Cobalt-modified crystalline carbon nitride homojunction with enhanced interfacial charge separation for photocatalytic pure water splitting

Photocatalytic hydrogen production in pure water without oxygen precipitation is highly effective owing to the minimal efficiency of water oxidation for oxygen generation and the complexity of the reaction, yet it presents a significant hurdle. Here, we report the preparation of crystalline carbon nitride (CCN) homojunction-anchored Co atoms using the molten salt and reflux method. Our findings indicate that elevated temperature during ionothermal synthesis promotes the phase transition of poly(heptazine) imides (PHI) to poly(triazine) imides (PTI), and the homogeneous junction formed in this process promotes exciton dissociation as well as carrier migration through the built-in electric field formed by the semi-coherent interface. During water splitting, the Co atom on CCN can modulate the generation of H2O2 and insitu decomposition to produce •OH. Consequently, the refined Co-modified crystalline carbon nitride homojunction exhibited an impressive hydrogen production rate of 425.81 μmol g-1 h-1 under visible light (λ > 400 nm), which provides new ideas for a green and clean process of coupled photocatalytic hydrogen production.

Preoxidation Assisted Alkali Activation Constructs Polyacrylonitrile-Based Porous Carbon for Supercapacitors

The porous structural tailoring of polyacrylonitrile-based carbon materials is the key to maximize capacitive performance. Herein, hierarchical porous carbons (HPC) with high specific surface area and controllable porosity are synthesized by preoxidation assisted alkali activation strategy using polyacrylonitrile as the precursor. The results show that high preoxidation temperature is beneficial to increase the specific surface area and pore volume of HPC. The optimized HPC-300 has a high BET specific surface area of 3161 m2 g-1, a micropore volume of 1.45 cm3 g-1, and an AD/AG of 3.56. Electrochemical test shows that the specific capacitances of HPC-300 in 6 M KOH electrolyte at 1 A g-1 and 10 A g-1 are 314.1 F g-1 and 213.0 F g-1, respectively, with a capacitance retention of 67.8 %. The assembled supercapacitors based on HPC-300 deliver an energy density of 11.7 Wh kg-1 at a power density of 250.0 W kg-1 in KOH electrolyte and 21.1 Wh kg-1 at 450.0 W kg-1 in Na2SO4 electrolyte and possess a capacitance retention of 98.1 % over 20,000 charge-discharge cycles. This preoxidation coupled activation method provides a potential strategy for the preparation of PAN-based porous carbon with high specific surface area and capacitance.

MOF-Derived Transition Metal Phosphides for Supercapacitors

Transition metal phosphides (TMPs) in supercapacitors (SCs) applications are increasingly attracting attention because of their exceptional electrochemical performance. MOF-derived TMPs, possess high specific surface areas, rich pore structure, and controllable chemical compositions, offering promising opportunities for supercapacitor applications. There is a wide variety of MOF-derived TMPs, and they exhibit different properties in SCs. This work mainly categorizes MOF-derived TMPs (FexP, CoxP, NixP, NixCoyP, CuxP), and then outlines the latest research advancements regarding their use as electrode materials in SCs, including the latest results of synthesis methods and structural modulation. Subsequently, the applications of MOF-derived TMPs as electrode materials in SCs are discussed. At the end, perspectives of future developments and key challenges in the applications of MOF-derived TMPs in SCs are highlighted, with the aim of providing guidance for future research.

Oxygen vacancies enhancing hierarchical NiCo2S4@MnO2 electrode for flexible asymmetric supercapacitors

The limited energy density of supercapacitors hampers their widespread application in electronic devices. Metal oxides, employed as electrode materials, suffer from low conductivity and stability, prompting extensive research in recent years to enhance their electrochemical properties. Among these efforts, the construction of core-shell heterostructures and the utilization of oxygen vacancy (VO) engineering have emerged as pivotal strategies for improving material stability and ion diffusion rates. Herein, core-shell composites comprising NiCo2S4 nanospheres and MnO2 nanosheets are grown in situ on carbon cloth (CC), forming nanoflower clusters while introducing VO defects through a chemical reduction method. Density functional theory (DFT) results proves that the existence of VO effectively enhances electronic and structural properties of MnO2, thereby enhancing capacitive properties. The electrochemical test results show that NiCo2S4@MnO2-V3 exhibits excellent 1376 F g-1 mass capacitance and 2.06 F cm-2 area capacitance at 1 A g-1. Moreover, NiCo2S4@MnO2-V3//activated carbon (AC) asymmetric supercapacitor (ASC) can achieve an energy density of 39.7 Wh kg-1 at a power density of 775 W kg-1, and maintains 15.5 Wh kg-1 even at 7749.77 W kg-1. Capacitance retention is 73.1 % after 10,000 cycles at 5 A g-1, and coulombic efficiency reaches 100 %, demonstrating satisfactory cycle stability. In addition, the device's excellent flexibility offers broad application prospects in wearable electronic applications.

Interface engineering based NiCoMoO4/Ti3C2Tx MXene heterostructure for high-performance flexible supercapacitors

The advancement of interface engineering has demonstrated remarkable efficacy in overcoming the primary impediment associated with sluggish reaction kinetics in supercapacitor electrodes. In this investigation, we employed a facile co-precipitation method to synthesize NiCoMoO4/MXene heterostructures utilizing Ti3C2Tx MXene nanosheets as carriers. This heterostructure inhibits the restacking of MXene nanosheets and simultaneously enhances the exposure of electrochemically active sites in NiCoMoO4 nanorods, thereby mitigating the reduction in specific capacitance resulting from volumetric fluctuations. The NiCoMoO4/MXene electrode, possessing pseudo-capacitance properties, demonstrates an impressive level of specific capacitance, exceptional performance across various charging rates, and consistent behavior throughout repeated cycles. By optimizing the mass ratio, this electrode achieves a specific capacity of 1900 F/g under a current density of 1 A/g. Even after enduring 10,000 cycles at a significantly higher current density of 5 A/g, it still maintains an impressive retention rate of 94.73 %. Our density functional theory (DFT) calculations indicate that the enhanced electrochemical performance can be attributed to the improved electronic coupling within the NiCoMoO4/MXene heterostructure. The integration of NiCoMoO4/MXene cathode and activated carbon (AC) anode with an alkaline gel electrolyte containing potassium ferricyanide in flexible quasi-solid-state supercapacitors (FSSCs) results in exceptional electrochemical performance and flexibility. These FSSCs demonstrate a maximum energy density of 72.89 Wh kg-1 at a power density of 850 W kg-1, while maintaining an impressive power output of 16,780 W kg-1 with an energy density of 37.28 Wh kg-1. Based on these outstanding properties, it is evident that the NiCoMoO4/MXene heterojunction possesses significant advantages as electrode material for supercapacitors, and the fabricated FSSCs devices pave a new pathway for flexible electronic devices.

Strategy for predicting catalytic activity of catalysts with hierarchical nanostructures

Three-dimensional hierarchical nanostructures have been employed as electrodes of solid oxide fuel cells (SOFCs) to notably improve the catalytic performance. Hierarchical nanoscale porous electrodes face a trade-off: macroscale pores enhance mass transfer but reduce the number of active sites, while microscale pores increase the number of active sites at the cost of higher transport resistance. Careful design of these structures is crucial for balancing mass transfer and reaction dynamics. A three-dimensional multiphysics model is developed in this paper to examine the influence of different hierarchical geometrical nanostructures on catalytic performance. Additionally, the effects of different diffusion coefficients are also investigated in this study to present the changes in catalytic activity in diffusion, mixed, and reaction-controlled regimes. The model shows good alignment with the experimentally obtained data. An improved Thiele modulus is formulated to quantitatively evaluate the efficiencies of complex hierarchical nanostructures by considering the detailed characteristics of the main and secondary structures.

A binary composite La(OH)3@Ni(OH)2 nanomaterial on carboxyl graphene for an efficient hybrid supercapacitor electrode

In this work, we present a binary composite of La(OH)₃@Ni(OH)₂ on carboxyl graphene (La@Ni/CG) as an electrode material. The layered La@Ni/CG double hydroxides (LDHs) were synthesized by a simple electrodeposition method in which La(OH)₃ nanoparticles were first adsorbed onto carboxyl graphene and then coated with Ni(OH)₂, with different particle shapes due to the large pH change near the cathodic region. Scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), cyclic voltammetry (CV) and galvanostatic charge-discharge (GCD) were used to characterise the as-prepared La@Ni/CG composite. These results showed that the La@Ni/CG composite exhibited improved electrochemical properties, including large specific capacitance (1334.7 F g^-1 at 1.4 A g^-1) and capacity retention of 90.6% even after 3000 cycles, and excellent rate capability. The improved electrochemical performance of the composite can be attributed to the synergistic effect of surface adsorption and conductive pathways provided by the multiple active species (Ni, La and C) in the La@Ni/CG composite. The results presented in this work provide advances in the efficient design of nanomaterial based electrochemical energy storage devices.

NiS Nanosheets Decorated on Hollow Carbon Spheres from Liquefied Wood for Supercapacitors

Carbon-based supercapacitors with high performance have a wide foreground among various energy storage devices. In this work, wood-based hollow carbon spheres (WHCS) were prepared from liquefied wood through the processes of emulsification, curing, carbonization, and activation. Then, the hydrodeposition method was used to introduce nickel sulfide (NiS) to the surface of the microspheres, obtaining NiS/WHCS as the supercapacitor electrode. The results show that NiS/WHCS microspheres exhibited a core-shell structure and flower-like morphology with a specific surface (307.55 m² g^-1) and a large total pore volume (0.14 cm³ g^-1). Also, the capacitance could be up to 1533.6 F g^-1 at a current density of 1 A g^-1. In addition, after 1000 charge/discharge cycles, the specific capacitance remained at 72.8% at the initial current density of 5 A g^-1. Hence, NiS/WHCS with excellent durability and high specific capacitance is a potential candidate for electrode materials.