Field‐Deployable Ammonia Sensor for Assessment of Wastewater Feedstocks and Their Utilization for Ammonia Synthesis

<jats:title>Abstract</jats:title><jats:p>Renewable energy‐driven electrochemical ammonia synthesis using nitrates presents a promising pathway for producing ammonia while utilizing wastewater as a feedstock. This approach enables decentralized ammonia production and addresses environmental concerns related to nitrate pollution. If the broader goal is to use real wastewater as a feedstock, various anions and their influence on ammonia selectivity must be carefully studied. However, two significant challenges hinder its practical implementation: interference from common wastewater anions (sulfate, chloride, phosphate) and the lack of rapid, cost‐effective ammonia monitoring methods suitable for process optimization. Here, an integrated solution combining fundamental studies of anion effects with an innovative paper‐based detection platform is presented. This systematic investigation reveals how competing ions influence electrochemical ammonia selectivity, providing crucial insights for catalyst design. More importantly, a paper‐based sensing protocol is developed that achieves sensitive ammonia quantification (10–500 µ<jats:sc>m</jats:sc> range with 35 µ<jats:sc>m</jats:sc> limit of detection) using merely 10 µL of sample. This field‐deployable system eliminates the need for sophisticated instrumentation, delivering results three times faster than standard colorimetric assays while maintaining >90% accuracy. The sensor's robust performance enabled real‐time monitoring of ammonia production from synthetic and real wastewater samples during electrochemical testing.</jats:p>