Capillary-Driven Separate Gas-Liquid Transport: Alleviating Mass Transport Losses for Efficient Hydrogen Evolution.

Developing earth-abundant transition metal electrodes with high activity and durability is crucial for efficient and cost-effective hydrogen production. However, numerous studies in the hydrogen evolution reaction (HER) primarily focus on improving the inherent activity of catalysts, and the critical influence of gas-liquid countercurrent transport behavior is often overlooked. In this study, we introduce the concept of separate-path gas-liquid transport to alleviate mass transport losses for the HER by developing a novel hierarchical porous Ni-doped cobalt phosphide electrode (CoNix-P@Ni). The CoNix-P@Ni electrodes with abundant microvalleys and crack structures facilitate the gas-liquid cotransport by separating the bubble release and water supply paths. Visualization and numerical simulation results demonstrate that cracks primarily serve as water supply paths, with capillary pressure facilitating the transport of water from the cracks to the microvalleys. This process ensures the continuous wetting of electrolytes in the electrode, reduces hydrogen supersaturation near the active site, and increases hydrogen transport flux to the microvalleys for accelerating bubble growth. Additionally, the microvalleys act as preferential sites for bubble evolution, preventing bubble coverage on other active sites. By regulating the amount of nickel, the CoNi1-P@Ni electrode exhibited the smallest and densest microvalleys and cracks, achieving superior HER performance with an overpotential of 51 mV at 10 mA cm-2. The results offer a promising direction for constructing high-performance HER electrodes.

Enabling All-Solid-State Lithium-Carbon Dioxide Battery Operation in a Wide Temperature Range.

Flexible all-solid-state lithium-carbon dioxide batteries (FASSLCBs) are recognized as a next-generation energy storage technology by solving safety and shuttle effect problems. However, the present FASSLCBs rely heavily on high-temperature operation due to sluggish solid-solid-gas multiphase mass transfer and unclear capacity degradation mechanism. Herein, we designed bicontinuous hierarchical porous structures (BCHPSs) for both solid polymer electrolyte and cathode for FASSLCBs to facilitate the mass transfer in all connected directions. The formed large Lewis acidic surface effectively promotes the lithium salt dissociation and the CO2 conversion. Furthermore, it is unraveled that the battery capacity degradation originates from the "dead Li2CO3" formation, which is inhibited by the fast decomposition of Li2CO3. Accordingly, the assembled FASSLCBs exhibit an excellent cycling stability of 133 cycles at 60 °C, which is 2.7 times longer than that without BCHPSs, and the FASSLCBs can be operated repeatedly even at room temperature. This BCHPS method and fundamental deactivation mechanism provide a perspective for designing FASSLCBs with long cycling life.

A Long-Life and Excellent Rate-Capability Aqueous Zn-Benzoquinone Battery Enabled by Iodine-Catalyzed Cathode.

Benzoquinone (BQ) is considered to be a desirable cathode material for aqueous zinc-based batteries. The major limitations of BQ electrode are the severe sublimation and poor electrical conductivity, which results in serious mass loss during electrode preparation and inferior rate performance. In this study, iodine (I2 ) species are utilized as an efficient catalyst for the highly reversible conversion of BQ/BQ2- couple in the Zn-BQ battery system, wherein N-doped porous carbon is employed as a host material for anchoring the BQ molecule. In the combination electrode (denoted as BQ-I@NPC) with 1wt% I2 additive where I2 can serve as a carrier to accelerates the Zn2+ transmission, and reduce the voltage hysteresis of the electrode. As a result, the BQ-I@NPC cathode delivers a high specific capacity of ≈482 mAh g-1 at 0.25 A g-1 , realizing a high energy density of 545 Wh kg-1 (based on BQ), which is the highest values among reported organic cathode materials for aqueous Zn-based batteries. Also, a high BQ loading (8 mg cm-2 ) can be attained, and achieving a superior cycling stability with a capacity retention of ≈80% after 20,000 times at 10 C. The work proposes an effective approach toward high performance organic electrode materials.

Sodium Storage Properties of Carbonaceous Flowers.

As a promising energy storage system, sodium-ion batteries face challenges related to the stability and high-rate capability of their electrode materials, especially carbon, which is the most studied anode. Previous studies have demonstrated that three-dimensional architectures composed of porous carbon materials with high electrical conductivity have the potential to enhance the storage performance of sodium-ion batteries. Here, high-level N/O heteroatoms-doped carbonaceous flowers with hierarchical pore architecture are synthesized through the direct pyrolysis of homemade bipyridine-coordinated polymers. The carbonaceous flowers could provide effective transport pathways for electrons/ions, thus allowing for extraordinary storage properties in sodium-ion batteries. As a consequence, sodium-ion battery anodes made of carbonaceous flowers exhibit outstanding electrochemical features, such as high reversible capacity (329 mAh g-1 at 30 mA g-1), superior rate capability (94 mAh g-1 at 5000 mA g-1), and ultralong cycle lifetimes (capacity retention rate of 89.4% after 1300 cycles at 200 mA g-1). To better investigate the sodium insertion/extraction-related electrochemical processes, the cycled anodes are experimentally analyzed with scanning electron microscopy and transmission electron microscopy. The feasibility of the carbonaceous flowers as anode materials was further investigated using a commercial Na3V2(PO4)3 cathode for sodium-ion full batteries. All these findings indicate that carbonaceous flowers may possess great potential as advanced materials for next-generation energy storage applications.

Zinc-Mediated Template Synthesis of Hierarchical Porous N-Doped Carbon Electrocatalysts for Efficient Oxygen Reduction.

The development of highly active and low-cost catalysts for use in oxygen reduction reaction (ORR) is crucial to many advanced and eco-friendly energy techniques. N-doped carbons are promising ORR catalysts. However, their performance is still limited. In this work, a zinc-mediated template synthesis strategy for the development of a highly active ORR catalyst with hierarchical porous structures was presented. The optimal catalyst exhibited high ORR performance in a 0.1 M KOH solution, with a half-wave potential of 0.89 V vs. RHE. Additionally, the catalyst exhibited excellent methanol tolerance and stability. After a 20,000 s continuous operation, no obvious performance decay was observed. When used as the air-electrode catalyst in a zinc-air battery (ZAB), it delivered an outstanding discharging performance, with peak power density and specific capacity as high as 196.3 mW cm-2 and 811.5 mAh gZn-1, respectively. Its high performance and stability endow it with potential in practical and commercial applications as a highly active ORR catalyst. Additionally, it is believed that the presented strategy can be applied to the rational design and fabrication of highly active and stable ORR catalysts for use in eco-friendly and future-oriented energy techniques.

Hierarchical porous tri-metallic NiCoFe-Se/CFP derived from Ni-Co-Fe Prussian blue analogues as efficient electrocatalyst for oxygen evolution reaction.

The progress of inexpensive, high-efficiency, and steady oxygen evolution reaction (OER) electrocatalysts is of great importance to promoting water splitting for green hydrogen production. Herein, tri-metallic NiCoFe selenide catalyst backed up by carbon fiber paper (CFP) was synthesized by a facile selenization of NiCoFe Prussian blue analogues (PBAs) for OER in alkaline solutions. The NiCoFe-Se/CFP inherited the porous nanostructure of the metal-organic frameworks (MOFs) precursors prepared by rapid cyclic voltammetry electrodeposition. Benefiting from the 3D hierarchical porous structure, optimized electronic structure of NiCoFe selenides and high conductivity, the synthesized electrocatalyst exhibits outstanding catalytic activity to the corresponding mono-metallic or bi-metallic selenides. Specifically, the NiCoFe-Se/CFP electrode demands an overpotential of 221 mV to attain the 10 mA cm-2 current density in 1.0 M KOH solution and a low Tafel slope of 38.6 mV dec-1. The prepared catalyst also displays good stability and durability. These findings prove a feasible strategy to further improve the catalytic activities of non-precious metal based OER electrocatalysts by the cooperation of structure design and chemical component modification.

Matching CP@NCOH/NF Cathode and GH/FNP/NF Anode for High-Performance Asymmetric Supercapacitor.

It is extremely crucial to design and match high-quality cathode and anode for achieving high-performance asymmetric supercapacitors (ASCs). Herein, Co3 (PO4 )2 @NiCo-LDH/Ni foam (CP@NCOH/NF) cathode with hierarchical morphology and graphene hydrogel/Fe-Ni phosphide/Ni foam (GH/FNP/NF) anode with the robust and porous structure are elaborately designed and prepared, respectively. Owing to their unique and profitable structures, both CP@NCOH/NF and GH/FNP/NF electrodes yield the superior capacity (10760 and 2236 mC cm-2 at 2 mA cm-2 , respectively), good rate capability (63% retention at 200 mA cm-2 and 52% retention at 50 mA cm-2 , respectively), and excellent cycling stability (72% and 74% retention after 10 000 cycles, respectively). Benefiting from their matchable electrochemical performances, the configured solid-state CP@NCOH/NF//GH/FNP/NF ASC outputs both competitive energy density (80.2 Wh kg-1 /4.1 mWh cm-3 ) and power density (14563 W kg-1 /750 mW cm-3 ), companied by remarkable cyclability (71% retention after 10 000 cycles), manifesting its great promise for large-scale integrated energy-storage system.

Porous Carbon Nanofiber Flexible Membranes via a Bottlebrush Copolymer Template for Enhanced High-Performance Supercapacitors.

We report a method to construct ordered hierarchical porous structures in carbon nanofiber membranes using poly(ethylene oxide)-block-polydimethylsiloxane bottlebrush block copolymers (BBCPs) as templates. The BBCPs self-assemble into a spherical morphology driven by small-molecule hydrogen bond donors which act as bridges between carbon precursors and templates to promote uniform dispersion of the templates. We successfully obtained flexible, self-supporting, and porous carbon nanofiber membranes (PCNFs) with high porosity. Then, a supercapacitor electrode was independently prepared using PCNFs as an active substance without infiltrating any conductive agents or binders. The PCNFs exhibit excellent performance with a capacitance of 234.1 F g-1 at a current density of 1 A g-1 owing to the abundant hierarchical porous structures and high content of nitrogen and oxygen elements internally. The aqueous symmetric supercapacitor prepared using PCNFs electrodes maintains more than 95% capacitance retention after 55,000 charge-discharge cycles. Furthermore, the capacitance retention reaches up to 67.72% at a current density of 50 A g-1 (compared to 1 A g-1), exhibiting excellent cycling stability and rate capability. Based on the excellent electrochemical performance and flexible self-supporting ability of PCNFs, this work is expected to facilitate the development of flexible displays, flexible sensors, wearable devices, and electrocatalysis.

Adaptive IR- and Water-Gating Textiles Based on Shape Memory Fibers.

Thermoregulation is an essential function of the human body for adapting to the surrounding temperature. Stimuli-responsive smart textiles can provide effective protection of the human skin temperature from a continuously changing environment. Herein, we develop a smart textile based on shape memory polymer (SMP) fibers for adaptive regulation of IR and water transmission on human skin. An SMP textile is fabricated with hierarchical micro/nanoporous structures to enhance thermal insulation performance, and silver nanowires are coated on one side to provide asymmetric IR reflectivity and hydrophilicity. The porous SMP textile shows great tunability of thermal insulation and asymmetric wettability by deformation and recovery of the shape and structure in response to stimuli. The degree of thermal insulation is controlled by 65.7% of the original value, and the surface temperature of the SMP textile on a hot plate is successfully controlled in the IR images due to adaptive IR reflectivity. Additionally, the directional transportation of water droplets can be switched on/off according to the shape of the SMP textiles, which can be employed for sweat removal from the human skin. This IR- and water-gating smart textile can provide a feasible strategy for protecting the human skin from external environmental changes.

Triple-Phase Interface Engineered Hierarchical Porous Electrode for CO2 Electroreduction to Formate.

The aqueous electrochemical CO2 reduction to valuable products is seen as one of the most promising candidates to achieve carbon neutrality yet still suffers from poor selectivity and lower current density. Highly efficient CO2 reduction significantly relies on well-constructed electrode to realize efficient and stable triple-phase contact of CO2 , electrolyte, and active sites. Herein, a triple-phase interface engineering approach featuring the combination of hierarchical porous morphology design and surface modification is presented. A hierarchical porous electrode is constructed by depositing bismuth nanosheet array on copper foam followed by trimethoxy (1H,1H,2H,2H-heptadecafluorodecyl) silane modification on the nanosheet surface. This electrode not only achieves highly selective and efficient CO2 reduction performance with formate selectivity above 90% over wide potentials and a partial current density over -90 mA cm-2 in H-cell but also maintains a superior stability during the long-term operation. It is demonstrated that this remarkable performance is attributed to the construction of efficient and stable triple-phase interface. Theoretical calculations also show that the modified surface optimizes the activation path by lowering thermodynamic barriers of the key intermediates *OCHO for the formation of formate during electrochemical CO2 reduction.

Directionally In Situ Self-Assembled, High-Density, Macropore-Oriented, CoP-Impregnated, 3D Hierarchical Porous Carbon Sheet Nanostructure for Superior Electrocatalysis in the Hydrogen Evolution Reaction.

3D ZIF-67-particles-impregnated cellulose-nanofiber nanosheets with oriented macropores are synthesized via directional-freezing-assisted in situ self-assembly, and converted to 3D CoP-nanoparticle (NP)-embedded hierarchical, but macropores-oriented, N-doped carbon nanosheets via calcination and phosphidation. The obtained nanoarchitecture delivers overpotentials at 10 and 50 mA cm-2 and Tafel slope of 82.1 and 113.4 mV and 40.8 mV dec-1 in 0.5 M H2 SO4 , and of 97.1 and 136.6 mV and 51.2 mV dec-1 in 1 M KOH, all of which are superior to those of the most reported non-noble-metal-based hydrogen evolution reaction (HER) catalysts. This catalyst even surpasses commercial Pt/C for a much lower overpotential at high current densities, which is essential for large-scale hydrogen production. Its catalytic activity can be further optimized to become one of the best in both 0.5 M H2 SO4 and 1 M KOH. The outstanding catalytic activity is ascribed to the uniformly-dispersed small CoP NPs in the 3D carbon sheets and the hierarchical nanostructure with rich oriented pores. This work develops a facile, economical, and universal self-assembly strategy to fabricate uniquely nanostructured hybrids to simultaneously promote charge transfer and mass transport, and also offers an inexpensive and high-performance HER catalyst toward industry-scale water splitting.

Robust Jumping Actuator with a Shrimp-Shell Architecture.

It is highly desirable to develop compact- and robust-film jumping robots that can withstand severe conditions. Besides, the demands for strong actuation force, large bending curvature in a short response time, and good environmental tolerance are significant challenges to the material design. To address these challenges, this paper reports the fabrication of a thin-film jumping actuator, which exhibits a shrimp-shell architecture, from a conjugated ladder polymer (cLP) that is connected by carbon nanotube (CNT) sheets. The hierarchical porous structure ensures the fast absorption and desorption of organic vapor, thereby achieving a high response rate. The actuator does not exhibit shape distortion at temperatures of up to 225 °C and in concentrated sulfuric acid, as well as when immersed in many organic solvents. This work avails a new design strategy for high-performance actuators that function under harsh and complicated conditions.

Hierarchical Porous, N-Containing Carbon Supports for High Loading Sulfur Cathodes.

The lithium-polysulfide (LiPS) dissolution from the cathode to the organic electrolyte is the main challenge for high-energy-density lithium-sulfur batteries (LSBs). Herein, we present a multi-functional porous carbon, melamine cyanurate (MCA)-glucose-derived carbon (MGC), with superior porosity, electrical conductivity, and polysulfide affinity as an efficient sulfur support to mitigate the shuttle effect. MGC is prepared via a reactive templating approach, wherein the organic MCA crystals are utilized as the pore-/micro-structure-directing agent and nitrogen source. The homogeneous coating of spherical MCA crystal particles with glucose followed by carbonization at 600 °C leads to the formation of hierarchical porous hollow carbon spheres with abundant pyridinic N-functional groups without losing their microstructural ordering. Moreover, MGC enables facile penetration and intensive anchoring of LiPS, especially under high loading sulfur conditions. Consequently, the MGC cathode exhibited a high areal capacity of 5.79 mAh cm-2 at 1 mA cm-2 and high loading sulfur of 6.0 mg cm-2 with a minor capacity decay rate of 0.18% per cycle for 100 cycles.

Lattice Matching Growth of Conductive Hierarchical Porous MOF/LDH Heteronanotube Arrays for Highly Efficient Water Oxidation.

The conjugation of metal-organic frameworks (MOFs) into different multicomponent materials to precisely construct aligned heterostructures is fascinating but elusive owing to the disparate interfacial energy and nucleation kinetics. Herein, a promising lattice-matching growth strategy is demonstrated for conductive MOF/layered double hydroxide (cMOF/LDH) heteronanotube arrays with highly ordered hierarchical porous structures enabling an ultraefficient oxygen evolution reaction (OER). CoNiFe-LDH nanowires are used as interior template to engineer an interface by inlaying cMOF and matching two crystal lattice systems, thus conducting a graft growth of cMOF/LDH heterostructures along the LDH nanowire. A class of hierarchical porous cMOF/LDH heteronanotube arrays is produced through continuously regulating the transformation degree. The synergistic effects of the cMOF and LDH components significantly promote the chemical and electronic structures of the heteronanotube arrays and their electroactive surface area. Optimized heteronanotube arrays exhibit extraordinary OER activity with ultralow overpotentials of 216 and 227 mV to deliver current densities of 50 and 100 mA cm-2 with a small Tafel slope of 34.1 mV dec-1 , ranking it among the best MOF and non-noble-metal-based catalysts for OER. The robust performance under high current density and vigorous gas bubble conditions enable such hierarchical MOF/LDH heteronanotube arrays as promising materials for practical water electrolysis.

Nitrogen- and Oxygen-Containing Three-Dimensional Hierarchical Porous Graphitic Carbon for Advanced Supercapacitor.

Three-dimensional hierarchical porous graphitic carbon (HPGC) were synthesized via one-step carbonization-activation and a catalytic strategy. The method can not only improve the graphitization degree of carbon materials, but also offer plentiful interfaces for charge accumulation and short paths for ion/electron transport. Polypyrrole, potassium hydroxide, and nickel acetate were used as the carbon precursors, activating agent, and catalyst, respectively. The retraction and dissolution of Ni caused the change of pore size in the material and led to the interconnected micro/nano holes. Nickel acetate played a significant role in enhancing the electrical conductivity, introducing pseudocapacitance, and promoting ion diffusion. In the supercapacitor, HPGC electrode exhibited a remarkable specific capacitance of 336.3 F g-1 under 0.5 A g-1 current density and showed high rate capability, even with large current densities applied (up to 50 A g-1). Moreover, HPGC showed optimal cycling stability with 97.4% capacitance retention followed by 3000 charge-discharge cycles. The excellent electrochemical performances coupled with a facile large-scale synthesis procedure make HPGC a promising alternative for supercapacitors.

Cellulose Fiber-Based Hierarchical Porous Bismuth Telluride for High-Performance Flexible and Tailorable Thermoelectrics.

Porous modification is a general approach to endowing the rigid inorganic thermoelectric (TE) materials with considerable flexibility, however, by which the TE performances are severely sacrificed. Thus, there remains an ongoing struggle against the trade-off between TE properties and flexibility. Herein, we develop a novel strategy to combine Bi2Te3 thick film with ubiquitous cellulose fibers (CFs) via an unbalanced magnetron sputtering technique. Owing to the nano-micro hierarchical porous structures and the excellent resistance to crack propagation of the Bi2Te3/CF architectures, the obtained sample with a nominal Bi2Te3 deposition thickness of tens of micrometers exhibits excellent mechanically reliable flexibility, of which the bending deformation radius could be as small as a few millimeters. Furthermore, the Bi2Te3/CF with rational internal resistance and tailorable shapes and dimensions are successfully fabricated for practical use in TE devices. Enhanced Seebeck coefficients are observed in the Bi2Te3/CF as compared to the dense Bi2Te3 films, and the lattice thermal conductivity is remarkably reduced due to the strong phonon scattering effect. As a result, the TE figure of merit, ZT, is achieved as high as ∼0.38 at 473 K, which competes with the best flexible TEs and can be further improved by optimizing the carrier concentrations. We believe this developed technique not only opens up a new window to engineer flexible TE materials for practical applications but also promotes the robust development of the fields, such as paper-based flexible electronics and thin-film electronics.

Organic dye removal from aqueous solutions by hierarchical calcined Ni-Fe layered double hydroxide: Isotherm, kinetic and mechanism studies.

Hierarchically porous nickel-iron-layered double hydroxide (NiFe-LDH) with a Ni2+/Fe3+ molar ratio of 3 was successfully synthesised through a simple hydrothermal route. After calcination at 400°C, NiFe-LDH transformed into nickel-iron-layered double oxides (NiFe-LDO). The as-prepared samples were characterised through X-ray powder diffraction, field emission scanning electron microscopy, energy dispersive X-ray spectroscopy, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy and nitrogen adsorption. The calcined and uncalcined NiFe-LDH was used as adsorbents to remove Congo red (CR) dye in an aqueous solution. The equilibrium adsorption data of NiFe-LDH and NiFe-LDO samples were well fitted to Langmuir model and were characterised by excellent adsorption capacities of 205 and 330mg/g, respectively. Pseudo-second-order kinetic and intra-particle diffusion models indicated that CR was well adsorbed on the adsorbent. The underlying adsorption mechanism was investigated and observed as anion exchange and reconstruction.

Colloidal Assembly of Hierarchically Structured Porous Supraparticles from Flower-Shaped Protein-Inorganic Hybrid Nanoparticles.

Mimicry of biomineralization is an attractive strategy to fabricate nanostructured hybrid materials. While biomineralization involves processes that organize hybrid clusters into complex structures with hierarchy, arrangement of artificial components in biomimetic approaches has been challenging. Here, we demonstrate self-assembly of hierarchically structured porous supraparticles from protein-inorganic hybrid flower-shaped (FS) nanoparticle building blocks. In our strategy, the FS nanoparticles self-assemble via high valency interactions in combination with interfacial adsorption and compression. The flower-like shape directed robust assembly of the FS nanoparticles into chain-like clusters in solution, which were further assembled into spherical supraparticles during rotation of FS nanoparticle solution. Continuously expanding and contracting the air-water interface during rotation catalyzed assembly of FS nanoparticle clusters, indicating that adsorption and compression of the building blocks at the interface were critical. The resulting supraparticles contain hierarchical pores which are translated from the structural characteristics of individual FS nanoparticle building blocks. The protein-inorganic supraparticles are protein-compatible, have large surface area, and provide specific affinity recognition for robust protein immobilization. A variety of functional proteins could be immobilized to the porous supraparticles, making it a general platform that could provide benefits for many applications.

Hierarchical Porous Polystyrene Monoliths from PolyHIPE.

Hierarchical porous polystyrene monoliths (HCP-PolyHIPE) are obtained by hypercrosslinking poly(styrene-divinylbenzene) monoliths prepared by polymerization of high internal phase emulsions (PolyHIPEs). The hypercrosslinking is achieved using an approach known as knitting which employs formaldehyde dimethyl acetal (FDA) as an external crosslinker. Scanning electron microscopy (SEM) confirms that the macroporous structure in the original monolith is retained during the knitting process. By increasing the amount of divinylbenzene (DVB) in PolyHIPE, the BET surface area and pore volume of the HCP-PolyHIPE decrease, while the micropore size increases. BET surface areas of 196-595 m(2) g(-1) are obtained. The presence of micropores, mesopores, and macropores is confirmed from the pore size distribution. With a hierarchical porous structure, the monoliths reveal comparable gas sorption properties and potential applications in oil spill clean-up.