Polymorphic ternary metal chalcogenide solid solution nanopowder as electrocatalyst for hydrogen and oxygen evolution reaction

Here, in this work, a novel synthesis route of polymorphic FexNi1-xSe2 nanopowders consisting of nanoparticles and nanorods for x = 0.2–0.8 has been investigated by a simple hydrothermal process. Coral shaped NiSe2 (x = 0) and nanorod structured FeSe2 (x = 1) are in pure cubic and orthorhombic phase, respectively whereas FexNi1-xSe2 solid solution nanopowder is a combination of both. After important basic characterizations, electrochemical hydrogen evolution reaction (HER) and oxygen evolution reactions (OER) are carried out using FexNi1-xSe2 as cathode and anode, respectively. Among all the variations, x = 0.4 has exhibited the highest HER activity with low overpotential of −106 mV for 10 mA/cm2 in acidic medium and x = 0.2 is the most efficient as anode in OER in alkaline medium with overpotential of 280 mV to drive the current density of 10 mA/cm2 with a small amount of oxidation. Long term stability is achieved without any degradation for both HER and OER in extreme pH for FexNi1-xSe2. The insertion of Fe in the lattice of NiSe2 has improved the conductivity thereby increasing the charge transfer phenomenon. The coexistence of two different morphologies for the optimum ratio of Fe/Ni has generated more active sites participating in the electrochemical reactions. The easy oxidation of catalysts during OER can be restricted by the polymorphic crystal structure of FexNi1-xSe2.