Electrocatalytic reduction of carbon dioxide by nickel cyclam2+ in water: study of the factors affecting the efficiency and the selectivity of the process

Abstract

rate in the Co' neutral complexes but not in the Coo anion radicals. This argues that the isomerization mechanism is different in the two different metal oxidation states.2. The rapid isomerization of the Coo complexes may arise from lifting of symmetry restrictions to the simplest molecular isomerization mechanism in the 19-electron monoanions.3. When dibenzocyclooctatetraene is used as the ligand, the Coo monoanion has a different ground state than [CpCo(cot)]-, and CpCo(dbcot) behaves more like a cod complex with electron-withdrawing substituents. The activation barrier to isomerization in [CpCo(dbcot)]-is raised at least 9.4 kcal/mol over that of [CpCo(cot)]-, a value consistent with the necessity to break up aromatic resonance in a 1,3-isomer of CpCo(dbcot).Acknowledgment. This work was generously supported by the National Science Foundation (CHE 83-03974). We are grateful to J. L. Spencer for an initial sample of 2, to J. Edwin for help on the synthesis of dbcot, and to C. H. Bushweller for aid in simulations of dynamic NMR spectra. A S . wishes to acknowledge the support of the Swiss National Science Foundation (2.165-0.83). Abstract:The electrocatalytic properties of Ni cyclam2+ in CO, reduction have been studied. The influence of various experimental factors on the course of the reaction has been investigated. Under given conditions, Ni cyclam2+ is remarkably efficient and selective for electroreduction of CO, into CO, even in water. The stability of the system has been tested in long range electrolysis, showing that even after thousands of catalytic cycles no deactivation occurs. The mechanistic investigation presently described points to the importance of molecular species adsorbed on the cathode surface. The contribution of reduced species in the bulk is marginal. In addition, during the electrocatalytic process, a nickel(1) carbonyl complex is present: [Ni(cyclam)(CO)]+. The latter complex may be involved in the catalytic reaction leading to CO evolution. Surprisingly, the behavior of Ni cyclam2+ as electrocatalyst is unique. Among the numerous complexes investigated, only Ni cyclam2+ shows such a large selectivity for the electroreduction of CO, over the electroreduction of water. The size of the cyclam ligand and the presence of secondary amine groups (NH) might account for the very special properties of the electrocatalyst.

Catalysis Research of Relevance to Carbon Management: Progress, Challenges, and Opportunities

“…This indicates high selectivity for CO 2 reduction over the more thermodynamically favored reduction of protons to H 2 . For example, the reduction of CO 2 to CO by nickel cyclam catalysts occurs with nearly 100% current efficiency in water at pH 4.1, 163 and CO 2 is reduced to CO in 0.02 M HBF 4 in dimethylformamide solutions with current efficiencies greater than 95%. 164 In addition, some of these catalysts operate at low overpotentials so that the conversion of electrical to chemical energy is highly efficient.…”

Organic, Organometallic and Bioorganic Catalysts for Electrochemical Reduction of CO2

“…Although various molecular catalysts (porphyrins, corroles, cyclams, naphthyridines, and so forth) with metal centers such as Pd, Ru, Fe, Co, and Ni were investigated,31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49 in the years after the discovery of Lehn's catalyst, most research has been focused on Re‐containing complexes. With an estimated average concentration of 1 ppb, Re, together with other noble metals, is one of the rarest elements in Earth's crust.…”

Electrocatalytic Reduction of CO2by Copper (II) Cyclam Derivatives

“…Among the homogeneous electrocatalysts, Ni(II)-cyclam (cyclam: 1,4,8,11-tetrazazcyclotetradecane) and its derivatives have been known to exhibit remarkable efficiency and selectivity in converting CO 2 to CO [4][5][6][7][8][9]. It has been revealed that Ni(I)-cyclam, generated by one-electron-reduction of Ni(II)-cyclam, is the active catalytic species and the cyclam ligand stabilizes the Ni(I) state [5,7,10]. Ni(II)-cyclam, however, still exhibits rather high overpotential (ca.…”

“…-0.6 V), leading to the low energy efficiency for CO 2 conversion. In addition, Ni(II)-cyclam necessitates a mercury electrode to avoid hydrogen evolution and shows much less electrocatalytic activities on other environmentally-benign electrodes [5][6][7].…”