Enhancing the Activity of a Carbon Nitride Photocatalyst by Constructing a Triazine-Heptazine Homojunction.

Establishing homojunctions at the molecular level between different but physicochemically similar phases belonging to the same family of materials is an effective approach to promoting the photocatalytic activity of polymeric carbon nitride (CN) materials. Here, we prepared a CN material with a uniform distribution of homojunctions by combining two synthetic strategies: supramolecular assemblies as the precursor and molten salt as the medium. We designed porous CN rods with triazine-heptazine homojunctions (THCNs) using a melem supramolecular aggregate (Me) and melamine as the precursors and a KCl/LiBr salt mixture as the liquid reaction medium. The triazine/heptazine ratio is controlled by varying the relative amounts of the chosen precursors, and the molten salt treatment enhances the structural order of the interplanar packing units for the THCN skeleton, leading to rapid charge migration. The resulting built-in electric field induced by the triazine-heptazine homojunction enhances photogenerated charge separation; the optimal THCN catalyst exhibits an excellent H2 evolution rate via photocatalytic water splitting, which is ∼24 times as high as that of reference bulk CN, with long-term stability.

FeN3 S1 ─OH Single-Atom Sites Anchored on Hollow Porous Carbon for Highly Efficient pH-Universal Oxygen Reduction Reaction.

Regulating the asymmetric active center of a single-atom catalyst to optimize the binding energy is critical but challenging to improve the overall efficiency of the electrocatalysts. Herein, an effective strategy is developed by introducing an axial hydroxyl (OH) group to the Fe─N4 center, simultaneously assisting with the further construction of asymmetric configurations by replacing one N atom with one S atom, forming FeN3 S1 ─OH configuration. This novel structure can optimize the electronic structure and d-band center shift to reduce the reaction energy barrier, thereby promoting oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) catalytic activities. The optimal catalyst, FeSA -S/N-C (FeN3 S1 ─OH anchored on hollow porous carbon) displays remarkable ORR performance with a half-wave potential of 0.92, 0.78, and 0.64 V versus RHE in 0.1 m KOH, 0.5 m H2 SO4 , and 0.1 m PBS, respectively. The rechargeable liquid Zn-air batteries (LZABs) equipped with FeSA -S/N-C display a higher power density of 128.35 mW cm-2 , long-term operational stability of over 500 h, and outstanding reversibility. More importantly, the corresponding flexible solid-state ZABs (FSZABs@FeSA -S/N-C) display negligible voltage changes at different bending angles during the charging and discharging processes. This work provides a new perspective for the design and optimization of asymmetric configuration for single-atom catalysts applied to the area of energy conversion and storage.

Mixed-valence Cu-based heterostructures for efficient electrochemical nitrate reduction to ammonia.

The electrocatalytic NO3- reduction reaction (NO3RR) to NH3 provides a promising pathway for ambient NH3 synthesis and environmental pollution treatment. Cu and its oxides are recognized as effective NO3RR electrocatalysts due to their favorable d-orbital energy levels and superior kinetics. In this work, mixed-valence Cu-based catalysts with tunable valence states were constructed via an inorganic salt-induced MOF-derived strategy. Notably, optimized Cu-CuxO/C-0.3 featured a Cu/Cu2O heterostructure and demonstrated the lowest Cu valence state. The resulting Cu/Cu2O heterointerface facilitated electron transfer and increased the density of electrochemically active sites, leading to an enhanced faradaic efficiency of 81.4% and a remarkable yield rate of 13.38 mg h-1 cm-2 (ca. 2.39 mol h-1 gcat.-1) at -0.8 V vs. RHE. This work presents insights for designing multi-phase heterostructured NO3RR catalysts and emphasizes their potential significance in efficient ammonia production.

Engineering improved strategies for spinel cathodes in high-performing zinc-ion batteries.

The development of high-performing cathode materials for aqueous zinc-ion batteries (ZIBs) is highly important for the future large-scale energy storage. Owing to the distinctive framework structure, diversity of valences, and high electrochemical activity, spinel materials have been widely investigated and used for aqueous ZIBs. However, the stubborn issues of low electrical conductivity and sluggish kinetics plague their smooth applications in aqueous ZIBs, which stimulates the development of effective strategies to address these issues. This review highlights the recent advances of spinel-based cathode materials that include the configuration of aqueous ZIBs and corresponding reaction mechanisms. Subsequently, the classifications of spinel materials and their properties are also discussed. Then, the review mainly summarizes the effective strategies for elevating their electrochemical performance, including their morphology and structure design, defect engineering, heteroatom doping, and coupling with a conductive support. In the final section, several sound prospects in this fervent field are also proposed for future research and applications.

Cascade Performance of Nitroarenes with Alcohols Boosted by a Hollow Flying Saucer-Shaped Ni-Al2O3 Catalyst via a MOF-Templated Strategy Induced by the Kirkendall Effect.

Catalysts with an open hollow structure can enhance the mass transfer capability of the catalyst during the reaction process, thereby further improving the catalytic performance. In this work, uniform and monodisperse flying-squircher-shaped Al-MOFs were synthesized via a solvothermal method. Furthermore, a hollow structure Al2O3-supported metallic Ni catalyst (termed Ni-Al2O3-HFA) was synthesized via the Kirkendall effect for the hydrogenation-alkylation cascade reaction by employing as-synthesized Al-MOFs as a carrier for impregnation of Ni(NO3)2·6H2O through further calcination and reduction. Various characterizations (e.g., XRD, HADDF-STEM, H2-TPR) were conducted to reveal the superior performance of the developed Ni-Al2O3-HFA catalyst compared to Ni/Al2O3-IWI (Al2O3 obtained from calcination of Al-MOFs) in cascade reaction between nitroarenes and alcohols. We hope to use the MOF template method via the Kirkendall effect to prepare hollow structure nanocatalysts, which can provide a guideline for the preparation of other hollow materials.

Se-doping-induced sulfur vacancy engineering of CuCo2S4 nanosheets for enhanced electrocatalytic overall water splitting.

The coordination of the electronic structure and charge transfer through heteroatomic doping and sulfur vacancies is one of the most vital strategies for enhancing the electrocatalytic performance of the oxygen and hydrogen evolution reactions (OER, HER) through water splitting. Se-doped CuCo2S4 nanosheets (CuCo2S3.68Se0.32) with abundant sulfur vacancies were synthesized via a simple hydrothermal method to achieve remarkably efficient electrocatalytic water splitting. Importantly, incorporating Se in three-dimensional nanosheet structures effectively fine-tunes the electronic structure, ensuring ample accessibility of active sites for swift charge carrier transfer and improved reaction kinetics. The optimized CuCo2S3.68Se0.32 offers substantially high electrocatalytic activity with overpotentials of 65 and 230 mV at the current density of 10 mA cm-2 for HER and OER, respectively, which is comparable to commercial catalysts. Combining Se-doping and rich sulfur vacancies facilitates fast charge transport, thus significantly boosting the electrocatalytic activity. Furthermore, utilizing CuCo2S3.68Se0.32 as both the cathode and anode, a two-electrode electrolyser exhibits remarkable performance. It achieves a low voltage of 1.52 V at 10 mA cm-2 and demonstrates exceptional durability over time. This study investigates the significance of doping and vacancies in enhancing electrocatalytic activity for water splitting.

Multiple Hydrogen Bonding-Assisted High-Strength Hydrogel of Silica/Polyacrylamide Nanocomposite Cross-Linked with Polyethylenimine.

The nanocomposite gel system has been successfully applied as a water shutoff agent to enhance oil recovery (EOR) or for plugging to control lost circulation events. In this study, the silica/polyacrylamide nanocomposite was synthesized via in situ free radical polymerization of acrylamide (AM) monomers in the presence of silica nanoparticles. The composite was cross-linked with polyethylenimine to prepare a high-strength hydrogel. The viscosity test was conducted to determine the gelation time of the gel. Rheological measurements and sand pack breakthrough pressure tests were carried out to measure the gel strength. Attenuated total reflectance-Fourier transform infrared (ATR-FTIR) and scanning electron microscopy (SEM) tests were adopted to characterize the structure and morphology of the gel. The results show that compared to polyacrylamide (PAM) gel, the gelation time of the nanocomposite gel will decrease with increasing gel elasticity modulus, and the breakthrough pressure of the nanocomposite gel is 29.82 MPa, which increased by 65%. As shown in the ATR-FTIR test, this can be attributed to the presence of multiple hydrogen bonds for the PAM molecule with both silica and quartz sand particles. In the composite gel, hydrogen bonding mainly forms between the O atoms of PAM and the H atom on the surface of silica, enhancing gel strength and elasticity modulus with more cross-linking density and less porosity. Moreover, H bonding between additional -NH2 of PAM and quartz sand particles helps improve gel plugging pressure. However, in the silica and PAM mixture gel, the H bonding of silica occupies -NH2 of PAM, which became unavailable to attach on the sand surface, reducing the breakthrough pressure by 30%, although it can enhance the rheological strength. This study suggests that in situ composite of silica in PAM can not only greatly improve gel rheological strength but also help maintain the strong adhesion of PAM molecules onto quartz sand, resulting in better plugging performance in the sand reservoir.

Mechanistic Insights into a Co(II)-Coordinated "Free" Metal Site of 2D Zinc-Based MOFs for ß-Alkylation of Secondary Alcohols with Primary Alcohols.

Through in-depth study of the properties and reaction mechanisms of catalysts, it is possible to better optimize catalytic systems and improve reaction efficiency and selectivity. This remains one of the challenges in the field of catalysis. Therefore, the research and design of catalysts play crucial roles in understanding and optimizing catalytic reaction mechanisms. A robust 2D zinc-based MOFs (Zn-HA) supported Co(II) ion catalyst (Zn-HA@Co) has been designed and synthesized via a coordination-assisted strategy for ß-alkylation of secondary alcohols with primary alcohols. The characterization demonstrated that the anchoring of Co(II) on Zn-HA via coordination could efficiently enhance the Co(II) ion dispersity and interaction between Co(II) and Zn-HA MOFs. Importantly, the density functional theory results have provided mechanistic insights into the energy of the HOMO and LUMO of the Zn-HA@Co catalyst as well as the energy change of the entire process after interacting with the reactants and the specific energy changes of each orbital. The synthesized Zn-HA@Co MOFs effectively lower the energy barrier of the catalytic reaction process. We expect that our research and design of catalysts will serve as valuable guideline for understanding and optimizing catalytic reaction mechanisms.

Recent progress in structural modification of polymer gel electrolytes for use in solid-state zinc-ion batteries.

Zinc-ion batteries are one of the promising energy storage devices, which have the advantages of environmental friendliness, high safety and low price and are expected to be used in large-scale battery application fields. However, four prominent water-induced adverse reactions, including zinc dendrite formation, zinc corrosion, passivation and the hydrogen evolution reaction in aqueous systems, seriously shorten the cycling life of zinc-ion batteries and greatly hinder their development. Based on this, polymer gel electrolytes have been developed to alleviate these issues due to their unique network structure, which can reduce water activity and suppress water-induced side reactions. Based on the challenges of polymer gel electrolytes, this review systematically summarizes the latest research progress in the use of additives in them and explores new perspectives in response to the existing problems with polymer electrolytes. In order to expand the performance of polymer gel electrolytes in zinc-ion batteries, a range of different types of additives are added via physical/chemical crosslinking, such as organic or inorganic substances, natural plants, etc. In addition, different types of additives and polymerization crosslinking from different angles essentially improve the ionic conductivity of the gel electrolyte, inhibit the growth of zinc dendrites, and reduce hydrogen evolution and oxygen-absorbed corrosion. After these modifications of polymer gel electrolytes, a more stable and superior electrochemical performance of zinc-ion batteries can be obtained, which provides some strategies for solid-state zinc-ion batteries.

Engineering metallenes for boosting electrocatalytic biomass-oxidation-assisted hydrogen evolution reaction.

Metallenes exhibit great potential for catalytic reaction, particularly for the hydrogen evolution reaction (HER) and biomass oxidation reaction, due to their favorable electronic configurations, ultrahigh specific surface areas, and highly accessible surface atoms. Therefore, metallenes can function as bifunctional electrocatalysts to boost the energy-saving biomass-oxidation-assisted HER, and have attracted great interest. Given the growing importance of green hydrogen as an alternative energy source in recent years, it is timely and imperative to summarize the recent progress and current status of metallene-based catalysts for the biomass-oxidation-assisted HER. Here, we review the recent advances in metallenes in terms of composition and structural regulations including alloying, nonmetal doping, defect engineering, surface functionalization, and heterostructure engineering strategies and their applications in driving electrocatalytic HER, with special focus on biomass-oxidation-assisted hydrogen production. The underlying structure-activity relationship and mechanisms are also comprehensively discussed. Finally, we also propose the challenges and future directions of metallene-based catalysts for the applications in biomass-oxidation-assisted HER.

3D Hollow Hierarchical Porous Carbon with Fe-N4 -OH Single-Atom Sites for High-Performance Zn-Air Batteries.

The development of innovative and efficient Fe-N-C catalysts is crucial for the widespread application of zinc-air batteries (ZABs), where the inherent oxygen reduction reaction (ORR) activity of Fe single-atom sites needs to be optimized to meet the practical application. Herein, a three-dimensional (3D) hollow hierarchical porous electrocatalyst (ZIF8@FePMPDA-920) rich in asymmetric Fe-N4 -OH moieties as the single atomic sites is reported. The Fe center is in a penta-coordinated geometry with four N atoms and one O atom to form Fe-N4 -OH configuration. Compared to conventional Fe-N4 configuration, this unique structure can weaken the adsorption of intermediates by reducing the electron density of the Fe center for oxygen binding, which decreases the energy barrier of the rate-determining steps (RDS) to accelerate the ORR and oxygen evolution reaction (OER) processes for ZABs. The rechargeable liquid ZABs (LZABs) equipped with ZIF8@FePMPDA-920 display a high power density of 123.11 mW cm-2 and a long cycle life (300 h). The relevant flexible all-solid-state ZABs (FASSZABs) also display outstanding foldability and cyclical stability. This work provides a new perspective for the structural design of single-atom catalysts in the energy conversion and storage areas.

Synergistically engineering of vacancy and doping in thiospinel to boost electrocatalytic oxygen evolution in alkaline water and seawater.

Electronic structure engineering lies at the heart of the catalyst design, however, utilizing one strategy to modify the electronic structure is still challenging to achieve optimal electronic states. Herein, an advanced approach that incorporating both Ru dopants and sulfur vacancies into thiospinel-type FeNi2S4 to synergistically modulate the electronic configuration, is proposed. Deep characterizations and theoretical study reveal that the in-situ formed Ni3+ species are real active centers. Ru doping and sulfur vacancies synergistically tune the electronic states of Ni2+ sites to a near-optimal value, leading to the formation of abundant oxygen evolution reaction (OER)-active Ni3+ species via electrochemical reconstruction. Consequently, the optimized Ru-FeNi2S4 catalyst can exhibit superb electrocatalytic performance towards OER, delivering the overpotentials of 253 mV and 340.8 mV at 10 mA·cm-2 in alkaline water and seawater, respectively. The proper combination of vacancy and heteroatom doping in this work may unlock the catalytic power of conventional catalysts toward electrochemical reactions.

Engineering defective trimetallic metal-organic framework nanosheets for advanced water oxidation electrocatalysis.

Limited by single metal active sites and low electrical conductivity, designing nickel-based metal-organic framework (MOF) materials with high activity and durability remains a challenge. Here, a novel class of two-dimensional trimetallic MOF nanosheets with plentiful active sites, rich metal defects, and facilitated mass and electron transfer channels is developed as efficient electrocatalysts for boosting oxygen evolution reaction (OER). The unique 2D nanosheet structure enlarges the active area; meanwhile, the organic ligand in the MOF can work as a pillar to enlarge the interplanar space to boost the ion and electron transportation, and the synergistic effect between multi-metal active sites can effectively promote the electrocatalytic activity. Interestingly, after an electrochemical activation process, the optimized NiFeZn MOF nanosheets can yield abundant metal defects, enabling them to deliver a low overpotential of 233 mV at 10 mA cm-2 with a much smaller Tafel slope of 37.8 mV dec-1. More importantly, this method is also universal for the synthesis of the NiFe-MOF family for achieving outstanding electrocatalytic OER performance. These findings present a universal strategy for the construction of a novel class of 2D trimetallic MOF nanosheets for the OER.

Etched High-Entropy Prussian Blue Analogues as Trifunctional Catalysts for Water, Ethanol, and Urea Electrooxidation.

The introduction of high-entropy and high specific surface area into Prussian blue analogues (PBAs) has yet to create interest in the field of electrocatalytic small-molecule oxidation reactions. Herein, we synthesize a novel class of high-entropy (HE) PBAs with a high specific surface area via a simple NH3·H2O-etching strategy and systematically investigate the electrocatalytic performance of HE-PBA toward electrocatalytic water, ethanol, and urea oxidation reactions. Importantly, the NH3·H2O-etched HE-PBA (denoted as HE-PBA-e) demonstrated enhanced electrocatalytic performance toward small-molecule oxidation compared to the pristine HE-PBA, reaching 10 mA cm-2 with potentials of 1.56, 1.41, and 1.37 V for the oxygen evolution reaction (OER), ethanol oxidation reaction (EOR), and urea oxidation reaction (UOR), respectively. Deep characterizations suggest that the NH3·H2O etching treatment not only creates rich nanopores to enlarge the surface area and boosts the mass transport and electron transfer but also facilitates the formation of high-valence metal oxides to improve the intrinsic activity. This demonstration of how systematically increasing the high oxidation state of metals will serve as a governing principle for the rational design of more advanced HE-PBAs toward the electrooxidation of small molecules.

Co-doped amorphous NiMoS4 modified with rGO for high-rate performance and long-cycling stability of hybrid supercapacitors.

The electrochemical performance of hybrid capacitors is seriously affected by the slow charging and discharging of the bulk phase. Here, Co-doped amorphous NiMoS4 modified with reduced graphene oxide (rGO) was prepared by a simple one-step hydrothermal method, and the obtained Co-doped NiMoS4/rGO nanocomposite (Ni1-xCoxMoS4/rGO) exhibits a high specific surface area, realizing the redox reaction from the bulk to the surface. Owing to the doping of Co with abundant redox active sites and the support of rGO sheets with high conductivity and a stable structure, the Ni1-xCoxMoS4/rGO anode assembled with an oxidized needle coke (NCO) cathode shows an excellent energy density of 28.9 W h kg-1 at a power density of 968.3 W kg-1. In addition, the hybrid supercapacitor displays a superior cycling performance with a capacity retention of 92.4% after 10 000 cycles. The construction of the Co-doped NiMoS4/rGO nanocomposite provides an effective strategy to boost the activity and stability of amorphous NiMoS4 for high-performance hybrid supercapacitors.

Recent advances in hollow nanomaterials with multiple dimensions for electrocatalytic water splitting.

Electrocatalytic water splitting has great research prospects in the production of green hydrogen energy, and electrocatalysts are the prerequisite. As widely employed efficient electrocatalysts, hollow nanostructures have attracted a lot of research attention due to their excellent catalytic activity and structural stability. Moreover, the abundant catalytically active sites and tunable morphology also make hollow nanomaterials promising electrocatalysts for water splitting. Despite these advantages, the industrial applications of these hollow nanocatalysts are impeded by limitations like the lack of effective synthesis methods and unclear formation mechanisms. Therefore, extensive efforts have been devoted to the development of efficient synthesis strategies to boost the development of more efficient hollow electrocatalysts, and great progress has been achieved in recent years. To gain a better understanding of the rapid development of hollow nanocatalysts for water splitting, we herein organize a review to summarize the recent synthetic methods and advantages of hollow materials with different dimensions. The specific advantages of hollow nanomaterials in electrocatalytic water splitting, such as abundant active sites, a stable structure, high mass transfer efficiency, and reduced aggregation of catalytic particles, are also summarized. Finally, the challenges and prospects of hollow nanostructures with multiple dimensions in electrocatalytic water splitting are further explored.

Hierarchical Hollow CoWO4-Co(OH)2 Heterostructured Nanoboxes Enabling Efficient Water Oxidation Electrocatalysis.

Rational design and construction of well-defined hollow heterostructured nanomaterials assembled by ultrathin nanosheets overtakes crucial role in developing high-efficiency oxygen evolution reaction (OER) electrocatalysts. Herein, a reliable metal-organic framework-mediated and cation-exchange strategy to tune the geometric structure and multicomponent heterostructures has been proposed for the fabrication of hollow CoWO4-Co(OH)2 hierarchical nanoboxes assembled by rich ultrathin nanosheets. Benefiting from the hierarchical hollow nanostructure, the CoWO4-Co(OH)2 nanoboxes offer plenty of metal active centers available for reaction intermediates. Moreover, the well-defined nanointerfaces between CoWO4 and Co(OH)2 can function as the bridge for boosting the efficient electron transfer from CoWO4 to Co(OH)2. As a consequence, the optimized CoWO4-Co(OH)2 nanoboxes can exhibit outstanding electrocatalytic performance toward OER by delivering 10 mA cm-2 with a low overpotential of 280 mV and a small Tafel slope of 70.6 mV dec-1 as well as outstanding electrochemical stability. More importantly, this CoWO4-Co(OH)2 heterostructured nanocatalyst can couple with Pt/C to drive overall water splitting to achieve 10 mA cm-2 with a voltage of 1.57 V.

Recent Advances in Solid-Electrolyte Interphase for Li Metal Anode.

Lithium metal batteries (LMBs) are considered to be a substitute for lithium-ion batteries (LIBs) and the next-generation battery with high energy density. However, the commercialization of LMBs is seriously impeded by the uncontrollable growth of dangerous lithium dendrites during long-term cycling. The generation and growth of lithium dendrites are mainly derived from the unstable solid-electrolyte interphase (SEI) layer on the metallic lithium anode. The SEI layer is a key by-product formed on the surface of the lithium metal anode during the electrochemical reactions and has been the barrier to development in this area. An ideal SEI layer should possess electrical insulating, superior mechanical modulus, high electrochemical stability, and excellent Li-ion conductivity, which could improve the structural stability of the electrode upon a long cycling time. This mini-review carefully summarizes the recent developments in the SEI layer for LMBs, and the relationship between SEI layer optimization and electrochemical property is discussed. In addition, further development direction of a stable SEI layer is proposed.

Engineering NiMoO4/NiFe LDH/rGO multicomponent nanosheets toward enhanced electrocatalytic oxygen evolution reaction.

Rational hybridization of two-dimensional (2D) nanomaterials with extrinsic species has shown great promise for boosting the electrocatalytic oxygen evolution reaction (OER). To date, the rational design and engineering of heterojunctions based on three or more components has been rather limited. Herein, by taking advantage of the high intrinsic activity of NiFe layered double hydroxide (LDH), strong synergistic effects between different components, and good electronic conductivity of reduced graphene oxide (rGO), we demonstrate the successful synthesis of NiMoO4/NiFe LDH/rGO nanosheets. As a proof-of-concept demonstration, the multicomponent nanosheet catalyst with a well-modified electronic structure is applied to boost the electrochemical OER and achieve decent electrocatalytic activity in 1 M KOH electrolyte, which can deliver a current density of 10 mA cm-2 with an overpotential of merely 270 mV and a small Tafel slope of 76.2 mV dec-1, which are markedly superior to those of the commercial RuO2 catalyst (303 mV, 131.9 mV dec-1). This work is expected to provide new insights into furnishing multi-component heterostructures with extended functionalities and more advantageous merits.

Engineering Heterostructured Pd-Bi2Te3 Doughnut/Pd Hollow Nanospheres for Ethylene Glycol Electrooxidation.

The electrooxidation of ethylene glycol (EG) is of vital significance for the conversion from biomass energy into electrical energy via direct fuel cells. However, the EG oxidation reaction (EGOR) suffers from poor efficiency due to the limitation of high-performance electrocatalysts for cleaving the C-C bonds. Herein, this limitation is successfully addressed by fabricating the doughnut-shaped Pd-Bi2Te3 heterostructured catalyst. Notably, the heterojunction Pd-Bi2Te3 nanocatalyst has been demonstrated to be highly active toward the EGOR with superb activity and durability, in which a mass activity as high as 2420.8 mA mg-1 is achieved in alkaline media, being 1.7 times higher than that of the commercial Pd/C catalyst. Upon combination of experimental results with mechanism studies, it is indicated that the remarkable EGOR performance is attributed to the enlarged active areas that stemmed from the doughnut-like structure, as well as the strong synergistic effect from Pd-Bi2Te3 and Pd. More importantly, the highly electroactive Pd-Bi2Te3 can accelerate charge transfer and boost the oxidation of CO-like intermediates, which are conducive to the enhancement in electrochemical stability.