# The Ethanol Oxidation Reaction Performance of Carbon-Supported PtRuRh Nanorods
## 1 Introduction  
Ethanol is one of the most promising sustainable energy in the future owing to its high energy density, non-toxicity, renewability, [1] and low green-house gas emission while produced [2, 3]. However, the high bond dissociation energy of carbon-carbon bond (C-C) in ethanol is a critical challenge for ethanol oxidation reaction (EOR), which also hinders the commercialization of direct ethanol fuel cell (DEFC). Therefore, much effort has been made to promote the EOR performance of catalysts. The oxidation of ethanol produces several products in which acetaldehyde and acetic acid are formed through 2 and 4 electrons (e\({}^{-}\)) transfer, respectively [4]. However, the desire pathway is to form CO\({}_{2}\) as a product, which not only requires 12 e\({}^{-}\) transfer, but also involves the cleavage of the C-C bond. Several undesired intermediates, such as CO\({}_{\rm ad}\) and CH\({}_{\rm x,ad}\), may be produced during the 12 e\({}^{-}\) transfer, poisoning the state-of-the-art anode Pt catalysts [5, 6, 7, 8, 9]. Generally, EOR on Pt catalysts starts from the dissociative adsorption of ethanol as described in Equation (1). \[\text{CH}_{3}\text{CH}_{2}\text{OH}+\text{Pt}\rightarrow\text{Pt-CH}_{3}\text{ CH}_{2}\text{OH}_{\rm ads} \tag{1}\]  
Pt then will be poisoned by undesired intermediates as shown in Equation (2). \[\text{Pt-CH}_{3}\text{CH}_{2}\text{OH}_{\rm ads}\rightarrow\text{Pt-CO}_{\rm ads }+\text{CH}_{3}+3\text{H}^{+}+3\text{e}^{-} \tag{2}\]Therefore, in order to prevent the poisoning of Pt catalysts, binary catalysts are employed to improve the CO tolerance of Pt catalysts for EOR, especially alloying or modifying Pt with oxyphilic metals, such as Sn [10; 11; 12; 13; 14] and Ru [10; 14; 15]. The presence of these oxyphilic metal atoms can combine with oxygen-containing species (OCS), such as hydroxyl species (OH\({}^{-}\)), which can further facilitate not only the incomplete oxidation of ethanol into acetic acid or CO\({}_{2}\) through so called bifunctional mechanism but also the anti-poisoning ability of Pt catalysts [16; 17] described in Equations (3)-(5):  
\[\text{Ru (or Sn)}+\text{H}_{2}\text{O}\rightarrow\text{Ru (or Sn)}-\text{OH}_{\text{ads}}+\text{H}^{+}+\text{e}^{-} \tag{3}\]  
\[\text{Pt-CH}_{3}\text{CHO}_{\text{ads}}+\text{OH}_{\text{ads}}\rightarrow \text{Pt}+\text{CH}_{3}\text{COOH}+\text{H}^{+}+\text{e}^{-} \tag{4}\]  
\[\text{Pt-CO}_{\text{ads}}+\text{Ru (or Sn)}-\text{OH}_{\text{ads}}\rightarrow \text{Pt}+\text{Ru (or Sn)}+\text{CO}_{2}+\text{H}^{+}+\text{e}^{-} \tag{5}\]  
Therefore, alloying with oxyphilic metal(s) is an efficient way to enhance the tolerance to poisoning intermediates for Pt catalysts. It has been reported that for [14] Pt/C, Pt-Ru (1:1) and Pt-Sn/C (3:1) catalysts, the oxidation of the adsorbed OCS is facilitated at lower potentials through supplying oxygen atoms from Ru or Sn oxides at an adjacent site. The PtRu/C catalyst is the state-of-the-art anode catalyst in direct methanol fuel cells and DEFC, owing to its remarkable CO tolerance that is usually ascribed to the bifunctional mechanism and ligand effects. The bifunctional mechanism is ascribed to the facilitation of CO\({}_{\text{ads}}\) oxidation on Pt by OCS from Ru at low potentials, and the ligand effect suggests that the electronic structure of Pt is modified through formation of PtRu alloy, weakening CO adsorption on Pt [18; 19; 20; 21]. However, Ru is easily dissolved into acid medium during the long-term operation of DEFC, which may degrade the CO tolerance and durability [22]. Besides PtRu/C catalysts, other binary and ternary catalysts, such as PtAu [23; 24], PtAg [25; 26], PtNi [27; 28], PtRh [29; 30], PtSnRh [31; 32] and PtRuSn [33; 34; 35], have shown enhanced EOR performance attributed to the bifunctional mechanism and synergistic effect. Among them, PtRh/C [36; 37] catalysts are regarded as the promising catalysts to decompose ethanol.