The ex‐solution phenomenon, a central platform for growing metal nanoparticles on the surface of host oxides in real time with high durability and a fine distribution, has recently been applied to ...various scientific and industrial fields, such as catalysis, sensing, and renewable energy. However, the high‐temperature processing required for ex‐solutions (>700 °C) limits the applicable material compositions and has hindered advances in this technique. Here, an unprecedented approach is reported for low‐temperature particle ex‐solution on important nanoscale binary oxides. WO3 with a nanosheet structure is selected as the parent oxide, and Ir serves as the active metal species that produces the ex‐solved metallic particles. Importantly, Ir doping facilitates a phase transition in the WO3 bulk lattice, which further promotes Ir ex‐solution at the oxide surface and eventually enables the formation of Ir particles (<3 nm) at temperatures as low as 300 °C. Low‐temperature ex‐solution effectively inhibits the agglomeration of WO3 sheets while maintaining well‐dispersed ex‐solved particles. Furthermore, the Ir‐decorated WO3 sheets show excellent durability and H2S selectivity when used as sensing materials, suggesting that this is a generalizable synthetic strategy for preparing highly robust heterogeneous catalysts for a variety of applications.
The in situ growth of Ir nanoparticles on a binary oxide as a new class in ex‐solution phenomena is described. The Ir nanoparticles are uniformly anchored on WO3 host oxides and their formation mechanism is demonstrated by in situ analysis and simulations. The Ir‐catalyst‐loaded WO3 shows extremely high selectivity to H2S with outstanding stability.
2D heterogeneous oxide nanosheets (NSs) have attracted much attention in various scientific fields owing to their exceptional physicochemical properties. However, the fabrication of 2D oxide NSs with ...abundant p–n interfaces and large amounts of mesopores is extremely challenging. Here, a facile synthesis of highly porous 2D heterogeneous oxide NSs (e.g., SnO2/CoOx) is suggested through a 2D oxide exfoliation approach combined with a fast galvanic replacement reaction (GRR). The ultrathin (<5 nm) layered CoOx NSs are simply prepared by ion‐exchange exfoliation and a subsequent GRR process that induces a rapid phase transition from p‐type CoOx to n‐type SnO2 metal oxides (<10 min). The controlled GRR process enables the creation of heterogeneous SnO2/CoOx NSs consisting of small SnO2 grain sizes (<10 nm), high porosity, numerous heterojunctions, and sub‐10 nm thickness, which are highly advantageous characteristics for chemiresistive sensors. Due to the advantage of these features, the porous SnO2/CoOx NSs exhibit an unparalleled HCHO‐sensing performance (Rair/Rgas > 35 @ 5 ppm with a response speed of 9.34 s) with exceptional selectivity compared to that of the state‐of‐the‐art metal oxide‐based HCHO gas sensors.
Highly porous heterogeneous SnO2/CoOx 2D nanosheets are successfully achieved by exfoliation combined with a galvanic replacement reaction. The thin‐walled (<5 nm) exfoliated p‐type CoOx nanosheets are transformed into porous, thin‐walled (<10 nm) n‐type SnO2 nanosheets via galvanic replacement. The porous SnO2/CoOx 2D nanosheets show superior HCHO‐sensing performance with stable mechanical flexibility compared to reported state‐of‐the‐art HCHO sensors.
2D Ru oxide nanosheets (NSs) with optically punched nanoholes are synthesized and integrated on a flexible heating substrate, i.e., silver nanowire (Ag NW)‐embedded colorless polyimide (cPI) film, ...for application in wearable chemical sensors. Multiple discrete pores on the sub‐5‐nm scale are formed on the basal planes of Ru oxide NSs by irradiation of intense pulsed light. The chemical sensing characteristic of the porous Ru oxide NSs toward nitrogen dioxide (NO2) is investigated under controlled temperatures by applying DC voltage to the Ag NW‐embedded cPI film. The improved NO2 responding and recovery kinetics are achieved using the porous Ru oxide NSs with sensitivity of 1.124% at 20 ppm at a film temperature of 80.3 °C. A wireless patch‐type sensor module is developed to demonstrate wearable sensing of NO2 using the Ru oxide NSs on Ag NW‐embedded cPI heating film. This work paved the new way for application of atomically thin and porous Ru oxide NSs in chemical sensors, which can detect hazardous species in real time.
Porous 2D Ru oxide nanosheets (NSs) are achieved on silver nanowire (Ag NW)‐embedded colorless polyimide (cPI) heating film for wearable chemical sensors. Atomically thin Ru oxide NSs with sub‐5‐nm‐scale pores exhibit improved response and recovery kinetics under the controlled operating temperatures of an Ag‐NW‐embedded cPI heater.
Conductive metal–organic frameworks (cMOFs) are emerging materials for various applications due to their high surface area, high porosity, and electrical conductivity. However, it is still ...challenging to develop cMOFs having high surface reactivity and durability. Here, highly active and stable cMOF are presented via the confinement of bimetallic nanoparticles (BNPs) in the pores of a 2D cMOF, where the confinement is guided by dipolar‐interaction‐induced site‐specific nucleation. Heterogeneous metal precursors are bound to the pores of 2D cMOFs by dipolar interactions, and the subsequent reduction produces ultrasmall (≈1.54 nm) and well‐dispersed PtRu NPs confined in the pores of the cMOF. PtRu‐NP‐decorated cMOFs exhibit significantly enhanced chemiresistive NO2 sensing performances, owing to the bimetallic synergies of PtRu NPs and the high surface area and porosity of cMOF. The approach paves the way for the synthesis of highly active and conductive porous materials via bimetallic and/or multimetallic NP loading.
Ultrasmall bimetallic nanoparticles (BNPs) are confined in pores of 2D conductive metal–organic frameworks (cMOFs). BNPs in cMOFs significantly improve the NO2‐sensing performance, owing to the bimetallic synergies of PtRu NPs and the high surface area and porosity of the cMOF.
Nanoscale materials offer enormous opportunities for catalysis, sensing, energy storage, and so on, along with their superior surface activity and extremely large surface area. Unfortunately, their ...strong reactivity causes severe degradation and oxidation even under ambient conditions and thereby deteriorates long‐term usability. Here superlative stable graphene‐encapsulated nanoparticles with a narrow diameter distribution prepared via in situ chemical vapor deposition (CVD) are presented. The judiciously designed CVD protocol generates 3 nm size metal and ceramic nanoparticles intimately encapsulated by few‐layer graphene shells. Significantly, graphene‐encapsulated Co3O4 nanoparticles exhibit outstanding structural and functional integrity over 2000 cycles of lithiation/delithiation for Li‐ion battery anode application, accompanied by 200% reversible volume change of the inner core particles. The insight obtained from this approach offers guidance for utilizing high‐capacity electrode materials for Li‐ion batteries. Furthermore, this in situ CVD synthesis is compatible with many different metal precursors and postsynthetic treatments, including oxidation, phosphidation, and sulfidation, and thus offers a versatile platform for reliable high‐performance catalysis and energy storage/conversion with nanomaterials.
Few‐layer‐graphene‐encapsulated 3 nm size metal and ceramic nanoparticles with a narrow distribution are generated via in situ chemical vapor deposition. Significantly, graphene‐encapsulated Co3O4 nanoparticles exhibit outstanding structural and functional integrity over 2000 cycles of lithiation/delithiation for Li‐ion battery anode application.
Nanoscale structure engineering is in high demand for various applications of 2D transition metal dichalcogenides (TMDs). An edge‐exposed 2D polycrystalline MoS2 nanomesh thin film is demonstrated ...via block copolymer (BCP) nanopatterning. Molybdenum nanomesh structure is formed by direct metal deposition of hexagonal cylinder BCP nanotemplate and the following lift‐off process. Subsequent sulfurization of the molybdenum nanomesh creates MoS2 nanomesh thin films without any degradative etching step. The approach is applicable to not only other metal sulfides and oxides but also other nanoscale structures of TMD thin films including nanodot and nanowire array by means of various BCP nanotemplate shapes. As the edge site of MoS2 is highly active for NO2 sensing, the edge‐exposed MoS2 nanomesh demonstrates sevenfold enhancement of sensitivity for NO2 molecules compared to uniform thin film as well as superior reversibility even under 80% relative humidity environment. This structure engineering method could greatly strengthen the potential application of 2D TMD materials with the optimal customized nanoscale structures.
Nanopatterning of transition metal dichalcogenides (TMD) is presented. By exploiting block copolymer nanotemplate, desired metal nanopattern, including nanomesh, nanodot, and nanowire arrays, can be readily obtained with large area. The post sulfurization process gives rise to nanopattered TMD. The edge‐exposed MoS2 nanomesh exhibits a sevenfold enhancement of sensitivity for NO2 sensing and superior reversibility compared to the uniform thin film.
In response to the demand for flexible and sustainable energy storage devices that exhibit high electrochemical performance, a supercapacitor system is fabricated using mulberry tree‐derived paper as ...a substrate and Poly(3,4‐ethylenedioxythiophene)‐poly(styrenesulfonate) (PEDOT:PSS) and carbon black as the active material. The mulberry paper‐based supercapacitor system demonstrates high energy density of 29.8–39.8 Wh kg−1 and power density of 2.8–13.9 kW kg−1 with 90.7% retention of its initial capacity over 15 000 charge–discharge cycles. In addition, the mulberry tree fibers are known to have superior mechanical strength and toughness and the mulberry paper‐based supercapacitor; as a result, exhibit high mechanical and chemical toughness; 99% of its initial capacity is retained after 100 repeated applications of bending strains, and twisting. 94% capacity retention is observed even after exposure to HCl and H2SO4 acid solutions. The fabrication methodology of the mulberry‐based supercapacitor is highly scalable and could be stacked to increase the energy storage capacity, where operation of light‐emitting diode lights with a drive voltage of 12 V integrated in a wearable device is demonstrated.
A supercapacitor system is fabricated using mulberry tree‐derived paper as a substrate and PEDOT:PSS and carbon black as the active material. The mulberry tree fibers are known to have superior mechanical strength and toughness and therefore, the mulberry paper‐based supercapacitor exhibits high mechanical and chemical toughness as well as high capacitance for potential large‐scale and wearable energy storage application.
Activation of metal oxides by light is a robust yet facile approach to manipulating their surface chemistry for favorable reactions with target molecules in heterogeneous catalysis and gas sensors. ...However, a limited understanding of interface chemistry and the involved mechanism impedes the development of a rational design of oxide interfaces for light‐activated gas sensing. Herein, the TiOx‐assisted photosensitization of In2O3 toward NO2 sensing is investigated as a case study to elucidate the detailed mechanism of light‐activated surface chemistry at the metal/gas interface. The resultant heterogeneous oxides exhibit outstanding NO2 sensing performance under light irradiation thanks to abundant photoexcited electrons and holes that serve as adsorption and desorption sites, respectively, to accelerate both surface reactions. Furthermore, the facile transfer of electrons and holes across the TiOx‐In2O3 interface contributes to improving the reversibility of sensing kinetics. Through this study, the mechanistic understanding is established of how the surface chemistry of metal oxide surfaces can be tuned by light activation providing an effective route to the design fabrication of high‐performance gas sensors.
The surface chemistry of metal oxides is systematically investigated in light‐activated NO2 detection. The heterojunction between oxide interfaces is the key to the significantly improved sensing performance under optimal light. An in‐depth understanding of the sensing mechanism mediated by photogenerated electrons and holes is also provided.
Design of bifunctional multimetallic alloy catalysts, which are one of the most promising candidates for water splitting, is a significant issue for the efficient production of renewable energy. ...Owing to large dimensions of the components and composition of multimetallic alloys, as well as the trade‐off behavior in terms of the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) overpotentials for bifunctional catalysts, it is difficult to search for high‐performance bifunctional catalysts with multimetallic alloys using conventional trial‐and‐error experiments. Here, an optimal bifunctional catalyst for water splitting is obtained by combining Pareto active learning and experiments, where 110 experimental data points out of 77946 possible points lead to effective model development. The as‐obtained bifunctional catalysts for HER and OER exhibit high performance, which is revealed by model development using Pareto active learning; among the catalysts, an optimal catalyst (Pt0.15Pd0.30Ru0.30Cu0.25) exhibits a water splitting behavior of 1.56 V at a current density of 10 mA cm−2. This study opens avenues for the efficient exploration of multimetallic alloys, which can be applied in multifunctional catalysts as well as in other applications.
Here, optimization process of bifunctional water splitting catalyst by the interplay of experiment and Pareto active learning is done to explore high‐performance catalyst. Out of 77946 possible data points, only 110 experimental data points are enough to effectively develop the model, and the discovered catalyst shows high performance both for hydrogen evolution reaction and oxygen evolution reaction.
