A Dinuclear Nickel Complex for Electrocatalytic Nitrite Reduction

While many mononuclear complexes for electrocatalytic NO x – reduction have been reported, there are few examples of dinuclear electrocatalysts. Here, we report on the electroreduction of NO 2 – by the dinuclear complex [Ni 2 (tpmc)(NO 3 ) 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 [Ni 2 (tpmc)(NO 3 ) 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 NH 4 + as the primary reduction product. Interestingly, in some respects, Ni 2+ (aq) is a better electrocatalyst for NO 2 – than [Ni(cyclam)] 2+, with faster electrocatalysis occurring at a more anodic onset potential, although the Faradaic efficiency for NH 4 + is lower.