Orthorhombic α-NiOOH Nanosheet Arrays: Phase Conversion and Efficient Bifunctional Electrocatalysts for Full Water Splitting

The development of efficient and earth-abundant electrocatalysts is essential for water splitting against future renewable energy systems. Generally, NiOOH is considered to play a key role in OER processes in alkaline electrolytes in the Ni-based OER catalysts (such as NiO, NiS, NiSe, and etc.). However, there are rare reports of NiOOH for both OER and HER electrocatalysis. Here, we proposed a facile strategy to obtain the vertically aligned orthorhombic alpha-NiOOH nanosheet arrays on 3D Ni foam (alpha-NiOOH/NF). The catalyst exhibited excellent OER activity obtaining 10 mA cm(-2) just affording a low overpotential of 266 mV. The performance was superior to those of the compared samples including Ni2Cl(OH)(3) nanosheets on NF, NiO nanosheets on NF, Ni microspheres on NF, Ni foam and even better than the commercial IrO2 as well as most of the reported OER electrocatalysts in references. Furthermore, the a-NiOOH/NF electrode demonstrated robust durability over a long period with the increase of current density, which was attributed to the phase conversion from alpha-NiOOH phase to the distorted beta-NiOOH phase. Additionally, the prepared orthorhombic a-NiOOH nanosheet arrays also showed the more active electrocatalysis for HER of water splitting than the above comparative samples. The a-NiOOH nanosheets therefore showed a high performance of bifunctional electrocatalysis for full water splitting with the onset potential of 1.66 V.