Boosting Nitrogen Activation via Ag Nanoneedle Arrays for Efficient Ammonia Synthesis

Area of Science:

• Electrochemistry
• Materials Science
• Sustainable Chemistry

Background:

• Electrocatalytic nitrogen reduction reaction (eNRR) is a sustainable alternative to the Haber-Bosch process for ammonia synthesis.
• The high thermodynamic stability of the N≡N bond presents a major challenge for efficient eNRR.
• Breaking the N≡N bond requires significant energy input, limiting current eNRR efficiency.

Purpose of the Study:

• To investigate the use of local enhanced electric fields (LEEFs) to promote nitrogen bond cleavage in eNRR.
• To develop a method for enhancing the efficiency and selectivity of electrocatalytic ammonia synthesis.
• To correlate LEEF strength with eNRR performance and ammonia selectivity.

Main Methods:

• Fabrication of silver (Ag) nanoneedle arrays to generate LEEFs.
• Electrocatalytic testing of Ag nanoneedle arrays for N2 reduction.
• Detection of reaction intermediates (N-N and N-H) to confirm N2 bond cleavage and hydrogenation.
• Tuning LEEF strength to optimize eNRR performance.

Main Results:

• LEEFs induced charge polarization on nitrogen atoms, lowering the energy barrier for N2 first-protonation.
• Experimental evidence confirmed N2 bond cleavage and hydrogenation facilitated by LEEFs.
• Optimized LEEFs (∼4 × 10^4 kV m^-1) significantly enhanced eNRR, achieving a Faradaic efficiency of 72.3 ± 4.0% for ammonia.
• LEEFs showed logarithmic growth for eNRR and exponential growth for hydrogen evolution reaction.

Conclusions:

• LEEFs generated by Ag nanoneedle arrays are effective in promoting N2 bond fracture for eNRR.
• Tuning LEEFs offers a viable strategy to enhance ammonia selectivity and efficiency in electrocatalytic synthesis.
• This approach presents a promising pathway towards carbon-neutral and sustainable ammonia production.