Performance evolution analysis of solid oxide electrolysis cells operating at high current densities

Abstract

Hydrogen generation by water electrolysis using solid oxide electrolysis cells (SOECs) is highly promising because of the favorable thermodynamics and kinetics. Commercial applications require SOEC operating at high current densities (ǀiǀ≥1 A·cm−2) to achieve substantial hydrogen production rates. This study demonstrates the operation of a full-size Ni–yttria-stabilized zirconia (Ni–YSZ) cell with an effective area of 16 cm2 at −2 A·cm−2 for 336 h, illustrating the feasibility of operating SOECs at a high current density. The electrochemical characteristics of the SOEC evolved during constant current electrolysis, exhibiting an activation stage with a degradation rate (DR) of 54.6 mV/100 h, followed by a rapid decline process(DR: 180.9 mV/100 h), a gentle decline period (DR: 105.5 mV/100 h), and a stable stage (DR: 11.0 mV/100 h). The contributions of individual processes to cell degradation during each process are identified using the distribution of relaxation times (DRT) and subsequent equivalent circuit model (ECM) fitting. The results suggest that the Ohmic resistance, ionic transport and charge-transfer reaction in the Ni-YSZ fuel electrode contribute the most to performance loss. Ni redistribution is regarded as the dominant degradation mechanism, as verified by detailed post-test characterization.