Abstract
Herein we have shown that electrodeposited NiSe2 can be used as a bifunctional electrocatalyst under alkaline conditions to split water at very low potential by catalyzing both oxygen evolution and hydrogen evolution reactions at anode and cathode, respectively, achieving a very high electrolysis energy efficiency exceeding 80% at considerably high current densities (100 mA cm−2). The OER catalytic activity as well as electrolysis energy efficiency surpasses any previously reported OER electrocatalyst in alkaline medium and energy efficiency of an electrolyzer using state-of-the-art Pt and RuO2 as the HER and OER catalyst, respectively. Through detailed electrochemical and structural characterization, we have shown that the enhanced catalytic activity is attributed to directional growth of the electrodeposited film that exposes a Ni-rich lattice plane as the terminating plane, as well as increased covalency of the selenide lattice which decreases the Ni(II) to Ni(III) oxidation potential. Thereby, the high efficiency along with extended stability makes NiSe2 as the most efficient water electrolyzer known to-date.
Highlights
Selenide, Ni3Se2 which shows a very low onset potential and overpotential at 10 mA cm−2 for oxygen evolution in alkaline medium[20]
The OER catalytic activity in these films with the onset potential for O2 evolution at 1.36 V and overpotential at 10 mA cm−2 at 140 mV in alkaline medium, was observed to be superior to any other OER electrocatalysts reported till date including state-of-the-art precious metal oxides, transition metal oxides, and other nickel chalcogenides
There has been another report of the OER catalytic activity of NiSe2 albeit with much higher overpotential at 10 mA cm−2 (~290 mV)[18, 23]
Summary
The oxygen and hydrogen evolution reactions (OER and HER, respectively), an intricate part in water oxidation/reduction, respectively, plays a crucial role in other alternative energy devices including fuel cells, metal-oxygen batteries and solar water splitting devices[1,2,3]. Among these the oxygen evolution reaction (OER) occurring at the anode is a major hurdle since it is a kinetically sluggish process that involves 4 electron transfer associated with the formation of dioxygen molecule from water, and requires a large anodic potential[4].
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