Electrolyte materials for protonic ceramic electrochemical cells:Main limitations and potential solutions

Solid oxide fuel cells(SOFCs)and electrolysis cells(SOECs)are promising energy conversion devices,on whose basis green hydrogen energy technologies can be developed to support the transition to a carbon-free future.As compared with oxygen-conducting cells,the operational temperatures of protonic ceramic fuel cells(PCFCs)and electrolysis cells(PCECs)can be reduced by several hundreds of degrees(down to low-and intermediatetemperature ranges of 400–700C)while maintaining high performance and efficiency.This is due to the distinctive characteristics of charge carriers for proton-conducting electrolytes.However,despite achieving outstanding lab-scale performance,the prospects for industrial scaling of PCFCs and PCECs remain hazy,at least in the near future,in contrast to commercially available SOFCs and SOECs.In this review,we reveal the reasons for the delayed technological development,which need to be addressed in order to transfer fundamental findings into industrial processes.Possible solutions to the identified problems are also highlighted.

High-temperature transport properties of BaSn_(1−x)Sc_(x)O_(3−δ) ceramic materials as promising electrolytes for protonic ceramic fuel cells

Protonic ceramic fuel cells(PCFCs)offer a convenient means for electrochemical conversion of chemical energy into electricity at intermediate temperatures with very high efficiency.Although BaCeO_(3)-and BaZrO_(3)-based complex oxides have been positioned as the most promising PCFC electrolytes,the design of new protonic conductors with improved properties is of paramount importance.Within the present work,we studied transport properties of scandium-doped barium stannate(Sc-doped BaSnO_(3)).Our analysis included the fabrication of porous and dense BaSn_(1−x)Sc_(x)O_(3−δ)ceramic materials(0≤x≤0.37),as well as a comprehensive analysis of their total,ionic,and electronic conductivities across all the experimental conditions realized under the PCFC operation:both air and hydrogen atmospheres with various water vapor partial pressures(p(H2O)),and a temperature range of 500–900℃.This work reports on electrolyte domain boundaries of the undoped and doped BaSnO_(3)for the first time,revealing that pure BaSnO_(3)exhibits mixed ionic–electronic conduction behavior under both oxidizing and reducing conditions,while the Sc-doping results in the gradual improvement of ionic(including protonic)conductivity,extending the electrolyte domain boundaries towards reduced atmospheres.This latter property makes the heavilydoped BaSnO_(3)representatives attractive for PCFC applications.

Performance of Pr_(2)(Ni,Cu)O_(4+δ) electrodes in protonic ceramic electrochemical cells with unseparated and separated gas spaces

The Ln_(2)NiO_(4+δ)-based layered phases have attracted much attention as components for high-performance protonic ceramic fuel cells(PCFCs)and electrolysis cells(PCECs)enabling energy conversion with good efficiency and low pollution.The present paper aims at rationally engineering the Cu-doped Pr_(2)NiO_(4+δ)materials and analysing their electrode behaviour for reversible protonic ceramic cells operating in both PCFC and PCEC modes.Complex oxides of Pr_(2)Ni_(1-x)CuxO_(4+δ)(x=0,0.1,0.2 and 0.3)were synthesised using the citrate-nitrate method.The obtained materials were characterised considering their crystalline structures,as well as thermal,thermomechanical and electrotransport properties.A special interest was focused on the quality of an electrode/electrolyte interface governing the electrochemical performance of the cells fabricated.It is shown that a copper doping of x=0.2 has a positive impact on the thermomechanical compatibility of the Ba(Ce,Zr)O_(3)-based electrolytes,providing a better adhesion to these electrolytes at low-temperature sintering and resulting in a decrease of the polarisation resistance of the air electrodes.A reversible protonic ceramic cell demonstrates a power density of~340 m W cm^(-2) and a hydrogen output flux of~3.8 ml cm^(-2) min^(-1) at 750℃.The presented results propose modernised alkaline-earth-element-free and cobalt-free electrodes that can be successfully used in the electrochemical cells based on the-state-of-the-art proton-conducting electrolytes.