Progress Report on the Evaluation of Porous Cathode for the Electrochemical Reduction of Nitrates and Nitrites in Liquid Wastes

This report describes the experimental and modeling work performed to evaluate porous cathodes for the electrochemical reduction of nitrates and nitrites in liquid wastes. The experiments were done using the MPt cell with two different porous cathodes: nickel foam and TySARm SBS. The experimental results are compared with each other and to those obtained with a planar nickel cathode. The results show that the ammonia production reaction is the dominant cathodic reaction (-80% efficiency) for all three electrodes. The temperature range used in this study was 29-37 "C while the catholyte feed was either 0.6M NaNO2 or 1.9M NaN03, both supported by a 1.33M NaOH solution. All experiments used a constant current density of 0.25 A/cm2. The experimental results suggest that the porous nickel electrode at lower temperatures (-3 1 "C) is the most . efficient ofthe three electrodes for-the reduction of nitratesand-nitrites.-The porous nickel electrode exhibited the highest conversion of nitrates and nitrites, and the lowest overpotential for a given current density. _ _ The partial current fiactions at known catholyte concentrations were used to extract the exchange-current densities for the five cathodic reactions. Using these kinetic parameters, dynamic simulations of the four hour experiments were performed. Agreement was found between the model and experimental results for changes in the moles of the nitrate and nitrite and the cell overpotential with time. Future work will determine the effects of temperature and current densities on the exchange-current densities and reaction product distributions. The performance of other porous cathode materials (TySARm EP5, TySmm M**) will also be evaluated.