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By tailoring the microenvironments of a Ni–N–C catalyst in an acidic MEA electrolyzer, we achieve a CO faradaic efficiency of 95% at 500 mA cm−2, and the CO2 loss is reduced by 86% at 300 mA cm−2 at pH 0.5, compared to alkaline CO2 electrolysis.

N2-plasma bombardment allows the large-area fabrication of high 1T phase N,Pt-doped MoS2 nanosheets with prominent alkaline HER activity.

Nitrogen reduction reaction (NRR) under ambient conditions is always a long-standing challenge in science, due to the extreme difficulty in breaking the strong N N triple bond. The key to resolving this issue undoubtedly lies in searching superior catalysts to efficiently activate and hydrogenate the stable nitrogen molecules. We herein evaluate the feasibility of WP2 for N2 activation and reduction, and first demonstrate WP2 with an impressive ammonia yield rate of 7.13 μg h−1 cm−2, representing a promising W-based catalyst for NRR. DFT analysis further reveals that the NRR catalysis on WP2 proceeds in a distal reaction pathway, and the exceptional NRR activity is originated from superior surface electron energy level matching between WP2 and NRR potential which facilitates the interfacial proton-coupled electron transfer dynamics. The successfully unraveling the intrinsic catalytic mechanism of WP2 for NRR could offer a powerful platform to manipulate the NRR activity by tuning the electron energy levels.

The design of efficient copper(Cu)-based catalysts is critical for CO

The high unoccupied d band energy of Ni3N basically results in weak orbital coupling with water molecule, consequently leading to slow water dissociation kinetics. Herein, we demonstrate Cr doping can downshift the unoccupied d orbitals and strengthen the interfacial orbital coupling to boost the water dissociation kinetics. The prepared Cr-Ni3N/Ni displays an impressive overpotential of 37 mV at 10 mA·cmgeo−2, close to the benchmark Pt/C in 1.0 M KOH solution. Refined structural analysis reveals the Cr dopant exists as the Cr-N6 states and the average d band energy of Ni3N is also lowered. Density functional theory calculation further confirms the downshifted d band energy can strengthen the orbital coupling between the unpaired electrons in O 2p and the unoccupied state of Ni 3d, which thus facilitates the water adsorption and dissociation. The work provides a new concept to achieve on-demand functions for hydrogen evolution catalysis and beyond, by regulating the interfacial orbital coupling.

Presently, there have been some limitations in most of methods to determine poly (γ-glutamic acid) (γ-PGA) content because of many impurities in test specimens. It is necessary to establish a rapid and accurate method to quantify γ-PGA content. In this work, γ-PGA and some impurities commonly seen in fermented broth like glucose, glutamic acid and proteins were used to complex with copper ions. The results show that only γ-PGA can make copper ion precipitated, which content linearly correlates with the precipitate amount. From the study on the validity of the method, it is found that the accuracy and precision are 95.82% and 99.29%, much higher than the ones of method UV and weighing. Therefore, the method via the complexation of copper ion will be popularized to determine γ-PGA content in crude biological samples.

We present a magnetic scanning microscope equipped with a nitrogen-vacancy (NV) center scanning probe that has the ability to mechanically tune the strain of soft matter in-situ. The construction of the microscope and a continuous strain-tuning sample holder are discussed. An optically detected magnetic resonance protocol utilized in the imaging is described. In order to show the reliability of this microscope, the strain conduction is estimated with finite element simulation, and x-ray diffraction is required for calibration when freestanding crystal films are under consideration. A magnetic imaging result is displayed to demonstrate the nano-scale imaging capability. The microscope presented in this work is helpful in studying strain-coupled magnetic physics such as magnetic phase transition under strain and strain-tuned cycloidal orientation tilting.

Tungsten oxide with strong acid resistance and weak O-binding ability could potentially achieve a tradeoff on the O-binding properties by constructing W and Ir dual sites for acidic oxygen evolution reaction (OER) catalysis. However, the peroxide intermediate formed during the OER process could react with tungsten oxide to produce soluble species, thereby severely limiting its application. Herein, we construct Ir–W@Ir–WO3−x core–shell nanoparticles with an Ir–W metallic core and an Ir-doped WO3−x (Ir–WO3−x) shell, which can deliver an impressive overpotential of 261 mV at 10 mA cm−2 for acidic OER catalysis and extraordinary catalytic stability. Spectroscopic analysis manifests that Ir–W@Ir–WO3−x could substantially suppress peroxide species formation and effectively avoid peroxide-induced corrosion during the OER process. Theoretical studies reveal that the moderate O-binding capability on Ir–W@Ir–WO3−x not only accelerates catalytic kinetics, but also restrains hydroperoxide formation. This work sheds light on the rational design of OER catalysts by modulating the adsorption behavior of oxygen-containing intermediates.

The interstitial structure and weak Ni-N interaction of Ni3N lead to high unoccupied d orbital energy and unsuitable orbital orientation, which consequently results in weak orbital coupling with H2O and slow water dissociation kinetics for alkaline hydrogen evolution catalysis. Herein, we successfully lower the unoccupied d orbital energy of Ni3N to strengthen the interfacial electronic coupling by employing the strong electron pulling capability of oxygen dopants. The prepared O-Ni3N catalyst delivers an overpotential of 55 mV at 10 mA cm−2, very close to the commercial Pt/C. Refined structural characterization indicates the oxygen incorporation can decrease the electron densities around the Ni sites. Moreover, density functional theory calculation further proves the oxygen incorporation can create more unoccupied orbitals with lower energy and superior orientation for water adsorption and dissociation. The concept of orbital-regulated interfacial electronic coupling could offer a unique approach for the rational design of hydrogen evolution catalysts and beyond.

Very high power conversion efficiencies (PCEs) have been demonstrated by multijunction cells made of epitaxial III–V semiconductors; but they are too expensive to manufacture for terrestrial applic...

Summary Evaporation-condensation of red phosphorous to prepare phosphorous-based anodes inevitably generates white P residual, severely limiting its practical application due to the serious safety concern. Rather than removing the white P residual by complicated post-treatments, essentially prohibiting the generation of white P is a more meaningful alternative, but unfortunately it has been rarely studied so far. Herein, we demonstrate that the generation of white P can be substantially suppressed via sulfur-mediated phosphorous activation. Moreover, the prepared sulfur-doped P also exhibits the ever-reported fastest redox kinetics for sodium-ion storage. Electron spin resonance spectra and density functional theory calculations reveal that the introduced sulfur lives in the high-spin state during the evaporation-condensation process, which could activate P4 for polymerization. Meanwhile, sulfur-induced electron delocalization can also accelerate the Na-P redox kinetics. The capability to modulate phosphorus polymerization via the high-spin mediator could revolutionize the application of phosphorous for batteries and beyond.

The electrochemical CO 2 reduction reaction (CO 2 RR) over Cu-based catalysts shows a great prospect with converting CO 2 into multicarbon (C 2+ ) fuels and chemicals. Herein, we introduce an A 2 M 2 O 7 structure into Cu-based catalyst through a solid-state reaction synthesis method. The Cu 2 P 2 O 7 catalyst is electrochemically reduced to metallic Cu with a significant structure evolution from grain aggregates to highly porous structure under CO 2 RR conditions. The reconstructed Cu 2 P 2 O 7 catalyst achieves a Faradaic efficiency of 73.6% for C 2+ products at an applied current density of 350 mA cm -2 , remarkably higher than the CuO counterparts. The reconstructed Cu 2 P 2 O 7 catalyst has high electrochemically active surface area and abundant defects and low-coordinated sites. In situ Raman spectroscopy and density functional theory calculation reveal that CO adsorption with bridge and atop configurations is largely improved on Cu with defects and low-coordinated sites, which decreased the energy barrier of C-C coupling reaction for C 2+ products.

The electrochemical CO

A digital image (DI) method is reported to determine the transmittance and the uniformity of transparent optical materials (TOMs) at the same time, in which an objective image (OI) with a two dimensional (2D) entropy of 3.45 is scanned using a scanner with a black background. The OI pictures covered without and with a TOM went through gamma correction and color correction. The two corrected pictures were transformed into two matrixes, between which the transparency ratio and the correlation coefficient refer to the transmittance and the uniformity of TOMs. As a result, a p-value of 0.97 and an r value of 0.92 were achieved from the paired T-test between the DI method and the ultraviolet spectrometry (UVS) method, indicating a similar accuracy in determining the transmittance of TOMs between them. In addition, the DI method is a simple and rapid method to evaluate the uniformity of TOMs and to reveal the correlation among transmittance, uniformity and thickness of TOMs, particularly applicable for inhomogeneous TOMs.

pH-sensitive hydrogels have been applied in delivering probiotics and drugs. However, pH sensitivity has been found to be contradictory with structural stability in hydrogel preparation. In this work, a novel strategy based on two systems of sodium carboxymethyl cellulose (CMC)/chitosan (CS) and sodium alginate (SA)/calcium chloride was designed to construct a reticulated shell structure stable for 3 h in simulated gastric fluid (pH 1.2) but began to break up at 2 h in simulated intestinal fluid (pH 6.8), exhibiting obvious pH sensitivity. The embedding rate of Bacillus subtilis natto reached to 67.3%, and the sustained release lasted for more than 10 h. It is implicated that the reticulated shell structure has harmoniously balanced the two incompatible properties of pH sensitivity and sustained release of CMC/CS/SA beads.

Molybdenum disulfide is naturally inert for alkaline hydrogen evolution catalysis, due to its unfavorable water adsorption and dissociation feature originated from the unsuitable orbital orientation. Herein, we successfully endow molybdenum disulfide with exceptional alkaline hydrogen evolution capability by carbon-induced orbital modulation. The prepared carbon doped molybdenum disulfide displays an unprecedented overpotential of 45 mV at 10 mA cm−2, which is substantially lower than 228 mV of the molybdenum disulfide and also represents the best alkaline hydrogen evolution catalytic activity among the ever-reported molybdenum disulfide catalysts. Fine structural analysis indicates the electronic and coordination structures of molybdenum disulfide have been significantly changed with carbon incorporation. Moreover, theoretical calculation further reveals carbon doping could create empty 2p orbitals perpendicular to the basal plane, enabling energetically favorable water adsorption and dissociation. The concept of orbital modulation could offer a unique approach for the rational design of hydrogen evolution catalysts and beyond., Technologies allowing for sustainable hydrogen production will contribute to the decarbonization of the future energy supply. Here the authors report that carbon induced orbital modulation can facilitate the otherwise inert MoS2 electrocatalyst superior alkaline hydrogen evolution reactivity.

Although Ni3N possesses superior hydrogen desorption behavior, its alkaline hydrogen evolution reaction (HER) catalysis is substantially hindered, due to the high-lying unoccupied orbital center induced sluggish water dissociation kinetics. Herein, we successfully endow Ni3N with exceptional alkaline HER activity by in situ interfacial engineering. The prepared Ni3N/MoO2 interfacial system delivers an ultra-small overpotential of 21 mV at 10 mA cm−2, which is very close to that of the benchmark Pt/C catalysts. Density functional theory (DFT) calculations reveal that MoO2 with a lower unoccupied orbital center could substantially boost the water dissociation kinetics, while the hydrogen desorption proceeds on Ni3N. The capability to understand and design interfacial systems provides an effective pathway for the rational construction of HER catalysts and beyond.

Recently, Li-O2 batteries have been considered to be promising next-generation energy storage devices owing to their high theoretical specific energy. However, due to the sluggish reaction kinetics of oxygen conversion, practical applications cannot achieve the desired results. By introducing vacancies in the MoS2 basal plane and using an in-situ synthesis method, we demonstrated the excellent catalysis of MoS2−x for oxygen redox kinetics, which can improve Li-O2 battery performance. The prepared MoS2−x displays little polarization, with a potential gap of 0.59 V and a high discharge capacity of 8,851 mA h g−1 at a current density of 500 mA g−1. The improved performance is mainly attributable to abundant S defects and plentiful diffusion channels in the MoS2−x/carbon 3D structural cathodes, which enable the adsorption of gaseous oxygen, reaction intermediates, and discharge products. To the best of our knowledge, these structures fabricated through 3D network design and surface modulation are among the best oxygen conversion catalysts developed so far, offering a new vista for the design of Li-O2 catalysts and beyond.

A porous chitosan (CS)/poly-(γ-glutamic acid) (γ-PGA) hydrogel was prepared by polymerization by electrostatic contacts of CS with γ-PGA without linker. The porosity of the hydrogel remarkably depends on γ-PGA content, pH regulator, and drying way. The optimization of them had given the hydrogel a high swelling capacity of 1398%, 11-fold higher than that of neat CS hydrogel. The hydrogel was applied to recover bovine serum albumin (BSA) from aqueous solution, and its adsorption capacity was influenced by the initial concentration and pH of BSA solution. Based on the studies of kinetics and isotherm, a high equilibrium adsorption capacity (qe = 948 mg/g) and a correlation coefficient of 0.996 were calculated from pseudo-second order kinetic equation, and a high affinitive constant (kF = 472 mL/mg) and a high saturated absorption capacity (qm = 1818.5 mg/g) were observed from Freundlich isotherm equation, indicating the porous hydrogel will be a good absorbent for protein recovery from sewage.

To study the effect of nattokinse (NK) on the synthesis of poly(γ-glutamic acid) (γ-PGA) in Bacillus subtilis natto. γ-PGA yield significantly decreased as NK was added in the original medium. With the increment of NK dosage, the yield decreased increasingly, but biomass increased instead of decreasing. The fact that cell density triggers the synthesis of γ-PGA is a controversial issue. γ-PGA yield and biomass closely correlate with addition time of NK. The later the addition of NK, the more γ-PGA yield decreased but the more biomass increased. It is concluded that cell hunger is a key factor to trigger the transmission of the cell density signal, and NK may inhibit γ-PGA synthesis by alleviating cell hunger. Besides, NK may reduce γ-PGA yield by degrading extracellular γ-PGA molecules. The study of adding L-glutamate of 0–20 g/L to the original medium showed that low concentration of L-glutamate (less than 5 g/L) could promote the synthesis of NK and γ-PGA, and thus NK may inhibit γ-PGA synthesis through strengthening substrate competition. NK mainly inhibits γ-PGA synthesis in Bacillus subtilis natto through alleviating cell starvation and strengthening substrate competition, and reduces γ-PGA yield through degrading extracellular γ-PGA molecules.

The HER activities of P-rich transition metal phosphides can be substantially boosted by N-induced lattice contraction., P-rich transition metal phosphides (TMPs) with abundant P sites have been predicted to be more favorable for hydrogen evolution reaction (HER) catalysis. However, the actual activities of P-rich TMPs do not behave as expected, and the underlying essence especially at the atomic level is also ambiguous. Our structural analysis reveals the inferior activity could stem from the reduced overlap of atomic wave functions between metal and P with the increase in P contents, which consequently results in too strong P-H interaction. To this end, we used N-induced lattice contraction to generally boost the HER catalysis of P-rich TMPs including CoP2, FeP2, NiP2, and MoP2. Refined structural characterization and theoretical analysis indicate the N-P strong interaction could increase the atomic wave function overlap and eventually modulate the H adsorption strength. The concept of lattice engineering offers a new vision for tuning the catalytic activities of P-rich TMPs and beyond.

Endowing materials with specific functions that are not readily available is always of great importance, but extremely challenging. Co4 N, with its beneficial metallic characteristics, has been proved to be highly active for the oxidation of water, while it is notoriously poor for catalyzing the hydrogen evolution reaction (HER), because of its unfavorable d-band energy level. Herein, we successfully endow Co4 N with prominent HER catalytic capability by tailoring the positions of the d-band center through transition-metal doping. The V-doped Co4 N nanosheets display an overpotential of 37 mV at 10 mA cm-2 , which is substantially better than Co4 N and even close to the benchmark Pt/C catalysts. XANES, UPS, and DFT calculations consistently reveal the enhanced performance is attributed to the downshift of the d-band center, which helps facilitate the H desorption. This concept could provide valuable insights into the design of other catalysts for HER and beyond.

Interfacial thermal transport plays a prominent role in the thermal management of nanoscale objects and is of fundamental importance for basic research and nanodevices. At metal/insulator interfaces, a configuration commonly found in electronic devices, heat transport strongly depends upon the effective energy transfer from thermalized electrons in the metal to the phonons in the insulator. However, the mechanism of interfacial electron-phonon coupling and thermal transport at metal/insulator interfaces is not well understood. Here, the observation of a substantial enhancement of the interfacial thermal resistance and the important role of surface charges at the metal/ferroelectric interface in an Al/BiFeO3 membrane are reported. By applying uniaxial strain, the interfacial thermal resistance can be varied substantially (up to an order of magnitude), which is attributed to the renormalized interfacial electron-phonon coupling caused by the charge redistribution at the interface due to the polarization rotation. These results imply that surface charges at a metal/insulator interface can substantially enhance the interfacial electron-phonon-mediated thermal coupling, providing a new route to optimize the thermal transport performance in next-generation nanodevices, power electronics, and thermal logic devices., Y.Z., C.D., and Z.G. contributed equally to this work. This work was supported by the National Natural Science Foundation of China (nos. 11774153, 51772143, 11474158, 11890700, 11904162, 1861161004, 11625418, 11974163, 51732006, 52027803, 61704074, and 91963211), the National Basic Research (Key R&D) Program of China (2017YFA0303702 and 2018YFA0306200), the introduced innovative R&D team of Guangdong (2017ZT07C062), the Foundation for Innovative Research Groups of the National Natural Science Foundation of China (51720001), and the Fundamental Research Funds for the Central Universities (nos. 0213-14380198 and 0213-14380167). Y.N. was supported by High-Level Entrepreneurial and Innovative Talents Introduction, Jiangsu Province. Theoretical work was funded by the Luxembourg National Research Fund through project FNR/C18/MS/12705883/REFOX. (H.A. and J.Í.). C.C. acknowledges support from the Spanish Ministry of Science, Innovation, and Universities under the “Ramón y Cajal” fellowship RYC2018-024947-I. R.R. acknowledges financial support by the Ministerio de Ciencia e Innovación (MICINN) under grant FEDER-MAT2017-90024-P and the Severo Ochoa Centres of Excellence Program under Grant CEX2019-000917-S and by the Generalitat de Catalunya under grants no. 2017 SGR 1506. The authors thank the Centro de Supercomputación de Galicia (CESGA) for the use of their computational resources. The authors thank Yaya Zhou for the support of SEM and EDS measurement., With funding from the Spanish government through the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000917-S).

Biopolymer-based hydrogel beads possessing intrinsic low-toxicity, biocompatibility and biodegradability have gained widespread utility in several applications. Among the biopolymers, cellulose is one of the most abundant renewable biomaterials. Herein cellulose hydrogel beads have been prepared by dissolving cellulose in 68% ZnCl2 solution and then crosslinking the polymer chains through calcium ions. The water and ethanol washing of the beads profoundly influences the beads architecture as characterized by Fourier transform infrared spectroscopy, Raman spectroscopy, X-ray powder diffraction and Scanning electron microscopy. The total crystallinity index of the beads increases with the amount of calcium ions that is further enhanced by water washing. These beads, possessing a layer-like nanoporous structure, are capable of loading bovine serum albumin (BSA) and releasing in a sustained manner. The outcome promises a large-scale production of cellulose beads having the potential to be eco-friendly and inexpensive delivery carriers in food, pharmaceutical, medical and agriculture applications.

Building the fundamental relation between the polysulfides adsorption on cathode additives and Li S chemistry kinetics is critical for the rational design of efficient and reliable Li S batteries. Herein, we reveal that Li S chemistry kinetics can be well regulated by manipulating the electron-filling state of d orbitals in Ta2O5. The prepared S@N-Ta2O5/rGO with moderate N contents delivers the lowest polarization for LiPSs conversion and the highest specific capacity of 1252.8 mAh g−1 at 0.2C. More importantly, the theoretical analysis unravel that the enhanced electrochemical performance is mainly originated from the orbital-induced adsorption modulation. This work could offer a powerful platform to manipulate the Li S chemistry by orbital engineering for high-performance Li S batteries.

Water electrolysis is considered as a promising sustainable technology to produce hydrogen thereby reducing dependence on fossil fuels. The oxygen evolution reaction (OER), a half reaction of water electrolysis is hampered by its slow kinetics. Developing high performance electrocatalysts for enhancing OER kinetics is the main bottleneck of this technology. In this study, we synthesize a ternary cobalt iron disulfide as a pre-catalyst for OER. After the activation step, the synthesized catalyst transformed to cobalt-iron amorphous oxide with oxygen defects as an efficient catalyst for OER. At its optimized Co/Fe ratio, equal to 3:1, the activated catalyst requires only 267 mV overpotential to reach the current density of 10 mA cm−2, while Tafel slope is 34 mV dec-1. Density functional theory calculation reveals that the active phase of the OER process is a thin layer of oxide that forms during the voltammetry activating process and the reduced energy barrier of rate determining step contributes to the excellent OER performance of cobalt-iron amorphous oxide.

Here we report the synthesis of Co/Co9S8 core-shell structures anchored onto S, N co-doped porous graphene sheets (Co/Co9S8@SNGS) from thiophene-2,5-dicarboxylate (Tdc) and 4,4ˊ-bipyridine (Bpy) dual organic ligands assembled Co-based metal-organic frameworks (Co-MOFs) in situ grown on graphene oxide sheets (Co-MOFs@GO) by a room-temperature solution reaction. S-containing Tdc and N-containing Bpy not only trigger the growth of Co-MOFs nanocrystals with a fixed S/N atomic ratio of 1:2.4 on GO sheets in the presence of Co2+ in H2O/NaOH system, but also provide S, N doping sources in the pyrolysis process of Co-MOFs to form Co/Co9S8 core-shell structure and S, N co-doping in graphene. The results demonstrate that the obtained Co/Co9S8@SNGS at 1000 °C (Co/Co9S8@SNGS-1000) by pyrolysis of Co-MOFs@GO exhibits superiorly bifunctional catalytic activities of the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) in 0.1 M KOH electrolyte, affording an overpotential of 290 mV for OER at a current density of 10 mA cm−2 and 350 mV for HER at a current density of 20 mA cm−2. The OER activity of Co/Co9S8@SNGS-1000 is slightly better than that of commercial RuO2 catalyst, simultaneously, Co/Co9S8@SNGS-1000 also exhibits good HER activity. As electrode material for full water splitting in 0.1 M KOH solution, the Co/Co9S8@SNGS-1000 electrodes exhibit O2 and H2 generation efficiencies of 2.48 and 4.87 μmol min−1 respectively, at an applied potential of 1.58 V (vs. RHE) under the given time range, affording nearly 100% Faradaic yield during electrocatalytic water splitting to produce O2 and H2.

The facet-dependent photocatalytic performance of TiO2 nanocrystals has been extensively investigated due to their promising applications in renewable energy and environmental fields. However, the intrinsic distinction in the photocatalytic oxidation activities between the {001} and {101} facets of anatase TiO2 nanocrystals is still unclear and under debate. In this work, a simple photoelectrochemical method was employed to meaningfully quantify the intrinsic photocatalytic activities of {001} and {101} faceted TiO2 nanocrystal photoanodes. The effective surface areas of photoanodes with different facets were measured based on the monolayer adsorption of phthalic acid on TiO2 photoanode surface by an ex situ photoelectrochemical method, which were used to normalize the photocurrents obtained from different faceted photoanodes for meaningful comparison of their photocatalytic activities. The results demonstrated that the {001} facets of anatase TiO2 nanocrystals exhibited much better photocatalytic activity than that of {101} facets of anatase TiO2 nanocrystals toward photocatalytic oxidation of water and organic compounds with different functional groups (e.g., –OH, –CHO, –COOH). Furthermore, the instantaneous kinetic constants of photocatalytic oxidation of pre-adsorbates on {001} faceted anatase TiO2 photoanode are obviously greater than those obtained at {101} faceted anatase TiO2 photoanode, further verifying the higher photocatalytic activity of {001} facets of anatase TiO2. This work provided a facile photoelectrochemical method to quantitatively determine the photocatalytic oxidation activity of specific exposed crystal facets of a photocatalyst, which would be helpful to uncover and meaningfully compare the intrinsic photocatalytic activities of different exposed crystal facets of a photocatalyst.

Electrocatalysts with high catalytic activity and stability play a key role in promising renewable energy technologies, such as fuel cells and metal-air batteries. Here, we report the synthesis of Fe/Fe2O3 nanoparticles anchored on Fe-N-doped carbon nanosheets (Fe/Fe2O3@Fe-N-C) using shrimp shell-derived N-doped carbon nanodots as carbon and nitrogen sources in the presence of FeCl3 by a simple pyrolysis approach. Fe/Fe2O3@Fe-N-C obtained at a pyrolysis temperature of 1,000 °C (Fe/Fe2O3@Fe-N-C-1000) possessed a mesoporous structure and high surface area of 747.3 m2·g−1. As an electrocatalyst, Fe/Fe2O3@Fe-N-C-1000 exhibited bifunctional electrocatalytic activities toward the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) in alkaline media, comparable to that of commercial Pt/C for ORR and RuO2 for OER, respectively. The Zn-air battery test demonstrated that Fe/Fe2O3@Fe-N-C-1000 had a superior rechargeable performance and cycling stability as an air cathode material with an open circuit voltage of 1.47 V (vs. Ag/AgCl) and a power density of 193 mW·cm−2 at a current density of 220 mA·cm−2. These performances were better than other commercial catalysts with an open circuit voltage of 1.36 V and a power density of 173 mW·cm−2 at a current density of 220 mA·cm−2 (a mixture of commercial Pt/C and RuO2 with a mass ratio of 1:1 was used for the rechargeable Zn-air battery measurements). This work will be helpful to design and develop low-cost and abundant bifunctional oxygen electrocatalysts for future metal-air batteries.

Development of cheap, abundant and metal-free N-doped carbon materials as high efficiency oxygen reduction electrocatalysts is crucial for their practical applications in future fuel cell devices. Here, three-dimensional (3D) N-doped porous carbon (NPC) materials have been successfully developed by a simple template-assisted (e.g., SiO2 spheres) high temperature pyrolysis approach using shrimp-shell derived N-doped carbon nanodots (N-CNs) as carbon and nitrogen sources obtained through a facile hydrothermal method. The shrimp-shell derived N-CNs with a product yield of ∼ 5% possess rich surface O- and N-containing functional groups and small nanodot sizes of 1.5-5.0 nm, which are mixed with surface acidification treated SiO2 spheres with an average diameter of ∼ 200 nm in aqueous solution to form a N-CNs@SiO2 composite subjected to a thermal evaporation treatment. The resultant N-CNs@SiO2 composite is further thermally treated in a N2 atmosphere at different pyrolysis temperatures, followed by acid etching, to obtain 3D N-doped porous carbon (NPC) materials. As electrocatalysts for oxygen reduction reaction (ORR) in alkaline media, the experimental results demonstrate that 3D NPC obtained at 800 °C (NPC-800) with a surface area of 360.2 m(2) g(-1) exhibits the best ORR catalytic activity with an onset potential of -0.06 V, a half wave potential of -0.21 V and a large limiting current density of 5.3 mA cm(-2) (at -0.4 V, vs. Ag/AgCl) among all NPC materials investigated, comparable to that of the commercial Pt/C catalyst with an onset potential of -0.03 V, a half wave potential of -0.17 V and a limiting current density of 5.5 mA cm(-2) at -0.4 V. Such a 3D porous carbon ORR electrocatalyst also displays superior durability and high methanol tolerance in alkaline media, apparently better than the commercial Pt/C catalyst. The findings of this work would be valuable for the development of low-cost and abundant N-doped carbon materials from biomass as high performance metal-free electrocatalysts.

In this work, shrimp-shell derived N-doped carbon nanodots (N-CNs) as carbon and nitrogen sources are assembled into particle-like aggregates by a simple polymerization reaction of pyrrole in the presence of Fe3+ to form Fe containing N-CN/polypyrrole (PPY) composites (Fe–N-CN/PPy). The resulting composites are thermally treated by a facile pyrolysis approach under a N2 atmosphere to obtain an Fe,N-doped porous graphitic carbon (Fe-N-PGC) material. The results demonstrate that the pyrolytically converted carbon material at 800 °C (Fe-N-PGC-800) exhibits an approximately mesoporous structure with a pore size distribution centered at ∼1.97 nm and ∼2.8 nm and a surface area of 806.7 m2 g−1. As an electrocatalyst for oxygen reduction reaction (ORR) in alkaline media, Fe-N-PGC-800 shows superior ORR catalytic activity with an onset potential of −0.017 V and a limiting current density of 5.42 mA cm−2 (at −0.4 V, vs. Ag/AgCl), which is superior to that of commercial Pt/C catalysts (onset potential of −0.018 V and a limiting current density of 5.21 mA cm−2 at −0.4 V, vs. Ag/AgCl). Additionally, Fe-N-PGC-800 also exhibits good ORR activity in acidic media with an onset potential of 0.53 V and a limiting current density of 5.58 mA cm−2 (at 0.1 V, vs. Ag/AgCl), comparable to that of most reported Fe-based N-doped carbon electrocatalysts. An air cathode made from Fe-N-PGC-800 shows high performance and superior cycling durability in zinc–air batteries (gravimetric energy density of 752 Wh kg−1), comparable to that of commercial Pt/C-based batteries (gravimetric energy density of 774 Wh kg−1). This work demonstrates the feasibility of utilizing biomass as a starting material to fabricate Fe,N-doped carbon materials as high performance ORR electrocatalysts for practical application in ORR-relevant energy devices.

The capability of manipulating the interfacial electronic coupling is the key to achieving on-demand functionalities of catalysts. Herein, it is demonstrated that the electronic coupling of Fe2 N can be effectively regulated for hydrogen evolution reaction (HER) catalysis by vacancy-mediated orbital steering. Ex situ refined structural analysis reveals that the electronic and coordination states of Fe2 N can be well manipulated by nitrogen vacancies, which impressively exhibit strong correlation with the catalytic activities. Theoretical studies further indicate that the nitrogen vacancy can uniquely steer the orbital orientation of the active sites to tailor the electronic coupling and thus benefit the surface adsorption capability. This work sheds light on the understanding of the catalytic mechanism in real systems and could contribute to revolutionizing the current catalyst design for HER and beyond.

The epitaxial crystal quality of strontium aluminate (Sr3Al2O6) films under various Sr/Al ratios were systematically investigated by reactive molecular beam epitaxy. Efficient guiding rules for real-time optimization are summarized that a four-fold reconstructed reflection high-energy electron diffraction (RHEED) pattern and 4 periods of RHEED oscillations coinciding in the growth of one unit cell of Sr3Al2O6 is the key signature for the optimal growth condition. Following above rules, atomically smooth Sr3Al2O6 and freestanding SrTiO3 films with a full width at half maximum less than 0.03∘ (mainly limited by the substrates) were synthesized. The high-crystalline quality of freestanding SrTiO3 and atomically smooth interface between SrTiO3 film and Sr3Al2O6 were highlighted by the appearance of well-defined fringes from X-ray diffraction data and well-organized atomic distribution from electron microscopy. The epitaxial optimization of Sr3Al2O6 buffer layer with atomic flatness and high-crystalline quality will shed light on the synthesis of ultrathin freestanding oxide perovskite films, paving the way to the exploration of incorporating strongly correlated properties in conventional semiconductors for a generation of multifunctional electronic devices.