Support effect boosting the electrocatalytic N2 reduction activity of Ni2P/N,P-codoped carbon nanosheet hybrids

Abstract

Electrochemical reduction of N₂ into NH₃ (N₂RR) under ambient conditions has emerged as a sustainable approach alternative to the Haber–Bosch process. However, the more favored H⁺ reduction in aqueous electrolytes can lead to low faradaic efficiency for NH₃ production. Thus, designing electrocatalysts to suppress proton reduction is the key to improve the activities towards the N₂RR. As an efficient strategy for modulating the associated electronic properties of surface catalysts, the support effect is drawing growing attention. Sparked by the support effect, Ni₂P nanoparticles supported by N,P co-doped carbon nanosheets (Ni₂P/N,P-C) were synthesized and found to have a higher affinity for N₂ molecules than for H⁺ which makes it a good candidate for the N₂RR. The prepared catalyst showed an NH₃ yield rate of 34.4 μg h⁻¹ mg_Ni2P⁻¹ at −0.2 V vs. the reversible hydrogen electrode (RHE) with a faradaic efficiency of 17.21% in 0.1 M HCl (22.89% and 57.2 μg h⁻¹ mg_Ni2P⁻¹ in 0.2 M PBS; 19.82% and 90.1 μg h⁻¹ mg_Ni2P⁻¹ in 0.1 M KOH), which is higher than the best values ever reported for noble-metal free catalysts in aqueous solution under ambient conditions. Importantly, the N,P-C substrate in this work is regarded as an electronic storage medium that regulates the electronic distribution of Ni₂P/N,P-C when N₂ is chemically adsorbed at the Ni site, playing a vital role in inhibiting the adsorption of H and promoting the adsorption and activation of N₂ molecules. This work not only gives a new insight into understanding the transformation of the HER to the N₂RR, but also provides a guideline for the development of highly active non-noble-metal catalysts.