Respective influence of stoichiometry and NiOOH formation in hydrogen and oxygen evolution reactions of nickel selenides

Understanding the inherent activity of an electrocatalyst is an effective way of studying its optimization conditions for harvesting better performance. In this, we studied the inherent electrocatalytic activity of nickel selenide catalysts of three different stoichiometry such as Ni_0.85Se, Ni₃Se₄ and NiSe₂ in which the Se:Ni ration varies as 1.176, 1.333 and 2.0 respectively. The hydrogen evolution reaction (HER) of these catalysts was found to increase with the increasing Se:Ni ratio due to which NiSe₂ turned out to be the better one among others. Interestingly, the oxygen evolution reaction (OER) of these catalysts showed a different trend irrespective of Se:Ni ratio where the ease of formation of NiOOH was found to control the kinetic current. Such influences of stoichiometry in HER and ease of NiOOH formation in OER had never been revealed before for nickel selenide system.