Oxalic acid enhanced nano zero-valent iron for Electrocatalytic nitrate reduction to Ammonia

Abstract

Ammonia (NH₃), a widely used chemical product, has various applications in numerous fields. However, the high energy consumption of the traditional ammonia synthesis process is inconsistent with the pursuit of “zero carbon,” and there is an urgent need for a new method to synthesize NH₃. The electrocatalytic NO₃⁻-to-NH₃ (NITRR) offers an ideal route to synthesizing NH₃ under ambient conditions. Nano zero-valent iron (nZVI) has been widely used in nitrate wastewater treatment due to its environmental friendliness, low cost, and high activity. However, nZVI is difficult to recover and prone to deactivation because of its tendency to corrode and agglomerate. Here, we report a method to enhance the activity and stability of nZVI through oxalic acid modification. In this study, oxalic acid and citric acid modified nZVI on foam nickel substrates (OA-nZVI/NF) was examined as examples. Experiments confirmed that the Faraday efficiency of NH₃ (FE_NH3) from OA-nZVI/NF was 84.9 %, respectively, at −0.4 V vs. RHE, which was significantly higher than that of nZVI/NF (64.5 %). More importantly, the FE_NH3 of OA-nZVI/NF electrod did not decrease significantly after continuous electrolysis for 100 h. Subsequently, electrochemical characterization and control experiments revealed that oxalic acid modification reduced the corrosion potential of nZVI/NF and promoted the generation of hydrogen-free radicals (H*) from nZVI/NF. This work provides an economical and feasible approach to improving the stability and activity of corrosion-prone and deactivated materials.