Photocatalytic Formic Acid Conversion on CdS Nanocrystals with Controllable Selectivity for H2 or CO

Formic acid is considered a promising energy carrier and hydrogen storage material for a carbon-neutral economy. We present an inexpensive system for the selective room-temperature photocatalytic conversion of formic acid into either hydrogen or carbon monoxide. Under visible-light irradiation (>420nm, 1sun), suspensions of ligand-capped cadmium sulfide nanocrystals in formic acid/sodium formate release up to 116 +/- 14mmolH(2)g(cat)(-1)h(-1) with >99% selectivity when combined with a cobalt co-catalyst; the quantum yield at =460nm was 21.2 +/- 2.7%. In the absence of capping ligands, suspensions of the same photocatalyst in aqueous sodium formate generate up to 102 +/- 13mmolCOg(cat)(-1)h(-1) with >95% selectivity and 19.7 +/- 2.7% quantum yield. H-2 and CO production was sustained for more than one week with turnover numbers greater than 6x10(5) and 3x10(6), respectively.