Nanocomposites Based on CoSe 2 -Decorated FeSe 2 Nanoparticles Supported on Reduced Graphene Oxide as High-Performance Electrocatalysts toward Oxygen Evolution Reaction.

FeCo-based materials are promising candidates as efficient, affordable, and sustainable electrocatalysts for oxygen evolution reaction (OER). Herein, a composite based on FeSe2 @CoSe2 particles supported on reduced graphene oxide (rGO) was successfully prepared as an OER catalyst. In the catalyst, the CoSe2 phase was located on the FeSe2 surface, forming a large number of exposed heterointerfaces with acidic iron sites because of strong charge interaction between CoSe2 and FeSe2 . It is believed that the exposed heterointerfaces act as catalytic active sites for OER via a two-site mechanism, manifesting an overpotential as low as 260 mV to reach the current density of 10 mA cm-2 in 1 M KOH and excellent stability for at least 6 h, which is superior to those of CoSe2 /rGO, FeSe2 /rGO, as well as most of the FeNi- and FeCo-based electrocatalysts reported in recent literatures. It was demonstrated that the most optimal composite electrocatalysts release more Fe species into the electrolyte during the OER process, whereas the releasing of Co species is negligible. When the FeSe2 @CoSe2 /rGO catalysts were loaded on a α-Fe2 O3 photoanode, the photocurrent density was increased by three times. These results may open up a promising avenue into the design and engineering of highly active and durable catalysts for water oxidation.