High steam utilization operation with high current density in solid oxide electrolysis cells

摘要

Feasibility of high steam utilization operation with high current density in solid oxide electrolysis cells (SOECs) was investigated. Although higher reactant utilization leads to high efficiency and flexibility in SOEC systems, it increases the concentration polarization resistance, consequently decreasing the limiting current density, namely, decreasing the production rate of the energy carrier. To decrease the concentration polarization resistance, a porous structure-controlled NiO and Y₂O₃-stabilized ZrO₂ (YSZ) composite substrate prepared via an extrusion process was therefore used for a fuel electrode of an SOEC. After reduction of the fuel electrode, the porosity reached 54 vol.% and Ni, YSZ, and pores were uniformly distributed. In electrochemical measurements, the SOEC showed a high current density of 1.43 A cm?2 at the thermo-neutral voltage at 800°C using a mixture of 20% steam in hydrogen (feed rate for excess supply). At high steam utilization of 90% and a resulting partial pressure of residual water of 0.02 atm, the SOEC could operate even at a high current density of 1.25 A cm?2. The calculated concentration overpotential suggested that high steam utilization with high current density is feasible by using highly porous fuel electrodes.