High Current Performance Research Articles

Flooding Control by Electrochemically Reduced Graphene Oxide Additives in Silver Catalyst Layers for CO2 Electrolysis.

Electrolyte flooding in porous catalyst layers on gas diffusion electrodes (GDE) limits the stability and high-current performance of CO2 and CO electrolyzers. Here, we demonstrate the in situ electroreduction of graphene oxide (GO) to reduced graphene oxide (r-GO) within a silver catalyst layer on a carbon GDE. The r-GO introduces hydrophobicity regions in the catalyst layer that help mitigate electrolyte flooding during high current density CO2 electrolysis to CO. The flooding-resistant r-GO/Ag-coated GDE achieves a sustained Faradaic efficiency of CO at 94% for more than 8 h, compared to a rapid drop from 95% to 66% in an Ag-coated GDE without r-GO at 100 mA·cm-2. We found that GO enhances the electrochemically active surface area of the catalyst layer during CO2 electrolysis tests because the incorporation of GO increases the roughness of the catalyst layer. The in situ method of electrochemically reducing GO to r-GO provides a low-cost, practical approach that can be applied during standard spray-deposition procedures to develop flooding-resistant GDEs.

Winners and losers in U.S. marine aquaculture under climate change

Abstract Mariculture will be important to meeting global seafood food demand in the coming decades. Yet, the threat of climate change—such as rising ocean temperatures—on mariculture performance remains uncertain. This is particularly true at small spatial scales relevant to most producers. Additionally, mariculture is often limited by regulations that impose restrictions on production, creating potential hurdles for anticipating and adapting to climate change. We focus on mariculture performance in the United States (U.S.), where state and federal policies and exposure to climate change vary substantially and likely interact. We map a current and future mariculture performance index by combining the first high resolution downscaled (0.083°) climate outputs for U.S. waters, species-specific physiological requirements, and policy restrictions. We find high current performance that will increase under warming oceans, with spatial variation that will amplify existing regional differences. Generally, performance will increase in the north and decrease in the south. While the permitting process is not intentionally climate-forward, permitted species outperformed taxon averages, yet state policies often limit production of seaweeds and finfishes, which perform well. Thus, we sit at a critical juncture where the U.S. could capitalize on its seemingly favorable environmental conditions through re-alignment of regulations to support portfolio diversification to include climate-resilient species.

Composite Anode for PEM Water Electrolyzers: Lowering Iridium Loadings and Reducing Material Costs with a Conductive Additive.

To enable the greater installed capacity of proton exchange membrane water electrolysis (PEMWE) for clean hydrogen production, associated costs must be lowered while achieving high current density performance and durability. Scarce and expensive iridium (Ir) required for the oxygen evolution reaction (OER) is a large contributor to the overall cost, yet high loadings of Ir (1-2 mgIr cm-2) are currently needed in commercial systems to maintain sufficient activity, conductivity, and durability. To meet the aggressive targets for low Ir loadings, we introduce a composite anode approach using a conductive additive that is less expensive than Ir to facilitate robust, high-performance operation with low Ir loading by retaining electrode thickness and in-plane electrical conductivity. In this demonstration, we use platinum (Pt) black as the conductive additive given its high electrical conductivity, acid stability, and current price one-fifth that of Ir. Using a high-activity commercial Ir oxide (IrO x ) catalyst, we present a 95% Ir loading reduction and 80% cost reduction of the anode catalyst materials while maintaining equal current density performance at a cell voltage of 1.8 V. Furthermore, we show enhanced stability of a composite anode compared to an IrO x anode with loadings of 0.10 mgIr cm-2 via accelerated stress test (AST) and postmortem imaging. With this approach, we show promising results toward lowering Ir loadings and material costs, addressing a significant barrier to the widespread adoption of PEMWE for clean hydrogen production.

Steam Gasification of PEMFC Catalysts: An Endothermal Process to Create Accessible Carbon Support Morphologies

Platinum catalysts supported on porous carbons are considered state-of-the-art for proton-exchange membrane fuel cells (PEMFCs) due to their ability to protect Pt nanoparticles within the internal pores of the primary carbon particles. This shielding enables high oxygen reduction reaction (ORR) activity by separating the Pt particles from ionomer contact and endows them with greater resilience against voltage cycling-induced degradation. However, the pore enclosure impedes oxygen diffusion to internal platinum particles at high current densities, incurring significant voltage losses particularly at low cathode loadings (∼0.07 mgPt cm−2). Such transport bottlenecks can be mitigated by localized oxidation, a thermal post-treatment enabling Pt particles to etch open the surrounding pore space via Pt-catalyzed carbon oxidation. The strong exothermicity of this reaction, however, is challenging for process scale-up. We explore Pt-catalyzed steam gasification of Pt/Ketjenblack as an endothermal, but otherwise functionally similar post-treatment to increase catalyst accessibility. Connecting physico- and electrochemical characterizations of steam-gasified catalysts, we identify the generation of mesopore volume to be crucial for high current density performance and efficient oxygen transport. Ultimately, locally oxidized and steam-gasified catalysts reveal subtle differences in their respective etching mechanisms, resulting in marginally less efficient pore opening, but also better ORR activity retention for steam gasification.

Nano-enhanced phase change materials for temperature regulation of a LiFePO4 lithium-ion pouch cell using CFD simulation

The temperature control of Lithium-ion (Li-ion) cells plays a crucial role in enabling high current discharge performance. To address this, the present study explores the use of RT35 phase change material (PCM) and single-walled carbon nanotubes (SWCNT) as an additive approach to regulate the temperature of LiFePO4 Li-ion cells. By employing computational fluid dynamics (CFD), incorporating buoyancy force and a turbulent approach, an unsteady problem was simulated to investigate the effects of key parameters such as SWCNT concentration and PCM thickness. Notably, SWCNT addition exhibits a double effect, reducing liquid PCM volume and modifying temperature profiles. The average melting fraction at SOC = 100 % decreased from 100 % to 88 % with increasing PCM thickness from 9δ to 17δ, while it reduced the battery temperature by 3394 K to 331 K. Additionally, the impact of SWCNT volume fraction is most pronounced at 0.02, with similar effects observed at 0.04 and 0.06.

(Invited) The Impact ofin-Situ Activation of a C-Coated Catalyst on the Performance and Durability in Proton-Exchange Membrane Fuel Cells

Zero-emission electricity production for stationary or mobile applications can be realized by PEM fuel cells (PEMFCs), making it an important constituent for a renewable energy transition. Especially relevant in heavy-duty applications, a high power output at low current densities (related to a high mass activity, MA) under dry conditions is necessary to meet the efficiency targets.[1] In general, mass activity of a Pt/C catalyst can be negatively affected by ionomer poisoning, which describes the adsorption of ionomer endgroups onto the active Pt surface. This effect is especially pronounced for platinum supported on so-called solid carbon supports (e.g., Vulcan – Pt/V)[2] and by operating a fuel cell at low relative humidity (RH).[3] In order to minimize performance losses due to ionomer poisoning, concepts exist to shield the Pt particle from the ionomer, e.g., by alkanethiol masking[4] or by Pt-overlayers of porous SiO2 [5] and carbon derived from dopamine coatings.[6] In the latter case, the authors observed that it was possible to decrease ionomer poisoning and increase MEA performance under dry conditions. However, the transport of reactants to the Pt active sites is hindered by the carbon-overlayer, resulting in inferior high current density (HCD) performance.In this work, we developed multiple in-situ activation strategies for a carbon-coated Pt/V cathode catalyst, synthesized following an adapted protocol from Yamada et al.[6] Our results show that apart from a significantly improved MA, high current density performance is retained for an activated carbon-coated Pt/V (C-Pt/Vactivated, solid orange symbols in Figure 1). Compared to the Pt/V baseline catalyst (blue symbols), the MA can be increased by a factor of ~2 (C-Pt/Vactivated with im 0.9V = 248±9 A gPt -1 and Pt/V with im 0.9V = 110±13 A gPt -1) while simultaneously maintaining comparable high current density performance at 90% RH. However, as we will show, the beneficial effect of the activated carbon-coated Pt/V is particularly pronounced at operation under dry conditions, where C-Pt/Vactivated outperformed the Pt/V baseline over the entire current density range (e.g., by 80 mV at 1.7 A cm-2).Furthermore, possible limitations in terms of durability of the C-overlayer used in this work will be discussed. Figure 1: Differential-flow H2/Air performance at 80 °C/90% RH and 145 kPaabs for different cathode catalysts: baseline catalyst (Pt/V), C-coated Pt/V catalyst before activation (C-Pt/Vb efore activation), and activated C-coated Pt/V catalyst (C-Pt/Va ctivated). In the 5 cm2 active area single-cell, the catalyst loadings were 0.25 mgPt cm-2 and 0.05 mgPt cm-2 on cathode and anode, respectively; a 15 µm reinforced low-EW PFSA membrane was used.

Scalable Synthesis of Bulk TiO2 Hybrids and Its Li-Storage Properties in “Rocking-Chair” Type Full-Cell Assembly with LiNi0.5Mn1.5O4 Cathode

TiO2 as an anode material in lithium-ion batteries (LIB) has abolished hurdles like irreversibility, cycling stability, rate capability, and energy density, which are vital for electrochemical performance. Conventionally, time-consuming and complex techniques like solvothermal methods are employed to synthesize TiO2. We herein open a new avenue towards a simple, scalable, and eco-friendly synthesis of bulk TiO2 anatase/bronze hybrids from sodium meta-titanate through a facile mechano-chemical and ion-exchange process under different temperature conditions (400, 450, and 500 °C). Structural and morphological features are analyzed through various characterization techniques such as XRD, FE-SEM, HR-TEM, and XPS. The bronze phase’s high reversibility, low redox potential, high current rate performance, and high power capability of the anatase phase make the hybrid attractive for fabricating high power and high energy density Li-ion power packs. The Li insertion/extraction properties are studied in half-cell assembly (Li/TiO2), where all three TiO2 hybrids exhibited promising results with an initial discharge capacity >165 mAh g-1 at a current rate of 0.05 A g-1 along with a capacity retention >90% after 100 cycles. A “rocking-chair” type full-cell configuration with high voltage LiNi0.5Mn1.5O4 cathode is fabricated, in which LNMO/TiO2-400 °C displayed a discharge capacity of ~88 mAh g-1 at a current rate of 0.05 A g-1. Moreover, the full cell exhibited a capacity retention of >70% after 100 cycles with a maximum energy density of 192.75 Wh kg-1. Figure 1

Interlayer-spacing regulation of NiFe LDH nanosheets cathode with high rate performance for chloride ion battery

Chloride ion batteries (CIBs) possess the multiple advantages of high theoretical volumetric energy density, abundant precursor resources and high safety due to the dendrit-free characteristic, which provide more choices and opportunities for electrochemical energy storage. In this work, NiFe LDH nanosheets with different interlayer spacing are prepared using a simple co-precipitation method with the interlayer spacing of LDH nanosheets extended from 7.695 Å to 24.114 Å. Expanding interlayer space of LDHs nanoplates helps to the promote ion diffusion and enhance their action kinetics. Additionally, the increased oleophobicity between NiFe LDH nanosheets cathode with increased interlayer spacing and solvent PC is beneficial for the structural stability of the materials during cycling. Compared with typical chloride ion-intercalated NiFe LDH nanosheets, the NiFe-C17H25O3 LDH with the maximum interlayer spacing demonstrates a performance improvement of about 213 % (with a discharge specific capacity of 64.2 mAh/g after 200 cycles) at high current density and good rate performance. This work provides a simple and effective interlayer spacing control strategy for the design of CIBs cathodes under high current density.

Trading Off Initial PEM Fuel Cell Performance versus Voltage Cycling Durability for Different Carbon Support Morphologies

Tailored design of carbon supports and their pore morphologies is crucial to achieve the ambitious durability and performance targets for future proton exchange membrane fuel cells (PEMFCs). We compared platinum catalysts supported on solid Vulcan carbon, porous Ketjenblack carbon, and accessible porous modified Ketjenblack carbon in a voltage cycling-based accelerated stress test (AST) with frequent intermittent characterizations. We derived how catalyst morphologies affect cell performance and electrochemical properties (electrode roughness factor, ORR activity, oxygen transport resistances) at beginning-of-life (BoL) and in various states of degradation up to 200,000 voltage cycles. We confirmed the enhanced Pt surface area retention of porous carbon-supported catalysts, ascribed to well-shielded Pt particles in internal pores, but find that this comes at the expense of lower initial high current density performance already at BoL. Accessible porous carbon-supported catalysts with wider pores mostly retain those durability benefits while, simultaneously, maximizing H2/air performance at all current densities due to improved oxygen transport. We also tracked changes in catalyst accessibility throughout voltage cycling by analyzing local oxygen transport resistances and relative humidity-dependent platinum utilization. We propose that catalysts with porous carbon supports undergo oxidative pore opening, followed by continuous migration of internal Pt particles to the external carbon surface.

CMP characteristics of IGZO thin film with a variety of process parameters

Recently, amorphous indium gallium zinc oxide (a-IGZO) has been studied in the field of 3D transistors as a channel material for high mobility, good uniformity, and low leakage current performance. The CMP process needs to be applied to fully remove surface IGZO in a multilayer film stack structure and achieve the purpose of planarization. As we all know, the CMP characteristics of the desired removal rate with stability and within-wafer non-uniformity (WIWNU%) play an important role in the CMP process. In this paper, the variation of the removal rate and the non-uniformity for IGZO thin film were studied with various process parameters (such as polishing time, slurry flow rate, slurry dilution, head pressure, head and table speed). The results mean that the removal rate and the non-uniformity of IGZO thin film can be tuned by changing process parameters, which can enhance the confidence about the feasibility of IGZO-CMP in the application of advanced technology.

Influence of pre-overpressure heat treatment on micro-structure and related properties of Bi-2212 round wire

The Bi2Sr2CaCu2O8+x (Bi-2212) material, a high-temperature superconductor, holds significant promise for future high-field applications because of its multifilamentary, twistable production capabilities, coupled with a high upper critical field. Bi-2212 round wire (RW) is made by the powder-in-tube (PIT) technique, and Bi-2212 coils are usually being developed using the wind-and-react method and a high temperature and over-pressure (OP) heat treatment (50 atm, 890℃) is then required to achieve the high current performance. However, over-pressure (OP) heat treatment can lead to a reduction in wire diameter, compromising the stability of the coil structure. Addressing this issue, the pre-overpressure (pre-OP) heat treatment is used and proves effective in mitigating the reduction in Bi-2212 wire diameter. In this paper, to comprehensively investigate the impact of pre-OP heat treatment on the microstructure of Bi-2212 wire, a metallographic analysis of two kinds of Bi-2212 wires was carried out by the scanning electron microscope (SEM) and the ImageJ software. It was found that larger-area filaments experienced a greater reduction in area after pre-OP heat treatment, that pre-OP heat treatment increases the aspect ratio of filaments, and polygonal bundle structure helps maintain filament structure stability during pre-OP heat treatment. Additionally, the impact of pre-OP heat treatment on the performance of Bi-2212 wires was analyzed through critical current testing under high fields.

DNA‐rGO Aerogel Bioanodes with Microcompartmentalization for High‐Performance Bioelectrochemical Systems

AbstractBioelectrochemical systems (BES) have garnered significant attention for their applications in renewable energy, microbial fuel cells, biocatalysis, and bioelectronics. In BES, bioelectrodes are used to facilitate extracellular electron transfer among microbial biocatalysts. This study is focused on enhancing the efficiency of these processes through microcompartmentalization, a technique that strategically organizes and segregates microorganisms within the electrode, thereby bolstering BES output efficiency. The study introduces a deoxyribonucleic acid (DNA)‐based reduced graphene oxide (rGO) aerogel engineered as a bioanode to facilitate microorganism compartmentalization while providing an expanded biocompatible surface with continuous conductivity. The DNA‐rGO aerogel is synthesized through the self‐assembly of graphene oxide and DNA, with thermal reduction imparting lightweight structural stability and conductivity to the material. The DNA component serves as a hydrophilic framework, enabling precise regulation of compartment size and biofunctionalization of the rGO surface. To evaluate the performance of this aerogel bioanode, measurements of current generation are conducted using Shewanella oneidensis MR‐1 bacteria as a model biocatalyst. The bioanode exhibits a current density reaching up to 1.5 A·m⁻2, surpassing the capabilities of many existing bioanodes. With its abundant microcompartments, the DNA‐rGO demonstrates high current generation performance, representing a sustainable approach for energy harvesting without reliance on metals, polymers, or heterostructures.

Reconfiguration of metal-organic frameworks to form ultrafine Bi dots as an excellent high-current performance of lithium-ion battery anode

The investigation of Bi-based metal-organic frameworks (Bi-MOFs) as anode materials has garnered significant attention because of their higher lithium storage capacity. Nevertheless, they are prone to structural collapse when undergoing the process of charging and discharging, resulting in irreversible capacity degradation. In this study, we develop novel Bi-MOF and reduced graphene oxide (RGO) composites named Bi-MOF@RGO-x, where “x” represents the amount of RGO incorporated during the synthesis process. As expected, when used as an anode for LIBs, the Bi-MOF@RGO-15 electrode exhibited an excellent capacity of 400 mAh·g−1 and ultra-long cycling stability of more than 3500 cycles at the current density of 10 A·g−1 (the specific capacity is the same as the second cycle). An interesting Bi-MOF@RGO reconfiguration phenomenon could be observed in that amorphous carbon layers and ultra-small bismuth dots could be obtained after repeated charging/discharging. Meanwhile, the amorphous carbon layers could uniformly wrap around the in-situ deposited bismuth dots to act as a buffer against volume fluctuations during bismuth lithiation and delithiation. The in-situ deposited bismuth dots had a shorter Li+ transport path, facilitating faster Li+ transport to obtain an excellent rate performance. This reconfiguration did not cause the degradation of battery performance, but on the contrary, was an important reason for obtaining high-performance MOF anodes. This study demonstrates that the reconfiguration of Bi-MOF is a favorable anodic conversion process, providing different insights into studying anodes for MOFs.

Unlocking High-Current Performance in Silicon Anode: Synergistic Phosphorus Doping and Nitrogen-Doped Carbon Encapsulation to Enhance Lithium Diffusivity.

The silicon (Si) offers enormous theoretical capacity as a lithium-ion battery (LIB) anode. However, the low charge mobility in Si particles hinders its application for high current loading. In this study, ball-milled phosphorus-doped Si nanoparticles encapsulated with nitrogen-doped carbon (P-Si@N-C) are employed as an anode for LIBs. P-doped Si nanoparticles are first obtained via ball-milling and calcination of Si with phosphoric acid. N-doped carbon encapsulation is then introduced via carbonization of the surfactant-assisted polymerization of pyrrole monomer on P-doped Si. While P dopant is required to support the stability at high current density, the encapsulation of Si particles with N-doped carbon is influential in enhancing the overall Li+ diffusivity of the Si anode. The combined approaches improve the anode's Li+ diffusivity up to tenfold compared to the untreated anode. It leads to exceptional anode stability at a high current, retaining 87 % of its initial capacity under a large current rate of 4000 mA g-1. The full-cell comprising P-Si@N-C anode and LiFePO4 cathode demonstrates 94 % capacity retention of its initial capacity after 100 cycles at 1 C. This study explores the effective strategies to improve Li+ diffusivity for high-rate Si-based anode.

Vascular tissue-derived hard carbon with ultra-high rate capability for sodium-ion storage

Vascular tissue helps quickly pass the nutrients and water through the plant. Inspiringly, the transport of electrolyte solutions within such biological tissue may also play an essential role in governing the high-current performance of sodium-ion storage. Herein, we report a facile and efficient approach to fabricate a vascular tissue-derived hard carbon (VHC) by an integrated procedure of leave stripping, carbonization and alkali/acid washing. By meticulously adjusting the pyrolysis temperatures, hierarchical microchannel carbon with abundant turbostratic nanodomains, suitable pore size and special surface functional groups can be obtained, enabling high specific capacity and excellent rate performances. It is believed that the vascular tissue-derived carbon can significantly shorten sodium ion transport paths and further enhance the storage performance on the surface and within the electrode materials, making it a promising candidate for sodium-ion batteries.

Pt Single-Atoms on Structurally-Integrated 3D N-Doped Carbon Tubes Grid for Ampere-Level Current Density Hydrogen Evolution.

To date, the excellent mass-catalytic activities of Pt single-atoms catalysts (Pt-SACs) toward hydrogen evolution reaction (HER) are categorically confirmed; however, their high current density performance remains a challenge for practical applications. Here, a binder-free approach is exemplified to fabricate self-standing superhydrophilic-superaerphobic Pt-SACs cathodes by directly anchoring Pt-SAs via Pt-NxC4-x coordination bonds to the structurally-integrated 3D nitrogen-doped carbon tubes (N-CTs) array grid (denoted as Pt@N-CTs). The 3D Pt@N-CTs cathode with optimal Pt-SACs loading is capable of operating at a high current density of 1000mA cm-2 with an ultralow overpotential of 157.9mV with remarkable long-term stability over 11 days at 500mA cm-2. The 3D super-wettable free-standing Pt@N-CTs possess interconnected vertical and lateral N-CTs with hierarchical-sized open channels, which facilitates the mass transfer. The binder-free immobilization adding to the large surface area and 3D-interconnected open channels endow Pt@N-CTs cathodes with high accessible active sites, electrical conductivity, and structural stability that maximize the utilization efficiency of Pt-SAs to achieve ampere-level current density HER at low overpotentials.

High Li+ Conductivity of Li1.3+xAl0.3−xMgxTi1.7(PO4)3 with Hybrid Solid Electrolytes for Solid‐State Lithium Batteries

Solid‐state electrolytes (SSEs) are promising future power sources for electronic vehicles (EVs) and devices due to their enhanced safety features, high energy density, and nonflammability. The NASICON structure has emerged as a frontrunner in oxide‐based electrolytes, boasting high Li‐ion conductivity and air stability. Nevertheless, developing high‐performance oxide‐based electrolytes remains challenging due to their inherently hard and brittle nature, presenting obstacles to achieving an optimal interface between the cathode and anode. In this study, to overcome this issue and enhance electrochemical stability and Li‐ion conductivity, a new approach employing a hybrid solid electrolyte amalgamating polymer electrolytes with inorganic Li1.3+xAl0.3−xMgxTi1.7(PO4)3 powder (x = 0, 0.015, 0.030, 0.045, and 0.060) was investigated. Notably, employing nanosized Li1.3Al0.3Ti1.7(PO4)3 (LATP) synthesized via the sol–gel method led to a remarkable increase in ionic conductivity to 7.29 × 10–4 S cm–1, which was attributed to enhanced pellet density. Electrochemical analysis revealed that Li1.345Al0.255Mg0.045Ti1.7(PO4)3 exhibited superior specific capacity, stable high current density performance, and capacity recoverability compared to LATP. This pioneering study highlights the potential of hybrid solid electrolytes incorporating Mg‐doped LATP as a promising material for practical solid‐state lithium batteries.

(Invited) Unravelling the Core of Fuel Cell Performance: Engineering the Electrolyte (ionomer)/Catalyst Interface

The biggest challenge of the widespread implantation of the polymer electrolyte membrane fuel cells (PEMFCs) is the cost, primarily due to the use of platinum catalysts. The high intrinsic catalyst activity exhibited using a rotating disc electrode (RDE) is rarely realized in the membrane electrode assembly (MEA), which is the core of PEMFC, due to the difference on the electrolyte(ionomer)/catalyst interfaces. To translate the catalyst RDE performance into MEA, the design of an ideal ionomer/catalyst interface is proposed: a thin, conformal ionomer film covers the maximum surface of a Pt nanoparticle that simultaneously maximizes catalyst utilization, (i.e. high mass activity and electrochemical active surface area) and O2 diffusion (i.e. high current density performance) without compromising proton conduction. Building such an interface is a long-standing challenge due to no control of ionomer distribution over catalyst particle, resulting in large ionomer agglomerates and inhomogeneous ionomer coverage over the catalyst nanoparticle, consequently, poor fuel cell performance. In this work, this ionomer/catalyst interface has been constructed utilizing the electrostatic charge attraction between positively charged catalyst and negatively charged ionomer particles in a liquid and preserved into a solid catalyst layer. Consequently, this interface leads to the previously unachieved fuel cell performance on both the catalyst utilization (75% vs. 45%) and the rated/peak power density (Pt/C, 0.910/1.430 W/cm2 for H2/Air, Pt loading: 0.1 mgPt/cm2), matching that of Pt alloy catalysts. This work demonstrated the formation of the interface in the liquid phase (using ultra-small angle x-ray scattering in combination with cryo-TEM, isothermal‐titration‐calorimetry) and the preserved interface in the solid catalyst layer (using TEM) and estimated the effective coverage and thickness of the ionomer film (using the limiting current density, RDE and fuel cell performance).

Optimizing the Charge Carrier Dynamics of Thermal Evaporated TexSe1‐x Films for High‐Performance Short‐Wavelength Infrared Photodetection

AbstractShort‐wavelength infrared photo‐sensing materials are dominated by germanium, indium gallium arsenide, indium antimonide, and mercury cadmium telluride. However, the complex fabrication process and high production cost hinder their widespread applications. Recently, TexSe1‐x has shown great potential for infrared photodetection, but TexSe1‐x‐based devices are still suffering from extremely high dark current and poor device performance. In this work, high‐quality TexSe1‐x films are fabricated by thermal evaporation and low‐temperature annealing. The optoelectronic properties of the TexSe1‐x thin films are systematically investigated and optimized. The absorption spectrum is carefully tuned to cover the broad range from 300 to 1600 nm by modulating the ratio of Te and Se. Photodiodes based on the optimized TexSe1‐x thin films are also fabricated, and achieve high responsivity, reduced dark and low noise current density, and a fast response time of <850 ns. Then, prototypical devices based on Te0.65Se0.35 thin films are demonstrated for optical communications, indicating the great potential for next‐generation, low‐cost short‐wavelength infrared photodetection.

(Invited) Lowering the Noble Metal Requirement for PEM Water Electrolysis: Membrane Electrode Assembly and Porous Transport Layer Design Considerations

The Net Zero Emission scenario proposed by the International Energy Agency projects a required electrolytic generation of hydrogen equivalent to 3600 GW by 2050 [1], averaging to an annual installation of ~130 GW/a between 2023 and 2050. If this were to be provided by proton exchange membrane based water electrolyzers (PEM-WEs) based on platinum catalysts for the hydrogen evolution reaction (HER) and iridium catalysts for the oxygen evolution reaction (OER), the current PEM-WE noble metal requirements of ~0.7 gIr/kW and ~0.3 gPt/kW [1] would have to be drastically reduced in view of the noble metal supply constraints. As argued previously, for PEM-WEs to be sustainable on such a large scale would require to achieve platinum and iridium loadings of ~0.05 mg/cm2 electrode [2,3]. While the former can be easily achieved due to the fast HER kinetics on Pt, the latter requires either ultra-thin OER catalyst layers or improved OER catalysts with a substantially reduced iridium packing density (in units of gIr/cm3 electrode) [2], like the recently developed catalyst with a hydrous iridium oxide shell supported on a titanium oxide core (IrOx/TiO2) [4,5].In this contribution, we will discuss the effect of the design of membrane electrode assemblies (MEAs) and of the adjacent porous transport layers on PEM-WE performance. In general, the preparation of MEAs with low platinum loading cathodes is straightforward, due to the availability of carbon supported platinum catalysts (Pt/C) with a low Pt packing density. For the optimization of the ionomer content in the cathode electrode, however, its effect on the high current density performance and on the hydrogen permeation rate from cathode to anode have to be considered [6,7].With regards to the anode electrode, we will further discuss the MEA design challenges when targeting ultra-low iridium loadings. In the case of the ultra-thin catalyst layers that result when using conventional OER catalysts, additional contact resistances between the anode catalyst layer and the titanium based porous transport layer (Ti-PTL) are observed [2]. As will be shown, these can be largely mitigated by the use of a titanium based microporous layer (MPL) coated on the Ti-PTL, highlighting the importance of the interface between the PTL and the anode catalyst layer. In case of using the above described IrOx/TiO2 catalysts with low iridium packing density, their typically lower electrical conductivity also results in apparent contact resistances within and across the anode catalyst layer [4], which poses an additional constraint on the allowable range of the catalyst/ionomer ratio in the anode electrode. The interplay between the anode catalyst type, the anode ionomer content, and the type of interface between the anode electrode and the PTL (i.e., with and without MPL) will be discussed.