Recovery of Active and Efficient Photocatalytic H2 Production for CdSe Quantum Dots

• Published in: Journal of physical chemistry. C 2018-06, Vol.122 (25), p.14099-14106
• Main Authors: Burke, Rebeckah, Cogan, Nicole M. B, Oi, Aidan, Krauss, Todd D
• Format: Article
• Language: English
• Subjects: INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; NANOSCIENCE AND NANOTECHNOLOGY
• ISSN: 1932-7447; 1932-7455
• DOI: 10.1021/acs.jpcc.8b01237

Recently, colloidal semiconductor quantum dots (QDs) have shown great promise as photocatalysts for the production of chemical fuels by sunlight. Here, the efficiency of photocatalytic hydrogen (H2) production for integrated systems of large diameter (4.4 nm) CdSe QDs as light harvesting nanoparticles with varying concentrations of nickel–dihydrolipoic acid (Ni–DHLA) small molecule catalysts is measured. While exhibiting excellent robustness and longevity, the efficiency of H2 production for equimolar catalyst and QDs is relatively poor. However, the efficiency is found to increase substantially with increasing Ni–DHLA/QD molar ratios. Surprisingly, this high activity is only observed with the use of 3-mercaptopropionic acid (MPA) ligands, while CdSe QDs capped with dihydrolipoic acid (DHLA) exhibit poor performance in comparison, indicating that the QD capping ligand has a substantial impact on the catalytic performance. Ultrafast transient absorption spectroscopic measurements of the electron transfer (ET) dynamics show fast ET to the catalyst. Importantly, an increase in ET efficiency is observed as the catalyst concentration is increased. Together, these results suggest that for these large QDs, tailoring the QD surface environment for facile ET and increasing catalyst concentrations increases the probability of ET from QDs to Ni–DHLA, overcoming the relatively small driving force for ET and decreased surface electron density for large diameter QDs.