Durable Solar-Powered Systems with Ni-Catalysts for Conversion of CO2 or CO to CH4

Photocatalytic conversion of CO2 to reduced carbon states using sunlight and an earth-abundant catalyst could provide a critically needed source of renewable energy. Very few earth-abundant catalysts have shown CO2 to CH4 reactivity, and significant opportunities exist to improve catalyst durability. Through the strategic design of a novel, redox-active bipyridyl-N-heterocyclic carbene macrocyclic ligand complexed with nickel, CO2 is converted into the energy-rich solar fuel, CH4, photocatalytically with a photosensitizer in the presence of water. Up to 19 000 turnovers of CH4 from CO2 are observed. An exceptional turnover number of 570 000 for CH4 production via a photodriven formal hydrogenation of CO to CH4 was also found. This unique reactivity from a tunable, highly durable macrocyclic framework was studied via a series of photocatalytic and electrocatalytic reactions varying the atmospheric composition, as well as by isotopic labeling experiments and quantum yield calculations to evaluate the effect of ligand structure on product generation.