A Dinuclear Nickel Complex for Electrocatalytic Nitrite Reduction

While many mononuclear complexes for electrocatalytic NOx– reduction have been reported, there are few examples of dinuclear electrocatalysts. Here, we report on the electroreduction of NO2– by the dinuclear complex [Ni2(tpmc)(NO3)2]2+ (tpmc = 1,4,8,11-tetrakis-(2-pyridylmethyl)-1,4,8,11-tetraazacyclotetradecane) and a mononuclear analogue [Ni(cyclam)]2+ (cyclam = 1,4,8,11-tetraazacyclotetradecane). Notably, the presence of the second metal ion in [Ni2(tpmc)(NO3)2]2+ shifts the onset of catalysis anodically by ca. 0.3 V compared to [Ni(cyclam)]2+, while maintaining a similar electrocatalytic rate and Faradaic efficiency. Both complexes produce NH4+ as the primary reduction product. Interestingly, in some respects, Ni2+(aq) is a better electrocatalyst for NO2– than [Ni(cyclam)]2+, with faster electrocatalysis occurring at a more anodic onset potential, although the Faradaic efficiency for NH4+ is lower.