Sandwiching h-BN Monolayer Films between Sulfonated Poly(ether ether ketone) and Nafion for Proton Exchange Membranes with Improved Ion Selectivity

Transfer of 2D Films: From Imperfection to Perfection

Atomically thin 2D films and their van der Waals heterostructures have demonstrated immense potential for breakthroughs and innovations in science and technology. Integrating 2D films into electronics and optoelectronics devices and their applications in electronics and optoelectronics can lead to improve device efficiencies and tunability. Consequently, there has been steady progress in large-area 2D films for both front- and back-end technologies, with a keen interest in optimizing different growth and synthetic techniques. Parallelly, a significant amount of attention has been directed toward efficient transfer techniques of 2D films on different substrates. Current methods for synthesizing 2D films often involve high-temperature synthesis, precursors, and growth stimulants with highly chemical reactivity. This limitation hinders the widespread applications of 2D films. As a result, reports concerning transfer strategies of 2D films from bare substrates to target substrates have proliferated, showcasing varying degrees of cleanliness, surface damage, and material uniformity. This review aims to evaluate, discuss, and provide an overview of the most advanced transfer methods to date, encompassing wet, dry, and quasi-dry transfer methods. The processes, mechanisms, and pros and cons of each transfer method are critically summarized. Furthermore, we discuss the feasibility of these 2D film transfer methods, concerning their applications in devices and various technology platforms.

A dual-functional cuprum coordination framework for high proton conduction and electrochemical dopamine detection

The present study selected 5, 5'-((6-(ethylamino)-1, 3, 5-triazine-2, 4-diyl) bis(azanediyl))diisophthalic acid (H4EATDIA) as ligand and an amino-functionalized cuprum-based MOF (EA-JUC-1000), successfully synthesized by microwave-assisted method, for proton conduction and dopamine sensing applications. In order to enhance the proton-conducting potential of EA-JUC-1000, the Brönsted acid (BA) encapsulated composites (BA@EA-JUC-1000) are dopped into chitosan (CS) to form a series of hybrid membranes (BA@EA-JUC-1000/CS). The impedance results display that the best proton conductivity of CF3SO3H@EA-JUC-1000/CS-8% reaches up to 1.23 × 10-3 S∙cm-1 at 338 K and ~ 98% RH, 2.6-fold than that of CS. Moreover, the EA-JUC-1000 is in-situ combined with reduced graphene oxide (rGO) (rGO/EA-JUC-1000), which makes EA-JUC-1000 have a wide detection range (0.1 ~ 500 μM) and a low limit of detection (50 nM), together with good anti-interference performance, reproducibility and repeatability. In addition, the electrochemical sensing method has been successfully applied to detect DA in bovine serum samples. The dual-functional MOF-based hybrid membrane and composites including proton conduction and DA sensing would provide an example of practical application for MOFs.

A Stable and Energy-Dense Polysulfide/Permanganate Flow Battery

Redox flow batteries (RFBs) as promising technologies for energy storage have attracted burgeoning efforts and have achieved many advances in the past decades. However, for practical applications, the exploration of high-performance RFB systems is still of significance. In this work, inspired by the high solubility and low cost of both polysulfides and permanganates, the S/Mn RFBs with S42-/S22- and MnO4-/MnO42- as negative and positive redox pairs are demonstrated. Moreover, to solve the poor cycling performance caused by the sluggish kinetics of polysulfide-involved redox reactions and instability of the carbon felt (CF) electrode in the strong oxidative and corrosive catholyte, both the anode and cathode are designed to obtain high performance. Herein, the NiSx/Ni foam exhibiting electrocatalysis activity toward polysulfide ions is prepared and works as the anode while the graphene-modified carbon felt (G/CF) with high stability is fabricated and utilized as the cathode. Additionally, NaMnO4 with a high solubility limit (3.92 M) in the alkaline supporting electrolyte is preferred to KMnO4 as the redox-active molecule in the catholyte. The resulting S/Mn RFB cells show outstanding cell performance, such as high energy density (67.8 Wh L-1), long cycling lifetime with a temporal capacity fade of 0.025% h-1, and low chemical cost of electrolytes (17.31 $ kWh-1). Moreover, a three-cell stack shows good cycling stability over 100 cycles (226.8 h) with high performance, verifying the good scalability of the proposed S/Mn RFB system. Therefore, the present strategy provides a reliable candidate for stable, energy-dense, and cost-effective devices for future energy storage applications.

Recent Progress of Crystalline Porous Frameworks for Intermediate-Temperature Proton Conduction

Proton exchange membranes (PEMs), especially for work under intermediate temperatures (100-200 °C), have attracted great interest because of the high CO toleration and facial water management of the corresponding proton exchange membrane fuel cells (PEMFCs). Traditional polymer PEMs faced challenges of low stability and proton carrier leaking. Crystalline porous materials, such as metal-organic frameworks (MOFs) and covalent organic frameworks (COFs), are promising to overcome these issues contributed by nanometer-sized channels. Herein we summarized the recent development of MOF/COF-based intermediate-temperature proton conductors. The strategies of framework engineering and pore impregnation were introduced in detail for raising proton conductivity. The proton-conducting mechanism was described as well. This spotlight will provide new insight into the fabrication of MOF/COF proton conductors under intermediate-temperature and anhydrous conditions.

Fully Dispersed IrOx Atomic Clusters Enable Record Photoelectrochemical Water Oxidation of Hematite in Acidic Media

Ir-based materials are still the benchmark catalysts for various reactions in acidic environment, but the high loading and low atom utilization limit their large-scale deployment. Herein, we report an effective strategy for implanting fully dispersed iridium-oxide atomic clusters onto hematite for boosting photoelectrochemical water oxidation in acidic solution. The resulting photoanode achieves a record-high photocurrent of 1.35 mA cm^-2 at 1.23 V, corresponding to a mass activity of 172.70 A g^-1 (3 times higher than electrodeposited control sample) and demonstrating the merits from the high atomic utilization of Ir. The systematically experimental and theoretical results reveal that the performance improvement correlates with the modulated electronic structure including the adjusted Fermi level and d-band center, which significantly enhances charge separation efficiency and promotes the conversion from intermediate *O into *OOH.

Electrolytes in Organic Batteries

Organic batteries using redox-active polymers and small organic compounds have become promising candidates for next-generation energy storage devices due to the abundance, environmental benignity, and diverse nature of organic resources. To date, tremendous research efforts have been devoted to developing advanced organic electrode materials and understanding the material structure-performance correlation in organic batteries. In contrast, less attention was paid to the correlation between electrolyte structure and battery performance, despite the critical roles of electrolytes for the dissolution of organic electrode materials, the formation of the electrode-electrolyte interphase, and the solvation/desolvation of charge carriers. In this review, we discuss the prospects and challenges of organic batteries with an emphasis on electrolytes. The differences between organic and inorganic batteries in terms of electrolyte property requirements and charge storage mechanisms are elucidated. To provide a comprehensive and thorough overview of the electrolyte development in organic batteries, the electrolytes are divided into four categories including organic liquid electrolytes, aqueous electrolytes, inorganic solid electrolytes, and polymer-based electrolytes, to introduce different components, concentrations, additives, and applications in various organic batteries with different charge carriers, interphases, and separators. The perspectives and outlook for the future development of advanced electrolytes are also discussed to provide a guidance for the electrolyte design and optimization in organic batteries. We believe that this review will stimulate an in-depth study of electrolytes and accelerate the commercialization of organic batteries.

High-Resolution Ion-Flux Imaging of Proton Transport through Graphene|Nafion Membranes

In 2014, it was reported that protons can traverse between aqueous phases separated by nominally pristine monolayer graphene and hexagonal boron nitride (h-BN) films (membranes) under ambient conditions. This intrinsic proton conductivity of the one-atom-thick crystals, with proposed through-plane conduction, challenged the notion that graphene is impermeable to atoms, ions, and molecules. More recent evidence points to a defect-facilitated transport mechanism, analogous to transport through conventional ion-selective membranes based on graphene and h-BN. Herein, local ion-flux imaging is performed on chemical vapor deposition (CVD) graphene|Nafion membranes using an "electrochemical ion (proton) pump cell" mode of scanning electrochemical cell microscopy (SECCM). Targeting regions that are free from visible macroscopic defects (e.g., cracks, holes, etc.) and assessing hundreds to thousands of different sites across the graphene surfaces in a typical experiment, we find that most of the CVD graphene|Nafion membrane is impermeable to proton transport, with transmission typically occurring at ≈20-60 localized sites across a ≈0.003 mm² area of the membrane (>5000 measurements total). When localized proton transport occurs, it can be a highly dynamic process, with additional transmission sites "opening" and a small number of sites "closing" under an applied electric field on the seconds time scale. Applying a simple equivalent circuit model of ion transport through a cylindrical nanopore, the local transmission sites are estimated to possess dimensions (radii) on the (sub)nanometer scale, implying that rare atomic defects are responsible for proton conductance. Overall, this work reinforces SECCM as a premier tool for the structure-property mapping of microscopically complex (electro)materials, with the local ion-flux mapping configuration introduced herein being widely applicable for functional membrane characterization and beyond, for example in diagnosing the failure mechanisms of protective surface coatings.

One-Atom-Thick Crystals as Emerging Proton Sieves

Two-dimensional (2D) crystals, despite their atomic thickness, have long been considered as impermeable membranes to all molecules and atoms under ambient conditions: even the smallest of atoms, hydrogen, is expected to take billions of years to penetrate the 2D lattice covered with dense electron clouds. Recently it has been found that monolayer graphene, hexagonal boron nitride, and some other one-atom-thick crystals are highly permeable to protons, raising fundamental questions about the details of the transport process. In this Perspective, we review the mechanism of proton transport through 2D crystals and the related room-temperature quantum effects; the potential applications of 2D membranes in proton-related separation and sieving techniques, including proton exchange membranes and hydrogen isotope separation; and factors that enhance proton permeation and in turn influence 2D membrane design.

Subatomic species transport through atomically thin membranes: Present and future applications

[Figure: see text].

Two-dimensional group-III nitrides and devices: a critical review

As third-generation semiconductors, group-III nitrides are promising for high power electronic and optoelectronic devices because of their wide bandgap, high electron saturation mobility, and other unique properties. Inspired by the thickness-dependent properties of two-dimensional (2D) materials represented by graphene, it is predicted that the 2D counterparts of group-III nitrides would have similar properties. However, the preparation of 2D group-III nitride-based materials and devices is limited by the large lattice mismatch in heteroepitaxy and the low rate of lateral migration, as well as the unsaturated dangling bonds on the surfaces of group-III nitrides. The present review focuses on theoretical and experimental studies on 2D group-III nitride materials and devices. Various properties of 2D group-III nitrides determined using simulations and theoretical calculations are outlined. Moreover, the breakthroughs in their synthesis methods and their underlying physical mechanisms are detailed. Furthermore, devices based on 2D group-III nitrides are discussed accordingly. Based on recent progress, the prospect for the further development of the 2D group-III nitride materials and devices is speculated. This review provides a comprehensive understanding of 2D group-III nitride materials, aiming to promote the further development of the related fields of nano-electronic and nano-optoelectronics.

Nafion-Based Proton-Exchange Membranes Built on Cross-Linked Semi-Interpenetrating Polymer Networks between Poly(acrylic acid) and Poly(vinyl alcohol)

We report semi-interpenetrating polymer network (semi-IPN) membranes prepared easily from a cross-linked network using poly(acrylic acid) (PAA) and poly(vinyl alcohol) (PVA) with interpenetrated Nafion for both proton-exchange membrane fuel cell (PEMFC) and proton-exchange membrane water electrolyzer (PEMWE) applications. Thermal esterification between PAA and PVA induced three-dimensional cross-linking to improve mechanical toughness and reduce hydrogen crossover, while the hydrophilic nature of the PAA-PVA-based cross-linked matrix still enhanced the water uptake (WU) and hence conductivity of the Nafion penetrant. The semi-IPN membrane (NPP-95) composed of Nafion, PAA, and PVA with a ratio of 95:2.5:2.5 showed a hexagonal cylindrical morphology and improved thermal, mechanical, and dimensional stability compared to a recast Nafion membrane (re-Nafion). The membrane was also highly effective at managing water due to its low WU and high conductivity. Furthermore, its hydrogen permeability was 49.6% lower than that of re-Nafion under the actual fuel cell operating conditions (at 100% RH and 80 °C). NPP-95 exhibited significantly improved conductivity and PEMFC performance compared to re-Nafion with a current density of 1561 mA/cm² at a potential of 0.6 V and a peak power density of 1179 mW/cm². Furthermore, in the PEMWE performances, NPP-95 displayed about a 1.5-fold higher current density of 4310 mA/cm² at 2.0 V and much lower ohmic resistance than re-Nafion between 60 and 80 °C.

Oriented Proton-Conductive Nanochannels Boosting a Highly Conductive Proton-Exchange Membrane for a Vanadium Redox Flow Battery

In this work, we propose a sulfonated poly (ether ether ketone) (SPEEK) composite proton-conductive membrane based on a 3-(1-hydro-imidazolium-3-yl)-propane-1-sulfonate (Him-pS) additive to break through the trade-off between conductivity and selectivity of a vanadium redox flow battery (VRFB). Specifically, Him-pS enables an oriented distribution of the SPEEK matrix to construct highly conductive proton nanochannels throughout the membrane arising from the noncovalent interaction. Moreover, the "acid-base pair" effect from an imidazolium group and a sulfonic group further facilitates the proton transport through the nanochannels. Meanwhile, the structure of the acid-base pair is further confirmed based on density functional theory calculations. Material and electrochemical characterizations indicate that the nanochannels with a size of 16.5 nm are vertically distributed across the membrane, which not only accelerate proton conductivity (31.54 mS cm^-1) but also enhance the vanadium-ion selectivity (39.9 × 10³ S min cm^-3). Benefiting from such oriented proton-conductive nanochannels in the membrane, the cell delivers an excellent Coulombic efficiency (CE, ≈ 98.8%) and energy efficiency (EE, ≈ 78.5%) at 300 mA cm^-2. More significantly, the cell maintains a stable energy efficiency over 600 charge-discharge cycles with only a 5.18% decay. Accordingly, this work provides a promising fabrication strategy for a high-performance membrane of VRFB.

Effect of Crosslinking Degree on Sulfonated Poly(aryl ether nitrile)s As Candidates for Proton Exchange Membranes

In order to investigate the effect of crosslinking degree on the water uptake, swelling ratio, and methanol permeability of sulfonated poly(aryl ether nitrile)s (SPENs), the molar content of sulfonated group in bisphenol monomer is fixed at 60% in this work. The properties of sulfonated poly (aryl ether nitrile) with different crosslinking degrees are studied by changing the content of propenyl group in sulfonated poly (aryl ether nitrile)s. The cross-linking reaction of the propenyl groups in the SPENs is cured at 230 °C. All the results show that this method is an effective way to improve the water uptake, swelling ratio, and methanol permeability to meet the application requirements of the SPENs membranes as proton exchange membranes in fuel cells.