Charge transfer and vacancy engineering of Fe2O3 nanoparticle catalysts for highly selective N2 reduction towards NH3 synthesis.

The development of electrocatalysts for N2 reduction reaction (NRR) is significant for scalable and renewable NH3 synthesis, but calls for a technology innovation to overcome the specific problems of low efficiency and poor selectivity. Herein, we prepare a core-shell nanostructure by coating polypyrrole (PPy) onto sulfur-doped iron oxide nanoparticles (denoted as S-Fe2O3@PPy) as the highly selective and durable electrocatalysts for NRR under ambient conditions. Sulfur doping and PPy coating remarkably improve the charge transfer efficiency of S-Fe2O3@PPy, and the interactions between PPy and Fe2O3 nanoparticles produce abundant oxygen vacancies as active sites for NRR. This catalyst achieves an NH3 production rate of 22.1 µg h-1 mgcat-1 and a very-high Faradic efficiency of 24.6%, surpassing other Fe2O3 based NRR catalysts. Density functional theory calculations show that the S-coordinated iron site can successfully activate the N2 molecule and optimize the energy barrier during the reduction process, resulting in a small theoretical limiting potential.

Highly Selective N2 Electroreduction to NH3 Using a Boron-Vacancy-Rich Diatomic NbB Catalyst.

The ambient electrochemical N2 reduction reaction (NRR) is a future approach for the artificial NH3 synthesis to overcome the problems of high-energy consumption and environmental pollution by Haber-Bosch technology. However, the challenge of N2 activation on a catalyst surface and the competitive hydrogen evolution reaction make the current NRR unsatisfied. Herein, this work demonstrates that NbB2 nanoflakes (NFs) exhibit excellent selectivity and durability in NRR, which produces NH3 with a production rate of 30.5 µg h-1 mgcat -1 and a super-high Faraday efficiency (FE) of 40.2%. The high-selective NH3 production is attributed to the large amount of active B vacancies on the surface of NbB2 NFs. Density functional theory calculations suggest that the multiple atomic adsorption of N2 on both unsaturated Nb and B atoms results in a significantly stretched N2 molecule. The weakened NN triple bonds are easier to be broken for a biased NH3 production. The diatomic catalysis is a future approach for NRR as it shows a special N2 adsorption mode that can be well engineered.

In Situ Generation of Vertically Crossed P-Cu3Se2 Ultrathin Nanosheets Derived from Cu2S Nanorod Arrays for High-Performance Supercapacitors.

Transition-metal selenides (TMSs) have great potential in the synthesis of supercapacitor electrode materials due to their rich content and high specific capacity. However, the aggregation phenomenon of TMS materials in the process of charging and discharging will cause capacity attenuation, which seriously affects the service life and practical applications. Therefore, it is of great practical significance to design simple and efficient synthesis strategies to overcome these shortcomings. Hence, P-doped Cu3Se2 nanosheets are loaded on vertically aligned Cu2S nanorod arrays to synthesize CF/Cu2S@Cu3Se2/P nanocomposites with a unique core-shell heterostructure. Notably, the Cu2S precursors can be rapidly converted into Cu3Se2 nanorod arrays in situ in just 30 min at room temperature. The unique core-shell heterostructure effectively avoids the aggregation phenomenon, and the doped P elements further enhance the electrochemical properties of the electrode materials. Therefore, the as-prepared CF/Cu2S@Cu3Se2/P electrode exhibits a high areal capacitance of 5054 mF cm-2 (1099 C g-1) at 3 mA cm-2 and still retains 90.2% capacitance after 10 000 galvanostatic charge-discharge (GCD) cycles. The asymmetric supercapacitor (ASC) device assembled from synthetic CF/Cu2S@Cu3Se2/P and activated carbon (AC) possesses an energy density of 41.1 Wh kg-1 at a power density of 480.4 W kg-1. This work shows that the designed CF/Cu2S@Cu3Se2/P electrode has broad application prospects in the field of electrochemical energy storage.

Compression-tolerant supercapacitor based on NiCo2O4/Ti3C2Tx MXene/reduced graphene oxide composite aerogel with insights from density functional theory simulations.

Compression-tolerant electrodes are critical for developing next-generation wearable energy storage devices. However, most of previous studies on compressible electrodes focus on carbon-based materials, whereas metal-based materials such as spinel metal oxide with faradaic nature have been rarely studied due to their lack of compressibility. Herein, NiCo2O4 (NCO) microtubes assembled by ultrathin and mesoporous nanosheets, are deposited on/into Ti3C2Tx MXene/reduced graphene oxide aerogel (MGA), an intrinsically compressible host template with high conductivity and specific surface areas. The optimized NCO/MGA-300 sample shows a reversible compressive strain of 60% and a superior durability. Density functional theory (DFT) calculations reveal that the NCO/MGA-300 heterojunction has high electronic conductivity, fast electron transfer ability, and low adsorption energy for OH- ions. As a result, the NCO/MGA-300 electrode exhibits superb electrochemical performance in terms of its high gravimetric capacitance (1633F g-1 at 1 A g-1), rate performance (1492F g-1 at 10 A g-1), and remarkable cycling stability of 86.6% after 10,000 charge-discharging cycles. Moreover, an assembled asymmetric supercapacitor based on compressible NCO/MGA-300 shows stable electrochemical performances under different compressive strains (20%. 40% and 60%), or after 100 compression-release cycles. This research finding demonstrates the possibility of metal-based electrode for wearable devices with high energy storage capability and good compressibility.

Embedding of conductive Ag nanoparticles among honeycomb-like NiMn layered double hydroxide nanosheet arrays for ultra-high performance flexible supercapacitors.

Layered double hydroxides are considered promising electrode materials for the preparation of high-energy-density supercapacitors owing to their suitable microstructure and significant electrochemical properties. In this study, honeycomb-like NiMn-layered double-hydroxide (NiMn-LDH) nanosheet arrays with numerous electron/ion channels, a large number of active sites, considerable redox reversibility, and significant electrical conductivity were synthesized by combining Co2(OH)2CO3 nanoneedle arrays with NiMn-LDH nanosheet arrays and Ag nanoparticles on a carbon cloth (CC) substrate through a hydrothermal strategy (CC@Co2CH/NM-LDH-Ag). The fabricated CC@Co2CH/NM-LDH-Ag binder-free electrode exhibited a high specific capacitance of 10,976 mF cm-2 (3092F/g, 1391.4C g-1) at 2 mA cm-2 (1 A/g), and a high capacitance retention of 93.2 % after 10,000 cycles at a current density of 20 mA cm-2. In addition, a solid-state asymmetric supercapacitor (ASC) device assembled using CC@Co2CH/NM-LDH-Ag as the cathode possessed an ultrahigh energy density of 68.85 Wh kg-1 at a power density of 722.6 W kg-1, and two fabricated ASC units in series were able to power a multifunctional display for more than 30 min. Therefore, this study provides a new approach for the design and synthesis of high-performance flexible electrodes.

Ternary NiCeCo-Layered Double Hydroxides Grown on CuBr2@ZIF-67 Nanowire Arrays for High-Performance Supercapacitors.

Ternary layered double-hydroxide-based active compounds are regarded as ideal electrode materials for supercapacitors because of their unique structural characteristics and excellent electrochemical properties. Herein, an NiCeCo-layered double hydroxide with a core-shell structure grown on copper bromide nanowire arrays (CuBr2@NCC-LDH/CF) has been synthesized through a hydrothermal strategy and calcination process and utilized to fabricate a binder-free electrode. Due to the unique top-tangled structure and the complex assembly of different active components, the prepared hierarchical CuBr2@NCC-LDH/CF binder-free electrode exhibits an outstanding electrochemical performance, including a remarkable areal capacitance of 5460 mF cm-2 at 2 mA cm-2 and a capacitance retention of 88% at 50 mA cm-2 as well as a low internal resistance of 0.163 Ω. Moreover, an all-solid-state asymmetric supercapacitor (ASC) installed with CuBr2@NCC-LDH/CF and activated carbon electrodes shows a high energy density of 118 Wh kg-1 at a power density of 1013 W kg-1. Three assembled ASCs connected in series can operate a multifunctional display for over three and a half hours. Therefore, this innovative work provides new inspiration for the preparation of electrode materials for supercapacitors.

Origami and layered-shaped ZnNiFe-LDH synthesized on Cu(OH)2 nanorods array to enhance the energy storage capability.

The combination of layered nanorod arrays with unique core-shell structure and transition metal layered double hydroxide (LDH) is considered as a feasible solution to improve the electrochemical performances of capacitor electrode. In this study, layered ZnNiFe-LDH@Cu(OH)2/CF core-shell nanorod arrays, which consist of ultrathin ZnNiFe-LDHs nanosheet shells and ordered Cu(OH)2 nanorod inner cores, are successfully designed and fabricated by a typical hydrothermal way and a simple in situ oxidation reaction. The electrode prepared using ZnNiFe-LDH@Cu(OH)2/CF nanomaterial reveals an remarkable area capacitance of 6100 mF cm-2 at 3 mA cm-2 current density, which is excellently superior than those of ZnFe-LDH@Cu(OH)2/CF, NiFe-LDH@Cu(OH)2/CF, Cu(OH)2/CF and CF. Additionally, the capacitance retention remains as high as 83.4% after 5000 cycles and a very small Rs (0.567 Ω) can be observed. In addition, an asymmetric supercapacitor device is successfully fabricated employing ZnNiFe-LDH@Cu(OH)2/CF. Meanwhile, the ZnNiFe-LDH@Cu(OH)2/CF//AC device can achieve an energy density of 44 Wh kg-1 and a corresponding power density of 720 W kg-1 and possess the capability to light up a multi-function monitor for 33 min just using two ASC equipments connected in series. Therefore, the prepared ZnNiFe-LDH@Cu(OH)2/CF composite materials with unique structure has great application potential in energy storage devices.