Current and further trajectories in designing functional materials for solid oxide electrochemical cells:A review of other reviews

Complex oxides are an important class of materials with enormous potential for electrochemical appli-cations.Depending on their composition and structure,such complex oxides can exhibit either a single conductivity(oxygen-ionic or protonic,or n-type,or p-type electronic)or a combination thereof gener-ating distinct dual-conducting or even triple-conducting materials.These properties enable their use as diverse functional materials for solid oxide fuel cells,solid oxide electrolysis cells,permeable membranes,and gas sensors.The literature review shows that the field of solid oxide materials and related electro-chemical cells has a significant level of research engagement,with over 8,000 publications published since 2020.The manual analysis of such a large volume of material is challenging.However,by examining the review articles,it is possible to identify key patterns,recent achievements,prospects,and remaining obstacles.To perform such an analysis,the present article provides,for the first time,a comprehensive summary of previous review publications that have been published since 2020,with a special focus on solid oxide materials and electrochemical systems.Thus,this study provides an important reference for researchers specializing in the fields of solid state ionics,high-temperature electrochemistry,and energyconversiontechnologies.

Hierarchically skeletal multi-layered Pt-Ni nanocrystals for highly efficient oxygen reduction and methanol oxidation reactions

Pt based materials are the most efficient electrocatalysts for the oxygen reduction reaction(ORR)and methanol oxidation reaction(MOR)in fuel cells.Maximizing the utilization of Pt based materials by modulating their morphologies to expose more active sites is a fundamental objective for the practical application of fuel cells.Herein,we report a new class of hierarchically skeletal Pt-Ni nanocrystals(HSNs)with a multi-layered structure,prepared by an inorganic acid-induced solvothermal method.The addition of H_(2)SO_(4)to the synthetic protocol provides a critical trigger for the successful growth of Pt-Ni nanocrystals with the desired structure.The Pt-Ni HSNs synthesized by this method exhibit enhanced mass activity of 1.25 A mgpt−1 at 0.9 V(versus the reversible hydrogen electrode)towards ORR in 0.1-M HClO_(4),which is superior to that of Pt-Ni multi-branched nanocrystals obtained by the same method in the absence of inorganic acid;it is additionally 8.9-fold higher than that of the commercial Pt/C catalyst.Meanwhile,it displays enhanced stability,with only 21.6%mass activity loss after 10,000 cycles(0.6–1.0 V)for ORR.Furthermore,the Pt-Ni HSNs show enhanced activity and anti-toxic ability in CO for MOR.The superb activity of the Pt-Ni HSNs for ORR and MOR is fully attributed to an extensively exposed electrochemical surface area and high intrinsic activity,induced by strain effects,provided by the unique hierarchically skeletal alloy structure.The novel open and hierarchical structure of Pt-Ni alloy provides a promising approach for significant improvements of the activity of Pt based alloy electrocatalysts.

Towards high-performance tubular-type protonic ceramic electrolysis cells with all-Ni-based functional electrodes

Protonic ceramic electrolysis cells(PCECs),which permit high-temperature electrolysis of water,exhibit various advantages over conventional solid oxide electrolysis cells(SOECs),including cost-effectiveness and the potential to operate at low-/intermediate-temperature ranges with high performance and efficiency.Although many efforts have been made in recent years to improve the electrochemical characteristics of PCECs,certain challenges involved in scaling them up remain unresolved.In the present work,we present a twin approach of combining the tape-calendering method with all-Ni-based functional electrodes with the aim of fabricating a tubular-designed PCEC having an enlarged electrode area(4.6 cm^2).This cell,based on a 25μm-thick BaCe0.5Zr0.3Dy0.2O3-δ proton-conducting electrolyte,a nickelbased cermet and a Pr1.95Ba0.05NiO4+δ oxygen electrode,demonstrates a high hydrogen production rate(19 m L min^-1 at 600℃),which surpasses the majority of results reported for traditional button-or planar-type PCECs.These findings increase the scope for scaling up solid oxide electrochemical cells and maintaining their operability at reducing temperatures.

Modeling the interaction of nitrate anions with ozone and atmospheric moisture

The molecular dynamics method is used to investigate the interaction between one-six nitrate anions and water clusters absorbing six ozone molecules. The infrared（IR） absorption and reflection spectra are reshaped significantly, and new peaks appear at Raman spectra due to the addition of ozone and nitrate anions to the disperse water system. After ozone and nitrate anions are captured, the average（in frequency） IR reflection coefficient of the water disperse system increased drastically and the absorption coefficient fell.

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.

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.

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.

Novel materials for solid oxide fuel cells cathodes and oxygen separation membranes:Fundamentals of oxygen transport and performance

In the field of modern hydrogen energy,obtaining pure hydrogen and syngas and then being able to use them for green energy production are significant problems.Developing solid oxide fuel cells(SOFC)and catalytic membranes for oxygen separation as well as materials for these devices is one of the most likely ways to solve these problems.In this work,the authors’recent studies in this field are reviewed;the fundamentals of developing materials for SOFC cathodes and oxygen separation membranes’permselective layers based on research of their oxygen mobility and surface reactivity are presented.Ruddlesden-Popper phases Ln_(2-x)Ca_(x)NiO_(4+δ)(LnCNO)and perovskite-fluorite nanocomposites PrNi_(0.5)Co_(0.5)O_(3-δ)-Ce_(0.9)Y_(0.1)O_(2-δ)(PNC-YDC)were studied by isotope exchange of oxygen with C_(18)O_(2)and^(18)O_(2)in flow and closed reactors.For LnCNO a high oxygen mobility was shown(D*~10^(-7)cm^(2)/s at 700℃),being provided by the cooperative mechanism of oxygen migration involving both regular and highly-mobile interstitial oxygen.For PNC-YDC dominated a wide fast diffusion channel via fluorite phase and interphases due to features of the redistribution of cations resulting in superior oxygen mobility(D*~10^(-8)cm^(2)/s at 700℃).After optimization of composition and nanodomain structure of these materials,as cathodes of SOFC they provided a high power density,while for asymmetric supported oxygen separation membranes-a high oxygen permeability.