(Invited, Digital Presentation) Infiltrated Electrodes for High Temperature Energy Conversion, Electrolysis, and Chemical Synthesis

Abstract

Solid oxide cell (SOC) infiltrated electrodes typically consist of a ceramic or cermet porous scaffold with the pore walls coated with catalyst particles. The pore size of the scaffold is 1 to 50 mm, whereas the catalyst particles are 10 to 300 nm. This scaffold provides a stable and durable mechanical structure, and the fine catalyst particles provide high surface area for electrochemical and heterogeneous reactions. The scaffold is sintered and bonded to the other layers of the complete cell. After this high temperature processing is finished, catalyst precursor solution is flooded into the scaffold and fired at moderate temperature to form the desired catalyst composition and phase. Because the scaffold is sintered in the absence of catalysts, re-optimization of the fabrication process, ink formulation, deposition process, and sintering protocol is not needed when a new catalyst is introduced to the cell design. Instead, a new precursor solution can be prepared from a stoichiometric mixture of metal salts, with minimal change in processing. This approach makes it straightforward to screen many catalyst compositions in a short period of time, and adapt an existing cell structure for a wide variety of applications.The Lawrence Berkeley National Laboratory metal-supported solid oxide cell (MS-SOC) design has a thin electrode scaffold of zirconia ceramic co-sintered on a thick porous stainless steel support layer. Both layers are coated with infiltrated catalysts. The catalyst precursor solution is an aqueous mixture of metal nitrate salts. After the solution is flooded into the pores of the scaffold, it is dried and heated in air to convert the nitrate salts to mixed metal oxides. The oxides can then be reduced to metals by firing in reducing atmosphere, if desired. The drying rate, heating rate, conversion temperature, and other processing parameters can have a dramatic impact on the catalyst particle morphology and ultimately on the performance and durability of the electrochemical device.Depending on the choice of catalyst composition, the MS-SOCs can be configured as fuel cells, electrolysis cells, or chemical conversion reactors. Several examples will be highlighted, including: fuel cell operation with hydrogen, ethanol, and natural gas; steam electrolysis for hydrogen production; and oxidative coupling of methane for valuable chemical synthesis. In each case, technical progress will be presented with a focus on catalyst development and device performance. Figure 1