Co9S8 catalyzed growth of thin-walled graphite microtubes for robust, efficient overall water splitting.

Co9S8 crystals can catalyze the growth of thin-walled graphite microtubes (GMTs) via a catalytic chemical vapor deposition (CCVD) process using thiourea as the precursors. The growth of the GMTs follows a tip-growth mechanism with tube diameters up to a few microns. The hollow interiors of the GMTs are filled with carbon nanotubes and wrinkled graphene layers, form a unique nanotube/graphene-in-microtube structure. As-formed GMTs are N, S-codoped with lots of Co9S8 nanoparticles encapsulated in their inner walls. These GMTs are room temperature ferromagnetic and can be loaded on Ni foams to work as binder-free electrocatalysts with low overpotential (310 mV at 50 mA cm-2 for OER and 284 mV at 50 mA cm-2 for HER) and long-term durability (continuously work for 120 h without loss in performance). Our research proves the 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.