Tailoring MOF-derived porous carbon nanorods confined red phosphorous for superior potassium-ion storage

The metal-organic framework Zn-MOF-74, which has abundant oxygen-containing groups and Zn elements as pore creators during pyrolysis, can be an ideal precursor for a porous carbon matrix in battery electrodes, but its irregular morphology at the micron size is unfavorable. Here we demonstrate the facile solvothermal synthesis of uniform Zn-MOF-74 hexagonal nano/microrods (ZRods) with an accurate diameter modulation from tens of nanometers to micron size through varying the H2O content in the mixed solvent. An inverted volcano relationship between the ZRod diameters and H2O contents is presented. CH3COO- is identified to be critical to the hexagonal pillar shape formation, while a competitive reaction of protons dissociated from H2O is responsible for the size modulation. After calcination, the obtained porous carbon nanorods enable a high loading capacity and perfect encapsulation of P while reserving free spaces to accommodate the volume change of P in the composite anode, resulting in outstanding potassium storage performance in terms of remarkable initial Coulombic efficiency (78.5%), top-ranking reversible capacity (up to 595.8 mAh g-1), superior rate capability (187.5 mAh g-1 at 5 A g-1), and robust long-term cycling stability (retaining 150.7 mAh g-1 at 2.5 A g-1 after 400 cycles). This morphology modulation of Zn-MOF-74 will promote the advanced applications of Zn-MOF-74 as well as its derived carbon materials, and potentially opens a general pathway for the oriented evolution of various carboxylate-based MOFs.