Insights into the endurance promotion of PtSn/CNT catalysts by thermal annealing for ethanol electro-oxidation

In the present work carbon nanotube supported PtSn (PtSn/CNT) nanocatalysts before (B) and after (A) annealing at 250 degrees C and their corresponding samples before and after voltammetric cycling (500 cycles) were prepared with nominal Pt:Sn atomic ratio of 3:1. X-ray diffraction results indicate that the PtSn nanoparticles in PtSn/CNTs (B) and PtSn/CNTs (A) were 3.4 nm and 3.5 nm, respectively. However, SnO2 only appeared in the diffraction pattern of PtSn/CNT (A). Transmission electron micrography images show that PtSn nanoparticles dispersed homogeneously on CNTs in both PtSn/CNTs (B) and PtSn/CNTs (A). While the PtSn nanoparticles in PtSn/CNTs (B) after voltammetric cycling became linked and agglomerated and SnO2 was also found in the catalyst as the corresponding catalyst nanoparticles in PtSn/CNTs (A) were still fine and uniform. X-ray photoelectron spectroscopy analyses suggest that the relative concentration of Sn (II/IV) species in Sn 3d(5/2) increased from 32% to 61% after thermal annealing. The electrochemical results show that PtSn/CNTs (A) had higher catalytic activity, much better stability (maintaining 1.5 times peak current dentsity of PtSn/CNTs (B) after 500 potential cycling), higher CO tolerance and smaller charge transfer resistance for ethanol electro-oxidation than PtSn/CNTs (B). The remarkable electrochemical performance of PtSn/CNTs (A) was analyzed based on potential cycling and ascribed to the appropriate content of tin oxides (61%) and Sn alloys (39%) which results in an appropriate combination of the bifunctional mechanism and the electronic effect and the high structural stability of the catalyst which results from the increase of SnO2 content. (C) 2016 Elsevier Ltd. All rights reserved.