Graphene-Mercury-Graphene Sandwich Electrode for Electroanalysis

We present a new class of hybrid 2D electrodes, where mercury is incorporated between two graphene monolayers, prepared by bottom-up assembly. First, the bottom graphene layer is electrochemically modified leading to the creation of fine mercury nanodroplets of variable size on the graphene surface. Although such electrodes show good sensitivity to heavy metal ions, their stability is limited due to the outgassing of mercury over time. After coverage with a top monolayer, the graphene surface is rendered with the favorable properties of mercury such as the high overpotential for hydrogen evolution, the ability to work at a broader cathodic potential range and higher sensitivity towards heavy metal ions such as Cd2+ and Pb2+. Most importantly, the outgassing of mercury is completely hindered by the top layer, which yields a stable mercury-like electrode but with a carbonaceous non-toxic interface. We attribute the favorable properties of the sandwich electrode to the subsurface mercury present below the top graphene sheet, which renders it with new electrochemical properties.