Active Site Iron Research Articles

Ball milling of pyrite in air to significantly promote the Fenton reaction: A mechanistic study

Natural pyrite (FeS2) has been widely used as heterogenous Fenton catalyst due to the unique iron supplying and ferrous regeneration performance, however, natural pyrite has poor catalytic activity due to the low surface reactivity. Ball milling is commonly used to modify pyrite, but the mechanism has not been thoroughly studied. In our work, by optimizing the ball milling conditions, the catalytic efficiency of modified pyrite is increased by 60 times compared to natural pyrite, and the ball milled pyrite Fenton system was able to degrade dyes and a series of antibiotics within 30 min. Compared to ball milling in nitrogen and vacuum, ball milling in air increased the proportion of S2− and active iron sites on the surface of pyrite, which assisted and accelerated the regeneration of ferrous and enhanced the iron supplying performance. This work explored the mechanisms of ball milling to modify the properties of pyrite, reported a green and efficient ball milled pyrite Fenton system, and provided a new insight in regulating ball milling conditions for mechanochemical modification.

Dynamic Activity and Stability of Transition Metal (oxy)Hydroxide Oxygen Evolution Electrocatalysts Under Steady and Intermittent Operation

The oxygen evolution reaction (OER) plays a critical role in several energy conversion technologies, requiring catalysts that combine high activity with stability for successful commercialization. Catalysts from first-row transition metal oxides have garnered considerable attention in this context. Their noteworthy OER activity and stability in alkaline environments position them as a more economical option than their counterparts in acidic media. However, recent studies have shown that these materials tend to experience significant dissolution issues and undergo changes in their chemical composition, a phenomenon observed even during steady-state operation.1–3 Addressing these challenges is essential for advancing commercial energy conversion technologies, which often face intermittent loads and reverse currents. A deeper understanding of the dynamic reconstruction under fluctuating conditions is crucial for developing more durable and efficient electrocatalytic materials.4 In this work, we investigate the dynamic performance of nickel cobalt (oxy)hydroxide electrocatalytic films containing iron active sites in alkaline media under steady and intermittent operation. First, we systematically examine the changes in OER catalytic activity in a typical three-electrode configuration, focusing on the incorporation and redissolution of iron and cerium during different electrochemical conditioning methods. As shown in Figure 1a, conditioning using chronopotentiometry decreases the OER overpotential without significantly shifting the redox peak. In contrast, conditioning using cyclic voltammetry significantly shifts the redox peak position (Figure 1b). These differences are attributed to the (oxy)hydroxide film thickness, which forms in situ during conditioning and affects the Fe dissolution and incorporation rates based on the conditioning method.5 We use different analytical techniques to probe chemical transformations during conditioning. Time-of-flight secondary ion mass spectrometry (TOF-SIMS) and X-ray photoelectron spectroscopy (XPS) are utilized to analyze compositional changes in the electrocatalytic films. Moreover, inductively coupled plasma mass spectrometry (ICP-MS) tracks metal dissolution.Next, we utilize an electrochemical flow electrolyzer with a zero-gap configuration, integrated with online ICP-MS and post-experimental TOF-SIMS and XPS, to study the reconstruction of these electrocatalysts under intermittent conditions. A NiFe anode operating in 6 M KOH with 1 ppm of Fe3+ shows a 40-mV change after 120 cycles of alternating low and high currents, including a simulated shutdown step (Figure 1c). This cell potential change, becoming more negative with continued cycling (Figure 1d), is attributed to the shutdown step. Our findings underscore how operating conditions affect the dynamic reconstruction of electrocatalytic materials, offering critical insights for developing more robust and resilient materials suitable for commercial applications.

Tuning Iron Active Sites of FeOOH via Al3+ and Heteroatom Doping-Induced Asymmetric Oxygen Vacancy Electronic Structure for Efficient Alkaline Water Splitting.

Oxygen evolution reaction is the essential anodic reaction for water splitting. Designing tunable electronic structures to overcome its slow kinetics is an effective strategy. Herein, the molecular ammonium iron sulfate dodecahydrate is employed as the precursor to synthesize the C, N, S triatomic co-doped Fe(Al)OOH on Ni foam (C,N,S-Fe(Al)OOH-NF) with asymmetric electronic structure. Both in situ oxygen vacancies and their special electronic configuration enable the electron transfer between the d-p orbitals and get the increase of OER activity. Density functional theory calculation further indicates the effect of electronic structure on catalytic activity and stability at the oxygen vacancies. In alkaline solution, the catalyst C,N,S-Fe(Al)OOH-NF shows good catalytic activity and stability for water splitting. For OER, the overpotential of 10 mAcm-2 is 264mV, the tafel slope is 46.4 mVdec-1, the HER overpotential of 10 mAcm-2 is 188mV, the tafel slope is 59.3 mVdec-1. The stability of the catalyst can maintain ≈100h. This work has extraordinary implications for understanding the mechanistic relationship between electronic structure and catalytic activity for designing friendly metal (oxy)hydroxide catalysts.

Unraveling the Mechanism of the Oxidative C-C Bond Coupling Reaction Catalyzed by Deoxypodophyllotoxin Synthase.

Deoxypodophyllotoxin synthase (DPS), a nonheme Fe(II)/2-oxoglutarate (2OG)-dependent oxygenase, is a key enzyme that is involved in the construction of the fused-ring system in (-)-podophyllotoxin biosynthesis by catalyzing the C-C coupling reaction. However, the mechanistic details of DPS-catalyzed ring formation remain unclear. Herein, our quantum mechanics/molecular mechanics (QM/MM) calculations reveal a novel mechanism that involves the recycling of CO2 (a product of decarboxylation of 2OG) to prevent the formation of hydroxylated byproducts. Our results show that CO2 can react with the FeIII-OH species to generate an unusual FeIII-bicarbonate species. In this way, hydroxylation is avoided by consuming the OH group. Then, the C-C coupling followed by desaturation yields the final product, deoxypodophyllotoxin. This work highlights the crucial role of the CO2 molecule, generated in the crevice between the iron active site and the substrate, in controlling the reaction selectivity.

Fe/Mn-MOFs with monocarboxylic acid-induced defects enhances the catalytic oxidation of calcium sulfite in desulfurization ash

The application of catalysis is an effective way to enhance calcium sulfite oxidation reactions, which is essential to the calcium-based wet flue gas desulfurization and the handle and/or utilization of the solid by-product from semi-dry desulfurization process, i.e., desulfurization ash. In this report, we present a method for constructing Fe/Mn(BDC)(DMF,OA) bimetallic catalysts with defect engineering by using monocarboxylic acids with varying chain lengths as regulators. After removing the monocarboxylic acid, the unsaturated coordinated iron and manganese active sites in Fe/Mn(BDC)(DMF,OA) become more abundant. This makes it easier to adsorb O2 and activate it into reactive oxygen species (O2–), which in turn activates the radical chain reaction and promotes the production of sulfur-oxygen free radicals(SO5−). Density functional theory (DFT) calculations show that the synergistic effect of Fe-Mn bimetallic catalysts reduces the energy barrier for SO42− formation, thereby accelerating the oxidation of sulfite. Upon addition of Fe/Mn(BDC)(DMF,OA), the oxidation rate of calcium sulfite within 3 h increased from 2.76 % to 96.09 %, compared to non-catalytic oxidation. After five cycles, the 3 h oxidation rate of calcium sulfite decreased by 10.42 % compared to the first cycle, and the higher leaching rate of Mn element was the main reason for the decrease in catalytic performance. The catalyst is non-toxic and economical, showing significant potential for resource utilization of CaSO3-containing desulfurization ash.

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.

Regulating the distribution of iron active sites on γ-Fe2O3via Mn-modified α-Fe2O3 for NH3-SCR

Developing below 150 °C highly activity and broad reaction window catalysts has been challenging by using Fe-based catalysts for NH3-SCR. The octahedral Fe3+ (Fe3+Oh) sites exist in hematite (α-Fe2O3) and maghemite (γ-Fe2O3) are inactive for NH3-SCR due to the redox circle of Fe2+→Fe3+ reliance on the distribution of iron sites in crystal structure. Here we modified the α-Fe2O3 crystal structure by substituting part inactive Fe3+Oh sites with catalytically active Mn3+Oh sites, which promoted the formation of γ-Fe2O3 to generate the active tetrahedral Fe3+ (Fe3+Td) sites and enhanced the magnetism of the Fe1−yMnyOx. The strong Fe-O-Mn interaction established by crystal coordinative configurations not only boosted the formation of NO2 but also facilitated the Brønsted acid circle. Surprisingly, the Fe0.85Mn0.15Ox exhibited the superior low temperature NH3-SCR activity, with NOx conversion above 100% at 100–275 °C under a GHSV of 60000 h−1.

Catalytic divergencies in the mechanism of L-arginine hydroxylating nonheme iron enzymes.

Many enzymes in nature utilize a free arginine (L-Arg) amino acid to initiate the biosynthesis of natural products. Examples include nitric oxide synthases, which generate NO from L-Arg for blood pressure control, and various arginine hydroxylases involved in antibiotic biosynthesis. Among the groups of arginine hydroxylases, several enzymes utilize a nonheme iron(II) active site and let L-Arg react with dioxygen and α-ketoglutarate to perform either C3-hydroxylation, C4-hydroxylation, C5-hydroxylation, or C4-C5-desaturation. How these seemingly similar enzymes can react with high specificity and selectivity to form different products remains unknown. Over the past few years, our groups have investigated the mechanisms of L-Arg-activating nonheme iron dioxygenases, including the viomycin biosynthesis enzyme VioC, the naphthyridinomycin biosynthesis enzyme NapI, and the streptothricin biosynthesis enzyme OrfP, using computational approaches and applied molecular dynamics, quantum mechanics on cluster models, and quantum mechanics/molecular mechanics (QM/MM) approaches. These studies not only highlight the differences in substrate and oxidant binding and positioning but also emphasize on electronic and electrostatic differences in the substrate-binding pockets of the enzymes. In particular, due to charge differences in the active site structures, there are changes in the local electric field and electric dipole moment orientations that either strengthen or weaken specific substrate C-H bonds. The local field effects, therefore, influence and guide reaction selectivity and specificity and give the enzymes their unique reactivity patterns. Computational work using either QM/MM or density functional theory (DFT) on cluster models can provide valuable insights into catalytic reaction mechanisms and produce accurate and reliable data that can be used to engineer proteins and synthetic catalysts to perform novel reaction pathways.

Confined MOF pyrolysis within mesoporous SiO2 core–shell nanoreactors for superior activity and stability of electro-Fenton catalysts

Despite the high density and uniform distribution of active sites in metal–organic frameworks (MOFs) and their derivatives, the relatively low stability in water still limits their utilization in heterogeneous catalysis. Herein, the confinement of pyrolyzed MIL-88B(Fe) derivatives within mesoporous SiO2 allowed fabricating core–shell nanoreactors (Fe/C@mSiO2) that served as heterogeneous electro-Fenton (HEF) catalysts for the first time, revealing an excellent performance. The as-prepared catalysts were featured by high specific surface area and dense active sites. During service as core–shell nanoreactors, they behaved as a dual function adsorbent-catalyst, exhibiting superior catalytic activity and recyclability as compared to HEF catalysts without shell. Using 0.2 g/L of catalyst, the complete removal of bisphenol A at pH 6.2 and 100 mA was achieved at 120 min, with extremely low iron leaching of 0.11 mg/L. The rigid mSiO2 shell not only protected the iron active sites from leaching, but it also provided porous and permeable channels for efficient mass transport. The unique core–shell architecture concentrates the catalytic sites and reactants within a confined space, promoting the fast degradation of bisphenol A. Furthermore, the defect-rich carbon substrate and the high dispersibility of iron-rich sites favor a fast electron transfer. The efficient treatment of several organic micropollutants in consecutive trials corroborated the high activity and stability of the Fe/C@mSiO2. This work contributes to the rational design of HEF catalysts, aiming at consolidating their practical application in advanced wastewater treatment.

The ultra-high oxygen evolution activity of Fe modified NiPt alloy assisted by Pt pre-oxidation in alkaline electrolyte

Constructing ultra-high activity, highly efficient and robust oxygen evolution reaction (OER) electrocatalysts, especially at large current density, plays a key role in the development of the electrolytic water industry but remains challenging. Highly dispersed alloy compound with large electrolyte contact area and excellent internal conductivity is considered as a kind of ideal candidate. Here, we have rationally designed and synthesized a nickel-platinum alloy with octahedral structure loaded on the surface of the carbon layer (NiPt/C). Under the in-situ modulation of the iron-containing electrolyte, the Fe modified NiPt/C catalyst displays an amazing OER activity in 1 M KOH, and only requires low overpotentials of 183 and 242 mV to reach 100 and 1000 mA cm−2, respectively. The comprehensive characterization analysis and property measurements reveal that the pre-oxidation of Pt at OER potential contribute to the rapid production of nickel hydroxide, thus promoting the deposition of more iron active sites on its surface. Moreover, the Pt/C/CP(−)//NiPt/C/CP(+) couple embedded in anion-exchange membrane water electrolyser also displays a low cell voltage of 2.03 V at 1000 mA cm−2 with significant electrochemical stability, which endows it a great potential in the field of hydrogen production and electrochemical energy storage.

Atomically Dispersed Iron Active Sites on Covalent Organic Frameworks for Artificial Photosynthesis of Hydrogen Peroxide

AbstractArtificial photosynthesis has been regarded as a promising solution toward solar energy conversion, generating storable and transportable chemical fuels such as hydrogen (H2) and hydrogen peroxide (H2O2). However, the design of robust catalytic sites not only affects the activity, but also identify the atomic‐level correlation between active sites and natural photosynthesis performance. Herein, a synthesis method of single‐atomic Iron (Fe) active sites anchored on novel covalent organic framework (COF) for the production of H2O2 under visible light irradiation. When benzyl alcohol is the most sacrificial agent, the state‐of‐the‐art Fe‐based COF exhibits an excellent H2O2 generation rate of 4130 µmol g−1 h−1, over 5.3 times higher than that of pristine COF, achieving an apparent quantum yield of 6.4% at 420 nm. The enhanced photocatalytic performance is ascribed to the synergistic effect of atomically dispersed Fe sites and COF hosts, reducing the reaction energy barrier for the formation of *OOH intermediates and optimizing the adsorption of O2 and thus promoting two‐electron oxygen reduction reaction (ORR). This work establishes an atomic‐level engineering approach to build atomically dispersed Fe active sites on COF photocatalysts and provides in‐depth insight upon the ORR mechanism for promising artificial photosynthesis of H2O2.

Morphological and structural design through hard-templating of PGM-free electrocatalysts for AEMFC applications.

This study delves into the critical role of customized materials design and synthesis methods in influencing the performance of electrocatalysts for the oxygen reduction reaction (ORR) in anion exchange membrane fuel cells (AEMFCs). It introduces a novel approach to obtain platinum-free (PGM-free) electrocatalysts based on the controlled integration of iron active sites onto the surface of silica nanoparticles (NPs) by using nitrogen-based surface ligands. These NPs are used as hard templates to form tailored nanostructured electrocatalysts with an improved iron dispersion into the carbon matrix. By utilizing a wide array of analytical techniques including infrared and X-ray photoelectron spectroscopy techniques, X-ray diffraction and surface area measurements, this work provides insight into the physical parameters that are critical for ORR electrocatalysis with PGM-free electrocatalysts. The new catalysts showed a hierarchical structure containing a large portion of graphitic zones which contribute to the catalyst stability. They also had a high electrochemically active site density reaching 1.47 × 1019 sites g-1 for SAFe_M_P1AP2 and 1.14 × 1019 sites g-1 for SEFe_M_P1AP2, explaining the difference in performance in fuel cell measurements. These findings underscore the potential impact of a controlled materials design for advancing green energy applications.

Mineral Phase Reconfiguration Enables the High Enzyme-like Activity of Vermiculite for Antibacterial Application.

Phyllosilicates-based nanomaterials, particularly iron-rich vermiculite (VMT), have wide applications in biomedicine. However, the lack of effective methods to activate the functional layer covered by the external inert layer limits their future applications. Herein, we report a mineral phase reconfiguration strategy to prepare novel nanozymes by a molten salt method. The peroxidase-like activity of the VMT reconfiguration nanozyme is 10 times that of VMT, due to the electronic structure change of iron in VMT. Density-functional theory calculations confirmed that the upward shifted d-band center of the VMT reconfiguration nanozyme promoted the adsorption of H2O2 on the active iron sites and significantly elongated the O-O bond lengths. The reconfiguration nanozyme exhibited nearly 100% antibacterial activity toward Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus), much higher than that of VMT (E. coli 10%, S. aureus 21%). This work provides new insights for the rational design of efficient bioactive phyllosilicates-based nanozyme.

Exploring the Methane to Methanol Oxidation over Iron and Copper Sites in Metal–Organic Frameworks

The direct oxidation of methane to methanol (MTM) is a significant challenge in catalysis and holds profound economic implications for the modern chemical industry. Bioinspired metal–organic frameworks (MOFs) with active iron and copper sites have emerged as innovative catalytic platforms capable of facilitating MTM conversion under mild conditions. This review discusses the current state of the art in applying MOFs with iron and copper catalytic centers to effectuate the MTM reaction, with a focus on the diverse spectroscopic techniques employed to uncover the electronic and structural properties of MOF catalysts at a microscopic level. We explore the synthetic strategies employed to incorporate iron and copper sites into various MOF topologies and explore the efficiency and selectivity of the MOFs embedded with iron and copper in acting as catalysts, as well as the ensuing MTM reaction mechanisms based on spectroscopic characterizations supported by theory. In particular, we show how integrating complementary spectroscopic tools that probe varying regions of the electromagnetic spectrum can be exceptionally conducive to achieving a comprehensive understanding of the crucial reaction pathways and intermediates. Finally, we provide a critical perspective on future directions to advance the use of MOFs to accomplish the MTM reaction.

Construction of highly dispersed iron active sites for efficient catalytic ozonation of bisphenol A

The essential factor of catalytic ozonation technology relies on an efficient and stable catalyst. The construction of highly dispersed active sites on heterogeneous catalysts is an ideal strategy to combine the merits of homogeneous and heterogeneous catalysis with high activity and stability. Herein, an iron-containing mesoporous silica material (Fe-SBA15) with sufficient iron site exposure and enhanced intrinsic activity of active sites was employed to activate ozone for bisphenol A (BPA) degradation. Approximately 100% of BPA and 36.6% of total organic carbon (TOC) removal were realized by the Fe-SBA15 catalytic ozonation strategy with a reaction constant of 0.076 min−1, well beyond the performance of FeOx/SBA15 mixture and Fe2O3. Radical quenching experiments and electron paramagnetic resonance (EPR) analysis demonstrated that the hydroxyl radicals (HO•) and superoxide radicals (O2•−) played an important role in the degradation process. The iron sites with recyclable Fe(III)/Fe(II) pairs act as both the electron donors and active sites for catalytic ozonation. The mesoporous framework of SBA15 in Fe-SBA15 stabilizes the iron sites that enhance its stability. With high catalytic performance and high reusability for catalytic ozonation of BPA, the Fe-SBA15 is expected to be a promising catalyst in catalytic ozonation for wastewater treatment.

Effect of Gas-Phase Nitric Oxide Adsorption on ORR Activity of Fe-N-C Catalysts

Significant progress has been made in recent years in developing platinum group metal-free catalysts, particularly so-called Fe-N-C materials, for the oxygen reduction reaction (ORR) in polymer electrolyte fuel cells.1 However, further improvement in both activity and, especially, durability are still necessary for practical applications. One of the major factors that hinder the further enhancement of the catalysts is the lack of clear understanding of the nature of the active sites in the Fe-N-C catalysts due to the complexity of the Fe-N-C catalysts’ composition and structure. Gaseous nitric oxide was reported to be a suitable probe molecule that can bond to Fe and impede the ORR of the Fe-N-C catalysts.2,3 In this work, the effect of nitric oxide gas-phase adsorption on Fe-N-C catalyst redox feature and ORR activity for a variety of Fe-N-C catalysts from different origin will be investigated. The implication of these results on the nature of the ORR active sites of the Fe-N-C catalysts will be discussed.AcknowledgementsThis work was supported by the U.S. Department of Energy (DOE), Energy Efficiency and Renewable Energy, Hydrogen and Fuel Cell Technologies Office (HFTO) under the auspices of the Electrocatalysis Consortium (ElectroCat 2.0). This work was partially authored by Argonne, a U.S. Department of Energy (DOE) Office of Science laboratory operated for DOE by UChicago Argonne, LLC under contract no. DE-AC02-06CH11357.References X.X. Wang, M.T. Swihart, and G. Wu, "Achievements, challenges, and perspectives on cathode catalysts in proton exchange membrane fuel cells for transportation", Nature Catalysis, 2 (2019) 578-589.J.L. Kneebone, et al., "A Combined Probe-Molecule, Mossbauer, Nuclear Resonance Vibrational Spectroscopy, and Density Functional Theory Approach for Evaluation of Potential Iron Active Sites in an Oxygen Reduction Reaction Catalyst", J. Phys. Chem. C 121 (2017) 16283-16290.P. Boldrin, D. Malko, A. Mehmood, U.I. Kramm, S. Wagner, S. Paul, N. Weidler, A. Kucernak, “Deactivation, reactivation and super-activation of Fe-N/C oxygen reduction electrocatalysts: Gas sorption, physical and electrochemical investigation using NO and O2”, Applied Catalysis B: Environmental 292 (2021) 120169.

Exploring the natural products chemical space through a molecular search to discover potential inhibitors that target the hypoxia-inducible factor (HIF) prolyl hydroxylase domain (PHD).

Introduction: Hypoxia-inducible factor (HIF) prolyl hydroxylase domain (PHD) enzymes are major therapeutic targets of anemia and ischemic/hypoxia diseases. To overcome safety issues, liver failure, and problems associated with on-/off-targets, natural products due to their novel and unique structures offer promising alternatives as drug targets. Methods: In the current study, the Marine Natural Products, North African, South African, East African, and North-East African chemical space was explored for HIF-PHD inhibitors discovery through molecular search, and the final hits were validated using molecular simulation and free energy calculation approaches. Results: Our results revealed that CMNPD13808 with a docking score of -8.690kcal/mol, CID15081178 with a docking score of -8.027kcal/mol, CID71496944 with a docking score of -8.48kcal/mol and CID11821407 with a docking score of -7.78kcal/mol possess stronger activity than the control N-[(4-hydroxy-8-iodoisoquinolin-3-yl)carbonyl]glycine, 4HG (-6.87kcal/mol). Interaction analysis revealed that the target compounds interact with Gln239, Tyr310, Tyr329, Arg383 and Trp389 residues, and chelate the active site iron in a bidentate manner in PHD2. Molecular simulation revealed that these target hits robustly block the PHD2 active site by demonstrating stable dynamics. Furthermore, the half-life of the Arg383 hydrogen bond with the target ligands, which is an important factor for PHD2 inhibition, remained almost constant in all the complexes during the simulation. Finally, the total binding free energy of each complex was calculated as CMNPD13808-PHD2 -72.91kcal/mol, CID15081178-PHD2 -65.55kcal/mol, CID71496944-PHD2 -68.47kcal/mol, and CID11821407-PHD2 -62.06kcal/mol, respectively. Conclusion: The results show the compounds possess good activity in contrast to the control drug (4HG) and need further in vitro and in vivo validation for possible usage as potential drugs against HIF-PHD2-associated diseases.

Air Contamination of Platinum-Group Metal-free Fuel Cell Cathodes with Atomically Dispersed Iron Active Sites

In a wide variety of applications, proton exchange membrane (PEM) fuel cells must be tolerant to contaminants from the ambient air and the degradation of the system components. Previous work has demonstrated the effects of some of the most common air contaminants on platinum-group metal (PGM) cathode fuel cells. However, the results of air contamination on the degradation in a side-by-side comparison between PGM and PGM-free based cathode fuel cells has yet to be shown. Herein, we investigate the effects of air contamination by acetonitrile and sulfur dioxide (SO2) on operating PGM and PGM-free cathode fuel cells. This was done by monitoring the changes in current density at a constant voltage hold before, during, and after sulfur dioxide and acetonitrile contamination. In addition, air polarization curves, cyclic voltammetry, and electrochemical impedance spectroscopy characterized the overall contamination effects of each cell. It is found that acetonitrile at 20 ppm and SO2 at 4.6 ppm do not result in any additional degradation in iron (Fe)-metal–organic framework (MOF) derived cathode fuel cells during operation, while current density losses greater than 70% are seen in platinum (Pt)-based cathode fuel cells. This tolerance to contaminants is an often-overlooked advantage of PGM-free catalyst cathode fuel cells, which suffered no additional degradation due to the introduction of air contaminants in this study.

Enhancing Sulfur Redox Conversion of Active Iron Sites by Modulation of Electronic Density for Advanced Lithium-Sulfur Battery.

Despite lithium-sulfur (Li-S) batteries possessing ultrahigh energy density as great promising energy storage devices, the suppressing shuttle effect and improving sulfur redox reaction (SROR) are vital for their practical application. Developing high-activity electrocatalysts for enhancing the SROR kinetics is a major challenge for the application of Li-S batteries. Herein, single-molecule iron phthalocyanine species are anchored on the N and P dual-doped porous carbon nanosheets (Fe-NPPC) via axial Fe-N coordination to optimize the electronic structure of active centers. The Fe-NPPC can promote the catalytic conversion of polysulfides by modulation of the electronic density in active moieties, endowing the Li-S battery with a high reversible capacity of 1023 mAh g-1 at 1 C as well as an ultralow capacity decay of 0.035% per cycle over 1500 cycles. Even with a high sulfur loading of 7.1mg cm-2 , the Li-S battery delivers a high areal capacity of 4.8 mAh cm-2 after 150 cycles at 0.2 C. With further increasing the sulfur loading to 9.2mg cm-2 , an excellent areal capacity of up to 9.3 mAh cm-2 is obtained at 0.1 C.

Structure and mutation of deoxypodophyllotoxin synthase (DPS) from Podophyllum hexandrum

Deoxypodophyllotoxin synthase (DPS) is a 2-oxoglutarate (2-OG) dependent non-heme iron (II) dioxygenase that catalyzes the stereoselective ring-closing carbon-carbon bond formation of deoxypodophyllotoxin from the aryllignan (−)-yatein. Deoxypodophyllotoxin is a precursor of topoisomerase II inhibitors, which are on the World Health Organization’s list of essential medicines. Previous work has shown that DPS can accept a range of substrates, indicating it has potential in biocatalytic processes for the formation of diverse polycyclic aryllignans. Recent X-ray structures of the enzyme reveal possible roles for amino acid side chains in substrate recognition and mechanism, although a mutational analysis of DPS was not performed. Here, we present a structure of DPS at an improved resolution of 1.41 Å, in complex with the buffer molecule, Tris, coordinated to the active site iron atom. The structure has informed a mutational analysis of DPS, which suggests a role for a D224-K187 salt bridge in maintaining substrate interactions and a catalytic role for H165, perhaps as the base for the proton abstraction at the final rearomatization step. This work improves our understanding of specific residues’ contributions to the DPS mechanism and can inform future engineering of the enzyme mechanism and substrate scope for the development of a versatile biocatalyst.