Influence of Surface State on the Electrochemical Performance of Nickel-Based Cermet Electrodes during Steam Electrolysis

Abstract

Due to their fuel flexibility and high efficiency, solid oxide cells are a promising technology for sustainable energy production and storage. Nickel in combination with yttria-stabilized zirconia (YSZ) or gadolinium-doped ceria (GDC), forming Ni-YSZ or Ni-GDC cermets respectively, are the most widely adopted electrodes in solid oxide fuel cell fabrication. Currently, there is an increasing interest in cermet electrodes for hydrogen generation through high temperature steam electrolysis using solid oxide electrolysis cells (SOECs). However, durability remains a major issue for reliable operation of SOEC systems. A variety of processes accountable for permanent performance degradation of SOECs has been identified based on post-mortem cell analysis. Besides, transient/reversible degradation processes are typically examined by indirect methods, like impedance spectroscopy. The reason is that the application of material characterization techniques during SOEC operational conditions is challenging. In this work we provide a direct correlation between Ni-YSZ and Ni-GDC electrode surface oxidation states and their performance during steam electrolysis using operando experimental evidence provided by near ambient pressure X-ray photoelectron and near edge X-ray absorption fine structure spectroscopy. We show that nickel surface oxidation may induce significant performance degradation in Ni-YSZ cathodes while, on the contrary, having minor effects in Ni-GDC. Remarkably, we found that in the case of Ni-GDC electrodes, small modification of the GDC oxidation state can have an important impact on the electrolysis performance. The results highlight the crucial role of the cathode electrode surface oxidation state on the SOEC functionality and have potential implications for the design and operation strategies of more efficient and durable SOEC devices.

Hydrogen Generation Using Solid Oxide Electrolysis Cells

“…Water reduction reaction (WRR) takes place at the cathode compartment and appropriate materials for the catalysis of WRR should possess high electrochemical activity and electrical conductivity. Composite of Ni metal and YSZ electrolyte 18–20 is a conventional and extensively studied electrode material for WRR and it has been applied to several types of cell configurations. However, one major drawback of using Ni‐YSZ cermet is poor redox stability under high steam content, which leads to microstructural coarsening and electrode delamination.…”

“…M. Morgensen et al [15] studied the electrolysis of water at 850°C, using yttria-stabilized zirconia (YSZ) electrolyte with the thickness of 10-15 mm. [18][19][20] is a conventional and extensively studied electrode material for WRR and it has been applied to several types of cell configurations. However, one major drawback of using Ni-YSZ cermet is poor redox stability under high steam content, which leads to microstructural coarsening and electrode delamination.…”

Enhancing the Electrocatalytic Activity of Redox Stable Perovskite Fuel Electrodes in Solid Oxide Cells by Atomic Layer-Deposited Pt Nanoparticles

“…The Ni-YSZ cathode in SOEC, however, is exposed to a variable oxygen partial pressure environment and, thus, is ultimately decaying due to the coarsening of the Ni particles. 7,8 To restrain Ni oxidation, a reducing agent, such as H 2 or CO, is co-introduced to the cathode atmosphere, hence increasing process' cost and complexity. 5,9 In view of this, redox stable perovskite (ABO 3 ) materials with mixed ionic−electronic conducting (MIEC) properties have been examined as the cathodic electrodes in SOECs.…”

The promoting effect of Fe on Ni/ GDC for the Solid Oxide H 2 O electrolysis

“…Moreover, the replacement of ZrO 2 (Y 2 O 3 ) (YSZ) with a porous mixed ionic‐electronic conductor (MIEC) material, which can also act as an electrocatalyst, has been considered as a method to increase the reaction sites of the electrocatalyst. Gadolinium‐doped ceria, CeO 2 (Gd 2 O 3 ) (GDC), is a quite suitable MIEC material for this purpose, since it combines good electronic and ionic conductivity with high electrochemical activity 8‐11 and fast interfacial charge transfer reactions, which could prove to be beneficial for the performance of the fuel electrode 12,13 …”

“…Moreover, the replacement of ZrO 2 (Y 2 O 3 ) (YSZ) with a porous mixed ionic-electronic conductor (MIEC) material, which can also act as an electrocatalyst, has been considered as a method to increase the reaction sites of the electrocatalyst. Gadolinium-doped ceria, CeO 2 (Gd 2 O 3 ) (GDC), is a quite suitable MIEC material for this purpose, since it combines good electronic and ionic conductivity with high electrochemical activity [8][9][10][11] and fast interfacial charge transfer reactions, which could prove to be beneficial for the performance of the fuel electrode. 12,13 Another promising approach in the field of high temperature Solid Oxide fuel cells is to promote the electrocatalytic activity of Ni-based electrodes, through the dispersion of small amounts of noble (eg, Pt, Pd, Rh, Ru, Au) or non-noble transition metal elements (eg, Sn, Cu, Mo, Bi).…”