Efficient Redox-Neutral Photocatalytic Formate To Carbon Monoxide Conversion Enabled By Long-Range Hot Electron Transfer From Mn-Doped Quantum Dots

Energetic hot electrons generated in Mn-doped quantum dots (QDs) via exciton-to-hot-electron upconversion possess long-range transfer capability. The long-range hot electron transfer allowed for superior efficiency in various photocatalytic reduction reactions compared to conventional QDs, which solely rely on the transfer of band edge electrons. Here we show that the synergistic action of the interfacial hole transfer to the initial reactant and subsequent long-range hot electron transfer to an intermediate species enables highly efficient redox-neutral photocatalytic reactions, thereby extending the benefits of Mn-doped QDs beyond reduction reactions. The photocatalytic conversion of formate (HCOO-) to carbon monoxide (CO), which is an important route to obtain a key component of syngas from an abundant source, is an exemplary redox-neutral reaction that exhibits a drastic enhancement of catalytic efficiency by Mn-doped QDs. Mn-doped QDs increased the formate to CO conversion rate by 2 orders of magnitude compared to conventional QDs with high selectivity. Spectroscopic study of charge transfer processes and the computational study of reaction intermediates revealed the critical role of long-range hot electron transfer to an intermediate species lacking binding affinity to the QD surface for efficient CO production. Specifically, we find that the formate radical (HCOO)(center dot), formed after the initial hole transfer from the QD to HCOO-, undergoes isomerization to the (HOCO)(center dot) radical that subsequently is reduced to yield CO and OH-. Long-range hot electron transfer is particularly effective for reducing the nonbinding (HOCO)(center dot) radical, resulting in the large enhancement of CO production by overcoming the limitation of interfacial electron transfer.