3D Edge-Enriched Fe3 C@C Nanocrystals with a Core-Shell Structure Grown on Reduced Graphene Oxide Networks for Efficient Oxygen Reduction Reaction

Controllable synthesis of Fe3C-reinforced petal-like lignin microspheres with boosted electrochemical performance and its application in high performance supercapacitors

One more effective measure to solve the energy crisis caused by the shortage of fossil energy is to convert natural renewable resources into high-value chemical products for electrochemical energy storage. Lignin has broad application prospects in this field. In this paper, three kinds of lignin with different molecular weights were obtained by the ethanol/water grading of Kraft lignin (KL). Then, different surface morphology lignin microspheres were prepared by spray drying. Finally, petal-like microspheres were successfully prepared by mixing and grinding the above four kinds of surface morphology lignin microspheres with potassium ferrate and cyanogen chloride and carbonizing at 800 °C and were later used as electrode materials for supercapacitors. Compared with the other microspheres, LMS-F3@Fe3C has the highest specific surface area (1041.42 m2 g-1), the smallest pore size (2.36 nm) and the largest degree of graphitization (ID/IG = 1.06). At a current density of 1 A g-1, the maximum specific capacitance is 786.7 F g-1. At a power density of 1000 W kg-1, the high energy density of 83.3 Wh kg-1 is displayed. This work provides a novel approach to the modulation of surface morphology and structure of lignin microspheres.

Research Progress on Porous Carbon-Based Non-Precious Metal Electrocatalysts

The development of efficient, stable, and economic electrocatalysts are key to the large-scale application of electrochemical energy conversion. Porous carbon-based non-precious metal electrocatalysts are considered to be the most promising materials to replace Pt-based catalysts, which are limited in large-scale applications due to high costs. Because of its high specific surface area and easily regulated structure, a porous carbon matrix is conducive to the dispersion of active sites and mass transfer, showing great potential in electrocatalysis. This review will focus on porous carbon-based non-precious metal electrocatalysts and summarize their new progress, focusing on the synthesis and design of porous carbon matrix, metal-free carbon-based catalysts, non-previous metal monatomic carbon-based catalyst, and non-precious metal nanoparticle carbon-based catalysts. In addition, current challenges and future trends will be discussed for better development of porous carbon-based non-precious metal electrocatalysts.

Interfacial Engineering of Bimetallic Carbide and Cobalt Encapsulated in Nitrogen-Doped Carbon Nanotubes for Electrocatalytic Oxygen Reduction

Heterojunction engineering is a fundamental strategy to develop efficient electrocatalysts for the oxygen reduction reaction by tuning electronic properties through interfacial cooperation. In this study, a heterojunction electrocatalyst consisting of bimetallic carbide Co₃ ZnC and cobalt encapsulated within N-doped carbon nanotubes (Co₃ ZnC/Co@NCNTs) is synthesized by a facile two-step ion exchange-thermolysis pathway. Co₃ ZnC/Co@NCNTs effectively promotes interfacial charge transport between the different components with optimizes adsorption and desorption of intermediate products at the heterointerface. In situ-grown N-doped carbon nanotubes (NCNTs) not only improve the electrical conductivity but also suppress the oxidation of transition metal nanoparticles in alkaline media. Moreover, the abundant nitrogen types (pyridinic N, Co-N_x , and graphitic nitrogen) in the carbon skeleton provide more active sites for oxygen adsorption. Benefitting from this optimized structure, Co₃ ZnC/Co@NCNTs hybrid not only demonstrates excellent oxygen reduction activity, with a half-wave potential of 0.83 V and fast mass transport with limited current density of 6.23 mA cm^-2 , but also exhibits superior stability and methanol tolerance, which surpass those of commercial Pt/C catalysts. This work provides an effective heterostructure for interfacial electronic modulation to improve electrocatalytic performance.

Scalable Production of Few-Layer Niobium Disulfide Nanosheets via Electrochemical Exfoliation for Energy-Efficient Hydrogen Evolution Reaction

Two-dimensional (2D) niobium disulfide (NbS₂) materials feature unique physical and chemical properties leading to highly promising energy conversion applications. Herein, we developed a robust synthesis technique consisting of electrochemical exfoliation under alternating currents and subsequent liquid-phase exfoliation to prepare highly uniform few-layer NbS₂ nanosheets. The obtained few-layer NbS₂ material has a 2D nanosheet structure with an ultrathin thickness of ∼3 nm and a lateral size of ∼2 μm. Benefiting from their unique 2D structure and highly exposed active sites, the few-layer NbS₂ nanosheets drop-casted on carbon paper exhibited excellent catalytic activity for the hydrogen evolution reaction (HER) in acid with an overpotential of 90 mV at a current density of 10 mA cm^-2 and a low Tafel slope of 83 mV dec^-1, which are superior to those reported for other NbS₂-based HER electrocatalysts. Furthermore, few-layer NbS₂ nanosheets are effective as bifunctional electrocatalysts for hydrogen production by overall water splitting, where the urea and hydrazine oxidation reactions replace the oxygen evolution reaction.

Stepwise Fabrication of Co-Embedded Porous Multichannel Carbon Nanofibers for High-Efficiency Oxygen Reduction

A novel nonprecious metal material consisting of Co-embedded porous interconnected multichannel carbon nanofibers (Co/IMCCNFs) was rationally designed for oxygen reduction reaction (ORR) electrocatalysis. In the synthesis, ZnCo2O4 was employed to form interconnected mesoporous channels and provide highly active Co3O4/Co core-shell nanoparticle-based sites for the ORR. The IMC structure with a large synergistic effect of the N and Co active sites provided fast ORR electrocatalysis kinetics. The Co/IMCCNFs exhibited a high half-wave potential of 0.82 V (vs. reversible hydrogen electrode) and excellent stability with a current retention up to 88% after 12,000 cycles in a current-time test, which is only 55% for 30 wt% Pt/C.