An important reason for the century-long debate concerning wetting dynamics is the lack of decisive information about the contact line. The contact line cannot be treated as a geometric line but is ...rather a region with complex structures. The contact line regions have been intensively explored in recent years by utilizing advanced nanoscopic experimental and modeling methods. This feature article summarizes the primary observation results and related modeling progress. A framework is then proposed for understanding the wetting dynamics. Basic questions are raised for future research on the partial wetting of nonvolatile as well as volatile liquids.
The bifunctional electrocatalysis of oxygen reduction reactions (ORRs) and oxygen evolution reactions (OERs) is critical for the development of rechargeable Zn–air batteries. Both ORRs and OERs ...suffer from sluggish kinetics and high overpotentials, and the bifunctional reactivity is limited by the scaling relationship. Therefore, smart designs on electrocatalysts are requested to achieve high bifunctional ORR/OER activity and excellent performance in Zn–air batteries. Herein, the requirements for bifunctional oxygen electrocatalysts are first introduced. Then the recent advances of precious‐metal‐free active materials and regulation methods of their intrinsic activity are introduced. The structural design principles to improve the accessibility of the active sites are further presented. Finally, a brief overview of the applications of bifunctional oxygen electrocatalysts in Zn–air batteries, including routine liquid batteries and flexible solid‐state batteries, is presented. This review affords rational design principles and strategies for nonprecious bifunctional ORR/OER electrocatalysts, which are expected to guide the targeted optimization of electrocatalysts and further exploration of emerging candidates.
The design strategies of nonprecious metal bifunctional oxygen electrocatalysts have been comprehensively summarized, considering the intrinsic activity and structure features. Recent progress on metal‐free and transition‐metal‐based bifunctional electrocatalysts for oxygen reduction and evolution reactions is reviewed. A brief overview of their applications in liquid and solid‐state Zn−air batteries is also presented.
Rechargeable flexible solid Zn‐air battery, with a high theoretical energy density of 1086 Wh kg−1, is among the most attractive energy technologies for future flexible and wearable electronics; ...nevertheless, the practical application is greatly hindered by the sluggish oxygen reduction reaction/oxygen evolution reaction (ORR/OER) kinetics on the air electrode. Precious metal‐free functionalized carbon materials are widely demonstrated as the most promising candidates, while it still lacks effective synthetic methodology to controllably synthesize carbocatalysts with targeted active sites. This work demonstrates the direct utilization of the intrinsic structural defects in nanocarbon to generate atomically dispersed Co–Nx–C active sites via defect engineering. As‐fabricated Co/N/O tri‐doped graphene catalysts with highly active sites and hierarchical porous scaffolds exhibit superior ORR/OER bifunctional activities and impressive applications in rechargeable Zn‐air batteries. Specifically, when integrated into a rechargeable and flexible solid Zn‐air battery, a high open‐circuit voltage of 1.44 V, a stable discharge voltage of 1.19 V, and a high energy efficiency of 63% at 1.0 mA cm−2 are achieved even under bending. The defect engineering strategy provides a new concept and effective methodology for the full utilization of nanocarbon materials with various structural features and further development of advanced energy materials.
A defect‐engineering strategy in nanocarbon is developed to generate atomically dispersed Co–Nx–C active sites for effective electrocatalysts. As‐obtained Co/N/O tri‐doped graphene exhibits excellent oxygen reduction reaction/oxygen evolution reaction bifunctional activities and impressive performances in rechargeable and flexible Zn‐air batteries. This work provides a novel concept to fully utilize the structural defects in nanocarbon for advanced energy storage and conversion.
It has always been critical to develop high‐performance polymeric materials with exceptional mechanical strength and toughness, thermal stability, and even healable properties for meeting performance ...requirements in industry. Conventional chemical cross‐linking leads to enhanced mechanical strength and thermostability at the expense of extensibility due to mutually exclusive mechanisms. Such major challenges have recently been addressed by using noncovalent cross‐linking of reversible multiple hydrogen‐bonds (H‐bonds) that widely exist in biological materials, such as silk and muscle. Recent decades have witnessed the development of many tailor‐made high‐performance H‐bond cross‐linked polymeric materials. Here, recent advances in H‐bond cross‐linking strategies are reviewed for creating high‐performance polymeric materials. H‐bond cross‐linking of polymers can be realized via i) self‐association of interchain multiple H‐bonding interactions or specific H‐bond cross‐linking motifs, such as 2‐ureido‐4‐pyrimidone units with self‐complementary quadruple H‐bonds and ii) addition of external cross‐linkers, including small molecules, nanoparticles, and polymer aggregates. The resultant cross‐linked polymers normally exhibit tunable high strength, large extensibility, improved thermostability, and healable capability. Such performance portfolios enable these advanced polymers to find many significant cutting‐edge applications. Major challenges facing existing H‐bond cross‐linking strategies are discussed, and some promising approaches for designing H‐bond cross‐linked polymeric materials in the future are also proposed.
Hydrogen‐bond cross‐linking has recently emerged as a promising strategy for creating high‐performance polymeric materials via self‐association of multiple hydrogen bonds or the addition of external cross‐linkers. These polymers exhibit a unique combination of high strength, large extensibility, thermostability, and even healable capability. Such a performance portfolio enables these polymeric materials to find many potential applications in the electronics and gas‐separation fields.
The emergence of van der Waals (vdW) heterostructures of 2D materials has opened new avenues for fundamental scientific research and technological applications. However, the current concepts and ...strategies of material engineering lack feasibilities to comprehensively regulate the as‐obtained extrinsic physicochemical characters together with intrinsic properties and activities for optimal performances. A 3D mesoporous vdW heterostructure of graphene and nitrogen‐doped MoS2 via a two‐step sequential chemical vapor deposition method is constructed. Such strategy is demonstrated to offer an all‐round engineering of 2D materials including the morphology, edge, defect, interface, and electronic structure, thereby leading to robustly modified properties and greatly enhanced electrochemical activities. The hydrogen evolution is substantially accelerated on MoS2, while the oxygen reduction and evolution are significantly improved on graphene. This work provides a powerful overall engineering strategy of 2D materials for electrocatalysis, which is also enlightening for other nanomaterials and energy‐related applications.
A 3D mesoporous van der Waals heterostructure of graphene and nitrogen‐doped MoS2 is fabricated through a two‐step sequential chemical vapor deposition method. This affords an all‐round engineering of 2D materials including the morphology, edges, defects, interfaces, and electronic structure, thereby leading to robustly modified properties and greatly enhanced electrochemical activities.
Oxygen reduction reaction (ORR), oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) are three key reactions for the development of green and sustainable energy systems. Efficient ...electrocatalysts for these reactions are highly desired to lower their overpotentials and promote practical applications of related energy devices. Metal-organic frameworks (MOFs) have recently emerged as precursors to fabricate carbon-based electrocatalysts with high electrical conductivity and uniformly distributed active sites. In this review, the current progress of MOF-derived carbon-based materials for ORR/OER/HER electrocatalysis is presented. Materials design strategies of MOF-derived carbon-based materials are firstly summarized to show the rich possibilities of the morphology and composition of MOF-derived carbon-based materials. A wide range of applications based on these materials for ORR, OER, HER and multifunctional electrocatalysis are discussed, with an emphasis on the required features of MOF-derived carbon-based materials for the electrocatalysis of corresponding reactions. Finally, perspectives on the development of MOF-derived carbon-based materials for ORR, OER and HER electrocatalysis are provided.
The morphology and composition design of MOF-derived carbon-based materials and their applications for electrocatalytic ORR, OER and HER are reviewed.
Bimetallic metal-organic frameworks (MOFs) have two different metal ions in the inorganic nodes. According to the metal distribution, the architecture of bimetallic MOFs can be classified into two ...main categories namely solid solution and core-shell structures. Various strategies have been developed to prepare bimetallic MOFs with controlled compositions and structures. Bimetallic MOFs show a synergistic effect and enhanced properties compared to their monometallic counterparts and have found many applications in the fields of gas adsorption, catalysis, energy storage and conversion, and luminescence sensing. Moreover, bimetallic MOFs can serve as excellent precursors/templates for the synthesis of functional nanomaterials with controlled sizes, compositions, and structures. Bimetallic MOF derivatives show exposed active sites, good stability and conductivity, enabling them to extend their applications to the catalysis of more challenging reactions and electrochemical energy storage and conversion. This review provides an overview of the significant advances in the development of bimetallic MOFs and their derivatives with special emphases on their preparation and applications.
This review summarizes the design and synthesis of bimetallic MOFs and their derivatives, with superior performance to their monometallic counterparts in many applications.
Conspectus Various gas-involving energy electrocatalysis, including oxygen reduction reaction (ORR), oxygen evolution reaction (OER), and hydrogen evolution reaction (HER), has witnessed increasing ...concerns recently for the sake of clean, renewable, and efficient energy technologies. However, these heterogeneous reactions exhibit sluggish kinetics due to multistep electron transfer and only occur at triple-phase boundary regions. Up to now, tremendous attention has been attracted to develop cost-effective and high-performance electrocatalysts to boost the electrocatalytic activities as promising alternatives to noble metal counterparts. In addition to the prolific achievements in materials science, the advances in interface chemistry are also very critical in consideration of the complex phenomena proceeded at triple-phase boundary regions, such as mass diffusion, electron transfer, and surface reaction. Therefore, insightful principles and effective strategies for a comprehensive optimization, ranging from active sites to electrochemical interface, are necessary to fully enhance the electrocatalytic performance aiming at practical device applications. In this Account, we give an overview of our recent attempts toward efficient gas-involving electrocatalysis with multiscale principles from the respect of electronic structure, hierarchical morphology, and electrode interface step by step. It is widely accepted that the intrinsic activity of individual active sites is directly influenced by their electronic structure. Heteroatom doping and topological defects are demonstrated to be the most effective strategies for metal-free nanocarbon materials, while the cationic (e.g., Ni, Fe, Co, Sn) and anionic (e.g., O, S, OH) regulation is revealed to be a promising method for transition metal compounds, to alter the electronic structure and generate high activity. Additionally, the apparent activity of the whole electrocatalyst is significantly impacted by its hierarchical morphology. The active sites of nanocarbon materials are expected to be enriched on the surface for a full exposure and utilization; the hybridization of other active components with nanocarbon materials should achieve a uniform dispersion in nanoscale and a strongly coupled interface, thereby ensuring the electron transfer and boosting the activity. Furthermore, steady and favorable electrochemical interfaces are strongly anticipated in working electrodes for optimal reaction conditions. The powdery electrocatalysts are suggested to be constructed into self-supported electrodes for more efficient and stable catalysis integrally, while the local microenvironment can be versatilely modified by ionic liquids with more beneficial gas solubility and hydrophobicity. Collectively, with the all-round regulation of the electronic structure, hierarchical morphology, and electrode interface, the electrocatalytic performances are demonstrated to be comprehensively facilitated. Such multiscale principles stemmed from the in-depth insights on the structure–activity relationship and heterogeneous reaction characteristics will no doubt pave the way for the future development of gas-involving energy electrocatalysis, and also afford constructive inspirations in a broad range of research including CO2 reduction reaction, hydrogen peroxide production, nitrogen reduction reaction, and other important electrocatalytic activation of small molecules.
Bifunctional electrocatalysis for oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) constitutes the bottleneck of various sustainable energy devices and systems like rechargeable ...metal–air batteries. Emerging catalyst materials are strongly requested toward superior electrocatalytic activities and practical applications. In this study, transition metal hydroxysulfides are presented as bifunctional OER/ORR electrocatalysts for Zn–air batteries. By simply immersing Co‐based hydroxide precursor into solution with high‐concentration S2−, transition metal hydroxides convert to hydroxysulfides with excellent morphology preservation at room temperature. The as‐obtained Co‐based metal hydroxysulfides are with high intrinsic reactivity and electrical conductivity. The electron structure of the active sites is adjusted by anion modulation. The potential for 10 mA cm−2 OER current density is 1.588 V versus reversible hydrogen electrode (RHE), and the ORR half‐wave potential is 0.721 V versus RHE, with a potential gap of 0.867 V for bifunctional oxygen electrocatalysis. The Co3FeS1.5(OH)6 hydroxysulfides are employed in the air electrode for a rechargeable Zn–air battery with a small overpotential of 0.86 V at 20.0 mA cm−2, a high specific capacity of 898 mAh g−1, and a long cycling life, which is much better than Pt and Ir‐based electrocatalyst in Zn–air batteries.
Transition metal hydroxysulfides are proposed as bifunctional electrocatalysts in working Zn–air batteries with high oxygen evolution reaction/oxygen reduction reaction reactivities, high power densities, large capacities, and extraordinary stabilities. These transition metal hydroxysulfides are fabricated through a novel room‐temperature sulfurization strategy, which opens new doors to materials innovation of transition metal (hydro/oxy)sulfides and their practical applications in hetero/electrocatalysis, energy storage, and healthcare applications.
A cost‐effective and highly efficient oxygen evolution reaction (OER) electrocatalyst will be significant for the future energy scenario. The emergence of the core–shell heterostructure has invoked ...new feasibilities to inspire the full potential of non‐precious‐metal candidates. The shells always have a large thickness, affording robust mechanical properties under harsh reaction conditions, which limits the full exposure of active sites with highly intrinsic reactivity and extrinsic physicochemical characters for optimal performance. Herein, a nanosized CoNi hydroxide@hydroxysulfide core–shell heterostructure is fabricated via an ethanol‐modified surface sulfurization method. Such a synthetic strategy is demonstrated to be effective in controllably fabricating a core–shell heterostructure with an ultrathin shell (4 nm) and favorable exposure of active sites, resulting in a moderately regulated electronic structure, remarkably facilitated charge transfer, fully exposed active sites, and a strongly coupled heterointerface for energy electrocatalysis. Consequently, the as‐obtained hydroxide@hydroxysulfide core–shell is revealed as a superior OER catalyst, with a small overpotential of 274.0 mV required for 10.0 mA cm−2, a low Tafel slope of 45.0 mV dec−1, and a favorable long‐term stability in 0.10 M KOH. This work affords fresh concepts and strategies for the design and fabrication of advanced core–shell heterostructures, and thus opens up new avenues for the targeted development of high‐performance energy materials.
A CoNi hydroxide@hydroxysulfide core–shell heterostructure is fabricated via an ethanol‐modified surface sulfurization method with favorable electronic and interface engineering, resulting in excellent intrinsic activity, favorable extrinsic physicochemical characters, and thereby superior water oxidation performances.
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