PtSnO2/C and Pt/C with preferential (100) orientation: High active electrocatalysts for ammonia electro-oxidation reaction

Abstract

Pt/C and PtSnO2/C (20 wt% of metal loadings on carbon) containing cubic Pt nanoparticles with preferential Pt(100) orientation synthesized by an alcohol-reduction process using KBr as a shape directing agent and also PtSnO2/C and Pt/C without morphological control were used as electrocatalysts for ammonia electro-oxidation reaction (AmER) in alkaline media. The catalytic activity of the materials were investigated by cyclic voltammetry (CV), chronoamperometry (CA) and electrochemical impedance spectroscopy (EIS). X-ray diffraction (XRD) showed Pt peaks attributed to the face-centered cubic (FCC) structure as well SnO2 cassiterite. Transmission electron microscopy (TEM) and Scanning transmission electron microscopy (STEM) images shows cubic Pt nanoparticles (PtNPs) as well SnO2 highly dispersed onto carbon support and surrounding the PtNPs. CV experiments show that the peak current density for AmER on Pt/C (100) is 2.83 times higher than on Pt/C. The presence of tin onto the catalysts (PtSnO2/C and PtSnO2/C (100)) promoted a decrease of about 70 mV on the onset potential for AmER. The current density at 60 min of CA measurements on PtSnO2/C (100) was 1.51 times higher than on Pt/C (100), and on PtSnO2/C was 1.76 times of Pt/C. The EIS experiments show that the charge transfer resistance decreases as the catalytic activity of the materials for AmER increases. The high catalytic activity of the materials with platinum (100) preferentially orientation might be due to the higher tolerance for the Nads poisoning intermediates. The presence of SnO2 might prevent platinum surface from deactivation caused by intermediates formed during the AmER process.