Modified Co4N by B-doping for high-performance hybrid supercapacitors

Nitrogen-Doped CoP-Co2P-Supported Ru with Interconnected Channels through a Microwave Quasi-Solid Approach for Hydrogen Evolution Reaction over a Wide pH Range

Transition-metal phosphides (TMPs) have attracted extensive attention in energy-related fields, especially for electrocatalytic hydrogen evolution reaction (HER). However, it is imperative to develop a facile and time-consuming approach to prepare metal phosphides with satisfactory catalytic performance. Herein, nitrogen-doped CoP-Co2P decorated with Ru (Ru/N-CoP-Co2P) is synthesized (Ru/N-CoP-Co2P) through a hydrothermal route and following an ultrafast and simple microwave avenue within 20 s. The achieved Ru/N-CoP-Co2P possesses an interconnected porous morphology to expose abundant active sites and accelerate the mass transport. Moreover, N doping and Ru-supported decorated Ru/N-CoP-Co2P also play a key role in promoting the electrocatalytic activity. Therefore, the as-designed Ru/N-CoP-Co2P presents good catalytic performance for the HER in a wide pH range. Ru/N-CoP-Co2P merely needs overpotentials of 63, 100, and 65 mV to obtain 10 mA cm-2 in acidic, alkaline, and seawater electrolytes. This research provides a novel and efficient strategy for the synthesis of TMPs with highly efficient catalytic activity.

Analyzing the charge contributions of metal-organic framework derived nanosized cobalt nitride/carbon composites in asymmetrical supercapacitors

Metal-organic framework derived nanostructures have recently received research attention owing to their inherent porosity, stability, and structural tailorability. This work involves the conversion of zeolitic imidazolate frameworks (ZIFs) into cobalt nitride nanoparticles embedded within a porous carbon matrix (Co4N/C). The as-prepared composite shows great synergy by providing a high surface area and efficient charge transfer, showcasing outstanding electrochemical performance by providing a specific capacitance of 313 F g-1. Moreover, we meticulously conducted calculations to derive the most precise values for the surface contribution, a crucial aspect often overlooked in existing literature, thereby ensuring the reliability of our calculated measurements. Correct calculations of surface and diffusion charge contributions are necessary for evaluating the overall electrochemical performance of supercapacitors. For practical utility, we successfully assembled an asymmetrical supercapacitor employing the Co4N/carbon composite as the negative electrode that achieved an impressive energy density of 26.6 W h kg-1 at a power density of 0.36 kW kg-1. This study opens up new avenues for investigating the use of other metal nitride nanoparticles embedded in carbon structures for various energy storage applications.

Advanced three-dimensional hierarchical porousα-MnO2nanowires network toward enhanced supercapacitive performance

Hierarchicalα-MnO2nanowires with oxygen vacancies grown on carbon fiber have been synthesized by a simple hydrothermal method with the assistance of Ti4+ions. Ti4+ions play an important role in controlling the morphology and crystalline structure of MnO2. The morphology and structure of the as-synthesized MnO2could be tuned fromδ-MnO2nanosheets to hierarchicalα-MnO2nanowires with the help of Ti4+ions. Based on its fascinating properties, such as many oxygen vacancies, high specific surface area and the interconnected porous structure, theα-MnO2electrode delivers a high specific capacitance of 472 F g-1at a current density of 1 A g-1and the rate capability of 57.6% (from 1 to 16 A g-1). The assembled symmetric supercapacitor based onα-MnO2electrode exhibits remarkable performance with a high energy density of 44.5 Wh kg-1at a power density of 2.0 kW kg-1and good cyclic stability (92.6% after 10 000 cycles). This work will provide a reference for exploring and designing high-performance MnO2materials.

Special NaBH4 hydrolysis achieving multiple-surface-modifications promotes the high-throughput water oxidation of CoN nanowire arrays

Designing an excellent OER catalyst in an alkaline environment is severe yet essential for industrial H₂ application under the electrochemical technique. This study has achieved multiple modifications on CoN nanowires, the classic OER catalyst, via a facile room-temperature NaBH₄ spontaneous hydrolysis. This facile process simultaneously generates oxygen vacancies and robust BN species. It wraps hydrophilic BO_x motifs on the OER response CoN nanowires, producing OER active Co-N-B species, increasing active numbers and guaranteeing structural stability. It suggests that a low NaBH₄ concentration (0.1 mol L^-1) treatment endows CoN_NWAs/CC with excellent OER performance and robust structure, which can drive a current density of 50 mA cm^-2 with only 325 mV overpotentials with more than 24 hours' durability. Even, the catalyst can drive 1000 mA cm^-2 around 480 mV overpotential. This study allows a novel strategy for designing high-performance OER catalysts.

Rational Design of Porous Nanowall Arrays of Ultrafine Co4N Nanoparticles Confined in a La2O2CN2 Matrix on Carbon Cloth for a High-Performing Supercapacitor Electrode

Transition metal nitrides (TMNs) have received special concern as important energy storage materials, owing to their high conductibility, good mechanical strength, and superior corrosion resistance. However, their insufficient capacitance and poor cycling stability limit their practical applications for supercapacitors. Here, a novel three-dimensional (3D) self-supported integrated electrode consisted of porous nanowall arrays of ultrafine cobalt nitride (Co₄N) nanoparticles encapsulated in a lanthanum oxycyanamide (LOC) matrix on carbon cloth (Co₄N@LOC/CC) for outstanding electrochemical energy storage is rationally designed and fabricated. The 3D monolithic configuration of porous nanowall arrays facilitates the mass/charge transfer, the exposure of electroactive sites, and the enhancement of electrical conductivity. Meanwhile, the unique core-shell structure of Co₄N@LOC can prevent ultrafine Co₄N nanoparticles from sintering, agglomeration, and oxidation and promotes electron transfer dynamics during the redox reaction, meanwhile enhancing the stability of the electrode. Additionally, the synergy of Co₄N and LOC can result in an efficient electron/ion transport in the process of the charge-discharge. Because of these features, the Co₄N@LOC/CC electrode displays superior specific capacitance (895.6 mF cm^-2 or 613.4 F g^-1 at 1 mA cm^-2) and admirable cycling durability (87.9% capacitance reservation after 10 000 cycles), surpassing the majority of nitride-based electrodes reported thus far. Furthermore, after being assembled into an asymmetric supercapacitor using active carbon (AC) as an anode, the obtained Co₄N@LOC/CC//AC/CC device displays a high energy density of 41.7 Wh kg^-1 at the power density of 875.8 W kg^-1 with a high capacitance reservation of 87.6% after 5000 cycles at 2 mA cm^-2. This work offers an efficient approach of combining TMNs with rare earth compounds to enhance the capacitance and stability of TMNs for supercapacitor electrodes.

Improvement of nickel-cobalt-based supercapacitors energy storage performance by modification of elements

Hybrid supercapacitors have the advantages of fast charging and discharging and long service life, which are an efficient and practical energy storage device. Therefore, the design of hybrid supercapacitors is the focus of current research. In this paper, the silver modified spinel NiCo₂S₄ nanorods (Ag₂S-NiCo₂S₄/CF) are synthesized by an efficient and economical method, which has excellent electrochemical performance. The Ag₂S-NiCo₂S₄/CF shows a high specific capacity of 179.7 mAh g^-1 at current density of 1 A g^-1, and excellent rate capability (capacitance retention of ~87% at 20 A g^-1). The corresponding Ag₂S-NiCo₂S₄/CF//AC/CF hybrid supercapacitor is assembled by Ag₂S-NiCo₂S₄/CF as the positive electrode, which can provide an energy density of 35.978 Wh kg^-1 at a high-power density of 800 W kg^-1 and has significant cyclic stability (~80% of the initial capacitor after ~9600 cycles). Therefore, Ag₂S-NiCo₂S₄/CF material is a promising electrode material that can be applied to hybrid supercapacitors.