Electrochemical Potential-Driven Shift of Frontier Orbitals in M-N-C Single-Atom Catalysts Leading to Inverted Adsorption Energies

Nitrogen mono-doping of graphene and co-doping with group 14 as a sensor for diisobutyl phthalate: Insight from a computational study

Diisobutyl phthalate (DIBP) is a highly toxic plasticizer found in edible consumer products and industrial products. It affects the male reproductive system, bioaccumulates in water, and poses health risks. Given its widespread occurrence, designing novel sensor materials for sensing of DIBP is necessary for environmental and health safety. In this research, density functional theory (DFT) at the DFT/MN15/LanL2DZ level was employed to study the structural analysis, electronic properties, visual studies, and sensor mechanisms of modified graphene systems for the detection of diisobutyl pththalate (DIBP). An increase in energy gap values was observed for all studied systems on complexation with gas molecules, which depicted the stable properties of the system. The electronic properties revealed that upon adsorption, the DIBP-Sn-N@GP energy gap was the smallest at 2.778 eV, which indicates great conductivity. The adsorption energy showed that chemisorption occurred in the studied systems. DIBP-Si-N@GP showed the strongest adsorption energy of -18.171 eV, while DIBP-N@GP showed weak chemisorption of -0.914 eV. According to the UV-visible spectrum, DIBP-Ge-N@GP has the greatest peak at a wavelength of 1979.79 nm in the first excited state, corresponding to the H-1→L+2 transition. The sensor mechanism showed that among the tested surfaces, DIBP-Si-N@GP showed the best sensing properties and can be considered good gas sensor materials, attributed to its highest adsorption energy, stabilization energy, and charge transfer values with the lowest back donation energy value.

Spatiotemporal Coordination-Engineered Core-Shell Zeolitic Imidazolate Frameworks Enable Self-Adaptive Electrocatalyst Reconstruction and Self-Tandem Sulfur Conversion

Upon electrocatalysts being intertwined with lithium polysulfides (LiPSs) in lithium-sulfur (Li-S) batteries, the intricate relationship between the spatial landscape of electrocatalysts and the corresponding electrocatalytic performance necessitates elaborate elucidation. Consequently, leveraging specialized functions of different components and organizing their spatial arrangement culminate in the holistic integration of spatial-temporal specificity, facilitating both self-adaptive electrocatalyst reconstruction and self-tandem LiPSs conversion. Inspired by the responsiveness and molecular recognition in cell membranes, a pertinent morphological design paradigm is proposed, which features a universal core-shell structure with spatially heterogeneous components. Specifically, ionic Zn conducive to Li+ mobility and covalent Co conducive to LiPSs immobilization are conscripted to ameliorate LiPSs redox kinetics. By configuring their specific spatial organization within core-shell zeolite imidazolate frameworks, we elucidate the distinguished role of the spatial landscape of covalency-ionicity couplings in steering the pathway of temporal-specific active site reconstruction and manipulating the self-regulation of LiPSs distribution. Ascribed to the in situ reconstructed spatial landscape for self-tandem LiPSs conversion, wherein the Zn-N shell facilitates Li+ transport and the Co-(S)-Zn-(N) core contributes to bidirectional electrocatalysis of LiPSs, thus-derived Ah-level pouch cell maintains a stable cycling for 100 cycles at 1C. Additionally, with an electrolyte-to-sulfur ratio of 3.3 μL mg-1 and a negative-to-positive capacity ratio of approximately 1.5, a high energy density of up to 374 W h kgtotal-1 is achieved. These findings highlight the spatial architectures of components in the design of heterogeneous electrocatalysts for advanced Li-S batteries.

A Pulsed Tandem Electrocatalysis Strategy for CO2 Reduction

Electroreduction of CO2 to value-added C2 products remains hindered by sluggish C-C coupling kinetics and competing side reactions. Inspired by the tandem catalytic mechanisms of multienzyme systems, we designed a dual-site single-atom nanozyme (DSAN) comprising FeN4 and FeO4 sites (FeN4-FeO4). Density functional theory (DFT) calculations under constant potential reveal that the FeN4 site functions as a CO generator, while the FeO4 site facilitates CO migration, C-C coupling, and subsequent C2 product formation. To further optimize the catalytic efficiency, we introduced a pulsed electrocatalysis strategy by alternating between zero potential and -0.7 V. This approach dynamically modulates active-site functions: at -0.70 V, CO2 adsorption and *CH3CH2OH formation are facilitated, while at 0 V, CO migration and C-C coupling are enhanced due to the spin-state transitions during potential switching. Additionally, the zero potential suppresses excessive hydrogenation of key intermediates, thereby improving CH3CH2OH selectivity. These findings highlight the synergistic strategy integrating tandem catalysis and pulsed potential control, offering a novel and effective approach for CO2-to-C2 conversion using SAN catalysts.

d-Orbital Single Electron Filling O─O π* Bonds on WO3S1 Sites for Highly Selective Generation of Hydroxyl Radicals

Hydroxyl radical (•OH) stemming from dissolved oxygen (O2) via photocatalysis is very attractive, but its poor selectivity and generation efficiency greatly limit its application. Herein, a kind of tungsten single site co-coordinated with O and S atoms (WO3S1) is established on ZnIn2S4 (W-ZIS). The strong interactions in WO3S1 shift the d-band center toward the Fermi level, enhancing the adsorption of O2. These interactions improve the accumulation of photo-generated electrons on WO3S1, facilitating the dissociation of O─O bonds in crucial intermediates and promoting the selective conversion from O2 into •OH. This brings a state-of-the-art selectivity (40.2%) and generation efficiency (1668.90 mmol. g-1. L-1. h-1) of •OH production. Experimental results and theoretical simulations have elucidated that O2 can be reduced by d-orbitals single electron (↑, _, _, _, _, _) of WO3S1 transfer to 2p-orbital O─O pi anti-bonding (π*: px and py), initially activating O2. Additionally, WO3S1 sites facilitate the cleavage of H2O, optimizing proton adsorption through W─O orbital coupling in WO3S1 and promoting the transformation of oxygen-containing intermediates. More importantly, d-orbitals single electron can fill O─O π* bond in •OOH intermediate, weakening the covalency of the O─O bond, mitigating the formation of H2O2 and shortening the pathway for •OH generation.).

Adapting Atomic Configuration Steers Dynamic Half-Occupied State for Efficient CO2 Electroreduction to CO

Electronic structures stand at the center to essentially understand the catalytic performance and reaction mechanism of atomically dispersed transition-metal-nitrogen-carbon catalysts (ADTCs). However, under realistic electrocatalytic conditions, the dynamic electronic disturbance at metal centers originating from complicated interactions with microenvironments is commonly neglected, which makes a true structure-property correlation highly ambiguous. Here, we employ operando time-resolved X-ray absorption spectroscopy to delve deeply into dynamic electronic behaviors of a family of transition-metal centers that are observed to adaptively vary in the metal-ligand configuration during the CO2 electroreduction reaction. We identify dynamic electronic/geometric configuration and d-orbital occupation under working conditions, demonstrating an unprecedentedly precise activity descriptor, i.e., dynamic axial dz2 electron, for the CO2-to-CO conversion. Direct results validate that the half-occupied state suggests the optimum binding behaviors with intermediates, significantly promoting CO production, which has been demonstrated by a significant kinetics enhancement of 1 to 2 orders of magnitude as compared with fully occupied and unoccupied states. This work presents the first empirical demonstration for a real correlation between the dynamic electronic/geometric configuration and catalytic kinetics in ADTCs, paving a new way for modulating catalysts and designing highly efficient reaction pathways.

Screening of single-atomic catalysts loaded on two-dimensional transition metal dichalcogenides for electrocatalytic oxygen reduction via high throughput ab initio calculations

The design and screening of low cost and high efficiency oxygen reduction reaction (ORR) electrocatalysts is vital in the realms of fuel cells and metal-air batteries. Existing studies largely rely on the calculation of absorption free energy, a method established 20 years ago by Jens K. Nørskov. However, the study of electrocatalysts grounded solely on free energy calculation often lacks in-depth analysis, particularly overlooking the influence of solvent and electrode potential. In this regard, we here present a novel approach using constant-potential and ab initio molecular dynamics (AIMD) simulation to screen single-atom catalysts loaded on transition metal dichalcogenides (SA@TMDs) for ORR. An extensive investigation of 1584 SA@TMDs results in 20 high performing ORR catalysts with overpotential less than 0.33 V and high working stability. In addition, our study shows that the electrode potential has different effects on the adsorption energy of *OOH, *O and *OH, which leads to a reversal of the rate-determining step (RDS) of the ORR. This work presents not only credible, high-performance catalyst candidates for experimental exploration, but also significantly improves our understanding on the reaction mechanism of ORR under realistic reaction conditions.

Photocatalytic Nitrogen Reduction for Ammonia Synthesis Accelerated by Overcoming Photo-Dember Effect

During photocatalytic nitrogen fixation for ammonia synthesis, the photo-Dember effect causes direct transmission of photogenerated electrons from the illuminated surface to the bottom of photocatalyst, thus significantly reducing the number of charge carriers migrating on the surface and nitrogen fixation efficiency. Herein, a bismuth oxychloride material with largely exposed (101) crystal plane and rich oxygen vacancies (BOC(101)-OVs) is synthesized, exhibiting a high NH3 yield of 591.94 µmol g-1 h-1) after photocatalytic N2 reduction under simulated solar light irradiation. The designed (101)/(001) interface in BOC(101)-OVs generates a self-built electric field (Eself) on the material surface due to different atomic arrangements. Therefore, the newly developed material achieved >95% of photogenerated electrons changing the transfer path, i.e., from bulk phase transfer to surface lateral transfer path, thus escaping confinement by the photo-Dember effect. Meanwhile, after OVs construction, each adsorbed N2 molecule simultaneously bonds with three Bi atoms of material through N 2p-Bi 6p bonding, accelerating the filling of high-energy electrons into the π* orbital of N2, leading to a new nitrogen reduction path with combined alternating hydrogenation and terminal hydrogenation. This study greatly advances the beneficial effect of charge carrier migration through overcoming the photo-Dember effect for ammonia synthesis.

Engineering TM-N2@C15N5S3H5-Based Covalent-Organic Frameworks for Enhanced Water-Splitting and Oxygen Reduction Reactions: A Constant Potential and Feature Coevaluation Approach

The development of highly active metal-based single-atom catalysts (SACs) is crucial for energy conversion and storage, offering optimized atom utilization and high catalytic activity, with bifunctional SACs for hydrogen evolution (HER) and oxygen evolution/reduction (OER/ORR) reactions providing greater efficiency and cost-effectiveness than monofunctional catalysts, making them scientifically and economically valuable. By integrating density functional theory and machine learning methods, we systematically evaluated the potential of TM-N2@C15N5S3H5 monolayers as efficient HER/OER/ORR catalysts, revealing that 27 TM atoms remain stable on N2@C15N5S3H5 with a TM-N2 coordination environment. Rh-N2@C15N5S3H5 outperforms Pt in HER, while Rh-N2@C15N5S3H5 drives both HER and OER, while Ni-N2@C15N5S3H5 catalyzes OER and ORR, making them bifunctional catalysts. Comparative activity analysis reveals that the Ni-d orbitals in Ni-N2@C15N5S3H5 interact with O-p orbitals, pairing up electrons from antibonding states into downward bonding orbitals, thus fitting OH* adsorption and enhancing catalytic performance. We further examined the pH and applied potential effects on OER/ORR performance of Ni-N2@C15N5S3H5 and Rh-N2@C15N5S3H5 monolayers, both show enhanced OER in acidic conditions, with Ni-N2@C15N5S3H5 excelling in ORR under alkaline conditions and Rh-N2@C15N5S3H5 in acidic conditions. Moreover, machine learning techniques were applied to explore the correlation between catalytic activity and a range of structural and atomic properties.

Spin polarization regulation of Fe-N4 by Fe3 atomic clusters for highly active oxygen reduction reaction

The Fe-N4 motif is regarded as a leading non-precious metal catalyst for the oxygen reduction reaction (ORR) with the potential to replace platinum (Pt), yet achieving or surpassing the performance of Pt-based catalysts remains a significant challenge. In this study, we introduce a modification strategy employing homogeneous few-atom Fe3 cluster to regulate the spin polarization of Fe-N4. Experimental research and theoretical calculations show that the incorporation of the Fe3 cluster significantly enhances the adsorption of Fe-N4 motif toward OH ligands, leading to a structural transformation from a square-planar field (Fe-N4) to a square-pyramid field structure (Fe(OH) -N4). This structural transformation reduces the spin polarization of 3dxz, 3dyz, and 3dz2 orbitals of Fe-N4, resulting in a decrease in unpaired electrons within 3d orbitals. As a result, this modulation leads to moderate adsorption/desorption energies of reaction intermediates, thereby facilitating the ORR process. Moreover, the in-situ spectroscopy confirms that the desorption of OH* on Fe3/Fe(OH) -NC motif is more favorable compared to atomic Fe-NC, indicating a lower energy barrier for ORR. Consequently, the Fe3/Fe-NC catalyst demonstrates outstanding ORR performance with a half-wave potential of 0.836 V vs. reversible hydrogen electrode (RHE) in 0.1 mol L-1 HClO4 solution and 0.936 V vs. RHE in 0.1 mol L-1 KOH solution, even surpassing commercial Pt/C catalyst. It also exhibits excellent Zn-air battery efficiency. Our study introduces a novel approach to modulating the electronic structure of single atoms catalysts by leveraging the robust interaction between single atoms and atomic clusters.

Practical Applications of Grand-canonical Electronic Structure Calculations in Electrochemical Simulation

Modeling electrified interfaces has long been a great challenge in electrochemistry. In recent years, the grand-canonical treatment for electrons has gradually been developed, and its combination with density functional theory has been widely used to simulate electrochemical processes on an atomistic scale. In this Perspective, we aim to discuss several practical applications of this powerful technique after a short review of necessary fundamentals. We will begin with capacitor-based parametrization method of grand-canonical calculated results. If considering the electrodes under different applied potentials as different materials, the parametrization can be viewed as a kind of "quadratic scaling relation", which might reduce the overall computational costs by data postanalysis rather than algorithm development. Following an example of the abnormal potential-independent energetic curve within the bandgap area, we turn the topic to the semiconducting electrodes. Meanwhile, the specific behaviors of the bandgap also indicate that besides the reaction thermodynamics and kinetics, the detailed electronic structure of the system can also be well described by the grand-canonical treatment on electrons. Several possibilities for further applications are proposed correspondingly and summarized at the end of paper. We believe that the grand-canonical treatment for electronic structure calculations can greatly enrich our understanding of the fundamental mechanisms under electrochemical environments.

Theoretical Insights into the Selectivity of Single-Atom Fe-N-C Catalysts for Electrochemical NOx Reduction

Single-atom Fe-N-C catalysts have attracted significant attention in the NOx reduction reaction (NOxRR). However, the origin of their selectivity in the NOxRR remains unclear, impeding further advancements in application. Herein, we investigate the potential-driven competitive mechanism for NH3 and NH2OH production in the NOxRR over single-atom pyridinic-FeN4 and pyrrolic-FeN4 sites using constant-potential density functional theory calculations. The origin of selectivity in the NOxRR is linked to the switching of Fe 3d orbitals as they interact with intermediates. The selectivity between NH3 and NH2OH is determined by the applied potentials. The pyridinic-FeN4 predominantly generates NH3 at higher reduction potentials (-0.6 to -1.2 V, vs SHE), while NH2OH is favored at lower reduction potentials (0.6 to -0.6 V). The pyrrolic-FeN4 shows a similar potential-dependent product distribution, with a crossover potential of -1.0 V. The selectivity-determining intermediates (SDIs) in the NOxRR are *NH2OH and *NH2 + *OH. The potential-dependent selectivity is governed by the switching of Fe 3d orbitals interacting with SDIs, from dumbbell-shaped Fe 3dz2 to four-leaf clover-like Fe 3dxz, 3dyz, and 3dx2-y2, which plays a crucial role in controlling product distribution based on applied potentials. These findings offer new insights into the product selectivity of single-atom catalysts for the NOxRR.

Single-atom lead ion adsorption behavior on Ti2CO2 MXene under different electrode potentials

First-principles calculations, particularly density functional theory (DFT) combined with D3 dispersion correction (DFT+D3), have proven to be valuable tools in simulating the adsorption of lead ions on Ti2CO2 surfaces. However, conventional theoretical models assume electrically neutral systems under vacuum conditions, neglecting the solvent environment and electrode potential's crucial effects. This study employed an implicit solvent model, treating the solvent as a continuous and homogeneous medium to capture the influence of different solvents by varying their dielectric constants. Additionally, the role of electrode potential on the adsorption behavior of lead ions on Ti2CO2 surfaces was explored. The findings demonstrated that electrode potential significantly affected lead ion adsorption with adsorption strength increasing as the electrode potential decreases. This observation was supported by electronic structure analyses, such as the density of states, band structure and ICOHP. This study provides important insights into the influence of electrode potential on metal ion adsorption on MXene materials, offering a theoretical foundation for the design and optimization of MXene-based adsorbents for environmental applications.

Clarifying the Active Structure and Reaction Mechanism of Atomically Dispersed Metal and Nonmetal Sites with Enhanced Activity for Oxygen Reduction Reaction

Atomically dispersed transition metal (ADTM) catalysts are widely implemented in energy conversion reactions, while the similar properties of TMs make it difficult to continuously improve the activity of ADTMs via tuning the composition of metals. Introducing nonmetal sites into ADTMs may help to effectively modulate the electronic structure of metals and significantly improve the activity. However, it is difficult to achieve the co-existence of ADTMs with nonmetal atoms and clarify their synergistic effect on the catalytic mechanism. Therefore, elucidating the active sites within atomically dispersed metal-nonmetal materials and unveiling catalytic mechanism is highly important. Herein, a novel hybrid catalyst, with coexistence of Co single-atoms and Co─Se dual-atom sites (Co─Se/Co/NC), is successfully synthesized and exhibits remarkable performance for oxygen reduction reaction (ORR). Theoretical results demonstrate that the Se sites can effectively modulate the charge redistribution at Co active sites. Furthermore, the synergistic effect between Co single-atom sites and Co─Se dual-atom sites can further adjust the d-band center, optimize the adsorption/desorption behavior of intermediates, and finally accelerate the ORR kinetics. This work has clearly clarified the reaction mechanism and shows the great potential of atomically dispersed metal-nonmetal nanomaterials for energy conversion and storage applications.

Catalysis under electric-/magnetic-/electromagnetic-field coupling

The ultimate goal of catalysis is to control the cleavage and formation of chemical bonds at the molecular or even atomic level, enabling the customization of catalytic products. The essence of chemical bonding is the electromagnetic interaction between atoms, which makes it possible to directly manipulate the dynamic behavior of molecules and electrons in catalytic processes using external electric, magnetic and electromagnetic fields. In this tutorial review, we first introduce the feasibility and importance of field effects in regulating catalytic reaction processes and then outline the basic principles of electric-/magnetic-/electromagnetic-field interaction with matter, respectively. In each section, we further summarize the relevant important advances from two complementary perspectives: the macroscopic molecular motion (including translation, vibration and rotation) and the microscopic intramolecular electron state alteration (including spin polarization, transfer or excitation, and density of states redistribution). Finally, we discuss the challenges and opportunities for further development of catalysis under electric-/magnetic-/electromagnetic-field coupling.

Unraveling the C-C Coupling Mechanism on Dual-Atom Catalysts for CO2/CO Reduction Reaction: The Critical Role of CO Hydrogenation

The electrochemical reduction reaction (RR) of CO to high value multicarbon products is highly desirable for carbon utilization. Dual transition metal atoms dispersed by N-doped graphene are able to be highly efficient catalysts for this process due to the synergy of the bimetallic sites for C-C coupling. In this work, we screened homonuclear dual-atom catalysts dispersed by N-doped graphene to investigate the potential in CO reduction to C2+ products by employing density functional theory calculations. We have demonstrated that the two adsorbed CO species on bimetallic sites cannot directly couple unless one of the CO molecules is hydrogenated. All the dual metal atom catalysts prefer a similar coupling mechanism, i.e., the asymmetric coupling of *CO on the bridged site and *CHO on the top site, while the Ni2 and Cu2 catalysts exhibit much better performance with moderate adsorption energies and low energy barriers. The enhanced activities are attributed to the decrease of the energy levels of *CO 2p states that weakens the metal-C bonding and thus facilitates the feasible C-C coupling with both low reaction energies and low barriers. These insights have revealed the significant role of the hydrogenation of CO species prior to the coupling step and may provide a theoretical perspective to understand the generation of C2+ products in the CO2/CORR.

Spin polarization induced by atomic strain of MBene promotes the ·O2- production for groundwater disinfection

Superbugs in groundwater are posing severe health risks through waterborne pathways. An emerging approach for green disinfection lies at photocatalysis, which levers the locally generated superoxide radical (·O2-) for neutralization. However, the spin-forbidden feature of O2 hinders the photocatalytic generation of active ·O2-, and thus greatly limited the disinfection efficiency, especially for real groundwater with a low dissolved oxygen (DO) concentration. Herein, we report a class of strained Mo4/3B2-xTz MBene (MB) with enhanced adsorption/activation of molecular O2 for photocatalytic disinfection, and find the strain induced spin polarization of In2S3/Mo4/3B2-xTz (IS/MB) can facilitate the spin-orbit hybridization of Mo sites and O2 to overcome the spin-forbidden of O2, which results in a 16.59-fold increase in ·O2- photocatalytic production in low DO condition (2.46 mg L-1). In particular, we demonstrate an In2S3/Mo4/3B2-xTz (50 mg)-based continuous-flow-disinfection system stably operates over 62 h and collects 37.2 L bacteria-free groundwater, which represents state-of-the-art photodisinfection materials for groundwater disinfection. Most importantly, the disinfection capacity of the continuous-flow-disinfection system is 25 times higher than that of commercial sodium hypochlorite (NaOCl), suggesting the practical potential for groundwater purification.

Graphene-supported MN4 single-atom catalysts for multifunctional electrocatalysis enabled by axial Fe tetramer coordination

Multifunctional electrocatalysts for oxygen reduction reaction (ORR), oxygen evolution reaction (OER), and hydrogen evolution reaction (HER) are crucial for development of the key electrochemical energy storage and conversion devices, for which single-atom catalyst (SAC) has present great promises. Very recently, some experimental works showed that structurally well-defined ultra-small transition-metal clusters (such as Fe and Co tetramers, denoted as Fe4 and Co4, respectively), can efficiently modulate the catalytic behavior of SACs by axial coordination. Herein, taking the graphene-supported MN4 SACs as representatives, we theoretically explored the feasibility of realizing multifunctional SACs for ORR, OER and HER by this novel axial coordination engineering. Through extensive first-principles calculations, from 23 candidates, IrN4 decorated with Fe4 (IrN4/Fe4) is identified as the promising trifunctional catalyst with the theoretical overpotential of 0.43, 0.51 and 0.30 V for OER, ORR and HER, respectively. RhN4/Fe4 and CoN4/Fe4 are recognized as potential OER and ORR bifunctional catalysts. In addition, NiN4/Fe4 exhibits the best ORR activity with an overpotential of 0.30 V, far superior to the pristine NiN4 SAC (0.88 V). Electronic structure analyses reveal that the significantly enhanced ORR/OER activity can be ascribed to the orbital and charge redistribution of Ni/Ir active center, resulting from its electronic interaction with Fe4 cluster. This work could stimulate and guide the rational design of graphene-based multifunctional SACs realized by axial coordination of small TM clusters, and provide insights into the modulation mechanism.

Valence-engineered catalysis-selectivity regulation of molybdenum oxide nanozyme for acute kidney injury therapy and post-cure assessment

The optimization of the enzyme-like catalytic selectivity of nanozymes for specific reactive oxygen species (ROS)-related applications is significant, and meanwhile the real-time monitoring of ROS is really crucial for tracking the therapeutic process. Herein, we present a mild oxidation valence-engineering strategy to modulate the valence states of Mo in Pluronic F127-coated MoO3-x nanozymes (denoted as MF-x, x: oxidation time) in a controlled manner aiming to improve their specificity of H2O2-associated catalytic reactions for specific therapy and monitoring of ROS-related diseases. Experimentally, MF-0 (Mo average valence 4.64) and MF-10 (Mo average valence 5.68) exhibit exclusively optimal catalase (CAT)- or peroxidase (POD)-like activity, respectively. Density functional theory (DFT) calculations verify the most favorable reaction path for both MF-0- and MF-10-catalyzed reaction processes based on free energy diagram and electronic structure analysis, disclosing the mechanism of the H2O2 activation pathway on the Mo-based nanozymes. Furthermore, MF-0 poses a strong potential in acute kidney injury (AKI) treatment, achieving excellent therapeutic outcomes in vitro and in vivo. Notably, the ROS-responsive photoacoustic imaging (PAI) signal of MF-0 during treatment guarantees real-time monitoring of the therapeutic effect and post-cure assessment in vivo, providing a highly desirable non-invasive diagnostic approach for ROS-related diseases.

Exploring Nitrogen Reduction Reaction Mechanisms with Graphyne-Confined Single-Atom Catalysts: A Computational Study Incorporating Electrode Potential and pH

This study reconciles discrepancies between practical electrochemical conditions and theoretical density functional theory (DFT) frameworks, evaluating three graphyne-confined single-atom catalysts (Mo-TEB, Mo@GY, and Mo@GDY). Using both constant charge models in vacuum and constant potential models with continuum implicit solvation, we closely mimic real-world electrochemical environments. Our findings highlight the crucial role of explicitly incorporating electrode potential and pH in the constant potential model, providing enhanced insights into the nitrogen reduction reaction (NRR) mechanisms. Notably, the superior NRR performance of Mo-TEB is attributed to the d-band center's proximity to the Fermi level and enhanced magnetic moments at the atomic center. This research advances our understanding of graphyne-confined single-atom catalysts as effective NRR platforms and underscores the significance of the constant potential model for accurate DFT studies of electrochemical reactions.

Nonbonding Metal-Metal Interaction in Metal-Nitrogen-Carbon Single-Atom Catalysts Boosts CO Electroreduction

Metal-nitrogen-carbon single-atom catalysts (SACs) have recently emerged as selective electrocatalysts for the reduction of CO2 to CO, but their ability to further electroreduce CO is poor. Here, based on constant-potential density functional theory simulations, we predict that Co-N-M (M = Fe, Co) SACs with nonbonding metallic centers bridged by a common nitrogen atom can catalyze four-electron reduction of CO to methanol at an ultralow overpotential of 220-310 mV. We show that the metal atoms in the SACs are terminated by H species which prevent the formation of σ bonding between CO and the metal atoms. Thanks to the nonbonding electrostatic repulsion between Co and its adjacent M atom, the Co dxz band is broadened and shifted toward the Fermi level, leading to enhanced dxz - 2π* interaction that gives rise to stable CO adsorption and promotes its active and selective reduction. This work offers an alternative strategy to tackle the challenge of CO electroreduction on SACs and highlights the role of nonbonding metal-metal interactions in modulating adsorption properties of SACs.

Unleashing the Potential of Single-Atom Nanozymes: Catalysts for the Future

Single-atom nanozymes (SANs) have become a breakthrough in atomically precise catalysis, which relies on the catalytic active site formed by the single-atom itself. From this angle, SANs and their advantages compared to natural enzymes as well as spaces for their application are emphasized. The SANs have outstanding control over their catalytic activities; this is compared with bulk materials and natural enzymes. The structure of the SANs has very promising potential for the next generation of biosensing and biomedical devices and environmental remediation. Although their capabilities are high, difficulties still arise. The specificity, scalability, biosafety, and catalysis mechanisms raise additional issues that require further research. We build up a vision of the perspectives of the better implementation of SANs, which are designed for diagnostic purposes, improving industrial technologies, and creating new sustainable technologies in the food processing industry. AI and machine learning systems may clarify the structure-performance relationship of SANs for improved material and process selectivity. The future of SANs is very promising, and by addressing these challenges and leveraging advancements in artificial intelligence and materials science, SANs have the potential to become powerful tools for a sustainable future.

Insights into the Optimization of Catalytic Active Sites in Lithium-Sulfur Batteries

ConspectusLithium-sulfur batteries (LSBs), recognized for their high energy density and cost-effectiveness, offer significant potential for advancement in energy storage. However, their widespread deployment remains hindered by challenges such as sluggish reaction kinetics and the shuttle effect of lithium polysulfides (LiPSs). By the introduction of catalytic materials, the effective adsorption of LiPSs, smooth surface migration behavior, and significantly reduced conversion energy barriers are expected to be achieved, thereby sharpening electrochemical reaction kinetics and fundamentally addressing the aforementioned challenges. However, driven by practical application targets, the demand for higher loadings and reduced electrolyte parameters inevitably exacerbates the burden on catalytic materials during their service. Additionally, given that catalytic materials contribute negligible electrochemical capacity, their incorporation inevitably increases the mass of nonactive components for reducing the energy density of LSBs. A meticulous insight into the lithium-sulfur catalytic reaction reveals that the conversion of LiPSs is dominated by active sites on the surfaces of catalytic materials. These microregions provide the necessary electron and ion transport for the conversion reaction of LiPSs, with their efficacy and quantity directly impacting the conversion efficiency. In light of these considerations, the strategic optimization of active sites emerges as a paramount pathway toward promoting the performance of LSBs while concurrently mitigating unnecessary mass. Here, we outline three strategies developed by our group to optimize active sites of catalytic materials: (1) Augmenting active sites by customizing structural modulation and precise dimensional control to maximize exposure. Emphasis has been placed on the approaches for material synthesis and the essence of reactions for achieving this strategy. (2) Regulating the microenvironment of active sites by integrating the coordination refinement, long-range atomic interactions, metal-support interactions, and other electronic regulation strategies, thereby providing an elevation in the intrinsic catalytic performance. (3) Implementing a self-cleaning mechanism for active sites to counteract deactivation by designing a tandem adsorption-migration-transformation pathway of sulfur contained within the molecular domain. Throughout this process, the intrinsic mechanisms driving performance enhancement through active site optimization strategies have been prominently emphasized, which encompass aspects such as electronic structure, atomic composition, and molecular configuration and significantly expand the comprehension of Li-S catalytic chemistry. Subsequently, considerations demanding heightened attention in future processes of active site optimization for catalytic materials have been delineated, including the in situ evolution patterns and resistance to the poisoning of active sites. It is noteworthy that given the similarity between Li-S catalysis chemistry and traditional electrocatalytic processes, this Account elucidates the concept of active site optimization by drawing insights from representative works and our own works in the field of electrocatalysis, which is relatively rare in previous reviews of LSBs. The proposed insights contribute to uncovering the intrinsic mechanisms of Li-S catalysis chemistry and introducing innovative ideas into active site optimization, ultimately advancing energy density and stability in LSBs.

Ni and Co Active Site Transition and Competition in Fluorine-Doped NiCo(OH)2 LDH Electrocatalysts for Oxygen Evolution Reaction

The oxygen evolution reaction (OER) performance of NiCo LDH electrocatalysts can be improved through fluorine doping. The roles of Ni and Co active sites in such catalysts remain ambiguous and controversial. In addressing the issue, this study draws upon the molecular orbital theory and proposes the active center competitive mechanism between Ni and Co. The doped F-atoms can directly impact the valence state of metal atoms or exert an indirect influence through the dehydrogenation, thereby modulating the active center. As the F-atoms are progressively aggregate, the eg orbitals of Ni and Co transition from e2 g to e1 g, and subsequently to e0 g. The corresponding valence state elevates from +2 to +3, and then to +4, signifying an initial increase followed by a subsequent decrease in the electrocatalytic performance. Furthermore, a series of F-NiCo LDH catalysts are synthesized to verify the eg orbital occupancy analysis, and the catalytic OER overpotentials are 303, 243, 240, and 246 mV at the current density of 10 mA cm-2, respectively, which coincides well with the theoretical prediction. This investigation not only provides novel mechanistic insights into the transition and competition of Ni and Co in F-NiCo LDH catalysts but also establishes a foundation for the design of high-performance catalysts.

Magnetic Order Transition of a Two-Dimensional Square-Lattice Electrocatalyst Assembled by Fe-N4 Units: Crucial Role on Oxygen Reduction

Herein, we theoretically investigate the effect of magnetic orders on electrocatalytic oxygen reduction reaction (ORR) properties on the Fe-N4 site-embedded two-dimensional (2D) covalent organic framework (Fe-N4@COF-C3N2) under realistic environments. The Fe-N4@COF-C3N2 shows a 2D square-lattice (sql) topology with three magnetic order states: one ferromagnetic state (FM) and two antiferromagnetic states (AFM1 and AFM2). Specially, the electrocatalyst in the AFM2 state shows a remarkable onset potential of 0.80 V/reversible hydrogen electrode (RHE) at pH 1, superior to the existing most excellent noble-metal catalysts. Thermodynamically, the onset potential for the 4e- ORR is 0.64 V/RHE at pH 1, with a magnetic state transition process of FM → AFM1 → FM → FM → FM, while at pH 13, the onset potential for the 4e- ORR is 0.54 V/RHE, with the magnetic transition process of FM → FM → AFM1 → FM → FM. Generally, this finding will provide new avenues to rationally design the Fe-N4 electrocatalyst.

Transition-Metal Porphyrin-Based MOFs In Situ-Derived Hybrid Catalysts for Electrocatalytic CO2 Reduction

Excellent electrocatalytic CO2 reduction reaction activity has been demonstrated by transition metals and nitrogen-codoped carbon (M-N-C) catalysts, especially for transition-metal porphyrin (MTPP)-based catalysts. In this work, we propose to use one-step low-temperature pyrolysis of the isostructural MTPP-based metal-organic frameworks (MOFs) and electrochemical in situ reduction strategies to obtain a series of hybrid catalysts of Co nanoparticles (Co NPs) and MTPP, named Co NPs/MTPP (M = Fe, Co, and Ni). The in situ introduction of Co NPs can efficiently enhance the electrocatalytic ability of MTPP (M = Fe, Co, and Ni) to convert CO2 to CO, particularly for FeTPP. Co NPs/FeTPP endowed a high CO faradaic efficiency (FECOmax = 95.5%) in the H cell, and the FECO > 90.0% is in the broad potential range of -0.72 to -1.22 VRHE. In addition, the Co NPs/FeTPP achieved 145.4 mA cm-2 at a lower potential of -0.70 VRHE with an FECO of 94.7%, and the CO partial currents increased quickly to reach 202.2 mA cm-2 at -0.80 VRHE with an FECO of 91.6% in the flow cell. It is confirmed that Co NPs are necessary for hybrid catalysts to get superior electrocatalytic activity; Co NPs also can accelerate H2O dissociation and boost the proton supply capacity to hasten the proton-coupled electron-transfer process, effectively adjusting the adsorption strength of the reaction intermediates.

Ambient Electrochemical Ammonia Synthesis: From Theoretical Guidance to Catalyst Design

Ammonia, a vital component in the synthesis of fertilizers, plastics, and explosives, is traditionally produced via the energy-intensive and environmentally detrimental Haber-Bosch process. Given its considerable energy consumption and significant greenhouse gas emissions, there is a growing shift toward electrocatalytic ammonia synthesis as an eco-friendly alternative. However, developing efficient electrocatalysts capable of achieving high selectivity, Faraday efficiency, and yield under ambient conditions remains a significant challenge. This review delves into the decades-long research into electrocatalytic ammonia synthesis, highlighting the evolution of fundamental principles, theoretical descriptors, and reaction mechanisms. An in-depth analysis of the nitrogen reduction reaction (NRR) and nitrate reduction reaction (NitRR) is provided, with a focus on their electrocatalysts. Additionally, the theories behind electrocatalyst design for ammonia synthesis are examined, including the Gibbs free energy approach, Sabatier principle, d-band center theory, and orbital spin states. The review culminates in a comprehensive overview of the current challenges and prospective future directions in electrocatalyst development for NRR and NitRR, paving the way for more sustainable methods of ammonia production.

Tip-like Fe-N4 Sites Induced Surface Microenvironments Regulation Boosts the Oxygen Reduction Reaction

Single atom catalysts with defined local structures and favorable surface microenvironments are significant for overcoming slow kinetics and accelerating O2 electroreduction. Here, enriched tip-like FeN4 sites (T-Fe SAC) on spherical carbon surfaces were developed to investigate the change in surface microenvironments and catalysis behavior. Finite element method (FEM) simulations, together with experiments, indicate the strong local electric field of the tip-like FeN4 and the more denser interfacial water layer, thereby enhancing the kinetics of the proton-coupled electron transfer process. In situ spectroelectrochemical studies and the density functional theory (DFT) calculation results indicate the pathway transition on the tip-like FeN4 sites, promoting the dissociation of O-O bond via side-on adsorption model. The adsorbed OH* can be facilely released on the curved surface and accelerate the oxygen reduction reaction (ORR) kinetics. The obtained T-Fe SAC nanoreactor exhibits excellent ORR activities (E1/2 =0.91 V vs. RHE) and remarkable stability, exceeding those of flat FeN4 and Pt/C. This work clarified the in-depth insights into the origin of catalytic activity of tip-like FeN4 sites and held great promise in industrial catalysis, electrochemical energy storage, and many other fields.

Modeling Interfacial Dynamics on Single Atom Electrocatalysts: Explicit Solvation and Potential Dependence

ConspectusSingle atom electrocatalysts, with noble metal-free composition, maximal atom efficiency, and exceptional reactivity toward various energy and environmental applications, have become a research hot spot in the recent decade. Their simplicity and the isolated nature of the atomic structure of their active site have also made them an ideal model catalyst system for studying reaction mechanisms and activity trends. However, the state of the single atom active sites during electrochemical reactions may not be as simple as is usually assumed. To the contrary, the single atom electrocatalysts have been reported to be under greater influence from interfacial dynamics, with solvent and electrolyte ions perpetually interacting with the electrified active center under an applied electrode potential. These complexities render the activity trends and reaction mechanisms derived from simplistic models dubious.In this Account, with a few popular single atom electrocatalysis systems, we show how the change in electrochemical potential induces nontrivial variation in the free energy profile of elemental electrochemical reaction steps, demonstrate how the active centers with different electronic structure features can induce different solvation structures at the interface even for the same reaction intermediate of the simplest electrochemical reaction, and discuss the implication of the complexities on the kinetics and thermodynamics of the reaction system to better address the activity and selectivity trends. We also venture into more intriguing interfacial phenomena, such as alternative reaction pathways and intermediates that are favored and stabilized by solvation and polarization effects, long-range interfacial dynamics across the region far beyond the contact layer, and the dynamic activation or deactivation of single atom sites under operation conditions. We show the necessity of including realistic aspects (explicit solvent, electrolyte, and electrode potential) into the model to correctly capture the physics and chemistry at the electrochemical interface and to understand the reaction mechanisms and reactivity trends. We also demonstrate how the popular simplistic design principles fail and how they can be revised by including the kinetics and interfacial factors in the model. All of these rich dynamics and chemistry would remain hidden or overlooked otherwise. We believe that the complexity at an electrochemical interface is not a curse but a blessing in that it enables deeper understanding and finer control of the potential-dependent free energy landscape of electrochemical reactions, which opens up new dimensions for further design and optimization of single atom electrocatalysts and beyond. Limitations of current methods and challenges faced by the theoretical and experimental communities are discussed, along with the possible solutions awaiting development in the future.