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•High P-doped (9.24 at%) thick carbon electrodes (CW-P) by phytic acid treatment.•SSC exhibits high capacitance of 4.7F cm−2/206.5F g−1 at 1.0 mA cm−2.•Excellent capacitance retention ...of 90.5% after 20 000 cycles (@20 mA cm−2).•High energy density up to 0.94 mW h cm−2 (41.2 Wh kg−1).•High power density up to 0.6 mW cm−2 (26.3 W kg−1).
Keeping outstanding electrochemical performance under high mass loading is critical to develop functional thick electrodes. Here, we report a high phosphorus-doped wood-derived carbon thick electrode for supercapacitor via phytic acid treatment, which can form hydrogen bonds with cellulose molecules in the wood. The content of phosphorus reaches up to 9.24 at% in carbonized wood with P-doping (CW-P-9.24), higher than most previously reported P-doped carbonaceous materials. CW-P-9.24 electrode (800 μm, 17.17 mg cm−2) exhibits greatly improved electrochemical performance, especially in energy density and cyclic stability. Significantly, the symmetrical supercapacitor device exhibits high areal and specific capacitance of 4.7 F cm−2 and 206.5 F g−1 at 1.0 mA cm−2 with prominent retention of 90.5% through the long-term cycling at 20 mA cm−2 for 20,000 cycles, and 0.94 mW h cm−2 (41.2 Wh kg−1) at power density of 0.6 mW cm−2 (26.3 W kg−1), and possesses excellent volumetric capacitance and energy density of 29.3 F cm−3 and 5.8 Wh cm−3, respectively. The outstanding performance can be attributed to the excellent hierarchical structure, low tortuosity, and high phosphorus doping with fast accessible channels at high current density. The extraordinary performance of CW-P has been elucidated by density functional theory calculations, which confirm the enhanced activity by P-doping. These results demonstrate that the CW-P electrode is promising for practical application in energy storage devices and encourage more investigations for thick electrode.
Searching for an optimal component and composition of multi‐metallic alloy catalysts, comprising two or more elements, is one of the key issues in catalysis research. Due to the exhaustive data ...requirement of conventional machine‐learning (ML) models and the high cost of experimental trials, current approaches rely mainly on the combination of density functional theory and ML techniques. In this study, a significant step is taken toward overcoming limitations by the interplay of experiment and active learning to effectively search for an optimal component and composition of multi‐metallic alloy catalysts. The active‐learning model is iteratively updated using by examining electrocatalytic performance of fabricated solid‐solution nanoparticles for the hydrogen evolution reaction (HER). An optimal metal precursor composition of Pt0.65Ru0.30Ni0.05 exhibits an HER overpotential of 54.2 mV, which is superior to that of the pure Pt catalyst. This result indicates the successful construction of the model by only utilizing the precursor mixture composition as input data, thereby improving the overpotential by searching for an optimal catalyst. This method appears to be widely applicable since it is able to determine an optimal component and composition of electrocatalyst without obvious restriction to the types of catalysts to which it can be applied.
A new and simple methodology is suggested in order to search for the optimal components and composition of multi‐metallic alloy catalysts regardless of the catalytic background by a combination of active learning and experiment. After conducting several iterations, the optimum ternary catalyst, which shows superior performance compared to unary or binary catalysts, is discovered.
Covalent organic frameworks (COFs), featuring ordered nanopores with numerous accessible redox sites, have drawn much attention as promising electrode materials for rechargeable batteries. Thus far, ...however, COF‐based battery electrodes have exhibited limited capacity and unsatisfactory cycling stability due to the unwanted side reactions over their large surface area. Herein, a fluorine‐rich covalent organic framework (F‐COF) as an electrode material with improved stability and performance for potassium‐ion batteries is developed. The fluorinated COF not only stabilizes intercalation kinetics of K+ ions but also reinforces its electron affinity and conductivity, improving the reversibility of bond transitions during discharge–charge cycles. As a result, F‐COF affords a high specific capacity (95 mAh g−1 at fast rates up to 5 C) and excellent cycling stability (5000 cycles with ≈99.7% capacity retention), outperforming the pristine COF‐based electrodes devoid of F atoms. Notably, the experimental capacity of F‐COF approaches its theoretical value, confirming that a large proportion of electroactive sites are being actively utilized. Altogether, this work addresses the significant role of F atoms in improving the K+‐ion storage capability of COFs and provides the rational design principles for the continued development of stable and high‐performance organic electrode materials for energy storage devices.
Fluorinated arenes in covalent organic framework enhance electrochemical activity and stabilize the interface between electrode and electrolyte, resulting in high ion storage capacity and fast ion transport. The unique role of F atoms in potassium ion batteriesis clarified at multiple angles through a pioneering in‐depth study coordinating experimental findings.
Metal oxide nanosheets having high mesoporosity, grain size distribution of 5–10 nm, and ultrathin thickness have attracted much attention due to their intriguing properties such as high ...surface‐to‐volume ratio and superior chemical activities. However, 2D nanostructures tend to restack, inducing a decrease in accessible surface area and a number of pores. To solve this problem, herein, a unique synthetic method of crumpled metal oxide nanosheets using spray pyrolysis of metal ion–coated graphene oxide, followed by heat treatment, is reported. This method is applicable not only to single‐component metal oxides but also to heterogeneous multicomponent metal oxides in which composition can be controlled. Crumpled SnO2, ZnO, and Co3O4 as well as SnO2/ZnO and SnO2/Co3O4 nanosheets with heterogeneous interfaces are successfully synthesized and used as superior gas sensing layers. Because of the abundant reaction sites, well‐developed porosity for high gas accessibility, the formation of heterojunctions, the crumpled SnO2/ZnO and SnO2/Co3O4 nanosheets exhibit outstanding sensing performance (Rair/Rgas = 20.25 toward 5 ppm formaldehyde, and Rair/Rgas = 14.13 toward 5 ppm acetone, respectively). This study can contribute to the realization of a family of heterogeneous crumpled metal oxide nanosheets that can be applied to various research fields.
A general synthetic platform of hierarchically structured holey metal oxide nanosheets is achieved via a graphene oxide templating route and spray pyrolysis technique. The crumpled heterogeneous 2D metal oxide (crumpled H_2D MO) as a sensing layer exhibits improved sensing performance of formaldehyde (crumpled 2D SnO2/ZnO) and acetone (crumpled 2D SnO2/Co3O4) molecules due to the high porosity, surface area, and heterojunction effect.
2D black phosphorus (BP) and MXenes have triggered enormous research interest in catalysis, energy storage, and chemical sensing. Unfortunately, the low stability of these materials under practical ...operating conditions remains a critical bottleneck, particularly as they are prone to oxidization under moisture. In this work, the design and application of stable 2D heterostructures obtained from decorating BP and MXene (Ti3C2Tx) with few‐layer holey graphene oxide (FHGO) membranes are presented. In the resulting heterostructured systems, FHGO serves as a multifunctional passivation layer that shields BP or MXene from oxidative degradation, while allowing the selective diffusion of target gas molecules through its micropores and toward the underlying 2D material. Through a case study of dilute NO2 sensing, it is demonstrated that these heterostructures show a greatly enhanced sensing performance under humid conditions, where fast sensing speed and response are consistently observed, and high stability is impressively retained upon repetitive sensing cycles for 1000 min. These results corroborate the efficacy of material decoration with porous FHGO membranes and suggest that this is a generalizable strategy for reliable high‐performance applications of 2D materials.
“Janus‐like” 2D porous heterostructures are described for realizing ultrastable surface reactivity of chemiresistive 2D materials as proven by a chemical sensing case study and multiscale simulations. The few‐layered holey graphene oxide passivation layer effectively shields the black phosphorus and MXene from oxidative degradation, while allowing the selective diffusion of NO2 molecules toward the underlying 2D sensing materials.
The physical and chemical degradations of a state‐of‐the‐art proton exchange membrane (PEM) composed of a perfluorinated sulfonic acid (PFSA) ionomer and polytetrafluoroethylene (PTFE) reinforcement ...are induced through the repeated expansion/shrinkage of the ionomer and free radical attacks. Such degradations essentially originate from the loose structure of the materials and the low interactive binding force among the PEM constituents. In this study, the need for simplified design principles of adhesives led to the use of mussel‐inspired polydopamine (PD) as an interfacial modifier for the fabrication of highly durable PEM. Indeed, a self‐polymerized dopamine layer acts as an interfacial glue, and enables efficient impregnation of a hydrophilic PFSA ionomer into porous hydrophobic PTFE with high packing density, resulting in strong adhesion between the PTFE and the PFSA polymers in the membrane. In addition, the redox property of the PD end groups spontaneously reduces the partial Ce salts in the ionomer solution and anchors them to the PD@PTFE substrate as defective cerium oxide (CeOx) nanoparticles, reducing the dissolution and subsequent migration under cell operations. Finally, a CePD@PTFE membrane shows outstanding durability in fuel cells under an accelerated humidity cycling test with a reduction in the degree of physical and chemical failures.
Mussel‐inspired polydopamine and Ce salts are introduced to porous polytetrafluoroethylene (PTFE) substrates for highly durable composite membranes. The multifunctional features of polydopamine, i.e., (i) interfacial glues between perfluorinated sulfonic acid and PTFE layers; and (ii) immobilization of Ce based radical scavengers give rise to outstanding cell performance with long‐term operation of proton exchange membrane fuel cells under humidity cycles.
Thermochromic sensors provide an intuitive and real‐time solution for monitoring the local temperature with naked eyes. Conventional thermochromic sensors often utilize either solution‐type or dense ...film‐type platforms, which are suboptimal morphologies for exposing a large number of dye molecules to the surface, leading to low sensitivity and sluggish responding speeds. Herein, this article introduces rational synthetic routes to fabricate highly sensitive nanofiber (NF) sensor membranes loaded with thermochromic dyes (C3H6N6·CH2O)x‐loaded nanofibers (NFs) sensor membranes by alignment‐controllable electrospinning techniques (x–y perpendicular and rotary). The NF‐based porous sensor membranes exhibit two‐ to fivefold improved thermochromic sensitivity (ΔRGB) compared to those of dense film‐type sensors at 31.6–42.7 °C. This is attributed to the uniform distribution of dyes throughout the porous NF structure (≈95.7%), which exhibits excellent light transmittance that is 10–30‐fold higher than that of film‐type sensors. Based on the available shape‐conforming synthetic strategies, this article further demonstrates wearable thermochromic sensors in the forms of mask‐, patch‐, and bracelet‐type devices, which can accurately monitor body temperature in real time.
Highly sensitive thermochromic sensors are developed using nanofiber (NF) membranes with tunable alignments of the fibers via fine‐tuned electric field during the electrospinning process. The porous NF membrane‐based sensors show five‐fold enhanced thermochromic sensing performance compared with dense film‐type sensors. The NF sensor membranes can be further integrated with masks, patches, and bracelets for wearable applications.
Iminosemiquinone‐linker‐based conductive metal–organic frameworks (c‐MOFs) have attracted much attention as next‐generation electronic materials due to their high electrical conductivity combined ...with high porosity. However, the utility of such c‐MOFs in high‐performance devices has been limited to date by the lack of high‐quality MOF thin‐film processing. Herein, a technique known as the microfluidic‐assisted solution shearing combined with post‐synthetic rapid crystallization (MASS‐PRC) process is introduced to generate a high‐quality, flexible, and transparent thin‐film of Ni3(hexaiminotriphenylene)2 (Ni3(HITP)2) uniformly over a large‐area in a high‐throughput manner with thickness controllability down to tens of nanometers. The MASS‐PRC process utilizes: 1) a micromixer‐embedded blade to simultaneously mix and continuously supply the metal–ligand solution toward the drying front during solution shearing to generate an amorphous thin‐film, followed by: 2) immersion in amine solution for rapid directional crystal growth. The as‐synthesized c‐MOF film has transparency of up to 88.8% and conductivity as high as 37.1 S cm−1. The high uniformity in conductivity is confirmed over a 3500 mm2 area with an arithmetic mean roughness (Ra) of 4.78 nm. The flexible thin‐film demonstrates the highest level of transparency for Ni3(HITP)2 and the highest hydrogen sulfide (H2S) sensing performance (2,085% at 5 ppm) among c‐MOFs‐based H2S sensors, enabling wearable gas‐sensing applications.
A microfluidic‐assisted solution shearing combined with post‐synthetic rapid crystallization (MASS‐PRC) process is introduced, which enables the formation of high‐quality conductive Ni3(HITP)2 thin‐films with thickness controllability down to 10 nm in a rapid large‐area scalable manner. This process can fabricate flexible and transparent Ni3(HITP)2 thin film for high‐performance wearable gas sensors.
Lithium–oxygen (Li–O2) batteries have been intensively investigated in recent decades for their utilization in electric vehicles. The intrinsic challenges arising from O2 (electro)chemistry have ...been mitigated by developing various types of catalysts, porous electrode materials, and stable electrolyte solutions. At the next stage, we face the need to reform batteries by substituting pure O2 gas with air from Earth’s atmosphere. Thus, the key emerging challenges of Li–air batteries, which are related to the selective filtration of O2 gas from air and the suppression of undesired reactions with other constituents in air, such as N2, water vapor (H2O), and carbon dioxide (CO2), should be properly addressed. In this review, we discuss all key aspects for developing Li–air batteries that are optimized for operating in ambient air and highlight the crucial considerations and perspectives for future air-breathing batteries.
Facile synthesis of porous nanobuilding blocks with high surface area and uniform catalyst functionalization has always been regarded as an essential requirement for the development of highly ...sensitive and selective chemical sensors. Metal–organic frameworks (MOFs) are considered as one of the most ideal templates due to their ability to encapsulate ultrasmall catalytic nanoparticles (NPs) in microporous MOF structures in addition to easy removal of the sacrificial MOF scaffold by calcination. Here, we introduce a MOFs derived n-type SnO2 (n-SnO2) sensing layer with hollow polyhedron structures, obtained from p–n transition of MOF-templated p-type Co3O4 (p-Co3O4) hollow cubes during galvanic replacement reaction (GRR). In addition, the Pd NPs encapsulated in MOF and residual Co3O4 clusters partially remained after GRR led to uniform functionalization of efficient cocatalysts (PdO NPs and p-Co3O4 islands) on the porous and hollow polyhedron SnO2 structures. Due to high gas accessibility through the meso- and macrosized pores in MOF-templated oxides and effective modulation of electron depletion layer assisted by the creation of numerous p–n junctions, the GRR-treated SnO2 structures exhibited 21.9-fold higher acetone response (R air/R gas = 22.8 @ 5 ppm acetone, 90%RH) compared to MOF-templated p-Co3O4 hollow structures. To the best of our knowledge, the selectivity and response amplitudes reported here for the detection of acetone are superior to those MOF derived metal oxide sensing layers reported so far. Our results demonstrate that highly active MOF-derived sensing layers can be achieved via p–n semiconducting phase transition, driven by a simple and versatile GRR process combined with MOF templating route.
