Protonic-Ceramic Supported Intermediate-Temperature Electrolysis Operations: From Unit-Cell to Utility-Scale
Authors: Thatte Amogh , Zhu Huayang , Kee Robert J. , Braun Robert 
Published: December 2024

Advancing protonic ceramic electrochemical cell technology continues to be explored for a variety of energy applications, including novel membrane reactors, electrochemical compression, fuel cells, and electrolyzers. The present work focuses on hydrogen production using protonic ceramic electrolysis cells (PCECs) at cell- and system-scales. New cell models are developed, which overcome previous limitations, and are experimentally validated for purposes of scale-up, performance prediction, and system analyses.

Computational modeling of PCECs is challenging due to tracking the movement of three charge carriers: protons, oxygen vacancies, and polarons to accurately predict the cell’s operating characteristics. The model-predictive cell performance is based on an experimentally validated, quasi-2D (1+1D) transient, dual-channel cell model capable of predicting the performance of a multiple-charged defect-conducting PCEC based on a BCZYYb electrolyte with the help of a Nernst-Planck formulation. The transient cell model is helpful in several aspects. First, it predicts the distribution of properties and key variables down the PCEC channel. Second, it estimates PCEC effectiveness in electrochemical steam splitting (i.e., faradaic efficiency) over a wide range of current densities. Third, it demonstrates that the PCEC’s actual thermal-neutral voltage decreases significantly as the faradaic efficiency decreases. Finally, it leads to the conclusion that operating a large adiabatic PCEC at its theoretical thermal-neutral voltage necessitates thermal management (e.g., convective heat loss) to regulate the cell temperature.

A detailed parametric analysis that follows the transient model development quantifies convective heat losses required for PCEC thermal management and predicts PCEC performance under different operating conditions. This analysis predicts that operating the cell at high feedstock steam concentration (40%), low operating temperature (873K), low cell voltage (1.28V), and low steam utilization (50%) results in high average faradaic efficiency (and hence low convective heat losses), high cell energy efficiency, and increased amount of hydrogen produced per cell. The parametric analysis also generates guidance on gas channel inlet mass flow rates to obtain high purity hydrogen outlet stream.

A wider perspective is then provided by examining the prospects for scale-up of PCEC technology to utility scale system design and techno-economics. An overview of a utility-scale PCEC electrolyzer capable of producing 50 ton dry hydrogen per day integrates stack with other balance of plant components, analyzes different design configurations for different feedstock steam concentrations, and identifies suitable steady-state operating conditions that improve the techno-economic performance of the system. This analysis shows that the feedstock steam concentration is the most critical factor in designing the utility-scale PCEC electrolyzer system. Operations at lower feedstock steam concentration results in lower system efficiency, high CAPEX and prohibitively high levelized cost of hydrogen (LCOH). Considering utility-scale PCEC electrolyzer system operations with stack cooling features, hydrogen can be produced in economical way ( $4.5/kg) at high feedstock steam concentration, lower operating temperature, and high steam utilization.