scholarly journals On the Common Ground of Thermodynamics and Kinetics: How to Pin Down Overpotential to Reversible Metal Hydride Formation and the Complete Ideal Gas Theory of Reversible Chemical Hydrogen Storage

2021 ◽  
Author(s):  
Roland Hermann Pawelke
Keyword(s):  
Hydrogen Storage ◽  
Metal Hydride ◽  
Common Ground ◽  
Chemical Potential ◽  
Applied Pressure ◽  
Ideal Gas ◽  
Practical Significance ◽  
Equilibrium Pressure ◽  
Tank Design ◽  
Chemical Hydrogen Storage

Ti-doped NaAlH<sub>4</sub> requires at 125 °C for [AlH<sub>4</sub>] formation more than twice the equilibrium pressure; while it is straightforward to relate this conditional surplus in hydrogenation pressure respective chemical potential to kinetic hindrance, it appears strange that this matter has not been duly theoretically addressed in literature to this day. The interest in identifying such overpotentials is not of purely academic interest but touches a problem of very practical significance as the maximum applied pressure is an important threshold to metal hydride tank design. A theory-based tool would be a resource-efficient complement or even alternative to PCI measurements. This paper tracks the formation overpotential issue down to its root and outlines a simple yet accurate general method based on Arrhenius and van’t Hoff data. Rather unexpectedly, the result is also the final missing piece towards a comprehensive understanding of reversible chemical hydrogen storage with regard to attainable hydrogen storage capacity.

scholarly journals On the Common Ground of Thermodynamics and Kinetics: How to Pin Down Overpotential to Reversible Metal Hydride Formation and the Complete Ideal Gas Theory of Reversible Chemical Hydrogen Storage

2020 ◽  
Author(s):  
Roland Hermann Pawelke
Keyword(s):  
Hydrogen Storage ◽  
Metal Hydride ◽  
Common Ground ◽  
Chemical Potential ◽  
Applied Pressure ◽  
Ideal Gas ◽  
Practical Significance ◽  
Equilibrium Pressure ◽  
Tank Design ◽  
Chemical Hydrogen Storage

Ti-doped NaAlH<sub>4</sub> requires at 125 °C for [AlH<sub>4</sub>] formation more than twice the equilibrium pressure; while it is straightforward to relate this conditional surplus in hydrogenation pressure respective chemical potential to kinetic hindrance, it appears strange that this matter has not been duly theoretically addressed in literature to this day. The interest in identifying such overpotentials is not of purely academic interest but touches a problem of very practical significance as the maximum applied pressure is an important threshold to metal hydride tank design. A theory-based tool would be a resource-efficient complement or even alternative to PCI measurements. This paper tracks the formation overpotential issue down to its root and outlines a simple yet accurate general method based on Arrhenius and van’t Hoff data. Rather unexpectedly, the result is also the final missing piece towards a comprehensive understanding of reversible chemical hydrogen storage with regard to attainable hydrogen storage capacity.

scholarly journals On the Common Ground of Thermodynamics and Kinetics: How to Pin Down Overpotential to Reversible Metal Hydride Formation and the Complete Ideal Gas Theory of Reversible Chemical Hydrogen Storage

2020 ◽  
Author(s):  
Roland Hermann Pawelke
Keyword(s):  
Hydrogen Storage ◽  
Metal Hydride ◽  
Common Ground ◽  
Chemical Potential ◽  
Applied Pressure ◽  
Ideal Gas ◽  
Practical Significance ◽  
Equilibrium Pressure ◽  
Tank Design ◽  
Chemical Hydrogen Storage

Ti-doped NaAlH<sub>4</sub> requires at 125 °C for [AlH<sub>4</sub>] formation more than twice the equilibrium pressure; while it is straightforward to relate this conditional surplus in hydrogenation pressure respective chemical potential to kinetic hindrance, it appears strange that this matter has not been duly theoretically addressed in literature to this day. The interest in identifying such overpotentials is not of purely academic interest but touches a problem of very practical significance as the maximum applied pressure is an important threshold to metal hydride tank design. A theory-based tool would be a resource-efficient complement or even alternative to PCI measurements. This paper tracks the formation overpotential issue down to its root and outlines a simple yet accurate general method based on Arrhenius and van’t Hoff data. Rather unexpectedly, the result is also the final missing piece towards a comprehensive understanding of reversible chemical hydrogen storage with regard to attainable hydrogen storage capacity.

scholarly journals On the Common Ground of Thermodynamics and Kinetics: How to Pin Down Overpotential to Reversible Metal Hydride Formation and the Complete Ideal Gas Theory of Reversible Chemical Hydrogen Storage

2020 ◽  
Author(s):  
Roland Hermann Pawelke
Keyword(s):  
Hydrogen Storage ◽  
Metal Hydride ◽  
Common Ground ◽  
Chemical Potential ◽  
Applied Pressure ◽  
Ideal Gas ◽  
Practical Significance ◽  
Equilibrium Pressure ◽  
Tank Design ◽  
Chemical Hydrogen Storage

Ti-doped NaAlH<sub>4</sub> requires at 125 °C for [AlH<sub>4</sub>] formation more than twice the equilibrium pressure; while it is straightforward to relate this conditional surplus in hydrogenation pressure respective chemical potential to kinetic hindrance, it appears strange that this matter has not been duly theoretically addressed in literature to this day. The interest in identifying such overpotentials is not of purely academic interest but touches a problem of very practical significance as the maximum applied pressure is an important threshold to metal hydride tank design. A theory-based tool would be a resource-efficient complement or even alternative to PCI measurements. This paper tracks the formation overpotential issue down to its root and outlines a simple yet accurate general method based on Arrhenius and van’t Hoff data. Rather unexpectedly, the result is also the final missing piece towards a comprehensive understanding of reversible chemical hydrogen storage with regard to attainable hydrogen storage capacity.

scholarly journals A Study of K/Ti-co-doped NaAlH4 on Thermodynamic Tailoring, Surplus Hydrogen Amount and Metal Hydride Molar Volume

2021 ◽  
Author(s):  
Roland Hermann Pawelke
Keyword(s):  
Hydrogen Storage ◽  
Molar Volume ◽  
Metal Hydride ◽  
Chemical Potential ◽  
Reaction Pathway ◽  
Ideal Gas ◽  
Point Of View ◽  
Phase Point ◽  
Desorption Enthalpy ◽  
Co Doped

A remarkable finding of metal hydride hydrogen storage is that substituting 4 mol % sodium by potassium in 4 mol % Ti-doped NaAlH<sub>4</sub> raises the reversible hydrogen storage capacity from 3.3 % w/w H to 4.7 % w/w H. This increase by 42% is concomitant with a slightly lower desorption enthalpy: intriguingly enough, it is substantially more hydrogen capacity at slightly less desorption enthalpy. The general solution to that puzzle has been already derived from a gas phase point of view, taking advantage of the equilibrium nature of the matter, which thus comes in terms of an ideal gas chemical potential. However, it is also interesting to investigate for the flipside effect in the sorbent phase, affecting molar volume. This paper elucidates by the example of K/Ti-co-doped NaAlH<sub>4</sub> the relation of doping modifications to surplus hydrogen amount and hydride molar volume, defining the term “reaction pathway” in this context, yielding the according figures.<br>

scholarly journals A Study of K/Ti-co-doped NaAlH4 on Thermodynamic Tailoring, Surplus Hydrogen Amount and Metal Hydride Molar Volume

2021 ◽  
Author(s):  
Roland Hermann Pawelke
Keyword(s):  
Hydrogen Storage ◽  
Molar Volume ◽  
Metal Hydride ◽  
Chemical Potential ◽  
Reaction Pathway ◽  
Ideal Gas ◽  
Point Of View ◽  
Phase Point ◽  
Desorption Enthalpy ◽  
Co Doped

A remarkable finding of metal hydride hydrogen storage is that substituting 4 mol % sodium by potassium in 4 mol % Ti-doped NaAlH<sub>4</sub> raises the reversible hydrogen storage capacity from 3.3 % w/w H to 4.7 % w/w H. This increase by 42% is concomitant with a slightly lower desorption enthalpy: intriguingly enough, it is substantially more hydrogen capacity at slightly less desorption enthalpy. The general solution to that puzzle has been already derived from a gas phase point of view, taking advantage of the equilibrium nature of the matter, which thus comes in terms of an ideal gas chemical potential. However, it is also interesting to investigate for the flipside effect in the sorbent phase, affecting molar volume. This paper elucidates by the example of K/Ti-co-doped NaAlH<sub>4</sub> the relation of doping modifications to surplus hydrogen amount and hydride molar volume, defining the term “reaction pathway” in this context, yielding the according figures.<br>

The Thermodynamic Way of Assessing Reversible Metal Hydride Volume Expansion: Getting a Grip on Metal Hydride Formation Overpotential

2021 ◽  
Author(s):  
Roland Hermann Pawelke
Keyword(s):  
Volume Change ◽  
Metal Hydride ◽  
Volume Expansion ◽  
Storage Systems ◽  
Metal Hydrides ◽  
Ideal Gas ◽  
Relative Volume ◽  
Hydride Formation ◽  
Chemical Hydrogen Storage ◽  
Insight Into

<p>The relative volume change of reversible metal hydrides upon hydrogenation is determined by means of the van’t Hoff reaction entropy and STP ideal gas parameters. This method allows insight into the requirements to metal hydride formation, outlined by example of Ti-NaAlH<sub>4</sub>. This work presents a timeless perspective on the sorbent phase thermodynamics of reversible chemical hydrogen storage systems.</p>

scholarly journals The Key to the Problem of Reversible Chemical Hydrogen Storage Is 12 kJ (mol H2)-1

2018 ◽  
Author(s):  
Roland Hermann Pawelke
Keyword(s):  
Hydrogen Storage ◽  
Ideal Gas ◽  
Solid Hydrogen ◽  
Hydrogen Sorption ◽  
Equilibrium Thermodynamics ◽  
Ideal Gas Law ◽  
Chemical Hydrogen Storage ◽  
The Ideal

This article outlines a simple theoretical formalism illuminating the boundaries to reversible solid hydrogen storage, based on the ideal gas law and classic equilibrium thermodynamics. A global picture of chemical reversible hydrogen sorption is unveiled, including a thermodynamic explanation of partial reversibility.<br>

scholarly journals The Master Key to the Problem of Reversible Chemical Hydrogen Storage is 12 kJ (mol H2)-1

2019 ◽  
Author(s):  
Roland Hermann Pawelke
Keyword(s):  
Energy Storage ◽  
Hydrogen Storage ◽  
Predictive Power ◽  
Storage Capacity ◽  
Reaction Pathway ◽  
Ideal Gas ◽  
Equilibrium Thermodynamics ◽  
Ideal Gas Law ◽  
Chemical Hydrogen Storage ◽  
The Ideal

<p>This article outlines a potent theoretical formalism illuminating the boundaries to reversible solid hydrogen storage based on the ideal gas law and classic equilibrium thermodynamics. A global picture of chemical reversible hydrogen sorption is unveiled including a thermodynamic explanation of partial reversibility. This is utilized to elucidate a multitude of issues from metal hydride chemistry: Highlights are why the substitution of a mere 4 mol % Na by K in Ti-doped NaAlH<sub>4</sub> raises the reversible storage capacity by 42 % and elaboration of the reaction pathway in (Rb/K)H-doped Mg(NH<sub>2</sub>)<sub>2</sub>/2LiH. The findings of this work allow for a change of paradigm towards the understanding of reversible chemical energy storage and provide a hitherto missing tool of ample analytic and predictive power, complementary to experiment.</p>

The Key to the Problem of Reversible Chemical Hydrogen Storage is 12 kJ (mol H2)-1

2019 ◽  
Author(s):  
Roland Hermann Pawelke
Keyword(s):  
Hydrogen Storage ◽  
Ideal Gas ◽  
Solid Hydrogen ◽  
Hydrogen Sorption ◽  
Equilibrium Thermodynamics ◽  
Ideal Gas Law ◽  
Chemical Hydrogen Storage ◽  
The Ideal

This article outlines a simple theoretical formalism illuminating the boundaries to reversible solid hydrogen storage, based on the ideal gas law and classic equilibrium thermodynamics. A global picture of chemical reversible hydrogen sorption is unveiled, including a thermodynamic explanation of partial reversibility.<br>

Performance of a Thermally Coupled Hydrogen Storage and Fuel Cell System Under Different Operation Conditions

2016 ◽  
Vol 13 (2) ◽  
Author(s):  
Gustavo A. Andreasen ◽  
Silvina G. Ramos ◽  
Hernán A. Peretti ◽  
Walter E. Triaca
Keyword(s):  
Fuel Cell ◽  
Hydrogen Storage ◽  
Metal Hydride ◽  
Cell System ◽  
Proton Exchange ◽  
Integrated System ◽  
Equilibrium Pressure ◽  
High Hydrogen ◽  
Hydrogen Flow ◽  
Operation Conditions

The performance of a hydrogen storage prototype loaded with AB5H6 hydride, whose equilibrium pressure makes it suitable for both feeding a H2/air proton exchange membrane (PEM) fuel cell and being charged directly from a low-pressure water electrolyzer, interacting thermally with the fuel cell exhaust air, is reported. The nominal 70 L hydrogen storage capacity of the prototype suffices for hydrogen delivery at 0.5 L min−1, which allows a power supply of 50 W for 140 min from the H2/air fuel cell in the absence of thermal interaction. The storage prototype was characterized by monitoring the internal pressure and the temperatures of the external wall and at the center inside the container at different hydrogen discharge conditions. The responses of the integrated system after either immersing the metal hydride container in air or exposing it to the fuel cell hot exhaust air stream under forced convection were compared. The system shows the best performance when the heat generated at the fuel cell is used to increase the metal hydride container temperature, allowing the operation of the fuel cell at 280 W for 16 min at a high hydrogen flow rate of 4 L min−1.

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