Nanostructured Nickel Cobaltite Antispinel as Bifunctional\nElectrocatalyst for Overall Water Splitting

Abstract

One major goal in\nthe field of catalysis is to develop efficient,\nlow-cost, and stable catalysts to replace noble-metal-based materials.\nHerein, we for the first time present the nickel cobaltite (NiCo₂O₄) of nanosheets morphology (NCO-NSs) and nanowires\nmorphology (NCO-NWs) as an efficient electrocatalyst for the hydrogen\nevolution reaction (HER) and oxygen evolution reaction (OER) in alkaline\nsolution, affording a current density of 10 mA cm^–2 at low overpotential of 170 mV for the HER and 230 mV for the OER,\nrespectively. With the aid of DFT calculation, we have evaluated their\nspecial catalytic activities by focusing on the position of d-band\ncenters and adsorption energy of intermediates (H₂*, H*,\nH₂O*, OH*, O*, OOH*, and O₂*) on catalyst surface.\nThe result reveals that the rate-determining-step for HER and OER\nis H* and O* adsorption, respectively, with the Ni_Td³⁺ (Ni³⁺ occupied at the tetrahedral site) being\nthe active site for water splitting. A highly efficient two-electrode\nelectrolyzer based on NCO-NSs∥NCO-NWs configuration is designed\nand tested for long-term stability evolution. Furthermore, a NCO-NSs∥NCO-NWs-based\nalkaline electrolyzer can be approach 15 mA cm^–2 at 1.65 V, superior to that of Pt∥IrO₂ couple,\nalong with strong stability.