Co₉S₈‐Catalyzed Growth of Thin‐Walled Graphite Microtubes for Robust, Efficient Overall Water Splitting

Co 9 S 8 crystals can catalyze the growth of thin‐walled graphite microtubes (GMTs) through a catalytic chemical vapor deposition (CCVD) process using thiourea as the precursor. The growth of GMTs follows a tip‐growth mechanism with tube diameters up to a few micrometer. The hollow interiors of the GMTs are filled with carbon nanotubes and wrinkled graphene layers, which form a unique nanotube/graphene‐in‐microtube structure. As‐formed GMTs are N,S‐codoped with lots of Co 9 S 8 nanoparticles encapsulated in their inner walls. These GMTs are room‐temperature ferromagnets and can be loaded on Ni foams to work as binder‐free electrocatalysts with low overpotential (310 mV at 50 mA cm −2 for the oxygen evolution reaction (OER) and 284 mV at 50 mA cm −2 for the hydrogen evolution reaction (HER)) and long‐term durability (continuous work for 120 h without loss in performance). Our research proves that metal sulfides can catalyze the growth of graphite microtubes and as‐formed GMTs may potentially be used as functional building blocks to construct new kinds of electrochemical devices for various energy‐related applications.