Thermoneutral Operation of Solid Oxide Electrolysis Cells in Potentiostatic Mode

Abstract

High temperature electrolysis based on solid oxide electrolysis cells (SOECs) is a promising technology for energy storage and synthetic fuel production. In recent years extensive efforts have been devoted to improving performance and durability of SOEC cells and stacks. Due to historical reasons and the convenience of doing constant current tests, (almost) all the reported SOEC tests have been galvanostatic. In this work, we report test results on two types of SOEC cells operated for electrolysis of steam in potentiostatic mode at 1.29 V. Both cells are Ni/YSZ fuel electrode supported type with different oxygen electrodes. The two cells exhibited different initial performance and different long-term degradation behavior. Detailed impedance analysis indicates that degradation happened mainly at the Ni/YSZ electrode for both cells. Large overpotential on the Ni/YSZ electrode was identified as the main cause of the degradation. Operation strategies were further proposed for electrolysis operation in potentiostatic mode.

3D Microstructural Characterization of Ni/YSZ Electrodes Exposed to 1 Year of Electrolysis Testing

“…The inlet side is supposed to be exposed to highest value of local current density which can contribute to a faster degradation. Chen et al [38] simulated the current density distribution in the cell in the direction of the steam flow for two cells with different oxygen electrodes, the average current density of the two cells was ~ 0.9 and ~ 1.2 A/cm 2 , respectively [38]. The differences between inlet and outlet in current density were ~ 0.19 and ~ 0.35 A/cm 2 , for the two cells respectively.…”

“…While similar nickel depletion in the active electrode can be detected at the inlet and outlet side of the cell, a more pronounced TPB length decrease is observed at the inlet side when compared to the outlet. This effect is presumably linked with an effect of the local polarization, which is much larger at the inlet compared to the outlet (the total cell overpotential was estimated to be ~ 420 mV at the inlet and ~ 320 mV at the outlet) resulting also in a higher local current density [38]. The same trend obtained in the cell analyzed in this study was qualitatively observed in the ~ 700 hours tested cells in reference [39], where 2D low voltage SEM images showed a lower percolation degree at the inlet side.…”

Unwinding Entangled Degradation Mechanisms in Solid Oxide Electrolysis Cells Through Electrode Modifications and Impedance Analysis

“…The electrochemical durability testing of the cells was carried out at 750 °C in co‐electrolysis mode with 65% H 2 O+ 25% CO 2 + 10% H 2 in the fuel feed corresponding to a theoretic thermodynamic equilibrium composition of 23% CO 2 + 2% CO + 8% H 2 + 67% H 2 O. The voltage was kept constant at 1.2 V, with varying current densities throughout the durability testing, as a consequence of degradation . Cell A and Cell‐C were tested for 1,000 h, while Cell B for 500 h. Analysis of the impedance data was performed using the software Ravdav .…”

Renewable production of ammonia and nitric acid

“…There are several advantages of doing so. First of all, the SOE can be operated in a different operating mode, that is, the thermal‐neutral or endothermic mode, with a higher utilization factor of the stack . Hence, the costly investment for the SOE is reduced.…”