Bismuth stabilized by ZIF derivatives for electrochemical ammonia production: Proton donation effect of phosphorus dopants

N-2 electroreduction reaction (NRR) offers a feasible and promising alternative for NH3 production by using clean energy sources. However, it is still obstructed by the pretty low NH3 yield rate and Faradaic efficiency (FE) primarily due to the undesired competing hydrogen evolution reaction and the extremely stable N N bond. Herein, bismuth nanoparticles were successfully embedded in N and P co-doped carbon nanoflakes (Bi/NPC) by high-temperature pyrolyzation of Bi-zeolitic imidazole frameworks (ZIF) followed by phosphorization, and used as a high-efficiency catalyst toward N-2 electroreduction to NH3. In 0.1 M KHCO3 electrolyte, Bi/NPC exhibits excellent NRR performances, including a high NH3 yield rate of 3.12 mu g.h(-1)cm(-2) (-0.6 V vs. reversible hydrogen electrode (RHE)), an outstanding FE of 13.58% (-0.4 V vs. RHE), and a remarkable stability up to 36 h under ambient conditions. This outstanding NRR catalytic activity is mainly attributed to the intrinsic electrocatalytic NRR activity combined with the inert hydrogen evolution reaction (HER) activity of Bi, the adsorption and activation of N-2 facilitated by N dopants, as well as the superior conductivity and the large specific surface area of the two-dimensional layered carbon matrix. Notably, the hydrogen source provided by P dopant promotes the hydrogenation of the adsorbed N, which further boosts the NRR performance in alkaline electrolyte. The ultralong durability of Bi/NPC is attributed to the highly dispersed bismuth catalytic active centers confined in the skeleton of N and P co-doped carbon nanoflakes, which inhibits the agglomeration of bismuth centers. This work presents a novel avenue for designation and fabrication of high-performance Bi-based electrocatalysts for NRR.

Automated summary

This study successfully prepares a catalyst with nanoparticles of bismuth embedded in co-doped carbon nanoflakes (Bi/NPC), which exhibits excellent performance in electroreduction reactions with high NH3 yield rate, Faradaic efficiency, and stability. This is attributed to the electrocatalytic activity of bismuth, the inhibition of hydrogen evolution reactions, the enhanced N-2 adsorption and activation facilitated by N-doping, as well as the superior conductivity and large specific surface area of the carbon matrix.