Local Coordination Environment Research Articles

Modulating RuO2 Electrocatalysis via Introducing Lanthanides for Enhanced Acidic Oxygen Evolution

AbstractThe low activity of ruthenium dioxide (RuO2) and the rapid dissolution of the ruthenium (Ru) site during acid oxygen evolution reaction (OER) at high current density restricts its application in proton exchange membrane (PEM) electrolyzers. In this work, a series of rare‐earth (RE) elements doped RuO2 nanorods is developed as high‐performance OER electrocatalysts. X‐ray absorption spectroscopy suggests that RE doping regulates the local coordination environment around Ru sites, lowers the valance of Ru, and shortens the Ru─O─Ru(M) bond length, which enhances structural stability. Among the RE‐RuO2 samples, Sm‐RuO2 exhibits remarkable performance with a low overpotential of 283 mV to reach 100 mA cm−2 and maintained stability for over 140 h at 10 mA cm−2. Moreover, the PEM electrolyzer using Sm‐RuO2 as the anode can be stably operated at 500 mA cm−2 for 15 h. Electrochemical analysis, X‐ray photoelectron spectroscopy, and in situ Raman spectroscopy show that Sm doping lowers the d‐band center, reduces the adsorption energy of O intermediates to enhance the OER activity, and restrains excessive oxidation of Ru sites while stabilizing lattice oxygen during the OER process, thereby enhancing OER stability. This work offers valuable insights into improving the stability of metal oxide catalysts in acidic electrolytes.

Potential-Driven Coordinated Oxygen Migration in an Electrocatalyst for Sustainable H2O2 Synthesis.

Local coordination environment (LCE) manipulation has emerged as a significant approach for modulating the electrocatalytic behavior of low-dimensional nanomaterials. However, challenges persist in accurately identifying active sites and understanding dynamic changes during operation. Here, we underscore the influence of LCE on the electrochemical production of H2O2, utilizing the Pd cluster as a model catalyst. Density functional theory (DFT) calculations illustrate the role of first- and second-coordinated sulfur and oxygen in modulating the binding strength of HOO*. Guided by DFT screening, the as-prepared Pd cluster (Pdx/HMCS) catalyst presents exceptional catalytic performance with a high mass activity of 4.06 A mg-1 at 0.45 V and selectivity above 94%. The Pdx/HMCS catalyst also delivers promising potential for industrial practices with a production rate of 16.3 mol gcat-1 h-1 in flow cell evaluation. Elaborated in situ characterizations confirm that under operation, oxygen migrates from the second coordination sphere (CS) to the first CS to achieve oxygen coverage on the catalyst surface. Such an oxygen migration phenomenon and the optimized first and second coordination environment give rise to the outstanding performance.

Modulating the Local Coordination Environment of M‐Nx Single‐Atom Site for Enhanced Electrocatalytic Oxygen Reduction

AbstractEfficient, durable, and economical oxygen reduction catalysts are key for practical applications such as fuel cells and metal–air batteries. Single atom catalysts (SACs) have attracted sustained and widespread attention owing to their unique electronic properties and exceptional atomic utilization, positioning them as promising electrocatalysts in energy conversion and storage. However, the symmetric charge distribution of the metal site in the symmetric M‐N4 configuration of SACs is not conducive to electron transfer and transport in electrocatalytic reactions, resulting in a low adsorption energy for oxygen reduction reaction (ORR) related species (*OH, *O, and *OOH), which severely limits the intrinsic activity of the electrocatalysts. To overcome this limitation and improve the activity and durability, heteroatom doping can effectively modulate the local coordination environment (LCE) of the metal atom, including the coordinating atoms, coordination shells and coordination number. These modifications have significantly improved the performance of carbon supported SACs with M‐N4 configuration in the ORR. Based on this, a thorough summary of the major progress made in recent years in adjusting the LCE of SACs through doping with heteroatoms is provided and a perspective on the future development is offered here.

Novel Large-scale Integrated Non-Precious Metal Electrodes for Efficient and Stable Oxygen Evolution Reaction at High Current Density in 2.5 kW Anion Exchange Membrane Water Electrolysis

The utilization of non-precious catalysts to substitute precious metal catalysts on anode side under high current density conditions and with long-term resistance is crucial for the implementation of alkaline anion-exchange membrane water electrolysis (AEMWE) applications. To accommodate industrial applications, a combination of chemical solution and electrodeposition was used to construct NiFeCo layered double hydroxide and NiS nanosheet heterostructures on Ni foam (NiFeCo LDH/NiS/NF). Both experiments and theoretical calculations show that the heterogeneous structure reduces the activation energy barrier of the catalytic reaction and provides an appropriate electronic structure. This not only guarantees the exposure of the active site but also adjusts the local coordination environment and chemisorption properties. Consequently, the reduction in energy barrier affects the rate-determining step (RDS) from *O to *OOH, as well as the energy barriers of all four steps in the oxygen evolution reaction (OER). Consequently, the optimized NiFeCo LDH/NiS/NF catalyst demonstrates a low voltage of 288mV to operate 1.0Acm-2. Additionally, the catalyst was conducted with commercial Pt/C coated onto carbon paper (Pt/C/CP) for 2×2 cm2 AEMWE exhibited 1.63V cell voltag to attain 1Acm−2 and operated for 2100h from 1Acm-2 to 2.5Acm-2 (1.69V to 1.92V). Further, the catalyst was prepared scalable to 15×15 cm2 for application into a 2.5kW AEMWE device, which required only 1.77V at 60 °C to catch 1Acm-2 for 1000h, which shows extremally promising application for stable AEMWE device.

Mechanistic Study of Highly Active Bifunctional Double-Atom Electrocatalysts for Oxygen Reduction and Oxygen Evolution Reactions.

Dual-atom catalysts (DACs) can be very effective for catalyzing both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Herein, we present theoretical evidence of a new class of highly active DACs, namely, the double-atom embedded in nitrogen-doped graphene sheet 2M-N-C (M = Mn, Fe) on the basis of density functional theory calculations. Importantly, we find that the double active sites of 2M-N-C DACs entail an unconventional catalytic reaction pathway for ORR and OER. We also show that the local coordination environment of the active sites can significantly affect the stability and oxygen catalytic activity of 2M-N-C DACs. In particular, MnFe-N-C DAC not only exhibits good stability but also possesses outstanding bifunctional ORR/OER catalytic activity with the potential difference (ΔE) between the OER and ORR as low as 0.34 V, notably lower than most bifunctional electrocatalysts reported in the literature. This finding suggests a new strategy toward the design of stable and highly active bifunctional electrocatalysts for both ORR/OER.

Thermal Quenching Mechanism of Mn4+ in Na2SiF6, NaKSiF6, and K2SiF6 Phosphors: Insights from the First-Principles Analysis.

This study aims to identify the key factors governing the thermal quenching of Mn4+ ion luminescence in fluoride-based phosphor materials used as red emitters in modern-day phosphor-converted LED devices. Here, we employ first-principles calculations for Mn4+-doped Na2SiF6, NaKSiF6, and K2SiF6 hosts to explore how host properties and local coordination environments influence thermal quenching behavior. The ΔSCF method was used to model the geometric structures of the Mn4+4A2 (ground) and 2E, 4T2 (excited) states and the energies of the optical transitions between these states. Our results reveal that thermal quenching in Na2SiF6 and K2SiF6 phosphors occurs through thermally activated 2E → 4T2 → 4A2 crossover. In contrast, thermal quenching in NaKSiF6 is due to other nonradiative decay pathways. Investigations of the mechanical stability of these fluorides show that NaKSiF6 is mechanically unstable. We suggest that this property of the host limits the luminescence efficiency of the embedded Mn4+ ions. We also determined the reason for the difference in the intensity of the 2E → 4A2 emission transition (ZPL) in the systems. These findings advance our fundamental understanding of the thermal quenching mechanism of Mn4+ ion luminescence in fluorides, and the results can aid future discoveries of technologically useful phosphors through high-throughput design methodologies.

Tailoring Li+ Local Coordination Environment of Solid Polymer Electrolytes to Boom Ionic Conductivity.

The low ionic conductivity is the key issue of solid polymer electrolytes (SPEs), hampering their practical application. Great efforts have been devoted to reducing their crystallinity to increase ionic conductivity but ignored their Li+ local coordination environment influence. Here, Li+ local coordination environment tunable poly(vinylidene fluoride-co-hexafluoropropylene)-based solid-state electrolytes are experimentally realized via d-cellobiose octaacetate. d-cellobiose octaacetate competes with anions and polymer chains for coordination of Li+ thorough C═O groups to weaken their coordination of Li+, increase the number of carriers, and strengthen the transport kinetics of Li+, booming the ionic conductivity of SPEs at room temperature. When used in lithium metal symmetric batteries and full batteries, SPEs greatly improve their electrochemical performance at 25°C. This work clarifies the important influence of Li+ local coordination environment on Li+ transport and provides a promising strategy to improve the ionic conductivity of SPEs.

Regulating Local Electron Distribution of Cu Electrocatalyst via Boron Doping for Boosting Rapid Absorption and Conversion of Nitrate to Ammonia

AbstractThe electrochemical reduction of nitrate to ammonia (NO3RR) is an effective route to ammonia synthesis with the characteristics of low energy input. However, the complex multi‐electron/proton transfer pathways associated with this reaction may trigger the accumulation of competitive by‐products. Herein, boron (B)‐doped Cu electrode (denoted as B–Cu2O/Cu/CP) as “all‐in‐one” catalyst is prepared by one‐step electrodeposition strategy. Caused by the B doping, the charge redistribution and local coordination environment of Cu2O/Cu species are modulated, resulting in the exposure of active sites on the Cu2O/Cu/CP catalyst. In‐situ Fourier transform infrared spectroscopy and theoretical investigations demonstrate that both Cu2O and Cu sites modulated by B can effectively enhance the adsorption of NO3− and facilitate the conversion of intermediate by‐products, thus promoting the direct reduction of NO3− to NH3. Consequently, a remarkable Faradaic efficiency of 92.74% can be obtained on B–Cu2O/Cu/CP catalyst with minimal accumulation of by‐products. It is expected that this work, based on the heterogeneous B doping, will open a maneuverable and versatile way for the design of effective catalysts.

Quantitatively Deciphering the Local Structure and Luminescence Spectroscopy of Pr3+-Doped Yttrium Lithium Fluoride.

Praseodymium (Pr3+)-doped LiYF4 nanophosphors have garnered significant interest for their potential applications in lasers, phosphors, and quantum memories. However, there remains a lack of comprehensive research on the local coordination environment and luminescence spectroscopy of Pr3+:LiYF4 nanocrystals. This study presents the first investigation of the ground-state structure of Pr3+:LiYF4 crystals by employing the crystal structure prediction method, and a [PrF8]5- ligand complex with S4 local symmetry is determined. The complete energy levels of the Pr3+ ions in LiYF4 nanocrystals are unveiled by using our newly developed well-established parametrization matrix diagonalization method. A novel set of free-ion and crystal-field parameters is derived through a good simulation with 45 experimental energy levels. Many of the emissions of Pr3+-doped LiYF4 are successfully reproduced based on Judd-Ofelt theory, and these transitions are comparable to the experimental ones. Moreover, two new prominent emission bands with their peaks at 675 and 849 nm originating from 1I6 → 3F4 and 1I6 → 1G4 transitions, respectively, are predicted by us for the first time. This study could provide a feasible method to search for practical laser transition channels of solid-state lasers based on Pr3+: LiYF4 nanophosphors.

Probing the Local Coordination Environment of Mononuclear Pd Ions Supported on Ceria Using CO Adsorption Infrared Vibrational Spectroscopy

Probing the Local Coordination Environment of Mononuclear Pd Ions Supported on Ceria Using CO Adsorption Infrared Vibrational Spectroscopy

Enhancing the Reaction Kinetics and Stability of Co-Free Li-Rich Cathode Materials via a Multifunctional Strategy.

Co-free Li-rich layered oxides (CFLLOs) with anionic redox activity are among the most promising cathode materials for high-energy-density and low-cost lithium-ion batteries (LIBs). However, irreversible oxygen release often causes severe structural deterioration, electrolyte decomposition, and the formation of unstable cathode-electrolyte interface (CEI) film with high impedance. Additionally, the elimination of cobalt elements further deteriorates the reaction kinetics, leading to reduced capacity and poor rate performance. Here, a multifunctional strategy is proposed, incorporating Li2MnO3 phase content regulation, micro-nano structure design, and heteroatom substitution. The increased content of Li2MnO3 phase enhances the capacity through oxygen redox. The smaller nanoscale primary particles induce greater tensile strain and introduce more grain boundaries, thereby improving the reaction kinetics and reactivity, while the larger micron-sized secondary particles help to reduce interfacial side reactions. Furthermore, Na⁺ doping modulates the local coordination environment of oxygen, stabilizing both the anion framework and the crystal structure. As a result, the designed cathode exhibits enhanced rate performance, delivering a capacity of 158 mAh g⁻¹ at 5.0 C and improved cyclic stability, with a high capacity retention of 99% after 400 cycles at 1.0 C. This multifunctional strategy holds great promise for advancing the practical application of CFLLOs in next-generation LIBs.

Oxophilic Low‐Coordination Gd‐N3 Single Atom Sites With P‐Enhanced Second Coordination for High‐Performance Al‐Air Batteries

AbstractThe development of efficient rare earth single‐atom (SA) catalysts for the oxygen reduction reaction (ORR) is essential yet challenging for high‐performance aluminum‐air batteries (AABs). This study introduces a concept‐to‐proof strategy for synthesizing a hollow carbon‐supported gadolinium (Gd) SA catalyst using low‐coordination and second‐coordination sphere engineering. In this design, Gd atoms are coordinated to three nitrogen (N) atoms in N‐doped carbon and surrounded by six phosphorus (P) atoms, forming Gd‐N3‐P6 sites. These catalysts demonstrated exceptional ORR performance, achieving a half‐wave potential of 0.895 V and superior durability compared to the commercial Pt/C benchmark. When integrated into AABs, they delivered impressive performance, with a peak power density of 257 mW/cm2 and an energy density of 2916 Wh/kg, alongside enhanced cycling stability. In situ characterization and theoretical calculations revealed that the strategic placement of P atoms in the second coordination sphere significantly enhanced the valence state of the Gd site. This enhancement improved the adsorption capacity for O2 and H2O while facilitating the rapid desorption of *OH intermediates during the ORR. This study offers valuable insights into the development of cost‐effective ORR catalysts, emphasizing the significance of modulating the local coordination environment of metal SA sites.

Why Colloidal Syntheses of Bimetallic Nanoparticles Cannot be Generalized.

Introducing one general synthesis to form bimetallic nanoparticles (NPs) could accelerate the discovery of NPs for promising energy applications. Although colloidal syntheses can provide precise structural and morphological control of bimetallic NPs, the complex chemical nature of multicomponent syntheses challenges the realization of such synthetic simplicity. Common synthetic issues are frequently ascribed to the variation in metal ion precursor reactivities and complex chemical interactions between the different metal surfaces and capping agents employed. However, no systematic studies have shown how these factors compete to ultimately assign the factor limiting the mixing and formation of bimetallic NPs. Here, we provide a parametric investigation of how the intrinsic standard reduction potentials (E0red) of the metal ions and cocapping agents influence the formation of bimetallic AuCu, AuPd, and PdCu NPs. Using a combination of in situ X-ray total scattering along with transmission electron microscopy and nuclear magnetic resonance spectroscopy, we illustrate the multifunctional role of the cocapping agents through interactions with both the metal ion precursors and NP surfaces to stabilize metastable structures. Additionally, we demonstrate how system-specific side reactions and the local metal ion coordination environment can be used to selectively tune the formation kinetics, structure, and morphology of bimetallic NPs. Ultimately, these insights show that the chemical interactions rather than the intrinsic E0red are responsible for the formation of bimetallic NPs. Broadly, these insights should aid the synthetic design of tailored multimetallic NPs.

Platinum‐Group Metal High‐Entropy Selenides for the Hydrogen Evolution Reaction

The selenides of platinum‐group metals (PGMs) are emerging as promising catalysts for diverse electrochemical reactions. To date, most studies have focused on single metal or bimetallic systems, whereas the preparation of a high‐entropy (HE) selenide consisting of five or more PGM elements holds the promise to further enhance catalytic performance by introducing abundant active sites with various local coordination environments and electronic structures. Herein, we report for the first time the synthesis of PGM‐based HE‐Selenide (HE‐Se) nanoparticles with a unique amorphous structure. The atomic metal–Se coordination and the presence of short‐range order were thoroughly revealed. It is further shown that the amorphous HE‐Se can be facilely transformed into a single‐phase crystalline HE‐Se with a cubic structure by thermal annealing. Catalytically, the amorphous HE‐Se showed better acidic hydrogen evolution activity over monometallic PGM‐based selenides and the crystalline counterpart, demonstrating the advantages of high‐entropy configuration and amorphous structure. Our findings may pave the way toward the synthesis and property exploration of amorphous PGM‐based selenides with tunable compositions.

Platinum-Group Metal High-Entropy Selenides for the Hydrogen Evolution Reaction.

The selenides of platinum-group metals (PGMs) are emerging as promising catalysts for diverse electrochemical reactions. To date, most studies have focused on single metal or bimetallic systems, whereas the preparation of a high-entropy (HE) selenide consisting of five or more PGM elements holds the promise to further enhance catalytic performance by introducing abundant active sites with various local coordination environments and electronic structures. Herein, we report for the first time the synthesis of PGM-based HE-Selenide (HE-Se) nanoparticles with a unique amorphous structure. The atomic metal-Se coordination and the presence of short-range order were thoroughly revealed. It is further shown that the amorphous HE-Se can be facilely transformed into a single-phase crystalline HE-Se with a cubic structure by thermal annealing. Catalytically, the amorphous HE-Se showed better acidic hydrogen evolution activity over monometallic PGM-based selenides and the crystalline counterpart, demonstrating the advantages of high-entropy configuration and amorphous structure. Our findings may pave the way toward the synthesis and property exploration of amorphous PGM-based selenides with tunable compositions.

Optimizing the Intermediates Adsorption by Manipulating the Second Coordination Shell of Ir Single Atoms for Efficient Water Oxidation

AbstractThe precise regulation of single‐atom catalysts (SACs) with the desired local chemical environment is vital to elucidate the relationship between the SACs structure and the catalytic performance. The debate on the effect of the local coordination environment is quite complicated even for the SACs with the same composition and chemical nature, calling for increased attention on the regulation of the second coordination shell. For oxide‐supported SACs, it remains a significant challenge to precisely manipulate the second coordination shell of single atoms supported on oxides due to the structural robustness of oxides. Here, Ir single atoms were anchored on NiO supports via different bonding strategies, resulting in the diverse Ir−O−Ni coordination numbers for Ir sites. Specifically, Ir1/NiO, Ir1−NiO, and Ir1@NiO SACs with increasing Ir−O−Ni coordination numbers of 3, 4, and 5 were synthesized, respectively. We found that the activity of the three samples towards oxygen evolution reaction (OER) exhibited a volcano‐shaped relationship with the Ir−O−Ni coordination number, with Ir1−NiO showing the lowest overpotential of 225 mV at 10 mA cm−2. Mechanism investigations indicate that the moderate coordination number of Ir−O−Ni in Ir1−NiO creates the higher occupied Ir dz2 orbital, weakening the adsorption strength for *OOH intermediates and thereby enhancing the OER activity.

Template‐Sacrificing Synthesis of Asymmetrically Coordinated Zn Single‐Atom Sites for High‐Performance Sodium–Sulfur Batteries

AbstractMetal single‐atom catalysts (SACs) are extensively investigated to accelerate the sulfur redox kinetics in room‐temperature sodium─sulfur (Na─S) batteries. Nevertheless, the influence of the structure symmetry of SACs center on the electrocatalytic mechanism and the precise pathway in which single‐atom active sites facilitate sodium polysulfides (Na2Sn) conversion remain unknown. To enable controlled construction of highly active single‐atom configuration, herein, Zn SACs with an asymmetrical Zn─N3O configuration are designed for sodium polysulfides conversion. Both theoretical and experimental explorations reveal that the Zn─N3O single‐atom center displays higher electrocatalytic activity for polysulfides conversion than the Zn─N4 single‐atom center. The N/O co‐coordination induces the localized charge at Zn single‐atom center, which strengthens the d‐p hybridization with Na2Sn and stretches Na─S bond length of Na2Sn, thus accelerating the sulfur redox reaction kinetics. Consequently, the as‐assembled Na─S batteries achieve a high capacity of 1016 mAh g−1 at 1.0 C with a capacity decay of 0.0186% per cycle over 1000 cycles. This work uncovers the subtle relationship between the electrocatalytic activity of species conversion and the local coordination environment of SACs, and offers a guidance for the design of efficient asymmetrical SACs for different catalysis applications.

Optimizing the Intermediates Adsorption by Manipulating the Second Coordination Shell of Ir Single Atoms for Efficient Water Oxidation.

The precise regulation of single-atom catalysts (SACs) with the desired local chemical environment is vital to elucidate the relationship between the SACs structure and the catalytic performance. The debate on the effect of the local coordination environment is quite complicated even for the SACs with the same composition and chemical nature, calling for increased attention on the regulation of second coordination shell. For oxide-supported SACs, it remains a significant challenge to precisely manipulate the second coordination shell of single atoms supported on oxides due to the structural robustness of oxides. Here, Ir single atoms are anchored on NiO supports via different bonding strategies, resulting in the diverse Ir-O-Ni coordination numbers for Ir sites. Specifically, Ir1/NiO, Ir1-NiO, and Ir1@NiO SACs with increasing Ir-O-Ni coordination numbers of 3, 4, and 5 were synthesized, respectively. We found that the activity of the three samples towards oxygen evolution reaction (OER) exhibited a volcano-shaped relationship with the Ir-O-Ni coordination number, with Ir1-NiO showing the lowest overpotential of 225 mV at 10 mA cm-2. Mechanism investigations indicate that the moderate coordination number of Ir-O-Ni in Ir1-NiO creates the higher occupied Ir dz2 orbital, weakening the adsorption strength for *OOH intermediates and thereby enhancing the OER activity.

Enhancing the oxygen evolution reaction activity and stability of high-valent CoOOH by switching the catalytic pathway through doping low-valent Cu

The oxygen evolution reaction (OER) is a critical process in electrochemical energy storage and conversion systems. The adsorbate evolution mechanism (AEM) pathway possesses the characteristics of high stability but slow catalytic kinetics. We propose that combining AEM with the lattice oxidation mechanism (LOM) pathway can potentially enhance the OER catalytic activity and stability. However, the triggering of LOM is an important challenge due to the high thermodynamic activation barrier of lattice oxygen. To solve this problem, we performed theoretical calculations and experiments which suggest that the introduction of low-valent Cu in CoOOH (CuxCo1−xOOH) could directionally modulate the local coordination environment of CoO bonds. This approach can activate lattice oxygen and generate oxygen vacancies to enhance the nucleophilic attack of *OH and directly establish OO coupling, thereby facilitating the smoothly switching from AEM to LOM pathway by increasing voltage and thus activating lattice oxygen in CuxCo1−xOOH. The switching of AEM and LOM enables CuxCo1−xOOH showing an outstanding overpotential of only 252 mV (10 mA cm−2) and durability of only 2.80 % degradation after 280h. This work provides a new way for designing efficient and stable electrocatalysts with AEM and LOM pathway switching.

Brightening dark excitons in inorganic halide perovskites by local symmetry breaking

Thermally activated delayed fluorescence (TADF) phenomenon, defined as thermal activation of triplet dark-state excitons into singlet state excitons through reverse intersystem crossing (RISC), has become a prevalent principle for designing organic-based electro-/photo-luminescent molecules. However, activating dark excitons in inorganic metal halide perovskites (MHPs) still remains challenging. Herein, we report an efficient strategy of doping-induced local symmetry breaking to brighten dark excitons in inorganic halide perovskite Cs2ZrCl6, which result in a 500 % enhancement of low-temperature luminescence emission. Lattice symmetry breaking confirmed by the X-ray absorption spectroscopy measurements could disturb the local coordination environment at the Zr site. The singlet-triplet energy gap (ΔEST) fitted from temperature-dependent photoluminescence decay curves decreases from 0.087 to 0.071 eV, thus reducing up-conversion barrier of dark excitons. Theoretical calculation indicates large spatial separation of charge density favorable for enhanced TADF emission. Furthermore, a flexible X-ray scintillator screen with poly (dimethylsiloxane) as the matrix could obtain high-quality X-ray imaging with a 14 lp mm−1 resolution. This work gives insights into improving photoemission of inorganic MHPs via brightening dark excitons.