Molecular Design of [Co11C2(CO)23]3- Both Enhances Rate and Lowers Overpoten-tial for Fast C-H Bond Formation with CO2

For electrochemically driven solar fuel-forming reactions thermochemistry dictates that the rate of the reaction will scale linearly with the overpotential of the catalyst, and for a molecular catalyst, overpotential is related to the redox couple (or E½) of the molecule. Enhancements in catalytic rates therefore rely on optimization of kinet-ic factors and this must be achieved by tuning catalyst structure and thereby reaction mechanism to influence reaction kinetics. In this report we use kinetic influences on the two chemical steps in the mechanism for CO2 electroreduction to achieve fast C-H bond-formation and formate formation at 127 M-1s-1 with an overpotential of just ~10 mV. Compared with molecular catalysts that have similar overpotential, this rate is enhanced by five orders of magnitude. As an alternative comparison, for reported molecular catalysts with similar rate, this over-potential is lowered by 100 mV. These combined enhancements derive from a detailed understanding of the cata-lyst mechanism. Moreover, the principles elucidated here for molecular design are general and can guide future and further improved catalyst development in hydride transfer and X-H bond forming reactions (X = C, N, or other).