Fabrication of Three-Dimensional Porous Materials with NiO Nanowalls for Electrocatalytic Oxygen Evolution

Nanosheets are two-dimensional (2D) nanocrystals that exhibit superior electrochemical performance. However, nanosheets are typically stacked horizontally toward the current collector, leading to poor utilization of individual nanosheets. Although most studies have fabricated three-dimensional (3D) structures using nanosheets, the wall thickness was a few hundred nanometers, suggesting that hundreds of nanosheets were restacked along the wall. In this study, we demonstrated the fabrication of a 3D structure constructed by NiO nanowalls with a thickness of 2-3 nm (3D-NiO). The specific surface area of 3D-NiO was found to be 42 m(2) g(-1), which is 2.6 times larger than that of NiO nanoparticles. The specific capacity of 3D-NiO was 2.5 times higher than that of NiO nanoparticles and could be attributed to the large specific surface area because of the nature of the thin nanowalls. The O-2-evolution reaction (OER) activity of 3D-NiO at 1.65 V vs RHE was sixfold greater than that of NiO nanoparticles. The enhanced OER activity of 3D-NiO could be attributed to both the large specific surface area and the fabrication of diffusion paths within the 3D structure. The OER activity of 3D-NiO after 500 cycles was four times higher than that of NiO nanoparticles. Our results show that the 3D structure fabricated with thin nanowalls is a promising porous material for capacitor electrodes and electrocatalysts for applications in electrolysis and fuel cells.