Efficient Production of Green Hydrogen by Ethanol Electrolysis at a PtRhRu Catalyst

Production of green hydrogen by electrolysis of ethanol is potentially a more efficient technology than water electrolysis because it requires much lower cell potentials. However, separation and valorization of the acetic acid and acetaldehyde byproducts are required, producing greater uncertainty in the cost of hydrogen. Fluctuations in commodity prices also make it difficult to select the most appropriate catalysts and operating conditions. These issues are addressed here by the analysis of electrochemical data and product distributions, over a range of potentials and ethanol concentrations, using a techno-economic framework to estimate the projected cost of hydrogen. For Jan 2025 prices, a minimum cost of 4.5 USD kg^–1 was obtained for the production of hydrogen using a PtRhRu catalyst, which is at the high end of a range estimated for water electrolysis. However, a sensitivity analysis shows that a doubling of the price of acetic acid to 1 USD kg^–1 would decrease the hydrogen cost to 1.1 USD kg^–1. The stoichiometry for ethanol oxidation has a strong influence on the cost, since it determines the selectivity for hydrogen production (hydrogen:ethanol ratio). Consequently, the PtRhRu catalyst is more efficient than the PtRu catalysts that are generally employed for ethanol electrolysis due to the high yields of acetic acid and CO₂ that it can produce. Overall, the results of the cost of hydrogen estimates and their dependence on the ethanol concentration and cell potential provide a comprehensive view of the economic potential of ethanol electrolysis and framework for optimizing catalysts and operating parameters in response to changing market conditions.