可逆固体氧化物电池La_(0.2)Sr_(0.8)TiO_(3–δ)基纤维燃料极的浸渍改性

Impregnation Modification of La_(0.2)Sr_(0.8)TiO_(3-δ)-Based Fiber Fuel Electrode for Reversible Solid Oxide Cells

开发适合可逆操作的高性能燃料极材料对可逆固体氧化物电池的发展至关重要。为解决LaxSr_(1-x)TiO_(3)燃料极材料催化活性差及离子电导率低等问题,采用静电纺丝技术直接制备富含连通孔洞的La_(0.2)Sr_(0.8)TiO_(3-δ)(LST)/氧化钇稳定型氧化锆(YSZ)复合纤维,构建了以LST骨架为电子通道主路、YSZ颗粒为离子通道穿插的三维网络混合导体通路,并通过浸渍Ce_(0.9)M_(0.1)O_(2-δ)(M=Fe、Co、Ni)纳米颗粒对燃料极骨架修饰改性,增强燃料极与电解质层间的界面结合,研究不同浸渍物对纤维基燃料极催化活性的影响。结果表明:浸渍Ce_(0.9)Ni_(0.1)O_(2-δ)的燃料极兼具有较强的氢氧化能力和氢还原能力,在浸渍物和Ni纳米颗粒析出的共同作用下,单电池在850℃、3%(体积分数)H_(2)O/H_(2)下的最高功率密度达到342 mW/cm^(2);在850℃、46.8%(体积分数)H_(2)O/H_(2)、1.3 V下的电解电流密度达到0.313 A/cm^(2)。

Introduction The development of high-performance fuel electrode materials suitable for reversible operation is crucial for the application of reversible solid oxide cells(RSOCs).The fuel electrode should have excellent catalytic activity such as hydrogen oxidation reaction and hydrogen evolution reaction in the solid oxide fuel cells/solid oxide electrolysis cells(SOFC/SOEC)dual mode.Conventional Ni-YSZ fuel electrode materials are susceptible to sulfur poisoning when using fuel gas containing sulfur impurities and carbon buildup when using hydrocarbon fuel.LaxSr_(1-x)TiO_(3)perovskite materials have a superior resistance to coking and sulfur poisoning,which is widely used in RSOCs fuel electrodes in recent years.However,the poor ionic conduction and the non-ideal catalytic ability of fuel gas affect the further application of LaxSr_(1-x)TiO_(3)fuel electrodes.It is thus necessary for the improvement of the catalytic activity and the electrochemical performance of the fuel electrodes to optimize the microstructure and surface modification.In this paper,La_(0.2)Sr_(0.8)TiO_(3-δ)(LST)/YSZ-based fiber fuel electrode by Ce_(0.9)M(0.1)O_(2-δ)(M=Fe,Co,Ni)impregnation modification was prepared,and the effect of impregnation on the electrochemical properties of fiber fuel electrode in SOFC/SOEC dual mode was investigated.Methods La(0.2)Sr(0.8)TiO(3-δ)(LST)/YSZ composite fibers were directly prepared by an electrospinning method.In the preparation,stoichiometric amounts of La(NO3)3·6H_(2)O,Sr(NO_(3))_(2)and C(16)H(36)O4Ti were weighed and dissolved with N,n-dimethylformamide(DMF)as a solvent and polyvinylpyrrolidone(PVP)as binder and one-dimensional template.The YSZ suspension was added to the LST precursor solution to obtain the LST/YSZ electrospinning solution for electrospinning.The high catalytic activity of Ce(0.9)M(0.1)O(2-δ)(M=Fe,Co,Ni,CMO)was loaded on LST/YSZ composite fiber skeleton by an ion impregnation method to prepare the fiber fuel electrode.The electrolyte-supported single cells(CMO@LST/YSZ||YSZ||YSZ||GDC||LSCF/GDC)were fabricated to evaluate the electrochemical performance of the fiber fuel electrode.The phase composition of the prepared composite fiber and the fuel electrode after immersion and calcination was determined by X-ray diffraction(XRD).The composite fiber morphology and the cross-section morphology of the tested fuel electrode were characterized by scanning electron microscopy(SEM).The two-phase distribution of the composite fiber was determined by high resolution transmission electron microscopy(HRTEM).The electrochemical performance of the fiber fuel electrodes in SOFC/SOEC dual-mode was tested via assembling a single cell.The impedance data were analyzed via the distribution of relaxation time(DRT),and the relationship between the microstructure and the electrochemical process was analyzed.Results and discussion The electrospinning solutions with stable spinning are prepared via adjusting the LST:YSZ mass ratio.The LST:YSZ with a mass ratio of 6:4 shows a criss-cross fiber morphology and smooth surface with uniform diameters(i.e.,150-200 nm)through the electrospinning and calcination.The composite fibers consist of the LST skeleton with YSZ particles dispersed and embedded,which is prepared directly by electrospinning,thus forming a three-dimensional network of mixed conductor channels with electronic channels as the main path and ionic channels interspersed.The LST:YSZ composite fiber was used to prepare a fuel electrode skeleton,and CMO precursor solution is prepared to impregnate and modify the fuel electrode.Compared with the fiber morphology,the morphology of fiber fuel electrode is smaller in length and diameter,showing a short rod-like morphology.The surface of the fiber is evenly covered by the impregnated CMO nanoparticles(i.e.,50-80 nm),still retaining abundant and interconnected pores.The three-dimensional network fiber electrode is constructed.The impregnate uniformly wraps on the fiber surface to strengthen the interfacial bonding between the fuel electrode and the YSZ transitional layer.The different impregnation modification has an effect on the catalytic activity of the fuel electrode in SOFC/SOEC dual mode.The fuel electrode using Ce_(0.9)Ni_(0.1)O_(2-δ)as an impregnate has more Ni nanoparticles exsolution after the testing,effectively increasing the length of the three-phase interface and the active sites for the catalytic reaction.Based on the comprehensive analysis of EIS and DRT,the modified fiber fuel electrode can significantly affect the interfacial charge transfer process corresponding to the middle-and low-frequency.Ni nanoparticles exsolution can adsorb/dissociate hydrogen,and have a tendency to form an activated complex with water molecules,so that the fiber fuel electrode has great hydrogen oxidation capacity and hydrogen reduction capacity.Conclusions LST/YSZ composite fiber with rich connected pores was directly prepared by an electrospinning technique.This fiber had a three-dimensional network hybrid conductor pathway with LST skeleton as the main electronic channel and YSZ particles as ion channel interspersed.The interface bond between the fuel electrode and the electrolyte layer was further enhanced via modifying the fuel electrode skeleton with CMO nanoparticles impregnation.The results showed that the fuel electrode with Ce_(0.9)Ni_(0.1)O_(2-δ)impregnation had a high hydrogen oxidation and reduction capacity.Under the combined action of the impregnation and the precipitation of Ni nanoparticles,the single cell had the maximum power density of 342 m W/cm^(2)at 850℃,3%(in volume fraction)H_(2)O/H_(2),and the current density of 0.313 A/cm^(2)under 46.8%H_(2)O/H_(2)for electrolysis at 1.3 V.