Active Sites Research Articles

Electrochemical Ammonia Synthesis at p-Block Active Sites Using Various Nitrogen Sources: Theoretical Insights.

Electrochemical nitrogen conversion for ammonia (NH3) synthesis, driven by renewable electricity, offers a sustainable alternative to the traditional Haber-Bosch process. However, this conversion process remains limited by a low Faradaic efficiency (FE) and NH3 yield. Although transition metals have been widely studied as catalysts for NH3 synthesis through effective electron donation/back-donation mechanisms, there are challenges in electrochemical environments, including competitive hydrogen evolution reaction (HER) and catalyst stability issues. In contrast, p-block elements show unique advantages in light of higher selectivity for nitrogen activation and chemical stability. The present article explores the potential of p-block element-based catalysts as active sites for NH3 synthesis, discussing their activation mechanisms, performance modulation strategies, and future research directions from a theoretical perspective.

Preparation of CuO–CeO2/CaO Composite Oxides and its Ablation Performances of CO/CO2

ABSTRACT CuO – CeO2/CaO composite oxide was prepared for mine special environment in this study through the solid-phase impregnation method using the traditional CuO – CeO2 and CaO as the CO catalyst and the modified additive, respectively, to address the CO poisoning in underground coal mines effectively. Influences of CaO mass on the ablation performances of CuO – CeO2/CaO were investigated under dynamic and static CO/CO2 heat capture experiments using the self-made activity testing device. Results demonstrated that adding CaO can realize in-situ adsorption of CO2, thus increasing utilization of oxygen and promoting CO catalysis of the prepared composite oxide. The performances of CuO – CeO2/0.15CaO was the best when the dosage of CaO was 15 wt%. The CO reaction capacity and CO2 adsorption capacity reached 1.17 and 0.56 mg·g−1, respectively. The thermodynamic properties and microstructural characteristics of the synthesized composite oxide were systematically investigated utilizing a simultaneous thermal analyzer, Fourier infrared spectrometer, XRD diffractometer, and scanning electron microscope. Adding CaO can also improve the thermostability of the composite oxide and increase active sites on the sample surface. The emergence of adsorption products Ca(OH)2 and CaCO3 proves that CuO – CeO2/CaO has relatively good moisture and CO2 adsorption. Analysis of the ablation performances of CO/CO2 after coal combustion with CuO – CeO2/CaO revealed that the prepared composite oxide not only effectively lowers CO concentration after coal combustion but also adsorbs CO2 during catalysis and decreases smoke risks. The released CO concentration from coal combustion after 240 s can be decreased to less than 0.0024% when the mass ratio of CuO – CeO2/0.15CaO and coal is 1:3. The ablation results confirm that, as a new type of composite material, the CuO – CeO2/0.15CaO composite oxide can provide a new technical means for CO control in coal mines.

Combination of FeII-O Species and Fe-O-Zr Bonds Empowers FeOx Nanoclusters Anchored on UiO-66 Robust H2S-Selective Catalytic Oxidation Performance.

The low sulfur selectivity of Fe-based H2S-selective catalytic oxidation catalysts is still a problem, especially at a high O2 content. This is alleviated here through anchoring FeOx nanoclusters on UiO-66 via the formation of Fe-O-Zr bonds. The introduced FeOx species exist in the form of FeIII and FeII. Therein the FeIII-O species are the predominant active sites for H2S-oxidation. The formed Fe-O-Zr bonds strengthen the redox cycle of FeIII/FeII through promoting electron transfer from Fe to Zr. The FeII-O species can activate molecular oxygen to oxidize H2S into elemental S, which accelerates the formation rate of atomic S, hindering its further oxidation into SO2. The combination of these factors empowers the catalysts, enabling 100% H2S conversion and 98.2% sulfur yield. The catalyst also has satisfactory stability with the sulfur selectivity only decreasing from 98.2% to 91.3% after the reaction going on 50 h. The decreased sulfur selectivity might be caused by the deterioration of pores and the deposition of elemental S on the surface. The former hinders the diffusion of sulfur oligomers timely from pores to the gas phase, while the latter is suspected to capture electrons to promote its further reaction with molecular oxygen.

Bifunctional mixed-valence ruthenium heterostructure for robust electrocatalytic water splitting in acid media

The incorporation of non-metal dopants can significantly enhance catalytic activity and improve stability. Furthermore, the creation of heterostructures is particularly advantageous to facilitate charge transfer and optimize electronic properties. This study presents an effective bifunctional mixed-valence Ruthenium heterostructure synthesized through a cascading process involving grinding with carbon nitride and subsequent thermal treatment. The catalyst exhibits outstanding electrocatalytic performance with remarkably low overpotentials of 197 mV for the oxygen evolution reaction (OER) and 24.8 mV for the hydrogen evolution reaction (HER), respectively, with the stability exceeding 24 h at a current density of 10 mA cm⁻2 in acidic media. Additionally, when employed in an acidic oxygen water splitting (OWS) electrolyzer, the bifunctional catalyst demonstrates excellent activity, achieving an ultralow cell voltage of 1.53 V to sustain 10 mA cm⁻2. Enhanced performance is attributed to efficient charge transfer and increased exposure of active sites, providing valuable insights for the development of effective acidic water-electrolysis catalysts for sustainable hydrogen production.

Non-metallic iodine single-atom catalysts with optimized electronic structures for efficient Fenton-like reactions

In this study, we introduce a highly effective non-metallic iodine single-atom catalyst (SAC), referred to as I-NC, which is strategically confined within a nitrogen-doped carbon (NC) scaffold. This configuration features a distinctive C-I coordination that optimizes the electronic structure of the nitrogen-adjacent carbon sites. As a result, this arrangement enhances electron transfer from peroxymonosulfate (PMS) to the active sites, particularly the electron-deficient carbon. This electron transfer is followed by a deprotonation process that generates the peroxymonosulfate radical (SO5•−). Subsequently, the SO5•− radical undergoes a disproportionation reaction, leading to the production of singlet oxygen (1O2). Furthermore, the energy barrier for the rate-limiting step of SO5•− generation in I-NC is significantly lower at 1.45 eV, compared to 1.65 eV in the NC scaffold. This reduction in energy barrier effectively overcomes kinetic obstacles, thereby facilitating an enhanced generation of 1O2. Consequently, the I-NC catalyst exhibits remarkable catalytic efficiency and unmatched reactivity for PMS activation. This leads to a significantly accelerated degradation of pollutants, evidenced by a relatively high observed kinetic rate constant (kobs ~ 0.436 min−1) compared to other metallic SACs. This study offers valuable insights into the rational design of effective non-metallic SACs, showcasing their promising potential for Fenton-like reactions in water treatment applications.

Tuning Dual Catalytic Active Sites of Pt Single Atoms Paired with High-Entropy Alloy Nanoparticles for Advanced Li-O2 Batteries.

To achieve a long cycle life and high-capacity performance for Li-O2 batteries, it is critical to rationally modulate the formation and decomposition pathway of the discharge product Li2O2. Herein, we designed a highly efficient catalyst containing dual catalytic active sites of Pt single atoms (PtSAs) paired with high-entropy alloy (HEA) nanoparticles for oxygen reduction reaction (ORR) in Li-O2 batteries. HEA is designed with a moderate d-band center to enhance the surface adsorbed LiO2 intermediate (LiO2(ads)), while PtSAs active sites exhibit weak adsorption energy and promote the soluble LiO2 pathway (LiO2(sol)). An optimal ratio between LiO2(ads) and LiO2(sol) pathway was realized to modulate PtSAs and HEA active sites via regulating the etching conditions in the dealloying synthesis process for obtaining high-performance Li-O2 batteries. The ORR kinetics are accelerated, and the parasitic reactions are restrained in the Li-O2 batteries. As a result, Li-O2 batteries based on the HEA@Pt-PtSAs catalyst demonstrate an ultralow overpotential (0.3 V) and ultralong cycling performance of 470 cycles at 1000 mA g-1. The insights into the synthetic strategies and the importance of balancing the ORR pathways will offer guidance for devising multisite synergistic catalysts to accelerate redox-reaction kinetics for Li-O2 batteries.

Insights into excitonic behavior in single-atom covalent organic frameworks for efficient photo-Fenton-like pollutant degradation

The generation of radicals through photo-Fenton-like reactions demonstrates significant potential for remediating emerging organic contaminants (EOCs) in complex aqueous environments. However, the excitonic effect, induced by Coulomb interactions between photoexcited electrons and holes, reduces carrier utilization efficiency in these systems. In this study, we develop Cu single-atom-loaded covalent organic frameworks (CuSA/COFs) as models to modulate excitonic effects. Temperature-dependent photoluminescence and ultrafast transient absorption spectra reveal that incorporating acenaphthene units into the linker (CuSA/Ace-COF) significantly reduces exciton binding energy (Eb). This modification not only enhances peroxymonosulfate adsorption at Cu active sites but also facilitates rapid electron transfer and promotes selective hydroxyl radical generation. Compared to CuSA/Obq-COF (Eb = 25.6 meV), CuSA/Ace-COF (Eb = 12.2 meV) shows a 39.5-fold increase in the pseudo-first-order rate constant for sulfamethoxazole degradation (0.434 min−1). This work provides insights into modulating excitonic behavior in single-atom catalysts via linker engineering for EOCs degradation.

Enhancing Catalytic Removal of Autoexhaust Soot Particles via the Modulation of Interfacial Oxygen Vacancies in Cu/CeO2 Catalysts.

The purification efficiency of autoexhaust carbon strongly depends on the heterogeneous interface structure between active metal and oxide, which can modulate the local electronic structure of defect sites to promote the activation of reactant molecules. Herein, the high-dispersion CuO clusters supported on the well-defined CeO2 nanorods were prepared using the complex deposition slow method. The formation of heteroatomic Cu+-Ov-Ce3+ interfacial structural units as active sites can capture electrons to achieve activation of the NO and O2 molecules. Among all of the synthesized catalysts, the Cu10/CeO2 catalyst exhibits superior catalytic performance (T50 = 351 °C) along with remarkable tolerance to H2O and SO2 in the removal of soot particles. Through a combination of comprehensive characterizations and density functional theory calculations, it is proposed that the interfacial Cu+-Ov-Ce3+ site, acting as an electron enrichment center, can capture electrons from the Cu d-band and Ce d/f-band to obtain high delocalized electron density, and then enhance the oxidation of NO to NO2, which plays a crucial role in the NOx-assisted catalytic mechanism for soot oxidation. This study presents a novel strategy for developing highly efficient catalysts that exhibit resistance to H2O and SO2, aimed at enhancing the removal of soot particles.

Yttrium-doped NiMo-MoO2 heterostructure electrocatalysts for hydrogen production from alkaline seawater

Active and stable electrocatalysts are essential for hydrogen production from alkaline water electrolysis. However, precisely controlling the interaction between electrocatalysts and reaction intermediates (H2O*, H*, and *OH) remains challenging. Here, we demonstrate an yttrium-doped NiMo-MoO2 heterogenous electrocatalyst that efficiently promotes water dissociation and accelerates the intermediate adsorption/desorption dynamics in alkaline electrolytes. Introducing yttrium into the NiMo/MoO2 heterostructure induces lattice expansion and optimizes the d-band center of NiMo alloy component, enhancing water dissociation and H* desorption. Yttrium doping also increases the concentration of oxygen vacancies in MoO2−x, which in turn accelerates the charge kinetics and the swift evacuation of *OH intermediates from the active sites. Consequently, the Y-NiMo/MoO2−x heterostructure exhibits notable performance by requiring only 189 and 220 mV overpotentials to achieve current density of 2.0 A cm−2 in alkaline water and seawater, respectively. This work provides a strategy to modulate heterostructure catalysts for scalable, economically viable hydrogen production from low-quality waters.

Soft nanoforest of metal single atoms for free diffusion catalysis.

Metal single atoms are of increasing importance in catalytic reactions. However, the mass diffusion is yet substantially limited by the confined surface of the support in comparison to homogeneous catalysis. Here, we demonstrate that cylindrical micellar brushes with highly solvated poly(2-vinylpyridine) coronas can immobilize 33 types of metal single atoms with 8.3 to 40.9 weight % contents on conventional electrodes under ambient conditions. This is favored by the forest-like hierarchically open soft structure of the micellar brushes and the dynamic coordination between the metals and the pyridine groups. It was found that the nanoforests of individual noble metal single atoms can be well solvated in an aqueous electrolyte to comprehensively expose the atomic active sites and the nanoforest of Pt single atoms on nickel foam reveals high electrochemical performance for hydrogen evolution. The micellar brush support also enables the simultaneous anchoring of multiple single atoms on the cathode of an anion-exchange membrane electrolyzer for long-term stable water electrolysis.

Refining the Distinct Cu-N4 Coordination in Mesoporous N-Doped Carbon to Boost Selective Deuteration under Mild Conditions.

Deuterated compounds have broad applications across various fields, with dehalogenative deuteration serving as an efficient method to obtain these molecules. However, the diverse electronic structures of active sites in the heterogeneous system and the limited recyclability in the homogeneous system significantly hinder the advancement of dehalogenative deuteration. In this study, we present a catalyst composed of copper single-atom sites anchored within an ordered mesoporous nitrogen-doped carbon matrix, synthesized via a mesopore confinement method. The Cu1/OMNC-1100 catalyst, characterized by Cu-N4 sites, demonstrates exceptional performance, high functional group tolerance, and remarkable durability in the deuteration of 2-bromo-6-methoxynaphthalene under relatively mild conditions (80 °C, 2 MPa of CO). Experimental results combined with X-ray absorption fine structure analysis reveal that Cu-N3 sites can be converted into more stable Cu-N4 counterparts at higher pyrolysis temperatures, resulting in enhanced catalytic activity. This work demonstrates a strategy for designing single-atom site catalysts with tunable coordination environments, providing a promising approach to improving catalytic performance in selective dehalogenative reactions under relatively mild conditions.

Lignin-Based Nanoparticles Stabilized Pickering Emulsion for Enhanced Catalytic Hydrogenation.

The development of green and easily regulated amphiphilic particles is crucial for advancing Pickering emulsion catalysis. In this study, lignin particles modified via sulfobutylation were employed as solid emulsifiers to support Pd nanoparticles (NPs), thereby enhancing the catalytic efficiency of biphasic reactions. Sulfobutylation of lignin effectively adjusted the hydrophilic-hydrophobic balance, resulting in controlled emulsion types and droplet sizes. Pd NPs were loaded onto lignin with a 50% sulfobutylation ratio through the in situ reduction of active functional groups, further stabilized by the cross-linked network structure of lignin. In the hydrogenation of nitrobenzene, the Lig-50S-0.6Pd catalyst exhibited superior activity compared to traditional Pd/C catalysts, which is attributed to the high retention of active sites and increased interfacial area. This work underscores the potential for designing lignin-based amphiphilic particles and developing Pickering emulsion-enhanced reactions.

Manganese Intercalation Enabling High-Performance Aqueous Fe-VO2 Batteries.

The aqueous iron ion batteries (AIIBs) are an attractive option for large-scale energy storage applications. However, the inadequate plating and stripping of Fe2+ ions underscore the need to explore more suitable cathode materials. Herein, we optimize the structure of tunnel-like VO2 nanosheets by introducing Mn2+ ion intercalation as a cathode material to enhance their performance in AIIBs. Mn2+ serves as a stabilizing pillar for VO2, which brings some oxygen vacancies to provide extra electrochemically active sites, and accelerates the reversible (de)insertion of Fe2+ ions. In addition, the density functional theory (DFT) calculations show that the introduction of Mn2+ reduces the band gap of VO2 and also decreases the electrostatic interaction between Fe2+ and VO2. Consequently, the VO2 with interlayer Mn2+ pillars (5% MVO) electrodes exhibit a remarkable capacity of 284.32 mAh g-1 at a current density of 0.1 A g-1 and demonstrate excellent cycle life, maintaining 81.7% of their capacity at 1.0 A g-1 after 600 cycles. Therefore, these results offer a promising choice for the cathode material to achieve outstanding electrochemical performance in AIIBs.

Strategic Nitrogen Site Alignment in Covalent Organic Frameworks for Enhanced Performance in Aqueous Zinc-Iodide Batteries.

Aqueous zinc-iodine batteries (AZIBs) are gaining attention as next-generation energy storage systems due to their high theoretical capacity, enhanced safety, and cost-effectiveness. However, their practical application is hindered by challenges such as slow reaction kinetics and the persistent polyiodide shuttle effect. To address these limitations, we developed a novel class of covalent organic frameworks (COFs) featuring electron-rich nitrogen sites with varied density and distribution (N1-N4) along the pore walls. These nitrogen sites enhance iodine species confinement and mass transport. Our experimental and theoretical studies reveal that the continuous and optimized distribution of nitrogen sites within the COF structure significantly reduces internal resistance and boosts redox activity. Moreover, the N4-COF demonstrates superior performance compared to other porous materials, due to its high density and strategic alignment of active sites. The I2@N4-COF cathode achieves a remarkable specific capacity of 348 mAh g⁻¹ at 1 C, almost 1.8 times greater than that of the I2@N1-COF, while also maintaining excellent cycling stability. This integration of a porous framework with aligned nitrogen sites in the N4-COF structure not only enhances iodine redox behavior but also offers a promising design strategy for developing high-performance AZIB electrodes.

Manipulating Charge Distribution at Organic-inorganic Interface via Optimizing Substituents for Sustainable Water Electrolysis.

The space charge effect induced by high-quality heterojunctions is essential for efficient electrocatalytic processes. Herein, we delicately manipulate intermolecular charge transfer by modifying substituents (-g = -CH3, -H, -NO2) with various electron donating/withdrawing capabilities in CoPc-g/CoS organic-inorganic heterostructures. CoPc-CH3, as a typical electron donor, transfers more electrons to CoS due to the presence of -CH3, forming the strongest space electric field and thus regulating the dual active sites at the interface. Furthermore, oxygen-containing intermediates preferentially adsorb on the positively charged CoPc-CH3 side, and the rapid accumulation of electrons on the CoS side decelerates catalyst dissolution at the oxygen evolution reaction (OER) potential, ensuring the stable OER process under the optimized adsorbate evolution mechanism. As a result, CoPc-CH3/CoS catalyst exhibits the lowest overpotential and remains stable for 150 h at 0.5 A cm-2 in the membrane electrode assembly electrolyzer. The method provides a novel strategy for accurately regulating the space electric field of heterojunctions.

Study of the self-degradation performance of a passive direct methanol fuel cell with an Fe-N-C catalyst.

Fe-N-C catalysts are considered promising substitutes for Pt-based catalysts at the cathode in direct methanol fuel cells (DMFCs) owing to their great methanol tolerance. However, Fe-N-C-based DMFCs commonly suffer from a decreased performance under extremely high methanol concentrations and exhibit poor stability, while the underlying mechanism remains controversial. In this study, a self-degradation phenomenon in a passive Fe-N-C-based DMFC was investigated in detail. The DMFC with an optimized ionomer content and catalyst loading delivered an extremely high peak power density of 28.85 mW cm-2 when fed with 3 M methanol solution, while the peak power density of the cell rapidly declined to 16.61 mW cm-2 after standing for 10 days without any discharging operation. Several electrochemical measurements were designed and conducted to explore the mechanism for this phenomenon. The results of these measurements revealed that methanol molecules are chemically adsorbed on the surface of the Fe-N-C catalyst, and the bonding cannot be reversed using simple physical methods, leading to the isolation of active sites from oxygen. Herein, we provide a new perspective on passive Fe-N-C-based DMFCs that would be significant for the technological development of portable power devices.

Hierarchical Selenium-Doped Nickel-Cobalt Hybrids on Carbon Paper for the Overall Water-Splitting Electrocatalytic System.

Designing and constructing hierarchically structured materials with heterogeneous compositions is the key to developing an effective catalyst for overall water-splitting applications. Herein, we report the fabrication of hollow-structured selenium-doped nickel-cobalt hybrids on carbon paper as a self-supported electrode (denoted as Se-Ni|Co/CP, where Ni|Co hybrids consist of nickel-cobalt alloy-incorporated nickel-cobalt oxide). The procedure involves direct growth of zeolitic imidazolate framework-67 (ZIF-67) on bimetal-based nickel-cobalt hydroxide (NiCoOH) electrodeposited on CP, followed by selenous etching and pyrolysis to obtain the final Se-Ni|Co/CP electrocatalytic system. The optimized Se-Ni|Co/CP [Se-Ni1|Co9/CP(0.3)] exhibits remarkable performance in the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), displaying a current density of 10 mA cm-2 at small overpotentials of 105 mV for HER and 235 mV for OER. Furthermore, it allows an alkali electrolyzer to achieve a current density of 10 mA cm-2 at a cell voltage of only 1.51 V. The outstanding catalytic activity of Se-Ni|Co/CP is ascribed to the high intrinsic activity of the bimetallic catalyst, efficient interfaces, and charge transport facilitated by the heterogeneous component, the hollow structure inherited from the metal-organic frameworks (MOF)-derived material providing ample porosity and active sites, and structural robustness achieved through self-supported construction.

Time-resolved spectroscopy uncovers deprotonation-induced reconstruction in oxygen-evolution NiFe-based (oxy)hydroxides

Transition-metal layered double hydroxides are widely utilized as electrocatalysts for the oxygen evolution reaction (OER), undergoing dynamic transformation into active oxyhydroxides during electrochemical operation. Nonetheless, our understanding of the non-equilibrium structural changes that occur during this process remains limited. In this study, utilizing in situ energy-dispersive X-ray absorption spectroscopy and machine learning analysis, we reveal the occurrence of deprotonation and elucidate the role of incorporated iron in facilitating the transition from nickel-iron layered double hydroxide (NiFe LDH) into its active oxyhydroxide. Our findings demonstrate that iron substitution promotes deprotonation process within NiFe LDH, resulting in the preferential removal of protons from the specific bridged hydroxyl group (Ni2+-OH-Fe3+) linked to edge-sharing [NiO6] and [FeO6] octahedron. This deprotonation behavior drives the formation of high-valence Ni3+δ species (0 <δ < 1), which subsequently serve as the active sites, thereby ensuring efficient oxygen evolution activity. This approach offers high-resolution insights of dynamic structural evolution, overcoming the limitations of extended acquisition times and advancing our understanding of OER mechanisms.

Interfacial Catalysis at Atomic Level.

Heterogeneous catalysts are pivotal to the chemical and energy industries, which are central to a multitude of industrial processes. Large-scale industrial catalytic processes rely on special structures at the nano- or atomic level, where reactions proceed on the so-called active sites of heterogeneous catalysts. The complexity of these catalysts and active sites often lies in the interfacial regions where different components in the catalysts come into contact. Recent advances in synthetic methods, characterization technologies, and reaction kinetics studies have provided atomic-scale insights into these critical interfaces. Achieving atomic precision in interfacial engineering allows for the manipulation of electronic profiles, adsorption patterns, and surface motifs, deepening our understanding of reaction mechanisms at the atomic or molecular level. This mechanistic understanding is indispensable not only for fundamental scientific inquiry but also for the design of the next generation of highly efficient industrial catalysts. This review examines the latest developments in atomic-scale interfacial engineering, covering fundamental concepts, catalyst design, mechanistic insights, and characterization techniques, and shares our perspective on the future trajectory of this dynamic research field.

The Impact of Electric Fields on Processes at Electrode Interfaces.

The application of external electric fields to influence chemical reactions at electrode interfaces has attracted considerable interest in recent years. However, the design of electric fields to achieve highly efficient and selective catalytic systems, akin to the optimized fields found at enzyme active sites, remains a significant challenge. Consequently, there has been substantial effort in probing and understanding the interfacial electric fields at electrode/electrolyte interfaces and their effect on adsorbates. In this review, we examine recent advances in experimental, computational, and theoretical studies of the interfacial electric field, the origin of the vibrational Stark effect of adsorbates on electrode surfaces, and the effects of electric fields on reactions at electrode/electrolyte interfaces. We also discuss recent advances in control of charge transfer and chemical reactions using magnetic fields. Finally, we outline perspectives on key areas for future studies.