Identification of active sites for oxygen evolution reaction (OER) plays a key role in the design and fabrication of high-performance cobalt-based electrocatalysts. Herein, we report the synthesis of two types of two-dimensional monometallic cobalt hydroxide nanoplates in aqueous solution for OER: α-Co(OH)₂ with both Co²⁺ _Td and Co²⁺ _Oh sites and β-Co(OH)₂ with Co²⁺ _Oh sites. Electrochemical characterization reveals that α-Co(OH)₂ is more active than β-Co(OH)₂ towards OER. The better activity can be attributed to the presence of Co²⁺ _Td sites in α-Co(OH)₂, which are more active than Co²⁺ _Oh sites. Our finding clarifies the contribution of the two catalytic sites and helps future rational design of high-performance OER electrocatalysts.

3D dendritic WSe ₂ on conductive carbon nanofiber mats (d-WSe ₂ /CFM) was synthesized and directly used as a hydrogen evolution cathode.