Nitrate and nitrite electrocatalytic reduction on Rh-modified pyrolytic graphite electrodes

The electrochemical reduction of nitrate and nitrite anions was investigated on Rh-modified pyrolytic graphite electrodes prepared by potentiostatic electrodeposition with the use of a double-pulse technique. Several important parameters (pH, temperature and composition of electrolytic medium, electrolysis potential) were varied. Only ammonia and nitrite ions were detected among NO3− reduction products, while NO2− ions are straightforwardly reduced to ammonia. The experimental data (CV measurements and the results of electrolyses) clearly show that Rh/graphite electrodes are much more efficient for NO2− reduction than for that of NO3− at room temperature which was confirmed by the determination of rate constants of corresponding reactions and the activation energy of NO2− reduction. The influence of carboxylate anions and tetraalkylammonium cations on the electrocatalytic activity of Rh/graphite electrodes was investigated and the inhibiting effect of HCOO− anions on hydrogen evolution reaction and nitrate reduction was demonstrated.