A NiCo2O4 Shell on a Hollow Ni Nanorod Array Core for Water Splitting with Enhanced Electrocatalytic Performance

Nickel cobaltite (NiCo2O4) nanostructures have been considered as promising bifunctional electrocatalyst materials for the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) in alkaline electrolyte. However, the activity of these materials toward overall water splitting is still unsatisfactory because a larger voltage is needed to drive the reactions. This study shows that more-efficient bifunctional catalysts based on NiCo2O4 materials can be obtained by adopting an integrated composite electrode with robust hollow structures. This novel electrode is constructed by the growth of hollow Ni@NiCo2O4 nanorod arrays on three-dimensional (3D) Ni foam. The interlayer of Ni hollow nanorods is conformally covered by NiCo2O4 nanosheets, providing large surface area and fast electron transport. Benefiting from these integrated characteristics, the hollow Ni@NiCo2O4 electrode as an oxygen evolution electrocatalyst can deliver a low overpotential of 270mV at 10mAcm(-2) and present excellent electrochemical durability. Meanwhile, the HER performance also impressive, with an overpotential of about 87mV at 10mAcm(-2). As a result, the hollow Ni@NiCo2O4 electrode as a bifunctional catalyst can achieve a current density of 10mAcm(-2) with a voltage of only 1.58V, showing promise for high performance yet cheap electrocatalysts for the overall water splitting reactions.