Carbon electrocatalysts consisting of metal complexes such as MNx or MSx are promising alternatives to high-cost Pt catalysts for the hydrogen evolution reaction (HER). However, the exact HER active sites remain elusive. Here, molecular metal dithiolene-diamine (MS2 N2 , M=Co and Ni), metal bis(dithiolene) (MS4 ), and metal bis(diamine) (MN4 ) complexes were selectively incorporated into carbon-rich 2D metal-organic frameworks (2D MOFs) as model carbon electrocatalysts. The 2D MOF single layers, powders, and composites with graphene were thus prepared and showed definite active sites for H2 generation. The electrocatalytic HER activity of the 2D MOF-based catalysts with different metal complexes follow the order of MS2 N2 >MN4 >MS4 . Moreover, the protonation preferentially occurred on the metal atoms, and the concomitant heterolytic elimination of H2 was favored on the M-N units in the MS2 N2 active centers. The results provide an in-depth understanding of the catalytic active sites, thus making way for the future development of metal complexes in carbon-rich electrode materials for energy generation.
Keywords: 2D materials; active sites; hydrogen evolution reaction; metal-organic frameworks; single-layer nanosheet.
© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.