The cobalt complex, [Co(CR)Br2]+, where CR is the redox active macrocycle 2,12-dimethyl-3,7,11,17-tetraazabicyclo-[11.3.1]-heptadeca-1(17),2,11,13,15-pentaene, has been investigated for the electrocatalytic reduction of aqueous NO2– and NO3– . At neutral pH, the bromide ligands are hydrolyzed, providing [Co(CR)(OH2)(OH)]2+ as the major species in aqueous solution. In the presence of nitrite, [Co(CR)(NO2)2]+ is formed as the major species in solution and is a precursor to the electrocatalytic reduction of NO2–, which is selectively converted to ammonium with high Faradaic efficiency. Although similar NO3– binding is not observed, electrocatalytic reduction to ammonium also occurs, albeit with a lower Faradaic efficiency. In this case, NO2– is generated as an intermediate product of NO3– reduction. The presence of phosphate buffer induces a new catalytic process in the electrocatalytic reduction of NO2–.

Electrocatalytic reduction of nitrogen oxyanions with a redox active cobalt macrocycle complex

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