Cobalt hydroxide species are at the origin of OER activity of multiheteroatom doped carbon catalysts.

Today, metal-N- as well as metal-S-doped carbon materials are known to catalyze the hydrogen evolution reaction (HER). However, especially N- and S-co-doped catalysts reach highest activity, but it remains unclear if the activity is related to MN or MS (M=metal) sites. In this work we apply a simple method for multi-heteroatom doping and investigate the effect of cobalt content on the HER in acidic medium. The CoN and CoS sites were evidenced on the basis of structural characterization by Raman, X-ray induced photoelectron spectroscopy, and TEM. The presence of sulfur enables the formation of a larger number of CoN sites. Structure-performance relationship proves that the HER activity is dominated by CoN rather than CoS sites. The most active catalysts also exhibit an excellent stability under galvanostatic conditions making them of interest for electrolyser application.