bluuebunny/crossref_metadata_2025 huggingface dataset:
Immobilization of PCET Materials for Electrochemical pH Swing Driven Carbon Capture
Authors: Bilger David , Ali Fawaz , Patamia Evan Douglas , Payne Camryn , Andrew Trisha L. , Kwabi David G.
Published: August 2024

Proton-coupled electron transfer (PCET) is a promising method in the realm of carbon capture and release mechanisms. Its fundamental capacity lies in electrochemically inducing pH swings within an aqueous solution, leveraging the high solubility of carbonates in highly alkaline water to capture CO2 and subsequently release iton demand when the aqueous solution is acidified. PCET-based methods promise higher energy efficiency for carbon capture compared to other electrochemical carbon capture methods because they feature fast charge transfer kinetics and can decouple gas-liquid contact and electrochemical activation. In theory, they also allow the use of cheap, widely available small-molecule PCET agents. However, in practice, PCET agents have shown a key limitation that has, thus far, hindered their scalability: oxygen-induced chemical degradation with continued electrochemical cycling. In this work we mitigate the prevailing issue of oxygen sensitivity by immobilizing PCET agents onto a fabric substrate. Via reactive vapor deposition (RVD), porous and conductive films composed of PEDOT-Cl and poly-aminoanthroquinone (PAAQ) are deposited on the surface of a wool felt blend fabric. This approach resulted in the development of a cost-effective, metal-free, and efficient electrode for both capture and release of CO2. Through electrochemical evaluation, the performance of PCET-active quinone moieties present on PAAQ was measured. The overall efficiency of electrochemical capture from gaseous CO2 was found to be 197 kJ/molCO2, substantiating the efficacy of this novel electrode. This work highlights the potential of fabric-immobilized PCET agents and presents a promising avenue towards a sustainable, efficient, and economically viable approach to carbon capture and release technologies.
(Invited) Retinomorphic Motion Detector and Supercapacitors Based on Organic Semiconductors
Authors: Ng Tse Nga
Published: August 2024

Organic retinomorphic sensors offer the advantage of in-sensor processing to filter out redundant static background and are well suited for motion detection. To improve this promising structure, here we studied the key role of interfacial energetics in promoting charge accumulation to raise the inherent photoresponse of the light-sensitive capacitor. Specifically, incorporating appropriate interfacial layers around the photoactive layer was crucial to extend the carrier lifetime, as confirmed by intensity-modulated photovoltage spectroscopy. Compared to its photodiode counterpart, the retinomorphic sensor showed better detectivity and response speed due to the additional insulating layer, which reduced the dark current and the resistor-capacitor time constant. Lastly, three retinomorphic sensors were integrated into a line array to demonstrate the detection of movement speed and direction, showing the potential of retinomorphic designs for efficient motion tracking.

In addition to discussing the development of organic optical sensors, this presentation will also show the use of the same class of organic semiconductors in energy storage applications, in particular for redox supercapacitors as portable power sources. We developed multifunctional structures, which combine load-bearing and energy-storage functions in one, resulting in weight savings and safety improvements. We demonstrated a gradient electrolyte design to facilitate high ionic conductivity at the electrode-electrolyte interfaces and transitioned to a composition with high mechanical strength in the bulk for load support. The gradient design enabled the multilayer structural supercapacitors to reach state-of-the-art performance matching the level of mono-functional supercapacitors. Finally, the structural supercapacitor was made into the hull of a model boat to demonstrate its multifunctionality.
(Invited) Minimizing or Maximizing Contact Effects in Organic Electronics
Authors: Kim Chang-Hyun
Published: August 2024

Contact resistance is an umbrella term capturing various current-limiting mechanisms existing at and around metal/semiconductor junctions of an electronic device. Despite its known detrimental impact on the performance of organic, oxide, and 2D semiconductor electronics, a quantitative and predictive description of contact resistance is still lacking. At the same time, recent evidences show that contact resistance can actually provide benefits to certain applications, thus challenging our common belief. This presentation will clarify why contact issues are so critical to the operation of general thin-film systems, and highlight our recent results on re-defining the role of contact resistance in organic diodes and transistors.
(Invited) Scalable 2-Step Fabrication of Core-Shell GaN Micropillars
Authors: Davydov Albert V. , Krylyuk Sergiy , Bonevich John E. , Motayed Abhishek
Published: August 2024

Group III-Nitride three-dimensional structures have gained substantial interest for application in optoelectronic, energy, and sensor devices with non-planar geometries [1-4]. The benefits of 3D structures, such as GaN-based nano-/micro-rods, compared to planar films include large surface area, high structural quality, non-polar-surface utilization, small footprint, mechanical flexibility, and enhanced light absorption/extraction efficiency. To advance the technology of non-planar III-Nitride semiconductors, it is necessary to optimize and scale up the fabrication of such structures with controlled geometries and desired electronic and optical properties. Here, we report the fabrication of wafer-scale periodic arrays of vertically aligned GaN core-shell micropillars using a combination of top-down etch and epitaxial overgrowth.

The two-step process consists of inductively coupled plasma (ICP) etching of lithographically patterned GaN-on-Si substrate to produce an array of micropillars followed by selective growth of GaN shells over these pillars using Hydride Vapor Phase Epitaxy (HVPE). The most significant aspect of the study is the demonstration of the sidewall facet control in the shells, ranging from truncated hexagonal pyramids with the (1-101) semi-polar sidewalls to hexagonal prisms with the (1-100) non-polar sidewalls, by employing a post-ICP wet chemical etch and by tuning the HVPE growth temperature. Optimization of both ICP etching and epitaxial overgrowth reduced dislocation density in the GaN shells, thus enhancing the transport and optical characteristics of these device platforms. Photo- and cathodoluminescence showed a substantial reduction of parasitic yellow luminescence as well as strain-relaxation in the core-shell structures, supported by Raman scattering, electron-backscatter-diffraction (EBSD), and X-ray-diffraction measurements. Transmission electron microscopy revealed improved crystal quality with reduced dislocation density in the epitaxially grown shells. This work demonstrates the feasibility of selective epitaxy on micro/nano-engineered 3D templates for realizing high-quality GaN-on-Si devices such as LEDs and p-i-n photodetectors.

References:

Zhao, Y.; Fu, H.; Wang, G.T.; Nakamura, S. Toward ultimate efficiency: progress and prospects on planar and 3D nanostructured nonpolar and semipolar InGaN light-emitting diodes. Opt. Photonics
2018, 10, 246-308.

Chen, F.; Ji, X.; Lau, S.P. Recent progress in group III-nitride nanostructures: From materials to Applications. Materials Science & Engineering R
2020, 142, No. 100578

Kazanowska, B.A.; Sapkota, K.R.; Lu, P.; Talin, A.A.; Bussmann, E.; Ohta, T.; Gunning, B.P.; Jones, K.S.; Wang, G.T. Fabrication and field emission properties of vertical, tapered GaN nanowires etched via phosphoric acid. Nanotechnology
2022, 33, No. 035301

Pandey, A.; Min, J.; Reddeppa, M.; Malhotra, Y.; Xiao, Y.; Wu, Y.; Sun, K.; Mi, Z. An Ultrahigh Efficiency Excitonic Micro-LED. Nano Letters
2023, 23, 1680-1687
Surface-Immobilized Ionophore Electric-Double-Layer (EDL) Extended-Gate Field-Effect Transistors for High Sensitivity to Detection of Mercury and Lead Ions
Authors: Zeng Guan-Cheng , Huang Hsuan-Wei , Lin Chia Kai , Kalaimani Vishal Mani , Kuo Tzu-Han , Wang Yu-Lin
Published: August 2024

In the field of sensors, particularly in FETs (Field-Effect Transistors), they have emerged as a promising solution for detecting heavy metal ions. These sensors offer high sensitivity, rapid response, compact and portable device sizes, and the potential for low cost. These advantages have led to their successful application in monitoring drinking water, environmental samples, and industrial wastewater, enabling rapid on-site detection of heavy metal ions.

At the molecular level, certain organic molecules or coordination compounds can selectively bind to specific ions through specific chemical reactions or coordination interactions. Therefore, designing ionophores specifically for capturing or transporting particular types of ions is possible. Previous research has employed the mechanism of Ion Selective Membranes (ISM) for detecting heavy metals. However, ISMs are typically polymer coatings applied through spinning, resulting in a thick layer that leads to longer diffusion times, requiring 15 minutes or more to achieve baseline stability, with a detection limit of µM to nM .

Many studies have also utilized aptamers for detecting metal ions, but aptamers are typically expensive and require controlled formation of specific structures to bind with ions. They are susceptible to interference signals from pH value or salt concentrations.

In environmental or food samples, the presence of heavy metals often needs to be detected. Electric-Double-layer (EDL) sensors exhibit better stability, with a monolayer recognition layer providing shorter detection times and higher sensitivity. This study successfully developed FET (Field-Effect Transistor) metal ionophores based on a specially designed ionophore with a double-layer expanded gate, including mercury ionophore sensors and lead ionophore sensors. By defining a gate sensing area with dimensions of 500 μm x 500 μm, significant detection limits of nM to pM were achieved within minutes. The combination of FETs, EDL, and ionophores in this study's development has resulted in highly efficient, sensitive, selective, and portable detection instruments.

Keywords: MOSFET, EDL, Aptamer, Ionophore, Heavy metal

Figure 1
ITO-Coated Vertical Nanowires-Based Biosensors for the Label-Free Detection of Escherichia coli
Authors: Kumar Nitish , Shia Wei -Yau , Lin Shu-Ping
Published: August 2024

A major concern in public health is the direct in-situ detection of pathogenic bacteria in food, beverages, and the air [1]. This study utilizes ITO-coated vertical nanowires (ITO-VNWs) as sensing substrates for the detection of Escherichia coli (E. coli). The innovation in this research lies in the direct detection of various concentrations of E. coli using boronic acid (BA)-modified ITO-VNWs connected to a benchtop E4980A precision LCR meter. Impedance spectra were expressed in terms of real and imaginary parts, corresponding to resistance (R) and reactance (X). Serial dilutions of E. coli were prepared in saline for bacterial enumeration and tested using the standard plate count method. Subsequently, 100 μl of each bacterial dilutions (107, 106, 105, 104, 103, 102, and 101 CFU/ml) were applied to BA-modified ITO-VNWs. In summary, BA-modified ITO-VNWs demonstrated accurate and distinct detection of varying concentrations of E. coli. This accomplishment highlights the promising potential of our BA-modified ITO-VNW biosensor for precise bacterial detection across diverse applications. Further exploration and optimization of this platform could lead to advancements in the rapid and specific identification of pathogenic bacteria, making it an invaluable tool in the realm of public health and environmental safety.

REFERENCES

[1] A. Ahmed, J.V. Rushworth, N.A. Hirst, P.A. Millner, Biosensors for whole-cell bacterial detection, Clin Microbiol Rev 27(3) (2014) 631-46.

Figure 1
Self-Powered Wearable Pressure Sensor System for Smart Healthcare Applications
Authors: Parashar Parag , Tseng Yao-Hsuan , Lin Zong-Hong
Published: August 2024

Wearable sensors mark a groundbreaking advancement in the realm of health monitoring technology. However, traditional wearable devices lack comprehensive solutions for tracking sports exercise behaviors and providing feedback on rehabilitation for those undergoing home-based recovery. To bridge this gap, a self-powered triboelectric nanogenerator (TENG)-based wearable sensing system has been developed with in-house monitoring capabilities. The wearable sensor system is composed of triboelectric pressure sensors with an electro-conductive silicone sheet and patterned Ecoflex film as the contact layers. Highly sensitive TENG sensors have been successfully embedded into a bicycle saddle and human shoe insole for real-time pressure monitoring. Experimental results demonstrate that biomechanical energy, originating from both the pelvic-saddle interactions on bicycle and human gait movements, has been successfully converted into electrical energy. The generated sensor voltage remains stable under frequency variations and external environmental conditions, such as temperature and humidity variations. Utilizing distinctive information contained in individual body mass imbalances and gait characteristics, a smart healthcare monitoring system is envisioned to extract essential biomechanical insights via artificial intelligence, facilitating a pivotal role in in-house monitoring and tracking of sports rehabilitation exercises. The as-designed low-cost, highly scalable self-powered wearable sensor system offers an accessible, user-friendly point-of-care solution for gait detection and rehabilitation monitoring for individuals with various physical impairments, with considerable potential for commercialization.

Figure 1
Solid-State Electrodes Towards a Real-Time Sensor Array for Health Monitoring
Authors: Brothers Michael , Leung Jennifer , Gazica Kiera E. , Chavez Jorge , Kim Steve
Published: August 2024

The healthcare industry has been transformed by advances in biotechnology, resulting in improved health outcomes. Central to this has been advances in medical diagnostics that can both monitor patients as well as provide actionable data at the point-of-care. However, further improvements are needed to maximize the utility of diagnostics at times where acute care may be required, such as when individuals are unstable after experiencing physical trauma. When medical resources are limited, the ability to rapidly and effectively triage patients that have experienced trauma is critical to maximizing health outcomes. Notably, individuals that have experienced significant trauma can degrade quickly. Therefore, continuous monitoring approaches are needed that can provide critical biometric and biomarker information that will enable updating of the triage in real-time.

At present time, patients are assessed continuously using biometric monitoring. However, biometrics are often a lagging indicator to biochemical markers, and thus while easier to measure, less informative. Currently, the ISTAT-8 is a point-of-care unit to perform an automated, rapid biochemical panel that can assess the patient’s ability to maintain homeostasis by monitoring eight biomarkers. However, the ISTAT-8 captures biochemical data only at a point in time instead of continuously; this is a drawback, as the health of patients who have undergone trauma can improve or deteriorate rapidly. Therefore, a continuous biochemical monitoring solution is needed to allow for triage to happen in real-time.

Advances in biotechnology have for the first time made real-time biochemical sensing a reality. Unfortunately, commercial continuous biochemical sensors to-date are limited to subcutaneous continuous glucose monitors (CGMs). CGMs monitor glucose concentrations in the interstitial fluid (ISF), which strongly correlates to blood values. While the CGM is now commonly used, the current devices are not easily multiplexed. Therefore, a scalable, easy to insert system is needed to perform multiplexed measurements; microneedle-based platforms have the promise to enable sensing in the ISF leveraging five or more distinct sensors.

Here we present a solid-state platform that can enable multiplexed sensing leveraging hollow, wicking microneedles in fluidic contact with solid-state electrodes. Our approach leverages optimized sensor formulations and electrode materials fabricated onto a printed circuit board (PCB). The putative sensor array can be produced in a modular fashion leveraging scalable technologies and processes. Notably, this talk focuses on methods and approaches to fabricate an array of solid-state sensors that are capable of detecting ions and metabolites over extended periods (> 1 week) and can be readily integrated with microneedles for sensing interstitial fluid.
Innovative Drug Screening Platform: The Triboelectric Frontier
Authors: Ganguly Anindita , Cheng Yu-Ying , Lin Zong-Hong , Yang Lee-Wei
Published: August 2024

In our ongoing battle against emerging diseases and drug resistance, the quest for new medications is a critical challenge. However, the traditional path to drug discovery is marred by complexities, lengthy timelines, exorbitant costs, and inherent risks. The conventional route to finding new drugs is challenging due to its complicated nature, long timeframes, high expenses, and built-in uncertainties. Typically, it takes a decade or more for a drug to gain clinical approval. Recognizing the need for a more efficient and precise drug development process, researchers are actively engaged in creating innovative drug screening platforms. Our focus is on pioneering a label-free, swift, user-friendly, and cost-effective screening method based on triboelectrification. Triboelectrification, or contact electrification, occurs when two surfaces come into contact, leading to a transfer of charge between them. Recently, a technology with immense potential, known as the triboelectric nanogenerator (TENG), has emerged. TENG can convert mechanical energy into electrical energy and has evolved into a self-powered sensor called a triboelectric nanosensor (TENS), combining TENG with sensing capabilities. This research marks the first-ever drug screening platform leveraging triboelectrification. In this work, the investigation of molecule-molecule interactions using voltage output variation measurement achieves unprecedented selectivity and sensitivity. The study combines computational analysis with molecular docking data, which is then validated experimentally using a highly sensitive solid-liquid triboelectric nanosensor. FKBP-rapamycin is used as a model compound to demonstrate the platform's feasibility due to its high binding affinity. Following that, the research is expanded to investigate drug interactions with the ATG4B model protein. The findings reveal the binding of S130 and Tioconazole to ATG4B, a critical cysteine protease involved in autophagy, while Dexamethasone does not share this affinity. This binding has a specific inhibitory effect on ATG4B activity, disrupting autophagy dynamics and causing cancer cell apoptosis. The findings of this study support the efficacy of a newly developed self-powered drug screening platform based on solid-liquid contact electrification principles. This innovative approach expertly addresses long-standing challenges in traditional drug development methods, providing a more accessible and economically viable alternative, leading to a new era in drug development. The promising results underscore the potential of our highly sensitive drug screening platform.
(Invited) Processing and Evaluation of Microneedle-Based Sensors for Biomedical Sensing
Authors: Narayan Roger
Published: August 2024

The biosensor applications of microneedles made by digital micromirror device-based stereolithography or two photon polymerization will be reviewed in this presentation. Microneedles are small lancet-shaped instruments that can be employed for bodily fluid sampling. In one study, carbon fiber electrodes were placed within the bores of hollow microneedles. The carbon fibers were chemically modified to enable detection of hydrogen peroxide and ascorbic acid; the functionality of the electrode-hollow microneedle devices were demonstrated with electrochemical measurements. In another study, metallized carbon paste transducers were filled within the bores of hollow microneedle arrays. Sensing of hydrogen peroxide and lactate with rhodium-dispersed carbon paste-filled microneedles was shown. Additionally, it was demonstrated that lactate was detected in the presence of physiologically relevant interfering molecules, such as uric acid, acetaminophen, and ascorbic acid. In another study, the enzymes glutamate oxidase and glucose oxidase were enclosed within poly(o-phenylenediamine) thin films; these films were incorporated in structures including hollow microneedles and solid microneedles. Detection of glutamate and glucose with high sensitivity, stability, and selectivity in undiluted human serum was shown. Another study considered the use of a solid-state ion selective electrode for potassium ions, which was prepared using three-dimensional porous carbon. This electrode was integrated with a two-photon polymerization-created hollow microneedle. The functionality of the ion selective electrode was shown over the physiologic range of potassium and in the presence of sodium ions, which served as an interferent. Application-specific and translation-relevant studies for microneedle-based biosensors will be considered.
(Invited) Supramolecular Hydrogels for Fabrications of Wearable Sensors and Medical Scaffolds
Authors: Zhao Yanli
Published: August 2024

While hydrogels have enabled a variety of applications in wearable sensors and electronic skins, they are susceptible to fatigue fracture during their cyclic deformations owing to the inefficient fatigue resistance. Design of hydrogels with excellent mechanical properties and highly stable performance during the practical long-term applications of produced wearable sensors and medical scaffolds remains a tremendous challenge. The supramolecular hydrogels with the topological networks consisting of mechanical interlocked units lead to high toughness and robust fracture resistance. In our studies, a type of polymerizable crosslinker is assembled by the precise host-guest recognition, which is then photocured to construct the conductive hydrogel system. This polymerizable crosslinker having the mobile junctions simultaneously endows the resulting conductive hydrogels with three important features in the applications of strain sensors and scaffolds: (1) high stretchability along with superior fatigue resistance, (2) hydrogels applicable for sensors with high conductivity and sensitivity, and (3) suitability for 3D printing fabrication of sensors with altitude complexity. In addition, we have developed a biological metabolism-inspired hydrogel from the dynamic cross-linked natural polymer for reshaping the hostile rheumatoid arthritis microenvironment. The engineered hydrogel exhibits injectable performance and self-healing ability. When the hydrogel is engineered as a 3D stem cell-laden scaffold, the satisfactory reconstruction of large-scale bone defects in rheumatoid arthritis is achieved with effective antioxidant and anti-inflammatory performance simultaneously.
Next Generation Heterogeneous 3D IC Chip Packaging
Authors: Winata Alvin , Lin Chia Kai , Kalaimani Vishal Mani , Wang Yu-Lin
Published: August 2024

The demand for a faster and more efficient IC has been steadily increasing more than ever to accommodate the trend of Artificial Intelligence, Industry 4.0, Machine Learning, and Big Data. Traditionally, the semiconductor industry has kept up with demand of faster and more efficient IC by shrinking the size of transistor. As we approach a 1 nm transistor the technological challenge will be challenging to overcome as quantum tunneling becomes more pronounced and would decrease the reliability of the chip. To overcome this technological challenge, an advance packaging of 3D IC chip technology has been developed and delivered to market such as CoWoS (Chip-on-Wafer-on-Substrate) and InFO (Integrated Fan-Out). However, the aforementioned technology have their drawbacks with CoWoS uses interposer and TSV (through-silicon substrate via) which make it costly, time consuming, and wastes a lot of energy and InFO is limited in the number of layers it can accommodate for chiplets. Both of those technology are currently limited to 2 or 3 layer of IC and difficult to be modularize. In this study, we aim to develop a heterogeneous 3D IC package that can overcome the aforementioned problem which is modular, cost-effective, able to integrate chip from different manufacturers, and capable to stack more than 3 layers of ICs. This study has successfully completed the first stage of development by employing an advanced package consisting of Epoxy substrate with 200Å Ti/500Å Pt/1000Å Au metal interconnects, previously fabricated as a base for 3D stacking.

Keywords : 3D IC Package, Advance Packaging, Modulable IC Packaging, Heterogeneous Integration

Figure 1
Electrokinetics with Surface-Enhanced Raman Spectroscopy for Bacterial Identification in Wastewater
Authors: Zhang Yirui , Herndon Liam , Padhy Punnag , Ogunlade Baba , Boehm Alexandria , Dionne Jennifer
Published: August 2024

Bacterial presence in wastewater serves as a crucial bioindicator for monitoring population-level infections and offering early disease outbreak warnings [1,2]. However, identifying bacteria in wastewater presents outstanding challenges; notably, current culturing or fluorescence-based methods [3] to identify bacteria are slow and expensive, unsuitable for high-throughput screening of diverse bacterial species, and may not work well in the complex wastewater matrix. Here, we harness the potential of surface chemistry and electrokinetics to introduce an innovative electro-optical approach that has the promise to detect a broad spectrum of pathogenic bacteria in wastewater.

We combine surface-enhanced Raman spectroscopy (SERS) [4] with alternating current electric fields, complemented by machine learning models [5], to enable rapid and amplification-free bacteria detection in filtered wastewater, at cell concentrations as low as 104 cells/mL. First, we synthesize gold nanorods that can electrostatically bind to bacteria surfaces, allowing for SERS from cell surfaces. We collect SERS from bacteria spiked into filtered wastewater, including Staphylococcus aureus, Staphylococcus epidermidis, and Escherichia coli, spanning concentrations from 109 cells/mL to 104 cells/mL. Spectral clustering analysis shows that bacteria signals become more indistinguishable from wastewater as the concentrations decrease. Further, we incorporate electrokinetic effects into SERS by employing gold microelectrodes to apply electric fields, utilizing dielectrophoresis [6] to rapidly displace and concentrate bacteria based on their dielectric responses within minutes. The enrichment of bacteria with nanorods is directly visualized through microscopy, resulting in Raman signal intensities increased by up to tenfold under electrical fields for bacterial concentrations ranging from 106 down to 104 cells/mL. Such enhancement may enable the detection sensitivity to reach environmentally-relevant concentrations. Moreover, employing data science analysis, we identify biologically-relevant “fingerprint” Raman peaks characterizing proteins, nucleic acids, and lipids from bacteria surfaces, allowing for rapid identification of bacteria species in wastewater. This novel method exhibits potential for generalized pathogen detection and molecular recognition in complex liquid samples, such as wastewater, blood, and seawater.

[1] Hellmér, et al. Applied and environmental microbiology. (2014).

[2] Keshaviah, et al. The Lancet Global Health. (2023).

[3] Jahn, et al. Nature Microbiology. (2022).

[4] Tadesse, et al., Nano Lett. (2020).

[5] Ho, et al., Nat. Comm. (2019).

[6] Pethig. John Wiley & Sons (2010).
Probing Mixed Phase Metallic Ni/Amorphous Nickel Phosphide Nanocatalysts during Oxygen Evolution Reaction Using Operando X-Ray Absorption Spectroscopy
Authors: Thompson David , York Sarah Meixin , Hoffman Adam S. , Hong Jiyun , Bare Simon R. , Chen Jingyi
Published: August 2024

Metal phosphide-containing nanomaterials have demonstrated remarkable efficacy as non-precious metal-based catalysts for the alkaline oxygen evolution reaction (OER). While it is widely acknowledged that various OER catalysts undergo structural reconstruction under applied OER potentials, monitoring these changes is challenging because they are often rapid and require instrumentation not typically found in the typical lab setting. In this study, we utilize operando X-ray absorption spectroscopy (XAS) to determine the structural reconstruction of nickel-based metal phosphide catalysts during OER. We have developed the synthesis of nickel-based phosphide nanoparticles with a range of phosphorus incorporation. These nanoparticles are composed of metallic nickel and amorphous nickel phosphide phases as determined by XRD, TEM and XAS. At low levels of P incorporation, from 2% to 15%, the synthesis results in the mixture of metallic nickel and amorphous phosphide phases. At higher levels of phosphorus incorporation, from 20% to 30%, amorphous nickel phosphide is the predominant phase. Electrochemical characterization of this nickel phosphide series for OER revealed that the catalysts with 20% phosphorus incorporation exhibited superior OER activity. The phosphides with lower phosphorus content, such as 2%, had smaller Ni2+/Ni3+ redox peaks which has been shown to suppress the conversion to Ni(OH)2, leading to lowered OER activity. Increased amorphous nickel phosphide phase led to greater activity, suggesting that the active component in the catalyst comes from the amorphous nickel phosphide phase. Meanwhile, higher phosphorus content (20-30%) where the amorphous phosphide is the predominate phase resulted in larger redox peaks, signifying greater conversion to Ni(OH)2. Operando XAS will be applied to investigate these metallic nickel/nickel phosphide nanocatalysts to elucidate their structural reconstruction during OER
Key Role of Oxidising Species for Water Oxidation on Iridium Oxides Revealed By Time-Resolved Optical and X-Ray Spectroscopies
Authors: Liang Caiwu , Rao Reshma R , Svane Katrine Louise , Moss Benjamin , Scott Søren Bertelsen , Ryan Mary P. , Rossmeisl Jan , Durrant James , Stephens Ifan
Published: August 2024

Iridium oxide is the state-of-the-art electrocatalyst for water oxidation in polymer electrolyte membrane (PEM) electrolysers, crucial for green hydrogen production. Despite its extensive industrial use, the water oxidation mechanism on this metal oxide and the key factors controlling the reaction rate remain unclear. Understanding these controls at a fundamental level on such benchmark metal oxides is vital for designing more active and stable electrocatalysts for water oxidation in PEM electrolysers.

In this talk, I will present our research on probing oxygen evolution reaction (OER) relevant species on iridium-based catalysts. This involves a combination of time-resolved operando optical spectroscopy, soft and hard X-ray absorption spectroscopy (XAS), and electrochemical mass spectrometry. Initially, I will discuss the intermediate and catalytically active states of iridium oxides. This is based on correlating optically detected states with oxygen molecular products identified through on-chip electrochemical mass spectrometry. Subsequently, I will demonstrate how we used optical spectroscopy to quantify these states as a function of potential. The nature of these states, including the Ir oxidation state and surface adsorbates on iridium sites, will be elucidated using a combination of time-resolved Ir-L edge XAS, O-K edge XAS, and supported by Density Functional Theory (DFT).

With these quantification results of active species for OER, I will compare the intrinsic kinetics of two state-of-the-art iridium oxide structures - amorphous IrOx versus crystalline rutile IrO2.[1] The effect of the electrolyte on the intrinsic activity of iridium oxides will also be discussed.[2]

Finally, based on this molecular-level understanding, I will present a modified volcano model for OER catalyst design. This model considers the impact of adsorbate-adsorbate interactions on binding energetics, demonstrating critical design principles for high intrinsic activity OER catalysts.

The authors acknowledge the funding support from the Imperial College-Chinese Scholarship Council Studentship and bp-ICAM 92, which made this research possible.

[1] Caiwu Liang, Reshma Rao, Karine Svane et al. Unravelling the effects of active site densities and energetics on the water oxidation activity of iridium oxides, 07 March 2023, PREPRINT (Version 1) available at Research Square [https://doi.org/10.21203/rs.3.rs-2605628/v1]

[2] Caiwu Liang, Yu Katayama, Yemin Tao, Asuka Morinaga, Benjamin Moss, Verónica Celorrio, et al. Role of electrolyte pH on water oxidation for iridium oxides. ChemRxiv. Cambridge: Cambridge Open Engage; 2023
Automated Microstructural Analysis of Anodic Catalyst Layers in Proton Exchange Membrane Water Electrolyzers (PEMWEs) Using Python-Based Image Processing Framework
Authors: Batool Mariah , Ahmadi Maryam , Sanumi Oluwafemi Joseph , Larose Ravel , Horstmann Jeronimo , Klose Selina , Franzetti Irene , Yang J.V. , Yilmaz Abdurrahman , Parrish Chance , Rice Robin , Iyer Radhika , Foster Jayson , Pylypenko Svitlana , Xu Hui , Mauger Scott A , Smolinka Tom , Groos Ulf , Zamel Nada , Jankovic Jasna
Published: August 2024

Adverse climatic conditions caused by greenhouse gas (GHG) emissions from non-renewables have led to increased focus on utilization of clean alternative fuels such as hydrogen (H2). Clean H2 can be obtained via electrochemical reaction of water splitting through proton exchange membrane water electrolyzers (PEMWEs). However, challenges to its widespread commercialization lie with the high H2 production cost, a large portion of which comes from use of expensive anodic catalyst materials. To improve anodic catalyst utilization to attain better performance at reduced cost, a thorough understanding of anodic catalyst layer microstructure is needed. In-depth characterization through scanning transmission electron microscopy with energy dispersive spectroscopy (STEM/EDS) can provide a comprehensive dataset, which can be processed further to extract structural parameters and correlate to electrochemical performance. However, extracting relevant information from these datasets can be very challenging and time-consuming.

In this study, an automatic python-based image processing framework is implemented to quantify compositional and microstructural parameters for different IrO2 based catalyst inks and their corresponding catalyst layers. The code can provide areal density of catalyst materials, pore/agglomerate size distribution, connectivity of phases, coverage of catalyst particles by ionomer, and its content percentage and distribution. Quantified parameters are then correlated with the electrochemical performance of the PEMWEs. The results provide adequate pointers to not only help capturing microstructural details of catalyst layers but also provide a basis to predict electrochemical behavior and performance of the inks and catalyst layers being studied.
(Invited) Dynamic Modeling of Liquid Alkaline Water Electrolyzers: From Laboratory Cells to Industrial-Sized Stacks
Authors: Turek Thomas , Becker Maik , Kirstein Fabian , Gäde Felix , Brauns Jörn , Lüke Lukas
Published: August 2024

The transition of the energy system towards renewable energies creates an enormous demand for green hydrogen produced by water electrolysis [1]. Among the available processes, alkaline water electrolysis (AEL) is already well-developed and cost-effective, as it does not require expensive or critical membrane and electrode materials [2]. If the liquid alkaline electrolyte is maintained at sufficient reaction temperature (60-90 °C), efficient operation of AEL systems is possible with rapid response to fluctuating renewable power supply [3]. However, a critical phenomenon for all low-temperature water electrolysis technologies is the increased gas impurity – especially for hydrogen in oxygen – during part-load operation [4]. This decreases the process efficiency and is safety-relevant as electrolysis systems must shut down when exceeding 50% of the lower explosive limit. These impurities become dominant at low current density since gas production decreases while the contamination mechanisms (diffusion through the separator and convective transport through electrolyte cycles mixing) are almost load-independent. We have developed a comprehensive dynamic model to properly describe the performance of an AEL system, including cell voltage, electrolyte temperature, electrolyte concentration, and gas purity [5]. With this model, it is possible to describe the dynamic operation of a laboratory AEL system with high accuracy. However, if this model is employed for an industry-sized shortstack with more than 1 m2 cell size, predictions and experimental results are in lesser agreement. This is most probably because the present model assumption of perfectly mixed half-cells no longer holds in large cells with a pronounced dependency of the gas fraction over the cell height. Thus, an improved model including this height dependence must be developed.

[1] M. Wappler, D. Unguder, X. Lu, H. Ohlmeyer, H. Teschke, W. Lueke, Int. J. Hydrogen Energ. 47 (2022) 33551

[2] J. Brauns, T. Turek, Processes 8 (2020) 248

[3] J. Brauns, T. Turek, Electrochim. Acta 404 (2022) 139715

[4] P. Trinke, P. Haug, J. Brauns, B. Bensmann, R. Hanke-Rauschenbach, T. Turek, J. Electrochem. Soc. 165 (2018) F502

[5] J. Brauns, T. Turek, J. Electrochem. Soc. 170 (2023) 064510
Distribution of Relaxation Times Analysis of PEMFC through Loewner Framework: A Direct and Regularization Free Approach
Authors: Patel Bansidhar , Sorrentino Antonio , Gosea Ion Victor , Vidakovic-Koch Tanja , Antoulas Athanasios C.
Published: August 2024

The analysis and interpretation of electrochemical impedance spectroscopy (EIS) data are often complex and challenging, despite its popularity within the field of electrochemistry. Hence, recently, we have introduced novel data-driven approach for extracting the distribution of relaxation times (DRT) from impedance data in order to improve further analysis [1, 2]. This approach is based on the Loewner framework, which is a versatile and straightforward data-driven modeling method that computes reduced-order models in a state-space representation directly from frequency response data. Thus, it allows estimation of DRT without need of regularization procedures or iterative optimization algorithms.

The effectiveness of this approach is successfully demonstrated by analysing the experimental EIS data of a polymer electrolyte membrane fuel cell (PEMFC). The results show that this method allows clear identification of the individual polarization processes based on their characteristic time constants (see Figure). Furthermore, the peaks observed in the DRT plot are correctly associated with different processes by examining spectra under various operating conditions. This is further validated by employing a physics-based model [3]. In this way, unambiguous fault identification and monitoring of the degradation state of the cell is possible and it can be the foundation for an on-board diagnostic tool.

References

[1] B. Patel, "Application of Loewner framework for data-driven modeling and diagnosis of polymer electrolyte membrane fuel cells," Master Thesis, Otto-von-Guericke-Universität Magdeburg, 2021.

[2] A. Sorrentino, B. Patel, I. V. Gosea, A. C. Antoulas, and T. Vidaković-Koch, "Determination of the distribution of relaxation times through Loewner framework: A direct and versatile approach," Journal of Power Sources, vol. 585, p. 233575, 2023/11/30/ 2023.

[3] A. Sorrentino, T. Vidakovic-Koch, R. Hanke-Rauschenbach, and K. Sundmacher, "Concentration-alternating frequency response: A new method for studying polymer electrolyte membrane fuel cell dynamics," Electrochimica Acta, vol. 243, pp. 53-64, 2017/07/20/ 2017.

Figure 1
Aspects of Reduced Performance of Proton-Exchange-Membrane Water Electrolysis Via Continuum Modeling
Authors: Dizon Arthur , Padgett Elliot , Adesso Anthony , Gawas Ramchandra , Goyal Priyamvada , Kushner Douglas I. , Wrubel Jacob A , Peng Xiong , Alia Shaun M , Mukundan Rangachary , Pivovar Bryan S. , Weber Adam Z.
Published: August 2024

Proton-exchange-membrane water electrolysis (PEMWE) is a technology, where hydrogen is electrochemically produced from water. Efficient industrial-scale production of hydrogen via PEMWE is contingent upon developing systems that are sufficiently resilient to operate under non-ideal operating conditions. Mathematical models can provide insight into the underlying physical mechanisms and inform the development of mitigating strategies. In the current work, a cell-level non-isothermal continuum model that is based on concentrated-solution theory that accounts for multiple ionic mobile species in the membrane and ionomer, energy transport, and fluid flow through porous media, was used to investigate two challenges to PEMWE becoming a viable technology, specifically contamination and hydrogen crossover. In cationic contamination, dissolved salts in the reactant water supplant protons in the membrane and ionomer and significantly increase the applied potentials required for operation. Hydrogen crossover is a concern especially in low-current operational modes, which can arise due to PEMWE powered by variable and cyclical renewable energy sources and can result in the production of combustible gas mixtures.

For cation-contaminated cells, simulation results suggest that the uptake of the contaminant cation increased as a function of current density until local conditions in the cathode catalyst layer (cCL) allowed the contaminant desorption to occur. The model suggests that the increased cell potential is primarily due to proton activity losses in the hydrogen evolution reaction within the cCL and that ionic conductivity losses are insufficient to cause the performance losses observed experimentally. Agreement with experimental data lends the model as a possible method or predictive models for PEMWE cell recovery methods. Observations of hydrogen crossover simulations suggest several aspects of hydrogen crossover, which include that localized pressures within the catalyst layers can enhance crossover, bubble-nucleation kinetics limit the exhaust of product gases, and convective fluxes due to electroomostic drag are negligible. An improved understanding of the crossover mechanisms can inform the development of low-crossover designs and mitigation strategies.

Figure 1
(Invited) Targeted Research to Develop Next Generation PEM Water Electrolyzers
Authors: Bender Guido , Duarte Ricardo Filipe Paz Moldes , Liu Chang , Ware Sam , Young James L. , Cullen David A. , Arregui-Mena David , Zenyuk Iryna , Lang Jack Todd , Engtrakul Chaiwat , Alia Shaun M , Badgett Alex , Pivovar Bryan S. , Padgett Elliot , Wrubel Jacob A
Published: August 2024

The utilization of low-carbon intensity hydrogen as an energy carrier promises a path to the decarbonization of sectors including electricity, heavy-duty transportation, and industry at scale. The United States Department of Energy is investing into this opportunity by heavily supporting research and development efforts for hydrogen production at scale. In recent years, the DOE has established the H2NEW consortium which consists of nine national labs and additional partners to focus on the advancement of water electrolysis. It also launched the Hydrogen Energy Earthshot in 2021, targeting the reduction of clean hydrogen production cost by 80% from $5 to $1 per 1 kg H2 produced in 1 decade. For these efforts to be successful, techno-economic analyses are used to identify the research and development areas with the greatest impact, supporting targeted studies on scalable manufacturing and materials that lower capital costs, produce hydrogen efficiently, and enable durable operation over the system lifetime.

In this presentation the challenges and trade-offs of electrolyzer operation for renewable hydrogen generation will be reviewed, and results from targeted NREL studies on components, materials and interfaces will be discussed in detail, including for example PTL morphology, PTL coatings, and PTL/catalyst layer interactions and their effect on operation with thin membrane materials, hydrogen crossover and voltage loss contributions. The presentation also touches on any advanced in-situ diagnostic development that was required for the studies, such as high pressure operation, hydrogen crossover quantification, high throughput testing, and spatial diagnostics.
(Invited) Integrated Approach of Modeling, X-Ray and Electrochemical Characterization to Understand Low Iridium Loading Catalyst Layers Integration and Durability
Authors: Zenyuk Iryna
Published: August 2024

Proton exchange membrane water electrolyzers (PEMWEs) will share more than 40 % of green hydrogen production market by 2050. Currently, iridium catalyst in the anode catalyst layers amounts to 1 mg/cm2. To enable low-loading (0.4 mg/cm2) or ultra-low loading (<0.1 mg/cm2) designs we need to better understand both integration of catalysts into catalyst layer and their durability. At low loadings catalyst layer in-plane electric conductivity can be compromised, requiring either supported catalyst layers or the need for microporous layer (MPL) design. For durability study it is necessary to understand the pathway of surface of IrOx transformation during accelerated stress tests (ASTs) and identify optimal beginning of life (BOL) structure for long-duration deployment. In this work we evaluate the structure and performance of amorphous and crystalline IrOx catalysts at the BOL and EOL to build structure-to-property relations. Rheology studies are conducted to identify the optimal ink recipe for each of the catalysts for blade coating deposition method. We use operando x-ray diffraction technique to evaluate catalyst structure evolution during AST cycling. X-ray computed tomography (CT) was used to evaluate catalyst layer – MPL interfaces under various operando conditions. The morphological information was integrated into the two-dimensional model to better understand interfaces for the low-loading PEMWEs.
Revolution of Electrode Design Toward Oxygen Evolution Reaction for Anion Exchange Membrane Water Electrolysis
Authors: Lyu Xiang , Serov Alexey
Published: August 2024

Anion exchange membrane water electrolyzer (AEMWE) is a promising next-generation technology for producing green hydrogen coupling with cost-effective, platinum group metal-free (PGM-free) catalysts. In AEMWE, oxygen evolution reaction (OER) at the anode plays a more vital role compared with the cathodic reaction of hydrogen evolution reaction (HER). While tremendous attention has been devoted to enhancing the activity of OER catalysts, the long-term stability and cost of OER catalysts, which may play an even more important role in large-scale electrolysis industrialization, have been much less emphasized. Herein, we designed electrodes toward OER from cheap and abundant stainless-steel (SS) foam via a green approach, and the obtained electrode shows excellent activity and stability under an alkaline medium. This work can address all three bottlenecks of activity, stability, and cost, thereby revolutionizing the electrode design for AEMWE.