Sensing nitrite by iron-nitrogen-carbon oxygen reduction electrocatalyst

Nitrite contamination of groundwater is a concerning consequence of anthropic activity. The electrochemical detection of nitrite in water is based on direct electrocatalytic oxidation of nitrite over modified electrodes. However, drawbacks associated to the high oxidation potential required, oxide layer formation, and O₂ interference are present. Considering the recent availability and low cost of platinum-group-metal-free (PGM-free) electrocatalyst, a new sensing strategy is presented based on this class of material commonly used for oxygen reduction reaction (ORR) in fuel cells. The working principle relies on the inhibition of ORR active sites of PGM-free caused by the interaction with nitrite. The parameters of interest for the ORR inhibition were determined through cyclic voltammetry and chronopotentiometry using a rotating disk electrode to minimize oxygen diffusion limitations at the working electrode. The linearity range of the sensor was 1–100 µM, with a sensitivity of 3.4 mV µM⁻¹, and a limit of detection (LOD) in the sub-µM range. Based on the optimization of the electrocatalyst thickness and its reusability, the cost of 1 USD for ∼2000 tests was calculated.