The Influence of Doping in the Electrocatalytic Properties of NiFe2O4-Derived Nitrides

Abstract

Transition metal nitrides (TMNs) have been widely studied in the last years due to their extraordinary properties such as high electrical conductivity and versatile physical and chemical properties. They can be easily synthesize from metal oxide precursors and, in addition, they display electrocatalytic activities similar to Pt and other conventional noble metal electrocatalysts.1 Among them, several Ni-, Co- and Fe-based nitrides have been studied as electrocatalysts for the hydrogen evolution reaction (HER), oxygen reduction reaction (ORR) and oxygen evolution reaction (OER).2–4 The combination of these metals in different proportions (stoichiometric and non-stoichiometric) can give place to a wide range of electrocatalysts with better electrochemical performance than the single metal nitrides. Apart from them, 2nd and 3rd row TMNs like Mo- and W-based nitrides can display high HER activity, surpassing those 1st row TMNs above-mentioned, therefore doping 1st row TMNs with Mo or W, even in very small amounts, can increase significantly the electrocatalytic performance of these materials.5 In this work, NiFe2O4-derived nitrides and their Mo- and W-doped versions were synthesized via the resorcinol-formaldehyde sol-gel polymerization method, followed by nitridation in ammonia atmosphere. The influence of doping for the HER, ORR and OER reactions in alkaline electrolyte has been studied. As observed, W-doping results in improved ORR and OER activities. Characterization techniques, such as XRD, TEM and XPS, are being performed in the initial and used catalysts, observing a structural change from the initial oxide (NiFe2O4) to the final nitride (NiFe2N), including the doped versions, which can help to understand their electrocatalytic properties.