Effect of Selenium Content on Nickel Sulfoselenide-Derived Nickel (Oxy)hydroxide Electrocatalysts for Water Oxidation

An efficient and inexpensive electrocatalyst for the oxygen evolution reaction (OER) must be found in order to improve the viability of hydrogen fuel production via water electrolysis. Recent work has indicated that nickel chalcogenide materials show promise as electrocatalysts for this reaction and that their performance can be further enhanced with the generation of ternary, bimetallic chalcogenides (i.e., Ni_1-MX₂); however, relatively few studies have investigated ternary chalcogenides created through the addition of a second chalcogen (i.e., NiX_2-Y). To address this, we studied a series of Se-modified Ni₃S₂ composites for use as OER electrocatalysts in alkaline solution. We found that the addition of Se results in the creation of Ni₃S₂/NiSe composites composed of cross-doped metal chalcogenides and show that the addition of 10% Se reduces the overpotential required to reach a current density of 10 mA/cm² by 40 mV versus a pure nickel sulfide material. Chemical analysis of the composites' surfaces shows a reduction in the amount of nickel oxide species with Se incorporation, which is supported by transmission electron microscopy; this reduction is correlated with a decrease in the OER overpotentials measured for these samples. Together, our results suggest that the incorporation of Se into Ni₃S₂ creates a more conductive material with a less-oxidized surface that is more electrocatalytically active and resistant to further oxidation. Importantly, oxidation does still occur, and the active catalyst is most likely a nickel (oxy)hydroxide surrounding a crystalline, conductive Ni₃S_2-Se core.