Advanced Characterization and Modeling to Understand Hydrogen Production by Solid Oxide Electrochemical Cells

Functional oxides are becoming more important in a wide variety of renewable applications, ranging from high temperature electronics, electric vehicles, and solid oxide electrolysis/fuel cells (SOEC/SOFC). They must meet a diversity of characteristics to achieve desired functionality in these harsh environments. Hydrogen is considered an enabler for the transition to sustainable and renewable society. Production of green hydrogen is a strong focus of modern research given the current global market of 170 billion dollars. Among the approaches for hydrogen generation are the use of SOECs. These utilize a stack of high temperature oxides operating in H₂/steam. While direct electrochemical measurements are key for quantifying progress towards the DOE Hydrogen Earthshot Goal of 1$/kg in the next decade they are insufficient to provide detailed materials science investigation of degradation pathways. We report on the development of a suite of synchrotron and conventionally based analysis tools to provide a set of detailed morphology, phase, and composition data which both provide detailed information about degradation mechanisms and provide foundational information for predictive models leading to ultimate materials improvement.<br/><br/>The solid oxide layers that comprise SOECs typically feature a layered structure composed of a Ni-YSZ fuel electrode/YSZ electrolyte/Gadolinium doped Ceria barrier layer and a Lanthanum Strontium Cobalt Iron Oxide oxygen electrode. The phase behavior especially at interfaces is complex starting from the deposition of materials to behavior during extensive aging. Recent analysis has confirmed a number of potential degradation mechanisms are operable including Sr, Ni, and Ag migration, interfacial phase formation and grain coarsening. We will discuss how a combination of synchrotron X-ray diffraction(XRD), nanoscale X-ray computed tomography (nano-XCT), and other X-ray spectroscopy techniques combined with electron microscopy can provide coupled insights on the nature of these mechanisms which can be incorporated into computational models which can provide predictive insights on cell/stack longevity. We also discuss how button cells can inform large area and stack behavior.<br/><br/>We will discuss our recent development of an in-operando system intended for the synchrotron techniques, especially XRD, to probe cell performance in real time.<br/><br/>Advanced characterization can couple to cell development and electrochemical testing towards achieving DOE Hydrogen Earthshot Goals.<br/><br/>This work is authored by the National Renewable Energy Laboratory (NREL), operated by Alliance for Sustainable Energy, LLC, for the U.S. Department of Energy (DOE) under Contract No. DE-AC36- 08GO28308. David Ginley, Sarah Shulda, Robert Bell, Nick Strange, Heather Slomski and Michael Dzara are funded primarily by the EERE Hydrogen and Fuel Cell Technology Office; The views expressed in the article do not necessarily represent those of the DOE or the U.S. Government.