Effect of Annealing Treatment on Structure and Electrochemical Properties of New Mg-free Y0.7La0.3Ni3.25Al0.1Mn0.15 Hydrogen Storage Alloys †

doi:10.7503/cjcu20190430

Abstract

Abstract:

Mg-free A₂B₇ type Y_0.7La_0.3Ni_3.25Al_0.1Mn_0.15 alloy of La-Y-Ni system was prepared by arc melting and annealed for 24 h in high purity Ar atmosphere at 800—1050 ℃. X-ray diffraction(XRD), neutron diffraction(ND), scanning electron microscopy and energy dispersive spectroscopy(SEM/EDS) and electrochemical test methods were used to research the influence of annealing temperature on the structure and properties of the alloys. Structural analysis shows that as-cast alloy consists of CaCu₅, Ce₅Co₁₉, Gd₂Co₇ and Ce₂Ni₇. As the annealing temperature increases, CaCu₅, Ce₅Co₁₉ and Gd₂Co₇ gradually decrease to disappear, while the phase abundance of Ce₂Ni₇ main phase increases gradually. When annealing at 900—950 ℃, the alloy is single-phase Ce₂Ni₇ structure. When annealing temperature continues to rise, a small amount of PuNi₃ phase appears in the alloy. The maximum discharge capacity of the alloy electrodes increases first and then decreases as the annealing temperature increases. It increases from 307.6 mA·h/g for the as-cast alloy to 393.1 mA·h/g at the nnealing temperature of 900 ℃, and then decreases to 366.4 mA·h/g at the nnealing temperature of 1050 ℃. The electrochemical cycle stability of alloy electrodes increase with the increase of annealing temperature. After 100 cycles, the electrochemical capacity retention rate(S₁₀₀) increases from 66% for the as-cast alloys to 88.5% at the nnealing temperature of 1050 ℃. When annealing at 900—950 ℃, the alloy electrodes have better comprehensive electrochemical properties.

Key words: Annealing treatment, Hydrogen storage alloy, Structure, Electrochemical property

CLC Number:

O646
TG139.7

TrendMD:

DENG Anqiang,LUO Yongchun,XIA Yuanhua,PENG Sihui,MA Weiqin,ZHAO Xudong,YANG Yang,HOU Xiaodong. Effect of Annealing Treatment on Structure and Electrochemical Properties of New Mg-free Y_0.7La_0.3Ni_3.25Al_0.1Mn_0.15Hydrogen Storage Alloys ^†[J]. Chem. J. Chinese Universities, 2020, 41(1): 145.

Figures/Tables 15

Fig.1 Backscattered SEM images of the as-cast(A) and annealed(B—G) alloys Y0.7La0.3Ni3.25Al0.1Mn0.15 Annealing temperature/℃: (B) 800; (C) 850; (D) 900; (E) 950; (F) 1000; (G) 1050.

Sample	Phase	Atomic fraction(%)					Stoichiometric B/A
Sample	Phase	La	Y	Ni	Al	Mn	Stoichiometric B/A
As-cast		0.3106	0.6894	3.2298	0.1021	0.1560	3.49
As-cast	A₂B₇	0.2806	0.7194	3.2273	0.0711	0.1302	3.43
	Ce₅Co₁₉	0.2525	0.7475	3.5112	0.1121	0.1595	3.78
	CaCu₅	0.2147	0.7853	4.6011	0.1791	0.1638	4.94
Annealed at 800 ℃	A₂B₇	0.3359	0.6641	3.1878	0.0804	0.1329	3.40
	CaCu₅	0.2021	0.7979	4.3549	0.2176	0.1536	4.73
Annealed at 850 ℃	A₂B₇	0.3020	0.6980	3.2045	0.0943	0.1388	3.44
	CaCu₅	0.2090	0.7910	4.3423	0.2736	0.1642	4.78
Annealed at 900 ℃	Ce₂Ni₇	0.2596	0.7404	3.1830	0.1106	0.1617	3.46
Annealed at 950 ℃	Ce₂Ni₇	0.3075	0.6925	3.1879	0.0961	0.1423	3.43
Annealed at 1000 ℃	Ce₂Ni₇	0.2958	0.7042	3.1633	0.1175	0.1317	3.41
	PuNi₃	0.3704	0.6296	2.7189	0.1099	0.1164	2.95
Annealed at 1050 ℃	Ce₂Ni₇	0.2600	0.7400	3.1340	0.1080	0.1280	3.37
	PuNi₃	0.3312	0.6688	2.7239	0.0942	0.1051	2.92

Fig.2 XRD patterns of as-cast and annealed alloys(A) and its partial magnification(B) a. As-cast; b. 800 ℃; c. 850 ℃; d. 900 ℃; e. 950 ℃; f. 1000 ℃; g. 1050 ℃.

Fig.3 Rietveld refinement patterns of XRD(A) and neutron diffraction(B) for the alloy annealed at 900 ℃

Condition	Phase	Space group(No.)	Phase abundance(%)	Lattice constant		V/nm³	Strain(%)	$d A B 2$ / $d A B 5$ Ce₂Ni₇
Condition	Phase	Space group(No.)	Phase abundance(%)	a/nm	c/nm	V/nm³	Strain(%)	$d A B 2$ / $d A B 5$ Ce₂Ni₇
As-cast	Ce₂Ni₇	P6₃/mmc(194)	65.78	0.50173	2.43745	0.53138	1.29	1.674
	Gd₂Co₇	R $3 ˉ$ m(166)	15.80	0.44902	3.93293	0.68672
	Ce₅Co₁₉	R $3 ˉ$ m(166)	8.37	0.50579	4.80588	1.06470
	CaCu₅	P6/mmm(191)	10.05	0.49621	0.40003	0.08530
Annealed at 800 ℃	Ce₂Ni₇	P6₃/mmc(194)	82.03	0.50191	2.43675	0.53161	0.80	1.247
	Gd₂Co₇	R $3 ˉ$ m(166)	9.01	0.44832	3.96713	0.69054
	CaCu₅	P6/mmm(191)	8.96	0.50048	0.40145	0.08708
Annealed at 850 ℃	Ce₂Ni₇	P6₃/mmc(194)	89.16	0.50172	2.44092	0.53211	0.55	1.116
	Gd₂Co₇	R $3 ˉ$ m(166)	6.45	0.44669	4.04017	0.69813
	CaCu₅	P6/mmm(191)	4.39	0.49996	0.40513	0.08770
Annealed at 900 ℃	Ce₂Ni₇	P6₃/mmc(194)	100.00	0.50281	2.44133	0.53451	0.17	1.030
Annealed at 950 ℃	Ce₂Ni₇	P6₃/mmc(194)	100.00	0.50202	2.43837	0.53219	0.20	1.030
Annealed at 1000 ℃	Ce₂Ni₇	P6₃/mmc(194)	89.92	0.50161	2.43729	0.53108	0.22	1.028
	PuNi₃	R $3 ˉ$ m(166)	10.08	0.49521	2.43776	0.51772
Annealed at 1050 ℃	Ce₂Ni₇	P63/mmc(194)	84.68	0.50158	2.43659	0.53087	0.24	1.020
	PuNi₃	R $3 ˉ$ m(166)	15.32	0.49448	2.43004	0.51456

Condition	Phase	Space group(No.)	Phase abundance(%)	Lattice constant		V/nm³	Strain(%)	$d A B 2$ / $d A B 5$ Ce₂Ni₇
Condition	Phase	Space group(No.)	Phase abundance(%)	a/nm	c/nm	V/nm³	Strain(%)	$d A B 2$ / $d A B 5$ Ce₂Ni₇
As-cast	Ce₂Ni₇	P6₃/mmc(194)	65.78	0.50173	2.43745	0.53138	1.29	1.674
	Gd₂Co₇	R $3 ˉ$ m(166)	15.80	0.44902	3.93293	0.68672
	Ce₅Co₁₉	R $3 ˉ$ m(166)	8.37	0.50579	4.80588	1.06470
	CaCu₅	P6/mmm(191)	10.05	0.49621	0.40003	0.08530
Annealed at 800 ℃	Ce₂Ni₇	P6₃/mmc(194)	82.03	0.50191	2.43675	0.53161	0.80	1.247
	Gd₂Co₇	R $3 ˉ$ m(166)	9.01	0.44832	3.96713	0.69054
	CaCu₅	P6/mmm(191)	8.96	0.50048	0.40145	0.08708
Annealed at 850 ℃	Ce₂Ni₇	P6₃/mmc(194)	89.16	0.50172	2.44092	0.53211	0.55	1.116
	Gd₂Co₇	R $3 ˉ$ m(166)	6.45	0.44669	4.04017	0.69813
	CaCu₅	P6/mmm(191)	4.39	0.49996	0.40513	0.08770
Annealed at 900 ℃	Ce₂Ni₇	P6₃/mmc(194)	100.00	0.50281	2.44133	0.53451	0.17	1.030
Annealed at 950 ℃	Ce₂Ni₇	P6₃/mmc(194)	100.00	0.50202	2.43837	0.53219	0.20	1.030
Annealed at 1000 ℃	Ce₂Ni₇	P6₃/mmc(194)	89.92	0.50161	2.43729	0.53108	0.22	1.028
	PuNi₃	R $3 ˉ$ m(166)	10.08	0.49521	2.43776	0.51772
Annealed at 1050 ℃	Ce₂Ni₇	P63/mmc(194)	84.68	0.50158	2.43659	0.53087	0.24	1.020
	PuNi₃	R $3 ˉ$ m(166)	15.32	0.49448	2.43004	0.51456

Subunit	Atom	Site	x	y	z	10²Biso/nm²	Occ
Laves	Y	4f	0.33333	0.66667	0.02776	1.24	1.00
CaCu₅	Y	4f	0.33333	0.66667	0.16953	0.78	0.40
	La	4f	0.33333	0.66667	0.16953	0.78	0.60
Laves	Ni	2a	0	0	0	0.66	0.92
	Al	2a	0	0	0	0.66	0.02
	Mn	2a	0	0	0	0.66	0.06
CaCu₅	Ni	4e	0	0	0.17051	1.60	0.83
	Al	4e	0	0	0.17051	1.60	0.08
	Mn	4e	0	0	0.17051	1.60	0.09
CaCu₅	Ni	4f	0.66667	0.33333	0.1681	0.39	0.90
	Al	4f	0.66667	0.33333	0.1681	0.39	0.05
	Mn	4f	0.66667	0.33333	0.1681	0.39	0.06
CaCu₅	Ni	6h	0.1692	0.33838	0.75	0.35	0.77
	Al	6h	0.1692	0.33838	0.75	0.35	0.10
	Mn	6h	0.1692	0.33838	0.75	0.35	0.13
Laves/CaCu₅	Ni	12k	0.167	0.33406	0.91513	0.21	0.81
	Al	12k	0.167	0.33406	0.91513	0.21	0.06
	Mn	12k	0.167	0.33406	0.91513	0.21	0.12

Fig.4 Phase abundance variation curves for different annealed alloys

Fig.5 Phase abundance and cell volume variation curves for Ce2Ni7 main phase

Fig.6 Model representation of Ce2Ni7-type(2H) structures for the alloy annealed at 900 ℃

Fig.7 Activation curves of different annealed alloy electrodes The inset shows the discharge capacity for different annealed alloys.

Fig.8 Discharge curve of different annealed alloy electrodes

Fig.9 Electrochemical desorption P-C isotherms(A) and its partial magnification(B) for different annealed alloy electrodes

Fig.10 Cyclic stability curves of different annealed alloy electrodes

Fig.11 Tafel curves of different annealed alloy electrodes(A) and its partial magnification(B)

Alloy	N^a	C_max/(mA·h·g^-1)	S₁₀₀(%)	E_corr/V	i_corr/(mA·cm^-2)
As-cast	2	307.6	66.0	-0.933	21.34
Annealed at 800 ℃	5	347.3	68.1	-0.925	18.56
Annealed at 850 ℃	3	372.8	79.2	-0.921	18.25
Annealed at 900 ℃	2	393.1	80.0	-0.906	14.06
Annealed at 950 ℃	3	371.8	88.0	-0.913	14.71
Annealed at 1000 ℃	3	366.4	87.5	-0.917	14.71
Annealed at 1050 ℃	6	366.4	88.5	-0.92	14.84

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