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.