Potassium-Assisted Fabrication of Intrinsic Defects in Porous Carbons for Electrocatalytic CO2 Reduction

Defective Poly(heptazine imide) Nanosheets for Efficient One-Step Two-Electron Photocatalytic O2 Reduction to Medical-Like H2O2

Poly(heptazine imide) (PHI) is a promising photocatalyst for hydrogen peroxide (H2O2) production; however, enhancing its specific surface area to expose internal active sites and understanding their roles in key mechanistic steps for the H2O2 synthesis remain challenging. Here, we utilized organic cations to exfoliate bulk PHI and fabricate PHI nanosheets for producing H2O2 at a rate of 27.35 mmol g-1 h-1 under simulated solar light irradiation, outperforming most of the reported carbon nitride-based catalysts. Importantly, after 36 h of cyclic accumulation reactions in a self-created spiral flow reactor, the H2O2 concentration stabilized at 2.7 wt.%, close to medical sterilization levels. In situ spectroscopic characterizations and density functional theory calculations revealed that the exfoliation results in molecular reconfiguration of the PHI basal planes, forming the active sites to promote charge separation and electron localization. This new structure also creates midgap states, enabling direct H2O2 production via a one-step, two-electron pathway, bypassing the superoxide radical pathway. Theoretical calculations suggest that the localized electronic structure created by the active sites favors the protonation of adsorbed O2 and stabilizes the *OOH species, which converts to H2O2. This study elucidates and underscores the importance of active-site reconfiguration for efficient photocatalytic oxygen reduction reaction (ORR) pathways.

Integrated Electrochemical Biomass Oxidation and CO2 Reduction over Ultra-wide Potential Window

Electrochemical reduction of carbon dioxide (CO2) coupled with biomass oxidation using renewable electricity is considered as a promising strategy for carbon management. However, achieving both high selectivity and large current density over wide potential window remains a significant challenge, hindering practical applications. In this study, a Ni/Fe dual metal-atom catalyst is developed for CO2 reduction, achieving nearly 100 % CO selectivity across an ultra-wide potential window of 1.6 V, surpassing state-of-the-art catalysts. Remarkably, this high CO selectivity is maintained above 98 % even after 100 hours of continuous operation at an industrial current density of 200 mA cm-2, demonstrating excellent long-term stability. When integrated into a solar electricity-driven CO2 reduction coupled 5-hydroxymethylfurfural oxidation system, nearly 100 % CO Faradaic efficiency and 90 % 2,5-furandicarboxylic acid yield are simultaneously obtained. Theoretical calculations reveal that the rate-limiting step for the CO2 reduction reaction varies with the applied potential, and the synergistic interaction between Ni and Fe atoms effectively lowers the limiting energy barrier. This work offers valuable insights for the strategic design and synthesis of catalysts with high activity and selectivity across wide potential window, providing a versatile platform for coupling CO2 reduction with diverse anodic biomass oxidation reactions and renewable energy sources.

Atomically precise Ni clusters inducing active NiN2 sites with uniform-large vacancies towards efficient CO2-to-CO conversion

CO2 electroreduction to CO promises to give an efficient strategy for CO2 fixation and transformation. However, current reported active sites fail to deliver sufficient activity with high CO Faradic efficiency (FEco) over a wide range of potential. Here, we show a general synthetic protocol to fabricate a batch of highly pure and active NiN2 catalysts with precise engineering of the uniform-large (UL) vacancy around the active sites, which is accomplished through the 'pre-deposition + pyrolysis' of various atomically precise Ni clusters (Nin) and in-situ etching of the support by the 'nano bomb' (sulfur-ligand in the clusters). The NiN2 sites with UL vacancies could achieve a high turnover frequency (TOF) of 350000 h-1 with ~100% FEco in a wide potential range of 1500 mV. In-situ infrared spectra and theoretical calculations reveal that a highly pure NiN2 site with UL vacancy contributes to this remarkable catalytic performance compared to the counterparts. This general synthetic strategy enables us to simultaneously engineer active sites and surrounding vacancies with the employment of atomically precise metal clusters, thereby enhancing catalytic performance for other specific reactions.

Synthesis of in-plane Mo2C/MoO3 heterostructures by a novel spatial-confined partial oxidation approach for enhanced TEA sensing

In-plane heterostructures exhibit extraordinary chemical and electron transfer properties, which have received remarkable research attention. However, the synthesis of an in-plane Mo2C/MoO3 heterostructure has been rarely reported, and the deep investigation of the effect of its fine structure on reactivity is of great significance. Notably, the in-plane heterostructures endow the material with abundant grain boundaries, which facilitate the formation of surface acid sites and active oxygen species, thus contributing to the sensing performance. Our work provides a promising platform to design in-plane heterostructures for various advanced applications.

Mesostructure-Specific Configuration of *CO Adsorption for Selective CO2 Electroreduction to C2+ Products

The multi-carbon (C2+) alcohols produced by electrochemical CO2 reduction, such as ethanol and n-propanol, are considered as indispensable liquid energy carriers. In most C-C coupling cases, however, the concomitant gaseous C2H4 product results in the low selectivity of C2+ alcohols. Here, we report rational construction of mesostructured CuO electrocatalysts, specifically mesoporous CuO (m-CuO) and cylindrical CuO (c-CuO), enables selective distribution of C2+ products. The m-CuO and c-CuO show similar selectivity towards total C2+ products (≥76 %), but the corresponding predominant products are C2+ alcohols (55 %) and C2H4 (52 %), respectively. The ordered mesostructure not only induces the surface hydrophobicity, but selectively tailors the adsorption configuration of *CO intermediate: m-CuO prefers bridged adsorption, whereas c-CuO favors top adsorption as revealed by in situ spectroscopies. Computational calculations unravel that bridged *CO adsorbate is prone to deep protonation into *OCH3 intermediate, thus accelerating the coupling of *CO and *OCH3 intermediates to generate C2+ alcohols; by contrast, top *CO adsorbate is apt to undergo conventional C-C coupling process to produce C2H4. This work illustrates selective C2+ products distribution via mesostructure manipulation, and paves a new path into the design of efficient electrocatalysts with tunable adsorption configuration of key intermediates for targeted products.

Addressing the Carbonate Issue: Electrocatalysts for Acidic CO2 Reduction Reaction

Electrochemical CO2 reduction reaction (CO2RR) powered by renewable energy provides a promising route to CO2 conversion and utilization. However, the widely used neutral/alkaline electrolyte consumes a large amount of CO2 to produce (bi)carbonate byproducts, leading to significant challenges at the device level, thereby impeding the further deployment of this reaction. Conducting CO2RR in acidic electrolytes offers a promising solution to address the "carbonate issue"; however, it presents inherent difficulties due to the competitive hydrogen evolution reaction, necessitating concerted efforts toward advanced catalyst and electrode designs to achieve high selectivity and activity. This review encompasses recent developments of acidic CO2RR, from mechanism elucidation to catalyst design and device engineering. This review begins by discussing the mechanistic understanding of the reaction pathway, laying the foundation for catalyst design in acidic CO2RR. Subsequently, an in-depth analysis of recent advancements in acidic CO2RR catalysts is provided, highlighting heterogeneous catalysts, surface immobilized molecular catalysts, and catalyst surface enhancement. Furthermore, the progress made in device-level applications is summarized, aiming to develop high-performance acidic CO2RR systems. Finally, the existing challenges and future directions in the design of acidic CO2RR catalysts are outlined, emphasizing the need for improved selectivity, activity, stability, and scalability.

Extent of As(III) versus As(V) adsorption on iron (oxyhydr) oxides depends on the presence of vacancy cluster-like micropore sites: Insights into a seesaw effect

Iron (oxyhydr)oxides are ubiquitous in terrestrial environments and play a crucial role in controling the fate of arsenic in sediments and groundwater. Although there is evidence that different iron (oxyhydr)oxides have different affinities towards As(III) and As(V), it is still unclear why As(V) adsorption on some iron (oxyhydr)oxides is larger than As(III) adsorption, while it is opposite for other ones. In this study, six typical iron (oxyhydr)oxides are selected to evaluate their adsorption capacities for As(III) and As(V). The characteristics of these iron minerals such as morphology, arsenic adsorption species, and pore size distribution are carefully examined using transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDS), positron annihilation lifetime (PAL) spectroscopy, and X-ray absorption spectroscopy (XAS). We confirm a seesaw effect occurred in different iron minerals for As(III) and As(V) immobilization, i.e., at pH 6.0, adsorption of As(V) on hematite (0.73 μmol m-2) and magnetite (0.33 μmol m-2) is higher than for As(III) (0.61 μmol m-2 and 0.27 μmol m-2, respectively), for goethite and lepidocrocite it is almost equal, while As(III) sorption on ferrihydrite (5.77 μmol m-2) and schwertmannite (28.41 μmol m-2) showed higher sorption than As(V) (1.53 μmol m-2 and 12.99 μmol m-2, respectively). PAL analysis demonstrates that ferrihydrite and schwertmannite have a large concentration of vacancy cluster-like micropores, significantly more than goethite and lepidocrocite, followed by hematite and magnetite. The difference of adsorption of As(III) and As(V) to different iron (oxyhydr)oxides is due to differences in the abundance of vacancy cluster-like micropore sites, which are conducive for smaller size As(III) immobilization but not for larger size of As(V). The findings of this study provide novel insights into a seesaw effect for As(III) and As(V) immobilization on naturally occurring iron mineral.

Multiscale Tunable Nanorings Based on Bi-Component Micellar-Configuration-Transformation Induced by Hydrophobicity

Ringy nanostructures are amazing materials, displaying unique optical, magnetic, and electronic properties highly related to their dimensions. A strategy capable of continuously tailoring the diameter of nanorings is the key to elucidating their structure-function relationship. Herein, a method of bi-component micellar-configuration-transformation induced by hydrophobicity for the synthesis of nanorings with diameters ranging from submicron (≈143 nm) to micron (≈4.8 µm) and their carbonaceous analogs is established. Remarkably, the nanorings fabricated with this liquid phase strategy achieve the record for the largest diameter span. Through varying the molecular lengths of fatty alcohols and copolymers, shortening the molecular length of fatty alcohol can swell the primary micelles, improve the exposure of hydrophobic component and boost the assembly kinetics for ultra-large nanorings is shown here. On the other hand, shortening the molecular length of the copolymer will give rise to ultra-small nanorings by reducing the size of primary micelles and shortening the assembly time. When assembling the nanorings into monolayer arrays and then depositing Au, such substrate displays enhanced surface-enhanced Raman scattering (SERS) performance. This research develops a facile method for the controllable synthesis of ringy materials with multiscale tunable diameters and may inspire more interesting applications in physics, optical, and sensors.

Balancing Edge Defects and Graphitization in a Pt-Fe/Carbon Electrocatalyst for High-Power-Density and Durable Flow Seawater-Al/Acid Hybrid Fuel Cells and Zn-Air Batteries

Overcoming the trade-off between the graphitization of the carbon substrate and enhanced electronic metal-support interaction (EMSI) and intrinsic activity of Pt-C catalysts remains a major challenge for ensuring the durable operation of energy conversion devices. This article presents a hybrid catalyst consisting of PtFe nanoparticles and single Pt and Fe atoms supported on N-doped carbon (PtFeNPs@PtFeSAs-N-C), which exhibits improved activities in hydrogen evolution and oxygen reduction reactions (HER and ORR, respectively) and has excellent durability owing to the high graphitization, rich edge defects, and porosity of the carbon in PtFeNPs@PtFeSAs-N-C, as well as strong EMSI between the PtFe nanoparticles and edge-defective carbon embedded with Pt and Fe atoms. According to theoretical calculations, the strong EMSI optimizes the H* adsorption-desorption and facilitates the adsorption OOH*, accelerating the HER and ORR processes. A novel flow seawater-Al/acid hybrid fuel cell using the PtFeNPs@PtFeSAs-N-C cathode can serve as a high-efficiency energy conversion device that delivers a high power density of 109.5 mW cm-2 while producing H2 at a significantly high rate of 271.6 L m-2 h-1. Moreover, PtFeNPs@PtFeSAs-N-C exhibits a remarkable performance (high power density of 298.0 mW cm-2 and long-term durability of 1000 h) in a flow Zn-air battery.

Remarkable Active Site Utilization in Edge-Hosted-N Doped Carbocatalysts for Fenton-Like Reaction

Improving the utilization of active sites in carbon catalysts is significant for various catalytic reactions, but still challenging, mainly due to the lack of strategies for controllable introduction of active dopants. Herein, a novel "Ar plasma etching-NH3 annealing" strategy is developed to regulate the position of active N sites, while maintaining the same nitrogen species and contents. Theoretical and experimental results reveal that the edge-hosted-N doped carbon nanotubes (E-N-CNT), with only 0.29 at.% N content, show great affinity to peroxymonosulfate (PMS), and exhibit excellent Fenton-like activity by generating singlet oxygen (1O2), which can reach as high as 410 times higher than the pristine CNT. The remarkable utilization of edge-hosted nitrogen atom is further verified by the edge-hosted-N enriched carbocatalyst, which shows superior capability for 4-chlorophenol degradation with a turnover frequency (TOF) value as high as 3.82 min-1, and the impressive TOF value can even surpass those of single-atom catalysts. This work proposes a controllable position regulation of active sites to improve atom utilization, which provides a new insight into the design of excellent Fenton-like catalysts with remarkable atom utilization efficiency.

Design and regulation of defective electrocatalysts

Electrocatalysts are the key components of electrochemical energy storage and conversion devices. High performance electrocatalysts can effectively reduce the energy barrier of the chemical reactions, thereby improving the conversion efficiency of energy devices. The electrocatalytic reaction mainly experiences adsorption and desorption of molecules (reactants, intermediates and products) on a catalyst surface, accompanied by charge transfer processes. Therefore, surface control of electrocatalysts plays a pivotal role in catalyst design and optimization. In recent years, many studies have revealed that the rational design and regulation of a defect structure can result in rearrangement of the atomic structure on the catalyst surface, thereby efficaciously promoting the electrocatalytic performance. However, the relationship between defects and catalytic properties still remains to be understood. In this review, the types of defects, synthesis methods and characterization techniques are comprehensively summarized, and then the intrinsic relationship between defects and electrocatalytic performance is discussed. Moreover, the application and development of defects are reviewed in detail. Finally, the challenges existing in defective electrocatalysts are summarized and prospected, and the future research direction is also suggested. We hope that this review will provide some principal guidance and reference for researchers engaged in defect and catalysis research, better help researchers understand the research status and development trends in the field of defects and catalysis, and expand the application of high-performance defective electrocatalysts to the field of electrocatalytic engineering.

Regulating Spin Polarization via Axial Nitrogen Traction at Fe-N5 Sites Enhanced Electrocatalytic CO2 Reduction for Zn-CO2 Batteries

Single Fe sites have been explored as promising catalysts for the CO2 reduction reaction to value-added CO. Herein, we introduce a novel molten salt synthesis strategy for developing axial nitrogen-coordinated Fe-N5 sites on ultrathin defect-rich carbon nanosheets, aiming to modulate the reaction pathway precisely. This distinctive architecture weakens the spin polarization at the Fe sites, promoting a dynamic equilibrium of activated intermediates and facilitating the balance between *COOH formation and *CO desorption at the active Fe site. Notably, the synthesized FeN5, supported on defect-rich in nitrogen-doped carbon (FeN5@DNC), exhibits superior performance in CO2RR, achieving a Faraday efficiency of 99 % for CO production (-0.4 V vs. RHE) in an H-cell, and maintaining a Faraday efficiency of 98 % at a current density of 270 mA cm-2 (-1.0 V vs. RHE) in the flow cell. Furthermore, the FeN5@DNC catalyst is assembled as a reversible Zn-CO2 battery with a cycle durability of 24 hours. In situ IR spectroscopy and density functional theory (DFT) calculations reveal that the axial N coordination traction induces a transformation in the crystal field and local symmetry, therefore weakening the spin polarization of the central Fe atom and lowering the energy barrier for *CO desorption.

Defect Engineering in a Nanoporous Thulium-Organic Framework in Catalyzing Knoevenagel Condensation and Chemical CO2 Fixation

Defect engineering is an extremely effective strategy for modifying metal-organic frameworks (MOFs), which can break through the application limitations of traditional MOFs and enhance their functionality. Herein, we report a highly robust nanoporous thulium(III)-organic framework, {[Tm2(BDCP)(H2O)5](NO3)·3DMF·2H2O}n (NUC-105), with [Tm(COO)2(H2O)]n chains and [Tm2(COO)4(H2O)8] dinuclears as metal nodes and 2,6-bis(2,4-dicarboxylphenyl)-4-(4-carboxylphenyl)pyridine (BDCP) linkers. In NUC-105, each of the four chains of [Tm(COO)2]n and the two rows of [Tm2(COO)4(H2O)8] units is unified by the organic skeleton, resulting in a rectangular nanochannel with dimensions of 15.35 Å × 11.29 Å, which leads to a void volume of 50%. It is worth mentioning that the [Tm2(COO)4(H2O)8] cluster is very rare in terms of its higher level of associated water molecules, implying that the activated host framework can serve as a strong Lewis acid. NUC-105a exhibited great heterogeneous catalytic performance for CO2 cycloaddition with epoxides under the reaction conditions (0.60 mol % NUC-105a, 5.0 mol % n-Bu4NBr, 65 °C, 5 h), ensuring exclusive selectivity and high conversion rates. In addition, NUC-105a's strong catalytic impact on the Knoevenagel condensation of aldehydes and malononitrile can be attributed to the collaboration between the drastically unsaturated Lewis acidic Tm3+ centers and Lewis basic pyridine groups.

Metal-Organic Frameworks Derived Carbon-Supported Metal Electrocatalysts for Energy-Related Reduction Reactions

Electrochemical reduction reactions, as cathodic processes in many energy-related devices, significantly impact the overall efficiency determined mainly by the performance of electrocatalysts. Metal-organic frameworks (MOFs) derived carbon-supported metal materials have become one of star electrocatalysts due to their tunable structure and composition through ligand design and metal screening. However, for different electroreduction reactions, the required active metal species vary in phase component, electronic state, and catalytic center configuration, hence requiring effective customization. From this perspective, this review comprehensively analyzes the structural design principles, metal loading strategies, practical electroreduction performance, and complex catalytic mechanisms, thereby providing insights and guidance for the future rational design of such electroreduction catalysts.

Long-range interactions driving neighboring Fe-N4 sites in Fenton-like reactions for sustainable water decontamination

Actualizing efficient and sustainable environmental catalysis is essential in global water pollution control. The single-atom Fenton-like process, as a promising technique, suffers from reducing potential environmental impacts of single-atom catalysts (SACs) synthesis and modulating functionalized species beyond the first coordination shell. Herein, we devised a high-performance SAC possessing impressive Fenton-like reactivity and extended stability by constructing abundant intrinsic topological defects within carbon planes anchored with Fe-N4 sites. Coupling atomic Fe-N4 moieties and adjacent intrinsic defects provides potent synergistic interaction. Density functional theory calculations reveal that the intrinsic defects optimize the d-band electronic structure of neighboring Fe centers through long-range interactions, consequently boosting the intrinsic activity of Fe-N4 sites. Life cycle assessment and long-term steady operation at the device level indicate promising industrial-scale treatment capability for actual wastewater. This work emphasizes the feasibility of synergistic defect engineering for refining single-atom Fenton-like chemistry and inspires rational materials design toward sustainable environmental remediation.

Metal-Organic Frameworks for Electrocatalytic CO2 Reduction: From Catalytic Site Design to Microenvironment Modulation

The electrochemical reduction of CO2 to high-value carbon-based chemicals provides a sustainable approach to achieving an artificial carbon cycle. In the decade, metal-organic frameworks (MOFs), a kind of porous crystalline porous materials featuring well-defined structures, large surface area, high porosity, diverse components, easy tailorability, and controllable morphology, have attracted considerable research attention, serving as electrocatalysts to drive CO2 reduction. In this review, the reaction mechanisms of electrochemical CO2 reduction and the structure/component advantages of MOFs meeting the requirements of electrocatalysts for CO2 reduction are analyzed. After that, the representative progress for the precise fabrication of MOF-based electrocatalysts for CO2 reduction, focusing on catalytic site design and microenvironment modulation, are systemically summarized. Furthermore, the emerging applications and promising research for more practical scenarios related to electrochemical CO2 conversion are specifically proposed. Finally, the remaining challenges and future outlook of MOFs for electrochemical CO2 reduction are further discussed.

Bifunctional Catalysts for CO2 Reduction and O2 Evolution: A Pivotal for Aqueous Rechargeable Zn-CO2 Batteries

The quest for the advancement of green energy storage technologies and reduction of carbon footprint is determinedly rising toward carbon neutrality. Aqueous rechargeable Zn-CO2 batteries (ARZCBs) hold the great potential to encounter both the targets simultaneously, i.e., green energy storage and CO2 conversion to value-added chemicals/fuels. The major descriptor of ARZCBs efficiency is allied with the reactions occurring at cathode during discharging (CO2 reduction) and charging (O2 evolution) which own different fundamental mechanisms and hence mandate the employment of two different catalysts. This presents an overall complex and expensive battery system which requires a concrete solution, while the development and application of a bifunctional cathode catalyst toward both reactions could reduce the complexity and cost and thus can be a pivotal for ARZCBs. However, despite the increasing research interest and ongoing research, a systematic evaluation of bifunctional catalysts is rarely reported. In this review, the need of bifunctional cathode catalysts for ARZCBs and associated challenges with strategies have been critically assessed. A detailed progress examination and understanding toward designing of bifunctional catalyst for ARZCBs have been provided. This review will enlighten the future research approaching boosted performance of ARZCBs through the development of efficient bifunctional cathode catalysts.

Ferrocene-modified covalent organic framework for efficient oxygen evolution reaction and CO2 electroreduction

A ferrocene-modified COF, namely Ni-Tph-COF-Fc, was synthesized and applied in OER. Compared with Ni-Tph-COF-OH, Ni-Tph-COF-Fc shows improved performance with a current density of 99.6 mA cm-2, an overpotential of 450 mV, and a Tafel slope of 73.1 mV dec-1, which may be attributed to a synergy between introduced ferrocene and metalloporphyrin in the COFs. Moreover, the enhanced OER performance leads to an improved CO2RR performance with an FECO of 93.1%. This work represents an effective strategy to enhance the anodic OER performance and realize efficient CO2RR.

Thermal-Driven Dispersion of Bismuth Nanoparticles among Carbon Matrix for Efficient Carbon Dioxide Reduction

The poor electrocatalytic stability and rapid deactivation of metal electrocatalysts are always present in the electrocatalytic conversion of carbon dioxide (CO2) due to the harsh reduction condition. Herein, we demonstrate the controllable dispersion of ultrafine bismuth nanoparticles among the hollow carbon shell (Bi@C-700-4) simply by a thermal-driven diffusion process. The confinement effect of nitrogen-doped carbon matrix is able to low the surface energy of bismuth nanoparticles against the easy aggregation commonly observed for the thermal treatment. On the basis of the synergistic effect and confinement effect between bismuth nanoparticles and carbon matrix, the highly dispersed active sites render the obviously improved electrocatalytic activity and stability for CO2 reduction into formate. The in situ experimental observations on the reduction process and theoretical calculations reveal that the incorporation of bismuth nanoparticles with nitrogen-doped carbon matrix would promote the activation of CO2 and the easy formation of key intermediate (*OCHO), thus leading the enhanced electrocatalytic activity, with a Faradaic Efficiency (FE) of formate about 94.8 % and the long-time stability. Furthermore, the coupling of an anode for 5-hydroxymethylfurfural oxidation reaction (HMFOR) in solar-driven system renders the high 2,5-furandicarboxylic acid (FDCA) yield of 81.2 %, presenting the impressive solar-to-fuel conversion.

Shear Field-Controlled Synthesis of Nitrogen-Doped Carbon Nanochains Forest with High-Density sp3 Defects for Efficient CO2 Electroreduction Reaction

Defect engineering and nitrogen doping being effective strategies for modulating the surface chemical state of the carbon matrix have been widely explored to promote the catalytic activity in the territory of electrochemical energy storage and conversion devices. However, the controllable synthesis of carbon material with high-density specific defects and high nitrogen doping is still full of challenges. Here, we first synthesize one-dimensional necklace-like nitrogen-doped carbon nanochains (N-CNCs) with abundant defects on carbon fiber paper (CFP) by chemical vapor deposition (CVD) method. The resultant nanostructures are a bunch of interconnected carbon spheres with a hollow structure at the internode and present the complete one-dimensional nanochain configuration. Specifically, the N-CNCs with a corrugated surface possesses high content of sp3 defects (31.2%) and nitrogen (23.6 at %). Combining finite element analysis and experimental results, it reveals that the robust shear field generated by etching gas releasing from thermal decomposition of melamine in situ modulates the CVD process via changing the size and force environment of the metal catalyst droplets for formation of N-CNCs. Benefiting from the high ratio of sp3/sp2 and nitrogen doped on the surface, the N-CNCs@CFP displays a superior electrocatalytic performance for CO2RR, delivering CO Faradaic efficiency of 95.9% and a current density of 23.2 mA cm-2 at -0.86 V vs RHE. This work provides promising synthesis strategy and some inspirations for construction of ultradense and specific defects coupling with nitrogen doping sites into carbon materials to achieve high-efficiency electrocatalysis applications.

Synthesis and Electrocatalytic Applications of Layer-Structured Metal Chalcogenides Composites

Featured with the attractive properties such as large surface area, unique atomic layer thickness, excellent electronic conductivity, and superior catalytic activity, layered metal chalcogenides (LMCs) have received considerable research attention in electrocatalytic applications. In this review, the approaches developed to synthesize LMCs-based electrocatalysts are summarized. Recent progress in LMCs-based composites for electrochemical energy conversion applications including oxygen reduction reaction, carbon dioxide reduction reaction, oxygen evolution reaction, hydrogen evolution reaction, overall water splitting, and nitrogen reduction reaction is reviewed, and the potential opportunities and practical obstacles for the development of LMCs-based composites as high-performing active substances for electrocatalytic applications are also discussed. This review may provide an inspiring guidance for developing high-performance LMCs for electrochemical energy conversion applications.

Regulating Local Atomic Environment around Vacancies for Efficient Hydrogen Evolution

Defect engineering is essential for the development of efficient electrocatalysts at the atomic level. While most work has focused on various vacancies as effective catalytic modulators, little attention has been paid to the relation between the local atomic environment of vacancies and catalytic activities. To face this challenge, we report a facile synthetic approach to manipulate the local atomic environments of vacancies in MoS2 with tunable Mo-to-S ratios. Our studies indicate that the MoS2 with more Mo terminated vacancies exhibits better hydrogen evolution reaction (HER) performance than MoS2 with S terminated vacancies and defect-free MoS2. The improved performance originates from the adjustable orbital orientation and distribution, which is beneficial for regulating H adsorption and eventually boosting the intrinsic per-site activity. This work uncovers the underlying essence of the local atomic environment of vacancies on catalysis and provides a significant extension of defect engineering for the rational design of transition metal dichalcogenides (TMDs) catalysts and beyond.

Microwave-Assisted Rapid Synthesis of MOF-Based Single-Atom Ni Catalyst for CO2 Electroreduction at Ampere-Level Current

Carbon-based single-atom catalysts (SACs) have attracted tremendous interest in heterogeneous catalysis. However, the common electric heating techniques to produce carbon-based SACs usually suffer from prolonged heating time and tedious operations. Herein, a general and facile microwave-assisted rapid pyrolysis method is developed to afford carbon-based SACs within 3 min without inert gas protection. The obtained carbon-based SACs present high porosity and comparable carbonization degree to those obtained by electric heating techniques. Specifically, the single-atom Ni implanted N-doped carbon (Ni1 -N-C) derived from a Ni-doped metal-organic framework (Ni-ZIF-8) exhibits remarkable CO Faradaic efficiency (96 %) with a substantial CO partial current density (jCO ) up to 1.06 A/cm2 in CO2 electroreduction, far superior to the counterpart obtained by traditional pyrolysis with electric heating. Mechanism investigations reveal that the resulting Ni1 -N-C presents abundant defective sites and mesoporous structure, greatly facilitating CO2 adsorption and mass transfer. This work establishes a versatile approach to rapid and large-scale synthesis of SACs as well as other carbon-based materials for efficient catalysis.

Regulation Strategy of Nanostructured Engineering on Indium-Based Materials for Electrocatalytic Conversion of CO2

Electrochemical carbon dioxide reduction (CO2 RR), as an emerging technology, can combine with sustainable energies to convert CO2 into high value-added products, providing an effective pathway to realize carbon neutrality. However, the high activation energy of CO2 , low mass transfer, and competitive hydrogen evolution reaction (HER) leads to the unsatisfied catalytic activity. Recently, Indium (In)-based materials have attracted significant attention in CO2 RR and a series of regulation strategies of nanostructured engineering are exploited to rationally design various advanced In-based electrocatalysts, which forces the necessary of a comprehensive and fundamental summary, but there is still a scarcity. Herein, this review provides a systematic discussion of the nanostructure engineering of In-based materials for the efficient electrocatalytic conversion of CO2 to fuels. These efficient regulation strategies including morphology, size, composition, defects, surface modification, interfacial structure, alloying, and single-atom structure, are summarized for exploring the internal relationship between the CO2 RR performance and the physicochemical properties of In-based catalysts. The correlation of electronic structure and adsorption behavior of reaction intermediates are highlighted to gain in-depth understanding of catalytic reaction kinetics for CO2 RR. Moreover, the challenges and opportunities of In-based materials are proposed, which is expected to inspire the development of other effective catalysts for CO2 RR.

Tailoring C─N Containing Compounds into Carbon Nanomaterials with Tunable Morphologies for Electrocatalytic Applications

Carbon materials with unique sp2 -hybridization are extensively researched for catalytic applications due to their excellent conductivity and tunable physicochemical properties. However, the development of economic approaches to tailoring carbon materials into desired morphologies remains a challenge. Herein, a convenient "bottom-up" strategy by pyrolysis of graphitic carbon nitride (g-C3 N4 ) (or other carbon/nitrogen (C, N)-enriched compounds) together with selected metal salts and molecules is reported for the construction of different carbon-based catalysts with tunable morphologies, including carbon nano-balls, carbon nanotubes, nitrogen/sulfur (S, N) doped-carbon nanosheets, and single-atom catalysts, supported by carbon layers. The catalysts are systematically investigated through various microscopic, spectroscopic, and diffraction methods and they demonstrate promising and broad applications in electrocatalysis such as in the oxygen reduction reaction and water splitting. Mechanistic monitoring of the synthesis process through online thermogravimetric-gas chromatography-mass spectrometry measurements indicates that the release of C─N-related moieties, such as dicyan, plays a key role in the growth of carbon products. This enables to successfully predict other widely available precursor compounds beyond g-C3 N4 such as caffeine, melamine, and urea. This work develops a novel and economic strategy to generate morphologically diverse carbon-based catalysts and provides new, essential insights into the growth mechanism of carbon nanomaterials syntheses.

Recent Advances in Hierarchical Porous Engineering of MOFs and Their Derived Materials for Catalytic and Battery: Methods and Application

Hierarchical porous materials have attracted the attention of researchers due to their enormous specific surface area, maximized active site utilization efficiency, and unique structure and properties. In this context, metal-organic frameworks (MOFs) offer a unique mix of properties that make them particularly appealing as tunable porous substrates containing highly active sites. This review focuses on recent advances in the types and synthetic strategies of hierarchical porous MOFs and their derived materials. Furthermore, it highlights the relationship between the mass diffusion and transport of hierarchical porous structures and the pore size with examples and simulations, while identifying their potential and limitations. On this basis, how the synthesis conditions affect the structure and electrochemical properties of MOFs based hierarchical porous materials with different structures is discussed, highlighting the prospects and challenges for the synthetization, as well as further scientific research and practical applications. Finally, some insights into current research and future design ideas for advanced MOFs based hierarchical porous materials are presented.

Electrocatalysis of nitrogen pollution: transforming nitrogen waste into high-value chemicals

On 16 June 2023, the United Nations Environment Programme highlighted the severity of nitrogen pollution faced by humans and called for joint action for sustainable nitrogen use. Excess nitrogenous waste (NW: NO, NO2, NO2-, NO3-, etc.) mainly arises from the use of synthetic fertilisers, wastewater discharge, and fossil fuel combustion. Although the amount of NW produced can be minimised by reducing the use of nitrogen fertilisers and fossil fuels, the necessity to feed seven billion people on Earth limits the utility of this approach. Compared to current industrial processes, electrocatalytic NW reduction or CO2-NW co-reduction offers a potentially greener alternative for recycling NW and producing high-value chemicals. However, upgrading this technology to connect upstream and downstream industrial chains is challenging. This viewpoint focuses on electrocatalytic NW reduction, a cutting-edge technology, and highlights the challenges in its practical application. It also discusses future directions to meet the requirements of upstream and downstream industries by optimising production processes, including the pretreatment and supply of nitrogenous raw materials (e.g. flue gas and sewage), design and macroscopic preparation of electrocatalysts, and upscaling of reactors and other auxiliary equipment.

Dual-Functionalized Ca Enables High Sodiation Kinetics for Hard Carbon in Sodium-Ion Batteries

Hard carbons (HCs), while a leading candidate for sodium-ion battery (SIB) anode materials, face challenges in their unfavorable sodiation kinetics since the intricate microstructure of HCs complicates the Na+ diffusion channel. Herein, a Hovenia dulcis-derived HC realizes a markedly enhanced high-rate performance in virtue of dual-functionalized Ca. The interlayer doped Ca2+ effectively enlarges the interlayer spacing, while the in situ-formed CaSe templates induce the formation of hierarchical pore structures and intrinsic defects, significantly providing fast Na+ diffusion channels and abundant active sites and thus enhancing the sodium storage kinetics. Achieved by the synergistic effect of regulation of intrinsic microcrystalline and pore structures, the optimized HC shows remarkable performance enhancements, including a high reversible capacity of 350.3 mA h g-1 after 50 cycles at 50 mA g-1, a high-capacity retention rate of 95.3% after 1000 cycles, and excellent rate performance (108.4 mA h g-1 at 2 A g-1). This work sheds light on valuable insight into the structural adjustment of high-rate HCs, facilitating the widespread utilization of SIBs.

Surface Activation by Single Ru Atoms for Enhanced High-Temperature CO2 Electrolysis

Cathodic CO2 adsorption and activation is essential for high-temperature CO2 electrolysis in solid oxide electrolysis cells (SOECs). However, the component of oxygen ionic conductor in the cathode displays limited electrocatalytic activity. Herein, stable single Ruthenium (Ru) atoms are anchored on the surface of oxygen ionic conductor (Ce0.8 Sm0.2 O2-δ , SDC) via the strong covalent metal-support interaction, which evidently modifies the electronic structure of SDC surface for favorable oxygen vacancy formation and enhanced CO2 adsorption and activation, finally evoking the electrocatalytic activity of SDC for high-temperature CO2 electrolysis. Experimentally, SOEC with the Ru1 /SDC-La0.6 Sr0.4 Co0.2 Fe0.8 O3-δ cathode exhibits a current density as high as 2.39 A cm-2 at 1.6 V and 800 °C. This work expands the application of single atom catalyst to the high-temperature electrocatalytic reaction in SOEC and provides an efficient strategy to tailor the electronic structure and electrocatalytic activity of SOEC cathode at the atomic scale.

Green synthesis of bifunctional phthalocyanine-porphyrin cofs in water for efficient electrocatalytic CO2 reduction coupled with methanol oxidation

Electrocatalytic CO2 reduction (ECR) coupled with organic oxidation is a promising strategy to produce high value-added chemicals and improve energy efficiency. However, achieving the efficient redox coupling reaction is still challenging due to the lack of suitable electrocatalysts. Herein, we designed two bifunctional polyimides-linked covalent organic frameworks (PI-COFs) through assembling phthalocyanine (Pc) and porphyrin (Por) by non-toxic hydrothermal methods in pure water to realize the above catalytic reactions. Due to the high conductivity and well-defined active sites with different chemical environments, NiPc-NiPor COF performs efficient ECR coupled with methanol oxidation reaction (MOR) (Faradaic efficiency of CO (FECO) = 98.12%, partial current densities of CO (jCO) = 6.14 mA cm-2 for ECR, FEHCOOH = 93.75%, jHCOOH = 5.81 mA cm-2 for MOR at low cell voltage (2.1 V) and remarkable long-term stability). Furthermore, experimental evidences and density functional theory (DFT) calculations demonstrate that the ECR process mainly conducts on NiPc unit with the assistance of NiPor, meanwhile, the MOR prefers NiPor conjugating with NiPc. The two units of NiPc-NiPor COF collaboratively promote the coupled oxidation-reduction reaction. For the first time, this work achieves the rational design of bifunctional COFs for coupled heterogeneous catalysis, which opens a new area for crystalline material catalysts.

Quantitative Contribution of Oxygen Vacancy Defects to Arsenate Immobilization on Hematite

Hematite is a common iron oxide in natural environments, which has been observed to influence the transport and fate of arsenate by its association with hematite. Although oxygen vacancies were demonstrated to exist in hematite, their contributions to the arsenate immobilization have not been quantified. In this study, hematite samples with tunable oxygen vacancy defect (OVD) concentrations were synthesized by treating defect-free hematite using different NaBH4 solutions. The vacancy defects were characterized by positron annihilation lifetime spectroscopy, Doppler broadening of annihilation radiation, extended X-ray absorption fine structure (EXAFS), thermogravimetric mass spectrometry (TG-MS), electron paramagnetic resonance (EPR), and X-ray photoelectron spectroscopy (XPS). The results revealed that oxygen vacancy was the primary defect type existing on the hematite surface. TG-MS combined with EPR analysis allowed quantification of OVD concentrations in hematite. Batch experiments revealed that OVDs had a positive effect on arsenate adsorption, which could be quantitatively described by a linear relationship between the OVD concentration (Cdef, mmol m-2) and the enhanced arsenate adsorption amount caused by defects (ΔQm, μmol m-2) (ΔQm = 20.94 Cdef, R2 = 0.9813). NH3-diffuse reflectance infrared Fourier transform (NH3-DRIFT) analysis and density functional theory (DFT) calculations demonstrated that OVDs in hematite were beneficial to the improvement in adsorption strength of surface-active sites, thus considerably promoting the immobilization of arsenate.

Creating interfaces of Cu0/Cu+ in oxide-derived copper catalysts for electrochemical CO2 reduction to multi-carbon products

Electrochemical carbon dioxide reduction reaction (CO₂RR) is an effective approach to capture CO₂ and convert it into value-added chemicals and fuels, thereby reducing excess CO₂ emissions. Recent reports have shown that copper-based catalysts exhibit excellent performance in converting CO₂ into multi-carbon compounds and hydrocarbons. However, theselectivityto the couplingproductsispoor. Therefore, tuningCO₂-reductionselectivitytoward C₂₊productsover Cu-based catalyst is one of the most important issues in CO₂RR. Herein, we prepare a nanosheet catalyst with interfaces of Cu⁰/Cu⁺. The catalyst achieves Faraday efficiency (FE) of C₂₊ over 50% in a wide potential window between - 1.2 V to - 1.5 V versus reversible hydrogen electrode (vs. RHE). Moreover, the catalyst exhibits maximum FE of 44.5% and 58.9% towards C₂H₄ and C₂₊, with a partial current density of 10.5 mA cm^-2 at - 1.4 V. Density functional theory (DFT) calculations show that the interface of Cu⁰/Cu⁺ facilitates CC coupling to form C₂₊ products, while inhibits CO₂conversion toC₁products.

Metal-organic framework-derived bird's nest-like capsules for phosphorous small molecules towards flame retardant polyurea composites

The loading treatment of phosphorus flame retardants can mitigate their migration and plasticization effect. However, designing suitable carriers has remained a great challenge. Herein, two kinds of Co-based isomers, namely cobalt-cobalt layered double hydroxides (CoCo-LDH) and cobalt basic carbonate (CBC), were synthesized by employing ZIF-67 as a self-template, assemblied into two different nanostructures namely multi-yolk@shell CBC@CoCo-LDH (m-CBC@LDH) and solid CBC nanoparticles by facilely tuning the reaction time, which were employed as carriers, respectively. Subsequently, triphenyl phosphate (TPP)-loaded m-CBC@LDH (m-CBC-P@LDH) was prepared using TPP as the guest. The m-CBC@LDH with high specific surface area and hollow structure exhibited up to more than 30% of TPP loading. The peak of heat release rate and total heat release of polyurea composite blended with 5 wt% m-CBC-P@LDH reduced by 41.7% and 20.6% respectively, and the mechanical properties were less damaged. This work complements a feasible approach for preparation of metal-organic frameworks-derived flame retardant carriers.

A rational design of functional porous frameworks for electrocatalytic CO2 reduction reaction

The electrocatalytic CO₂ reduction reaction (ECO₂RR) is considered one of the approaches with the most potential to achieve lower carbon emissions in the future, but a huge gap still exists between the current ECO₂RR technology and industrial applications. Therefore, the design and preparation of catalysts with satisfactory activity, selectivity and stability for the ECO₂RR have attracted extensive attention. As a classic type of functional porous framework, crystalline porous materials (e.g., metal organic frameworks (MOFs) and covalent organic frameworks (COFs)) and derived porous materials (e.g., MOF/COF composites and pyrolysates) have been regarded as superior catalysts for the ECO₂RR due to their advantages such as designable porosity, modifiable skeleton, flexible active site structure, regulable charge transfer pathway and controllable morphology. Meanwhile, with the rapid development of nano-characterization and theoretical calculation technologies, the structure-activity relationships of functional porous frameworks have been comprehensively considered, i.e., metallic element type, local coordination environment, and microstructure, corresponding to selectivity, activity and mass transfer efficiency for the ECO₂RR, respectively. In this review, the rational design strategy for functional porous frameworks is briefly but precisely generalized based on three key factors including metallic element type, local coordination environment, and microstructure. Then, details about the structure-activity relationships for functional porous frameworks are illustrated in the order of MOFs, COFs, composites and pyrolysates to analyze the effect of the above-mentioned three factors on their ECO₂RR performance. Finally, the challenges and perspectives of functional porous frameworks for the further development of the ECO₂RR are reasonably proposed, aiming to offer insights for future studies in this intriguing and significant research field.