Designing few-layered graphitic carbons with atomic-sized cobalt hydroxide by harnessing hollow metal–organic frameworks†

Graphitic carbon exhibits distinctive characteristics that can be modulated by varying the number of carbon layers. Here, we developed a method to control the growth of graphitic carbon layers through pyrolysis of zeolitic imidazolate frameworks (ZIFs). The key is to pyrolyze hollow-structured ZIF-8 containing Co ions to simultaneously obtain an amorphous carbon source for graphitic carbons and Co metal nanoparticles for catalyzing graphitization of amorphous carbons. Owing to sparsely distributed Co ions within ZIF-8, Co nanoparticles are formed, which leads to localized graphitization. The graphitic carbon obtained contained two to five layers, unlike carbonized ZIF-67. The few-layered graphitic carbon was subjected to KOH activation and employed as a support for atomic-sized Co(OH)₂ owing to the short routes for Co nanoparticle egress and OH⁻ ion movement. Our strategy does not involve any highly corrosive process for catalyst leaching and can even be used to produce atomic-sized Co(OH)₂ with few-layered graphitic carbons.