Protonic ceramic fuel cells and electrolysis cells represent low- and intermediate-temperature electrochemical devices, which allow chemical-to-electrical energy conversion with very high efficiency and low environmental impact. In order to ensure the long-term operability of these devices, as well as to provide for their up-scaling, a number of existing challenges associated with chemical and thermal incompatibilities pertaining to the functional materials remain to be overcome. This work presents a comprehensive overview of new electrode materials based on barium cerate/zirconate. The structural fragments of these materials are similar to those of the proton-conducting Ba(Ce,Zr)O3 electrolytes, which causes superior chemical compatibility between different functional materials. The primary emphasis of the research is on the functional properties of these materials such as chemical stability, thermal expansion behaviour and transport features. This in turn determines the electrochemical performance of the designed electrodes. In addition, the possibility of obtaining triple-conducting materials is discussed as means of designing electrodes with a high electrochemical active surface area required for the design of high-performance protonic ceramic fuel and electrolysis cells.
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The design of new electrode materials with high redox stability has great potential for the fabrication of solid oxide fuel and electrolysis cells having a symmetrical configuration; such a configuration is particularly promising in terms of economic and technological factors due to involving a reduced number of functional materials and technological steps. Under the framework of the present study, we developed new Nd 1-x Ba x Fe 0.9 M 0.1 O 3-δ materials (where M = Cu or Ni, x = 0.4 or 0.6), characterizing their functional properties (oxygen non-stoichiometry, thermomechanical and electrical properties) under both oxidizing and reducing conditions, as well as demonstrating the principal capability of their application as symmetrical electrodes in proton-conducting electrochemical cells. The obtained results demonstrate the desirability of a low barium content due to decreased thermal expansion coefficients and chemical strain contribution and Cu-doping due to the formation of an electrochemically active scaffold having nano-sized sediments. The Nd 0.6 Ba 0.4 Fe 0.9 Cu 0.1 O 3-δ electrodes fabricated onto the BaCe 0.5 Zr 0.3 Y 0.1 Yb 0.1 O 3-δ proton-conducting electrolytes exhibit polarization resistances of 1.1 and 15.1 Ω cm 2 at 600°C in wet air and wet hydrogen measuring atmospheres, respectively. These reported results are among the first concerning the effective operation of symmetrical electrodes in systems with proton-conducting electrolytes.
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