Due to their high conductivity and low cost, carbon materials have attracted great attention in the field of energy storage, especially as anode material for sodium ion batteries. Current research focuses on introducing external defects through heteroatom engineering to improve the sodium storage performance of carbon materials. However, there is still a lack of systematic investigation of the effects of intrinsic defects prevalent in carbon materials on sodium storage performance. Herein, template‐assisted method was used to design carbon materials with different degrees of intrinsic defects and explore their sodium storage properties. The experimental results show that the intrinsic defects in the carbon materials facilitates the adsorption behavior of Na+ during the surface induction capacitance process. Among them, the best carbon anode material exhibits high reversible capacity (221 mAh g−1 at 1 A g−1) and excellent rate performance. In addition, the density functional theory calculations also show that the existence of intrinsic defects can optimize the distribution of electron density, thereby increasing the Na‐adsorption capacity. This work makes an important contribution to understanding the role of intrinsic defects in the sodium storage performance of carbon materials.
Heteroatom doping plays a significant role in optimizing the catalytic performance of electrocatalysts. However, research on heteroatom doped electrocatalysts with abundant defects and well-defined morphology remain a great challenge. Herein, a class of defect-engineered nitrogen-doped Co 3 O 4 nanoparticles/nitrogen-doped carbon framework (N-Co 3 O 4 @NC) strongly coupled porous nanocubes, made using a zeolitic imidazolate framework-67 via a controllable N-doping strategy, is demonstrated for achieving remarkable oxygen evolution reaction (OER) catalysis. X-ray photoelectron spectroscopy, X-ray absorption fine structure, and electron spin resonance results clearly reveal the formation of a considerable amount of nitrogen dopants and oxygen vacancies in N-Co 3 O 4 @NC. The defect engineering of N-Co 3 O 4 @NC makes it exhibit an overpotential of only 266 mV to reach 10 mA cm −2 , a low Tafel slope of 54.9 mV dec −1 and superior catalytic stability for OER, which is comparable to that of commercial RuO 2 . Density functional theory calculations indicate N-doping could promote catalytic activity via improving electronic conductivity, accelerating reaction kinetics, and optimizing the adsorption energy for intermediates of OER. Interestingly, N-Co 3 O 4 @ NC also shows a superior oxygen reduction reaction activity, making it a bifunctional electrocatalyst for zinc-air batteries. The zinc-air battery with the N-Co 3 O 4 @NC cathode demonstrates superior efficiency and durability, showing the feasibility of N-Co 3 O 4 /NC in electrochemical energy devices.
Carbon nanomaterials with both doped heteroatom and porous structure represent a new class of carbon nanostructures for boosting electrochemical application, particularly sustainable electrochemical energy conversion and storage applications. We herein demonstrate a unique large-scale sustainable biomass conversion strategy for the synthesis of earth-abundant multifunctional carbon nanomaterials with well-defined doped heteroatom level and multimodal pores through pyrolyzing electrospinning renewable natural alginate. The key part for our chemical synthesis is that we found that the egg-box structure in cobalt alginate nanofiber can offer new opportunity to create large mesopores (∼10–40 nm) on the surface of nitrogen-doped carbon nanofibers. The as-prepared hierarchical carbon nanofibers with three-dimensional pathway for electron and ion transport are conceptually new as high-performance multifunctional electrochemical materials for boosting the performance of oxygen reduction reaction (ORR), lithium ion batteries (LIBs), and supercapacitors (SCs). In particular, they show amazingly the same ORR activity as commercial Pt/C catalyst and much better long-term stability and methanol tolerance for ORR than Pt/C via a four-electron pathway in alkaline electrolyte. They also exhibit a large reversible capacity of 625 mAh g–1 at 1 A g–1, good rate capability, and excellent cycling performance for LIBs, making them among the best in all the reported carbon nanomaterials. They also represent highly efficient carbon nanomaterials for SCs with excellent capacitive behavior of 197 F g–1 at 1 A g–1 and superior stability. The present work highlights the importance of biomass-derived multifunctional mesoporous carbon nanomaterials in enhancing electrochemical catalysis and energy storage.
Searching the long-life transition-metal oxide (TMO)-based materials for future lithium-ion batteries (LIBs) is still a great challenge because of the mechanical strain resulting from volume change of TMO anodes during the lithiation/delithiation process. To well address this challenging issue, we demonstrate a controlled method for making the multishelled TMO hollow microfibers with tunable shell numbers to achieve the optimal void for efficient lithium-ion storage. Such a particularly designed void can lead to a short diffusion distance for fast diffusion of Li ions and also withstand a large volume variation upon cycling, both of which are the key for high-performance LIBs. Triple-shelled TMO hollow microfibers are a quite stable anode material for LIBs with high reversible capacities (NiO: 698.1 mA h g at 1 A g; CoO: 940.2 mA h g at 1 A g; FeO: 997.8 mA h g at 1 A g), excellent rate capability, and stability. The present work opens a way for rational design of the void of multiple shells in achieving the stable lithium-ion storage through the biomass conversion strategy.
Highlights A new class of TiO2 nanofiber/red phosphorus (TiO2/RP) nanolayer core/shell heterostructure was fabricated by vaporization-deposition strategy. TiO2/RP exhibits enhanced photocatalytic pure water splitting performance. Decoration of RP extends the optical light harvesting ability. P 5+ doping induced oxygen vacancies improve the charge separation efficiency.
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