My focus relies on obtaining the theoretical values for the PCT curve which I could plot and then compare with the instrument data to understand the concept better, I have elucidate what I have done and the direction which I am gravitating towards. I have assumed the absorption temperature at 25C and the saturated LaNi5 follows the stoichiometry of LaNi5H7
So I am trying to calculate the maximum amount of hydrogen which could be stored in the metal hydride (which is $LaNi_5$ here), Now I used the formula for the calculation as:
%wt. of Hydrogen in MH = \frac{molar mass of hydrogen}{molar mass of LaNi5},
I was able to get 1.605%wt. When converting into the %wt. of hydrogen stored I found the value of hydrogen in grams using the formula as:
grams of hydrogen as : \frac{%wt. of hydrogen}{100}*\frac{weight of metal hydride}{molar mass of hydrogen} * H/M here based on LaNi5H7, I took H/M as 7/6, the value for the hydrogen stored maximum was found to be 0.4094 grams , and 30 grams of LaNi5 was considered.
Now with an assumption of absorption temperature of 25C, I am trying to get the pressure at which this occurs based on the previous calculations , this could then help for me to do some PCT theoretical calculation, but the values which I obtained are very large pressures , usually not possible for this type of metal hydride, can please anyone guide me through any metal hydride calculations errors which I am pursuing and correct me or gravitate me towards the correct direction. (updates in the calculations could occur when the experimental results are obtained)
Dear friend Ketan Karkare
Based on your calculations, you are trying to determine the pressure at which hydrogen is absorbed by LaNi5. The pressure-temperature-composition (PCT) curve is a useful tool for understanding the hydrogen absorption properties of metal hydrides. The PCT curve shows the relationship between the pressure, temperature, and composition of the metal hydride. The theoretical calculations for the PCT curve can be obtained using thermodynamic models such as CALPHAD (Hydrogen sorption...).
The Gibbs energy for LaNi5-xAlxHy (0 ≤ x ≤ 1, 0 ≤ y ≤ 7) phase was obtained using a full CALPHAD assessment. The results showed good agreement between experimental and calculated results (Hydrogen sorption...).
It is important to note that the PCT curve is influenced by various factors such as temperature, pressure, and composition of the metal hydride. The idealized PCT curve is shown in Fig 1 (NIST-MSEL hydrogen...).
I hope this helps! Let me know if you have any more questions.
Source:
(1) Hydrogen sorption in the LaNi5-xAlx-H system (0 ≤ x ≤ 1). https://www.researchgate.net/publication/274706204_Hydrogen_sorption_in_the_LaNi5-xAlx-H_system_0_x_1.
(2) NIST-MSEL Hydrogen Storage Program: Research - Introduction. https://www.ctcms.nist.gov/hydrogen_storage/tutorials_PCT.html.
(3) Surface Properties of LaNi5 and TiFe—Future Opportunities of .... https://www.frontiersin.org/articles/10.3389/fenrg.2021.719375/full.
(4) LaNi5 related AB5 compounds: Structure, properties and applications. https://www.sciencedirect.com/science/article/pii/S0925838820345266.
Kaushik Shandilya Hello Sir ! Thanks for the suggestion, it is a great help! I was wondering if we could use the kinetics for the absorption and desorption for the theoretical calculations based on how a PCT curve should be , any recommendations ???
Hello, I would definietly start with LaNi5H6 not "7" ... in fact its even less then stoichiometric value... This may help in the calculations;)
Dear Ketan Karkare.
You may want to use Calphad databases and thermodynamic engines to calculate what you need.
You may use the thermodynamic database provided here:
Article Thermodynamic assessment of the H-La-Ni system
or here:
Article Experimental investigation and thermodynamic reassessment of...
These thermodynamic databases usually are referenced in a standard system of reference that makes them useful to be extended to other systems etc, and the compounds, their solubility, and invariant points of phase transformation used to optimize and assess thermodynamic model parameters
You then can use thermodynamic engines like:
- OpenCalphad (free): www.opencalphad.com
- PyCalphad (free): pycalphad.org
- ThermoCalc : thermocalc.com
To calculate the fraction of the phases, the composition of the phases, the equilibrium pressure of solid phases with the gas, PCI curves, and many other thermodynamic equilibrium properties and non-equilibrium properties of the system.
Please let me know if you have any questions.
Best wishes,
Ebert
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