▎ 摘　　要

The presence of unwanted impurities in graphene is known to have a significant impact on its physical and chemical properties. Similar to carbon nanotubes, any trace metals present in graphene will affect the electrocatalytic properties of the material. Here, we show by direct electroanalysis that traces of copper still remain in transferred CVD (chemical vapor deposition)-grown graphene (even after the usual copper etching process) and strongly influence its electrochemical properties. Subsequently, we use a real-time electrochemical etching procedure to remove more than 90% of the trace metal impurities, with a clear improvement in both the electrochemical and electronic-transport properties of monolayer graphene.