Solid-oxide fuel cells (SOFCs) are established energy conversion devices capable of producing electrical energy efficiently using hydrogen and various hydrocarbon fuels.  Over the past few decades, these devices have shown great promise to fulfill a need of energy production and conversion applications, such as high-power density for prolonged durations.  SOFCs are composed of multiple layers of mixed-conducting oxide electrodes and an ionic conducting oxide electrolyte layer. Generally, in order to produce the required complex porous electrode and dense electrolyte microstructures needed for SOFCs, these layered composite ceramics must be thermally processed (sintered) to temperatures ranging between 1100-1450 °C in sequential thermal cycles (typically two to three temperature cycles).  The total processing time, energy consumption and cost can be extensive to produce SOFCs, and these processing issues are some of the greatest barriers for mass production and application of the SOFC technology.  Embedded within these manufacturing losses is the seemingly negative sustainability of the overall technology, which goes against the sole purpose of developing and implementing this technology.    
 
Over the past decade, a previously known mechanism of densification to geologist has been applied to the modern ceramic processing to lower the sintering temperature.  The method termed cold sintering process (CSP) permits the densification of a specific subset of oxide compositions in the presence of a liquid phase (typically water) through a liquid-phase sintering-like mechanism.  The CSP method typically occurs at temperatures <400 °C under uniaxial pressures <500 MPa within a uniaxial die.  As stated in a recent review article by Grady et al. (2020), CSP has been applied to an array of electrolyte/electrode and dielectric systems for energy and electronics applications.  The authors list some of the major benefits of this sintering process as: fast processing time, lower processing cost, ability to process unique composites, scalable, and addresses chemical instabilities (such as high-temperature vaporization).  These benefits address many of those processing limitations for the SOFC technology.     
 
The objective of our work was to investigate the cold sintering of ferrite and cobaltite SOFC cathodes and cathode composites.  Both the processing of monolithic cathode supports and films were investigated in this work.  A range of both nano- and micro-scale cathode powders were utilized as the precursor materials.   The cathode compositions were processed with a range of water contents (0-30%) within the initial compacts.  In addition, various inorganic and organic based liquids were also investigated for the interparticle liquid phase.  The processing temperatures ranged between 200-400 °C and pressures between 200-500 MPa.  The incorporation of pore formers within the compacts were also evaluated in order to control the distribution and shape of the porosity within the final cathode microstructure.  The microstructure was characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) in order to define the phase and grain development/evolution during the process.  The total conductivity, grain boundary resistance, and interfacial resistance were characterized by electrochemical impedance spectroscopy (EIS).  The final chemistry and microstructure were contrasted to the electrochemical performance and compared against baseline high-temperature processed cathode materials of the same composition.