Structure Effects of 2D Materials on α-Nickel Hydroxide for Oxygen Evolution Reaction.

To engineer low-cost, high-efficiency, and stable oxygen evolution reaction (OER) catalysts, structure effects should be primarily understood. Focusing on this, we systematically investigated the relationship between structures of materials and their OER performances by taking four 2D α-Ni(OH)2 as model materials, including layer-stacked bud-like Ni(OH)2-NB, flower-like Ni(OH)2-NF, and petal-like Ni(OH)2-NP as well as the ultralarge sheet-like Ni(OH)2-NS. For the first three (layer-stacking) catalysts, with the decrease of stacked layers, their accessible surface areas, abilities to adsorb OH-, diffusion properties, and the intrinsic activities of active sites increase, which accounts for their steadily enhanced activity. As expected, Ni(OH)2-NP shows the lowest overpotential (260 mV at 10 mA cm-2) and Tafel slope (78.6 mV dec-1) with a robust stability over 10 h among the samples, which also outperforms the benchmark IrO2 (360 mV and 115.8 mV dec-1) catalyst. Interestingly, Ni(OH)2-NS relative to Ni(OH)2-NP exhibits even faster substance diffusion due to the sheet-like structure, but shows inferior OER activity, which is mainly because the Ni(OH)2-NP with a smaller size possesses more active boundary sites (higher reactivity of active sites) than Ni(OH)2-NS, considering the adsorption properties and accessible surface areas of the two samples are quite similar. By comparing the different structures and their OER behaviors of four α-Ni(OH)2 samples, our work may shed some light on the structure effect of 2D materials and accelerate the development of efficient OER catalysts.