Pristine Wood-Supported Electrodes With Intrinsic Superhydrophilic/Superaerophobic Surface Intensify Hydrogen Evolution Reaction.

Wood, as a renewable material, has been regarded as an emerging substrate for self-supporting electrodes in large-scale water electrolysis due to numerous merits such as rich pore structure, abundant hydroxyl groups, etc. However, poor conductivity of wood can greatly suppress the performance of wood-based electrodes. Carbonization process can improve wood's conductivity, but the loss of hydroxyl groups and the required high energy consumption are the drawbacks of such a process. Here, a facile strategy is developed to prepare pristine wood-supported electrode (Ni-NiP/W) for enhanced hydrogen evolution reaction (HER); this improves electrical conductivity of wood while retaining its excellent intrinsic properties. The preparation process involves the deposition of copper on the untreated wood followed with the loading of Ni-NiP catalyst at room temperature. Encouragingly, the Ni-NiP/W exhibits conductive and inherited pristine wood's superhydrophilic and superaerophobic properties, that effectively boost mass and charge transfer. It demonstrates high activity and excellent stability in acidic, alkali, and seawater conditions as well as high current densities of up to 2000 mA cm-2; particularly a record-low HER overpotential of 206 mV in acidic conditions at 1000 mA cm-2. This work fully unlocks the admiring potential of pristine wood as superior substrate for high-performance electrochemical electrodes.

Vertical Conductive Metal-Organic Framework Single-Crystalline Nanowire Arrays for Efficient Electrocatalytic Hydrogen Evolution.

The construction of crystalline metal-organic frameworks with regular architectures supportive of enhanced mass transport and bubble diffusion is imperative for electrocatalytic applications; however, this poses a formidable challenge. Here, a method is presented that confines the growth of nano-architectures to the liquid-liquid interface. Using this method, vertically oriented single crystalline nanowire arrays of an Ag-benzenehexathiol (BHT) conductive metal-organic framework (MOF) are fabricated via an "in-plane self-limiting and out-of-plane epitaxial growth" mechanism. This material has excellent electrocatalytic features, including highly exposed active sites, intrinsically high electrical conductivity, and superhydrophilic and superaerophobic properties. Leveraging these advantages, the carefully designed material demonstrates superior electrocatalytic hydrogen evolution activity, resulting in a low Tafel slope of 66 mV dec-1 and a low overpotential of 275 mV at a high current density of 1 A cm-2. Finite element analysis (FEA) and in situ microscopic verification indicates that the nanowire array structure significantly enhances the electrolyte transport kinetics and promotes the rapid release of gas bubbles. The findings highlight the potential of using MOF-based ordered nanoarray structures for advanced electrocatalytic applications.

Enhancing electrochemical water-splitting efficiency with superaerophobic nickel-coated catalysts on Chinese rice paper.

The quest for efficient hydrogen production highlights the need for cost-effective and high-performance catalysts to enhance the electrochemical water-splitting process. A significant challenge in developing self-supporting catalysts lies in the high cost and complex modification of traditional substrates. In this study, we developed catalysts featuring superaerophobic microstructures engineered on microspherical nickel-coated Chinese rice paper (Ni-RP), chosen for its affordability and exceptional ductility. These catalysts, due to their microspherical morphology and textured surface, exhibited significant superaerophobic properties, substantially reducing bubble adhesion. The nickel oxy-hydroxide (NiOxHy) and phosphorus-doped nickel (PNi) catalysts on Ni-RP demonstrated effective roles in oxygen evolution reaction (OER) and hydrogen evolution reaction (HER), achieving overpotentials of 250 mV at 20 mA cm-2 and 87 mV at -10 mA cm-2 in 1 M KOH, respectively. Moreover, a custom water-splitting cell using PNi/Ni-RP and NiOxHy/Ni-RP electrodes reached an impressive average voltage of 1.55 V at 10 mA cm-2, with stable performance over 100 h in 1 M KOH. Our findings present a cost-effective, sustainable, and easily modifiable substrate that utilizes superaerophobic structures to create efficient and durable catalysts for water splitting. This work serves as a compelling example of designing high-performance self-supporting catalysts for electrocatalytic applications.

Bioinspired Gas Manipulation for Regulating Multiphase Interactions in Electrochemistry.

The manipulation of gas in multiphase interactions plays a crucial role in various electrochemical processes. Inspired by nature, researchers have explored bioinspired strategies for regulating these interactions, leading to remarkable advancements in design, mechanism, and applications. This paper provides a comprehensive overview of bioinspired gas manipulation in electrochemistry. It traces the evolution of gas manipulation in gas-involving electrochemical reactions, highlighting the key milestones and breakthroughs achieved thus far. The paper then delves into the design principles and underlying mechanisms of superaerophobic and (super)aerophilic electrodes, as well as asymmetric electrodes. Furthermore, the applications of bioinspired gas manipulation in hydrogen evolution reaction (HER), carbon dioxide reduction reaction (CO2RR), and other gas-involving electrochemical reactions are summarized. The promising prospects and future directions in advancing multiphase interactions through gas manipulation are also discussed.

The Superaerophobic N-Doped Carbon Nanocage with Hydrogen Spillover Effort for Enhanced Hydrogen Evolution.

Under the high current density, the excessive strong adsorption of H* intermediates and H2 accumulation the catalysts are the major obstacle to the industrial application of hydrogen evolation reaction (HER) catalysts. Herein, through experimental exploration, it is found that the superaerophobic Nitrogen (N)-doped carbon material can promote the rapid release of H2 and provide H* desorption site for the hydrogen spillover process, which makes it have great potential as the catalysts support for hydrogen spillover. Based on this discovery, this work develops the hydrogen spillover catalyst with electron-rich Pt sites loaded on N-doped carbon nanocage (N-CNC) with adjustable work function. Through a series of comprehensive electrochemical tests, the existence of hydrogen spillover effort has been proved. Moreover, the in situ tests showed that pyrrolic-N can activate adjacent carbon sites as the desorption sites for hydrogen spillover. The Pt@N-1-CNC with the minimum work function difference (ΔΦ) between Pt NPs and support shows superior hydrogen evolution performance, only needs overpotential of 12.2 mV to reach current density of 10 mA cm-2 , outstanding turnover frequency (TOF) (44.7 s-1 @100 mV) and superior durability under the 360 h durability tests at current density of 50 mA cm-2 .

Efficient electrocatalyst for solar-driven electrolytic water splitting: Phosphorus (P) and niobium (Nb) co-doped NiFe2O4 nanosheet.

In the context of hydrogen production through water electrolysis, the development of efficient and stable electrocatalysts is of paramount importance. However, the creation of cost-effective electrocatalysts poses a significant challenge. In this study, a P and Nb co-doped NiFe2O4 nanosheet is designed and grown on Fe foam (referred to as P, Nb-NiFe2O4/FF). The P, Nb-NiFe2O4/FF exhibits a distinctive crystalline/amorphous heterostructure, and the co-doping of P and Nb in the material leads to the exposure of additional catalytic active sites, optimization of the electronic structure, and enhancement of charge conductivity. Additionally, the P, Nb-NiFe2O4/FF possesses a superhydrophilic surface for the enhancement of charge/mass transfer at interface and a superaerophobic surface, facilitating the efficient release of gas. The P, Nb-NiFe2O4/FF demonstrates remarkable oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) activities, achieving overpotential as low as 247 mV and 127 mV, respectively, to attain the current density response of 100 mA cm-2. Based on the high bifunctional activities, the P, Nb-NiFe2O4/FF requires only a working voltage of 1.56 V to obtain the current density of 10 mA cm-2 in overall water splitting. Furthermore, the overall water splitting device of P, Nb-NiFe2O4/FF is integrated with a commercial solar cell to simulate a solar-powered water splitting system, resulting in as superior solar-to-hydrogen conversion efficiency of 15.11%.

Engineering Superaerophobic Electrodes Using Hydrophilic PEDOT and Colloidal Lithography for Enhanced Bubble Release and Efficient Hydrogen Evolution Reaction.

The efficient removal of gas bubbles is essential to reduce the reaction overpotential and improve the electrode stability in the hydrogen evolution reaction (HER). To address this challenge, the current study combines hydrophilic functionalized poly(3,4-ethylenedioxythiophene) (PEDOT) with colloidal lithography to create superaerophobic electrode surfaces. The fabrication process involves the use of polystyrene (PS) beads with varying sizes (100, 200, and 500 nm) as hard templates and the electropolymerization of EDOTs with hydroxymethyl (EDOT-OH) and sulfonate (EDOT-SuNa) functional groups. The surface properties and HER performances of the electrodes are investigated. The electrode modified with poly(EDOT-SuNa) and 200 nm PS beads (SuNa/Ni/Au-200) exhibits the best hydrophilicity with a water contact angle of 37°. Moreover, the overpotential required at -10 mA cm-2 is substantially reduced from -388 mV (flat Ni/Au) to -273 mV (SuNa/Ni/Au-200). This approach is further applied to commercially available nickel foam electrodes, showing improved HER activity and electrode stability. These results highlight the potential for promoting catalytic efficiency by constructing a superaerophobic electrode surface.

Overcoming Long-Range Unidirectional Transport of Underwater Bubbles on Laser-Textured Single-Layer Superaerophobic Dual-Rail Arrays.

Understanding the behavior of gas bubbles in aqueous media has been a hot topic because of their vital roles in both scientific research and industrial applications. Wettability gradient force and Laplace pressure are two typical characteristics of bubble transport. However, most work about bubble transport is limited to a short distance. Therefore, we took inspiration from the structure of the Nepenthes pitcher and prepared superaerophobic dual-rail arrays (SDRA). Upon SDRA, with this structure of a uniform distribution of superaerophobic and superaerophilic zones, bubbles can be transported over long distances on the structure's surface. The underlying principle is that gas bubbles tend to spread out on the superaerophilic region until they make contact with the asymmetric superaerophobic barriers. An asymmetric spreading resistance force is generated, which is attributed to the different lengths of the three-phase contact line (TCL) between gas bubbles and superaerophobic barriers. In addition, diverse parameters are quantified to investigate the critical transport state between unidirection and bidirection. Under the function of SDRA, the structure surface can realize bubble collection. The transporter as well as the light-control-light shutter is also successfully deployed. The present study will inspire people to develop innovative strategies to effectively manipulate gas bubbles in practical applications.

Ultrafine NiFe-Based (Oxy)Hydroxide Nanosheet Arrays with Rich Edge Planes and Superhydrophilic-Superaerophobic Characteristics for Oxygen Evolution Reaction.

NiFe-based (oxy)hydroxides are the benchmark catalysts for the oxygen evolution reaction (OER) in alkaline medium, however, it is still challenging to control their structures and compositions. Herein, molybdates (NiFe(MoO4 )x ) are applied as unique precursors to synthesize ultrafine Mo modified NiFeOx Hy (oxy)hydroxide nanosheet arrays. The electrochemical activation process enables the molybdate ions (MoO4 2- ) in the precursors gradually dissolve, and at the same time, hydroxide ions (OH- ) in the electrolyte diffuse into the precursor and react with Ni2+ and Fe3+ ions in confined space to produce ultrafine NiFeOx Hy (oxy)hydroxides nanosheets (<10 nm), which are densely arranged into microporous arrays and maintain the rod-like morphology of the precursor. Such dense ultrafine nanosheet arrays produce rich edge planes on the surface of NiFeOx Hy (oxy)hydroxides to expose more active sites. More importantly, the capillary phenomenon of microporous structures and hydrophilic hydroxyl groups induce the superhydrophilicity and the rough surface produces the superaerophobic characteristic for bubbles. With these advantages, the optimized catalyst exhibits excellent performance for OER, with a small overpotential of 182 mV at 10 mA cm-2 and long-term stability (200 h) at 200 mA cm-2 . Theoretical calculations show that the modification of Mo enhances the electron delocalization and optimizes the adsorption of intermediates.

Kirkendall effect Strengthened-Superhydrophilic/superaerophobic Co-Ni3N/NF heterostructure as electrode catalyst for High-current hydrogen production.

The development of efficient electrocatalysts for large-scale water electrolysis is crucial and challenging. Research efforts towards interface engineering and electronic structure modulation can be leveraged to enhance the electrochemical performance of the developed catalysts. In this work, a surface-engineered Co-Ni3N/NF heterostructure electrode was prepared based on Kirkendall effect for high-current water electrolysis. In the experiments, the textural feature and intrinsic activity of the Co-Ni3N/NF heterostructure were tuned through cobalt-doping and the creation of structural defects. As a result, the increased surface energy endowed Co-Ni3N/NF heterostructure with superhydrophilic and superaerophobic properties. Meanwhile, the contact area of the gas-liquid-solid three phases was optimized. With a large underwater bubble contact angle (CA) of 169°, the electrolyte solution can infiltrate the Co-Ni3N/NF electrode within 150 ms. Sequentially, the generated gas bubbles were able to detach at high frequency, which ensured the rapid mass exchange. The performance tests showed that the optimal Co-Ni3N/NF electrode sample reached current densities of 100 mA cm-2 and 500 mA cm-2 at the overpotentials of 98 mV and 123 mV, respectively. Benefiting from the reduction of hydrogen embrittlement, the HER performance of the prepared Co-Ni3N/NF electrode sample decreased slightly after 100 h durability test, but the overall structure remained well. Those results allowed us to conclude that the prepared Co-Ni3N/NF electrocatalyst holds the promises for large-scale water electrolysis in industries. More specifically, this work provided a new perspective that the efficiency of electrocatalysts for large-scale water electrolysis can be enhanced by constructing a heterostructure with good wettability and gas repellency.

Approaching well-dispersed MoS2 assisted with cellulose nanofiber for highly durable hydrogen evolution reaction.

The agglomeration and low conductivity of molybdenum disulfide (MoS2) electrocatalysts restrict the presentation of its real intrinsic reaction activity, which leads to challenges for the high-performance hydrogen evolution reaction (HER). Herein, a well-dispersed and superhydrophilic/superaerophobic MoS2 catalyst with uniform three-dimensional conductive networks have been prepared assisted with cellulose nanofiber (CNF) and carboxylated multi-walled carbon nanotubes (cMWCNT). The resulted CNF/cMWCNT/MoS2 catalysts present a superhydrophilic/superaerophobic state with contact angles for water and bubble of 0° and 154.1° respectively. This structure effectively disperses MoS2 nanoparticles through uniform embeddedness and promotes gas-liquid mass transfer via wettability. Benefiting from these optimizations, the CNF/cMWCNT/MoS2 exhibits better HER performance and a low overpotential (154 mV @ 10 mA/cm2). Encourangingly, CNF/cMWCNT/MoS2 catalysts have a slight decay of 6.99 % at 10 mA/cm2 after 100 h, while the cMWCNT/MoS2 shows a decay of 35.83 %. This approach using natural CNF for well-dispersed catalysts provides a potential for high-performance HER electrode design.

Superhydrophilic/Superaerophobic Hierarchical NiP2@MoO2/Co(Ni)MoO4 Core-Shell Array Electrocatalysts for Efficient Hydrogen Production at Large Current Densities.

Rationally constructing low-cost, high-efficiency, and durable electrocatalysts toward the hydrogen evolution reaction at large current densities is imperative for water splitting, especially for large-scale industrial applications. Herein, a hierarchical core-shell NiP2@MoO2/Co(Ni)MoO4 cuboid array electrode with superhydrophilic/superaerophobic properties is successfully fabricated and the formation mechanism of the core-shell structure is systematically investigated. Through an in situ partially converted gas-solid reaction during the phosphating process, Ni and Co elements are leached and rearranged to form NiP2 particles and amorphous CoO as the shell layer and the inner undecomposed Co(Ni)MoO4 crystals serve as the core layer. Because of its seamless core-shell structure and superhydrophilicity/superaerophobicity of hierarchical cuboid arrays, NiP2@MoO2/Co(Ni)MoO4 exhibits superior HER activity in 1 M KOH with only an overpotential of 297 mV to deliver 1000 mA cm-2 and can work steadily for 650 h at 200 mA cm-2. Remarkably, when coupled with NiFe LDH for overall water splitting, it can drive an AA battery with an ultralow cell voltage of 1.49 V to deliver 10 mA cm-2. This work sheds new light on designing large-current-density efficient HER electrocatalysts for large-scale industrial applications.

Superaerophobic copper-based nanowires array for efficient nitrogen reduction.

Electrocatalytic N2 reduction reaction (NRR) provides a promising route for NH3 production under ambient conditions to replace traditional Haber-Bosch process. For this purpose, efficient NRR electrocatalysts with high NH3 yield rate and high Faradaic efficiency (FE) are required. Cu-based materials have been recognized catalytic active for some multi-electron-involved reduction reactions and usually exhibit inferior catalytic activities for hydrogen evolution reaction. We report here the preparation and characterization of a series of Cu-based nanowires array (NA) catalysts in situ grown on Cu foam (CF) substrate, including Cu(OH)2 NA/CF, Cu3N NA/CF, Cu3P NA/CF, CuO NA/CF and Cu NA/CF, which are directly used as self-supported catalytic electrodes for NRR. The electrochemical results show that CuO NA/CF achieves a highest NH3 yield rate of 1.84 × 10-9 mol s-1 cm-2, whereas Cu NA/CF possesses a highest FE of 18.2% for NH3 production at -0.1 V versus reversible hydrogen electrode in 0.1 M Na2SO4. Such catalytic performances are superior to most of recently reported metal-based NRR electrocatalysts. The contact angle measurements and the simulated calculations are carried out to reveal the important role of the superaerophobic NA surface structure for efficient NRR electrocatalysis.

Boosting Electrocatalytic Oxygen Evolution: Superhydrophilic/Superaerophobic Hierarchical Nanoneedle/Microflower Arrays of CexCo3-xO4 with Oxygen Vacancies.

The oxygen evolution reaction has become the bottleneck of electrochemical water splitting for its sluggish kinetics. Developing high-efficiency and low-cost non-noble-metal oxide electrocatalysts is crucial but challenging for industrial application. Herein, superhydrophilic/superaerophobic hierarchical nanoneedle/microflower arrays of Ce-substituted Co3O4 (CexCo3-xO4) in situ grown on the nickel foam are successfully constructed. The hierarchical architecture and superhydrophilic/superaerophobic interface can be facilely regulated by controlling the introduction of Ce into Co3O4. The unique feature of hierarchical architecture and superhydrophilic/superaerophobic interface is in favor of electrolyte penetration and bubbles release. In addition, the presence of oxygen vacancy and Ce endows the catalyst with enhanced intrinsic activity. Benefiting from these advantages, the optimized Ce0.12Co2.88O4 catalyst shows a superior electrocatalytic performance for the oxygen evolution reaction (OER) with an overpotential of 282 mV at 20 mA cm-2, and a Tafel slope of 81.4 mV dec-1. The turnover frequency of 0.0279 s-1 for Ce0.12Co2.88O4 is 9.3 times larger than that for Co3O4 at an overpotential of 350 mV. Moreover, the optimized Ce0.12Co2.88O4 catalyst shows a robust long-term stability in alkaline media.

Wettability-Engineered Meshes for Gas Microvolume Precision Handling in Liquids.

The interaction of rising gas bubbles with submerged air-repelling or air-attracting surfaces is relevant to various technological applications that rely on gas-microvolume handling or removal. This work demonstrates how submerged metal meshes with super air-attracting/repelling properties can be employed to manipulate microvolumes of air, rising buoyantly in the form of bubbles in water. Superaerophobic meshes are observed to selectively allow the passage of air bubbles depending on the mesh pore size, the bubble volume-equivalent diameter, and the bubble impact velocity on the mesh. On the other hand, superaerophilic meshes reduce or amplify the volume captured from a train of incoming bubbles. Finally, a spatial wettability pattern on the mesh is used to control the size of the outgoing bubble, and an empirical relation is formulated to predict the released gas volume. The study demonstrates how porous materials with controlled wettability can be used to precisely modulate and control the outcome of bubble/mesh interactions.

High-Performance Water Electrolysis System with Double Nanostructured Superaerophobic Electrodes.

Catalysts screening and structural optimization are both essential for pursuing a high-efficient water electrolysis system (WES) with reduced energy supply. This study demonstrates an advanced WES with double superaerophobic electrodes, which are achieved by constructing a nanostructured NiMo alloy and NiFe layered double hydroxide (NiFe-LDH) films for hydrogen evolution and oxygen evolution reactions, respectively. The superaerophobic property gives rise to significantly reduced adhesion forces to gas bubbles and thereby accelerates the hydrogen and oxygen bubble releasing behaviors. Benefited from these metrics and the high intrinsic activities of catalysts, this WES affords an early onset potential (≈1.5 V) for water splitting and ultrafast catalytic current density increase (≈0.83 mA mV(-1) ), resulting in ≈2.69 times higher performance compared to the commercial Pt/C and IrO2 /C catalysts based counterpart under 1.9 V. Moreover, enhanced performance at high temperature as well as prominent stability further demonstrate the practical application of this WES.

Superaerophobic electrodes for direct hydrazine fuel cells.

Direct liquid-feed fuel cells possess high energy and power densities, but suffer from severe adhesion of gas products. Here, a "superaerophobic" surface that enables a small release size and fast evolution behavior of the gas product is introduced, thereby, maximizing and stabilizing the working area. Consequently, the "superaerophobic" nanostructured Cu electrodes exhibit excellent performance as anodes in a direct hydrazine fuel cell.