The reaction kinetics of hydrogen oxidation reactions (HOR) unfavorably decreases by 2~3 orders of magnitude under alkaline conditions, even on the most active platinum-group-metal (PGM) electrocatalysts. This sticky problem severely restricts the efficiency and commercialization of anion-exchange membrane fuel cells (AEMFCs). So far, no other material has HOR electrocatalytic performance comparable to PGM-based electrocatalysts. Forced by the scarce reserves and high prices of PGMs, it is significant to elaborately design and synthesize PGM-based electrocatalysts with ultimately atomic utilization and substantially improved alkaline HOR performance. In this review, we summarize recent advances in the structure engineering approaches to synthesis of advanced PGM-based nanocatalysts toward enhanced alkaline HOR performance. The generally acknowledged catalytic mechanisms with corresponding activity descriptors are reviewed firstly to deeply understand the discrepancies in the HOR kinetics of alkaline and acidic reactions. Then, several representative strategies are emphasized and discussed at length by changing the chemical and coordination environment and size/morphology of nanocatalysts. Meanwhile, the influence factors for the performance of AEMFC devices constructed by PGM-based anode catalysts are briefly highlighted. In conclusion, strategies for boosting the electrocatalytic performance and challenges on the roles of catalytic mechanism insights and practical AEMFC applications are finally outlined. We hope this review will guide the design and catalytic mechanism research of novel PGM-based alkaline HOR catalysts, thereby promoting their further development and application in AEMFC technologies.

Well-dispersed and few-layered molybdenum disulfide (MoS₂) has been considered as a suitable electrode material for pseudocapacitive capacitive deionization (CDI) due to its lamellar structure, flexible interlayer intercalation, and high theoretical capacity. However, the serious aggregation, low electrical conductivity and poor hydrophilicity of MoS₂ have limited its desalination application. To address these issues, few-layered MXene is used as a conductive and hydrophilic skeleton to support MoS₂ nanosheets. In this study, a hierarchical MoS₂/MXene heterostructure is fabricated for highly efficient CDI of saline water. The designed heterostructure effectively inhibits the agglomeration of MoS₂ and MXene nanosheets, exposes more active electrochemical sites, and improves the wettability, thereby enhancing ion/charge transport. The MoS₂/MXene heterostructure electrode exhibits low electrical resistance (3.2 Ω), along with a high specific capacitance of 171.8 F·g^-1 at 2 A·g^-1. Furthermore, the MoS₂/MXene-based CDI electrode demonstrates an excellent desalination capacity of 55.8 mg·g^-1 and a fast desalination rate of 13 mg·g^-1·min^-1. This study paves the way for novel applications in the CDI field.

Piezopotential-assisted catalysis has been proven to be a low-cost and high-efficiency environmental purification process. Herein, Au/bismuth vanadate (BiVO₄) piezoelectric photocatalysts are prepared by modifying highly dispersed Au nanoparticles (AuNPs) on piezoelectric BiVO₄ microcrystal by a deposition-precipitation approach. Under visible light irradiation and assisted ultrasound excitation, the removal rate of tetracycline was 95% within 60 min, demonstrating the optimum photocatalytic performance over 3Au/BiVO₄. The significantly enhanced photocatalytic performance is due to the synergistic coupling of plasmonic and piezotronic effect based on facet engineering. Single-particle spectroscopy technology can provide photoluminescence (PL) lifetime and PL spectra information in the micro-/nano regions, thereby exploring the charge transfer behavior of heterostructures. Single-particle PL images revealed a significant attenuation of PL emission and shortened PL lifetime of 3Au/BiVO₄, compared with BiVO₄, indicating that high-density dispersed AuNPs promote charge transfer. In situ monitoring of individual BiVO₄ and 3Au/BiVO₄ particles before and after polarization treatment confirms that the piezoelectric field of the BiVO₄ decahedron further promotes separation of photogenerated carriers induced by plasmonic effect. Driven by the piezoelectric potential induced by ultrasonic vibration near the heterostructures, high-energy hot electrons excited on plasmonic AuNPs can be effectively extracted to BiVO₄. This work provides new choices for designing high-performance pollutant treatment catalysts.

The use of porous solid adsorbents is an effective and excellent approach for the separation and purification of methanol-to-olefins product and methane (CH₄). In this particular study, a series of adenine (AD)-based biological metal–organic frameworks (Bio-MOFs) {Their general formula is Cu₂(AD)₂(X)₂ [X = formic acid, acetic acid (AA), and propionic acid]} were proposed, which exhibited remarkable efficiency in the purification of CH₄ and the separation of C₃H₆ from methanol-to-olefins product, ultimately yielding purified C₂H₄. The experimental findings demonstrate that different terminal ligands induce alterations in the pore microenvironment, consequently leading to variations in adsorption capacities and stability. Specifically, Cu-AD-AA exhibits the highest adsorption capacity and selectivity among the three MOFs, as confirmed by static adsorption isotherm testing and theoretical evaluation using ideal adsorbed solution theory (IAST) simulation. At 298 K and 1 bar, Cu-AD-AA exhibits 786 and 10.9 selectivity for C₃H₈/CH₄ and C₃H₆/C₂H₄, respectively, surpassing the majority of MOFs materials. Furthermore, breakthrough experiments conducted in ambient conditions reveal that Cu-AD-AA possesses commendable separation capabilities, enabling one-step purification of C₂H₄ at varying proportions (C₂H₄/C₃H₆ = 50:50, 50:20, and 90:10), along with satisfactory recycling performance. Importantly, the synthesis of Cu-AD-AA utilizes simple and easily obtainable raw materials, thereby offering advantages such as cost-effectiveness, low toxicity, and facile synthesis that enhance its potential for industrial applications.

Covalent organic frameworks (COFs) represent an emerging class of crystalline porous polymers characterized by their pre-designed interconnected structures formed via dynamic covalent bonds. These materials have garnered widespread attention in recent years. While applications of two-dimensional (2D) COFs have been extensively investigated since 2005, their practicality has been impeded by their limited specific surface area and the robust π-π stacking interaction. In contrast, three-dimensional (3D) COFs boast enhanced porosity, larger specific surface area, well-exposed functional groups, and an abundance of reaction sites, positioning them at the forefront of porous material research. They find extensive applications in diverse fields, including adsorption, separation, catalysis, and so on. This featured article provides a comprehensive exploration of the latest advancements in 3D COFs across their respective application domains. Additionally, we outline the current challenges that must be addressed and shed light on the promising prospects for the utilization of 3D COFs.

Selective adsorption of carbon dioxide (CO₂) is significant for carbon neutrality, where searching for efficient CO₂ adsorbents is very important. In addition, coal fly ash (CFA) is one of the largest industrial solid wastes with environmental damages, where conversion of the wastes into costly functional materials is attractive. This work showed sustainable synthesis of Fe-containing mordenite (Fe-MOR) zeolite from the CFA waste under solvent-free conditions, and this zeolite is an efficient capturer for CO₂ in the mixture of CO₂/N₂ (15/85, v/v), giving adsorption capacity of 2.07 mmol/g and separation coefficient of 58.9 at 298 K. Very interestingly, the capture of CO₂ in the mixture of CO₂/N₂ (15/85, v/v) is recyclable. This work not only solved the accumulation and pollution of CFA but also prepared a highly efficient adsorbent of Fe-MOR zeolite, which would open a door for utilizing environmentally unfriendly solid wastes as value-added functional materials in the future.

Amidst the urgent demand for carbon-neutral strategies, electrocatalytic hydrogen evolution reaction (HER) has garnered significant attention as an efficient and environmentally friendly energy conversion pathway. Non-precious metal layered transition metal carbides, particularly various modified two-dimensional molybdenum carbides (2D Mo₂C), have emerged as promising HER catalysts due to their superior intrinsic catalytic activity. While common non-metal doping strategies have been widely employed to enhance the electronic configuration and bulk/interface activity, the mechanism of HER performance dependence on the doping-induced electronic configuration in 2D Mo₂C remains unclear, especially for more complex binary or ternary doping configurations. To address the issue of uncontrollable doping atom percentages in conventional methods, herein, we propose a strategy for rapidly synthesizing highly tunable non-metal multielement-doped 2D Mo₂C using microwave pulse-assisted synthesis. By designing doping configurations with similar atomic ratios, we delve into the impact mechanisms of various doping configurations on the HER performance of 2D Mo₂C, with phosphorus doping potentially exerting the most significant positive influence. Furthermore, leveraging the unique thermodynamic and kinetic advantages of microwaves, this approach efficiently prevents potential side reactions associated with multi-element doping, enabling the rapid and precise synthesis of binary and ternary-doped 2D Mo₂C. The synthesized ternary-doped 2D Mo₂C with the same doping atomic ratios (2D P,N,S-Mo₂C) exhibits outstanding HER performance. This method not only offers a novel approach for precisely designing non-metallic atomic doping configurations in 2D TMCs but also provides insights into the theoretical structure-activity mechanism for other carbides with unique structures.

Owing to their distinct structural properties, low-dimensional zeolites are rising stars in the field of catalysis. However, shortening their size while maintaining the acidity continues to be challenging. In addition, simplified synthesis methods to efficiently prepare low-dimensional zeolites with more skeleton types and extended frame components are also of great interest. Herein, a facile strategy is developed for fabricating ultrathin nanoneedle (ca. 6-8 nm in diameter of each needle) ZSM-48 mesocrystals with a low Si/Al ratio (ca. 27, close to the lowest synthesized so far). This is achieved by adding potassium ions in a ZSM-12 synthetic system. The promoting effect of appropriate K⁺ ions was confirmed by adjusting the gel composition and tracking the crystallization process. Moreover, a superior conversion, reusability and regeneration performance for xylose to furfural is achieved with more accessible acidity and a more suitable Lewis/Brønsted acid ratio, which further expands the development of ZSM-48 zeolite.

Ammonia (NH₃) is an important chemical feedstock and a clean energy carrier that has a pivotal impact on the sustainable energy circle. Its electrocatalytic production is evolving into a green alternative to the traditional Haber-Bosch process. A key strategy in enhancing the performance of this electrocatalytic ammonia synthesis is crystal facet engineering of electrocatalysts, which could significantly influence the reaction mechanism, kinetics, and thermodynamics. This review summarizes the recent advancements in crystal facet engineering for electrocatalytic nitrate reduction to ammonia. Through this review, we hope to shed light on the significant role of crystal facet engineering in advancing electrocatalytic ammonia production and provide useful guidance on the design of high-performance electrocatalysts.

Metal–organic frameworks (MOFs) have garnered significant attention in the field of catalysis due to their unique advantages such as diverse coordination geometry, variable metal nodes, and organic linkers, facilitating precise structural and compositional control for achieving programmable catalytic functionalities. Although their inherent microporous structure could provide excellent shape selectivity during catalysis, it typically impedes the mass transfer process, thereby reducing the use of internal active sites and overall catalytic efficiency. Additionally, employing single MOFs as catalysts presents challenges in achieving complex catalytic reactions that require multifunctional active sites. In recent years, considerable research efforts have focused on designing and constructing hierarchical nanostructured MOFs to alleviate substrate diffusion limitations by introducing secondary nanopores, shortening diffusion distances via the construction of low-dimensional nanoarchitectures, and constructing multifunctional catalysts by integrating distinct MOFs with suitable functions. This review provides a comprehensive overview of the design, synthesis methods, and formation mechanisms of MOF-based hierarchical nanostructures in recent years. Subsequently, it further highlights their applications in thermal catalysis, electrocatalysis, and photocatalysis, along with the relationship between their hierarchical nanostructures and catalytic performances. Finally, it provides an outlook on the challenges and potential development directions of hierarchically structured MOF nanocatalysts.

On-surface molecular self-assembly in solution can produce two-dimensional (2D) materials with unique surface nanostructures that have the potential to create new functionalities. The surface completely differs from the uniform flat surface of conventional 2D materials such as graphene, MoS₂, and 2D van der Waals nanosheets. The recently developed on-surface chemical synthesis of amino-ferrocene (AFc) nanoclusters on a graphene oxide (GO) nanosheet is a technique based on molecular self-assembly. Here, this method is applied to other ferrocene derivatives whose ferrocene units are covalently bonded to an amino group and several other molecules. The structure of the on-surface synthesized nanoclusters is analyzed by high-resolution transmission electron microscopy and atomic force microscopy. The molecules in the nanoclusters are densely and regularly arranged, and the distance between the Fe ions of the constituent molecules is longer than that in the AFc nanoclusters. Band-through electron transfer occurs between the Fe ions and the GO nanosheet, generating unpaired 3d electrons whose magnetic state is in the high spin state (S = 5/2). The present study demonstrates the feasibility of the design and synthesis of functional molecular nanostructures with molecular precision by on-surface chemistry, leading to the fabrication of nanoscale building blocks with molecular precision and 2D platforms for next-generation molecular spintronic and neuromorphic devices.

Titanium dioxide (TiO₂) is one of the optimal semiconductor metal oxide photocatalysts with a wide range of application fields, such as heterogeneous catalysis, energy science, and environmental science. Solid-state nuclear magnetic resonance (NMR) spectroscopy is a powerful tool for characterizing both structure and dynamics at an atomic-molecular level in heterogeneous catalysts. In this review, we first provide a brief discussion on the progress in investigating the structures of titanium and oxygen in bulk and on the surface of TiO₂ by using various solid-state NMR techniques. Advances in the understanding of electronic structure and properties of TiO₂ with distinct surface features, including various crystal facets and heteroatomic adsorption by chemical probe-assisted NMR techniques, are secondly presented. The solid-state NMR characterization of heteroatom active sites (such as ¹³C, ¹⁵N, ¹¹B, ²⁷Al) and their function in TiO₂ photocatalysts is described in detail. Finally, a critical discourse assesses the current limitations and prospects of solid-state NMR in its application to the optimization and design of advanced TiO₂ photocatalysts.

Cu-catalyzed electrochemical CO₂ reduction reaction (CO₂RR) to multi-carbon (C₂₊) products is often plagued by low selectivity because the adsorption energies of different reaction intermediates are in a linear scaling relationship. Development of Cu-based bimetallic catalysts has been considered as an attractive strategy to address this issue; however, conventional bimetallic catalysts often avoid metals with strong CO adsorption energies to prevent surface poisoning. Herein, we demonstrated that limiting the amount of Co in CuCo bimetallic catalysts can enhance C₂₊ product selectivity. Specifically, we synthesized a series of CuCo_x catalysts with trace amounts of Co (0.07-1.8 at%) decorated on the surface of Cu nanowires using a simple dip coating method. Our results revealed a volcano-shaped correlation between Co loading and C₂₊ selectivity, with the CuCo_0.4% catalyst exhibiting a 2-fold increase in C₂₊ selectivity compared to the Cu nanowire sample. In situ Raman and Infrared spectroscopies suggested that an optimal amount of Co could stabilize the Cu oxide/hydroxide species under the CO₂RR condition and promote the adsorption of CO, thus enhancing the C₂₊ selectivity. This work expands the potential for developing Cu-based bimetallic catalysts for CO₂RR.

The slow oxygen evolution kinetics of iron oxide nanorod arrays have limited their applications in photocatalytic water splitting. Herein, we introduce p-type semiconductor cuprous oxide and further cover cobalt hydroxide ultrathin nanosheets on the surface of both by electrochemical deposition; these methods obviously enhanced the photoelectrochemical (PEC) water splitting performance of iron oxide nanorods on titanium sheet substrate. The photocurrent of this heterostructure reached 4.8 mA/cm² at 1.23 V (vs. reversible hydrogen electrode) in a 1 M KOH aqueous solution under AM 1.5G illumination, which is much higher than the currently reported photocatalytic water splitting performance of iron oxide nanoarrays. The construction of Fe₂O₃/Cu₂S p-n heterojunction accelerates the separation of photogenerated carriers in the main body of Fe₂O₃ nanorod arrays; as an excellent oxygen evolution catalyst (OEC), the introduction of Co(OH)_x accelerates the kinetic process of interfacial water oxidation leading to the rapid depletion of photogenerated holes, which further improves the charge separation on the photoanode surface. Thus, the synergistic effect between Fe₂O₃/Cu₂S p-n heterojunctions and oxygen evolution catalysts enhanced the iron oxide nanorod array photoanodes.

The reduction of CO₂ to C₂₊ products using photoelectrochemistry (PEC) is significant and highly challenging. However, systematic summaries on PEC CO₂ conversion into C₂₊ products are lacking. Therefore, this paper systematically reviews the current research status of the PEC CO₂ conversion for the preparation of C₂₊ products, including the pathways of C₂₊ products, the usage of catalysts and reactors, and methods for improving C₂₊ product selectivity. Besides, the deficiencies in current research are analyzed, and future developments are discussed.

As an indispensable raw material for silicon-based semiconductor industry, carbon tetrafluoride (CF₄) is widely used as plasma etching and cleaning gas in the manufacture of semiconductors. How to efficiently remove the C₂F₆ impurity during the CF₄ production process is a challenging task as semiconductor industry requires high-purity CF₄ gas. Herein, two fluorine-functionalized porous organic frameworks (F-POFs) named SPPOF-4F and SPPOF-8F were synthesized and used for separation of C₂F₆/CF₄ gases. Single-component gas adsorption experiments and ideal adsorbed solution theory (IAST) calculations indicate that two porous organic frameworks can selectively adsorb C₂F₆ from C₂F₆/CF₄ mixture. Molecular simulations have further complemented these experimental findings by revealing F-induced host-guest interactions between F-POFs and C₂F₆ at a molecular level. Additionally, dynamic breakthrough experiments verified that the F-POFs can capture C₂F₆ in C₂F₆/CF₄ mixture at practical conditions. These results indicate that F-POFs have great potential for application in the separation and purification of CF₄ electronic special gases.