International audienceInsights into the ethanol electro-oxidation reaction mechanism on palladium in alkaline media are presented combining polarization modulation infrared reflec- tion absorption spectroscopy (PM-IRRAS) and density functional theory (DFT) calculations. The synergy between PM-IRRAS and DFT calculations helps to explain why the C− C bond is not broken during ethanol electro-oxidation, and the reaction stops at acetate. Coupling chronoamperometry (CA) with in situ PM-IRRAS enables us to simultaneously identify ethanol electro-oxidation products on the catalyst surface and in the bulk solution. We show that, at lower potential, it is possible to break the C−C bond on Pd/C in alkaline media to form CO2. However, the selectivity is poor, because of competition with the formation of acetate and other side products, which gets worse at higher potentials. DFT computations complete the picture using the computational hydrogen electrode approach. The computations highlight the pivotal role of the CH3CO intermediate that can either undergo a C−C bond scission yielding CO and then CO2 or that can be oxidized toward CH3COO−. The latter is a dead end in the reaction scheme toward CO2 production, since it cannot be easily oxidized nor broken into C1 fragments. However, CH3CO is not the most favored intermediate formed from ethanol electro-oxidation on Pd, hence limiting the production of CO2

The promotional role of oxide supports (CeO2, SnO2, TiO2) on ethanol electrooxidation in alkaline media over Pd nanoparticles (NPs) is presented and compared to Pd on carbon. XPS revealed a shift to lower binding energy of the Pd 3d peak when Pd NPs were deposited on metal oxides, implying a charge transfer from the oxides to the Pd. The catalytic activity of the supported NPs for ethanol electrooxidation was assessed by using cyclic voltammetry and chronoamperometry. The electrooxidation products were monitored in situ, using polarization modulation–infrared reflection absorption spectroscopy (PM‐IRRAS), which revealed that the supports influence the selectivity of reactions on Pd. Pd/CeO2 has superior selectivity towards breaking the C−C bond to produce CO2 compared to the other three supports. Acetate, as a product, was evident on all of the catalysts, but at different ratios. Pd supported on metal oxides showed higher activity and, in particular, CeO2 and SnO2 stand out as the best supports.

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The efficiency of direct ethanol fuel cells suffers from the partial oxidation of ethanol into acetic acid as opposed to the complete oxidation of this fuel to CO 2 . Herein, we support the quest for a selective catalyst for ethanol electro-oxidation to CO 2 , building on our previous mechanistic hypothesis based on experimental insight and DFT computations. We derive a simple descriptor of the expected selectivity towards full oxidation, Ω, as a function of the adsorption energy of atomic C and O. Three different families of catalyst surfaces are screened using this descriptor: monometallics, bimetallics and conducting metal oxides, totaling to 600 surfaces. In agreement with available experimental data, no single metal surface is more selective for total oxidation than platinum and palladium. While the selected conducting oxides were not predicted to be selective towards splitting the C-C bond, structurally-controlled monometallics (such as Pd (100)) or some bimetallics (Pd 3 Ag) are found to be competitive with the most stable facet, (111), of Pd and Pt. Despite this very extensive screening, no very promising catalyst has been identified. This highlights the need to identify catalysts for acetate oxidation or to exploit support effects and electrolyte engineering to profit from the full power of direct ethanol fuel cells.