In situ characterization techniques for electrochemical nitrate-to-ammonia conversion

Abstract

Ammonia (NH₃) is a vital industrial raw material, crucial for global industrialization and economic growth. The conventional Haber–Bosch process, though dominant in NH₃ synthesis, suffers from high energy demands and substantial CO₂ emissions, driving the need for sustainable alternatives. In this context, electrochemical nitrate reduction (eNO₃⁻RR) has emerged as a promising pathway for NH₃ production due to its mild operating conditions and environmentally friendly nature. Optimizing electrochemical nitrate reduction (eNO₃⁻RR) for ammonia synthesis demands deep mechanistic insights into surface-driven reactions. Traditional electrochemical methods, though effective for analyzing reaction kinetics (e.g., reactant adsorption and rate-determining steps), struggle to track dynamic and intricate surface processes inherent to eNO₃⁻RR. Consequently, advancing mechanistic studies of eNO₃⁻RR critically depends on developing in situ characterization techniques. This review highlights recent progress in methods such as in situ Fourier transform infrared (FTIR) spectroscopy, in situ Raman spectroscopy, differential electrochemical mass spectrometry (DEMS), and in situ electron paramagnetic resonance (EPR) for probing nitrate-to-ammonia reaction pathways. These tools have deepened mechanistic understanding of eNO₃⁻RR and show significant potential for future applications. Finally, this review discusses the key challenges that persist in unraveling the detailed mechanisms of this process.