Abstract
2-Propanol and its dehydrogenated counterpart acetone can be used as a rechargeable electrofuel. The concept involves selective oxidation of 2-propanol to acetone in a fuel cell coupled with reverse catalytic hydrogenation of acetone to 2-propanol in a closed cycle. We studied electrocatalytic oxidation of 2-propanol on complex model Pt/Co3O4(111) electrocatalysts prepared in ultra-high vacuum and characterized by scanning tunneling microscopy. The electrocatalytic behavior of the model electrocatalysts has been investigated in alkaline media (pH 10, phosphate buffer) by means of electrochemical infrared reflection absorption spectroscopy and ex-situ emersion synchrotron radiation photoelectron spectroscopy as a function of Pt particle size and compared with the electrocatalytic behavior of Pt(111) and pristine Co3O4(111) electrodes under similar conditions. We found that the Co3O4(111) film is inactive towards electrochemical oxidation of 2-propanol under the electrochemical conditions (0.3–1.1 VRHE). The electrochemical oxidation of 2-propanol readily occurs on Pt(111) yielding acetone at an onset potential of 0.4 VRHE. The reaction pathway does not involve CO but yields strongly adsorbed acetone species leading to a partial poisoning of the surface sites. On model Pt/Co3O4(111) electrocatalysts, we observed distinct metal support interactions and particle size effects associated with the charge transfer at the metal/oxide interface. We found that ultra-small Pt particles (around 1 nm and below) consist of partially oxidized Pt δ + species which show minor activity towards 2-propanol oxidation. In contrast, conventional Pt particles (particle size of a few nm) are mainly metallic and show high activity toward 2-propanol oxidation.
Highlights
The temporal fluctuations in the availability of renewable energies require the development of efficient energy storage systems
We studied particle size effects [25, 28], electronic metal–support interactions (EMSIs) [25, 27, 29], and investigated how these effects affect the stability of the model electrocatalysts [26]
All oxide-based samples were prepared by physical vapor deposition (PVD) in ultra-high vacuum (UHV)
Summary
The temporal fluctuations in the availability of renewable energies require the development of efficient energy storage systems. Alternative concepts for hydrogen storage are rechargeable fuels like, e.g. liquid organic hydrogen carriers (LOHCs), which are compatible with the common infrastructure for the distribution of liquid fuels [3, 4]. In LOHCs, hydrogen is reversibly bound to an organic carrier molecule like N-ethylcarbazole [3, 5,6,7,8] or Malotherm and catalytically released when required [9]. While the 2-propanol/acetone couple has a relatively low hydrogen storage capacity, successful strategies were devised which employ the 2-propanol/acetone couple in combination with classical LOHCs [10]. Long-term storage is established using the LOHC Malotherm, providing high hydrogen storage capacity. We avoid any molecular hydrogen in the system and increase the efficiency of energy conversion from LOHC-bound hydrogen to electricity from less than 38% for conventional LOHC concepts to over 50% [10]
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