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

Abstract

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 H2 gcat−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 gcat−1 h−1 with >95 % selectivity and 19.7±2.7 % quantum yield. H2 and CO production was sustained for more than one week with turnover numbers greater than 6×105 and 3×106, respectively.

Solar Hydrogen Generation from Lignocellulose

“…[41] Accumulation of formate was seen during cellulose PR at CdS/CdO x , [31] as formic acid PR was slower than cellulose PR. Formic acid could be further photoreformed at CdS to H 2 or CO. [57] Alternatively,r educing equivalents generated upon biomass photo-oxidation can be used for organic transformations instead of H 2 generation. Photocatalytic conversion of glucose to arabinose and erythrose over Pd/TiO 2 could be coupled with the reduction of nitroarenes and aldehydes to anilines and alcohols,respectively,thus producing high-value products from both half-reactions.…”

Photocatalytic Dehydrogenation of Formic Acid on CdS Nanorods through Ni and Co Redox Mediation under Mild Conditions

“…The generated excitons (positive holes and electrons) can provide necessary energy to activate organic molecules for their conversion to products (FA does not absorb visible light). In spite of the recent advances in heterogeneous/homogeneous catalysis for the release of hydrogen from FA, examples of photocatalysis are scarce and show substantially lower activities . Only recently, CdS has been identified as a potential candidate material for photodecomposition of FA‐to‐H 2 owing to its low cost, suitable valence and conduction band positions, and high visible light activity .…”

Sonnengetriebene Wasserstofferzeugung aus Lignocellulose

“…Ameisensäure kann durch CdS weiter zu H 2 oder CO photoreformiert werden. [57] Alternativ kçnnen die durch Biomasseoxidation erzeugten Reduktionsäquivalente fürorganische Reaktionen anstatt fürd ie H 2 -Entwicklung verwendet werden. So kann in Gegenwart von Pd/TiO 2 die Photooxidation von Glucose zu Arabinose und Erythrose mit der Reduktion von Nitroarenen und Aldehyden zu Anilinen bzw.A lkoholen verbunden werden, wodurch beide Halbreaktionen hochwertige Verbindungen liefern.…”