La_(0.7)Mg_(0.3-x)Ca_xNi_(2.5)Co_(0.5)(x=0～0.15)储氢合金的放电容量衰退机理研究
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摘要
采用感应熔炼结合粉末烧结两步法制备了La_(0.7)Mg_(0.3-x)Ca_xNi_(2.5)Co_(0.5)(x=0～0.15)储氢合金,并对合金的放电容量衰退机理进行了研究.研究结果显示随着Ca含量的增加,合金的相结构没有发生明显变化,只是晶胞参数逐渐增大,即Ca主要替代了超晶格结构AB2结构单元中的Mg,但在AB5结构单元中少量的Ca恰恰对合金的放电容量产生了重要的影响.Ca在AB2和AB5两种结构单元中的存在会降低储氢过程中晶胞内部的膨胀应力,Ca的溶解能够抑制Mg的腐蚀,生成微溶于水的腐蚀产物,并提高了合金表面具有催化活性的Ni含量,改善了合金的循环寿命.较高的Ca含量会严重破坏合金的相结构,生成过量的腐蚀产物因不能完全溶于水而在合金表面形成包覆层,阻碍了电极反应,造成合金循环过程中放电容量的急剧下降.
The La_(0.7)Mg_(0.3-x)Ca_xNi_(2.5)Co_(0.5)(x=0-0.15)hydrogen storage alloys were prepared by induction melting combined with powder sintering method,and the degradation mechanism of discharge capacity was also studied.The results showed that phase structures of the alloys were not changed significantly with the increase of Ca contents,while the lattice parameters increased gradually,indicated that Ca mainly replaced Mg in AB2 structural unit of superlattice structure.But the small amount of Ca dopants in AB5 structural unit had an important impact on discharge capacity.The existence of Ca in AB2 and AB5 structural units reduced the expansion stress during the hydrogen absorption and desorption.The dissolution of Ca inhibited corrosion of Mg and formed slightly soluble corrosion products,which increased catalytic Ni content on the surface and improved the cycle life.Nevertheless,the phase structures of the alloys with a large amount of Ca destroyed and resulted in a sharp decline in discharge capacities.This was due to the excessive corrosion products were not completely soluble in water and hindered electrochemical reaction.
The La_(0.7)Mg_(0.3-x)Ca_xNi_(2.5)Co_(0.5)(x=0-0.15)hydrogen storage alloys were prepared by induction melting combined with powder sintering method,and the degradation mechanism of discharge capacity was also studied.The results showed that phase structures of the alloys were not changed significantly with the increase of Ca contents,while the lattice parameters increased gradually,indicated that Ca mainly replaced Mg in AB2 structural unit of superlattice structure.But the small amount of Ca dopants in AB5 structural unit had an important impact on discharge capacity.The existence of Ca in AB2 and AB5 structural units reduced the expansion stress during the hydrogen absorption and desorption.The dissolution of Ca inhibited corrosion of Mg and formed slightly soluble corrosion products,which increased catalytic Ni content on the surface and improved the cycle life.Nevertheless,the phase structures of the alloys with a large amount of Ca destroyed and resulted in a sharp decline in discharge capacities.This was due to the excessive corrosion products were not completely soluble in water and hindered electrochemical reaction.
引文
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[2]Casini J C S,Guo Z P,Liu H K,et al.Effect of Sn substitution for Co on microstructure and electrochemical performance of AB5type La0.7Mg0.3Al0.3Mn0.4Co0.5-xSnxNi3.8(x=0-0.5)alloys[J].Transactions of Nonferrous Metals Society of China,2015,25(2):520-526.
[3]Miyamura H,Sakai T,Oguro K,et al.Hydrogen absorption and phase transitions in rapidly quenched La-Ni alloys[J].Journal of the LessCommon Metals,1989,146(1):197-203.
[4]Miyamura H,Kuriyama N,Sakai T,et al.Characteristics of electrodes using amorphous AB2hydrogen storage alloys[J].Journal of the Less-Common Metals,1991,172/173/174(1):1205-1210.
[5]Liu J J,Han S M,Li Y,et al.Phase structures and electrochemical properties of La-Mg-Ni-based hydrogen storage alloys with superlattice structure[J].International Journal of Hydrogen Energy,2016,41(44):20261-20275.
[6]Kohno T,Yoshida H,Kawashima F,et al.Hydrogen storage properties of new ternary system alloys:La2MgNi9,La5Mg2Ni23,La3MgNi14[J].Journal of Alloys and Compounds,2000,311(2):5-7.
[7]刘永锋.La-Mg-Ni-Co系贮氢电极合金的相结构及电化学性能研究[D].杭州:浙江大学,2005.
[8]Yasuoka S,Ishida J,Kishida K,et al.Effects of cerium on the hydrogen absorption-desorption properties of rare earth-Mg-Ni hydrogen-absorbing alloys[J].Journal of Power Sources,2017,346(1):56-62.
[9]Tian X,Wei W,Duan R X,et al.Preparation and electrochemical properties of La0.70MgxNi2.45Co0.75Al0.30(x=0,0.30,0.33,0.36,0.39)hydrogen storage alloys[J].Journal of Alloys and Compounds,2016,672(1):104-109.
[10]Kadir K,Sakai T,Uehara I.Structural investigation and hydrogen capacity of YMg2Ni9and(Y0.5Ca0.5)(MgCa)Ni9:new phases in the AB2C9system isostructural with LaMg2Ni9[J].Journal of Alloys and Compounds,1999,287(1/2):264-270.
[11]Chen J,Takeshita H T,Tanaka H,et al.Hydriding properties of LaNi3and CaNi3and their substitutes with PuNi3-type structure[J].Journal of Alloys and Compounds,2000,302(1/2):304-313.
[12]Zhang P,Liu Y N,Tang R,et al.Effect of Ca on the microstructural and electrochemical properties of La2.3-xCaxMg0.7Ni9hydrogen storage alloys[J].Electrochimica Acta,2006,51(28):6400-6405.
[13]柳东明,王常春,斯庭智,等.La2Mg4-xCaxNi13贮氢合金的相结构与电化学性能[C]//第六届中国功能材料及其应用学术会议论文集.重庆:功能材料期刊社,2007:1619-1621.
[14]Denys R V,Yartys V A.Effect of magnesium on the crystal structure and thermodynamics of the La3-xMgxNi9hydrides[J].Journal of Alloys and Compounds,2011,509(2):540-548.
[15]Kadir K,Sakai T,Uehara I.Synthesis and structure determination of a new series of hydrogen storage alloys:RMg2Ni9(R=La,Ce,Pr,Nd,Sm and Gd)built from MgNi2Laves-type layers alternating with AB5layers[J].Journal of Alloys and Compounds,1997,257(1/2):115-121.
[16]Kadir K,Kuriyama N,Sakai T,et al.Structural investigation and hydrogen capacity of CaMg2Ni9:a new phase in the AB2C9system isostructural with LaMg2Ni9[J].Journal of Alloys and Compounds,1999,284(1/2):145-154.
[17]Dong Z W,Ma L Q,Wu Y M,et al.Electrochemical hydrogen storage properties of non-stoichiometric La0.7Mg0.3-xCaxNi2.8Co0.5(x=0-0.10)electrode alloys[J].Journal of Alloys and Compounds,2011,509(17):5280-5284.
[18]Dong Z W,Wu Y M,Ma L Q,et al.Microstructure and electrochemical hydrogen storage characteristics of La0.67Mg0.33-xCaxNi2.75Co0.25(x=0-0.15)electrode alloys[J].International Journal of Hydrogen Energy,2011,36(4):3050-3055.