Impact of Local Microenvironments on the Selectivity of Electrocatalytic Nitrate Reduction in a BPM-MEA System

Electrochemical nitrate reduction reaction (NO3RR) has garnered increasing attention as a pathway for converting a harmful pollutant (nitrate) into a value-added product (ammonia). However, high selectivity toward ammonia (NH3) is imperative for process viability. Optimizing proton availability near the catalyst is important for achieving selective NH3 production. Here, the aim is to systematically examine the impacts of proton availability on NO3RR selectivity in a bipolar membrane (BPM)-based membrane electrode assembly (MEA) system. The BPM generates a proton flux from the membrane toward the catalyst during electrolysis. Thus, the BPM-MEA system can modulate the proton flux during operation. The impact of interposer layers, proton scavenging electrolytes (CO32-), and catalyst configurations are also examined to identify which local microenvironments favor ammonia formation. It is found that a moderate proton supply allows for an increase in ammonia yield by 576% when compared to the standard MEA setup. This also results in a high selectivity of 26 (NH3 over NO2-) at an applied current density of 200 mA cm-2. High selectivity toward ammonia is vital for the feasibility of the electrochemical nitrate reduction reaction (NO3RR). This study employs a bipolar membrane-based membrane electrode assembly system to investigate the influence of proton availability on the selectivity of NO3RR. The results underscore the pivotal importance of moderate proton supply for achieving highly selective NH3 production in NO3RR. image