Under the DOE-Nuclear Hydrogen Initiative, Idaho National Laboratory (INL) is working on a project to generate hydrogen using solid oxide electrolysis cells (SOEC). Experimental results were obtained from a stack of planar SOEC fabricated by Ceramatec, Inc. The SOEC stacks operate in the range 800 - 900°C to achieve a thermal-to-hydrogen conversion efficiency of 45-55%. Experimental results were obtained from a planar SOEC stack, with a per-cell active area of 64 cm². The electrolysis cells are electrolyte-supported, with scandia-stabilized zirconia electrolytes (~140 μm thick), nickel–cermet steam/hydrogen electrodes, and manganite air-side electrodes. The experiments were performed over a range of steam inlet mole fractions (0.1–0.6), gas flow rates (1000–4000 sccm), and current densities (0–0.38A/cm²). Hydrogen production rates in excess of to 90 NL/h were achieved. A three-dimensional computational fluid dynamics (CFD) model was also created to model a single electrolysis cell as it would exist in the experimental planar stack. Mass, momentum, energy, and species conservation and transport are provided via the core features of the commercial CFD code FLUENT. A solid-oxide electrolysis model adds the electrochemical reactions and loss mechanisms and computation of the electric field throughout the cell. Model results provide detailed local profiles of temperature, Nernst potential, operating potential, anode-side gas composition, cathode-side gas composition, current density and hydrogen production over a range of stack operating conditions. Mean model results were shown to compare favorably with the experimental results obtained from the 10-cell stack tested at INL.

The research results reported here have been obtained in a laboratory-scale apparatus. These results and common scale-up issues also indicate that for the technology to be successful in a large industrial setting, several technical, manufacturing, and economical issues have to be resolved. Some of the issues related to solid oxide cells are stack design and performance optimization, identification and evaluation of cell performance degradation parameters and processes, integrity and reliability of the SOEC stacks, life-time prediction and extension of the SOEC stack, and cost reduction and economic manufacturing of the SOEC stacks. Besides the solid oxide cells, balance of the hydrogen generating plant also needs significant development. These issues are process and ohmic heat source needed for maintaining the reaction temperature (~830°C), high temperature heat exchangers and recuperators, equal distribution of the reactants into each cell, system analysis of hydrogen and associated energy generating plant, and cost optimization by switching back and forth between hydrogen (electrolysis) and power generation power modes.

These issues need interdisciplinary research effort of solid oxide cell manufacturers, hydrogen consumers, federal laboratories, and other such stakeholders. This paper discusses such issues with a view that for hydrogen to become an economical and viable option, a collaborative effort of all the stakeholders is needed.