Controllable 1D and 2D Cobalt Oxide and Cobalt Selenide Nanostructures as Highly Efficient Electrocatalysts for the Oxygen Evolution Reaction.

The relationship between controllable morphology and electrocatalytic activity of Co3 O4 and CoSe2 for the oxygen evolution reaction (OER) was explored in alkaline medium. Based on the time-dependent growth process of cobalt precursors, 1D Co3 O4 nanorods and 2D Co3 O4 nanosheets were successfully synthesized through a facile hydrothermal process at 180 °C under different reaction times, followed by calcination at 300 °C for 2 h. Subsequently, 1D and 2D CoSe2 nanostructures were derived by selenization of Co3 O4 , which achieved the controllable synthesis of CoSe2 without templating agents. By comparing the electrocatalytic behavior of these cobalt-based catalysts in 1 m KOH electrolyte toward the OER, both 2D Co3 O4 and 2D CoSe2 nanocrystals have lower overpotentials and better electrocatalytic stability than that of 1D nanostructures. The 2D CoSe2 nanosheets require overpotentials of 372 mV to reach a current density of 50 mA cm-2 with a small Tafel slope of 74 mV dec-1 . A systematic contrast of the electrocatalytic performances for the OER increase in the order: 1D Co3 O4 <2D Co3 O4 <1D CoSe2 <2D CoSe2 . This work provides fundamental insights into the morphology-performance relationships of both Co3 O4 and CoSe2 , which were synthesized through the same approach, providing a solid guide for designing OER catalysts.