Ethanol electrolysis in a PEM cell: Dependence of the PtRu surface composition on the EOR activity under dynamic potential application

The effect of the PtRu/C anodic catalyst morphology on the ethanol electrolysis process was investigated for green hydrogen production. To that purpose, three different PtRu/C electrocatalysts with a Pt:Ru mass ratio of 1:2 were prepared by means the polyol modified method and their particle size, alloying degree, oxidation state and dispersion were characterized by X-ray diffraction, transmission electron microscopy and X-ray photoelec-tron spectroscopy. In general terms, high pH values during the synthesis of the electrocatalyst foster the for-mation of quite small particles size, a low alloying degree and a high oxidized surface. Conversely, the alloying percentage and particle size increased when a lower pH range was employed. The ethanol electrolysis was evaluated in a PEM cell through linear voltammetry tests, electrochemical impedance spectroscopy essays, galvanostatic transients at different current density levels and mild-term stability essays. The main impact of the study is that a clear relationship between the cell potential window and the main electrocatalytic properties (PtRu alloying degree, ECSA and OH- species activation) was established. Hence, at intermediate cell potential values (0.3-1 V), an anodic catalyst with a high PtRu alloying degree and, therefore, low amounts of oxidized species, resulted to be more active in electrocatalytic terms boosting the acetic acid production at low energy consumption values. However, at high cell potential range (V-cell>1 V), electrocatalysts with smaller crystallite sizes and lower alloying degree achieved the best electrochemical performance due to a higher availability of the active sites. By this way the new idea proposed on this study is a change in the limiting factor of the ethanol electrolysis process depending on the cell potential working range. As a result, we propose, the synthesis of anodic catalyst with low Pt:Ru ratio and tailored alloying degrees as a good strategy to reduce the Pt loading simultaneously boosting the ethanol electrolysis activity at low potential values.