Hierarchical N-Doped Porous Carbons for Zn–Air Batteries and Supercapacitors

Nitrogen-doped carbon materials with a large specific surface area,high conductivity,and adjustable microstructures have many prospects for energy-related applications.This is especially true for N-doped nanocarbons used in the electrocatalytic oxygen reduction reaction(ORR)and supercapacitors.Here,we report a low-cost,environmentally friendly,large-scale mechanochemical method of preparing N-doped porous carbons(NPCs)with hierarchical micro-mesopores and a large surface area via ball-milling polymerization followed by pyrolysis.The optimized NPC prepared at 1000°C(NPC-1000)offers excellent ORR activity with an onset potential(Eonset)and half-wave potential(E1/2)of 0.9 and 0.82 V,respectively(vs.a reversible hydrogen electrode),which are only approximately 30 mV lower than that of Pt/C.The rechargeable Zn–air battery assembled using NPC-1000 and the NiFe-layered double hydroxide as bifunctional ORR and oxygen evolution reaction electrodes offered superior cycling stability and comparable discharge performance to RuO2 and Pt/C.Moreover,the supercapacitor electrode equipped with NPC prepared at 800℃ exhibited a high specific capacity(431 F g^−1 at 10 mV s^−1),outstanding rate,performance,and excellent cycling stability in an aqueous 6-M KOH solution.This work demonstrates the potential of the mechanochemical preparation method of porous carbons,which are important for energy conversion and storage.     

Hierarchical Carbon Microtube@Nanotube Core-Shell Structure for High-Performance Oxygen Electrocatalysis and Zn-Air Battery

Zinc-air batteries(ZABs)hold tremendous promise for clean and efficient energy storage with the merits of high theoretical energy density and environmental friendliness.However,the performance of practical ZABs is still unsatisfactory because of the inevitably decreased activity of electrocatalysts when assembly into a thick electrode with high mass loading.Herein,we report a hierarchical electrocatalyst based on carbon microtube@nanotube core-shell nanostructure(CMT@CNT),which demonstrates superior electrocatalytic activity for oxygen reduction reaction and oxygen evolution reaction with a small potential gap of 0.678 V.Remarkably,when being employed as air-cathode in ZAB,the CMT@CNT presents an excellent performance with a high power density(160.6 mW cm^−2),specific capacity(781.7 mAhgZn^−1)as well as long cycle stability(117 h,351 cycles).Moreover,the ZAB performance of CMT@CNT is maintained well even under high mass loading(3 mg cm−2,three times as much as traditional usage),which could afford high power density and energy density for advanced electronic equipment.We believe that this work is promising for the rational design of hierarchical structured electrocatalysts for advanced metal-air batteries.     

Mott–Schottky Effect in Core–Shell W@WxC Heterostructure: Boosting Both Electronic/Ionic Kinetics for Lithium Storage

The dynamics rate of traditional metal carbides (TMCs) is relatively slow, severely limiting its fast-charging capacity for lithium-ion batteries (LIBs). Herein, the core–shell W@W_xC heterostructure is developed to form Mott–Schottky heterostructure, thereby simultaneously accelerating the electronic and ionic transport kinetics during the charging/discharging process. The W nanoparticles are partially reduced into W_xC to form a particular core–shell structure with abundant heterogeneous interfaces. Benefiting from the Mott–Schottky effect, the electrons at the metal/semiconductor heterointerface can migrate spontaneously to realize an equal work function on both sides. In addition, the independent nanoparticle as well as the unique core–shell structure facilitate the ionic diffusion kinetics. As expected, the W@W_xC electrode exhibits excellent electrochemical stability for LIBs, whose capacity can be maintained at 173.8 mA h g⁻¹ after 1600 cycles at a high current density of 5 A g⁻¹. When assembled into a full cell, it can achieve an energy density of 360.2 Wh kg⁻¹. This work presents a new avenue to promote the electronic and ionic kinetics for LIBs anodes by constructing the unique Mott–Schottky heterostructure.     

Influence of Additives on Performance of Polypyrrole–Carbon Nanotube Supercapacitors

Polypyrrole (PP) and composite PP–multiwalled carbon nanotube (MWNT) materials were prepared for supercapacitors (SC) using new dopants for PP. The MWNT dispersion was achieved using advanced dispersants. The 36 mg cm^?2 PP electrochemical electrodes showed a capacitance of 6.3 F cm^?2 at 2 mV s^?1 scan rate. PP–MWNT composites showed enhanced capacitance for high charge–discharge rates and large electrode mass with enhanced cyclic stability. The mechanisms of MWNT dispersion and composite microstructure formation were discussed. Capacitance measurements provided new insight into the effect of additives on the characteristics of electrodes and cells. The SC cells have been manufactured, which showed promising performance for application in energy storage systems.     

Template-Free Synthesis of Phosphorus-Doped g-C3N4 Micro-Tubes with Hierarchical Core–Shell Structure for High-Efficient Visible Light Responsive Catalysis

This work reports a new form of tubular g-C₃N₄ that is featured with a hierarchical core–shell structure introduced with phosphorous elements and nitrogen vacancies. The core is self-arranged with randomly stacked g-C₃N₄ ultra-thin nanosheets along the axial direction. This unique structure significantly benefits electron/hole separation and visible-light harvesting. A superior performance for the photodegradation of rhodamine B and tetracycline hydrochloride is demonstrated under low intensity visible light. This photocatalyst also exhibits an excellent hydrogen evolution rate (3631 µmol h⁻¹g⁻¹) under visible light. Realizing this structure just requires the introduction of phytic acid into the solution of melamine and urea during hydrothermal treatment. In this complex system, phytic acid plays as the electron donor to stabilize melamine/cyanuric acid precursor via coordination interaction. Calcination at 550 °C directly renders the transformation of precursor into such hierarchical structure. This process is facile and shows the strong potential toward mass production for real applications.     

Core–Shell Tandem Catalysis Coupled with Interface Engineering For High-Performance Room-Temperature Na–S Batteries

The sluggish redox kinetics and shuttle effect seriously impede the large application of room-temperature sodium–sulfur (RT Na–S) batteries. Designing effective catalysts into cathode material is a promising approach to overcome the above issues. However, considering the multistep and multiphase transformations of sulfur redox process, it is impractical to achieve the effective catalysis of the entire S₈→Na₂S_x→Na₂S conversion through applying a single catalyst. Herein, this work fabricates a nitrogen-doped core–shell carbon nanosphere integrated with two different catalysts (ZnS-NC@Ni-N₄), where isolated Ni–N₄ sites and ZnS nanocrystals are distributed in the shell and core, respectively. ZnS nanocrystals ensure the rapid reduction of S₈ into Na₂S_x (4 < x ≤ 8), while Ni–N₄ sites realize the efficient conversion of Na₂S_x into Na₂S, bridged by the diffusion of Na₂S_x from the core to shell. Besides, Ni–N₄ sites on the shell can also induce an inorganic-rich cathode–electrolyte interface (CEI) on ZnS-NC@Ni-N₄ to further inhibit the shuttle effect. As a result, ZnS-NC@Ni-N₄/S cathode exhibits an excellent rate-performance (650 mAh g⁻¹ at 5 A g⁻¹) and ultralong cycling stability for 2000 cycles with a low capacity-decay rate of 0.011% per cycle. This work will guide the rational design of multicatalysts for high-performance RT Na–S batteries.     

Reconfiguring the Electronic Structure of Heteroatom Doped Carbon Supported Bimetallic Oxide@Metal Sulfide Core–Shell Heterostructure via In Situ Nb Incorporation toward Extrinsic Pseudocapacitor

High-energy-density battery-type materials have sparked considerable interest as supercapacitors electrode; however, their sluggish charge kinetics limits utilization of redox-active sites, resulting in poor electrochemical performance. Here, the unique core–shell architecture of metal organic framework derived N–S codoped carbon@Co_xS_y micropetals decorated with Nb-incorporated cobalt molybdate nanosheets (Nb-CMO₄@C_xS_yNC) is demonstrated. Coordination bonding across interfaces and π–π stacking interactions between CMO₄@C_xS_y and N and, S–C can prevent volume expansion during cycling. Density functional theory analysis reveals that the excellent interlayer and the interparticle conductivity imparted by Nb doping in heteroatoms synergistically alter the electronic states and offer more accessible species, leading to increased electrical conductivity with lower band gaps. Consequently, the optimized electrode has a high specific capacity of 276.3 mAh g⁻¹ at 1 A g⁻¹ and retains 98.7% of its capacity after 10 000 charge–discharge cycles. A flexible quasi-solid-state SC with a layer-by-layer deposited reduced graphene oxide /Ti₃C₂T_X anode achieves a specific energy of 75.5 Wh kg⁻¹ (volumetric energy of 1.58 mWh cm⁻³) at a specific power of 1.875 kWh kg⁻¹ with 96.2% capacity retention over 10 000 charge–discharge cycles.     

Enriched Fe Doped on Amorphous Shell Enable Crystalline@Amorphous Core–Shell Nanorod Highly Efficient Electrochemical Water Oxidation

The rational design of efficient and cost-effective electrocatalysts for oxygen evolution reaction (OER) with sluggish kinetics, is imperative to diverse clean energy technologies. The performance of electrocatalyst is usually governed by the number of active sites on the surface. Crystalline/amorphous heterostructure has exhibited unique properties and opens new paradigms toward designing electrocatalysts with abundant active sites for improved performance. Hence, Fe doped Ni–Co phosphite (Fe-NiCoHPi) electrocatalyst with cauliflower-like structure, comprising crystalline@amorphous core–shell nanorod, is reported. The experiments uncover that Fe is enriched in the amorphous shell due to the flexibility of the amorphous component. Further density functional theory calculations indicate that the strong electronic interaction between the enriched Fe in the amorphous shell and crystalline core host at the core–shell interface, leads to balanced binding energies of OER intermediates, which is the origin of the catalyst-activity. Eventually, the Fe-NiCoHPi exhibits remarkable activity, with low overpotentials of only 206 and 257 mV at current density of 15 and 100 mA cm⁻². Unceasing durability over 90 h is achieved, which is superior to the effective phosphate electrocatalysts. Although the applications at high current remain challenges , this work provides an approach for designing advanced OER electrocatalysts for sustainable energy devices.     

Yolk–Shell Cu2O@CuO-decorated RGO for High-Performance Lithium-Ion Battery Anode

Based on the great advantages of an inner hollow structure and excellent solid counterpart capacity, complex hierarchical structures have been widely used as electrodes for lithium-ion batteries. Herein, hierarchical yolk–shell Cu₂O@Cu O-decorated RGO(YSRs) was designed and synthesized via a multistep approach. Octahedron-like Cu₂O-decorated RGO was firstly produced, in which GO was reduced slightly while cuprous oxide was synthesized.Subsequently, the controlled oxidation ...     

Gradient-Concentration Design of Stable Core–Shell Nanostructure for Acidic Oxygen Reduction Electrocatalysis

Manipulating the surface structure of electrocatalysts at the atomic level is of primary importance to simultaneously achieve the activity and stability dual-criteria in oxygen reduction reaction (ORR) for proton exchange membrane fuel cells. Here, a durable acidic ORR electrocatalyst with the “defective-armored” structure of Pt shell and Pt–Ni core nanoparticle decorated on graphene (Pt–Ni@Pt_D/G) using a facile and controllable galvanic replacement reaction to generate gradient distribution of Pt–Ni composition from surface to interior, followed by a partial dealloying approach, leaching the minor nickel atoms on the surface to generate defective Pt skeleton shell, is reported. The Pt–Ni@Pt_D/G catalyst shows impressive performance for ORR in acidic (0.1 m HClO₄) electrolyte, with a high mass activity of threefold higher than that of Pt/C catalyst owing to the tuned electronic structure of locally concave Pt surface sites through synergetic contributions of Pt–Ni core and defective Pt shell. More importantly, the electrochemically active surface areas still retain 96% after 20 000 potential cycles, attributing to the Pt atomic shell acting as the protective “armor” to prevent interior Ni atoms from further dissolution during the long-term operation.     

Synthesis of Palladium-Based Crystalline@Amorphous Core–Shell Nanoplates for Highly Efficient Ethanol Oxidation

Phase engineering of nanomaterials (PEN) offers a promising route to rationally tune the physicochemical properties of nanomaterials and further enhance their performance in various applications. However, it remains a great challenge to construct well-defined crystalline@amorphous core–shell heterostructured nanomaterials with the same chemical components. Herein, the synthesis of binary (Pd-P) crystalline@amorphous heterostructured nanoplates using Cu_3−χP nanoplates as templates, via cation exchange, is reported. The obtained nanoplate possesses a crystalline core and an amorphous shell with the same elemental components, referred to as c-Pd-P@a-Pd-P. Moreover, the obtained c-Pd-P@a-Pd-P nanoplates can serve as templates to be further alloyed with Ni, forming ternary (Pd-Ni-P) crystalline@amorphous heterostructured nanoplates, referred to as c-Pd-Ni-P@a-Pd-Ni-P. The atomic content of Ni in the c-Pd-Ni-P@a-Pd-Ni-P nanoplates can be tuned in the range from 9.47 to 38.61 at%. When used as a catalyst, the c-Pd-Ni-P@a-Pd-Ni-P nanoplates with 9.47 at% Ni exhibit excellent electrocatalytic activity toward ethanol oxidation, showing a high mass current density up to 3.05 A mg_Pd⁻¹, which is 4.5 times that of the commercial Pd/C catalyst (0.68 A mg_Pd⁻¹).     

Shedding Light on the Role of Misfit Strain in Controlling Core–Shell Nanocrystals

Heteroepitaxial modification of nanomaterials has become a powerful means to create novel functionalities for various applications. One of the most elementary factors in heteroepitaxial nanostructures is the misfit strain arising from mismatched lattices of the constituent parts. Misfit strain not only dictates epitaxy kinetics for diversifying nanocrystal morphologies but also provides rational control over materials properties. In recent years, advances in chemical synthesis along with the rapid development of electron microscopy and X-ray diffraction techniques have enabled a substantial understanding of strain-related processes, which offers theoretical foundation and experimental guidance for researchers to refine heteroepitaxial nanostructures and their properties. Herein, recent investigations on heterogeneous core–shell nanocrystals containing misfit strains are summarized, with a focus on the mechanistic understanding of strain and strain-induced effects such as tuning the epitaxial habit, modulating the optical emission, and enhancing the catalytic activity and magnetic coercivity.     

Asymmetric Air Cathode Design for Enhanced Interfacial Electrocatalytic Reactions in High-Performance Zinc–Air Batteries

The rechargeable zinc–air battery (ZAB) is a promising energy storage technology owing to its high energy density and safe aqueous electrolyte, but there is a significant performance bottleneck. Generally, cathode reactions only occur at multiphase interfaces, where the electrocatalytic active sites can participate in redox reactions effectively. In the conventional air cathode, the 2D multiphase interface on the surface of the gas diffusion layer (GDL) inevitably results in an insufficient amount of active sites and poor interfacial contact, leading to sluggish reaction kinetics. To address this problem, a 3D multiphase interface strategy is proposed to extend the reactive interface into the interior of the GDL. Based on this concept, an asymmetric air cathode is designed to increase the accessible active sites, accelerate mass transfer, and generate a dynamically stabilized reactive interface. With a NiFe layered-double-hydroxide electrocatalyst, ZABs based on the asymmetric cathode deliver a small charge/discharge voltage gap (0.81 V at 5.0 mA cm⁻²), a high power density, and a stable cyclability (over 2000 cycles). This 3D reactive interface strategy provides a feasible method for enhancing the air cathode kinetics and further enlightens electrode designs for energy devices involving multiphase electrochemical reactions.     

1T-WS2 Nanosheet-Modified Biomass Carbon as Sulfur Host for High-Performance Lithium–Sulfur Batteries

The sluggish sulfur reaction kinetics and fast capacity attenuation still pose great challenges to lithium–sulfur (Li–S) batteries. Herein, tubular carbonl (HPOC) is obtained by carbonization of the cattail fiber. 1T-WS₂@HPOC is prepared by solvothermal method, and their sulfur composite, 1T-WS₂@HPOC/S and HPOC/S as sulfur host composite, is obtained by sulfur melting. The composite materials are characterized by scanning electron microscopy, X-ray diffraction, thermogravimetry, X-ray photoelectron spectroscopy, etc. Results show that 1T-WS₂ grows uniformly on the HPOC substrate and has abundant active sites, which can effectively improve the physicochemical adsorption capacity of S-fixation (76 wt%) and polysulfide. Battery assembly and electrochemical performance tests are conducted for the HPOC/S and 1T-WS₂@HPOC/S composites. Results show that the initial discharge capacity of the 1T-WS₂@HPOC/S positive electrode is 1272 mAh g⁻¹ at 0.1 C, higher than the HPOC/S positive electrode (1025 mAh g⁻¹). 1T-WS₂@HPOC/S maintains a discharge capacity of 695 mAh g⁻¹ after 500 cycles at 0.5 C, with a capacity decay rate of only 0.054% per cycle. With a discharge capacity of 504 mAh g⁻¹ after 400 cycles at 1 C, the Coulomb efficiency is 98.9%. The 1T-WS₂@HPOC/S composites with unique structure and excellent electrochemical performance have broad application prospects in the field of Li–S batteries.