Core‐Shell Structured NiCo 2 O 4 @FeOOH Nanowire Arrays as Bifunctional Electrocatalysts for Efficient Overall Water Splitting

Exploring earth‐abundant and high‐performance catalysts for water‐splitting is extremely crucial to produce clean hydrogen fuel. In this work, FeOOH was electrodeposited on NiCo 2 O 4 nanowire to form a three dimensional (3D) core‐shell structure on Ni foam (NiCo 2 O 4 @FeOOH/NF) as bifunctional catalyst for overall water splitting. To control the thickness of FeOOH shell layer by optimizing electrodeposition time, the NiCo 2 O 4 @FeOOH/NF(500s) with FeOOH layer of ∼7 nm thickness exhibits excellent catalytic activity and stability for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in alkaline solution. Moreover, in a two‐electrode water splitting system, extremely small potential of 1.52 V can be achieved for NiCo 2 O 4 @FeOOH/NF(500s), giving a current density of 10 mA cm −2 . Detailed investigation reveals that the thickness of FeOOH layer, strong electronic interaction at the interface between NiCo 2 O 4 and FeOOH play critical role in the excellent catalytic property.