JPH07120420A - Evaluation method for characteristic of hydrogen storage alloy - Google Patents

Abstract

PURPOSE:To omit opening/closing operation of a valve so as to facilitate automation of measurement, and improve reproducibility of measuring result even in case of a low equilibrium hydrogen pressure, in a characteristic evaluation method of hydrogen storage allay by the use of Sivert's device. CONSTITUTION:In a system constituted of a vessel 3 receiving the sample 2 of hydrogen storage alloy and pipings, the pressure in the system is measured by means of a pressure sensor 6 while varying the sample temperature by means of a heater 8, and the characteristic of the sample is evaluated based on the pressure-temperature curve in this process.

Description

Detailed Description of the Invention

[0001]

The present invention relates to the reversible absorption of hydrogen,
The present invention relates to a hydrogen storage alloy that can be released, and more particularly to a method for evaluating the characteristics of the hydrogen storage alloy using a Sibelts apparatus.

[0002]

2. Description of the Related Art Hydrogen storage alloys have been attracting attention as a new energy source to replace fossil fuels, and various application systems have been studied because of their excellent energy conversion function. By the way, the equilibrium reaction between the hydrogen storage alloy and hydrogen is evaluated by a hydrogen pressure-composition (hydrogen absorption amount) isotherm curve. As shown in FIG. 9, the hydrogen pressure-composition isotherm (P-C-T curve) has a steeply sloped hydrogen solid solution region (α phase) and a metal hydride compound region (β phase), and between them. It has a flat plateau region sandwiched between. This P-C-T
By measuring the curve, the characteristics of the individual hydrogen storage alloys can be grasped (Japanese Patent Laid-Open No. 60-251238, Report 80, No. 11, No. 11, pp. 35-45, Institute of Chemical Research).

Conventionally, the P-C-T curve has been measured by using a Sibelts apparatus as shown in FIG. sample
A sample container (3) filled with (2) is housed in a constant temperature bath (7), and the sample container (3) is connected to a gas holder (1) via a valve (4). Further, the pipe for connecting the gas holder (1) and the valve (4) is connected to the hydrogen introduction / exhaust pipe (13) through the valve (5), and the pressure inside the gas holder (1) is measured by the pressure sensor ( 6).

The measurement of the P-C-T curve using the above-mentioned Sibelts apparatus is performed by executing the following steps. Open both valves (4) and (5) to open the hydrogen introduction / exhaust pipe (1
The gas is discharged from 3) and the system is evacuated. Process After closing the valve (4) and introducing the water gas from the hydrogen introduction / exhaust pipe (13) to the gas holder (1), the valve (5)
Close. The process valve (4) is opened to allow the sample (2) to absorb the hydrogen gas in the gas holder (1). Along with this, the gas pressure in the gas holder (1) gradually decreases. After a sufficient time has passed and the gas pressure becomes constant, that is, equilibrium is reached, the valve (4) is closed and the process returns to the process.

[0005]

However, in the conventional characteristic evaluation method by measuring the P-C-T curve using the Sibelts apparatus, it is necessary to open and close the valve frequently, so that the measurement can be automated. It was difficult and there was a high risk of gas leakage. Further, since the origin of the hydrogen absorption amount in the sample varies depending on the vacuum exhaust conditions (exhaust temperature, exhaust time, vacuum degree) before the measurement, there is a problem that the reproducibility of the measurement result is poor.

In particular, Ni-H, which has been put into practical use in recent years,
_{2 In the} hydrogen storage alloy used as the hydrogen negative electrode of the battery, the equilibrium hydrogen pressure is 0.5 atm or less, and the pressure range of the hydrogen absorption region is wide, so the pressure change over a wide range is accurately measured for the characteristic evaluation. There is a need. But,
In the measurement using a general pressure gauge, the measurement error increases as the pressure range increases, and the reproducibility of the measurement result deteriorates significantly. An object of the present invention is to improve the reproducibility of measurement results even when the equilibrium hydrogen pressure is low, while facilitating the automation of the measurement by omitting the valve opening / closing operation in the characteristic evaluation method using the Sibelts apparatus. That is.

[0007]

A method for evaluating the characteristics of a hydrogen storage alloy according to the present invention is to measure the pressure in the system while changing the temperature of the sample in a system of a constant volume containing a sample of the hydrogen storage alloy. The measurement is performed and the characteristics of the sample are evaluated based on the pressure-temperature curve in this process.

Specifically, the temperature range is set when the sample temperature Ts is changed by setting the relationship between the pressure P and the hydrogen absorption amount C when the hydrogen storage alloy as a sample releases hydrogen at a constant temperature.
(P-C-T curve) is performed by setting a pressure range in which a hydrogen absorption amount according to the intended use of the hydrogen storage alloy is obtained.

For example, the temperature and the pressure at the start of the temperature rise are set to values which are the hydrogen desorption starting point in the actual use of the hydrogen storage alloy, and this is the origin. Then, the temperature Ts and the pressure P at the end of the temperature rise are represented by the following formula 2 in relation to the temperature and the pressure of the hydrogen desorption completion point on the P-C-C curve in the actual use of the hydrogen storage alloy. The relational expression of't Hoff is set to a value such that the same coefficient A and B holds below, or a value close to the value.

[0010]

[Formula 1] lnP = A / Ts + B

[0011]

[Function] When a sample of a hydrogen storage alloy is housed in a system having a constant volume and, for example, the temperature of the sample is raised from a hydrogen absorption state,
The hydrogen storage alloy gradually releases hydrogen into the system, and the pressure in the system rises accordingly. In this process, the relationship between temperature and pressure is measured, and the measurement result is graphed as shown in FIG.
This pressure-temperature curve is unique to each sample, and the sample can be specified by the pressure-temperature curve. Then, the characteristics of the sample can be evaluated by comparing the pressure-temperature curves. Further, the amount of hydrogen released can be calculated from the sample temperature and pressure at the start of measurement and the sample temperature and pressure at the end of measurement based on the equation of state of hydrogen gas. By comparing the hydrogen absorption amounts, it is possible to evaluate the superiority or inferiority of the characteristics of the sample regarding the hydrogen absorption and desorption.

Here, if the temperature range for changing the sample temperature Ts is set to a pressure range in which the same hydrogen absorption amount as the hydrogen absorption amount in the actual use of the hydrogen storage alloy is obtained, The characteristics of hydrogen absorption and desorption processes when the hydrogen storage alloy is actually applied can be evaluated by the pressure-temperature curve.

[0013]

The method for evaluating the characteristics of a hydrogen storage alloy according to the present invention can be carried out by using a Sibelts apparatus, and in this case, a system in which an active sample is placed is partitioned by a valve. It is sufficient to raise the temperature as it is, and it is not necessary to open and close the valve. Therefore, automation of measurement is easy. In addition, the pressure rise in the process of raising the temperature with the inside of the system partitioned is smaller than that in the case of the conventional P-C-T curve measurement, and by setting the hydrogen absorption state as the origin of the pressure rise, the accuracy can be improved. High pressure measurement is possible. Therefore, high reproducibility of the measurement result can be obtained.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a measuring apparatus of the present invention to which the Sibelts apparatus is applied, and the construction of the Sibelts apparatus itself is the same as the conventional one. Constant temperature chamber (7) containing sample container (3)
The heater (8) and the temperature sensor (9) are installed in the
The heating control by the heater (8) is performed by the temperature controller (10) based on the detection signal from the temperature sensor (9). As a result, the sample temperature rises at a predetermined temperature rising rate.

Further, the temperature detection signal from the temperature sensor (9) and the pressure detection signal from the pressure sensor (6) are sent to an arithmetic processing circuit (11) composed of a microcomputer, and are subjected to the arithmetic processing described later to perform the sample processing. The characteristic of (2) is evaluated. The result is an output device such as a printer or display (12).
Is output from.

An embodiment of the present invention using the above measuring device will be described below. As an alloy sample, MmNi _3.2 C
o _1.0 Al _0.2 Mn _0.6 alloy was used. This alloy is Ni
A hydrogen storage alloy for a -H ₂ battery, and the P-C-T curve when absorbing hydrogen as shown in Fig. 6 shows that the equilibrium hydrogen pressure is 1 at.
It extends to the low pressure range of m or less, and the conventional PC-
In the T-curve measurement, it was difficult to measure this wide pressure range with high accuracy.

After crushing this alloy to a particle size of about 300 μm, 5.0 g of the alloy was sampled, sealed in a sample container (3) and subjected to activation treatment. As the activation treatment, first, the sample (2) was heated to 80 ° C., the valves (4) and (5) were opened, and the entire system was evacuated by a rotary pump from the hydrogen introduction / exhaust pipe (13). Next, 10 atm of hydrogen gas was introduced into the system through the hydrogen introduction / exhaust pipe (13), and then the sample temperature was lowered to room temperature to allow the sample to absorb hydrogen. The above-mentioned temperature rising of the sample, vacuum evacuation, temperature lowering of the sample, and hydrogen gas pressurization were repeated 5 times to complete the activation treatment.

Subsequently, the sample was placed at room temperature (20 ° C.) and hydrogen pressure of 8
A hydrogen absorption state (point P in FIG. 6) was set under the pressure of atm, and this was set as the origin of the hydrogen absorption amount. This origin corresponds to the state of charge (room temperature and pressure 8 atm) when the hydrogen storage alloy is actually applied to a Ni-H ₂ battery. Then, the sample was heated from the state of the origin at a rate of 2 ° C./min, and changes in the sample temperature and the hydrogen pressure in this process were measured. As the temperature rises, hydrogen is released from the sample alloy depending on the temperature at that time, and the pressure in the system rises. As a result of the measurement, a hydrogen pressure (P) -sample temperature (Ts) curve shown in FIG. 5 was obtained.

Here, the hydrogen release amount C at the hydrogen pressure P
Can be calculated by the following equation 2 based on the equation of state for an ideal gas, for example.

[0020]

[Equation 2] C = (V / RT) * (201.6 / w) * (P-Pi) where C is the amount of released hydrogen (w
t%), V is the volume in the system consisting of the sample container and piping, R is the gas constant, T is the hydrogen gas temperature in the system inside the system consisting of the sample container and piping, w is the weight of the sample, and Pi is at the origin. The pressure and P are hydrogen pressures when the sample temperature is Ts.

Here, the setting of the sample temperature to be the measurement end point will be considered. Ni-H in the hydrogen-absorbing alloy for ₂ battery, generally, the charge state corresponding to the origin (2
Hydrogen is released from 0 ° C, 8 atm), and 20 ° C, 0.01
A discharge state corresponding to atm is reached. Therefore, the temperature rise in the measurement of the present invention may be carried out to a temperature at which a hydrogen release amount equivalent to the hydrogen release process up to this discharge state is obtained.

For example, in the P-C-T curve shown in FIG. 3, the charged state, that is, room temperature Ta (= 20 ° C.), hydrogen pressure Pa
From the state of (= 8 atm) (point a in the figure), discharging is performed at a constant temperature, that is, the state of discharge at room temperature Ta (= 20 ° C.) and hydrogen pressure Pf (= 0.01 atm) (in the figure). It has been changed to point f). In this case, the temperature rise in the measurement of the present invention may be performed up to a state (point d) where the hydrogen absorption amount is equal to the hydrogen absorption amount at point f. In the case of the hydrogen storage alloy of this example, the measurement end point was 20 ° C. and 0.01 at
The amount of hydrogen absorbed at m is 0.13 wt%. It should be noted that points a, b, c, d and e in FIG. 3 indicate the temperature rising process (Ta → Tb → Tc → Td → Te) from the origin to the measurement end point.

In the hydrogen storage alloy, if the hydrogen absorption amount is the same, it is known that the relational expression of Van't Hoff expressed by the following equation 3 is established between the hydrogen pressure P and the sample temperature Ts. Has been.

[0024]

LnP = A / Ts + B where A and B are constants determined by the amount of absorbed hydrogen.

That is, at points f, g, h and d where the hydrogen absorption amount is the same in FIG. 3, lnP and 1 / Ts as shown in FIG.
A linear relationship is established between. In the hydrogen storage alloy of this example, the relational expression of Van't Hoff at the point f is expressed by the following equation 4.

[0026]

LnP = 5220 / Ts + 11.4 Therefore, in the temperature rising process in the measurement of the present invention,
The hydrogen absorption amount at the pressure and temperature (point d in FIG. 3) satisfying the above conditions corresponds to the capacity as the hydrogen storage alloy for the Ni-H ₂ battery, and the temperature rise can be terminated at this point. . In the hydrogen storage alloy of this example, for example, when the capacity of the system is 320 cc, the hydrogen absorption amount at the measurement end point is 1.15 wt%. At this time, the sample temperature is 300 ° C,
Hydrogen pressure is 10 atm (point d in FIG. 5, Q in FIG. 6)
point).

As a result, it can be evaluated that when the present alloy is used as a negative electrode of a Ni-H ₂ battery, charging / discharging corresponding to a hydrogen amount of 1.15 wt% is possible. In the actual measurement, the pressure and the temperature are measured at a constant sampling cycle, so the measurement is finished at the point e where the temperature is slightly higher than the point d in FIG.

FIG. 2 shows a procedure for carrying out the above-mentioned measuring method. First, in step S1, the origin of the hydrogen absorption amount is set, and then in step S2, the temperature rise is started. Then, in step S3, the sample temperature Ts, the hydrogen gas temperature T, and the pressure P are measured at a constant sampling cycle, and in step S4, the measured pressure P is the above number each time one measurement is completed. Pressure calculated on the right side of 3 (=
A / Ts + B), and if NO, the process returns to step S3 to perform the next measurement. If YES, the hydrogen absorption amount (capacity) is calculated in step S5, and the measurement is completed.

As described above, according to the measuring method of the present invention, the valve can be opened and closed only when hydrogen is introduced, so that the measurement can be easily automated.

When the measurement from the initial activation to the calculation of the amount of absorbed hydrogen was repeated 5 times to examine the reproducibility, the results shown in FIG.
Very high reproducibility was confirmed for the P-Ts curve and the hydrogen absorption amount (capacity) shown in.

Next, the above MmNi _3.2 Co _1.0 Al _0.2
Mn _0.6 alloy (A1), Mm slightly different in composition from the alloy
The above-mentioned characteristic evaluation was performed for three types of samples, that is, the Ni _3.1 Co _1.0 Al _0.2 Mn _0.7 alloy (A2) and the known LaNi ₅ alloy (A3), and the difference in P-Ts curve due to the difference in alloy composition was investigated. It was The result is shown in FIG. 7. As shown in the figure, for alloys A1 and A3 having greatly different compositions, P
A large difference is observed in the -Ts curve. However, a clear difference appears in the P-Ts curve even between the alloys A1 and A2 in which only a slight difference in composition exists. As described above, according to the method for evaluating characteristics of the hydrogen storage alloy of the present invention,
Differences in characteristics due to slight differences in alloy composition can also be evaluated accurately.

The above description of the embodiments is for explaining the present invention and should not be construed as limiting the invention described in the claims or reducing the scope. The configuration of each part of the present invention is not limited to the above-mentioned embodiment, and it goes without saying that various modifications can be made within the technical scope described in the claims.

[Brief description of drawings]

FIG. 1 is a diagram showing an apparatus configuration for carrying out a method for evaluating characteristics of a hydrogen storage alloy according to the present invention.

FIG. 2 is a flowchart showing a characteristic evaluation procedure.

FIG. 3 is a graph showing a P-C-T curve.

FIG. 4 is a graph showing the relationship between hydrogen pressure and sample temperature when the amount of absorbed hydrogen is the same.

FIG. 5 is a graph showing the relationship between hydrogen pressure and sample temperature during the temperature rising process in the measurement of the present invention.

FIG. 6 is a graph showing a charged state and a discharged state of a hydrogen storage alloy used in a Ni-H ₂ battery.

FIG. 7 is a graph showing measurement results of alloys having different compositions.

FIG. 8 is a diagram showing a configuration of a conventional Sibelts device.

FIG. 9 is a graph showing the results of conventional P-C-T curve measurement.

[Explanation of symbols]

 (1) Gas holder (2) Sample (3) Sample container (4) Valve (5) Valve (6) Pressure sensor (7) Temperature chamber (8) Heater (9) Temperature sensor

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hiroshi Watanabe 2-18 Keihanhondori, Moriguchi-shi, Osaka Sanyo Electric Co., Ltd. (72) Ikuro Yonezu 2-chome Keihanhondori, Moriguchi-shi, Osaka Sanyo Denki Within the corporation

Claims (2)

[Claims] 1. The characteristics of the sample are measured by measuring the pressure in the system while changing the temperature of the sample in a system of a constant volume in which the sample of the hydrogen storage alloy is housed. A method for evaluating the characteristics of a hydrogen storage alloy for evaluating. 2. The temperature range for changing the sample temperature is
In the relationship between the pressure and the hydrogen absorption amount when the sample hydrogen storage alloy releases hydrogen at a constant temperature, the hydrogen release amount is set to a range such that the hydrogen release amount according to the application of the hydrogen storage alloy is obtained. 1. The method for evaluating characteristics of a hydrogen storage alloy as described in 1.