Rational element-doping of FeOOH-based electrocatalysts for efficient ammonia electrosynthesis

Electrocatalysis has been intensively studied in nitrogen (N2) reduction for its sustainable power and stable catalytic performance, but it is still limited by weak activation of N2 at the catalytic sites, and the competition from the hydrogen evolution reaction (HER). The special d-orbital electron arrangement of transition metals and the tuning of the microenvironment provide possible strategies to enhance the activation of N2, while improving the selectivity of the eNRR. Herein, FeO(OH, S) with high spin state and Mo–FeOOH with low spin state were designed around the FeOOH-based catalysts through elemental doping, which could achieve excellent ammonia yield performance of 80.1 ± 4.0 μg h−1 mgcat−1 (FE 36.9 ± 0.5%) and 86.8 ± 4.1 μg h−1 mgcat−1 (FE 29.1 ± 0.8%) in 0.1 M LiClO4 at −0.6 V vs. RHE, respectively, coupled with polyethylene glycol (PEG) to inhibit the HER. Based on theoretical calculations to investigate the adsorption of N2 on Fe sites, the FeO(OH, S) catalyst has stronger adsorption ability, which may originate from the high spin effect, which means that the more isolated and highly active eg orbital electrons are more beneficial to realize the electronic feedback mechanism, promoting the d–π* orbital interaction with N2.