▎ 摘　　要

Here we demonstrate that graphene nanoribbons (GNRs) free of oxidized surfaces can be prepared in large batches and 100% yield by splitting multiwalled carbon nanotubes (MWCNTs) with potassium vapor. If desired, exfoliation is attainable in a subsequent step using chlorosulfonic acid. The low-defect density of these GNRs Is indicated by their electrical conductivity, comparable to that of graphene derived from mechanically exfoliated graphite. The possible origins of directionally selective splitting of MWCNTs have been explored using computer modeling, and plausible explanations for the unique role of potassium were found.