# The Ethanol Oxidation Reaction Performance of Carbon-Supported PtRuRh Nanorods
## 3 Results and Discussion
The TPR spectra of PtRu, PtRh, and PtRuRh are displayed in Figure 3. The main reduction peaks for the catalysts located between 200 and 230 K are assigned to the reduction of the surface platinum oxides (PtO\({}_{x}\)). For the reduction of ruthenium oxides (RuO\({}_{x}\)) and rhodium oxides (RhO\({}_{x}\)), the reduction peaks are located between 300 and 400 K [56; 57] and above 500 K, respectively. The peak located at 250 K for PtRh may be owing to the reduction of surface PtRh alloy oxide (APtRh). Therefore, the main surface species of PtRuRh is Pt/Ru/Rh. The CO-stripping experiments are performed, and the results for Pt, PtRu, PtRh, and PtRuRh are displayed in Figure 4a and Table S3. It is obvious that the onset potential of Pt is much higher than those of the binary and ternary catalysts, implying a more effective CO oxidation reaction for the latter ones. Overall, PtRu performs the lowest onset potential, followed by PtRuRh \(<\) < PtRh [58; 59; 60; 61; 62], indicating that the incorporation of second or third metal can indeed enhance the CO oxidation by the bi-functional mechanism. On the other side, the ECSA\({}_{\text{CO}}\) is compared in Table S3 in which PtRuRh has the largest value among all catalysts, suggesting that PtRuRh can provide the largest Pt surface area for CO oxidation. Besides, it has been reported that RuO\({}_{x}\) helps the desorption of CO adsorbed on Pt [63]. Thus, it appears that PtRuRh is superior to promote the electro-oxidation of adsorbed CO than other samples. Figure 2: X-ray photoelectron spectroscopy (XPS) spectra of (**a**) Pt, (**b**) PtRu, (**c**) PtRh, and (**d**) PtRuRh. On the other hand, the CV diagrams of Pt, PtRu, PtRh, and PtRuRh catalysts are shown in Figure 4b, and the areas under the curves of the hydrogen desorption region used to calculate the adsorption and adsorption of PtRuRh. Figure 4: (**a**) CO-stripping voltammograms, (**b**) CV diagrams, (**c**) ethanol oxidation reaction (EOR) performance, and (**d**) CA curves of catalysts at a constant potential of 0.6 V vs. the normal hydrogen electrode (NHE) for Pt, PtRu, PtRh, and PtRuRh. Figure 3: Temperature-programmed reduction (TPR) traces of PtRu, PtRh, and PtRuRh. ECSA\({}_{\rm H}\) for each catalyst are displayed in Table 1. The ECSA\({}_{\rm H}\) of ternary catalysts are also larger than those of Pt and binary ones, suggesting better Pt utilization from the former. However, when comparing the calculated ECSA\({}_{\rm CO}\) with ECSA\({}_{\rm H}\), large differences are noted for the same catalysts. This phenomenon has been reported by [PERSON] et al., who suggest that the uncertainty of the CO-stripping method is the type of the CO bonding on the surface, rather than the H-adsorption method giving the maximum number of surface reactive Pt sites [51]. As a result, the ECSA\({}_{\rm H}\) is relatively accurate compared to ECSA\({}_{\rm CO}\). The EOR performances of Pt, PtRu, PtRh, and PtRuRh catalysts are summarized in Table 1, and their activities are shown in Figure 4c. All current densities are normalized by the ECSA\({}_{\rm H}\) and the potentials are also adjusted to the normal hydrogen electrode (NHE). Besides, specific activity at 0.6 V (SA\({}_{06}\)), maximum specific activity (SA\({}_{\rm max}\)), mass activity (MA) at 0.6 V (I\({}_{06}\)) and the maximum MA (I\({}_{\rm max}\)) of catalysts are also compared in Table 1. It can be observed that the SA\({}_{06}\) of the PtRuRh catalyst is 0.38 mA/cm\({}^{2}\), which is 2.5, 1.9, and 1.6 times higher than that of Pt, PtRu, and PtRh, respectively and superior to PtRu and PtRh-based ternary catalysts as compared in Table S4. In terms of MA, the I\({}_{06}\) of PtRuRh catalyst is 29.4 A/g(r\({}_{0}\)), which is 4.4, 3.1, and 2.7 times higher than that of Pt, PtRu, and PtRh, respectively.