Effect of nickel oxide morphology on the nitrogen electrochemical reduction reaction

Abstract

In order to study the effect of catalysts’ morphology on the electrochemical reduction of nitrogen gas, sample catalysts of NiO with four different morphologies (hollow spherical, sea urchin-shape, cubic block, and rod-like) were prepared. Characterization of the NiO catalysts was carried out using SEM, BET, XRD and electrochemical investigation techniques. The results indicated that the nitrogen reduction reaction (NRR) is strictly dependent on the morphology of the NiO catalysts, as the hollow spherical NiO showed the best electrochemical NRR performance of NH 3 yield rate (3.21 μg h -1 mg -1 cat. , 4.19 × 10 -11 mol cm -2 s -1 ) and Faradaic efficiency (1.37%), which was higher than the yields and efficiencies of the rod-NiO (1.8 μg h -1 mg -1 cat. , 3.24 × 10 -11 mol cm -2 s -1 , 1.17%), sea urchin-NiO (1.66 μg h -1 mg -1 cat. , 2.44 × 10 -11 mol cm -2 s -1 , 1.08%) and cubic block-NiO (1.32 μg h -1 mg -1 cat. , 2.14 × 10 -11 mol cm -2 s -1 , 0.81%), respectively. These results match the order of the specific surface area of the NiO samples, with hollow spherical (113.91 m 2 g -1 ) > rod-NiO (55.12 m 2 g -1 ) ≈ sea urchin-NiO (55.29 m 2 g -1 ) > cubic block-NiO (38.57 m 2 g -1 ). This correlation can be attributed to the fact that large specific surface areas can provide more active sites for electrocatalysis. This work demonstrates the effect of the morphology of the NiO catalysts on its electrochemical NRR properties, which could offer some opportunity for the preparation of new electrode materials with improved electrocatalytic properties.