Membraneless Electrochemical Synthesis Strategy toward Nitrate-to-Ammonia Conversion

Area of Science:

• Electrochemistry
• Materials Science
• Chemical Engineering

Background:

• Ammonia synthesis via nitrate electroreduction (NO3RR) in membraneless electrolyzers offers cost and energy savings.
• Challenges include chemical crossover and side reactions, hindering efficient ammonia production.
• Existing membrane-based systems are expensive and energy-intensive.

Purpose of the Study:

• To develop an efficient membraneless strategy for nitrate electroreduction to ammonia.
• To screen catalysts with low oxygen reduction activity and optimize counter electrodes for ammonia synthesis.
• To investigate the impact of a pulse process on catalyst performance and side reaction suppression.

Main Methods:

• Screening of catalysts for NO3RR with low oxygen reduction activity.
• Matching counter electrodes with high oxygen evolution activity.
• Utilizing a pulse process to induce reversible surface reconstruction of cobalt-based catalysts.
• Electrochemical performance evaluation in a membraneless cell.

Main Results:

• The Co-Co system in a membraneless cell outperformed traditional H-type cells.
• Achieved a 4 V lower full-cell voltage and 56.9% energy savings per kg of ammonia.
• The pulse process improved NO3RR efficiency and suppressed side reactions.
• A maximum NH3 yield rate of 1500.9 μmol cm-2 h-1 with 92.6% Faraday efficiency was obtained.

Conclusions:

• A pulse-coupled membraneless strategy is effective for efficient ammonia synthesis.
• This approach offers significant energy and cost reductions compared to membrane-based methods.
• The findings provide new insights into designing complex electrochemical synthesis systems.