Mixed NiO/NiCo₂O₄ Nanocrystals Grown from the Skeleton of a 3D Porous Nickel Network as Efficient Electrocatalysts...

Mixed NiO/NiCo₂O₄ 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/NiCo₂O₄ nanocrystals and the charge transport highway to accelerate the sluggish kinetics of the OER. The mixed NiO/NiCo₂O₄ 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 NiCo₂O₄ (9.35). The NiO/NiCo₂O₄@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.