Journal
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY
Volume 140, Issue 28, Pages 8732-8738Publisher
AMER CHEMICAL SOC
DOI: 10.1021/jacs.8b03774
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Funding
- Air Force Office of Scientific Research under AFOSR Award [FA9550-14-1-0254]
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The active intermediate responsible for pyridine (Py)-catalyzed reduction of CO2 on a p-GaP photoelectrode is currently under debate. Exploration of the proposed intermediates available pathways for further reaction may yield a deeper understanding of the CO2 reduction mechanism that will be essential to designing better cocatalysts in such photoelectrochemical systems. Adsorbed 2-pyridinide (2-PyH-*) was recently proposed by Carter and co-workers to be an intermediate that facilitates hydride transfer (HT) to CO2 to produce formate. However, the lifetime of 2-PyH-*, most likely controlled by the rate of 2-PyH-* protonation to form adsorbed dihydropyridine (DHP-*), is still in question. In this work, we provide evidence for the transient existence of 2-PyH-* on a p-GaP surface by comparing the activation energy for HT to CO2 to those predicted for 2-PyH-* being protonated to form either DHP-* or Py-* + H-2 via a hydrogen evolution reaction (HER). We predict that 2-PyH-* situated next to an adjacent surface hydroxide (OH-*) will be the most effective intermediate leading to CO2 reduction on p-GaP. Predicted high barriers of HER (via either 2-PyH (-)* or H-*) also explain the high selectivity toward CO2 reduction observed in experiments.
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