Will LIHC (Liquid Inorganic Hydrogen Carriers) be the next - - PDF document

UDT 2020

Will LIHC (Liquid Inorganic Hydrogen Carriers) be the next breakthrough in underwater propulsion?

• Y. Shaham1

1Electriq Global, Tirat Carmel, Israel

The entrance of AIP (Air Independent Propulsion) systems into the conventional submarine market, made a tremendous improvement in the operational capabilities of submarines. One of the most common AIP systems is a fuel cell system. In order to get the electrical power, the fuel cell requires constant supply of hydrogen and

• xygen and the storage medium is a key limitation. Electriq~Global presents a solution in developing a

hydrogen-based power generator technology through a safe and cost-effective H2 on-demand solution, using hydrogen-rich liquid carrier operated in ambient pressure, activated by a low-cost catalyst.

1 Introduction

The entrance of AIP (Air Independent Propulsion) systems into the conventional submarine market, made a tremendous improvement in the operational capabilities

• f submarines. The higher endurance enables submarines

to extend their operational time and thereby provides two crucial benefits: it postpones the need to charge the batteries and allows the submarine to conduct its

• perative mission in a stealthier manner.

One of the most common AIP systems is a fuel cell

• system. In order to get the electrical power, the fuel cell

requires constant supply of hydrogen and oxygen. Despite its common use, the fuel cell system currently has a key limitation – the hydrogen storage medium, energy density and capacity. A typical way for carrying the hydrogen on board, is using a metal hydride cylinders, installed in the keel area

• utside
• f

the pressure hull. However, Storing the hydrogen on-board the submarines implies significant weight and volume constrains, due to the low weight and volume hydrogen density of the metal hydride cylinders (less than 1.5% of H2 storage capacity), which is used to carry the hydrogen. This limitation forces submarine manufactures to build a bigger pressure hull and due to general arrangement aspects, the amount of hydrogen is limited and so is the endurance. In the quest of providing the ideal power generation solution for AIP systems, Electriq~Global is developing a hydrogen based power generator technology through a safe and cost-effective H2 on-demand solution, using hydrogen-rich liquid carrier operated in ambient pressure, activated by a low-cost catalyst. The LIHC, ranges in hydrogen weight density of 2.7%-8%. The LIHC can be stored inside the pressure hull or in tanks outside. The benefits of using this type of hydrogen source are substantial as detailed below:

• Increased weight efficiency.
• Easy to implement Layout on board (compare to

metal hydride cylinders) e.g., only tanks inside or outside the pressure hull and a relatively small size system.

• No additional O2 consumption for H2 production.
• No Carbon emissions – no CO2 discharged.
• Low temperature range: 80-100°C, cooling by sea

water.

• Low signature footprint – acoustic and magnetic.
• Safety – no hydrogen refueling on board.
• Engineering system easy to construct.
• Low CapEx investment.
• Pressure Range and hydrogen purity suitable for

Fuel cells.

• Suitable for all submarine sizes.

In order to provide a clear power generation on-board a submarine, Electriq~Global developed its patented Electriq~System, that produces hydrogenation, by immersing the catalyst (Electriq~Switch) in Electriq~Fuel (LIHC) with. The catalyst innovation can be summarized as:

• Highly active: nanoclusters ensuring fast release of

H2.

• Resilient and durable catalyst.
• Low cost: Catalyst is based only on non-precious

and widely available material and commonly used procedures. To ensure the fuel will be “cost competitive”, Electriq~Global is currently developing a recycling process, where used fuel can be recycled and replenished with hydrogen and turned into fresh fuel that can be reused.

2 Technology

Our technology is based on three components: 2.1 Fuel

UDT 2020 The reaction of borohydride (

) has been known and

studied since the 1950s.[1] Borohydride combined with alkali metal (M= , , etc.) are the most well- known composite of borohydride. Their attraction is linked to the high gravimetric percentage of hydrogen that they store. The reaction, where H2 (together with MBO2) is released, is either thermolysis or hydrolysis.[2] When the potassium borohydride comes in contact with water, it produces 4 moles of H2 for every mole of KBH4, as the following hydrolysis reaction shows: Most of studies has been focused on sodium borohydride (NaBH4). Sodium borohydride is stable in dry air and easily handled.[3] Our fuel is based on different novel approach, using Potassium Borohydride (KBH4). The hydrolysis with NaBH4 releases more energy than KBH4 (-

mol and - mol respectively, see table 1)

and has higher kinetics. This result in faster, hotter, less controllable reaction. Consequently, although KBH4 has lower gravimetric percentage of Hydrogen, it makes him a safer, non-flammable, non-explosive solution and a better candidate for more certain applications. [4,5]

Table 1- Energy releases in the hydrolysis[8]

X= K X= Na XBO2

• 981.6
• 977

XBH4

• 227.4
• 188.6

H2 H2O

• 285.8

f mol

• 182.6
• 216.8

There are many parameters that can affect the KBH4 hydrolysis. Amongst are concentration, pH, and

• temperature. Higher temperature can accelerate the

reaction by kinetic manners, while the highest temperature that can be achieved is C as it’s the water boiling point. H2 can also release in low temperatures as 25°C has been tested in our lab. Adding alkaline to the solution can help control the H2 spontaneous release by KBH4

• 5. In figure 1, we see a

solubility test of KBH4 in water at 25°C as a function of its weight percent and the KOH weight percent. We can see that when KOH is present, KBH4 above 9wt% (the solubility of KBH4 is

g g at 25°C), display

solubility issues and adding more KOH does not necessarily benefit us. However, experiments in higher temperature of 65°C, show us that KOH can delay the H2 spontaneous release and that is why it is necessary.

• Fig. 1- Solubility of KBH4 in water as a function of weight

percent and KOH weight percent at 25°C

We work with several types of fuel that can be roughly divided in to 2 groups, liquid fuel and paste like

• fuel. Liquid fuel contains different amounts of KBH4 and

KOH and will work only when in contact with catalyst (that will be discussed later). Paste like fuel contains higher concentration of KBH4 and without any KOH. This fuel takes advantage of the spontaneous release that occurs when water meets the borohydride. After first contact, a catalyst is inserted and stimulate the reaction even more. Both types of fuel harness different and

• pposite advantages of the KBH4 and are ideal for

different applications. In figure 2 we can see an experiment of hydrogen spontaneous release. The experiment was done with paste like fuel with relatively small concentrations of KBH4. 50g of 5.3M KBH4 solution was prepared and a reaction

• ccurred at 40°C. After six minutes a total of 0.8L of H2

was released without any external stimulant in form of catalyst or heat. When mixing 50g of 7.5M KBH4 solution, the reaction started spontaneously at 60°C. After 6 min, 2.65L of H2 was released. The reaction was exhausted after 5.5 hours while most of the reaction happened after 4 hours. At the end of the reaction, the fuel produced 25.73L of H2 while the theoretical H2 production of 7.5M KBH4 is 31.18L, only 17% less than the theoretical value.

UDT 2020

• Fig. 1- Spontaneous release (without catalyst and heating) of (a)

5.3M KBH4 ;(b) 7.5M KBH4

2.2 Catalyst The purpose of a catalyst is to lower the energy barrier of the hydrolysis reaction. Thus, enabling a significantly accelerated borohydride reaction implementing a solid catalyst which enables immediate termination of the reaction by removal of the catalyst subject from the

• solution. Controlling the hydrogen release via catalyst

can also control the rate of the hydrogen generation to match the consumption of the fuel cell. The rate can be controlled by integrating two parameters, the catalyst activity (the amount of hydrogen that is being released per sec) and the catalyst area that we expose to the fuel. When more catalyst surface area is being immersed in the fuel, more hydrogen will be released per second. Many researches focus on creating catalyst from precious metals such as Ru, Pt, Pd etc. and its alloys. But also, other heterogeneous compounds from other metals such as Ni, B, Fe, Co, Cu and their combinations.[3,6] Our catalyst is based on layers of unique composition

• f non-precious metals deposited using electrodeposition.

In figure 3, we can see the operation of large reactors for vehicle engines. The reactor is constructed from catalyst and liquid fuel. The fuel was heated to 45°C and after that it flowed to the reactor. When the hot fuel started reaching the reaction, is point 0 seconds (before the tank was full). The temperature in the reactor started at room temperature and the hot fuel heated it. We can see a small step around 40°C, after that the reactor kept heating itself from the energy of the exothermic reaction. The rise in temperature helps accelerate the reaction even more.

• Fig. 2- catalyst activity in an engine system as a function of

time

The flow from the reactor is pre-determined externally and each rise in flow was intentional and determined by the operator. Therefore, we can see the flow changes in step. Each step is an outer increase of the

• flow. The flow can be determined by using valves and

controlling the area of the catalyst that encounters the fuel. 2.3 Recycling While producing H2 on demand from KBH4 can be a promising solution, the KBH4 is still quite costly and generates by-products. In an effort to increase the efficiency and decrease our cost and associated waste (and in so becoming more environmentally friendly), we developed a method of recycling our fuel. As shown in equation 1, KBH4 dissolved in water produces H2 and also KBO2 as a by-product. KBO2 is a highly stable precipitant that doesn’t rinse with DI or organic solvants2. In the recycling process we reverse equation 1 by using hydrogen pressure and scavenger metal alloy of the

• xygen to be released from the KBO2 as following:

Where M is alloy of metals selected from the II column of the periodic table of elements. In choosing the right alloy, we need to give into consideration the overall

(enthalpy of formation) of the reaction because this

will determine the standard free energy that will let us know if the reaction is possible and if so, in which

• conditions. Usually, if , the process will involve

extreme environment in the form of high pressure and high temperature. On top of the need to satisfy those conditions, the temperature still needs to be under the melting point of the alloy and the KBO2.[7]

UDT 2020 One of the advantages of using alloy is to be able to use used scrapes of metal sourced from industrial waste and in so, decreasing the cost and the “footprint” of the process. In figure 3, we can see how the reaction is dependent

• n H2. The flow of H2 into the reaction chamber is

handled externally. The reaction consumes the H2, the pressure decreases, the valve is opened manually and H2 flows into the chamber, then, the equilibrium breaks, and more KBO2 becomes KBH4 and so on. The reaction that we see in equation 2 in endothermic, in figure 3 we can clearly this dependence. Each time more H2 inserted to the chamber, the temperature drops (and heated with a heater). This is the indicator that the reaction occurs. In this method of constant flow of hydrogen, we can reach high regeneration percentage of our fuel.

• Fig. 3- Reaction temperature and H2 flow into the reaction

chamber as a function of time

3 Summary

Ultimately, Electriq~Global’s innovation enables easier and safer logistics of handling hydrogen, with the required purity (5/9), in a simple engineering system to support the production. This enables to carry much more hydrogen in the same size of a submarine and increases dramatically the endurance time. Electriq~Global has already proven its technology in a large-scale demonstrator for a fuel cell truck, where the Electriq~System displayed a hydrogen filling capacity of 500 SLPM (Standard Liter Per Minute), equivalent to 41.6 kW. In summary, EG’s technological breakthrough provides submarine manufactures and operators with an

• pportunity

to significantly improve

• verall

duration/range and performance, that was never seen before.

References

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