A Dinuclear Nickel Complex for Electrocatalytic Nitrite Reduction

While many mononuclear complexes for electrocatalytic NO_<i>x</i>^- 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.