bluuebunny/crossref_metadata_2025 huggingface dataset:
(Invited) High-Throughput Production of 2D Materials and Their 1D Structures
Authors: Liu Fang
Published: December 2024

Two dimensional (2D) materials and their artificial structures hold great promises for electronic, optoelectronic, and photonic applications. The best quality monolayers for exploring the exotic quantum properties so far are mostly produced by scotch tape exfoliation. It often yields microscopic sized monolayers, limiting the measurement capabilities with device implementation. We developed a few new scalable and controllable top-down processes to construct monolayers, moiré structures, and monolayer nanoribbons directly from a variety of van der Waals (vdW) single crystals, with high yield, high quality, and macroscopic dimensions. The high throughput production will allow us to further assemble them into artificial heterostructures, and integrate into multiple photonic devices and pump probe spectroscopic experiments to explore the key static and dynamic properties in these low dimensional systems. Obtaining high quality materials with enhanced yield will take us one step closer to mass production and commercialization of the 2D devices in the future.
A New Patterning Method of SnO2-Based Transparent Conductive Oxide Films By Two-Step Wet Processes Using Reduction in Gluconic Acid Aqueous Solution
Authors: Ogawa Daisuke , Namiki Hiromasa , Miyashita Yuito , Isoda Kazutaka
Published: December 2024

In order to realize a sustainable, recycling-oriented society, it is intrinsically important to develop new technologies to substitute rare elements with elements abundant in resoueces, to save energy, to introduce renewable energy, or recyce the devices.

Transparent conductive oxide (TCO) films are essential materials for transparent electrodes in clean energy production sources (solar cells) and energy-saving devices (liquid crystal displays, light-emitting diodes, etc.). Indium tin oxide (ITO) is currently the most widely used TCO film. However, ITO is mainly composed of indium, a rare-earth. From the perspective of the SDGs, there is a strong need to promote the use of alternative materials to ITO, that are mainly composed of elements abundant in resources and can also be recycled.

Tin dioxide (SnO2) is a TCO film in practical use during more than half a century. It is mainly composed of tin (Sn), which is abundant in resources, and has excellent weatherability and chemical resistance. It is used in solar cells, heater glass to prevent fogging, and viewing windows of analyzers. If SnO2 can replace ITO, it will have a very large impact on the realization of a recycling society.

TCO films are generally patterned when used as transparent electrodes. ITO films can be easily patterned by wet processes using commercially available etchants the photoresist masks fabricated by photolithography. In contrast, SnO2 films are quite difficult to pattern by wet processes due to its high chemical resistance. SnO2 films are mainly patterned by dry processes, such as laser processing or sandblasting. However the former is expensive in cost, and the latter may cause substrates to break after shipping. If SnO2-based TCO films can be patterning by wet process, it will directly lead to improved throughput, cost reduction, and lower product defect rate, and will be a step forward toward the major goal of replacing ITO.

We developed a new patterning method of SnO2-based TCO films by two-step wet processes. In the first step, the SnO2 was reduced to metallic Sn by applying voltage in gluconic acid aqueous solution (Figure 1). The reduction to Sn was confirmed by X-ray diffraction measurements. Cross-sectional observation by a scanning electron microscope (SEM) revealed that reduction proceeds from the surface of the SnO2 film toward the inside.

In the second step, Sn was removed by acid, base, or electrolysis. The complete removal of the SnO2 film was confirmed by SEM and energy-dispersive X-ray spectroscopy. In addition, transmittance and reflectance of the glass substrate after removal of SnO2 film were measured.

It was found that patterning SnO2-based TCO films in the micrometer order scale is possible by combining the developed two-step method with the photoresist masks fabricated by photolithography.

Figure 1
(Invited) Improving Resilience of Wide Bandgap Electronics
Authors: Rasel Md Abu Jafar , Al-Mamun Nahid , Haque Amanul , Wolfe Douglas , Ren Fan , Pearton Stephen J
Published: December 2024

Wide-bandgap electronics operate at much higher voltages and frequencies compared to silicon counterparts. They are more resilient as well, being able to withstand much higher electrical field and temperature. However, a gap remains between their potential and measured performance and reliability. This gap is typically sought to be closed by perfecting materials synthesis and device fabrication processes.

In this presentation, we offer a different perspective by focusing on the residual defects and stresses that are localized in these devices. Typically, average values of such stresses are not high enough to draw attention. However, the core contribution of this research is to highlight that the localized values can be deceptively high to impact the device properties even though their global average could be negligible. We study SiC, Ga2O3 diodes and AlGaN/GaN high electron mobility transistors (HEMTs) to show that mechanical confinements lead to enhanced radiation vulnerability and accelerated ageing degradation. The reverse is also true; removal of the confined stresses leads to enhanced performance. We will present some extreme examples where we rejuvenate the degraded devices to demonstrate the resilience achieved from the ability to control defects and microstructures. Rejuvenation is achieved through a unique room temperature, ultrafast processing technique that requires only the electrodes, hence it can be performed in-operando. We exploit high resolution techniques such as transmission electron microscopy (TEM) and micro-Raman spectroscopy to spatially resolve the stress field in GaN HEMTs to demonstrate the localization effects on degradation.
Stacking Fault Analysis for the Early-Stages of PVT Growth of 4H-SiC Crystals
Authors: Hu Shanshan , Chen Zeyu , Cheng Qianyu , Raghothamachar Balaji , Dudley Michael
Published: December 2024

With wide band gap, high thermal conductivity, and high breakdown field, silicon carbide, typically 4H-SiC, has steadily become the material of choice for next generation high-power electronic devices[1]. However, the presence of defects especially dislocations and stacking faults (SFs), such as threading screw dislocations (TSDs), threading edge dislocations (TEDs), threading mixed dislocations (TMDs), basal plane dislocations (BPDs), Frank dislocations, Shockley SFs and Frank SFs, are hindering the widespread application of 4H-SiC device due to their harmful effects on the reliability of high-performance SiC power devices[2]. In particular, SFs are particularly deleterious as they degrade the blocking and on-state conduction performance and/or reliability of devices[3].

A recent approach to lowering defect densities is to closely examine the early-stages of crystal growth when many defects are nucleated. Recently, we have reported on the expansion of Shockley stacking faults in the facet region during the early growth stage[4]. Continuing these early-stage studies, we seek to better understand the effects of various growth parameters on resulting defect structures, especially stacking fault formations. Multiple short duration growths have been carried out under varying conditions of nucleation temperature, thermal gradients, and N incorporation. In this study, three types of Frank type or Frank+Shockley stacking faults are observed distributed across the growth surface: Type A, stacking faults bounded by 2 opposite sign Frank type dislocations; Type B, stacking faults bounded by a pair of same sign Frank-type dislocations. As higher partial pressures of N2 are deployed, the occurrence of the Type B stacking fault is found to be suppressed (Figure 1); Type C, stacking faults regions shown as “carrot” defects on the as-grown surface of crystal (Figure 2). The formation mechanisms of these stacking fault formation will be suggested. The implications of these observations to achieve better control of the PVT growth process and resultant defect reduction will be discussed.

Figure 1
Photosensitive Adhesive Bonding between Laser Diode and Optical Nonreciprocal Device
Authors: Yokoi Hideki , Ikeda Hiroki
Published: December 2024

INTRODUCTION

In optical communication systems, optical nonreciprocal devices such as optical isolators or optical circulators are indispensable for protecting active photonic devices from unwanted reflected light. In the near-infrared region, magnetic garnet crystals are necessary components of optical nonreciprocal devices because of their transparency and large magneto-optic coefficient. Active photonic devices consist of III-V compound semiconductors. Therefore, a novel integrating technology must be developed for integration of a semiconductor laser diode and an optical isolator employing magnetic garnet crystals. In this paper, the authors report on an integrating technique between a laser diode and an optical isolator by means of photosensitive adhesive bonding.

DEVICE STRUCTURE

Figure 1 shows a laser diode integrated with an interferometric optical isolator by photosensitive adhesive bonding. The optical isolator employing a nonreciprocal phase shift has a magneto-optic waveguide with a (CeY)3Fe5O12 (Ce:YIG) layer. The nonreciprocal phase shift occurs in TM modes that travel in magneto-optic waveguides in which magnetization is aligned transverse to the light propagation direction in the film plane. An optical interferometer is comprised of two multimode interference couplers, nonreciprocal phase shifters in two arms and a reciprocal phase shifter in one of the arms. The reciprocal phase shift is obtained by an optical path difference between the two arms. An external magnetic field is applied to two arms in the interferometer in order to achieve a push-pull nonreciprocal phase shift.

The magneto-optic waveguide includes the magnetic garnet layer as either a guiding layer or a cladding layer. When the refractive index of the strip is less than that of Ce:YIG, the magneto-optic waveguide has a Ce:YIG guiding layer. On the other hand, when the refractive index of the strip is more than that of Ce:YIG, the magneto-optic waveguide has a Ce:YIG cladding layer.

The coupling efficiency from an active layer of the laser diode to a guiding layer of the optical isolator was calculated by use of beam propagation method.

Photosensitive adhesive bonding between III-V compound semiconductors and magnetic garnet crystals was studied. The adhesive bonding of two planar substrates was successfully achieved with the heat treatment at 160°C. The adhesive bonding between a planar substrate and a nonplanar one with rib structures was also successful.

ACKNOWLEDGMENT

This work was partially supported by the SIT Research Center for Green Electronics.

Figure 1
(Invited) sald: Versatility of the Deposition Process Combined with in-Situ Characterization Methods
Authors: Barr Maissa K. S.
Published: December 2024

We have proposed and demonstrated a novel thin film deposition technique by transferring the principles of atomic layer deposition (ALD), known with gaseous precursors, towards precursors dissolved in a liquid. 'Solution ALD'(sALD) shares the fundamental properties of standard ‘gas ALD’ (gALD), specially the self-limiting growth and the ability to coat conformally deep pores. It has been already shown that it is possible to transfer standard reactions from gALD to sALD such as oxides and sulfides deposition. However, sALD also offers novel opportunities such as overcoming the need for volatile and thermally robust precursors, offering the possibility to grow materials that cannot be obtained by gALD and using mild conditions which allow the growth on sensitive substrates. Recently we extended the understanding of the nucleation of selected materials grown by sALD such as Cu-BDC, MAPI, CuSCN, TiO2 and SnSx. The study of the nucleation process relies on, first the identification of the absorbed chemical species at the surface by in-situ infra-red spectroscopy, second the ability to determine the type of interaction of the precursor with the surface by ex-situ solid state nuclear magnetic resonance (NMR) and third the evolution of nuclei formation with in-situ x-ray reflectometry (XRR) and atomic force microscopy. We developed the necessary instrumentation to obtain measurement compatible in liquid environment for each in-situ method. Form IR we can identify the phase preferential phase that is obtained as well as the defects formation for extremely thin films and NMR shows the chemical bonding of precursors at an early stage. Additionally, the AFM and XRR investigations are needed to follow the evolution of the nuclei size and their distribution of a surface as well as the nuclei density of each half cycle.

The extension of the knowledge on the reaction mechanism in sALD process appears to be crucial to design next reactions and to understand later on the properties of the layers obtained with sALD.

Wu, D. Döhler, M. Barr, E Oks,M. Wolf, L. Santinacci and J. Bachmann, Nano Lett. 2015, 15, 6379 Fichtner, Y. Wu, J. Hitzenberger, T. Drewello and J. Bachmann, ECS J. Solid State Sci. Technol. 2017,6, N171 M. K. S. Barr, S. Nadiri, D.-H. Chen, P. G. Weidler, S. Bochmann, H. Baumgart, et al, .Chemistry of Materials 2022, 34, 9836-9843
Photoelectrochemical Three-Dimensional Fabrication of Conductive Polymers Using Multi-Photon Absorption Process
Authors: Suzuki Ayumu , Yamada Katsumi
Published: December 2024

Micro-nano 3D printing of conductive polymers is a technology developed by our research group for the first time in the world. Many monomers of conductive polymers are liquid state at normal pressure, but when polymerized, the product becomes an infusible and insoluble solid state, so three-dimensional structures can be obtained. Pyrrole undergoes polymerization through oxidation to become polypyrrole, and in this research, the photo-electrochemical oxidation reaction is achieved by multi-photon absorption sensitization. The multi-photon absorption reactions have extremely high spatial selectivity and can produce fine three-dimensional structures of conductive polymers. Extremely high electrical conductivity of up to 410 S/cm for polypyrrole (PPy) and up to 3500 S/cm for poly-3,4-ethylenedioxy-thiophene (PEDOT) were achieved using this method. The following two factors are thought to have contributed to these results. The extremely strong electromagnetic field of the femtosecond laser light source assists in the orientation of the polymer chain. Since a perfluoro-alkylsulfonic acid polymer (Nafion®) is used as the three-dimensional support, sulfonic acid ions serve as dopants and contribute to carrier generation. In this study, the effects of the laser scanning direction and method during modeling were discussed for appropriate evaluation of electrical conductivity. The electrical conductivity of the polypyrrole line shaped product obtained by the improved method was evaluated using a two-terminal method. As a representative result, the current-voltage characteristics are shown in Figure 1. The electrical conductivity obtained under the conditions of incident laser intensity of 2.2 mW, focus movement pitch of 0.005 μm, and waiting time at focus position of 0.1 seconds was 1203 S/cm. This value was a significant improvement over the value of 410 S/cm obtained using our previous method. The scanning method of the laser focus was changed to improve polypyrrole deposition on the lower surface of the Nafion sheet. It is thought that this effect resulted in higher conductivity than before.

Figure 1
Improved Electrochromic Stability in Reversible Metal Electrodeposition Devices Using Gel Electrolytes
Authors: Lee Ji-Hyeong , Kang Kwang-Mo , Nah Yoon-Chae
Published: December 2024

The reversible metal electrodeposition (RME) process in electrochromic mirrors enables the implementation of reflective-transparent optical states by depositing and removing metals on a transparent conductive substrate. Specifically, electrochromic mirrors employing gel electrolytes, such as polyvinyl alcohol (PVA) or polyvinyl butyral (PVB), are anticipated to exhibit reduced electrolyte leakage and improved mechanical stability compared to traditional liquid electrolyte devices. Additionally, they offer the advantage of achieving various colors by controlling the size of the metal particles. In this study, we investigated the enhanced performance of electrochromic mirrors, which includes long-term stability and diverse reflection spectra at different voltages. Furthermore, the incorporation of PVB revealed more pronounced distinctions in the reflection spectra.
Fabrication and Performance of Transmissive Light-Emitting Electrochemical Cells Using Spray- Coated Silver Nanowires(AgNW) Cathode
Authors: Akamatsu Ayumu , Aoki Atsushi
Published: December 2024

In recent years, transmissive light-emitting devices have been in demand for digital signage, smart glasses, and other applications. In this study, we aimed to achieve both transparency and luminescence performance of light-emitting electrochemical cells (LECs) by thinning the thickness of the silver cathode of LECs until being semitransparent and depositing silver nanowires (AgNW), which are transparent conductive films, on the semitransparent silver cathode.

Cationic ruthenium complex Ru(bpy)3(TFSI)2 was used as an electrochemical luminescent chromophore. The LECs were fabricated as follows. The luminescent layer was spin-coated onto a patterned ITO substrate (anode). The luminescent layer solution was made of Ru complex (40 mg/mL) and polymethyl methacrylate (PMMA) (3 mg/mL) dissolved in acetonitrile. LiF and Ag were vacuum deposited at the film thickness of 0.5 nm as an electron injection layer on the top of the luminescent layer and as a cathode at the film thickness from 0 nm to 75 nm, respectively.

The transmittance of the LECs with the different film thickness of Ag cathode was investigated from UV-vis spectra in the visible region. The luminescence performance was measured by applying a constant current to LECs and obtaining voltage and luminance responses. The average transmittance in the visible region was confirmed to decrease with increasing film thickness of the Ag cathode until 20 nm. There is almost no transmittance in LECs with the film thickness above 20 nm. The luminescence performance of the LECs with the different film thickness of Ag cathode was then investigated by applying a constant current to the LECs. The voltage responses indicate that the voltage decays with time and became the constant voltage of about 2.7 V because of the formation of the electric double layer in the LECs with more than 10 nm film thickness. From the luminance responses, the light emission was observed. Meanwhile, it kept the upper limit voltage of 5.0 V in the LECs with less than 5 nm film thickness and no emission took place. It means that the film thickness less than 5 nm is too thin to flow current due to the formation of the sea-island structure of silver. Furthermore, the light emission was observed from both sides of not only the transparent ITO anode but also the semitransparent Ag cathode in the range of the film thickness between15 and 30 nm. Therefore, we demonstrated the transmissive LECs using Ag cathode at the film thickness of 15 nm.

However, the average transmittance in the visible region is even 10 % using Ag cathode at the film thickness of 15 nm. Therefore, in order to increase the transmittance and to decrease cathode resistance, we attempted to deposit AgNW on the semitransparent Ag cathode by spray coating. Unfortunately, Ru complex layer was dissolved by ethanol which was the solvent dispersed AgNW. Thus, we are underway to change solvent from ethanol to non-polar solvent such as hexane.
Exploring Domain Engineering in Bismuth Ferrite for Enhanced Photoelectrochemical Performance
Authors: Huang Yen-Lin
Published: December 2024

Over the past two decades, Bismuth ferrite (BiFeO3, BFO) has risen as a prominent single-phase multiferroic material operating at room temperature, sparking considerable interest within research circles. Its sturdy ferroelectric traits, coupled with promising magnetic interactions, have contributed to a wide array of physical phenomena and functionalities. The intricate ferroic domain structures inherent in BFO play a central role in governing both its static configurations and dynamic behaviors of order parameters, forming a fundamental framework for understanding and manipulating its macroscopic properties. In this presentation, I will discuss the current progress in BFO research regarding water splitting, particularly within the domain engineering approach. Finally, I will showcase the diverse oxide photoelectrodes that the pulsed laser deposition process can offer for enhancing photoelectrochemical performance.
Bifunctional Photocatalysis Via Doped TiO2: Antibiotic Degradation and CO2 Reduction
Authors: Yu Ya-Chi , Cheng Wen-Hui (Sophia)
Published: December 2024

Tetracycline (TC) as a typical antibiotic often applied in the medical industry or animal husbandry. Due to the stable chemical structure and difficult biological metabolism of TC, it will enter the aquatic ecosystem, threatening the health of humans. In recent years, photocatalysis has attracted attention due to its ability to rapidly degrade antibiotic pollutants. TiO2 is especially promising due to its non-toxicity and easy fabrication. Modifying TiO2 with metal doping can introduce defect levels and provide possible active sites. After the hydrothermal synthesis process, all samples are characterized by XRD, Raman, and SEM. We perform photodegradation experiments with inline gas phase analysis. For TC degradation, the reaction rates of the Cu-doped samples are superior to the pristine TiO2. However, the intrinsic catalytic property of Cu-TiO2 for CO2 reduction is limited. In contrast, Mg-TiO2 can effectively degrade TC and efficiently reduce CO2 as well. In this work, we experimentally demonstrate the bifunctional photocatalysis with degradation of TC and converting the produced CO2 into CO. The role of doping and further optimization of the catalyst will be discussed.
Design of Innovative Janus Phase/Structure-Engineered Two-Dimensional Layered Heterostructures with Enhanced Catalysis Effect on Green Energy Applications
Authors: Chueh Yu-Lun
Published: December 2024

A new class of two-dimensional (2D) materials called Janus TMDs have sparked research interest in recent years due to their myriad of possible applications, which include photocatalysis, optoelectronics, valleytronics, water splitting, and sensing, among others. Compared to traditional TMDs, Janus TMDs are composed of different chalcogen atoms, which breaks the out-of-plane symmetry. The asymmetrical structure, like in Janus MoSSe, generates out-of-plane dipoles between the top Se and bottom S atoms. This intrinsic dipole moment contributes to efficient charge separation, enhancement of Raman scattering and large Rashba splitting. Unlike conventional 2D materials, Janus TMDs do not exist in nature and have only been fabricated synthetically from a parent TMD (e.g., MoS2 or WS2). The fabrication techniques for synthesizing Janus TMDs require extreme precision to obtain high-quality flakes and avoid alloying or randomized orientation distribution of chalcogen atoms. An inductively coupled plasma (ICP) was used to synthesize Transition Metal Dichalcogenides (TMDs) through a plasma-assisted selenization process of metal oxide (MOx) at a low temperature. Compared to other CVD processes, ICP facilitates the decomposition of the precursors at lower temperatures. Here, we designed innovative Janus phase/structure-engineered two-dimensional layered heterostructures with enhanced catalysis effect on green energy applications derived from the MOx 3D-hierarchical nanostructures through a low-temperature plasma-assisted selenization process. The applications, including the catalysis effect for water splitting, nitrogen reduction, and battery, will be reported.
Bidirectional Polarization-Integrated Van Der Waals Ferroelectric Field-Effect Transistor for Multi-State Storage and Dual-Logic-in-Memory Computing
Authors: Niu Jingjie , Jeon Sumin , Kim Donggyu , Baek Sungpyo , Yoo Hyun Ho , Li Jie , Park Jisang , Lee Yoonmyung , Lee Sungjoo
Published: December 2024

The rapidly growing number of AI-enabled applications is driving the need for development of energy efficient computing hardware that can handle massive amount of computations required for neural network operation. As one of the promising approaches for processing data within memory, Logic-in-memory is parallel execution of reconfigurable logic operation within memory allows fast and efficient computations. For realizing the logic-in-memory hardware, implementing practical logic functions with high density is of critical concern.

Here, we demonstrate a multi-state dual-logic-in-memory device implemented via a single bidirectional polarization-integrated ferroelectric field-effect transistor (BPI-FeFET) by integrating the in-plane vdW ferroelectric semiconductor SnS and the out-of-plane vdW ferroelectric gate dielectric CuInP2S6 (CIPS). Four reliable resistance/conductance states (two-bit storage) with an on/off ratio between the highest and the lowest channel current of >105, high switching endurance (>104 cycles), and stable retention characteristics (>104 s). The mechanism of two-bit storage in a single BPI-FeFET is analyzed from two perspectives: carrier density and carrier injection controls, originating from the out-of-plane polarization of the gate dielectric and in-plane polarization of the semiconductor, respectively.

Unlike the conventional multilevel FeFET, direct conversions among the four-memory states of proposed BPI-FeFET without pre-examination or additional erasing step are demonstrated experimentally. The potential of the BPI-FeFET as a low-cost and high-density in-memory computing circuit was further explored. To utilize the fabricated BPI-FeFET as a dual-logic-in-memory device, two logical operations are selected (e.g. XOR and AND) by properly setting initial states, and their parallel execution is demonstrated. Additionally, these logical computations are reconfigurable when the initial state of the device is set to different states, making it flexible for implementing various types of functions that can be potentially required for different types of neural networks. We believe the flexibility and efficiency of dual-logic-in-memory devices provide a promising pathway for realizing next generation low power computing systems.
Spin-State Analysis for a Fourteen-Membered Macrocyclic Fe Complex for Oxygen Reduction
Authors: Nabae Yuta , Feng Zhiqing , Honda Sotaro , Machida Masato , Ohyama Junya , Moriya Makoto
Published: December 2024

For the broad application of polymer electrolyte fuel cells (PEFCs), the development of non-precious-metal (NPM) catalysts for oxygen reduction is extremely important. To date, many NPM catalyst have been synthesized by pyrolyzing Fe-, N-, and C-containing precursors, but they suffer from the low density and uncertain chemical structure of their active sites. On the contrary, our research group has been studying a 14-membered macrocyclic Fe complex, which was inspired by the FeNx sites embed in graphene sheets.

In this study, a fourteen-membered macrocyclic Fe complex was loaded on a carbon support and then heat-treated, and found to be quite active as a non-precious metal oxygen reduction catalyst. The improvement is attributed to a high turnover frequency rather than the number of active sites. To fully understand the mechanism for the improved catalytic activity, the spin-state of the catalysts was evaluated by X-ray emission spectroscopy, and the results were discussed in comparison to a simulation study based on the density functional theory (DFT). The obtained results suggest that the Fe-based active sites are working in a middle-spin state.

Figure 1
Composition-Activity-Stability Relationship Investigation of Trimetallic Pt-Ni-Au Oxygen Reduction Reaction Catalyst
Authors: Xie Xianxian , Briega Martos Valentin , Vorochta Michael , Matolínová Iva , Cherevko Serhiy , Khalakhan Ivan
Published: December 2024

Hydrogen-fuelled proton-exchange membrane fuel cells (PEMFCs) offer a promising path towards zero-emission energy, but their commercialization is hindered by challenges, particularly in the cathode catalysts responsible for the oxygen reduction reaction (ORR). Current catalysts rely heavily on expensive platinum, which degrades quickly in the harsh cathodic environment. Efforts are thus focused on developing cost-effective and stable catalysts. Recent research has shown that alloying platinum with earth-abundant transition metals can reduce costs and improve ORR activity. Bimetallic Pt-M (M=Ni, Cu, Co, Fe, etc.) alloy catalysts, particularly those incorporating gold, have demonstrated superior performance. However, achieving both high activity and long-term stability remains a challenge. Our recent work emphasizes the importance of precise catalyst engineering to optimize both activity and durability, highlighting the need for a balanced alloy structure and compositional profile in Pt–Au catalysts.

In this work, a magnetron co-sputtering technique was utilized to introduce a small amount of Au (5, 10, and 20 at%) into Pt50Ni50 alloy. The resulting ternary PtNiAu alloy demonstrated enhanced stability compared to PtNi, as evidenced by reduced platinum and nickel dissolution with increasing Au content, confirmed over a wide potential range up to 1.5 VRHE. On the other hand, at elevated concentrations, Au showed a detrimental effect on the ORR activity. Despite showing lower activity than PtNi, the ternary PtNiAu alloy still displayed superior activity compared to pure Pt. The investigation employed robust characterization methods, including synchrotron radiation photoelectron spectroscopy (SRPES), in-situ scanning flow cell coupled with inductively coupled plasma mass spectrometer (SFC-ICP-MS), and rotating disc electrode (RDE), to probe the composition-activity-stability relationship and identify the optimal Pt-Ni-Au composition meeting both high activity and stability requirements.
Optimization of Pt-Based Nanocatalysts Loading to Improve MEA Performance
Authors: Chen Shutang
Published: December 2024

Platinum (Pt) catalysts have been considered as the most active electrocatalyst for the oxygen reduction reaction (ORR) in fuel cells. However, high rotating disc electrode (RDE) activities have rarely translated into membrane electrode assemblies (MEA) performance. There are several technical issues that must be solved before they can be applied in fuel cell vehicles, for example, cost/durability, transition metal leakage, and high-density loading catalyst for closing the gap between RDE and MEA experiments. In this talk, we will introduce our catalysts loading method and strategy how to improve MEA performance. We believe our method provides an effective strategy for the rational design of Pt-based alloy nanostructures and will help guide the future development of catalysts for their practical applications in energy conversion technologies.
Facile Engineering of Self-Repairing Ni-Rich Stainless-Steel Electrode Toward Oxygen Evolution Reaction
Authors: Lyu Xiang , Serov Alexey , Yang Jun
Published: December 2024

In the past few decades, tremendous attention has been devoted to enhancing the activity of oxygen evolution reaction (OER) catalysts for hydrogen generation, while the cost and long-term stability of OER catalysts, which can play an even more important role in large-scale electrolysis industrialization, have been much less emphasized. Herein, we engineered an OER electrode from cheap and abundant stainless steel (SS) via facile approaches. An outstanding activity is observed with a low overpotential at 10 mA cm-2 and a small Tafel slope, which is among the best performances in the published literature. Additionally, a self-repairing catalyst concept on the electrode is proposed in which the Ni-rich catalyst layer can regenerate from the metallic substrate under the OER induction due to the different diffusion and dissolution rates of metal oxides/hydroxides. The facile engineering of OER electrodes from SS combined with the self-repairing catalyst can potentially address the cost and long-term stability barriers for OER catalysts in alkaline electrolysis.
The Catalytic Effect of Hydroxide Layer on the Metal Surface in Alkaline Water Electrolysis
Authors: Kim Hye Ri , Yeon Changho , Lee Gahyeon , Baek Seulgi , Lee Chan-Woo , Joo Jong Hoon
Published: December 2024

The production of hydrogen has been extensively studied since hydrogen is an ideal energy, high quality and clean energy carrier. Currently, the hydrogen is mainly produced by the fossil fuels or other carbon-based fuels. However, the production technology of hydrogen via the fossil fuels causes global warming by emitting environmental pollutions such as CO, CO2, and CH4. Thus, a lot of efforts have been dedicated to the production of hydrogen through the clean renewable energy sources such as water, biomass. Among these technologies, an alkaline water electrolysis has been considered as the promising candidate for the green hydrogen technology. The high catalytic activity and durability of the electrodes should be guaranteed for commercialization of alkaline water electrolysis. Platinum group metals are renowned for their exceptional catalytic activity in alkaline water electrolysis. However, their widespread commercial adoption is hindered by the substantial costs involved and their tendency to dissolve during the oxygen evolution reaction (OER). For this reason, catalysts from the hydroxide family, such as NiFe LDH, currently dominate the field of OER catalysis. This paper introduces a novel technique: hydrating metal substrates to significantly enhance OER efficiency. Utilizing a straightforward hydration, the hydroxide layer with a thickness of only a few nanometers can be developed on the Ni surface.The ability to significantly enhance OER performance through the simple hydration of metals suggests a promising strategy for the development of new electrocatalysts.
Analysis of Crystalline and Amorphous Iridium Oxide Catalyst Layers after Accelerated Durability Test
Authors: Ishida Takanobu , Takeda Yuko , Watanabe Yuta , Aoki Naoya
Published: December 2024

PEM water electrolysis has advantages such as high current density operation and quick response to input power.From these advantages, PEM water electrolysis is adequate to the hydrogen mass production system adopted the renewable energy.Iridium oxide shows good oxygen evolution reaction(OER) activity and durability for PEM water electrolysis anode catalyst, but there are material supply and cost issues as it is precious metal.To solve these issues, several studies have been conducted to improve OER activity of Iridium oxide.

Last year, we reported on highly active crystalline iridium oxide catalysts.In this work, we performed accelerated durability tests in single cell on crystalline and amorphous iridium oxide.After the durability test, the CCM was analyzed to investigate degradation factors.The results will be discussed on the day of the meeting.
Electrochemical Ammonia Oxidation Using a Nickel Phosphide Catalyst Incorporating N-Doped Carbon for Efficient Hydrogen Production
Authors: Jo Chanmin , Surendran Subramani , Kim Min-Cheol , Lim Yoongu , Moon Dae Jun , Kim Joon Young , Jeong Gyoung Hwa , Kim Jung Kyu , Sim Uk
Published: December 2024

Reducing carbon emissions is important for sustainable development, and most carbon emissions occur during the production and use of fossil fuel-based energy. In order to reduce carbon emissions, it is essential to discover new energy sources without carbon emissions. There are several candidates, including new and renewable energy, but the most realistic energy is hydrogen energy, and hydrogen is abundant as an energy source, renewable, and environmentally friendly. However, hydrogen has a loss problem during the transportation process, and this needs to be supplemented. To solve this issue, various hydrogen carriers have been studied. Among them, ammonia is considered the closest to commercialization because it has an existing transportation infrastructure and does not contain carbon. In addition, ammonia can be electrochemically hydrogenated, and the theoretical reaction potential for this is 0.07 V vs. RHE, which is significantly lower than water electrolysis (1.23 V vs. RHE). This work uses a one-pot synthesis method to synthesize a catalyst that co-forms nickel phosphide and nitrogen-doped carbon, and investigates its utilization as a bi-functional catalyst for both hydrogen evolution reaction (HER) and AOR. To improve this, developing effective catalysts based on non-precious metal materials is important. Ni, which has excellent nitrogen adsorption and AOR (Ammonia Oxidation Reaction) characteristics, was converted to phosphide and the ammonia oxidation reaction was analyzed. The Ni2P@N-C catalyst exhibited approximately 78% ammonia decomposition compared to the initial concentration, and the amount of hydrogen generated in 30 minutes in the electrolyte containing 0.5 M ammonia was about 2.144 mmol (H2) / mol (NH3) h cm2. The ammonia electrolysis cell constructed for hydrogen production evaluation showed a relatively low energy consumption rate of 8.611 KWh kg (H2).
The Impact of Progressive Buildup of Trapped Gas Bubbles on the Performance of Oxygen Evolution Reaction Electrodes during Alkaline Water Electrolysis
Authors: Hoffmann Jeff Owen , Wang Lan , Yan Yushan
Published: December 2024

Hydroxide exchange membrane electrolyzers (HEMELs) stand to be an effective means of achieving low-cost green hydrogen. However, HEMEL durability remains a substantial barrier to realizing this goal. The United States Department of Energy has set a durability target of a voltage increase of 2 µV/hr1. We have previously demonstrated constant current degradation rates of 1810 and 560 µV/hr with applied current densities of 500 and 200 mA/cm2, respectively, thus illustrating the substantial gap between our current achievable HEMEL durability and our target durability2.

Gaseous products are formed at both electrodes in a HEMEL; by manipulating the wettability of the electrodes, recent studies have shown that the failure of gas bubbles to detach from the electrode surface leads to overpotentials associated with the loss of accessible reaction sites and exacerbated mass transport to those sites that remain accessible3,4. While these studies have demonstrated the impact of gas bubbles on acute water electrolyzer performance, we have found little work to investigate the impact of trapped gas bubbles from a durability perspective.

Here we find that electrode wettability can change throughout the lifetime of a device. We investigate the durability of an FexNiyOOH – nF anode catalyst supported on nickel felt in a three-electrode setup with 1M KOH. We find that at a moderately low current density of 50 mA/cm2 the performance of this catalyst degrades by tens of mV over several hundred hours and that this performance loss is recoverable with the removal of oxygen bubbles adhered to the anode surface at open circuit. Moreover, when we resume the passage of current, the surface layer of oxygen (and associated performance loss) evolves more rapidly – suggesting that the wettability of the anode has decreased throughout the experiment. This is further supported by contact angle measurements of pre- and post-mortem anodes. Finally, we investigate whether the introduction of hydrophilic ion-conducting polymers can mitigate the emergent hydrophobicity of the anode catalyst layer.

Technical Targets for Proton Exchange Membrane Electrolysis, Hydrogen and Fuel Cell Technologies Office. https://www.energy.gov/eere/fuelcells/technical-targets-proton-exchange-membrane-electrolysis.

J. Xiao et al., ACS Catal., 11, 264-270 (2021).

R. Iwata et al., Joule, 5(4), 887-900 (2021).

Z. Kang et al., Electrochimica Acta, 354 (2020).
Performance and Durability of Metallic Aerogel Anode Catalyst in Pure-Water-Fed Hydroxide Exchange Membrane Electrolyzers
Authors: Zeng Yachao , Qi Manman , Yan Yushan
Published: December 2024

Hydrogen holds significance as a versatile energy carrier that can be used in various sectors. Recently, hydroxide exchange membrane electrolyzers (HEMELs) towards clean hydrogen production have gained intensive attention, due to the possibility to use low-cost platinum group metal (PGM)-free electrocatalysts and cheaper membranes, ionomers.1 Although a variety of PGM-free catalysts have shown promising activities towards the alkaline oxygen evolution reaction (OER), few of them delivered sufficient stability in the pure-water-fed HEMELs.2 In this work, metallic aerogel, featured with high porosity and amorphous metal oxide shells, was deployed as platform to study the structural-performance relationship in HEMELs. A poly(aryl piperidinium) membrane and ionomer with high hydroxide conductivity were integrated to study the evolution in the composition and structure of PGM-free anode catalysts.3 Owing to unique properties of the 3D metallic aerogel, the optimal aerogel anode outperformed the Ir-based anode in the KOH-fed HEMELs. A transition in the HEMEL performance with different anode catalyst was observed when shifting from alkaline electrolyte to pure water, implying a steering in the rate limiting steps in the different anode feedings. The limiting factor of pure-water-fed HEMEL was probed by deconvoluting the contributions from ohmic resistance, electrode kinetic, and mass transport. The optimal metallic aerogel anode showed no performance loss during the 580-hour stability test at an industrial electrolyzer-relevant current density of 1 A cm−2 in pure water feeding. The HEMEL performance was monitored, revealing the degradations of critical components in the membrane-electrode-assembly. The structural performance relationship in HEMEL was probed by linking the physical properties of the catalysts with HEMEL performance. The gained insight will shed light on the development of highly efficient PGM-free anode catalysts for viable pure-fed HEMELs.

References

R. Abbasi, B. P. Setzler, S. Lin, J. Wang, Y. Zhao, H. Xu, B. Pivovar, B. Tian, X. Chen, G. Wu and Y. Yan, Advanced Materials, 31, 1805876 (2019).

M. Chatenet, B. G. Pollet, D. R. Dekel, F. Dionigi, J. Deseure, P. Millet, R. D. Braatz, M. Z. Bazant, M. Eikerling, I. Staffell, P. Balcombe, Y. Shao-Horn and H. Schäfer, Chemical Society Reviews, 51, 4583 (2022).

J. Wang, Y. Zhao, B. P. Setzler, S. Rojas-Carbonell, C. Ben Yehuda, A. Amel, M. Page, L. Wang, K. Hu, L. Shi, S. Gottesfeld, B. Xu and Y. Yan, Nature Energy, 4, 392 (2019).
Industrial Scale Anodes and Cathodes for Conventional Alkaline Electrolysis and Anion Exchange Membrane Water Electrolysis
Authors: Abellán Gonzalo , Abellán Gonzalo , Lloret Segura Vicent , Seijas Da Silva Alvaro
Published: December 2024

The merging of conventional Alkaline Electrolysis (AEL) and Proton Exchange Membrane Water Electrolysis (PEMWE) has led to the development of Anion Exchange Membrane Water Electrolysis (AEMWE). At this juncture, both AEL and AEMWE technologies offer an advantage over PEMWE as they do not require critical raw components and/or materials (CRM and PFAS).[1] While AEMWE has demonstrated higher efficiencies than AEL with thin membranes and low concentrations of KOH, AEL technology addresses the significant stability challenge posed by anionic membranes by employing KOH electrolyte in a zero-gap configuration, relying on stable diaphragms. Consequently, AEL technology offers a more cost-effective and scalable solution for current large-scale hydrogen production, while AEMWE remains a promising solution that will most probably be implemented on larger scales in the following decade.

New and scalable synthetic routes for more efficient catalysts and electrodes that lower the overall cell voltage of electrolyzers are required on a large scale to reach the readiness level of alkaline technologies. Matteco’s patented processes stand at the forefront of manufacturing highly active and stable catalysts and electrodes crafted from Layered Double Hydroxides (LDHs), which have gained increasing attention due to their low overpotentials and promising stabilities.[2] Beyond the intrinsic properties of the catalysts, a myriad of factors—electrolyte concentration, substrate type, loading, and the catalyst/substrate interface—play pivotal roles in determining electrolyzer activity and stability, forming a complex multiparameter matrix.

This work presents the electrochemical performance and stability of novel and scalable anode and cathode catalyst coated substrates for both AEL and AMWE technologies.

References:

[1] N. Du, C. Roy, R. Peach, M. Turnbull, S. Thiele and C. Bock, Chemical Reviews, 122, 11830 (2022).

[2] L. Hager, M. Hegelheimer, J. Stonawski, A. T. S. Freiberg, C. Jaramillo-Hernández, G. Abellán, A. Hutzler, T. Böhm, S. Thiele and J. Kerres, Journal of Materials Chemistry A, 11, 22347 (2023).