A Metal-Organic Framework Nanorod-Assembled Superstructure and Its Derivative: Unraveling the Fast Potassium Storage Mechanism in Nitrogen-Modified Micropores

Hierarchically Superstructured Anisotropic Carbon Particles by Multiscale Assembly Driven by Spinodal Decomposition

Hierarchical superstructures have novel shape-dependent properties, but well-defined anisotropic carbon superstructures with controllable size, shape, and building block dimensionality have rarely been accomplished thus far. Here, a hierarchical assembly technique is presented that uses spinodal decomposition (SD) to synthesize anisotropic oblate particles of mesoporous carbon superstructure (o-MCS) with nanorod arrays by integrating block-copolymer (BCP) self-assembly and polymer-polymer interface behaviors in binary blends. The interaction of major and minor phases in binary polymer blends leads to the formation of an anisotropic oblate particle, and the BCP-rich phase enables ordered packing and unidirectional alignment of carbon nanorods. Consequently, this approach enables precise control over particles' size, shape, and over the dimensionality of their components. Exploiting this functional superstructure, o-MCS are used as an anode material in potassium-ion batteries, and achieve a notable specific capacity of 156 mA h g-1 at a current density of 2 A g-1 , and long-term stability for 3000 cycles. This work presents a significant advancement in the field of hierarchical superstructures, providing a promising strategy for the design and synthesis of anisotropic carbon materials with controlled properties, offering promising applications in energy storage and beyond.

Rationally Tailoring Superstructured Hexahedron Composed of Defective Graphitic Nanosheets and Macropores: Realizing Durable and Fast Potassium Storage

Multipores engineering composed of micro/mesopores is an effective strategy to improve potassium storage performance via providing enormous adsorption sites and shortened ions diffusion distance. However, a detailed exploration of the role played by macropores in potassium storage is still lacking and has been barely reported until now. Herein, a superstructure carbon hexahedron (DGN-900) is synthesized using poly tannic acid (PTA) as precursor. Due to the spatially confined two-step local contraction of PTA along different directions and dimensions during pyrolysis, defective nanosheets with macropores are formed, while realizing a balance between defects content and graphitization degree by regulating temperature. The presence of macropores is conducive to accelerating electrolyte ions rapid infiltration within electrode, and its pore volume can accommodate electrode structure fluctuation upon cycling, while the most suitable ratio of defects to graphitic provides rich ions adsorption sites and sufficient electrons transfer channels, simultaneously. These advantages enable a prominent electrochemical performance in DGN-900 electrode, including high rate (202.9 mAh g^-1 at 2 A g^-1 ) and long cycling stability over 2000 cycles. This unique fabrication strategy, that is, defects engineering coupled with macropores structure, makes fast and durable potassium storage possible.

Puffing Up Hollow Carbon Nanofibers with High-Energy Metal-Organic Frameworks for Capacitive-Dominated Potassium-Ion Storage

Nitrogen-doped carbon materials with abundant defects and strong potassium adsorption ability have been recognized as potential anodes for potassium ion batteries (PIBs). However, the limited content and uncontrolled type of nitrogen-doped sites hinder the further performance improvement of PIBs. Herein, this work proposes nitrogen phosphorous co-doped hollow carbon nanofibers (PNCNFs) derived from high-energy metal-organic frameworks (MOFs) with an ultra-high nitrogen content of 19.52 wt% and a high portion of more reactive pyridinic N sites. Furthermore, the highly open architecture exploded by released gases from high-energy MOFs provides sufficient edge sites to settle the N atoms and further form pyridinic N sites induced by phosphorous dopants. The resulting PNCNFs achieve excellent potassium ion storage performance with high reversible capacity (466.2 mAh g^-1 ), superb rate capability (244.4 mAh g^-1 at 8 A g^-1 ), and excellent cycling performance (294.6 mAh g^-1 after 3250 cycles). The density functional theory calculation reveals that the N/P defects enhance the potassium adsorption ability and improve the conductivity.