Sharply expanding single-atomically dispersed Fe-N active sites through bidirectional coordination for oxygen reduction.

For Fe-NC systems, high-density Fe-N sites are the basis for high-efficiency oxygen reduction reaction (ORR), and P doping can further lower the reaction energy barrier, especially in the form of metal-P bonding. However, limited to the irregular agglomeration of metal atoms at high temperatures, Fe-P bonds and high-density Fe-N cannot be guaranteed simultaneously. Here, to escape the random and violent agglomeration of Fe species during high-temperature carbonization, triphenylphosphine and 2-methylimidazole with a strong metal coordination capability are introduced together to confine Fe growth. With the aid of such bidirectional coordination, the high-density Fe-N site with Fe-P bonds is realized by in situ phosphorylation of Fe in an Fe-NC system (Fe-P-NC) at high temperatures. Impressively, the content of single-atomically dispersed Fe sites for Fe-P-NC dramatically increases from 2.8% to 65.3% compared with that of pure Fe-NC, greatly improving the ORR activity in acidic and alkaline electrolytes. The theoretical calculation results show that the generated Fe2P can simultaneously facilitate the adsorption of intermediates to Fe-N4 sites and the electron transfer, thereby reducing the reaction energy barrier and obtaining superior ORR activity.

Fast and In-Depth Reconstruction of Two-Dimension Cobalt-Based Zeolitic Imidazolate Framework in Glucose Oxidation Processes.

Currently, metal-organic frameworks (MOFs) have emerged as viable candidates for enduring electrode materials in nonenzyme glucose sensing. However, given the inherent water susceptibility of MOFs and their complete self-reconstruction during the process of electrochemical oxygen evolution in alkaline conditions, we are motivated to explore the truth of MOFs catalyzing glucose oxidation. In this work, we fabricated a two-dimensional cobalt-based zeolitic imidazolate framework (ZIF-L) as the electrode material for catalyzing glucose oxidation in alkaline conditions. Our explorations revealed that while the initial glucose catalytic response varied among ZIF-L samples with differing thicknesses, the ultimate steady-state catalytic performance remained largely consistent. This phenomenon arose from the transformation of ZIF-L with distinct thicknesses into CoOOH with uniform morphological and structural characteristics during the glucose catalysis process. And in situ Raman spectroscopy elucidated the sustained equilibrium within the glucose catalytic system, wherein the dynamic interconversion between CoOOH and Co(OH)2 governs the overall process. This study contributes to an enhanced understanding of the glucose catalytic mechanism aspects of nonenzymatic glucose sensor electrode materials, offering insights that serve as inspiration for the development of advanced glucose electrode materials.

Tuning Active Metal Atomic Spacing by Filling of Light Atoms and Resulting Reversed Hydrogen Adsorption-Distance Relationship for Efficient Catalysis.

Precisely tuning the spacing of the active centers on the atomic scale is of great significance to improve the catalytic activity and deepen the understanding of the catalytic mechanism, but still remains a challenge. Here, we develop a strategy to dilute catalytically active metal interatomic spacing (dM-M) with light atoms and discover the unusual adsorption patterns. For example, by elevating the content of boron as interstitial atoms, the atomic spacing of osmium (dOs-Os) gradually increases from 2.73 to 2.96 Å. More importantly, we find that, with the increase in dOs-Os, the hydrogen adsorption-distance relationship is reversed via downshifting d-band states, which breaks the traditional cognition, thereby optimizing the H adsorption and H2O dissociation on the electrode surface during the catalytic process; this finally leads to a nearly linear increase in hydrogen evolution reaction activity. Namely, the maximum dOs-Os of 2.96 Å presents the optimal HER activity (8 mV @ 10 mA cm-2) in alkaline media as well as suppressed O adsorption and thus promoted stability. It is believed that this novel atomic-level distance modulation strategy of catalytic sites and the reversed hydrogen adsorption-distance relationship can shew new insights for optimal design of highly efficient catalysts.

Spherical Ni3 S2 /Fe-NiPx Magic Cube with Ultrahigh Water/Seawater Oxidation Efficiency.

The rational construction of earth-abundant and advanced electrocatalysts for oxygen evolution reaction (OER) is extremely desired and significant to seawater electrolysis. Herein, by directly etching Ni3 S2 nanosheets through potassium ferricyanide, a novel self-sacrificing template strategy is proposed to realize the in situ growth of NiFe-based Prussian blue analogs (NiFe PBA) on Ni3 S2 in an interfacial redox reaction. The well-designed Ni3 S2 @NiFe PBA composite as precursor displays a unique spherical magic cube architecture composed of nanocubes, which even maintains after a phosphating treatment to obtain the derived Ni3 S2 /Fe-NiPx on nickel foam. Specifically, in alkaline seawater, the Ni3 S2 /Fe-NiPx as OER precatalyst marvelously realizes the ultralow overpotentials of 336 and 351 mV at large current densities of 500 and 1000 mA cm-2 , respectively, with remarkable durability for over 225 h, outperforming most reported advanced OER electrocatalysts. Experimentally, a series of characterization results confirm the reconstruction behavior in the Ni3 S2 /Fe-NiPx surface, leading to the in situ formation of Ni(OH)2 /Ni(Fe)OOH with abundant oxygen vacancies and grain boundaries, which constructs the Ni3 S2 /Fe-NiPx reconstruction system responsible for the remarkable OER catalytic activity. Theoretical calculation results further verify the enhanced OER activity for Ni3 S2 /Fe-NiPx reconstruction system, and unveil that the Fe-Ni2 P/FeOOH as active origin contributes to the central OER activity.

Ultra-Fast and In-Depth Reconstruction of Transition Metal Fluorides in Electrocatalytic Hydrogen Evolution Processes.

Hitherto, there are almost no reports on the complete reconstruction in hydrogen evolution reaction (HER). Herein, the authors develop a new type of reconfigurable fluoride (such as CoF2 ) pre-catalysts, with ultra-fast and in-depth self-reconstruction, substantially promoting HER activity. By experiments and density functional theory (DFT) calculations, the unique surface structure of fluorides, alkaline electrolyte and bias voltage are identified as key factors for complete reconstruction during HER. The enrichment of F atoms on surface of fluorides provides the feasibility of spontaneous and continuous reconstruction. The alkaline electrolyte triggers rapid F- leaching and supplies an immediate complement of OH- to form amorphous α-Co(OH)2 which rapidly transforms into ß-Co(OH)2 . The bias voltage promotes amorphous crystallization and accelerates the reconstruction process. These endow the generation of mono-component and crystalline ß-Co(OH)2 with a loose and defective structure, leading to an ultra-low overpotential of 54 mV at 10 mA cm-2 and super long-term stability exceeding that of Pt/C. Moreover, DFT calculations confirm that F- leaching optimizes hydrogen and water adsorption energies, boosting HER kinetics. Impressively, the self-reconstruction is also applicable to other non-noble transition metal fluorides. The work builds the fundamental comprehension of complete self-reconstruction during HER and provides a new perspective to conceive advanced catalysts.

Sulfate Ions Induced Concave Porous S-N Co-Doped Carbon Confined FeCx Nanoclusters with Fe-N4 Sites for Efficient Oxygen Reduction in Alkaline and Acid Media.

To improve the catalytic activity of the catalysts, it is key to intensifying the intrinsic activity of active sites or increasing the exposure of accessible active sites. In this work, an efficient oxygen reduction electrocatalyst is designed that confines plentiful FeCx nanoclusters with Fe-N4 sites in a concave porous S-N co-doped carbon matrix, readily accessible for the oxygen reduction reaction (ORR). Sulfate ions react with the carbon derived from ZIF-8 at high temperatures, leading to the shrinkage of the carbon framework and then forming a concave structure with abundant macropores and mesopores with S incorporation. Such an architecture promotes the exposure of active sites and accelerates remote mass transfer. As a result, the catalyst (Fe/S-NC) with a large number of C-S-C, Fe-N4 , and FeCx nanoclusters presents impressive ORR activity and stability. In alkaline media, the half-wave potential of the best catalyst (Fe/S2 -NC) is 0.91 V, which far exceeds that of commercial platinum carbon (0.85 V), while in acidic media the half-wave potential reaches 0.784 V, comparable to platinum carbon (0.812 V). Furthermore, for the zinc-air battery, the outstanding peak power density of Fe/S2 -NC (170 mW cm-2 ) superior to platinum carbon (108 mW cm-2 ) also highlights its great application potential.

Synergistic Coupling of Ni Nanoparticles with Ni3 C Nanosheets for Highly Efficient Overall Water Splitting.

Exploring earth-abundant bifunctional electrocatalysts with high efficiency for water electrolysis is extremely demanding and challenging. Herein, density functional theory (DFT) predictions reveal that coupling Ni with Ni3 C can not only facilitate the oxygen evolution reaction (OER) kinetics, but also optimize the hydrogen adsorption and water adsorption energies. Experimentally, a facile strategy is designed to in situ fabricate Ni3 C nanosheets on carbon cloth (CC), and simultaneously couple with Ni nanoparticles, resulting in the formation of an integrated heterostructure catalyst (Ni-Ni3 C/CC). Benefiting from the superior intrinsic activity as well as the abundant active sites, the Ni-Ni3 C/CC electrode demonstrates excellent bifunctional electrocatalytic activities toward the OER and hydrogen evolution reaction (HER), which are superior to all the documented Ni3 C-based electrocatalysts in alkaline electrolytes. Specifically, the Ni-Ni3 C/CC catalyst exhibits the low overpotentials of only 299 mV at the current density of 20 mA cm-2 for the OER and 98 mV at 10 mA cm-2 for the HER in 1 m KOH. Furthermore, the bifunctional Ni-Ni3 C/CC catalyst can propel water electrolysis with excellent activity and nearly 100% faradic efficiency. This work highlights an easy approach for designing and constructing advanced nickel carbide-based catalysts with high activity based on the theoretical predictions.

Double Metal Diphosphide Pair Nanocages Coupled with P-Doped Carbon for Accelerated Oxygen and Hydrogen Evolution Kinetics.

Developing efficient and durable bifunctional transition metal phosphide (TMP) electrocatalysts is still a great challenge because of its relatively sluggish kinetics of oxygen evolution reaction (OER). Herein, we report a unique bimetallic diphosphide pair (FeP2-NiP2) forming spherical nanocages encapsulated in P-doped carbon layers (FeP2-NiP2@PC) as advanced bifunctional electrocatalyst synthesized by a very facile phosphorization approach. The obtained FeP2-NiP2@PC electrocatalyst exhibits an outstanding OER activity with an ultralow overpotential of 248 mV in 1 M KOH and a low overpotential of 117 mV for HER in 0.5 M H2SO4 (@10 mA·cm-2). Also it gives an exceptional long-term durability toward OER (60 h) and HER (20 h). Differently from the electrocatalysts as reported, after successive 3000 cycles CV acceleration, its overpotential decreases about 10 mV. Further investigation unveils that the electrochemical activation process boosts in situ phase transformation of oxides and phosphides to oxyhydroxides as the vital intermediates in FeP2-NiP2@PC during OER electrocatalysis. The direct observation of vital intermediates has been rarely reported on Fe/Ni-based phosphide electrocatalysts. Our exploration demonstrates an extraordinarily efficient and stable nonprecious TMP bifunctional electrocatalyst and provides a novel prospect to shed light on the intrinsic OER electrocatalytic behavior of Fe/Ni-based phosphide electrocatalysts.

Corrigendum: Superparamagnetic enhancement of thermoelectric performance.

This corrects the article DOI: 10.1038/nature23667.

Superparamagnetic enhancement of thermoelectric performance.

The ability to control chemical and physical structuring at the nanometre scale is important for developing high-performance thermoelectric materials. Progress in this area has been achieved mainly by enhancing phonon scattering and consequently decreasing the thermal conductivity of the lattice through the design of either interface structures at nanometre or mesoscopic length scales or multiscale hierarchical architectures. A nanostructuring approach that enables electron transport as well as phonon transport to be manipulated could potentially lead to further enhancements in thermoelectric performance. Here we show that by embedding nanoparticles of a soft magnetic material in a thermoelectric matrix we achieve dual control of phonon- and electron-transport properties. The properties of the nanoparticles-in particular, their superparamagnetic behaviour (in which the nanoparticles can be magnetized similarly to a paramagnet under an external magnetic field)-lead to three kinds of thermoelectromagnetic effect: charge transfer from the magnetic inclusions to the matrix; multiple scattering of electrons by superparamagnetic fluctuations; and enhanced phonon scattering as a result of both the magnetic fluctuations and the nanostructures themselves. We show that together these effects can effectively manipulate electron and phonon transport at nanometre and mesoscopic length scales and thereby improve the thermoelectric performance of the resulting nanocomposites.