Stability Of Active Sites Research Articles

Hydrothermal Stability of Active Sites in Cu-exchanged Small-pore Zeolites for the Selective Catalytic Reduction of NOx.

Combining operando X-ray absorption spectroscopy (XAS) and computational modelling shows unequivocally the distribution of active species in fresh and hydrothermally aged Cu-CHA and Cu-AEI zeolites during NH3-assisted selective catalytic reduction of NOx. Four principal species co-exist: (i) CuI cations coordinated to NH3, (ii) CuI cations coordinated to the zeolite framework, (iii) solvated CuII cations, and (iv) framework-coordinated CuII species (CuIIst) formed upon hydrothermal ageing of the zeolite sample. The CuIIst species were only observed in the hydrothermally aged zeolite samples and are formed upon the interaction of hydrated CuII cations with extra-framework Al generated during the hydrothermal treatment. These sites are inactive for NOx reduction, leading to a decrease in the catalytic performance of the hydrothermally aged zeolites. CuIIst formation was higher in Cu-CHA (~46%) than in Cu-AEI (~28%). The better hydrothermal stability of Cu in the AEI framework is attributed to the tortuous channel structure of AEI that hinders the migration of hydrated CuII cations during hydrothermal ageing.

Fe‐N‐C in Proton Exchange Membrane Fuel Cells: Impact of Ionomer Loading on Degradation and Stability

AbstractFe single atoms in N‐doped C (Fe‐N‐C) present the most promising replacement for carbon‐supported Pt‐based catalysts for the O2 reduction reaction at the cathode of proton exchange membrane fuel cells (PEMFCs). However, it remains unclear how the I/C ratio affects Fe‐N‐C degradation and the stability of single Fe atom active sites (FeNx). Here, an accelerated stress test (AST) protocol is combined with emerging electrochemical techniques for a porous Fe‐N‐C in PEMFC with a range of I/C ratios. The PEMFC current density degradation rates are found to be comparable; however, with increased I/C ratio the additional FeNx sites accessed are more stable, as shown by their higher active site stability number (electrons passed per FeNx lost) at the end of the AST protocol. Meanwhile, the initial rate of TOF decay is suppressed with increasing I/C. Electrochemical process changes are studied via distribution of relaxation times analysis. Minor changes in H+ and O2 transport resistance at low current density prove kinetic degradation dominants at high potentials. These findings demonstrate how electrochemical techniques can be combined with stability metrics to determine and deconvolute changes from the active site to device level electrochemical processes in PEMFCs.

Designed of dual direct band gap graphdiyne/Co2VO4 S-scheme heterojunction: Enhance the bonding stability of Co active sites to promote photocatalytic hydrogen evolution

The selection of direct band gap semiconductors with high-efficiency electron transitions and the rational adjustment of the d-band center of transition metal atoms can effectively enhance photocatalytic hydrogen evolution. Based on this premise, the double direct band gap graphdiyne/Co2VO4 S-scheme heterojunction was designed via an immersion method. DFT calculation, in-situ XPS and EPR analysis not only provided support for the formation of graphdiyne /Co2VO4 S-scheme heterojunction but also demonstrated that Co maybe served as the most efficient active site for hydrogen evolution. Furthermore, the design of S-scheme heterojunction effectively prolongs the carrier lifetime of the photocatalyst, resolves the deficiency in high electron-hole pair recombination rate of direct band gap semiconductors, and maintains its efficient electronic transition. PDOS analysis revealed that the interaction between graphdiyne and Co2VO4 at the microscopic interface tends to modulate the d-band center of cobalt atoms, resulting in a decrease in electron occupation on antibonding orbitals and consequently enhancing bonding stability at Co active sites. Moreover, introducing graphdiyne effectively increases electron state density near the Fermi level of Co2VO4, facilitating rapid migration of photogenerated charges. This study provides valuable insights into the regulating d-band centers of transition metal and the development of double direct band-gap S- scheme heterojunctions.

Propane Dehydrogenation on PtxZny Active Sites in Silicalite‐1

AbstractThe improvement of Pt‐based catalysts for propane dehydrogenation (PDH) has progressed by recent investigations that have identified Zn as a promising promoter for Pt subnanometer catalysts. It is desirable to gain insights into the structure, stability, and activity of such active sites and the factors that influence them, such as Zn : Pt ratio, Pt coordination and nuclearity. Here, we employ density functional theory and microkinetic simulations to investigate the stability of PtxZny (x=1–3, y=0–3) active sites grafted on silanols of Silicalite‐1 and the PDH activity of Pt. We find that the coordination of a Pt atom to a nest of grafted Zn(II) atoms increases the stability of the Pt1Zny sites, whose activity is similar for y=0–2 and drops dramatically for y>2. We further demonstrate, via linear scaling relations and microkinetic simulations, that the turnover frequency obeys a volcano law as a function of propylene binding strength. The Pt2Zn1 and Pt3Zn1 sites are stable and exhibit activity similar to Pt1Zn2, but only Pt1Zn2 manifests reaction kinetics consistent with experimental data, strongly suggesting the active site composition in the synthesized catalyst samples. The methodology presented here suggests a general strategy for deducing active site information such as composition through simple kinetic experiments.

Propane Dehydrogenation on PtxZny Active Sites in Silicalite-1.

The improvement of Pt-based catalysts for propane dehydrogenation (PDH) has progressed by recent investigations that have identified Zn as a promising promoter for Pt subnanometer catalysts. It is desirable to gain insights into the structure, stability, and activity of such active sites and the factors that influence them, such as Zn:Pt ratio, Pt coordination and nuclearity. Here, we employ density functional theory and microkinetic simulations to investigate the stability of PtxZny (x=1-3, y=0-3) active sites grafted on silanols of Silicalite-1 and the PDH activity of Pt. We find that the coordination of a Pt atom to a nest of grafted Zn(II) atoms increases the stability of the Pt1Zny sites, whose activity is similar for y=0-2 and drops dramatically for y>2. We further demonstrate, via linear scaling relations and microkinetic simulations, that the turnover frequency obeys a volcano law as a function of propylene binding strength. The Pt2Zn1 and Pt3Zn1 sites are stable and exhibit activity similar to Pt1Zn2, but only Pt1Zn2 manifests reaction kinetics consistent with experimental data, strongly suggesting the active site composition in the synthesized catalyst samples. The methodology presented here suggests a general strategy for deducing active site information such as composition through simple kinetic experiments.

A(CoFe)(S2)2/CoFe heterostructure constructed in S, N co-doped carbon nanotubes as an efficient oxygen electrocatalyst for zinc-air battery

Transition metal alloys can exhibit synergistic intermetallic effects to obtain high activities for oxygen reduction/evolution reactions (ORR/OER). However, due to the insufficient stability of active sites in alkaline electrolytes, conventional alloy catalysts still do not meet practical needs. Herein, by using polypyrrole tubes and cobalt-iron (CoFe) Prussian blue analogs as precursors, CoFe sulfides is in-situ formed on CoFe alloys to construct (CoFe)(S2)2/CoFe heterostructure in sulfur (S) and nitrogen (N) co-doped carbon nanotubes (CoFe@NCNTs-nS) via a low-temperature sulfidation strategy. The as-marked CoFe@NCNTs-12.5S exhibits a comparable ORR activity (half-wave potential of 0.901 V) to Pt/C (0.903 V) and a superior OER activity (overpotential of 272 mV at 10 mA cm−2) to RuO2 (299 mV). CoFe@NCNTs-12.5S also exhibits ultralow charge transfer resistances (ORR-6.36 Ω and OER-0.21 Ω) and an excellent potential difference of 0.617 V. The sulfidation-induced (CoFe)(S2)2/CoFe heterojunctions can accelerate interfacial charge transfer process. Tubular structure not only disperses the (CoFe)(S2)2/CoFe heterostructure, but also reduces the corrosion of active-sites to enhance catalysis stability. Zinc-air battery with CoFe@NCNTs-12.5S achieves a high specific capacity (718.1 mAh g−1), maintaining a voltage gap of 0.957 V after 400 h. This work reveals the potential of interface engineering for boosting ORR/OER activities of alloys via in-situ heterogenization.

Recent progress in the synthesis and electrocatalytic application of MXene‐based metal phosphide composites

AbstractIn the domain of novel catalyst design and application, metal phosphides have attracted widespread interest due to their unique electronic structure and potential catalytic activity. Various types of supports that can effectively anchor metal phosphides have been reported, among which MXene have received significant attention due to their two‐dimensional (2D) structure, adjustable composition, and composite variability. This work mainly aims to elucidate the preparation of novel MXene carriers and their unique roles in loading metal phosphides and participating in catalytic reactions. We will clarify the preparation strategy of MXene, the interaction between metal phosphides and MXene carriers, to explain the stabilization of metal phosphide active sites and the rational adjustment of electronic structure. In addition, we will comprehensively summarize recent research progress of MXene‐based metal phosphide composites, with particular emphasis on advancements in the synergistic effect of heterostructures. Regarding applications, we review the utilization of MXene‐based metal phosphide composites in electrocatalysis, including hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and oxygen reduction reaction (ORR). Finally, some fundamental challenges and prospects for the efficient electrocatalysis of MXene‐based metal phosphide composites are introduced.

Synergic Effects of Ordered Mesoporous Bifunctional Ionic Liquid: A Recyclable Catalyst to Access Chemoselective N-Protected Indoline-2,3-dione Analogous

SBA-15 and organic ionic liquid were incorporated in a post-grafting technique for generating a bifunctional ionic liquid embedded mesoporous SBA-15. The prepared heterogeneous catalyst was employed for the first time to synthesize N-alkylated indoline-2,3-dione at mild conditions to afford excellent yields in a short reaction time. The synthesized DABCOIL@SBA-15 catalyst was meticulously characterized by various techniques, such as FT-IR, solid-state 13C NMR, solid-state 29Si NMR, small-angle X-ray diffraction (XRD), and N2 adsorption–desorption. Further, the morphological behavior of the catalyst was studied by SEM and TEM. The thermal stability and number of active sites were determined by thermogravimetric analysis (TGA). The Hammett equation was used to analyze the synergetic effect of the catalyst and substituent effects on the N-alkylated products of 5-substituted isatin derivatives, which resulted in a negative slope. This negative slope indicates a positive charge in the transition state. Notably, the DABCOIL@SBA-15 catalyst demonstrated its practicality by being reused for seven cycles with consistently high catalytic activity.

Organic municipal solid waste derived hydrogen production through supercritical water gasification process configured with K2CO3/SiO2: Performance study

Cities worldwide face a significant public health and environmental challenge in handling municipal solid waste (MSW). This research exposed an effective utilization of MSW as the source for hydrogen production via a supercritical water gasification process under 450–650 °C at 15–45 min processing time. The impacts of gasification temperature and processing time on the functional properties of hydrogen production are studied. Its results are compared to identify the optimum processing temperature and processing time to adopt the system. Integrating 3 wt% silicon dioxide (SiO2) nanoparticles/3 wt% of potassium carbonate (K2CO3) enhances hydrogen production by increasing the catalyst's surface area and improving the stability of active sites, leading to more efficient gasification reactions. Increasing the gasification temperature from 450 to 650 °C significantly raises the hydrogen molar fraction and gas yield with peak gasification efficiency (GE) and hydrogen efficiency (HE) values. The gasifier functioned with catalyst (3 wt% K2CO3/SiO2) under 650 °C gasification temperature and 45min gasification time influenced better output responses like improved hydrogen gas yield of 63.7 mol/kg, higher gasification efficiency of 59.8 %, better hydrogen efficiency (63.4 %) and increased carbon conversion efficiency of 63.4 and 42.5 % respectively.

Engineering the Sandwich-Type Porphyrinic MOF-Ruthenium-Nickel Foam Electrode for Boosting Overall Water Splitting via Self-Reconstruction.

The rational construction of a hierarchical noble metal-metal-organic frameworks (MOFs) structure is anticipated to yield enduring and highly efficient performance in alkaline electrocatalytic water splitting. Herein, a sandwich construction strategy is employed to enhance the stability, wherein active RutheniRu (Ru) nanosheets are incorporated onto nickel foam (NF) and subsequently covered with porphyrinic MOFs (PMOFs). In addition, activated PMOF-NiOOH-Ru20/NF-C/A electrodes are obtained by electrochemical self-reconstruction as cathode and anode, respectively. Density functional theory (DFT) calculations demonstrated that the resulting PMOF-NiOOH-Ru heterointerface effectively facilitated electron transfer, enhanced H2O adsorption capacity, and optimized ΔG values for *H and *O to *OOH. Consequently, PMOF-NiOOH-Ru20/NF-C/A exhibited low overpotentials for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), accompanied by minimal Ru leakage. Furthermore, stable overall water splitting can be achieved with a low voltage of 1.456 V@10mA cm-2 for over 120h. Even when operated in simulated seawater, the prepared electrodes demonstrated similar activity and stability. This study contributes to a deeper understanding of the regulation mechanism for the performance and stability of active sites in the electrocatalytic self-reconstruction process.

Development of CuO/ZnO/Al2O3-hydrotalcite −based catalysts for middle temperature water gas shift reaction: Impact of calcination temperature and residual carbonates

A series of Cu/ZnO/Al2O3 catalysts are synthesized using a reverse co-precipitation method and subjected to calcination at different temperatures ranging from 300 to 650 °C. Characterization of the resulting powders is carried out through ICP, N2-physisorption, XRD, TGA, H2-TPR, N2O chemisorption and SEM techniques. Subsequently, the catalytic performance of the final samples is assessed in the medium-temperature water gas shift reaction across a broad temperature range from 200 to 330 °C. The precursor predominantly featured a hydrotalcite-like structure, undergoing decomposition through three main stages by losing structural H2O and CO2 molecules. All catalysts demonstrated stable performance without by-products during accelerated aging under reaction conditions. The results revealed that the partial elimination of carbonate ions at 300 °C resulted in easily reducible and consequently less thermally stable active sites. For calcined samples at 450 °C and 550 °C the thermal sintering played a pivotal role, leading the less copper surface area and subsequently higher CO slip values. In the case of the calcined sample at 650 °C, despite larger CuO and ZnO crystals, a trade-off between the emission of high-temperature carbonates and thermal sintering led to acceptable activity and thermal stability. Ultimately, the highest Cu surface are of 222 m2gr cat −1 along with the lowest amount of CO slip are observed for calcined sample at 350 °C, attributed to an optimal amount of carbonate, resulting in the superior catalytic performance. This effective balance between thermal sintering and the amount of residual carbonates yielded a final catalyst with outstanding activity and stable performance.

Enhancing hydrogen production via dry reforming of methane: Optimization of Co and Ni on scandia-ceria-zirconia supports for catalytic efficiency and economic feasibility

The Novel “Scandia-ceria incorporated zirconia” (10ScCeZr) is a well-recognized material in ceramic and solid oxide electrolytes due to stable phases (like cubic ZrO2) and oxide conducting phases (like hexagonal Sc4Zr3O12 phases). The objective of the current study is to introduce 10ScCeZr as support for bearing a proportional ratio of active sites (Ni and Co), investigating catalytic performance in DRM and studying the economic viability with respect to other catalysts. The 10ScCeZr support is used first time where the concentration of ceria is minimal to minimize the risk of oxidation of active sites but achieve the benefit of mobile lattice oxygen along with scandia and zirconia. Upon dispersion of different proportions of Ni and Co over 10ScCeZr, the reducibility pattern, stability of active sites, stability of oxide vacancy, and type of carbon deposit are modified markedly. Upon using 3: 1 Ni and Co over 10ScCeZr, the crystallinity of the catalyst is minimal, and the total concentration of active site and stable active sites doesn’t fluctuate more than 5Ni/10ScCeZr, and active sites are majorly derived by NiO. During the DRM, less inert carbon is deposited over the catalyst (than 5Ni/10ScCeZr). These physiochemical modifications over 3.75Ni1.25Co/10ScCeZr result in the highest 45 % H2 yield at 700 °C and 79 % H2 yield at 800 °C at the end of 300 min. The significant high operational savings due to the 0.44 % increased H2-yield validate the long-term financial benefits upon industrialization of the current catalyst. Now, this catalyst is open for further investigation on promotors’ effect and process optimization for developing a high-performance catalyst with excellent savings in H2-production through DRM.

Ex Situ Synthesis of Ti3C2@Fe-Ni-NC Heterostructure Towards an Efficient Bifunctional Electrocatalyst for High-Performance Zinc-Air Batteries

Zinc-air batteries (ZABs) with sustainable electrocatalysts have seen a lot of efforts to address oxygen reaction challenges to increase their lifespan and energy efficiency. Metal-organic frameworks (MOFs) and their derived materials are potential bifunctional electrocatalysts for addressing the oxygen reactions kinetics. However, under operational circumstances, MOFs and derived materials typically exhibit subpar electrochemical and conductivity. In this study, embedding MOF derived FeNi-N-C porous material in a few layer MXene nanosheets was effective strategy, enabling adequate conductivity, stability, and exposure number of active sites with better electrocatalytic activity towards oxygen reduction and oxidation reactions (ORR and OER). The resulting FeNi-NC@Ti3C2 hybrid exhibits notable bifunctional activities with a half-wave potential of 0.85 V and a low overpotential of 1.56 V, remarkable long-term cycle durability, as well as strong alcohol tolerance in an alkaline electrolyte. In addition, there is conductive MXene scaffold to achieve the highest ORR and OER activities with an ΔE value of 0.70 V. Furthermore, the FeNi-NC@Ti3C2 air-cathode-based assembled ZAB exhibits remarkable long-term cycling stability at 10 mA cm-2, a peak power density of 201 mW cm-2, and a high open circuit voltage (OCV) of 1.5 V. Ti3C2 MXene nanosheets provide a synergistic effect between two different materials in addition to protecting the surfaces of composite. This work provides a useful technique for enhancing ZAB's oxygen redox reactions, which could be used to aid in the development of efficient MOF@MXene based catalysts for electrochemical energy reactions.

ZIF-8 nanoparticles densely covered MXene as functionalized platform for electrochemical detection of medical small molecules

The high-performance electrochemical detection relies on sensing material with highly active structure, which requires the development of advanced synthesis technique and the study of its structure-activity mechanism. Herein, the few-layer Ti3C2Tx nanosheets densely coated zeolitic imidazole framework-8 nanoparticles (Ti3C2Tx@ZIF-8) have been successfully prepared as a unique precursor, which combines the structural advantages of two-dimensional Ti3C2Tx and porous ZIF-8 nanoparticles, leading to the vast interior spaces for loading electrocatalytic nanomaterials. For this purpose, Ti3C2Tx@Au nanoparticles-ZnO nanoparticles@N-doped carbon (Ti3C2Tx@AuNPs-ZnO@NC) has been obtained for the simultaneous electrochemical detection of pharmaceutical molecules including dopamine (DA), acetaminophen (AC), and xanthine (XA). The materials characterization and sensing analysis results of Ti3C2Tx@AuNPs-ZnO@NC reveal the structure-activity relationship of Ti3C2Tx, AuNPs and NC resulting in the high-performance behaviors, which can be summed up as stable electrochemical active sites and efficient electron transport channels. First, the abundant anchor points are offered by NC for immobilizing AuNPs, which ensure the electrochemical activity of such material. Second, the close combination of few-layer Ti3C2Tx nanosheets and NC provides an ideal channel for electron transmission along with the electrochemical reaction process. The potential application of Ti3C2Tx@AuNPs-ZnO@NC is displayed to develop the electrochemical medical sensor. The detection limits are 41 nM towards DA, 59 nM towards AC, and 67 nM towards XA. The linear ranges are 3–200 μM for DA, 15–500 μM for AC, and 8–350 μM for XA.

Fabrication of Ru-doped CuMnBP micro cluster electrocatalyst with high efficiency and stability for electrochemical water splitting application at the industrial-level current density

Electrochemical water splitting has been considered as a key pathway to generate environmentally friendly green hydrogen energy and it is essential to design highly efficient electrocatalysts at affordable cost to facilitate the redox reactions of hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). In this work, a novel micro-clustered Ru/CuMnBP electrocatalyst is introduced, prepared via hydrothermal deposition and soaking-assisted Ru doping approaches on Ni foam substrate. Ru/CuMnBP micro-clusters exhibit relatively low HER/OER turnover overpotentials of 11 mV and 85 mV at 10 mA/cm2 in 1 M KOH. It also demonstrates a low 2-E turnover cell voltage of 1.53 V at 10 mA/cm2 for the overall water-splitting, which is comparable with the benchmark electrodes of Pt/C||RuO2. At a super high-current density of 2000 mA/cm2, the dual functional Ru/CuMnBP demonstrates an exceptionally low 2-E cell voltage of 3.13 V and also exhibits superior stability for over 10 h in 1 M KOH. Excellent electrochemical performances originate from the large electrochemical active surface area with the micro cluster morphology, high intrinsic activity of CuMnBP micro-clusters optimized through component ratio adjustment and the beneficial Ru doping effect, which enhances active site density, conductivity and stability. The usage of Ru in small quantities via the simple soaking doping approach significantly improves electrochemical reaction rates for both HER and OER, making Ru/CuMnBP micro-clusters promising candidates for advanced electrocatalytic applications.

Bifunctional silver-metal organic gels with catalytic and electrochemiluminescence properties applied for ratio detection of I27L gene

The rate of maturity-onset diabetes of the young (MODY) is significantly increased by the common I27L gene variant of the hepatocyte nuclear factor-1α (HNF1A), hence achieving sensitive and precise I27L gene detection is the focus of early monitoring and diagnosis of HNF1A-MODY. In this study, we developed a silver-metal organic gels (Ag MOGs)/ K2S2O8-O2 system-based electrochemiluminescence resonance energy transfer (ECL-RET) ratio biosensor for detecting the I27L gene. The novel Ag MOGs were synthesized by simply mixing Ag+ and Luminol at ambient temperature. On the one hand, Ag MOGs could generate excellent anodic ECL signals in phosphate buffer without requiring exogenous co-reactants, which were derived from the Luminol ligand. On the other hand, Ag MOGs facilitated the electrocatalytic reduction of K2S2O8 by providing stable catalytic active sites and enhancing electron transfer rates, thereby leading to enhanced cathodic ECL emission from K2S2O8-O2. We constructed an ECL-RET ratio biosensor utilizing a DNA walker cycle amplification strategy. The biosensor leveraged the anodic ECL emission from the Ag MOGs/K2S2O8-O2 system as a donor and Atto 425 as a receptor, achieving ultra-sensitive detection of the I27L gene within a linear range of 100 amol/L to 100 pmol/L, and featuring a detection limit of 72 amol/L. Therefore, a direct synthesis technique of bifunctional materials with catalysis and electrochemiluminescence has been developed. Additionally, the ECL-RET ratio biosensor provided a universal platform for the detection of diabetes subtypes.

Cu single atoms regulating nitrogen active-sites of g-C3N4 for sodium ion storage

Nitrogen-rich material of graphitic carbon nitride (g-C3N4) with cost-effectiveness and easy accessibility has been considered as one of the most promising anode materials for sodium ion batteries (SIBs). However, the excessive presence of non-stable nitrogen sites in low crystallinity carbon nitrides would result in significant irreversibility, inadequate ion conductivity and structural instability, thereby limiting its practical application. Herein, a novel low-temperature strategy is proposed to stabilize the g-C3N4 by modulating the nitrogen configuration with single-atoms copper. The formed copper single atoms serving as anchors effectively regulate the coordination environment of nitrogen atoms in carbon nitride, thereby constructing stable nitrogen active sites for Na+ storage and conductive networks for rapid Na+ transport. Therefore, the Cu1.0/NC exhibits superior capacity (350.4 mAh g−1 at 50 mA g−1), exceptional rate performance (252.3 mAh g−1 at 1000 mA g−1), and long-cycle stability (capacity retention rate of 80.3 % after 1000 cycles at 5A g−1). Furthermore, in-situ Raman, ex-situ XANES and XPS technologies jointly reveal that the Cu atoms significantly influence the charge transfer process of Na+ and change the storage mode of sodium through redox effects during the sodiation/desodiation process. This work proves that single-atom engineering is a novel and feasible strategy to optimize the high-performance electrode materials for rechargeable batteries.

High-Valence Cu Induced by Photoelectric Reconstruction for Dynamically Stable Oxygen Evolution Sites.

Oxygen vacancies are generally considered to play a crucial role in the oxygen evolution reaction (OER). However, the generation of active sites created by oxygen vacancies is inevitably restricted by their condensation and elimination reactions. To overcome this limitation, here, we demonstrate a novel photoelectric reconstruction strategy to incorporate atomically dispersed Cu into ultrathin (about 2-3 molecular) amorphous oxyhydroxide (a-CuM, M = Co, Ni, Fe, or Zn), facilitating deprotonation of the reconstructed oxyhydroxide to generate high-valence Cu. The in situ XAFS results and first-principles calculations reveal that Cu atoms are stabilized at high valence during the OER process due to Jahn-Teller distortion, resulting in para-type double oxygen vacancies as dynamically stable catalytic sites. The optimal a-CuCo catalyst exhibits a record-high mass activity of 3404.7 A g-1 at an overpotential of 300 mV, superior to the benchmarking hydroxide and oxide catalysts. The developed photoelectric reconstruction strategy opens up a new pathway to construct in situ stable oxygen vacancies by high-valence Cu single sites, which extends the design rules for creating dynamically stable active sites.

Strengthening the oxygen reduction stability and activity of single iron active sites via a simultaneously electronic regulation and structure design strategy

Single-atom iron-nitrogen-carbon materials have demonstrated remarkable potential in catalyzing the oxygen reduction reaction (ORR). In this study, a novel approach is proposed for regulating the microenvironment of single iron sites through the coupling of neighboring Zn with an open-mesoporous carbon plane. This structural arrangement effectively modulates the density of states and d-band center of Fe atoms, resulting in moderate adsorption and desorption of oxygen intermediates and thereby reducing the energy barrier of the ORR. Moreover, the open-mesoporous structure ensures the accessibility of the active sites and facilitates the mass transfer of reactants, intermediates, and products during the ORR. Consequently, the synthesized M-Fe-ZnNC catalyst exhibits enhanced ORR performance and excellent stability. This study serves to inspire the exploration of high-performance non-precious metal catalysts for the ORR, leveraging simultaneous electronic regulation and structure design.

Construction of Fe(III) Active Sites on Phenanthroline-Grafted g-C3N4: Reduced Work Function and Enhanced Intramolecular Charge Transfer for Efficient N2 Photofixation.

Photocatalytic nitrogen fixation is one of the important pathways for green and sustainable ammonia synthesis, but the extremely high bonding energy of the N≡N triple bond makes it difficult for conventional nitrogen fixation photocatalysts to directly activate and hydrogenate. Given this, we covalently grafted the phenanthroline unit onto graphitic carbon nitride nanosheets (CN) by the simple thermal oxidation method and complexed it with transition metal Fe3+ ions to obtain stable dispersed Fe active sites, which can significantly improve the photocatalytic activity. The Fe(III)-4-P-CN photocatalyst morphology consists of porous lamellar structures internally connected by nanowires. The special morphology of the catalysts gives them excellent nitrogen fixation performance, with an average NH3 yield of 492.9 μmol g-1 h-1, which is 6.5 times higher than that of the pristine CN, as well as better photocatalytic cycling stability. Comprehensive experiments and density-functional theory results show that Fe(III)-4-P-CN is more favorable than pristine CN for *N2 activation, effectively lowering the reaction energy barrier. Moreover, other byproducts (such as nitrate and H2O2) are also produced during the photocatalytic nitrogen fixation process, which also provides a new way for nitrogen-fixing photocatalysts to achieve multifunctional applications.