PtRu Binary System

The HOR performance of PtRu alloys in the presence of CO has been studied extensively [20, 209] and it has been shown that the HOR overpotential for CO-containing hydrogen deereases as the ruthenium content increases, reaehing a minimum around the 1 1 (atomic ratio) composition. 

4 Stability of PtRu Catalysts and the Impact on Oxygen Reduction Reaction 

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Okada et al. investigated the binary system Pt-Co(MPQH) (where MPQH mono-8-quinolyl-o-phenylenediamine) [89]. The catalysts were heat treated in Ar atmosphere for 2 h. The optimum heat treatment temperature was 873 K. The mass specific catalytic activity of the binary catalysts supported on carbon was 5 A gn compared to 40-60 A gpt for PtRu. It was also shown that the nature and structure of the ligand coordinating the Co had an effect on performance. Co(NH3)6Cl3 did not exert any catalytic effect when combined with Pt, while porphyrin based complexes of Co heat treated at 1073 K yielded approximately 20 to 30 mV lower overpotentials compared to catalyst formulatiorrs using Co(MPQH). 

It has been found that the use of a second element wifli Pt, sueh as Ru, Sn, Co, Cr, Fe, Ni, Pd, Os, Mo, Mn, etc., in the form of an alloy or a co-deposit yields significant improvement in the CO-tolerance relative to pure Pt [29-38]. Among these various Pt-based binary systems, the most commonly used eatalyst is carbon-supported PtRu alloy (PtRu/C). This material is known to enhance CO tolerance, which can be ascribed to the electronic modification of Pt-Ru in PtRu alloys that decreases the CO binding energy on Pt and also binds OH strongly on the Ru active sites in the PtRu alloys [39]. Within this system, the performance of PEMFCs has been improved for fuel streams containing CO [40-42]. 

The studies listed in Table 7.1 are all experimental studies. They are focused on investigating the CO tolerance of PEM fuel cells running with different catalysts. The catalyst type referred to as "other systems" consists of binary and higher systems. Metals, such as Mo, Nb, and Ta, are used along with platinum on carbon support as the catalyst. In some other cases, these same metals are used in combination with PtRu on carbon support. Other high order catalysts are PtRu-H MOj/C (with M = Mo and W). 

Ternary M-PtRu/C and M-PtSn/C systems have been studied, but only studies with M-PtSn/C have shown solid results for the enhancement of ethanol electrooxidation compared to base bimetallic electrocatalysts. Ribeiro [99] studied PtSn-Ir systems and reported that a composition 9 1 0.2 was slightly better than base PtSn (9 1). PtSnRu (Ru/Snbinary catalysts without affecting product distribution [68,81]. Leger et al. [100] also reported a better performance of PtSn-W (9 1 1 to 3 1 0.5) as compared to binary PtSn with an increase in the selectivity to acetic acid. Similarly, a general improvement in the ethanol electrooxidation activity adding W to PtSn catalyst with... 

In the following, we discuss the PtRu system as a model catalyst. Binary PtRu electrocatalysts are presently studied in many different forms, PtRu alloys [65-68], Ru electrodeposits on Pt [69, 70], PtRu... 

Oxidation of Methanoi The oxidation of methanol via a binary catalyst will be discussed for PtRu combinations as a model system. As known from early investigations [59, 63] and already demonstrated here with the IR results of Fig. 16, PtRu surfaces are strongly enhancing the oxidation of methanol. In order to approach the behavior in the stationary case, we analyze the activity mainly in the form ofi(f)-curves. 

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