Selective Nitrate Electroreduction to Ammonia on CNT Electrodes with Controllable Interfacial Wettability

Abstract

The development of electrocatalysts that can efficiently reduce nitrate (NO 3 − ) to ammonia (NH 3 ) has garnered increasing attention due to their potential to reduce carbon emissions and promote environmental protection. Intensive efforts have focused on catalyst development, but a thorough understanding of the effect of the microenvironment around the reactive sites of the catalyst is also crucial to maximize the performance of the electrocatalysts. This study explored an electrocatalytic system that utilized quaternary ammonium surfactants with a range of alkyl chain lengths to modify an electrode made of carbon nanotubes (CNT), with the goal of regulating interfacial wettability toward NO 3 − reduction. Trimethyltetradecylammonium bromide with a moderate alkyl chain length created a very hydrophobic interface, which led to a high selectivity in the production of NH 3 (∼87%). Detailed mechanistic investigations that used operando Fourier-transform infrared (FTIR) spectroscopy and online differential electrochemical mass spectrometry (DEMS) revealed that the construction of a hydrophobic modified CNT played a synergistic role in suppressing a side reaction involving the generation of hydrogen, which would compete with the reduction of NO 3 − . This electrocatalytic system led to a favorable process for the reduction of NO 3 − to NH 3 through a direct electron transfer pathway. Our findings underscore the significance of controlling the hydrophobic surface of electrocatalysts as an effective means to enhance electrochemical performance in aqueous media.

Effects of Ionic Interferents on Electrocatalytic Nitrate Reduction: Mechanistic Insight

“…For example, one of the primary design goals can be the enhancement of adsorption affinity for NO 3 – over ionic impurities in IHP. These features could be achieved by developing materials with tandem catalytic functions, abundant oxygen vacancies or defects, or a positively charged surface via surface coatings. ,, Reconstruction of the electronic structure during electroreduction can also tailor the catalyst surface to enhance the adsorption of intermediates through the interaction with co-existing ions. ,, Developing electrodes with optimal cation-induced electric fields for the stabilization of intermediates and the dissociation of water molecules within the EDL would be of great interest. , Furthermore, given the improved selectivity for NH 3 , albeit often accompanied by an undesired increase in the HER activity, electrodes characterized by an optimal HBE are deemed ideal. , Adjusting catalytic materials to limit HER by minimizing exposure of reactive H* adsorption sites is feasible. Achieving this may involve diminishing the prevalence of surface-terminated OH* and O* groups, which function as active sites for the HER through the facilitation of hydrogen bond formation .…”