Cerium-Mediated Hydrogen Production and Energy Storage System

Abstract

The implementation of electrolysis systems for electrochemical hydrogen production has continued to grow as the paradigm shift towards renewable energy and fuels progresses. However, some issues regarding conventional polymer electrolyte membrane (PEM) electrolysis systems still remain; the performance of PEM electrolyzers degrade if operated with intermittent energy sources, while the cost of electricity continues to be the highest cost contributor (over 70% of hydrogen production cost). In order to make electrochemical hydrogen production more feasible and compete with methane reforming on a large scale, renewable energy sources and new strategies are needed to reduce the electricity cost. Decoupled electrolysis systems have been studied to temporally and spatially separate the evolution of hydrogen and oxygen, making the electrolysis system safer, but these systems only add an additional electricity burden. In this presentation, I will describe a cerium-mediated decoupled water electrolysis system that can produce hydrogen and store energy through a redox cycle that bridges the hydrogen evolution and oxygen evolution reactions. Cerium (III/IV) was chosen as a redox couple given that it exhibits a higher oxidation potential (~1.6V) than water. This high redox potential of Ce allows for the design of a dual function (i.e., energy storage and hydrogen generation) system consisting of a hydrogen evolution cell which requires an energy input to oxidize Ce(III) and reduce protons, and an oxygen evolution cell which outputs energy by reducing Ce(IV) and oxidizing water. This dual function design can reduce the costs of electrochemical hydrogen production in renewable-rich electricity grids by operating the hydrogen evolution cell when the electricity prices are low and the oxygen evolution cell when they are high. In this talk, I will discuss the electrochemical performance of this system with regards to operational factors such as temperature, flow rate, and concentrations of reactants. In addition, I will discuss the technoeconomic factors that drive the hydrogen production cost in the redox-mediated system and compare them to PEM electrolysis under grid scenarios with various degrees of renewable energy penetration. Finally, I will discuss on-going research into the improvement of the electrochemical performance and efficiency of this system, focusing on enhancing mass transport and faradaic efficiencies in Ce redox processes. Figure 1