Interfacial and Alloying Effects on Activation of Ethanol from First-Principles

We present a first-principles density-functional theory study of ethanol activation at oxide/Rh(111) interface and the alloying effect on mitigating carbon deposition, which are essential to direct ethanol fuel cell (DEFC) anode reaction and steam reforming of ethanol (SRE) reaction. Our calculated results show that charge can transfer from Rh(111) substrate to MO<sub><i>x</i></sub> chain (e.g., MoO<sub>3</sub> and MnO<sub>2</sub>), or from MO<sub><i>x</i></sub> chain (e.g., MgO, SnO<sub>2</sub>, ZrO<sub>2</sub>, and TiO<sub>2</sub>) to Rh(111) substrate. The OH-binding strength is increased exponentially with M<sup>δ+</sup> charge ranging from 1.4 to 2.2, which renders MnO<sub>2</sub>/Rh­(111) and MgO/Rh(111) interfaces weaker OH-binding, and thereby enhanced oxidizing functionality of OH* for promoting ethanol oxidation reaction (EOR) at DEFC anode. For efficient C–C bond breaking, a large number of Rh ensemble sizes are critically needed at the interface of MO<sub><i>x</i></sub>/Rh­(111). We found that Rh<sub>1</sub>Au<sub>3</sub> near surface alloy has the weakest C* and CO* binding, followed by Rh<sub>1</sub>Cu<sub>3</sub> and Rh<sub>1</sub>Pd<sub>3</sub> near surface alloys, while Rh<sub>1</sub>Ir<sub>3</sub> and Rh<sub>1</sub>Ru<sub>3</sub> surface alloys have C* and CO* binding strength similar to that of pure Rh metal. The general implication of this study is that by engineering alloyed structure of weakened C* and CO* binding complemented with metal oxides of weakened OH-binding, high-performance DEFC anode or SRE catalysts can be identified.