (HyS) process. During the HyS electrolysis step, SO2 and H2O are converted to H2 and H2SO4. The proton exchange membrane (PEM) used for this process should have both a high proton conductivity and acid stability. Since the widely used perfluorosulfonic type materials are restricted by their humidification requirements, materials such as polybenzimidazole (PBI) has been found to be promising in blends with partially fluorinated polyaromatic polymers at operating temperatures of 80 and 95 °C within the SO2 electrolyser. Operation at higher temperatures (>100 °C) however holds many advantages such as improved reaction kinetics and simplified water management. For this study a cross-linked partially fluorinated polyaromatic PBI blended membrane was evaluated at 120 °C. Humidified SO2 was supplied to the anode to produce sulfuric acid while hydrogen was formed at the cathode. The SO2:H2O feed was managed at the applied current densities until a constant voltage was obtained, and there after increased accordingly with increasing current density. Polarisation curves (Figure 1) recorded for the blended PBI membrane were comparable with reported s-PBI in literature values in the lower current density region (< 0.5 A/cm2). A maximum current density of 1.1 A/cm2 was reached in comparison to the 0.5 A/cm2 for s-PBI at a temperature of 110 °C. Voltage stability was monitored at a current density of 0.3 and 0.6 A/cm2 for a duration of 6 hours or until the maximum voltage had been reached. The lower current density (0.3 A/cm2) was more constant over the course of the measurement, with a standard deviation of 3 mV, when compared to the higher applied current density. These results are promising for further testing and optimization of the blended PBI membranes for higher temperature SO2 electrolysis.

Figure 1
Electrochemical Reduction of Carbon Dioxide at Alloy Systems: Cu-In and Cu-Bi
Authors: Zangari Giovanni
Published: February 2020

The ability to maintain high efficiencies while simultaneously tuning the selectivity of the electrochemical reduction of CO2 (ERC) using low cost electrodes has proven to be one of the greatest obstacles to the widespread commercialization of this technology. In this study, we prepare dendritic copper-indium and copper-bismuth alloys of various compositions and investigate their catalytic activity and selectivity towards the reduction of CO2. The Cu-In electrocatalysts are increasingly dendritic with higher In fraction and, depending on composition, consist of mixed phases of Cu, In and Cu-In intermetallic phases. ERC at these electrodes produces formate at high efficiencies (up to 62% with a 80 at% alloy, -1 V)) while also tuning the CO/H2 ratio to achieve an ideal syngas composition with a 40 at% In alloy, -1 V. The observed product distribution as a function of alloy composition and applied potential is rationalized in terms of the relative adsorption strengths of CO and COOH intermediates at Cu and In sites, and their distinct variation with applied potential may be induced by the differences in electronic structure.

We also studied dendritic Cu, Bi, and Cu-Bi alloys with various compositions. The dendritic structures exhibit a high density of defect sites such as grain boundaries and twins, with these defects being increased at alloy dendrites. While the pure metals exhibited high H2 production and relatively high formate formation, the alloys exhibit a lower overall current density and a much higher selectivity towards formate, up to about 90%. Most importantly we show in this work that a combination of a d metal (Cu) with a p-block metal (In, Bi) with intimate contact between the two components is capable to tune the relative adsorption strength of the intermediates, thus steering the product distribution towards formate. The relatively purity of this product would be of interest for the direct feed of a direct formate fuel cell. Differences between In and Bi will be discussed in terms of the affinity for oxygen.

This study highlights the opportunities of using alloys to enhance control over the product distribution and suggests that suitable alloys could be promising catalysts for the inexpensive and efficient production of fuels.
In-Situ XRD during Electrochemical CO Reduction on Cu
Authors: Bertheussen Erlend , Scott Søren B. , Hogg Thomas , Hahn Christopher , Higgins Drew Christopher , Lin John , Landers Alan Taylor , Jaramillo Thomas F , Chorkendorff Ib , Seger Brian
Published: February 2020

Almost all-successful CO2 and CO reduction catalysts to higher chain carbons are based on copper,1 however various facets and pre-treatments of copper have shown to give a wide variety of product selectivity.2, 3 Currently there are many unanswered questions regarding active sites and mechanisms thus fundamental studies are essential for this reaction. This talk will focus on in-situ monitoring the copper-copper oxide crystal structure at a variety of oxidative and reductive potentials. Using the synchrotron facilities at the SLAC national laboratory we were able to achieve an in-depth understand both of how deep the native oxide layer penetrates and how this oxide becomes reduced as we shift towards more cathodic potentials. This talk was also discuss under what conditions there is an amorphous copper oxide layer and what conditions lead to a crystalline copper oxide surface. This will be followed by a discussion of how the copper oxide effects the crystal structure of the metallic copper at the operating conditions.

The in-situ work focused on a preferentially oriented <111> thin film, however there were other facets to a lesser extent. This talk will discuss the degree to which these facets are modified during in-situ operating conditions at various potentials.

Hori, Y.; Wakebe, H.; Tsukamoto, T.; Koga, O., Electrocatalytic Process of CO Selectivity in Electrochemical Reduction of CO2 at Metal-Electrodes in Aqueous Media. Electrochimica Acta
1994,
39 (11-12), 1833-1839.

Li, C. W.; Ciston, J.; Kanan, M. W., Electroreduction of carbon monoxide to liquid fuel on oxide-derived nanocrystalline copper. Nature
2014,
508 (7497), 504-+.

Hori, Y.; Takahashi, I.; Koga, O.; Hoshi, N., Electrochemical reduction of carbon dioxide at various series of copper single crystal electrodes. Journal of Molecular Catalysis a-Chemical
2003,
199 (1-2), 39-47.
Electrochemical Reduction of CO2 at Multi-Metallic Nano-Interfaces
Authors: Rasul Shahid , Pugnant Andrien , Yu Eileen
Published: February 2020

The critical reason for the ineffectiveness of the metal electrocatalysts for aqueous CO2 reduction is H2 generation due to competitive proton (H+)/ water (H2O) reduction. P-block based electrocatalysts are among the potential candidates for CO2 reduction due to their high hydrogen overpotentials. Tin (Sn), Lead (Pb) and Indium (In) metal electrodes are well known electrocatalysts for CO2 reduction to formate but little work has been done to engineer the surface structuring and analysis of the surface bound species. It is reported1 that the presence of metastable oxides on the surface of metal catalyst accelerates the CO2 conversion process by stabilizing the CO2
•− intermediate on the nano-interface contrary to pure metallic interfaces. Taking inspiration from the fact that activity of a catalyst depends upon the active nano-interface under exquisite control of local conditions, herein we report the modification of Sn and Sn-Pb-Sb alloy catalysts for CO2 conversion reaction. Thus in this study, we report the fabrication of oxide-derived (OD) Sn and multi−metallic alloy (Sn−Pb−Sb) electrodes which were prepared by electrochemical oxidation treatment at different potentials (4V, 5.5V, 7V and 9V vs. Ag/AgCl) in electrolyte of aqueous 0.3 M oxalic acid. We hypothesized that metastable oxides on multi-metallic nano-interfaces2 would not only stabilize the CO2
•− but would prefer C coordination of CO2
•− with evolved grain boundaries. The phase structure, morphology, oxidation state, and electrochemical behaviour of the electrodes were probed systematically. The results demonstrate that pristine Sn electrodes show higher CO2 conversion efficiency to formate (80% vs. 66%) compared to pristine Sn−Pb−Sb alloy electrode at −1.4 V vs. RHE. In contrast, the oxide derived alloy electrodes (OD−Sn−Pb−Sb) demonstrate higher CO2 reduction activity and enhanced selectivity to formic acid (90% vs. 85%) when compared to pristine OD-Sn electrodes under identical conditions. The improved CO2 reduction activity on preferentially grown OD-electrodes relative to the pristine metallic electrodes in both Sn and Sn−Pb−Sb alloy could be attributed to the presence of highly active sites on the grain boundary surfaces.

Y. Chen and M. W. Kanan, J. Am. Chem. Soc., 2012, 134, 1986-1989.

2. S. Rasul, D. H. Anjum, A. Jedidi, Y. Minenkov, L. Cavallo and K. Takanabe, Angew. Chem., 2015, 127, 2174-2178.
Electrodeposition of Ag Catalysts for Electrochemical CO2 Reduction
Authors: Ham YuSeok , Kim Myung Jun , Lim Taeho , Kim Soo-Kil , Kim Jae Jeong
Published: February 2020

The electrochemical reduction of CO2 to useful products has been considered as a promising technology for reducing the greenhouse gas [1]. Among the various products, CO has been targeted in this study since it can be directly used in Fischer-Tropsch process [2]. For CO production, Ag has received the great attention due to its electrocatalytic performance and moderate price compared to other noble metals [3, 4].

To improve the performance of the catalysts, structure engineering to enlarge the surface area have been widely investigated [4, 5]. In particular, fabrication of nano catalysts with large surface area on the carbon paper is required for MEA-type CO2 electrolyzer for large scale production. For this purpose, electrodeposition is efficient method to fabricate the catalyst on the carbon paper for various gas reduction reactions. In addition, the morphologies and coverage of catalyst layer could be easily controlled using various deposition method such as pulse electrodeposition [6, 7].

In this research, a galvanostatic pulse electrodeposition method was used to fabricate the Ag catalyst on the carbon paper. Increasing the off-time value during the galvanostatic pulse deposition, large surface area was developed. Using the optimized deposition conditions, high current density of CO production was achieved with large surface area of Ag catalysts. The CO production was further enhanced by removal of produced gases bubbles with surfactant.

References

[1] B. Endrődi et al., Progr. Energy Combust. Sci., 62, 133-154 (2017).

[2] Q. Lu et al., Nano Energy, 29, 439-456 (2016).

[3] J. Rosen et al., ACS Catal., 5, 4293-4299 (2015).

[4] Q. Lu et al., Nat. Commun., 5, ncomms4242 (2014).

[5] A. S. Hall et al., J. Am. Chem. Soc., 137, 14834-14837 (2015).

[6] G. Adilbish et al., Int. J. Hydrogen Energy, 42, 1181-1188 (2017).

[7] A. Egetenmeyer et al., Int. J. Hydrogen Energy, 42, 13649-13660 (2017).

*Corresponding author E-mail: jjkimm@snu.ac.kr, Tel: +82-2-880-8863

**Corresponding author E-mail: sookilkim@cau.ac.kr, Tel: +82-2-820-5770
(Invited) Low Temperature Electrolysis for Hydrogen and Oxygen Generation - a Tutorial on Catalyst and Electrode Development for Proton and Anion Exchange Membrane-Based Systems
Authors: Ayers Katherine E
Published: February 2020

Hydrogen generation via electrolysis is rapidly gaining international interest for energy storage applications due to the carbon-free chemical cycle and response characteristics of the technology. At the same time, the need for a sustainable source of hydrogen has been widely recognized, not just as a potential transportation fuel, but to limit CO2 production and fossil fuel consumption from existing industrial processes such as ammonia generation. Currently over 95% of hydrogen is made from fossil fuels through natural gas reforming or coal gasification. Significant growth has therefore occurred in recent years in water electrolysis research, especially in catalyst research for the hydrogen (HER) and oxygen (OER) evolution reactions.

Commercial proton exchange membrane (PEM)-based electrolysis has reached scales of several hundred kg/day, providing a relevant pathway for industrial scale hydrogen generation. PEM electrolysis also has tremendous potential for continuing cost reduction, leveraging system and manufacturing scaling laws as well as leveraging advancements in PEM fuel cell materials, manufacturing, and analysis tools. Order of magnitude improvements in some of the highest cost elements are easily achievable. Many of the technology elements are known, but need to be refined and validated in a manufacturing environment, including modifications in materials and methods of fabrication. At the same time, alternate pathways based on anion exchange membranes (AEMs) are showing promise, as membrane chemistry has advanced and understanding of electrode processing has developed. The basic environment of the AEM electrolysis cell enables a broader range of catalyst materials and the potential to eliminate the highest cost materials such as platinum group metals and commercially pure titanium from the stack.

However, in both the AEM and PEM case, there are complex interactions at the electrode level which need to be considered in catalyst and membrane development. First, the liquid electrolyte environment used for catalyst activity screening, where all of the catalyst surface is accessible to the reactant is often not comparable to a complex, 3-dimensional, ionomer-based electrode. Also, similar to automotive fuel cells, the operating environment is highly important and should be considered when claiming improvements over state of the art. For example, catalyst performance at very low current densities may indicate inherent activity but may not represent capability at typical device operating currents. Similarly, a membrane which cannot operate at differential pressure may be highly limited in utility even if more efficient than current commercial solutions. This talk will describe some of the complex interactions that need to be considered, typical operating requirements, and stages of development where relevant conditions should be introduced.
Oxidative Chemical Vapor Deposition of 3D Graphene Oxide on Nickel Foam for Hydrogen Evolution Reaction in Acidic Electrolyte
Authors: Sarawutanukul Sangchai , Phattharasupakun Nutthaphon , Wutthiprom Juthaporn , Sawangphruk Montree
Published: February 2020

The development of cheaper non-noble metal electrocatalysts for hydrogen evolution reaction (HER) that can withstand in acidic environment is one attractive route for renewable energy applications. The 3D graphene oxide on nickel skeleton has been recently developed as electrocatalyst in acid solution since it is less expensive than existing noble metal-based catalysts and yet exhibits promising potential for efficient reaction between molecules such as H2O, H2, NH3, O2 etc. In this work, the 3D graphene oxide was synthesized as a thin film coated on Ni foam substrate by the CVD method using methanol and water as a carbon precursor and a weak oxidizing agent, respectively. The influence of oxidation level of 3D graphene oxide to the overpotential, Tafel slope, and band gap energy was investigated in 0.5 M H2SO4 solution. It was found that 3D graphene oxide can improve electrocatalytic property of Ni by the oxygen-functional groups, which can act as an alternative path for H2 production by the recombination of the spilled Hads from Ni. This novel 3D graphene oxide/ nickel foam may be a good electrocatalyst for practically producing H2 fuel.
Layer-Dependent Photoelectrochemical Performance of Multi-Layer Graphene Catalysts on Silicon Photocathode
Authors: Sim Uk , Moon Joonhee , Lee Joohee , Jeon Cheolho , Han Seungwu , Hong Byung Hee , Nam Ki Tae
Published: February 2020

Development of sustainable energy sources is an urgent issue to meet growing demand in world energy consumption. Photoelectrochemical cells are used to split hydrogen and oxygen from water molecules to generate chemical fuels to satisfy our ever-increasing energy demands. However, it is a major challenge to design efficient catalysts to use in the photoelectrochemical process. Recently, research has focused on carbon-based catalysts, as they are non-precious and environmentally benign. Especially, graphene possesses excellent transmittance and superior intrinsic carrier mobility, thus there have been several attempts to use graphene as a catalyst. We are the first to investigate the use of monolayer graphene as an electrocatalyst for efficient hydrogen evolution reaction (HER), employing a Si substrate as a photocathode. The understanding of the correlated interaction between solid catalysts/electrode and liquid electrolyte during HER operation is also very important for efficient hydrogen production, however, few researches have been conducted before to study the interface between carbon catalysts/semiconductor electrode and aqueous solution. Here, we have explored to develop an enabling technology and design rules for the efficient and durable catalyst/electrode system. We prepared mono-, double-, tri-, and multilayer graphene on p-Si photocathodes and investigated the layer dependence of catalytic activity for HER. Interestingly, double-layer graphene/Si exhibits noticeably improved photon-to-current efficiency and modifies the band structure of the graphene/Si photocathode. Based on in-depth electrochemical and electrical analyses, the band structure of graphene/Si was shown to result in a much lower work function than Si, accelerating the electron-to-hydrogen production potential. Specifically, plasma-treated double-layer graphene exhibited the best performance and the lowest work function. We electrochemically analyzed the mechanism at work in the graphene-assisted photoelectrode. Atomistic calculations based on the density functional theory were also carried out to more fully understand our experimental observations. We believe that investigation of the underlying mechanism in this high-performance electrode is an important contribution to efforts to develop high-efficiency metal-free carbon-based catalysts for photoelectrochemical cell hydrogen production.
Model-Supported Analysis of Degradation Phenomena of a PEM Water Electrolysis Cell Under Dynamic Operation
Authors: Frensch Steffen Henrik , Simon Araya Samuel , Olesen Anders Christian , Kær Søren Knudsen
Published: February 2020

PEM water electrolysis for large-scale energy storage may also serve as an actor for grid stability in energy grids with a high share of fluctuating, renewable energy sources. The major challenge the technology is facing is to reduce the system cost. In that context, acceptable lifetime under variable operation conditions has yet to be proven. Degradation studies are still scarce, but considered crucial for a further market implementation.

In this study, a small single cell set up is utilized to extract information about degradation mechanisms. The major parameters of interest are the operational conditions. Therefore, long term tests are performed with electrochemical characterization through polarization curves and EIS while changing the input signal.

Preliminary results of the study show a high reversible share of the voltage increase, which can be recovered through a short interruption of cell operation (see figure). That is particularly interesting for grid service applications, since the data suggests that dynamic operation may be beneficial.

However, the voltage profiles alone do not reveal enough information about what causes the degradation. Periodically performed EIS experiments on the operational cell support the analysis of which part of the cell causes performance loss. It was found that the purely ohmic contribution to cell impedance is mostly affected in the initial period and stabilizes afterwards. Other contributions on the other hand influence cell aging throughout the whole investigated timespan of 1000h so far.

Furthermore, a model-based analysis of the changes in polarization curves over time is carried out as in previous studies on cell performance. The extracted parameters are linked to activation processes and ohmic contributions that stem from the membrane and the contacts resistances.

Figure 1
Non-Precious Electrocatalysts for Anion Exchange Membrane Water Electrolysis Cell
Authors: Choi Sung Mook , Choi Woo-Sung , Seo Min Ho , Jang Myeong Je , Park Yoo Sei , Lee Kyu Hwan
Published: February 2020

The hydrogen has been recognized as a clean, nonpolluting and unlimited energy source that can solve fossil fuel depletion and environmental pollution problems at the same time. Water electrolysis has been the most attractive technology in a way to produce hydrogen, because it does not emit any pollutants compared to other methods such as natural gas steam reforming and coal gasification etc. In order to improve efficiency and durability of the water electrolysis, comprehensive studies for highly active and stable electrocatalysts have been performed. The platinum group metal (PGM; Pt, Ru, Pd, Rh, etc.) and its oxide catalysts showed a higher activity and stability compared with other non-precious catalysts in operating condition. It is necessary to develop non-precious catalysts with high activity and durability because the PGM catalysts are expensive materials with insufficient it’s reserves. In the water electrolysis field, the numerous researchers have been focused on the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) because the OER and HER are a key process (slow kinetics) compared with other resistances such as bubble, electrolyte, diaphragm, membrane, etc. On a point of view of a catalyst, slow kinetics and the use of precious metal (PGM) for high performance should be solved to popularize water electrolysis.

The target of this study is the development of non-precious catalysts with high activity via simple and efficient synthesis method that is a wet-chemical based method. The Ni-LaCeO/C (HER catalysts) and CuCoO (OER catalyst) were synthesized through the co-precipitation with oxidation and reduction heat treatment. The catalysts were characterized by various physicochemical analyses such as X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDS), and X-ray photoelectron spectroscopy (XPS). To investigate electrocatalytic properties of prepared catalysts, we carried out electrooxidation activity measurements such as cyclic voltammetry (CV), linear sweep voltammetry (LSV), long-term stability test, and electrochemical impedance spectroscopy (EIS). The relationship between their physicochemical properties and electrocatalytic activities will be explored and discussed.
Role of Surface Area on the Performance of Iron Nickel Nanoparticles for the Oxygen Evolution Reaction (OER)
Authors: Acharya Prashant , Burrow James , Greenlee Lauren F
Published: February 2020

Iron nickel based bimetallic catalysts have recently emerged as one of the best candidates for oxygen evolution reaction (OER) in alkaline conditions [1]. It is crucial to understand the composition and morphology of iron nickel nanoparticles to optimize the catalysts for enhanced performance [2]. One key aspect to understand in the study of OER performance, in addition to the function of composition and morphology, is the physical surface area and the electrochemically active surface area (ECSA) of the catalysts. In this study, three different iron nickel nanoparticles will be synthesized. The three nanoparticles will be varied based on morphology (alloy vs core-shell) and composition (high vs low amount of stabilizer). Brauner-Emmett-Tellet (BET) surface area analysis will be conducted on the as synthesized iron nickel nanoparticles using Autosorb-iQTM to calculate the physical surface area while electrochemical impedance spectroscopy (EIS) will be employed to quantify the ECSA [3]. In addition, electrochemical performance will be measured using techniques such as cyclic voltammetry (CV), chronopotentiometry (CP), and chronoamperometry (CA).

[1] M. W. Louie and A. T. Bell, J. Am. Chem. Soc., 135, 12329 (2013)

[2] S. L. Candelaria, N. M. Bedford, T. J. Woehl, N. S. Rentz, A. R. Showalter, S.

Pylypenko, B. A. Bunker, S. Lee, B. Reinhard, Y. Ren, S. P. Ertem, E. B. Coughlin, N. A.

Sather, J. L. Horan, A. M. Herring and L. F. Greenlee, ACS Catal., 7, 365 (2017).

[3] C.C. McCrory, S. Jung, J. C. Peters, and T. F. Jaramillo, J. Am. Chem. Soc., 135, 16977

(2013)
Carbon-Free Perovskite Oxide Oxygen Evolution Reaction Catalysts for AEM Electrolyzer
Authors: Chung Hoon T , Lee Albert Sung Soo , Kim Yu Seung , Fujimoto Cy , Wang Lin-Wang , Teeter Glenn , Bender Guido , Zelenay Piotr
Published: February 2020

In alkaline electrolysis of water, kinetic limitations account for up to 85% of the total efficiency losses [1]. In particular, the efficiency of water electrolysis is largely limited by the high overpotential of the oxygen evolution reaction (OER). Therefore, reducing the reaction overpotential at the OER catalysts is critical for the overall efficiency improvement of alkaline water electrolysis.

Perovskite oxides are promising non-precious metal OER catalysts showing high activity in oxygen evolution in alkaline electrolytes, comparable to that of the state-of-the-art IrO2 catalysts [2], but their stability is in need of improvement. As these oxides exhibit relatively low electronic conductivity carbon, typically acetylene black (AB), is added to enhance their conductivity. However, the thermodynamic potential of carbon oxidation (C + 4OH- → CO2 + 2H2O + 4e-) is 1.03 V vs. RHE at pH 14, much below the OER onset potential. Carbon oxidation causes an increase in the electrode resistance and weakens the carbon-catalyst interaction, eventually limiting the electrolyzer lifespan. Consequently, improving the stability and electronic conductivity of the perovskite-oxide OER catalysts with further enhancement of the OER activity is critical to the application of perovskites as OER catalysts for anion exchnange membrane (AEM) electrolyzer.

In this work, perovskite (La1-xSrx)CoyFe1-yO3-δ (LSCF) was chosen to study the OER activity, stability, and electronic conductivity. In typical ABO3 perovskites, the valance state of cations, i.e., the sum of A and B, should be +6 to balance the overall oxygen valence of -6. The non-stoichiometry caused by the change in the ratio of La/Sr and Co/Fe in the LSCF will affect the OER activity, stability and the electronic conductivity. The effect of this non-stoichiometry of LSCF on the OER performance in alkaline electrochemical cells and AEM electrolyzer, in conjunction with DFT calculations, will be presented in this talk.

Acknowledgements

This work was supported by the U.S. Department of Energy, Energy Efficiency and Renewable Energy, Fuel Cell Technologies Office under the auspices of the HydroGEN Consortium.

References

[1] J. Greeley, N. M. Markovic, Energy Environ. Sci., 5 (2012) 9246-9256.

[2] J. Suntivich, K. J. May, H. A. Gasteiger, J. B. Goodenough, Y. Shao-Horn, Science, 334 (2011) 1383-1385.