Fabrication and electrochemical performance of nickel-alloy-foam-supported solid oxide electrolysis cell for hydrogen production from steam

Abstract

The effect of CuO as a sintering additive on the electrolyte of solid oxide electrolysis cell (SOEC) was investigated. 0.5 wt.% CuO was added into Sc0.1Ce0.05Gd0.05Zr0.89O2 (SCGZ) electrolyte as a sintering additive. An electrolyte-supported cell (Pt/SCGZ/Pt) was fabricated. Phase formation, relative density, and electrical conductivity were investigated. The cells were sintered at 1373 K to 1673 K for 4 h. The CuO significantly affected the sinterability of SCGZ. The SCGZ with 0.5 wt.% CuO achieved 95% relative density at 1573 K while the SCGZ without CuO could not be densified even at 1673 K. Phase transformation and impurity after CuO addition were not detected from XRD patterns. The electrochemical performance was evaluated at the operating temperature from 873 K to 1173 K under steam to hydrogen ratio at 70:30. Adding 0.5 wt.% CuO insignificantly affected the electrochemical performance of the cell. The activation energy of conduction (Ea) was 72.34 kJ mol-1 and 74.93 kJ mol-1 for SCGZ and SCGZ with CuO, respectively. A thin-cell composed of nickel-Sc0.1Ce0.05Gd0.05Zr0.89O2 (Ni-SCGZ) cathode, SCGZ electrolyte and Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF) anode, having Ni-iron (Ni-Fe) alloy foam (porosity: 5-130 ppi) as a support is successfully fabricated by the sequence wet-chemical coating. The cathode green tape is deposited on the support with viscosity and thermal expansion coefficient (TEC) gradient multi-layers. Two-step firing processes are applied - pre-cathode firing (1373 K, 2 h) and electrolyte sintering (1623 K, 4 h) with multi heating rate and compressive loading. The thickness of functional cathode layer, electrolyte, and anode is 150, 25 and 30 μm, respectively. The fabricated cell of the alloy foam supported SOEC shows excellent current density with 0.95 Acm-2 operated at 1.1 V with H2O:H2 = 70:30, 1073 K, providing hydrogen production rate at 4.95x10-6 mols-1 However, the durability of the cell is rather poor under prolong operation with the degradation rate of 0.08 Vh-1