Electrocatalytic hydrogen evolution reaction promoted by Co/N/C catalysts with Co−N x active sites derived from precursors forming N-doped graphene Nanoribbons

Abstract : Cobalt and nitrogen co-doped carbon (Co/N/C) catalysts prepared by pyrolysis are promising electrocatalysts for hydrogen evolution reaction (HER). Construction of Co−N$_x$ active sites is an important strategy for improving HER activity. We developed a method for thermally controlled construction of the Co−N$_x$ 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−N$_x$ sites in the catalysts are observed by electron microscopy. Moreover, the amount of Co−N$_x$ 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 HClO$_{4aq}$) and 311 mV (in 0.1 M HClO$_{4aq}$) at 10 mA·cm$^{−2}$, and with a long-term stability.