High surface area tin oxide nanocrystals prepared by a facile hydrothermal method are evaluated as electrocatalysts toward CO2 reduction to formate. At these novel nanostructured tin catalysts, CO2 reduction occurs selectively to formate at overpotentials as low as ∼340 mV. In aqueous NaHCO3 solutions, maximum Faradaic efficiencies for formate production of >93% have been reached with high stability and current densities of >10 mA/cm(2) on graphene supports. The notable reactivity toward CO2 reduction achieved here may arise from a compromise between the strength of the interaction between CO2(•-) and the nanoscale tin surface and subsequent kinetic activation toward protonation and further reduction.

Nitrogen-doped carbon nanotubes are selective and robust electrocatalysts for CO2 reduction to formate in aqueous media without the use of a metal catalyst. Polyethylenimine (PEI) functions as a co-catalyst by significantly reducing catalytic overpotential and increasing current density and efficiency. The co-catalysis appears to help in stabilizing the singly reduced intermediate CO2(•-) and concentrating CO2 in the PEI overlayer.

A self-assembly-formed triglycylglycine macrocyclic ligand (TGG(4-)) complex of Cu(II), [(TGG(4-))Cu(II)-OH(2)](2-), efficiently catalyzes water oxidation in a phosphate buffer at pH 11 at room temperature by a well-defined mechanism. In the mechanism, initial oxidation to Cu(III) is followed by further oxidation to a formal "Cu(IV)" with formation of a peroxide intermediate, which undergoes further oxidation to release oxygen and close the catalytic cycle. The catalyst exhibits high stability and activity toward water oxidation under these conditions with a high turnover frequency of 33 s(-1).

Iridium dihydride complexes supported by PCP-type pincer ligands rapidly insert CO(2) to yield κ(2)-formate monohydride products in THF. In acetonitrile/water mixtures, these complexes become efficient and selective catalysts for electrocatalytic reduction of CO(2) to formate. Electrochemical and NMR spectroscopic studies have provided mechanistic details and structures of key intermediates.

Electrocatalytic reduction of CO(2) by [Ru(tpy)(bpy)(solvent)](2+) (tpy = 2,2':6',2''-terpyridine, bpy = 2,2'-bipyridine) and its structural analogs is initiated by sequential 1e(-) reductions at the tpy and bpy ligands followed by rate limiting CO(2) addition to give a metallocarboxylate intermediate. It undergoes further reduction and loss of CO.