Photocatalytic Formic Acid Conversion on CdS Nanocrystals with Controllable Selectivity for H(2) 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 (λ>420 nm, 1 sun), suspensions of ligand-capped cadmium sulfide nanocrystals in formic acid/sodium formate release up to 116±14 mmol H(2) g(cat)(−1) h(−1) with >99 % selectivity when combined with a cobalt co-catalyst; the quantum yield at λ=460 nm was 21.2±2.7 %. In the absence of capping ligands, suspensions of the same photocatalyst in aqueous sodium formate generate up to 102±13 mmol CO g(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 6×10(5) and 3×10(6), respectively.