Boosting Nitrogen Activation via Ag Nanoneedle Arrays for Efficient Ammonia Synthesis

Electrocatalytic N2 reduction reaction (eNRR) provides a promising carbon neutral and sustainable ammonia-synthesizing alternative to the Haber-Bosch process. However, the nonpolar N2 has significant thermodynamic stability and requires ultrahigh energy to break down the N=N bond. Here, we report the construction of local enhanced electric fields (LEEFs) by Ag nanoneedle arrays to promote N=N fracture thus assisting the eNRR. The LEEFs could induce charge polarization on nitrogen atoms and reduce the energy barrier in the N2 first-protonation step. The detected N -N and N -H intermediates prove the cleavage of the N=N bond and the hydrogenation of N2 by LEEFs. The increased LEEFs lead to logarithmic growth rates for the targeted eNRR and exponential growth rates for the unavoidable competitive hydrogen evolution reaction. Thus, regulation and tuning of LEEFs to similar to 4 x 104 kV m-1 endows the raise of eNRR to the summit, achieving high ammonia selectivity with a Faradaic efficiency of 72.3 +/- 4.0%.

Automated summary

The construction of local enhanced electric fields (LEEFs) by Ag nanoneedle arrays promotes the fracture of nitrogen gas (N2) and assists in the electrocatalytic N2 reduction reaction (eNRR). The LEEFs induce charge polarization on nitrogen atoms and lower the energy barrier in the first-protonation step of N2. The cleavage of the N=N bond and the hydrogenation of N2 by LEEFs are confirmed by the detected N-N and N-H intermediates. Regulation and tuning of LEEFs to around 4 x 104 kV m-1 enables the achievement of high ammonia selectivity with a Faradaic efficiency of 72.3 +/- 4.0% in eNRR.