Engineered thickness-gradient electrolytes resolve current and thermal imbalances in solid oxide fuel cells

A novel single-cell architectural strategy published in ENGINEERING Energy demonstrates up to an 80% reduction in current density deviation and significant improvements in durability for high-efficiency fuel cell operation.

Solid oxide fuel cells (SOECs and SOFCs) are widely recognized as high-efficiency, environmentally friendly energy conversion systems capable of converting chemical energy directly into electricity. However, when operating large-planar SOFCs under practical, high fuel-utilization conditions, severe hydrogen depletion occurs along the gas flow direction. This depletion creates steep fuel concentration gradients, resulting in highly non-uniform current density distributions, localized overheating, and thermal stress that degrades cell lifetime and performance.

In a landmark study published in ENGINEERING Energy, a collaborative research team from Nanjing University of Science and Technology, Beihang University, The University of Tokyo, and industry partners at Xuzhou Huatsing Jingkun Energy Co., Ltd. has proposed and successfully fabricated a thickness-gradient electrolyte to solve this persistent engineering bottleneck at the single-cell architecture level.

Rather than relying on complex stack-level flow field redesigns or high-parasitic-power cooling systems, the researchers engineered the local ohmic resistance across the cell area. By applying a thicker YSZ (yttria-stabilized zirconia) electrolyte at the fuel-rich inlet (suppressing excessive local current) and a thinner electrolyte at the fuel-depleted outlet (boosting electrochemical reaction rates), the spatial current distribution is effectively homogenized across the entire active area.

Using a scalable wet-spraying process, the team manufactured industrial-sized 10 cm × 10 cm single cells featuring a continuous YSZ electrolyte thickness gradient ranging from 5 µm to 13 µm, coupled with an in situ hydrothermally self-crystallized dense 1.8 µm GDC (gadolinia-doped ceria) barrier layer.

Key Research Highlights & Breakthroughs

• First-of-Its-Kind Single-Cell Architecture: The study demonstrates the successful manufacturing and physical field regulation of industrial-scale SOFCs with a continuous thickness-gradient electrolyte, establishing a simple and highly scalable manufacturing route.
• Dramatic Reduction in Current Imbalance: Multiphysics simulations and local cell testing revealed that under 0.8 V operation and 80% fuel utilization, an optimized gradient electrolyte configuration (5–45 µm) decreased the current density deviation between the fuel inlet and outlet by 76% compared to a conventional 25 µm uniform electrolyte.
• Superior Electrical Efficiency & Power Output: At a high fuel utilization of 90%, the industrial-scale gradient-electrolyte cell achieved an electrical efficiency of 43%–58% (up to a 10% absolute increase over conventional uniform-electrolyte cells) and delivered a maximum fuel utilization exceeding 92%.
• Enhanced Long-Term Stability: In a 100-hour continuous constant-current durability test at 750 °C, the gradient-electrolyte cell exhibited exceptional stability with a voltage loss of merely ~0.4% (0.004 V loss), compared to a ~1.6% loss (0.016 V) in standard uniform cells.
• New Adaptability Evaluation Framework: The authors introduced key thermodynamic parameters—including optimum fuel utilization rate and minimum critical fuel utilization rate—to quantitatively evaluate how gradient-thickness electrolyte structures adapt to internal physical field gradients.

"This work fundamentally shifts the paradigm of physical field regulation in high-temperature electrochemical devices from external flow-field engineering to internal cell architecture design," the researchers stated. "The thickness-gradient strategy provides a practical, robust solution for mitigating thermal stress and degradation, opening new avenues for commercializing large-scale SOFCs, solid oxide electrolysis cells (SOECs), and other high-capacity energy storage platforms."

Journal: ENGINEERING Energy

Read the full article for free: https://rdcu.be/fAthS

Cite this article: Sun, H., Lyu, Z., Lyu, Q., Zhao, H., Sun, Z., Sun, K., Zhong, Q., & Zhu, T. (2026). Thickness-gradient electrolytes for homogenizing the current distribution in solid oxide fuel cells. ENGINEERING Energy, 20(5), 10878. https://doi.org/10.1007/s11708-026-1087-8