Optimizing Solid Oxide Electrolysis Cell Performance and Lifetime Under High Pressure and Dynamic Conditions

The transition to renewable energy is crucial in addressing climate change, yet the intermittent availability of wind and solar power presents challenges to energy reliability. To overcome this, effective energy storage solutions are essential for stabilizing and scaling energy supply. Power-to-X (P2X) technologies have emerged as a key strategy for converting surplus renewable electricity into storable energy carriers, with hydrogen production through electrolysis being a prominent approach. By splitting water into hydrogen and oxygen, excess renewable energy can be efficiently stored and later utilized as a clean and versatile fuel. Solid Oxide Electrolysis Cells (SOECs) offer a highly efficient pathway for large-scale hydrogen production in P2X systems. However, widespread deployment is hindered by challenges such as material degradation, thermal instability, and high operational costs. Operating SOECs under elevated pressure has been identified as an effective method to enhance performance, reduce capital expenditures (CAPEX), and improve hydrogen output. This study introduces a novel high-pressure SOEC setup, integrating nickel/yttria-stabilized zirconia (YSZ) cathodes, YSZ electrolytes, and lanthanum strontium cobaltite (LSC) air electrodes. The system operates in a controlled gas environment, with precise pressure regulation maintained via Equilibar back-pressure regulators. To ensure system stability, pressure is gradually increased at a rate of 0.5–1 bar per hour. Electrochemical performance is assessed through open-circuit voltage (OCV) measurements, current-voltage (I/V) curves, and electrochemical impedance spectroscopy (EIS). A novel AC:DC cycling strategy has been developed to enhance thermal and electrochemical stability under pressurized conditions. This method alternates between electrolysis and fuel cell modes, incorporating periodic reverse pulses to regulate thermal distribution and mitigate nickel migration—a primary cause of SOEC degradation. The optimization of the AC:DC cycling profile is currently under investigation, with switching frequencies ranging from 30 Hz to 0.91 Hz. Experimental results reveal a slight voltage drop and a notable increase in cell impedance as frequency increases during electrolysis and fuel cell operations, respectively. At low frequencies, a significant voltage drop in fuel cell mode is observed, likely due to mass transfer limitations affecting hydrogen availability at the reaction site (electrode/electrolyte interface), leading to localized "starvation" of the cell. The findings suggest that operating at frequencies above 10 Hz improves system performance. At different cycling frequencies, local SOEC temperature variations along the gas flow direction play a crucial role. Higher frequencies lead to more uniform temperature distribution, increasing the overall average operating temperature and reducing thermal gradients. When the cycling frequency exceeds 10 Hz, both the average operating temperature and the maximum temperature gradient stabilize, as shorter cycle durations prevent significant gas composition fluctuations. At the lowest tested frequency (0.91 Hz), gas composition and temperature undergo considerable variations within each cycle, influencing overall system stability. By maintaining a thermoneutral balance, this cycling strategy promotes system stability and mitigates stress-induced degradation. Long-term testing exceeding 600 hours is currently underway, comparing DC-only and AC:DC cycling modes. Post-mortem analysis is being conducted to evaluate degradation mechanisms and material stability. Preliminary results indicate enhanced charge and mass transfer, increased hydrogen production efficiency, and reduced degradation under pressurized conditions. These findings demonstrate the feasibility of integrating high-pressure SOEC operation with dynamic cycling for large-scale hydrogen production. The advancements presented in this study contribute to the development of more durable and cost-effective electrolysis technologies, supporting the transition to sustainable hydrogen production and green energy solutions on a global scale.