Electrochemical reduction of nitrate to ammonia using Fe-based catalyst: Insights into N2, CO2, and CO environments

Abstract

Electrochemical (EC) reduction of nitrate/nitrite for ammonia production is a key area of research in the realm of nitrogen pollutant treatment and recycling efforts. In this study, we utilized a commercial Fe(Mn) alloy to investigate EC reductions of nitrate/nitrite ions under N2, CO, and CO2-saturated conditions, shedding light on the influences of different feeding gases. Under N2 conditions, the ammonia production Faradaic efficiency (FE) reached 60 %; however, it significantly decreased under CO2 conditions. The presence of CO as a feeding gas proved detrimental, resulting in no ammonia production. Surprisingly, the Fe(Mn) alloy demonstrated superior EC Fischer-Tropsch (F-T) synthesis chemistry under CO conditions, generating CH4 and long-chain hydrocarbons (CnH2n+2 and CnH2n, where n=2–7). This contrasts with existing literature, where such alloys typically perform better under CO2 conditions. Notably, alkanes were found to be more predominant than their corresponding alkenes. The Anderson-Schulz-Flory equation plots exhibited significant linearity, resembling the traditional Fischer-Tropsch chain growth mechanism. This original discovery introduces new possibilities for employing commercial-grade Fe alloy in the direct EC F-T synthesis using CO, facilitating the production of long-chain hydrocarbons. Moreover, it paves the way for nitrate/nitrite ion treatments in analogous processes within diverse gas environments.