A practical FeP nanoarrays electrocatalyst for efficient catalytic reduction of nitrite ions in wastewater to ammonia

Ammonia production is an energy-intensive process while nitrite ions are a substantial environmental pollutant, therefore the conversion of nitrite ions (NO2-) into ammonia (NH3) via an electrochemical process is of great significance. Using a hydrothermal method plus a low temperature phosphating process, iron phosphide nanoarrays (FeP NA) were prepared on a Ti plate to form FeP NA|Ti, which was then used to efficiently convert NO2- ions into NH3. In a single-chamber cell using a neutral pH electrolyte, the Faradaic efficiency for nitrite to ammonia conversion reached 82.5 ± 2.3 %. Various parameters were optimized to ensure the high performance of FeP NA|Ti which were explained with mechanistic studies. It was found that atomic hydrogen (H*) greatly impacts both the reaction rate and selectivity. Furthermore, density functional theory (DFT) calculations reveal that the (211) and (011) facets of FeP are the main active faces for nitrite reduction where the nitrite ions tend to bind with two adjacent Fe atoms of FeP to ensure maximum performance.