Thermodynamic and Economic Potential of Glycerol Oxidation to Replace Oxygen Evolution in Water Electrolysis

Abstract

In electrochemical hydrogen production, a major contribution to the energy demand is the anodic oxygen evolution reaction, although byproduct oxygen is often not utilized. This motivates the search for alternative anodic oxidation reactions. Glycerol has been proposed as a promising reagent for the anode since it is widely available, cheap, and green. However, it is still unclear if this would have energetic and economic benefits. To this end, we evaluated the anodic oxidation of glycerol to the 14 alternative products that have been mentioned in the literature. We screened these possible oxidation products based on two criteria: (i) a surrogate for the energy demand (reversible and thermoneutral voltages) and (ii) an economic value. To address the challenge of data availability, we took thermodynamic properties estimated by group contribution methods and machine learning. For the economic data, we use both laboratory price data from Sigma-Aldrich and industry price data from ChemAnalyst and Kahlstorf et al. We also compare the current and projected production rates of hydrogen and find that the current glycerol supply will not suffice to cover the hydrogen demand, yet still coupled glycerol oxidation and hydrogen evolution can serve as an alternative to convert glycerol waste streams from biodiesel plants to higher value while additionally producing hydrogen. All glycerol oxidation reactions considered have the potential to significantly reduce the energy demand for green hydrogen production. Some of them potentially add value through byproducts, although product prices are highly uncertain.