Perspectives on Cathodes for Protonic Ceramic Fuel Cells

Abstract

Protonic ceramic fuel cells (PCFCs) are promising electrochemical devices for the efficient and clean conversion of hydrogen and low hydrocarbons into electrical energy. Their intermediate operation temperature (500–800 °C) proffers advantages in terms of greater component compatibility, unnecessity of expensive noble metals for the electrocatalyst, and no dilution of the fuel electrode due to water formation. Nevertheless, the lower operating temperature, in comparison to classic solid oxide fuel cells, places significant demands on the cathode as the reaction kinetics are slower than those related to fuel oxidation in the anode or ion migration in the electrolyte. Cathode design and composition are therefore of crucial importance for the cell performance at low temperature. The different approaches that have been adopted for cathode materials research can be broadly classified into the categories of protonic–electronic conductors, oxide-ionic–electronic conductors, triple-conducting oxides, and composite electrodes composed of oxides from two of the other categories. Here, we review the relatively short history of PCFC cathode research, discussing trends, highlights, and recent progress. Current understanding of reaction mechanisms is also discussed.

Electrochemistry and energy conversion features of protonic ceramic cells with mixed ionic-electronic electrolytes

“…This strategy is constantly developing due to the design of new electrolyte materials, 121,138–141 novel thin-film technologies, 32,142,143 and innovative highly active electrode systems. 144–148…”

Advanced Materials for Thin‐Film Solid Oxide Fuel Cells: Recent Progress and Challenges in Boosting the Device Performance at Low Temperatures

“…A couple of reviews focusing on cathode materials for PCFCs are available in literature. [139,[171][172][173][174][175][176] Some examples are highlighted below.…”

Layered Oxygen-Deficient Double Perovskites as Promising Cathode Materials for Solid Oxide Fuel Cells

“…Recently, it has been shown that effective cathodes for proton-conducting SOFCs operating at low and intermediate temperatures are Ba(Ce,Zr)O 3 -based solid solutions doped with transition elements in high concentration. These phases demonstrate excellent chemical compatibility with typical proton-conducting solid electrolytes due to the similarity of their compositions [ 43 , 44 ]. These compounds belong to the triple-conducting oxides (TCOs) [ 45 , 46 , 47 ], in which transport species are simultaneously protons, oxygen ions, and electrons (holes).…”

“…The advantage of TCOs as cathode materials for proton-conducting SOFCs is that both protons from the solid electrolyte and oxygen species adsorbed from the air may migrate through the bulk and over the surface of the cathode, which extends the reaction area over the whole electrode. We should note that LODPs, such as Ln Ba 0.5 Sr 0.5 Co 1.5 Fe 0.5 O 5+δ ( Ln = Pr, Nd), when used as cathodes for proton-conducting SOFCs, also belong to the class of TCOs [ 9 , 44 ]. According to [ 48 ], triple conductivity in LODPs can appear due to the formation of impurity phases, which should be taken into account for the development of new TCOs.…”