Electrocatalytic Hydrogen Evolution Reaction Promoted by Co/N/C Catalysts with Co–Nx Active Sites Derived from Precursors Forming N-Doped Graphene Nanoribbons

Cobalt and nitrogen co-doped carbon (Co/N/C) catalysts prepared by pyrolysis are promising electrocatalysts for hydrogen evolution reaction (HER). Construction of Co–Nx active sites is an important strategy for improving HER activity. We developed a method for thermally controlled construction of the Co–Nx active sites by applying a bottom-up synthetic methodology using an N-doped graphene nanoribbon (N-GNR). Preorganized aromatic rings in the precursors assist graphitization during generation of N-GNR which has N2 sites that coordinate to a cobalt ion. Atomically dispersed Co–Nx sites in the catalysts are observed by electron microscopy. Moreover, the amount of Co–Nx sites increases up to 0.31 wt% as confirmed by XPS and elemental analysis. The Co/N/C catalyst prepared from the precisely designed precursor forming an N-GNR shows HER activity with a low overpotential of 258 mV (in 1.0 M HClO4aq) and 311 mV (in 0.1 M HClO4aq) at 10 mA·cm−2, and with a long-term stability. Synthetic methodology based on an N-doped graphene nanoribbon (N-GNR) is applied to the construction of a Co–Nx structure in Co/N/C catalysts. Precursors, pyridine-substituted triphenylene polymers, are converted to N-GNR with cobalt-chelating N2 ligand structures during pyrolysis, and the cobalt-bonded N-GNR is incorporated into the graphene layer. The resulting Co/N/C catalysts are highly active toward hydrogen evolution reaction (HER).