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Carbon supported and nitrogen coordinated single Mn site (Mn-N-C) catalysts are the most desirable platinum group metal (PGM)-free cathode catalysts for proton-exchange membrane fuel cells (PEMFCs) due to their insignificant Fenton reactions (vs. Fe), earth abundances (vs. Co), and encouraging activity and stability. However, current Mn-N-C catalysts suffer from high overpotential due to low intrinsic activity and less dense MnN4 sites. Herein, we present a sulfur-doped Mn-N-C catalyst (Mn-N-C-S) synthesized through an effective adsorption-pyrolysis process. Using electron microscopy and X-ray absorption spectroscopy (XAS) techniques, we verify the uniform dispersion of MnN4 sites and confirm the effect of S doping on the Mn-N coordination. The Mn-N-C-S catalyst exhibits a favorable oxygen reduction reaction (ORR) activity in acidic media relative to the S-free Mn-N-C catalyst. The corresponding membrane electrode assembly (MEA) generates enhanced performance with a peak power density of 500 mW cm-2 under a realistic H2/air environment. The constant voltage tests of fuel cells confirm the much-enhanced stability of the Mn-N-C-S catalyst compared to the Fe-N-C and Fe-N-C-S catalysts. The electron microscopy and Fourier transform XAS analyses provide insights into catalyst degradation associated with Mn oxidation and agglomeration. The theoretical calculation elucidates that the promoted ORR activity is mainly attributed to the spatial effect stemmed from the repulsive interaction between the ORR intermediates and adjacent S dopants.

Developing efficient electrocatalysts for an oxygen evolution reaction (OER) is important for renewable energy storage. Here, we design high-density Ir single-atom catalysts supported by CoOx amorp...

Atomically dispersed and nitrogen coordinated single metal sites (M-N-C, M=Fe, Co, Ni, or Mn) are the popular platinum group-metal (PGM)-free catalysts for many electrochemical reactions. Traditional wet-chemistry catalyst synthesis often requires complex procedures with unsatisfied reproducibility and scalability. Here, we report a chemical vapor deposition (CVD) strategy to synthesize the promising single metal site (M-N-C) catalysts. The deposition of gaseous 2-methylimidazole onto ZnO substrates doped with M, followed by an in-situ thermal activation, was proved effective in generating single metal sites well dispersed into porous carbon. In particular, an optimal CVD-derived Fe-N-C catalyst is featured with atomically dispersed FeN4 sites with increased Fe loading relative to other catalysts from wet-chemistry synthesis. The catalyst exhibited outstanding oxygen-reduction activity in acidic electrolytes, which was further studied in proton-exchange membrane fuel cells with encouraging performance. The CVD synthesis sheds some light on the mass production of single metal site catalysts towards advanced electrocatalysis.

Electrochemical reduction of CO2 is a promising route for sustainable production of fuels. A grand challenge is developing low-cost and efficient electrocatalysts that can enable rapid conversion with high product selectivity. Here we design a series of nickel phthalocyanine molecules supported on carbon nanotubes as molecularly dispersed electrocatalysts (MDEs), achieving CO2 reduction performances that are superior to aggregated molecular catalysts in terms of stability, activity and selectivity. The optimized MDE with methoxy group functionalization solves the stability issue of the original nickel phthalocyanine catalyst and catalyses the conversion of CO2 to CO with >99.5% selectivity at high current densities of up to −300 mA cm−2 in a gas diffusion electrode device with stable operation at −150 mA cm−2 for 40 h. The well-defined active sites of MDEs also facilitate the in-depth mechanistic understandings from in situ/operando X-ray absorption spectroscopy and theoretical calculations on structural factors that affect electrocatalytic performance. Widespread deployment of electrochemical CO2 reduction requires low-cost catalysts that perform well at high current densities. Zhang et al. show that methoxy-functionalized nickel phthalocyanine molecules on carbon nanotubes can operate as high-performing molecularly dispersed electrocatalysts at current densities of up to −300 mA cm–2.

Iron (Fe) is a productivity-limiting nutrient in the ocean. However, the sources of dissolved Fe (dFe) in the deep ocean and how they respond to tectonic and climate changes are still poorly understood. In the northern hemisphere, dust flux to the low-latitude western Pacific has increased dramatically since the late Miocene associated with intense aridification of the Asian inland. Meanwhile, the terrigenous material supply to the open ocean might have also changed as a result of the reorganization of the Pacific circulation due to the gradual closure of seaways in the low latitudes. Therefore, the western Pacific is a characteristic region for understanding the sources of dFe in the deep ocean and their responses to long term climate changes. Here, we present data on isotopic evolution of dFe and dissolved Pb since ∼8 Ma based on ferromanganese crust METG-03 (16.0°N, 152.0°E, 3850 m water depth) in the western Pacific deep water. Our results show that δ56Fe of the crust remains fairly stable since the late Miocene, i.e., about −0.32±0.08‰ (2SD). We infer that δ56Fe of dFe in the deep western Pacific is relatively invariant at ∼0.45 ±0.1‰ based on the Fe isotopic fractionation between hydrogenetic crust and the seawater dissolved component. The reconstructed isotope signature is similar to the measured δ56Fe value (0.37±0.15‰) of the intermediate to deep waters in the modern low-latitude western Pacific region close to the island arcs, but is significantly higher than that of the eastern Pacific deep waters near South America which is controlled by the reductive dissolution of continental shelf sediments and the hydrothermal inputs (δ56Fe

Engineering single-atom electrocatalysts with high-loading amount holds great promise in energy conversion and storage application. Herein, we report a facile and economical approach to achieve an unprecedented high loading of single Ir atoms, up to ∼18wt%, on the nickel oxide (NiO) matrix as the electrocatalyst for oxygen evolution reaction (OER). It exhibits an overpotential of 215 mV at 10 mA cm-2 and a remarkable OER current density in alkaline electrolyte, surpassing NiO and IrO2 by 57 times and 46 times at 1.49 V vs RHE, respectively. Systematic characterizations, including X-ray absorption spectroscopy and aberration-corrected Z-contrast imaging, demonstrate that the Ir atoms are atomically dispersed at the outermost surface of NiO and are stabilized by covalent Ir-O bonding, which induces the isolated Ir atoms to form a favorable ∼4+ oxidation state. Density functional theory calculations reveal that the substituted single Ir atom not only serves as the active site for OER but also activates the surface reactivity of NiO, which thus leads to the dramatically improved OER performance. This synthesis method of developing high-loading single-atom catalysts can be extended to other single-atom catalysts and paves the way for industrial applications of single-atom catalysts.

The sluggish rate of the oxygen reduction reaction (ORR) reduces the performance of fuel cell devices. We demonstrated that ordered intermetallic Pd3Bi and Pd31Bi12 are up to ∼11× more active than ...

Proton-exchange membrane fuel cells (PEMFCs) and direct methanol fuel cells (DMFCs) are promising power sources from portable electronic devices to vehicles. The high-cost issue of these low-temperature fuel cells can be primarily addressed by using platinum-group metal (PGM)-free oxygen reduction reaction (ORR) catalysts, in particular atomically dispersed metal–nitrogen–carbon (M–N–C, M = Fe, Co, Mn). Furthermore, a significant advantage of M–N–C catalysts is their superior methanol tolerance over Pt, which can mitigate the methanol cross-over effect and offer great potential of using a higher concentration of methanol in DMFCs. Here, we investigated the ORR catalytic properties of M–N–C catalysts in methanol-containing acidic electrolytes via experiments and density functional theory (DFT) calculations. FeN4 sites demonstrated the highest methanol tolerance ability when compared to metal-free pyridinic N, CoN4, and MnN4 active sites. The methanol adsorption on MN4 sites is even strengthened when electrode potentials are applied during the ORR. The negative influence of methanol adsorption becomes significant for methanol concentrations higher than 2.0 M. However, the methanol adsorption does not affect the 4e− ORR pathway or chemically destroy the FeN4 sites. The understanding of the methanol-induced ORR activity loss guides the design of promising M–N–C cathode catalyst in DMFCs. Accordingly, we developed a dual-metal site Fe/Co–N–C catalyst through a combined chemical-doping and adsorption strategy. Instead of generating a possible synergistic effect, the introduced Co atoms in the first doping step act as “scissors” for Zn removal in metal–organic frameworks (MOFs), which is crucial for modifying the porosity of the catalyst and providing more defects for stabilizing the active FeN4 sites generated in the second adsorption step. The Fe/Co–N–C catalyst significantly improved the ORR catalytic activity and delivered remarkably enhanced peak power densities (i.e., 502 and 135 mW cm−2) under H2–air and methanol–air conditions, respectively, representing the best performance for both types of fuel cells. Notably, the fundamental understanding of methanol tolerance, along with the encouraging DMFC performance, will open an avenue for the potential application of atomically dispersed M–N–C catalysts in other direct alcohol or ammonia fuel cells.

As an essential part of DC-Link in the power converter, capacitor plays a crucial role in absorbing ripple current and suppressing ripple voltage. The health and residual service life of the DC-Link capacitor is one of the decisive factors for the safety, stability, and efficiency of the system in which it is located. Aiming at the shortcomings of existing methods, such as low dynamic sensitivity of data update and fluctuation of identification results, a capacitor state identification method based on improved RLS is proposed in this paper. The proposed method is optimized by introducing the forgetting factor algorithm and root means square algorithm to modify the iterative formula and final identification results. Compared with existing methods, this method can identify the capacitor's current state in real time and accurately. Finally, we successfully verified the accuracy, robustness, and adaptability of the proposed method by a series of experimental tests on a dSPACE platform.

Electrides are ionic crystals in which the electrons prefer to occupy free space, serving as anions. Because the electrons prefer to be in the pockets, channels, or layers to the atomic orbitals around the nuclei, it has been challenging to find electrides with partially filled d-shell transition metals, since an unoccupied d-shell provides an energetically favorable location for the electrons to occupy. We recently predicted the existence of electrides with partially filled d-shells using high-throughput computational screening. Here, we provide experimental support using X-ray absorption spectroscopy and X-ray and neutron diffraction to show that Sr3CrN3 is indeed an electride despite its partial d-shell configuration. Our findings indicate that Sr3CrN3 is the first known electride with a partially filled d-shell transition metal, in agreement with theory, which significantly broadens the criteria for the search for new electride materials.

Carbon materials embedded with atomically dispersed metal sites have recently demonstrated intriguing performance as electrocatalysts. However, it remains challenging to construct abundant single m...

The development of commercially friendly and stable catalysts for oxygen reduction reaction (ORR) is critical for many energy conversion systems such as fuel cells and metal-air batteries. Many Co-based perovskite oxides such as LaCoO3 have been discovered as the stable and active ORR catalysts, which can be good candidates to replace platinum (Pt). Although researchers have tried substituting various transition metals into the Co-based perovskite catalysts to improve the ORR performance, the influence of substitution on the ORR mechanism is rarely studied. In this paper, we explore the evolution of ORR mechanism after substituting Fe into LaCoO3, using the combination of X-ray photoelectron spectroscopy, high-resolution X-ray microscopy, X-ray diffraction, surface-sensitive soft X-ray absorption spectroscopy characterization, and electrochemical tests. We observed enhanced catalytic activities and increased electron transfer numbers during the ORR in Co-rich perovskite, which are attributed to the optimized eg filling numbers and the stronger hybridization of transition metal 3d and oxygen 2p bands. The discoveries in this paper provide deep insights into the ORR catalysis mechanism on metal oxides and new guidelines for the design of Pt-free ORR catalysts.

TiO2 is manufactured for white pigments, solar cells, self-cleaning surfaces and devices, and other photocatalytic applications. The industrial synthesis of TiO2 entails: (1) the dissolution of ilmenite ore (FeTiO3) in aqueous sulfuric acid which precipitates the Fe while retaining the Ti in solution, followed by (2) dilution or heating the Ti sulfate solution to precipitate the pure form of TiO2. The underlying chemistry of these processing steps remains poorly understood. Here we show that the dissolution of a simple TiIV-sulfate salt, representative of the industrial sulfate process for the production of TiO2, immediately self-assembles into a soluble Ti-octadecameric cluster, denoted as {Ti18}. We observed {Ti18} in solution by small-angle X-ray scattering and Ti extended X-ray absorption fine structure (Ti-EXAFS) analysis, and ultimately crystallized it for absolute identification. The {Ti18} metal-oxo cluster was previously reported as a polycation; but shown here, it can also be a polyanion, dependent on the number of sulfate ligands it carries. After immediate self-assembly, the {Ti18}-cluster persists until TiO2 precipitates, with no easily identified structural intermediates in the solution or solid state, despite the fact that the atomic arrangement of {Ti18} differs vastly from that of titania. The evolution from solution phase {Ti18} to precipitated TiO2 nanoparticles was detailed by X-ray scattering and Ti-EXAFS. We offer a hypothesis for the key mechanism of complete separation of Fe from Ti in the industrial sulfate process. These findings also highlight the emerging importance of the unusual Ti(Ti)5 pentagonal building unit, featured in {Ti18} as well as other early d0 transition metal-oxo clusters including Nb, Mo and W. Finally, this study presents an example of crystal growth mechanisms in which the observed “pre-nucleation cluster” does not necessarily predicate the structure of the precipitated solid.

Carbon supports used in oxygen-reduction cathode catalysts for proton exchange membrane fuel cells (PEMFCs) are vulnerable to corrosion under harsh operating conditions, leading to poor performance durability. To address this issue, we have developed highly stable porous graphitic carbon (PGC) produced through pyrolysis of a 3D polymer hydrogel in combination with Mn. The resulting PGC features multilayer carbon sheets assembled in porous and flower-like morphologies. In situ high-temperature electron microscopy was employed to dynamically monitor the carbonization process up to 1100 °C, suggesting that the 3D polymer hydrogel provides high porosity at multiple scales, and that Mn catalyzes the graphitization process more effectively than other metals. Compared to conventional carbon supports such as Vulcan, Ketjenblack, and graphitized carbon, PGC provides an improved balance between high graphitization and hierarchical porosity, which is favorable for uniform Pt nanoparticle dispersion and enhanced corrosion resistance. As a result, Pt supported on PGC exhibits remarkably enhanced stability. In addition to thorough testing in aqueous electrolytes, we also conducted fuel cell testing using durability protocols recommended by the U.S. Department of Energy (DOE). After 5000 voltage cycles from 1.0 to 1.5 V, the Pt/PGC catalyst only lost 9 mV at a current density of 1.5 A cm−2, dramatically exceeding the DOE support durability target (

In this study, we report a nonprecious metal catalyst for high-efficiency hydrogen evolution reaction (HER). A self-organized S-doped MoP nanoporous layer (S-MoP NPL) is achieved through a facile e...

Lithium-ion batteries (LIBs) as energy storage devices play an important role in all aspects of our life. The increasing energy demand of the society requires LIBs with higher energy density and better performance. We here develop a new and easy-to-scaleup sol-gel method to coat a surface protection layer on commercial LiCoO2 cathode. We demonstrate that a proper thickness can improve the cycling life with a higher cut-off potential (4.5 V), larger energy capacity (180 mAh/g at 0.5C) and better energy density (35% more compared to non-coated LiCoO2). The mechanism of the protection layer is also revealed by a combination of electron microscopy and synchrotron X-ray spectroscopy.

Metal anode instability, including dendrite growth, metal corrosion, and hetero-ions interference, occurring at the electrolyte/electrode interface of aqueous batteries, are among the most critical issues hindering their widespread use in energy storage. Herein, a universal strategy is proposed to overcome the anode instability issues by rationally designing alloyed materials, using Zn-M alloys as model systems (M = Mn and other transition metals). An in-situ optical visualization coupled with finite element analysis is utilized to mimic actual electrochemical environments analogous to the actual aqueous batteries and analyze the complex electrochemical behaviors. The Zn-Mn alloy anodes achieved stability over thousands of cycles even under harsh electrochemical conditions, including testing in seawater-based aqueous electrolytes and using a high current density of 80 mA cm−2. The proposed design strategy and the in-situ visualization protocol for the observation of dendrite growth set up a new milestone in developing durable electrodes for aqueous batteries and beyond., Metal anode instability due to several intrinsic factors limits their widespread use in energy storage. Here, the authors report a 3D alloy anode via a universal alloy electrodeposition approach to overcome the anode instability issues and demonstrate a seawater-based aqueous battery.

This study aimed to develop a highly selective, sensitive and fast liquid chromatography tandem mass spectrometric (LC-MS/MS) method for the determination of obacunone in rat plasma. Sample preparation was accomplished by a simple solid-phase extraction procedure. Chromatographic separation was carried out on an ACQUITY BEH C18 column using acetonitrile/methanol (1:1, v/v) and 0.1% formic acid in water as mobile phase at a flow rate of 0.4 mL/min. Quantification was performed with multiple reactions monitoring in positive ion mode with the precursor-to-product ion transitions at m/z 455.2 > 161.1 for obacunone and m/z 515.2 > 161.1 for nomilin (internal standard). The assay was demonstrated to be linear over the concentration range of 0.1-1,000 ng/mL with correlation coefficient >0.999 (r > 0.999). The intra- and inter-day accuracy ranged from -8.33 to 10.40%, while the precision was 75.32%, and the assay was free of matrix effect. The validated LC-MS/MS method was successfully applied to the pharmacokinetic study of obacunone in rats after oral and intravenous administrations. The oral bioavailability of obacunone was 13.59%.

Increasing catalytic activity and durability of atomically dispersed metal-nitrogen-carbon (M-N-C) catalysts for the oxygen reduction reaction (ORR) cathode in proton-exchange-membrane fuel cells remains a grand challenge. Here, a high-power and durable Co-N-C nanofiber catalyst synthesized through electrospinning cobalt-doped zeolitic imidazolate frameworks into selected polyacrylonitrile and poly(vinylpyrrolidone) polymers is reported. The distinct porous fibrous morphology and hierarchical structures play a vital role in boosting electrode performance by exposing more accessible active sites, providing facile electron conductivity, and facilitating the mass transport of reactant. The enhanced intrinsic activity is attributed to the extra graphitic N dopants surrounding the CoN4 moieties. The highly graphitized carbon matrix in the catalyst is beneficial for enhancing the carbon corrosion resistance, thereby promoting catalyst stability. The unique nanoscale X-ray computed tomography verifies the well-distributed ionomer coverage throughout the fibrous carbon network in the catalyst. The membrane electrode assembly achieves a power density of 0.40 W cm-2 in a practical H2 /air cell (1.0 bar) and demonstrates significantly enhanced durability under accelerated stability tests. The combination of the intrinsic activity and stability of single Co sites, along with unique catalyst architecture, provide new insight into designing efficient PGM-free electrodes with improved performance and durability.

The development of an efficient electrocatalyst toward the hydrogen evolution reaction (HER) is of significant importance in transforming renewable electricity to pure and clean hydrogen by water splitting. However, the construction of an active electrocatalyst with multiple sites that can promote the dissociation of water molecules still remains a great challenge. Herein, a partial‐single‐atom, partial‐nanoparticle composite consisting of nanosized ruthenium (Ru) nanoparticles (NPs) and individual Ru atoms as an energy‐efficient HER catalyst in alkaline medium is reported. The formation of this unique composite mainly results from the dispersion of Ru NPs to small‐size NPs and single atoms (SAs) on the Fe/N codoped carbon (Fe–N–C) substrate due to the thermodynamic stability. The optimal catalyst exhibits an outstanding HER activity with an ultralow overpotential (9 mV) at 10 mA cm−2 (η 10), a high turnover frequency (8.9 H2 s−1 at 50 mV overpotential), and nearly 100% Faraday efficiency, outperforming the state‐of‐the‐art commercial Pt/C and other reported HER electrocatalysts in alkaline condition. Both experimental and theoretical calculations reveal that the coexistence of Ru NPs and SAs can improve the hydride coupling and water dissociation kinetics, thus synergistically enhancing alkaline hydrogen evolution performance., A nanocomposite of partial‐single‐atom and partial‐nanoparticle formed within the Fe–N–C matrix serves as a multiple‐site electrocatalyst toward hydrogen evolution reaction with an ultralow overpotential of 9 mV to achieve 10 mA cm−2, a high turnover frequency, and ≈100% Faradaic efficiency. Theoretical calculations reveal that ruthenium single‐atoms effectively facilitate water dissociation, and ruthenium nanoparticles promote hydrogen desorption.

Single-atom nanozymes (SANs) possess unique features of maximum atomic utilization and present highly assembled enzyme-like structure and remarkable enzyme-like activity. By introducing SANs into immunoassay, limitations of ELISA such as low stability of horseradish peroxidase (HRP) can be well addressed, thereby improving the performance of the immunoassays. In this work, we have developed novel Fe-N-C single-atom nanozymes (Fe-N x SANs) derived from Fe-doped polypyrrole (PPy) nanotube and substituted the enzymes in ELISA kit for enhancing the detection sensitivity of amyloid beta 1-40. Results indicate that the Fe-N x SANs contain high density of single-atom active sites and comparable enzyme-like properties as HRP, owing to the maximized utilization of Fe atoms and their abundant active sites, which could mimic natural metalloproteases structures. Further designed SAN-linked immunosorbent assay (SAN-LISA) demonstrates the ultralow limit of detection (LOD) of 0.88 pg/mL, much more sensitive than that of commercial ELISA (9.98 pg/mL). The results confirm that the Fe-N x SANs can serve as a satisfactory replacement of enzyme labels, which show great potential as an ultrasensitive colorimetric immunoassay.

The ability to tune magnetic orders, such as magnetic anisotropy and topological spin texture, is desired to achieve high-performance spintronic devices. A recent strategy has been to employ interfacial engineering techniques, such as the introduction of spin-correlated interfacial coupling, to tailor magnetic orders and achieve novel magnetic properties. We chose a unique polar–nonpolar LaMnO3/SrIrO3 superlattice because Mn (3d)/Ir (5d) oxides exhibit rich magnetic behaviors and strong spin–orbit coupling through the entanglement of their 3d and 5d electrons. Through magnetization and magnetotransport measurements, we found that the magnetic order is interface-dominated as the superlattice period is decreased. We were able to then effectively modify the magnetization, tilt of the ferromagnetic easy axis, and symmetry transition of the anisotropic magnetoresistance of the LaMnO3/SrIrO3 superlattice by introducing additional Mn (3d) and Ir (5d) interfaces. Further investigations using in-depth first-principles calculations and numerical simulations revealed that these magnetic behaviors could be understood by the 3d/5d electron correlation and Rashba spin–orbit coupling. The results reported here demonstrate a new route to synchronously engineer magnetic properties through the atomic stacking of different electrons, which would contribute to future applications in high-capacity storage devices and advanced computing. Ministry of Education (MOE) Nanyang Technological University National Research Foundation (NRF) Published version X.R.W. acknowledges support from the Nanyang Assistant Professorship grant from Nanyang Technological University and Academic Research Fund Tier 1 (Grant Nos. RG108/17 and RG177/18) and Tier 3 (Grant No. MOE2018-T3-1-002) from the Singapore Ministry of Education. L.S. acknowledges support from Singapore MOE Tier 1 (Grant No. R-265-000-615-114). N.S. and P.S. acknowledge the support of Grant No. MOE2014-T2-2-112 from the Ministry of Education, Singapore, and the computational resources of the NSCC ASPIRE1 cluster in Singapore. D.Q. acknowledges the support of the Australian Research Council (Grant No. FT160100207). C.P. acknowledges financial support from the Academic Research Fund Tier 3 (Reference No. MOE5093) and the National Research Foundation (Reference No. NRF-NRFI2015-04). C.W.N. acknowledges support from the Basic Science Center Program of NSFC (Grant No. 51788104). Part of this research was undertaken on the soft X-ray spectroscopy beamline at the Australian Synchrotron, part of ANSTO, and the rest of the soft X-ray spectroscopy measurements were performed at beamline 6.3.1 of Advanced Light Source, which is an Office of Science User Facility operated for the U.S. DOE Office of Science by Lawrence Berkeley National Laboratory and supported by the DOE under Contract No. DEAC02-05CH11231.

Platinum group metal (PGM)-free catalysts that are also iron free are highly desirable for the oxygen reduction reaction (ORR) in proton-exchange membrane fuel cells, as they avoid possible Fenton reactions. Here we report an efficient ORR catalyst that consists of atomically dispersed nitrogen-coordinated single Mn sites on partially graphitic carbon (Mn-N-C). Evidence for the embedding of the atomically dispersed MnN4 moieties within the carbon surface-exposed basal planes was established by X-ray absorption spectroscopy and their dispersion was confirmed by aberration-corrected electron microscopy with atomic resolution. The Mn-N-C catalyst exhibited a half-wave potential of 0.80 V versus the reversible hydrogen electrode, approaching that of Fe-N-C catalysts, along with significantly enhanced stability in acidic media. The encouraging performance of the Mn-N-C catalyst as a PGM-free cathode was demonstrated in fuel cell tests. First-principles calculations further support the MnN4 sites as the origin of the ORR activity via a 4e− pathway in acidic media. Platinum group metal- and iron-free catalysts are highly desirable for the oxygen reduction reaction in proton-exchange membrane fuel cells. Now, Wu and co-workers show a carbon catalyst with atomically dispersed single Mn sites as an efficient catalyst with enhanced stability in acidic media.

Herein, we report the exploration of understanding the reactivity and structure of atomically dispersed M–N4 (M = Fe and Co) sites for the CO2 reduction reaction (CO2RR). Nitrogen coordinated Fe or Co site atomically dispersed into carbons (M–N–C) containing bulk- and edge-hosted M–N4 coordination were prepared by using Fe- or Co-doped metal–organic framework precursors, respectively, which were further studied as ideal model catalysts. Fe is intrinsically more active than Co in M–N4 for the reduction of CO2 to CO, in terms of a larger current density and a higher CO Faradaic efficiency (FE) (93% vs. 45%). First principle computations elucidated that the edge-hosted M–N2+2–C8 moieties bridging two adjacent armchair-like graphitic layers is the active sites for the CO2RR. They are much more active than previously proposed bulk-hosted M–N4–C10 moieties embedded compactly in a graphitic layer. During the CO2RR, when the dissociation of *COOH occurs on the M–N2+2–C8, the metal atom is the site for the adsorpt...

It remains a grand challenge to replace platinum group metal (PGM) catalysts with earth-abundant materials for the oxygen reduction reaction (ORR) in acidic media, which is crucial for large-scale deployment of proton exchange membrane fuel cells (PEMFCs). Here, we report a high-performance atomic Fe catalyst derived from chemically Fe-doped zeolitic imidazolate frameworks (ZIFs) by directly bonding Fe ions to imidazolate ligands within 3D frameworks. Although the ZIF was identified as a promising precursor, the new synthetic chemistry enables the creation of well-dispersed atomic Fe sites embedded into porous carbon without the formation of aggregates. The size of catalyst particles is tunable through synthesizing Fe-doped ZIF nanocrystal precursors in a wide range from 20 to 1000 nm followed by one-step thermal activation. Similar to Pt nanoparticles, the unique size control without altering chemical properties afforded by this approach is able to increase the number of PGM-free active sites. The best ORR activity is measured with the catalyst at a size of 50 nm. Further size reduction to 20 nm leads to significant particle agglomeration, thus decreasing the activity. Using the homogeneous atomic Fe model catalysts, we elucidated the active site formation process through correlating measured ORR activity with the change of chemical bonds in precursors during thermal activation up to 1100 °C. The critical temperature to form active sites is 800 °C, which is associated with a new Fe species with a reduced oxidation number (from Fe

Transition-metal-based molecular complexes are a class of catalyst materials for electrochemical CO2 reduction to CO that can be rationally designed to deliver high catalytic performance. One common mechanistic feature of these electrocatalysts developed thus far is an electrogenerated reduced metal center associated with catalytic CO2 reduction. Here we report a heterogenized zinc–porphyrin complex (zinc(II) 5,10,15,20-tetramesitylporphyrin) as an electrocatalyst that delivers a turnover frequency as high as 14.4 site–1 s–1 and a Faradaic efficiency as high as 95% for CO2 electroreduction to CO at −1.7 V vs the standard hydrogen electrode in an organic/water mixed electrolyte. While the Zn center is critical to the observed catalysis, in situ and operando X-ray absorption spectroscopic studies reveal that it is redox-innocent throughout the potential range. Cyclic voltammetry indicates that the porphyrin ligand may act as a redox mediator. Chemical reduction of the zinc–porphyrin complex further confirms that the reduction is ligand-based and the reduced species can react with CO2. This represents the first example of a transition-metal complex for CO2 electroreduction catalysis with its metal center being redox-innocent under working conditions., A zinc−porphyrin complex, with the redox-innocent Zn ion binding reaction intermediates and the ligand mediating electron transfer, catalyzes CO2 electroreduction to CO in high Faradaic efficiency.

Atomically dispersed and nitrogen coordinated single iron site (i.e., FeN4) catalysts (Fe-N-C) are the most promising platinum group metal (PGM)-free cathode for the oxygen reduction reaction (ORR) in proton-exchange membrane fuel cells (PEMFCs). However, current Fe-N-C catalysts are limited by the inferior exposure of active FeN4 sites due to the inevitable agglomeration of particles in cathodes. Herein, we report a self-assembled strategy to synthesize the atomically dispersed FeN4 site catalysts with a hierarchically porous matrix derived from dual-size Fe-doped ZIF-8 crystal precursors by using large particles to support small particles. The tailored structure is effective in mitigating the particle migration, agglomeration, and spatial overlap, thereby exposing increased accessible active sites and facilitating mass transport. The best performing catalyst composed of 100 nm “nucleated seed” assembled by 30 nm “satellite” demonstrates exceptional ORR activity in acidic electrolyte and membrane electrode assembly. This work provides new concepts for designing hierarchically porous catalysts with single metal atom dispersion via self-assembly of ZIF-8 crystal precursors with tunable particle sizes and nanostructures.

Rice black-streaked dwarf disease, caused by the rice black-streaked dwarf virus (RBSDV), can lead to severe yield losses in rice. The deployment of resistant cultivars is an effective disease control measure, but few studies related to the genetics and breeding of RBSDV resistance have been reported in rice. Here, we identified ‘IR36’ (indica) and ‘L5494’ (japonica) as resistant and susceptible parents, respectively, using a field test, and 208 recombinant inbred lines were derived from their cross. A genetic analysis indicated that the resistance of rice materials to RBSDV was controlled by quantitative trait loci (QTLs). A total of 12 QTLs for RBSDV resistance on chromosomes 1, 6, 8 and 9 were identified in three environments (2013–2015), and QTLs in two marker intervals, RM19234–CHR6-2 and RM3700–RM160 on chromosomes 6 and 9, respectively, were consistently detected. These QTLs explained 6.19–29.00 % of the total phenotypic variation for rice black-streaked dwarf disease incidence. The alleles enhancing resistance on chromosomes 6 and 8 originated from ‘IR36’, whereas the alleles on chromosomes 1 and 9 originated from ‘L5494’. The materials and identified resistance QTLs in this study are expected to be useful resources for efficiently breeding rice cultivars resistant to RBSDV.

Restructuring-induced catalytic activity is an intriguing phenomenon of fundamental importance to rational design of high-performance catalyst materials. We study three copper-complex materials for electrocatalytic carbon dioxide reduction. Among them, the copper(II) phthalocyanine exhibits by far the highest activity for yielding methane with a Faradaic efficiency of 66% and a partial current density of 13 mA cm−2 at the potential of – 1.06 V versus the reversible hydrogen electrode. Utilizing in-situ and operando X-ray absorption spectroscopy, we find that under the working conditions copper(II) phthalocyanine undergoes reversible structural and oxidation state changes to form ~ 2 nm metallic copper clusters, which catalyzes the carbon dioxide-to-methane conversion. Density functional calculations rationalize the restructuring behavior and attribute the reversibility to the strong divalent metal ion–ligand coordination in the copper(II) phthalocyanine molecular structure and the small size of the generated copper clusters under the reaction conditions., The catalytic conversion of carbon dioxide into value-added products requires an understanding of the active species present under working conditions. Here, the authors discover copper-containing complexes to reversibly transform during electrocatalysis into methane-producing copper nanoclusters.

Aqueous sodium-ion batteries are attractive battery alternatives for stationary energy storage due to their inherently low cost and high safety. The development of advanced electrode materials with excellent performance and low cost is crucial for the success of aqueous Na-ion batteries. Albeit the high capacity and stable cycling of the leading anode of NaTi2(PO4)3, the high price of titanium element and the low Na-insertion potential close to the hydrogen evolution reaction may plague its application. Here we introduced a NASICON-type Na3Fe2(PO4)3 as a promising anode alternative for aqueous Na-ion batteries. Synchrotron X-ray diffraction and spectroscopy confirm its phase and atomic structure. Electrochemical characterization and X-ray photoelectron spectroscopy reveal the reversible Na+ insertion in Na3Fe2(PO4)3 due to the Fe3+/Fe2+ redox couple, which renders a specific capacity of ∼60 mAh g−1 and excellent cycling of 1000 cycles at 10C rate. A Super high rate of 100C was also achieved for this anode with a capacity retention of 61% after 1000 cycles. In addition, the Na3Fe2(PO4)3 anode is paired with a Prussian white analogue of Na2Mn[Fe(CN)6] into a full cell, exhibiting promising cell performance and material sustainability. Our work underlines the importance of fabricating aqueous batteries on the basis of the Earth-abundant, cost-effective, and non-toxic elements.

Motivated by the advanced photon source upgrade, a new hard X-ray microscope called "Velociprobe" has been recently designed and built for fast ptychographic imaging with high spatial resolution. We are addressing the challenges of high-resolution and fast scanning with novel hardware designs, advanced motion controls, and new data acquisition strategies, including the use of high-bandwidth interferometric measurements. The use of granite, air-bearing-supported stages provides the necessary long travel ranges for coarse motion to accommodate real samples and variable energy operation while remaining highly stable during fine scanning. Scanning the low-mass zone plate enables high-speed and high-precision motion of the probe over the sample. With an advanced control algorithm implemented in a closed-loop feedback system, the setup achieves a position resolution (3σ) of 2 nm. The instrument performance is evaluated by 2D fly-scan ptychography with our developed data acquisition strategies. A spatial resolution of 8.8 nm has been demonstrated on a Au test sample with a detector continuous frame rate of 200 Hz. Using a higher flux X-ray source provided by double-multilayer monochromator, we achieve 10 nm resolution for an integrated circuit sample in an ultrafast scan with a detector's full continuous frame rate of 3000 Hz (0.33 ms per exposure), resulting in an outstanding imaging rate of 9 × 104 resolution elements per second.

Due to the Fenton reaction, the presence of Fe and peroxide in electrodes generates free radicals causing serious degradation of the organic ionomer and the membrane. Pt-free and Fe-free cathode catalysts therefore are urgently needed for durable and inexpensive proton exchange membrane fuel cells (PEMFCs). Herein, a high-performance nitrogen-coordinated single Co atom catalyst is derived from Co-doped metal-organic frameworks (MOFs) through a one-step thermal activation. Aberration-corrected electron microscopy combined with X-ray absorption spectroscopy virtually verifies the CoN4 coordination at an atomic level in the catalysts. Through investigating effects of Co doping contents and thermal activation temperature, an atomically Co site dispersed catalyst with optimal chemical and structural properties has achieved respectable activity and stability for the oxygen reduction reaction (ORR) in challenging acidic media (e.g., half-wave potential of 0.80 V vs reversible hydrogen electrode (RHE). The performance is comparable to Fe-based catalysts and 60 mV lower than Pt/C -60 μg Pt cm-2 ). Fuel cell tests confirm that catalyst activity and stability can translate to high-performance cathodes in PEMFCs. The remarkably enhanced ORR performance is attributed to the presence of well-dispersed CoN4 active sites embedded in 3D porous MOF-derived carbon particles, omitting any inactive Co aggregates.