The active intermediate responsible for pyridine (Py)-catalyzed reduction of CO 2 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 CO 2 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 CO 2 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 CO 2 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 CO 2 reduction on p-GaP. Predicted high barriers of HER (via either 2-PyH - ∗ or H - ∗) also explain the high selectivity toward CO 2 reduction observed in experiments.
All Science Journal Classification (ASJC) codes
- Colloid and Surface Chemistry