Spontaneous Internal Electric Field in Heterojunction Boosts Bifunctional Oxygen Electrocatalysts for Zinc–Air Batteries: Theory,Experiment, and Application

Heterojunctions are a promising class of materials for high-efficiency bifunctional oxygen electrocatalysts in both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). However, the conventional theories fail to explain why many catalysts behave differently in ORR and OER, despite a reversible path (^*O₂⇋^*OOH⇋^*O⇋^*OH). This study proposes the electron-/hole-rich catalytic center theory (e/h-CCT) to supplement the existing theories, it suggests that the Fermi level of catalysts determines the direction of electron transfer, which affects the direction of the oxidation/reduction reaction, and the density of states (DOS) near the Fermi level determines the accessibility for injecting electrons and holes. Additionally, heterojunctions with different Fermi levels form electron-/hole-rich catalytic centers near the Fermi levels to promote ORR/OER, respectively. To verify the universality of the e/h-CCT theory, this study reveals the randomly synthesized heterostructural Fe₃N-FeN_0.0324 (Fe_xN@PC with DFT calculations and electrochemical tests. The results show that the heterostructural F₃N-FeN_0.0324 facilitates the catalytic activities for ORR and OER simultaneously by forming an internal electron-/hole-rich interface. The rechargeable ZABs with Fe_xN@PC cathode display a high open circuit potential of 1.504 V, high power density of 223.67 mW cm⁻², high specific capacity of 766.20 mAh g⁻¹ at 5 mA cm⁻², and excellent stability for over 300 h.     

Mechanisms of High Coercivity in Ni/NiO Composite Films by Post Annealing

A coercivity as large as 2.4 kOe has been achieved in the Ni/NiO composite film after an annealing under a magnetic field of 10 kOe and an O2 partial pressure of 0.001 torr. The coercivity was attributed to the strong exchange coupling of Ni and NiO. Small grain size of Ni and NiO was observed after the post-annealing. The enhanced coercivity is probably associated with the domain wall pinning by local energy minima, the distribution of Ni and NiO, and the domain structure in the interface of Ni/NiO generated under the presence of the magnetic field during the post-annealing.     

Designed Formation of Double-Shelled Ni–Fe Layered-Double-Hydroxide Nanocages for Efficient Oxygen Evolution Reaction

Delicate design of nanostructures for oxygen-evolution electrocatalysts is an important strategy for accelerating the reaction kinetics of water splitting. In this work, Ni–Fe layered-double-hydroxide (LDH) nanocages with tunable shells are synthesized via a facile one-pot self-templating method. The number of shells can be precisely controlled by regulating the template etching at the interface. Benefiting from the double-shelled structure with large electroactive surface area and optimized chemical composition, the hierarchical Ni–Fe LDH nanocages exhibit appealing electrocatalytic activity for the oxygen evolution reaction in alkaline electrolyte. Particularly, double-shelled Ni–Fe LDH nanocages can achieve a current density of 20 mA cm⁻² at a low overpotential of 246 mV with excellent stability.     

Three-Dimensional Hierarchical Nanostructured Cu/Ni–Co Coating Electrode for Hydrogen Evolution Reaction in Alkaline Media

Nano-Micro Letters - In this work, three-dimensional hierarchical nickel–cobalt alloy coating for hydrogen evolution cathode was fabricated by electrodeposition processes. The coatings’...     

Electrodeposition and Characterization of Ni/Ti3Si（Al）C2 Composite Coatings

Pure nickel and Ni/Ti3Si(Al)C2 composite coatings were prepared by electrodeposition method from an additive-free nickel Watt’s bath and were characterized by X-ray diffraction, laser confocal microscopy and scanning electron microscopy. The e?ect of current and Ti3Si(Al)C2 concentration in the solution on the composition, grain size, preferred orientation and surface morphology of the electrodeposited coatings were investigated. (200)-oriented Ni coatings could be deposited at high current (62.5 mA), while (220)-oriented Ni coatings could be obtained at low current (25 mA). However, the presence of Ti3Si(Al)C2 particles disturbed the surface texture of Ni crystallites in the composite coatings. Based on the simulated morphology and the observed microstructure, the mechanisms for the change of preferred orientation and crystallite shapes in the presence of Ti3Si(Al)C2 particles were discussed. Moreover, microhardness and friction properties of pure nickel and Ni/Ti3Si(Al)C2 composite coatings were also compared.     

Interfacial Electronic Modulation of Dual-Monodispersed Pt–Ni3S2 as Efficacious Bi-Functional Electrocatalysts for Concurrent H2 Evolution and Methanol Selective Oxidation

Constructing the efficacious and applicable bifunctional electrocatalysts and establishing out the mechanisms of organic electro-oxidation by replacing anodic oxygen evolution reaction(OER) are critical to the development of electrochemicallydriven technologies for efficient hydrogen production and avoid CO₂ emission. Herein, the hetero-nanocrystals between monodispersed Pt(～ 2 nm) and Ni₃S₂(～ 9.6 nm) are constructed as active electrocatalysts through interfacial...     

Preparation of the YBCO/SmBiO3/NiO/Ni–W New Structure for Coated Conductors

A new structure basis of SmBiO₃ (SBO) potential buffer layer for low-cost coated conductors fabrication methods has been introduced in this paper, and studied with XRD, SEM and AFM analyses. It is found that highly in-plane and out-of-plane oriented, dense, smooth, and crack-free SBO buffer layer has been prepared on NiO-buffered Ni-5 %W (NiW) tapes via a CSD route. YBCO epitaxial film was obtained on CSD-YBCO/CSD-SmBiO₃/SOE-NiO/NiW by using F-free CSD method which shows a new route to search for SmBiO₃ new buffer layer material for coated conductors.     

Flexible Co–Mo–N/Au Electrodes with a Hierarchical Nanoporous Architecture as Highly Efficient Electrocatalysts for Oxygen Evolution Reaction

Designing highly active and robust electrocatalysts for oxygen evolution reaction (OER) is crucial for many renewable energy storage and conversion devices. Here, self-supported monolithic hybrid electrodes that are composed of bimetallic cobalt–molybdenum nitride nanosheets vertically aligned on 3D and bicontinuous nanoporous gold (NP Au/CoMoN_x) are reported as highly efficient electrocatalysts to boost the sluggish reaction kinetics of water oxidation in alkaline media. By virtue of the constituent CoMoN_x nanosheets having large accessible CoMoO_x surface with remarkably enhanced electrocatalytic activity and the nanoporous Au skeleton facilitating electron transfer and mass transport, the NP Au/CoMoN_x electrode exhibits superior OER electrocatalysis in 1 m KOH, with low onset overpotential (166 mV) and Tafel slope (46 mV dec⁻¹). It only takes a low overpotential of 370 mV to reach ultrahigh current density of 1156 mA cm⁻², ≈140-fold higher than free CoMoN_x nanosheets. The electrocatalytic performance makes it an attractive candidate as the OER catalyst in the water electrolysis.     

Ultra-Low Pt Doping and Pt–Ni Pair Sites in Amorphous/Crystalline Interfacial Electrocatalyst Enable Efficient Alkaline Hydrogen Evolution

Noble metal doping can achieve an increase in mass activity (MA) without sacrificing catalysis efficiency and stability, so that alkaline hydrogen evolution reaction (HER) performance of the catalyst can be optimized to the maximum degree. However, its excessively large ionic radius makes it difficult to achieve either interstitial doping or substitutional doping under mild conditions. Herein, a hierarchical nanostructured electrocatalyst with enriched amorphous/crystalline interfaces for high-efficiency alkaline HER is reported, which is composed of amorphous/crystalline (Co, Ni)₁₁(HPO₃)₈(OH)₆ homogeneous hierarchical structure with an ultra-low doped Pt (Pt-a/c-NiHPi). Benefiting from the structural flexibility of the amorphous component, extremely low Pt (0.21 wt.%, totally 3.31 µg Pt on 1 cm⁻² NF) are stably doped on it via a simple two-phase hydrothermal method. The DFT calculations show that due to the strongly electron transfer between the crystalline/amorphous components at the interfaces, electrons finally concentrate toward Pt and Ni in the amorphous components, thus the electrocatalyst has near-optimal energy barriers and adsorption energy for H₂O^* and H^*. With the above benefits, the obtained catalyst exhibits an exceptionally high MA (39.1 mA µg⁻¹_Pt) at 70 mV, which is almost the highest level among the reported Pt-based electrocatalysts for alkaline HER.     

Synergistic Modulation of Electronic Interaction to Enhance Intrinsic Activity and Conductivity of Fe–Co–Ni Hydroxide Nanotube for Highly Efficient Oxygen Evolution Electrocatalyst

The large-scale hydrogen production and application through electrocatalytic water splitting depends crucially on the development of highly efficient, cost-effective electrocatalysts for oxygen evolution reaction (OER), which, however, remains challenging. Here, a new electrocatalyst of trimetallic Fe–Co–Ni hydroxide (denoted as FeCoNiO_xH_y) with a nanotubular structure is developed through an enhanced Kirkendall process under applied potential. The FeCoNiO_xH_y features synergistic electronic interaction between Fe, Co, and Ni, which not only notably increases the intrinsic OER activity of FeCoNiO_xH_y by facilitating the formation of *OOH intermediate, but also substantially improves the intrinsic conductivity of FeCoNiO_xH_y to facilitate charge transfer and activate catalytic sites through electrocatalyst by promoting the formation of abundant Co³⁺. Therefore, FeCoNiO_xH_y delivers remarkably accelerated OER kinetics and superior apparent activity, indicated by an ultra-low overpotential potential of 257 mV at a high current density of 200 mA cm⁻². This work is of fundamental and practical significance for synergistic catalysis related to advanced energy conversion materials and technologies.     

Band Engineering and Morphology Control of Oxygen‑Incorporated Graphitic Carbon Nitride Porous Nanosheets for Highly Efficient Photocatalytic Hydrogen Evolution

Graphitic carbon nitride(g-C3N4)-based photocatalysts have shown great potential in the splitting of water.However,the intrinsic drawbacks of g-C3N4,such as low surface area,poor diffusion,and charge separation efficiency,remain as the bottleneck to achieve highly efficient hydrogen evolution.Here,a hollow oxygen-incorporated g-C3N4 nanosheet(OCN)with an improved surface area of 148.5 m2 g^−1 is fabricated by the multiple thermal treatments under the N2/O2 atmosphere,wherein the C–O bonds are formed through two ways of physical adsorption and doping.The physical characterization and theoretical calculation indicate that the O-adsorption can promote the generation of defects,leading to the formation of hollow morphology,while the O-doping results in reduced band gap of g-C3N4.The optimized OCN shows an excellent photocatalytic hydrogen evolution activity of 3519.6μmol g^−1 h^−1 for~20 h,which is over four times higher than that of g-C3N4(850.1μmol g^−1 h^−1)and outperforms most of the reported g-C3N4 catalysts.     

Evolution of Magnetocaloric Behavior in Oxygen Deficient La2/3Ba1/3MnO3−δ Manganites

Effects of oxygen deficiency on the thermomagnetic properties of La_2/3Ba_1/3MnO_3?δ polycrystalline perovskites have been predicted. By the help of the phenomenological model, the temperature dependences of the magnetization for La_2/3Ba_1/3MnO_3?δ with δ=0.0, 0.02, 0.05, 0.08, and 0.1 upon 1 T magnetic field were simulated. The behavior of the temperature dependent magnetocaloric effect, in the vicinity of magnetic phase transitions, was investigated. The magnetic entropy change, specific heat, and adiabatic temperature change for several δ were obtained. The values of maximum magnetic entropy change, full-width at half-maximum, and relative cooling power, in 1 T magnetic field variation, were calculated. As the oxygen content increases, the magnetocaloric effect of La_2/3Ba_1/3MnO_3?δ , decreases and shifts to room temperature. The results obtained show a strong dependence on the oxygen deficiency of the materials. The magnetocaloric effect of these materials is large and tunable, suggesting a possible technical application of the materials at moderate magnetic fields near room temperature. It is shown that for La_2/3Ba_1/3MnO_3?δ , the magnetic entropy change and adiabatic temperature change follows a master curve behavior.     

NbCl5 and CrCl3 catalysts effect on synthesis and hydrogen storage performance of Mg–Ni–NiO composites

Two kinds of novel materials, Mg–1·6 mol%Ni–0·4 mol%NiO–2 mol%MCl (MCl = NbCl ₅ , CrCl ₃ ), along with Mg–1·6 mol%Ni–0·4 mol%NiO for comparison, were examined for their potential use in hydrogen storage applications, having been fabricated via cryomilling. The effects of NbCl ₅ and CrCl ₃ on hydrogen storage performance were investigated. A microstructure analysis showed that besides the main Mg and Ni phases, NiO and Mg ₂ Ni phases were present in all samples. MgCl ₂ was only found in halide-doped samples and NbO was only found in NbCl ₅ -doped samples after ball milling. The particle size decreased significantly after 7 h of cryomilling. MgH ₂ , Mg ₂ NiH ₄ and Mg ₂ NiH_0·3 were present in all the samples, while NbH ₂ was only observed in the NbCl ₅ -doped sample afterabsorption. The NbCl ₅ -containing composite exhibited a low onset absorption temperature of 323 K, which was 10 K lower than that of the no-halide doped catalyst. It absorbed 5·32 wt% of hydrogen in 370 s at 623 K under 4 MPa hydrogen pressure and can absorb 90% of its full hydrogen capacity in 50 s. Having an onset desorption temperature of 483 K in vacuum, the NbCl ₅ -containing composite desorbed hydrogen faster than the no-halide doped sample. The hydriding–dehydriding kinetics performance of the CrCl ₃ -doped sample did not improve, but it did exhibit a lower onset desorption temperature of 543 K under 0·1 MPa, which was 20 K lower than that of the no-halide doped sample. NbO, NiO and NbH ₂ played important roles in improving absorption and desorption performances.     

Tensile and fatigue behaviour of Ni–Ni3Si eutectic in situ composites

A Ni–Ni₃Si composite was fabricated via a eutectic reaction (Ni–Ni₃Si) using a rapidly cooled directional solidification technique at a solidification rate of 40?μm?s^?1. The composite consisted of approximately 62.2% Ni–Si solid solution and 37.8% Ni–Ni₃Si eutectic phase in volume. Four-point bend fatigue tests were carried out on the composite. The fatigue strength of the alloy was measured to be 520?MPa (maximum cyclic stress). It was found that the fatigue cracks were preferably initiated in the Ni–Ni₃Si eutectic phase, and that the Ni matrix was fractured in a cleavage fashion. It was probably attributed to the high level of supersaturated Si in the Ni matrix, which led to inducing the embrittlement of the Ni matrix.     

Preparation and Optical Properties of Glasses in the TeO2–MoO3–Pr2O3 System

Inorganic Materials - We have studied glass formation and located the boundaries of the glass-forming region in the TeO2–MoO3–Pr2O3 system. The results demonstrate the possibility of...     

Nanostructured and Nonsymmetrical NiO–SDC/SDC Composite Anode Performance via a Microwave-Assisted Route for Intermediate-Temperature Solid Oxide Fuel Cells

This work investigates the electrical properties of NiO–SDC/SDC anode sintered at approximately 1200°C for 1 h via the microwave method. Nanopowders Sm_0.2Ce_0.8O_1.9 (SDC—samaria-doped ceria) and NiO were mixed using a high-energy ball mill and subsequently co-pressed at three different compaction pressures of 200, 300, and 400 MPa. This study determines the effect of compaction pressure on the electrochemical performance of Ni–SDC/SDC anode, with no binder used between layers. The electrical behavior of the prepared anode was studied via electrochemical impedance spectroscopy in controlled atmospheres, operating at high temperatures (600–800°C). The results indicate that decreasing the compaction pressure and increasing the operating temperature lead to a high electrochemical performance of the nonsymmetrical NiO–SDC/SDC anode. The mechanism for manufacturing NiO–SDC/SDC involves ball milling, dry pressing, and microwave furnace sintering processes.     

Interface kinetics of combustion–diffusion bonding of Ni3Al/Ni and TiAl/Ti under direct current field

The bonding of TiB₂–Ni and TiC–Ni composites to, respectively, Ni and Ti substrates was investigated by field-activated and pressure-assisted synthesis. Bonding and in situ synthesis was utilized to prepare (TiB₂)_pNi/Ni₃Al/Ni (Composition 1) and (TiC)_pNi/TiAl/Ti (Composition 2) joining structures. The effect of applied current on the kinetics of formation of the diffusion layer between the substrate (Ni or Ti) and the respective intermetallic layer (Ni₃Al or TiAl) was investigated. For both compositions, the current was shown to have a marked influence of the activation energy of formation of the layer, decreasing it by as much as 31 %. Calculations of adiabatic temperatures suggest a possible current contribution to interdiffusion, as has been reported previously.     

Preferentially Engineering FeN4 Edge Sites onto Graphitic Nanosheets for Highly Active and Durable Oxygen Electrocatalysis in Rechargeable Zn–Air Batteries

Single-atom FeN₄ sites at the edges of carbon substrates are considered more active for oxygen electrocatalysis than those in plane; however, the conventional high-temperature pyrolysis process does not allow for precisely engineering the location of the active site down to atomic level. Enlightened by theoretical prediction, herein, a self-sacrificed templating approach is developed to obtain edge-enriched FeN₄ sites integrated in the highly graphitic nanosheet architecture. The in situ formed Fe clusters are intentionally introduced to catalyze the growth of graphitic carbon, induce porous structure formation, and most importantly, facilitate the preferential anchoring of FeN₄ to its close approximation. Due to these attributes, the as-resulted catalyst (denoted as Fe/N-G-SAC) demonstrates unprecedented catalytic activity and stability for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) by showing an impressive half-wave potential of 0.89 V for the ORR and a small overpotential of 370 mV at 10 mA cm⁻² for the OER. Moreover, the Fe/N-G-SAC cathode displays encouraging performance in a rechargeable Zn–air battery prototype with a low charge–discharge voltage gap of 0.78 V and long-term cyclability for over 240 cycles, outperforming the noble metal benchmarks.