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WIREs Energy Environ.
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Electrochemical conversion of alcohols for hydrogen production: a short overview

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In the emerging hydrogen economy, one of the major objectives is the production of electricity using fuel cells, particularly proton exchange membrane fuel cells (PEMFC). In this perspective, high purity hydrogen is needed. Hydrogen is currently mainly produced from fossil fuels (natural gas, oil, and coal) by energy‐consuming and environmentally unfriendly industrial processes that also involve complicated clean up steps for the removal of carbon monoxide and carbon dioxide. Water electrolysis (particularly the proton exchange membrane electrolysis technology, which allows higher efficiency than alkaline technology) appears to be a good candidate for the production of clean hydrogen. The use of renewable primary energy sources, such as wind, solar, tidal, etc., makes this technology greener. However, the low kinetics of water oxidation, which implies high cell voltage (i.e. high energy consumption) even when using noble metal‐based catalysts (Pt, Ru, Ir), makes this technology expensive. Biosourced alcohols can be interesting alternatives as hydrogen carriers in an electrolysis cell; their reversible oxidation potentials are much lower than that of water, ca 0.1 V versus SHE (standard hydrogen electrode) against 1.23 V versus SHE, so that the cell voltages for hydrogen production are lower (and so is the energy consumption). However, the low kinetics of alcohol oxidation in acidic media requires high Pt‐based catalyst loadings at the anode. Direct alcohol alkaline electrolysis cells can be operated with low Pt loading and even non‐noble metals. In the case of glycerol, generation of hydrogen at the cathode can be performed simultaneously with the formation of value‐added products at the anode for a more profit‐making process. WIREs Energy Environ 2016, 5:388–400. doi: 10.1002/wene.193 This article is categorized under: Bioenergy > Science and Materials Fuel Cells and Hydrogen > Science and Materials Energy Efficiency > Science and Materials
Hydrogen evolution at different current densities for the proton exchange membrane electrolysis cells (PEMEC) (0.5 M H2SO4, Pt/C, N117, different anodes), 2 M CH3CH2OH at 30°C. j = 20 mA/cm2, j = 50 mA/cm2, j = 100 mA/cm2.
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Cyclic voltammograms recorded in a 0.1 M HClO4 + 0.1 M ethanol solution on different Pt‐based electrodes with a Pt loading of 0.1 mgPt cm−2 at v = 5 mV/s and T = 20°C.
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Electrolysis cell voltage versus current density Ucell(j) for the oxidation in proton exchange membrane electrolysis cells (PEMEC) of (a) water (anode PtRu/C) at 90°C and (b) 2 M CH3CH2OH at 20°C.
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Comparison of the theoretical j (E) electric characteristics representative of the Buttler‐Volmer kinetics law for water oxidation, alcohol oxidation, oxygen reduction, and proton reduction. UEC (water), UEC (alcohol), and UFC (O2/H2) are the cell voltages for water electrolysis, alcohol electrolysis, and hydrogen/oxygen fuel cell at a current density of 1 A/cm2, respectively.
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Working principle of proton exchange membrane electrolysis cells (PEMECs) for (a) water splitting reaction and (b) alcohol oxidation reaction.
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Rates of the different hydrogen sources for world hydrogen production.
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Ragone diagram presenting the correlation between the theoretical specific energy density and the theoretical specific power density for different electric power sources and comparison with the internal combustion engine (ICE).
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Working principle of a proton exchange membrane fuel cell (PEMFC) and components of the membrane–electrode assembly (MEA).
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Schema of the process for the synthesis of pure hydrogen convenient for feeding a proton exchange membrane electrolysis cells (PEMFC) from natural gas steam reforming.
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