X-ray Photoelectron Spectroscopic Investigation of Plasma-Enhanced Chemical Vapor Deposited NiO_<i>x</i>, NiO_<i>x</i>(OH)_<i>y</i>, and CoNiO_<i>x</i>(OH)_<i>y</i>: Influence of the Chemical Composition on the Catalytic Activity for the Oxygen Evolution Reaction

We report here the plasma-enhanced chemical vapor deposition and electrocatalytic characterization of pure NiOx and NiOx(OH)y. Whereas NiOx is deposited if oxygen is used as a reactive gas, the use of air as a reactive gas leads to the deposition of the NiOx(OH)y, which is electrochemically more active than the NiOx. By recording X-ray photoelectron spectra from the as-deposited catalysts and after their electrochemical investigations, we determined that the electrochemical activity correlates with the amount of hydroxide sites on the surface. Such a behavior was already observed for CoOx and CoOx(OH)y. As a consequence, CoNiOx(OH)y was deposited using air as a reactive gas to study the influence of nickel on the electronic structure of CoOx(OH)y and its effect on the electrochemical activity.