Relationship between Hydrogen Evolution and Wettability for Multiscale Hierarchical Wrinkles

Superhydrophilic and Underwater Superaerophobic Dual-Function Peony-Shaped Selenide Micro-nano Array Self-Supported Electrodes for High-Efficiency Overall Water Splitting Driven by Renewable Energy

With the intensification of global environmental pollution and resource scarcity, hydrogen has garnered significant attention as an ideal alternative to fossil fuels due to its high energy density and nonpolluting nature. Consequently, the urgent development of electrocatalytic water-splitting electrodes for hydrogen production is imperative. In this study, a superwetting selenide catalytic electrode with a peony-flower-shaped micronano array (MoS2/Co0.8Fe0.2Se2/NixSey/nickel foam (NF)) was synthesized on NF via a two-step hydrothermal method. The optimal catalytic activity of cobalt-iron selenide was achieved by adjusting the Co/Fe ratio. The intrinsic catalytic activity of the electrodes was enhanced by incorporating transition metal selenides, which then served as a precursor for the subsequent loading of MoS2 nanoflowers on the surface to fully expose the active sites. Furthermore, the superwetting properties of the electrode accelerated electrolyte penetration and electron/mass transfer, while also facilitating bubble detachment from the electrode surface, thereby preventing "bubble shielding effect". This resulted in superior oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) performance, as well as overall water splitting capabilities. In a 1.0 M KOH solution, the electrode required only 166 and 195 mV overpotential to achieve a current density of 10 mA cm-2 for OER and HER, respectively. When functioning as a bifunctional catalytic electrode, only 1.60 V of voltage was necessary to drive the electrolyzer to reach a current density of 10 mA cm-2. Moreover, laboratory simulations of wind and solar energy-driven water splitting validated the feasibility of establishing a sustainable energy-to-hydrogen production chain. This work provides new insights into the preparation of low-overpotential, high-catalytic-activity superhydrophilic and underwater superaerophobic catalytic electrodes by rationally adjusting elemental ratios and exploring changes in electrode surface wettability.

Locally Strained 2D Materials: Preparation, Properties, and Applications

2D materials are promising for strain engineering due to their atomic thickness and exceptional mechanical properties. In particular, non-uniform and localized strain can be induced in 2D materials by generating out-of-plane deformations, resulting in novel phenomena and properties, as witnessed in recent years. Therefore, the locally strained 2D materials are of great value for both fundamental studies and practical applications. This review discusses techniques for introducing local strains to 2D materials, and their feasibility, advantages, and challenges. Then, the unique effects and properties that arise from local strain are explored. The representative applications based on locally strained 2D materials are illustrated, including memristor, single photon emitter, and photodetector. Finally, concluding remarks on the challenges and opportunities in the emerging field of locally strained 2D materials are provided.

Effect of Feature Shape and Dimension of a Confinement Geometry on Selectivity of Electrocatalytic CO2 Reduction

The local confinement effect, which can generate a high concentration of hydroxide ions and reaction intermediates near the catalyst surface, is an important strategy for converting CO2 into multi-carbon products in electrocatalytic CO2 reduction. Therefore, understanding how the shape and dimension of the confinement geometry affect the product selectivity is crucial. In this study, we report for the first time the effect of the shape (degree of confinement) and dimension of the confined space on the product selectivity without changing the intrinsic property of Cu. We demonstrate that geometry influences the outcomes of products, such as CH4 , C2 H4 , and EtOH, in different ways: the selectivity of CH4 and EtOH is affected by shape, while the selectivity of C2 H4 is influenced by dimension of geometry predominantly. These phenomena are demonstrated, both experimentally and through simulation, to be induced by the local confinement effect within the confined structure. Our geometry model could serve as basis for designing the confined structures tailored for the production of specific products.

Bubble Management for Electrolytic Water Splitting by Surface Engineering: A Review

During electrocatalytic water splitting, the management of bubbles possesses great importance to reduce the overpotential and improve the stability of the electrode. Bubble evolution is accomplished by nucleation, growth, and detachment. The expanding nucleation sites, decreasing bubble size, and timely detachment of bubbles from the electrode surface are key factors in bubble management. Recently, the surface engineering of electrodes has emerged as a promising strategy for bubble management in practical water splitting due to its reliability and efficiency. In this review, we start with a discussion of the bubble behavior on the electrodes during water splitting. Then we summarize recent progress in the management of bubbles from the perspective of surface physical (electrocatalytic surface morphology) and surface chemical (surface composition) considerations, focusing on the surface texture design, three-dimensional construction, wettability coating technology, and functional group modification. Finally, we present the principles of bubble management, followed by an insightful perspective and critical challenges for further development.

Electrolyte-Wettability Issues and Challenges of Electrode Materials in Electrochemical Energy Storage, Energy Conversion, and Beyond

The electrolyte-wettability of electrode materials in liquid electrolytes plays a crucial role in electrochemical energy storage, conversion systems, and beyond relied on interface electrochemical process. However, most electrode materials do not have satisfactory electrolyte-wettability for possibly electrochemical reaction. In the last 30 years, there are a lot of literature have directed at exploiting methods to improve electrolyte-wettability of electrodes, understanding basic electrolyte-wettability mechanisms of electrode materials, exploring the effect of electrolyte-wettability on its electrochemical energy storage, conversion, and beyond performance. This review systematically and comprehensively evaluates the effect of electrolyte-wettability on electrochemical energy storage performance of the electrode materials used in supercapacitors, metal ion batteries, and metal-based batteries, electrochemical energy conversion performance of the electrode materials used in fuel cells and electrochemical water splitting systems, as well as capacitive deionization performance of the electrode materials used in capacitive deionization systems. Finally, the challenges in approaches for improving electrolyte-wettability of electrode materials, characterization techniques of electrolyte-wettability, as well as electrolyte-wettability of electrode materials applied in special environment and other electrochemical systems with electrodes and liquid electrolytes, which gives future possible directions for constructing interesting electrolyte-wettability to meet the demand of high electrochemical performance, are also discussed.

CoW Bimetallic Carbide Nanocatalysts: Computational Exploration, Confined Disassembly-Assembly Synthesis and Alkaline/Seawater Hydrogen Evolution

Earth-abundant tungsten carbide exhibits potential hydrogen evolution reaction (HER) catalytic activity owing to its Pt-like d-band electronic structure, which, unfortunately, suffers from the relatively strong tungsten-hydrogen binding, deteriorating its HER performance. Herein, a catalyst design concept of incorporating late transition metal into early transition metal carbide is proposed for regulating the metal-H bonding strength and largely enhancing the HER performance, which is employed to synthesize CoW bi-metallic carbide Co₆ W₆ C by a "disassembly-assembly" approach in a confined environment. Such synthesized Co₆ W₆ C nanocatalyst features the optimal Gibbs free energy of *H intermediate and dissociation barrier energy of H₂ O molecules as well by taking advantage of the electron complementary effect between Co and W species, which endows the electrocatalyst with excellent HER performance in both alkaline and seawater/alkaline electrolytes featuring especially low overpotentials, elevated current densities, and much-enhanced operation durability in comparison to commercial Pt/C catalyst. Moreover, a proof-of-concept Mg/seawater battery equipped with Co₆ W₆ C-2-600 as cathode offers a peak power density of 9.1 mW cm^-2 and an open-circuit voltage of ≈1.71 V, concurrently realizing hydrogen production and electricity output.

Self-supported Co9S8-Ni3S2-CNTs/NF electrode with superwetting multistage micro-nano structure for efficient bifunctional overall water splitting

Electrochemical water splitting for hydrogen production using cost-effective and high-efficiency electrocatalysts in alkaline electrolytes is of great significance for solving energy crisis and environmental pollution. Herein, we reported a superhydrophilic and underwater superaerophobic multistage layered micro-nano structure ofCo₉S₈-Ni₃S₂-CNTs/NF on nickel foam (NF) prepared by a simple one-step hydrothermal procedure. Particularly, the multistage layered micro-nano structure makes the electrode superhydrophilic and superaerophobic, which can facilitate the exposure of active sites, accelerate the tansfer of electrolyte and the release of gas bubbles. Consequently, the rough electrode demonstrated excellent catalytic performance in alkaline condition, which only need a low overpotential 127 mV for oxygen evolution reaction (OER) and 243 mV for hydrogen evolution reaction (HER) at 10 mA cm^-2 and can keep a long durability for 10 h at 10 mA cm^-2. In addition, the production of hydrogen in an electrolytic water device with Co₉S₈-Ni₃S₂-CNTs/NF as bifunctional electrode prowered by the electricity derived from solar and wind energy in laboratory condition was artificially simulated. This work represents a perspective in improving the electrocatalytic performance of water splitting by structure and wettability regulation and opens a new avenue for clean energy generation.

Effect of Highly Periodic Au Nanopatterns on Dendrite Suppression in Lithium Metal Batteries

Despite the extremely high energy density of the lithium metal, dendritic lithium growth caused by nonuniform lithium deposition can result in low Coulombic efficiency and safety hazards, thereby inhibiting its practical applications. Here, we report a new strategy for adopting a nanopatterned gold (Au) seed on a copper current collector for uniform lithium deposition. We find that Au nanopatterns enhance lithium metal battery performance, which is strongly affected by the feature dimensions of Au nanopatterns (diameter and height). Ex situ scanning electron microscopy images confirm that this can be attributed to the perfectly selective lithium nucleation and uniform growth resulting from the spatial confinement effect. The spatial arrangement of Au dot seeds homogenizes the Li⁺ flux and electric field, and the size-controlled Au seeds prevent both seed-/substrate-induced agglomeration and interseed-induced lithium growth, leading to uniform lithium deposition. This dendrite-free lithium deposition results in the improvement of electrochemical performance, and the system showed cyclic stability over 300 cycles at 0.5 mA cm^-2 and 200 cycles at 1.0 mA cm^-2 (1 mA h cm^-2) and a high rate capability. This study provides in-depth insights into the more complicated and diverse seed geometry control of seed materials for the development of high-performance lithium metal batteries.

Wetting-regulated gas-involving (photo)electrocatalysis: biomimetics in energy conversion

(Photo)electrolysis of water or gases with water to species serving as industrial feedstocks and energy carriers, such as hydrogen, ammonia, ethylene, propanol, etc., has drawn tremendous attention. Moreover, these processes can often be driven by renewable energy under ambient conditions as a sustainable alternative to traditional high-temperature and high-pressure synthesis methods. In addition to the extensive studies on catalyst development, increasing attention has been paid to the regulation of gas transport/diffusion behaviors during gas-involving (photo)electrocatalytic reactions towards the goal of creating industrially viable catalytic systems with high reaction rates, excellent long-term stabilities and near-unity selectivities. Biomimetic surfaces and systems with special wetting capabilities and structural advantages can shed light on the future design of (photo)electrodes and address long-standing challenges. This article is dedicated to bridging the fields of wetting and catalysis by reviewing the cutting-edge design methodologies of both gas-evolving and gas-consuming (photo)electrocatalytic systems. We first introduce the fundamentals of various in-air/underwater wetting states and their corresponding bioinspired structural properties. The relationship amongst the bubble transport behavior, wettability, and porosity/tortuosity is also discussed. Next, the latest implementations of wetting-related design principles for gas-evolving reactions (i.e. the hydrogen evolution reaction and oxygen evolution reaction) and gas-consuming reactions (i.e. the oxygen reduction reaction and CO2 reduction reaction) are summarized. For photoelectrode designs, additional factors are taken into account, such as light absorption and the separation, transport and recombination of photoinduced electrons and holes. The influences of wettability and 3D structuring of (photo)electrodes on the catalytic activity, stability and selectivity are analyzed to reveal the underlying mechanisms. Finally, remaining questions and related future perspectives are outlined.

Towards controlled bubble nucleation in microreactors for enhanced mass transport

The exact location of bubbles with respect to the catalytic layer impacts the microreactor performance. In this work, we propose to control bubble nucleation using micropits to maximize the microreactor efficiency.

Advanced Bifunctional Oxygen Reduction and Evolution Electrocatalyst Derived from Surface-Mounted Metal-Organic Frameworks

Metal-organic frameworks (MOFs) and their derivatives are considered as promising catalysts for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), which are important for many energy provision technologies, such as electrolyzers, fuel cells and some types of advanced batteries. In this work, a "strain modulation" approach has been applied through the use of surface-mounted NiFe-MOFs in order to design an advanced bifunctional ORR/OER electrocatalyst. The material exhibits an excellent OER activity in alkaline media, reaching an industrially relevant current density of 200 mA cm-2 at an overpotential of only ≈210 mV. It demonstrates operational long-term stability even at a high current density of 500 mA cm-2 and exhibits the so far narrowest "overpotential window" ΔEORR-OER of 0.69 V in 0.1 m KOH with a mass loading being two orders of magnitude lower than that of benchmark electrocatalysts.

Nano-folded Gold Catalysts for Electroreduction of Carbon Dioxide

The local structure and geometry of catalytic interfaces can influence the selectivity of chemical reactions. Selectivity is often critical for the practical realization of reactions such as the electroreduction of carbon dioxide (CO₂). Previously developed strategies to manipulate the structure and geometry of catalysts for electroreduction of CO₂ involve complex processes or fail to efficiently alter the selectivity. Here, using a prestrained polymer, we uniaxially and biaxially compress a 60 nm gold film to form a nano-folded electrocatalyst for CO₂ reduction. We observe two kinds of folds and can tune the ratio of loose to tight folds by varying the extent of prestrain in the polymer. We characterize the nano-folded catalysts using X-ray diffraction, scanning, and transmission electron microscopy. We observe grain reorientation and coarsening in the nano-folded gold catalysts. We measure an enhancement of Faradaic efficiency for carbon monoxide formation with the biaxially compressed nano-folded catalyst by a factor of about nine as compared to the flat catalyst (up to 87.4%). We rationalize this observation by noting that an increase of the local pH in the tight folds of the catalyst outweighs the effects of alterations in grain characteristics. Together, our studies demonstrate that nano-folded geometries can significantly alter grain characteristics, mass transport, and catalytic performance.

Designing Hierarchical Nanostructures from Conformable and Deformable Thin Materials

This Perspective focuses on the design of hierarchical structures in deformable thin materials by patterning mechanical instabilities. Fabrication of three-dimensional (3D) structures with multiple length scales-starting at the nanoscale-can result in on-demand surface functionalities from the modification of the mechanical, chemical, and optical properties of materials. Conventional top-down lithography, however, cannot achieve 3D patterns over large areas (>cm²). In contrast, a bottom-up approach based on controlling strain in layered nanomaterials conformally coated on polymeric substrates can produce multiscale structures in parallel. In-plane and out-of-plane structural hierarchies formed by conformal buckling show unique structure-function relationships. Programmable hierarchical surfaces offer prospects to tune global- and local-level characteristics of nanomaterials that will positively impact applications in nanomechanics, nanoelectronics, and nanophotonics.