Hierarchical Porous Prism Arrays Composed of Hybrid Ni-NiO-Carbon as Highly Efficient Electrocatalysts for Overall Water Splitting.

Searching for an economical and efficient water splitting electrocatalyst is still a huge challenge for hydrogen production. This work reports one-step synthesis of hierarchical porous prism arrays (HPPAs) composed of Ni-NiO nanoparticles embedding uniformly in graphite carbon (Ni-NiO/C HPPAs), which is derived from metal-organic framework (CPO-27-Ni) prism arrays grown on nickel foam (NF). Remarkable features of the prism arrays, synergistic effect of Ni-NiO/C, porous graphite carbon, high conductive NF, and good contact between catalyst and current collector result in excellent electrocatalytic performance of Ni-NiO/C HPPAs@NF. Ni-NiO/C HPPAs@NF shows a small overpotential of ∼49.48 mV at the current density of 10 mA cm, low Tafel slope of 74 mV dec and robust stability for hydrogen evolution reaction (HER) in alkaline media. Especially, the overpotential for HER of Ni-NiO/C HPPAs@NF is only ∼132 mV at the current density of 185 mA cm, almost the same as the value from the Pt/C. Furthermore, for oxygen evolution reaction in basic media, Ni-NiO/C HPPAs@NF shows better catalytic activity, lower Tafel slope and higher durability than precious IrO. The above finding offers an effective strategy to design the bifunctional electrocatalysts for overall water splitting.