Combinatorial Materials Science for Protonic Electrochemical Energy Conversion

There is an increasing demand for electrochemical energy conversion technologies to balance the intermittent nature of renewable energy. Energy carriers such as hydrogen are therefore attracting significant interest. For the reversible conversion of steam and electricity to hydrogen, solid oxide cells show great promise due to their flexibility and high efficiency, particularly when integrated with waste-heat sources. The so-called Protonic Ceramic Electrochemical Cells (PCECs) are among the most promising candidates due to their reduced operating temperature of 350-650°C. Further development of PCEC technologies require improved functional materials, particularly to enhance the reaction rates at the oxygen/steam electrode. However, the materials properties that govern the performance of these electrodes remain elusive and have contributions from several underlying physical properties. In this project, combinatorial materials science is used to address these challenges towards the main objective: Establish correlations and fundamental relationships between key physical properties of electrode materials and how they merge to macroscopic electrochemical performance. The project thereby aims to provide strategies for the development of high-performance electrode materials. The combinatorial approach is enabled by a novel fabrication method for thin films with gradients in chemical composition. Important properties such as electronic conductivity and kinetic activity towards the reactions at the oxygen/steam electrodes can thereby be characterized as a function of composition. These measurements will be supported by a range of spatially resolved structural and chemical characterization methods to obtain materials properties that may correlate with electrochemical performance. The project will employ a PhD candidate and a postdoctoral researcher, and organize an international scientific workshop in Oslo.

The project addresses with the materials science of protonic ceramic electrochemical cells, specifically the oxygen/steam electrodes that are often limited by the oxygen reduction/evolution reactions. Little is known about the detailed reaction mechanisms of positrodes and the rate determining steps of the electrochemical processes at the electrode surfaces and interface to the electrolyte. Another major challenge in the development and understanding of these electrodes is that their target property – electrochemical activity – represents a lumped parameter with contribution from several underlying physical properties of the electrode material and its surface. The project will apply combinatorial materials science to address the multiple and complex relationships between basic and electrochemical materials properties. This approach is made possible by combinatorial pulsed laser deposition (C-PLD), using segmented PLD targets, to prepare continuous compositional spread (CCS) thin films. Isotope exchange annealing followed by (time-of-flight) secondary ion mass spectroscopy (ToF-SIMS), combined with Fick’s laws of diffusion to access the central surface exchange coefficient and diffusion coefficients, is of particular importance. These measurements will be supported by a range of spatially resolved structural and chemical characterization methods. Synchrotron X-ray absorptions spectroscopy (XAS) will be used with focus on mapping the oxygen p-band center across CCS films, as a potentially important descriptor for the crucial oxygen evolution and reduction reactions. Moreover, full electrochemical characterization as a function of atmospheric conditions and anodic/cathodic bias will be performed on selected compositions. The role of bulk protonic transport through the electrodes will be clarified by fabrication of model electrodes with well-defined geometries and imaging of the active regions by ToF-SIMS after electrochemical operation in isotope mixtures.