Mixed NiO/NiCo₂O₄ Nanocrystals Grown from the Skeleton of a 3D Porous Nickel Network as Efficient Electrocatalysts for Oxygen Evolution Reactions

Mixed NiO/NiCo 2 O 4 nanocrystals grown in situ from the skeleton of a 3D porous nickel network (3DPNN) were prepared with a simple hydrothermal method followed by a low temperature calcination, exhibiting outstanding electrocatalytic efficiencies toward oxygen evolution reactions (OER). The 3DPNN was prepared with a novel leaven dough method and served as both the nickel source for growth of the mixed NiO/NiCo 2 O 4 nanocrystals and the charge transport highway to accelerate the sluggish kinetics of the OER. The mixed NiO/NiCo 2 O 4 nanocrystals exhibited pronounced synergistic effects to achieve a high mass activity of 200 A g –1 at the catalyst mass loading of 0.5 mg cm –2, largely outperforming the corresponding single component nanocrystal systems, NiO (5.87) and NiCo 2 O 4 (9.35). The NiO/NiCo 2 O 4 @3DPNN composite electrocatalyst achieved a low overpotential of 264 mV at the current density of 10 mA cm –2 and 389 mV at the practically high current density of 250 mA cm –2, which compete favorably among the top tier of previously reported OER electrocatalysts. Moreover, it exhibited good stability even at the high current density of 250 mA cm –2, showing only 9.40% increase in working applied potential after a continuous 12 h operation. The present work demonstrates a new design for highly efficient OER catalysts with in situ growth of mixed oxide nanocrystals of pronounced synergistic effects.