To lessen our dependence on foreign oil, many researchers are investigating alternative fuel sources. Hydrogen gas (H2) is one forerunner due to its high energy density and clean combustion. H2 may be obtained by the electrochemical splitting of water, which is comprised of two half reactions: the reduction of protons (H+) to H2, and the oxidation of water to O2. Homogeneous electrocatalytic H+ proton reduction is an attractive approach, as these systems require minimal chemical consumption and are easy to modify. Dirhodium complexes of the type [Rh2(μ-form)2(L)2]2+ (form = formamidinate; L = bidentate chelating diimine ligand) explored by our group were found to be efficient and robust H+ reduction electrocatalysts. Upon electrochemical reduction of the complex, protons in solution are able to bind to a metal center and undergo reduction to form H2 at high turnover frequencies and modest overpotentials. Additionally, carbon dioxide (CO2) reduction has garnered interest by researchers in recent years. At ~400 ppm, atmospheric CO2 levels are at an all-time high, and could serve as an abundant source of carbon for the production of useful chemical feedstocks and fuels. Further electrochemical studies revealed that these dirhodium complexes are capable of reducing CO2 to formic acid (HCOOH), which has many industrial applications. The proposed mechanism for this reaction involves CO2 insertion into a Rh-hydride bond, followed by reduction to release HCOOH. These complexes are highly selective for H+ reduction even in the presence of CO2, however, preliminary results indicate that by simply changing the bridging ligand on the dirhodium core, the selectivity is significantly altered in favor of enhanced CO2 reduction. This exemplifies the versatility and tunability of catalysts of this architecture.

Cationic dirhodium(II,II) complexes as dual action electrocatalysts for H+ and CO2 reduction

253rd National Meeting (2017)

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