Defective TiO2−x for High-Performance Electrocatalytic NO Reduction toward Ambient NH3 Production

Abstract

Synthesis of green ammonia (NH3) via electrolysis of nitric oxide (NO) is extraordinarily sustainable, but multielectron/proton-involved hydrogenation steps as well as low concentrations of NO can lead to poor activities and selectivities of electrocatalysts. Herein, it is reported that oxygen-defective TiO2 nanoarray supported on Ti plate (TiO2−x/TP) behaves as an efficient catalyst for NO reduction to NH3. In 0.2 m phosphate-buffered electrolyte, such TiO2−x/TP shows competitive electrocatalytic NH3 synthesis activity with a maximum NH3 yield of 1233.2 µg h−1 cm−2 and Faradaic efficiency of 92.5%. Density functional theory calculations further thermodynamically faster NO deoxygenation and protonation processes on TiO2−x (101) compared to perfect TiO2 (101). And the low energy barrier of 0.7 eV on TiO2−x (101) for the potential-determining step further highlights the greatly improved intrinsic activity. In addition, a Zn-NO battery is fabricated with TiO2−x/TP and Zn plate to obtain an NH3 yield of 241.7 µg h−1 cm−2 while providing a peak power density of 0.84 mW cm−2.