Effect of Ru surface composition on the CO tolerance of Ru modified carbon supported Pt catalysts

Abstract

A series of ruthenium modified carbon supported catalysts have been prepared by surface organometallic chemistry (SOMC) with the following nominal Ru∶Pt surface ratios, (1∶4)RuPt/C, (1∶2)RuPt/C, (3∶4)RuPt/C and (1∶1)RuPt/C. The catalysts were characterised using X-ray diffraction (XRD), extended X-ray absorption fine structure (EXAFS), cyclic voltammetry (CV), and half-cell polarisation studies. The XRD measurements showed that a bulk PtRu alloy was not formed following SOMC modification. However, the EXAFS measurements indicated that a surface alloy is formed upon electrochemical reduction of the Ru modified catalysts. The CV studies show that the electrooxidation of CO on the Ru modified Pt/C catalysts occurs at lower potentials than on the unmodified Pt/C catalysts, but at higher potentials than on an alloyed PtRu/C with a bulk composition of 1∶1 Pt∶Ru. Half cell polarisation measurements in 100 ppm CO in H₂ show that the CO tolerance of the SOMC RuPt/C catalysts approached that of the conventional PtRu/C alloy catalyst. The results therefore indicate that a bulk alloy phase is not an essential factor in the improvement in CO tolerance of PtRu/C catalysts over that of Pt/C.