Unveiling the role of cobalt doping in optimizing ammonia electrosynthesis on iron-cobalt oxyhydroxide hollow nanocages

3d transition metal catalysts are effective for the electrocatalytic nitrogen (N-2) reduction reaction (NRR) to produce ammonia (NH3), but the role of active sites remains elusive. Herein, a series of iron-cobalt oxyhydroxide hollow nanocages (FeCoOOH HNCs) were constructed via controlled Co doping. The as-obtained FeCoOOH HNCs with an Fe/Co ratio of 1 : 1 exhibited a high faradaic efficiency of 14.7% and superior NH3 formation rate of 16.8 & mu;g h(-1) mg(cat)(-1) at -0.3 V vs. RHE. In situ Raman spectra disclose the existence of intermediates and identify the reaction pathway. Density functional theory (DFT) calculations reveal that Co doping could lower the energy barrier of *N-2 & RARR; *NNH & RARR; *NNHH, induced by the preferential proton adsorption on Co sites to drive NH3 electrosynthesis. Moreover, FeCoOOH HNCs with a suitable Fe/Co ratio could boost the *N-2 activation due to the bolstered polarization of adsorbed N-2, while increasing the energy barrier for the hydrogen evolution reaction. This work provides an intriguing strategy towards efficient NRR electrocatalysis by the elaborate design of two 3d transition metals.

Automated summary

In this study, a series of iron-cobalt oxyhydroxide hollow nanocages were constructed via controlled Co doping, which exhibited high efficiency and superior NH3 formation rate in electrocatalytic nitrogen reduction reaction. In situ Raman spectra revealed the existence of intermediates and identified the reaction pathway. Density functional theory calculations showed that Co doping could lower the energy barrier and drive NH3 electrosynthesis through preferential proton adsorption on Co sites. Moreover, these hollow nanocages with a suitable Fe/Co ratio could boost N-2 activation.