α‐Ni(OH)2 Originated from Electro‐Oxidation of NiSe2 Supported by Carbon Nanoarray on Carbon Cloth for Efficient Water Oxidation

Abstract Development of effective oxygen evolution reaction (OER) electrocatalysts has been intensively studied to improve water splitting efficiency and cost effectiveness in the last ten years. However, it is a big challenge to obtain highly efficient and durable OER electrocatalysts with overpotentials below 200 mV at 10 mA cm −2 despite the efforts made to date. In this work, the successful synthesis of supersmall α‐Ni(OH) 2 is reported through electro‐oxidation of NiSe 2 loaded onto carbon nanoarrays. The obtained α‐Ni(OH) 2 shows excellent activity and long‐term stability for OER, with an overpotential of only 190 mV at the current density of 10 mA cm −2 , which represents a highly efficient OER electrocatalyst. The excellent activity could be ascribed to the large electrochemical surface area provided by the carbon nanoarray, as well as the supersmall size (≈10 nm) of α‐Ni(OH) 2 which possess a large number of active sites for the reaction. In addition, the phase evolution of α‐Ni(OH) 2 from NiSe 2 during the electro‐oxidation process was monitored with in situ X‐ray absorption fine structure (XAFS) analysis.