Unraveling the Potential-Dependent Selectivity of Propylene Electrooxidation: The Role of Electrochemistry-Induced Reconstruction.

Abstract

Using Pd or Pt to achieve propylene electrooxidation is a sustainable electrosynthesis technique to produce oxy-organics. However, the origin behind their potential-dependent product selectivity still remains unclear. Herein, we integrate advanced theoretical methods across grand-canonical ensemble density functional theory (DFT) calculations, Pourbaix analyses, and microkinetic modeling to uncover the completed reaction network of propylene electrooxidation for the first time and found that the electrochemistry-induced reconstructed active center under working potentials, including phase conversion and surface coverage, dominates the potential-dependent selectivity of propylene electrooxidation over Pd and Pt catalysts. With increasing working potential (0.7-1.4 V vs reversible hydrogen electrode, RHE), the active center of the Pd electrode gradually reconstructs from partially O-covered (1/3 ML O*) metallic Pd surface to PdO with partial surface hydroxylation (1/2 ML OH*), and the main product is acrolein at first, then changes to acetone and propylene glycol (PG). On the contrary, the electrochemically reconstructed PtO₂ with partial surface hydroxylation (1/2 ML OH*) is the active center of the Pt electrode under the whole operating conditions (1.2-1.6 V_RHE), and the main products are propylene oxide (PO) and acetone. Our results reproduce the potential-dependent performance of Pd and Pt electrodes from available experiments. In short, this work has clarified the long-standing controversies over the key factors determining propylene electrooxidation products on Pd and Pt, and it reveals the key role of surface reconstruction and active site switching under working potential.