Electrocatalytic Reduction of Nitrogen Oxyanions with a Redox-Active Cobalt Macrocycle Complex.

The cobalt complex, [Co(CR)Br], 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 NO and NO. At neutral pH, the bromide ligands are hydrolyzed, providing [Co(CR)(OH)(OH)] as the major species in aqueous solution. In the presence of nitrite, [Co(CR)(NO)] is formed as the major species in solution and is a precursor to the electrocatalytic reduction of NO, which is selectively converted to ammonium with high Faradaic efficiency. There is evidence for both homogeneous and heterogeneous electrocatalysis. Although similar NO binding is not observed, electrocatalytic reduction to ammonium also occurs, albeit with a lower Faradaic efficiency. In this case, NO is generated as an intermediate product of NO reduction.