N-Doped Porous Carbon Self-Generated on Nickel Oxide Nanosheets for Electrocatalytic N2 Fixation with a Faradaic Efficiency beyond 30%

Abstract

The electrocatalysis conversion of N2 to NH3 at ambient conditions is promising for achieving clean and sustainable NH3 production with low energy consumption. However, this process suffers from the low yield rate of NH3 and low Faradaic efficiency (FE) by the previously reported electrocatalysts. In this work, a nanocomposite of nickel oxide coated with nitrogen-doped porous carbon distributed on graphite paper (N-C@NiO/GP) with remarkable electrocatalytic activity for nitrogen reduction reaction (NRR) is reported. N-C@NiO/GP attains an impressive Faradaic efficiency of 30.43% for NH3 production, and the NH3 yield rate reaches 14.022 μg h–1 mgcat.–1 (1.15 × 10–10 mol s–1 cm–2) at −0.2 V vs the reversible hydrogen electrode. The composite also shows excellent electrocatalytic activity and structure stability with an electrocatalytic period of up to 20 h. When the 15N2 is used as the feeding gas, the produced species are 14NH4+ and 15NH4+, which suggests that the reaction follows a Mars–van Krevelen mechanism. The synthesized NH3 is determined from the introduced N2 as indicated by no obvious change in N/Ni ratio. The microstructure before and after the durability test is similar and the catalytic performance during the 2 h NRR process, which is repeated six times, is stable. This work not only exploits an excellent electrocatalyst for N2 fixation to NH3 but also provides a direction for the inexpensive preparation of highly active and stable transition metal oxide catalysts.