Pd₄O₃ Subsurface Oxide on Pd(111) Formed during Oxygen Adsorption-Induced Surface Reconstruction and Its Activity toward Formate Oxidation Reactions

Abstract

Surface reconstruction and surface oxide formation on Pd(111) facet are investigated using density functional theory calculations coupled with particle swarm optimization (PSO) algorithms, and a series of surface oxides and isomers are obtained and evaluated for the catalytic activity toward formate oxidation reactions for the first time. A globally stable Pd 4 O 3 subsurface oxide is identified on Pd(111) facet during the oxygen adsorbedinduced surface reconstruction and featured by three subsurface oxygen atoms. The Pd(111) surface during the surface reconstruction undergoes two phase transitions starting from the oxygen-adsorbed surface to the surface oxide with an activation energy barrier of 0.366 eV and then to the Pd 4 O 3 subsurface oxide with an activation energy barrier of 0.231 eV. During the formate oxidation reaction, the limiting potentials for the Pd(111) clean surface, Pd(111) oxygen-adsorbed surface, Pd 4 O 3 surface oxide, and Pd 4 O 3 subsurface oxide are 0.612, 0.232, 0.828, and 0.141 eV, respectively, indicating that the catalytic activity is suppressed when the surface is oxidized to form Pd 4 O 3 surface oxide and then enhanced as Pd 4 O 3 subsurface oxide further forms. The reconstructed Pd 4 O 3 subsurface oxide has the highest activity among various Pd 4 O x (x = 1−4) (sub)surface oxides and isomers. Overall, this work identifies a previously unknown surface reconstruction on Pd(111) facet and proposes a mechanism of oxygen-induced surface reconstruction on Pd(111) facet and a new strategy to identify active species for reconstructed electrocatalysts in the formate oxidation reactions.

Reconstruction of an AgPd nanoalloy with oxidation for formate oxidation electrocatalysis

“…Taking the AgPd–Ag 2 O interface as an example, Fig. 7(c) shows the schematic diagram of the FOR process, and it has been demonstrated that the FOR on Pd-based catalysts in alkaline medium will not generate the poisoning CO* intermediate, so the reaction pathway is considered to occur through the pathway of HCOO − , HCOO − bi *, HCOO − mo *, CO 2 * + H* and CO 2 + H. 6,54…”

“…[3][4][5] Unfortunately, the development of DFFCs suffers from the bottleneck of poor kinetics for the anodic formate oxidation reaction (FOR). 6 Designing and preparing a FOR catalyst with high catalytic performance and low price is crucial for the wide application of DFFCs.…”

“…11,12 While substantial efforts have been devoted to designing nanoalloy catalysts, it should be noticed that the nanoalloy surface will undergo reconstruction in a catalytic environment, which involves the evolution of the chemical composition, shape, strain, valence state, etc., resulting in the variation of the surface structure and catalytic performance in comparison with the as-prepared state. 6,13,14 For example, Kim et al 15 demonstrated that the surface of the as-prepared PdAu nanoalloy was rich in Au, while Pd segregated to the surface in a CO atmosphere due to the stronger Pd-CO binding. Dang et al 16 reported that amorphous RuO 2 was partially reduced to Ru during the hydrogen evolution reaction (HER), resulting in the enhancement of HER catalytic performance.…”

“…The introducing of ultra-thin 2D adlayers such as oxides, phosphides, uorides and suldes on a nanoalloy 20,21 could properly modify the surface reconstruction pathway of the nanoalloy to achieve optimal catalytic performance. 6,22 The hitherto-developed synthesis methods for 2D materials on metals or 2D heterointerfaces mainly include self-limiting growth during reconstruction treatment. [23][24][25][26][27] For example, Daeneke et al 28 reported that a 2D SnO lm on molten Sn with a thickness of 0.6 nm could be self-limiting synthesized in a glovebox at an oxygen concentration of 10-100 ppm.…”

“…, resulting in the variation of the surface structure and catalytic performance in comparison with the as-prepared state. 6,13,14 For example, Kim et al 15 demonstrated that the surface of the as-prepared PdAu nanoalloy was rich in Au, while Pd segregated to the surface in a CO atmosphere due to the stronger Pd–CO binding. Dang et al 16 reported that amorphous RuO 2 was partially reduced to Ru during the hydrogen evolution reaction (HER), resulting in the enhancement of HER catalytic performance.…”