Effect of molybdenum content on the morphology and electronic characteristics of Pd–MoOx nanomaterials and activity evaluation for ethylene glycol electro–oxidation

• Published in: Applied surface science Vol. 498
• Main Authors: Ambriz-Peláez, Oscar, Durón, Sergio, Olivas, Amelia, Valdez, Ricardo, Arriaga, Luis Gerardo, Álvarez-Contreras, Lorena, Guerra-Balcázar, Minerva, Arjona, Noé
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 31-12-2019
• Subjects: Electrocatalysis; Ethylene glycol; Molybdenum oxides; Oxygen vacancies; PdMo; Ethylene glycol; Electrocatalysis; Oxygen vacancies; PdMo; Molybdenum oxides
• ISSN: 0169-4332; 1873-5584
• DOI: 10.1016/j.apsusc.2019.143842

In this work, Pd–MoOx nanomaterials were developed changing the Mo/Pd precursor ratio and tested for ethylene glycol electro–oxidation reaction (EGOR) in alkaline medium. Mo atomic % compositions of 0, 15, 35, 45 and 75 at. % were evaluated. The increase of Mo at. % resulted in morphology changes due to the directing effect of hexadecyltrimethylammonium bromide (CTAB) on molybdenum passing from hemispheres to nanobelts + hemispheres (15 at. % Mo denoted as Pd85Mo15), then only nanobelts (35 at. % Mo, Pd65Mo35), and nanosheets (45 at. % Mo, Pd55Mo45), and hemispheres were newly obtained at the higher Mo concentration (75 at. % Mo, Pd25Mo75). The activity evaluation of EGOR at 60 °C indicated that Pd25Mo75 supported on Vulcan carbon (Pd25Mo75/C) displayed the highest current density (63.80 mA cm−2), and according with X–ray photoelectron spectroscopy (XPS) the highest activity of Pd25Mo75/C can be related to the abundance of Mo5+ species, which have oxygen vacancies with a single positive charge. Additionally, the analysis of O 1s core–level corroborated the abundance of oxygen with high number of defects sites. Thereby, it was found that Pd loading can be decreased without comprising the activity by increasing oxygen vacancies of MoOx as co–catalyst.
Pd–MoOx nanomaterials were developed changing the Mo/Pd precursor ratio. Pd25Mo75/C displayed the highest current density (63.80 mA cm−2) at 60 °C due to abundance of oxygen vacancies, which according with XPS the percentage between oxygen vacancies and oxygen bounded to metals was 69.4%. [Display omitted]
•Morphology of Pd-MoOx changed due to the interaction between Mo species and CTAB.•Pd-MoOx hemispheres, nanobelts, and nanosheets had different activity for EGOR.•Pd25Mo75/C hemispheres had the highest % of oxygen vacancies (69.4%).•The activity of Pd25Mo75/C was ascribed to Mo5+ species and oxygen vacancies.•Oxygen vacancies promoted the decrease of Ea, app, improving the activity to EGOR.