Method and system for hydrogen generation from aluminum corrosion using organic acids

Abstract

The present invention is directed to a method of generating hydrogen. The method comprises the steps of: combining aluminum or an aluminum alloy with gallium or a gallium eutectic to form a compound; placing the compound in contact with a solution comprising an aliphatic diprotic or triprotic carboxylic acid to corrode the aluminum or aluminum alloy, and generating hydrogen and hydrolyzed aluminum as a byproduct; collecting the generated hydrogen; and recovering the solution for reuse. The present method is an environmentally sound, highly efficient method, which generates useful quantities of hydrogen in a scalable system.

Description

[0001] METHOD AND SYSTEM FOR HYDROGEN GENERATION FROM ALUMINUM CORROSION USING ORGANIC ACIDS

[0002] Technical Field

[0003] The present invention provides a method using certain aliphatic diprotic or triprotic carboxylic acids with gallium as an activating agent to accelerate the corrosion reaction of aluminum or aluminum alloys to generate hydrogen (H2) in gaseous form as a reaction product.

[0004] Background

[0005] Hydrogen (H2) energy, generated by hydrogen and / or hydrogen-containing compounds, is considered one of the most promising energy sources for a sustainable society owing to its high gravimetric energy density, also referred to as low heating value (122 kJ / g), combustion value, also referred to as high heating value (141.8 kJ / g), and potential for zero carbon emissions. Hydrogen has very low density which demands greater space for its storage than conventional fuels unless it is compressed at cryogenic temperatures. The transportation of hydrogen is also an issue because of its explosive nature. As an alternative to storing H2, it is possible and preferred to generate H2 on demand at the point of use. This provides a solution to issues related to both storage and transportation of hydrogen.

[0006] Numerous methods to generate H2 have been proposed including electrolysis, thermomechanical, photobiological, photochemical, and photocatalytic water splitting, steam reforming of fossil fuels, nuclear H2 production, biomass processing, and metal corrosion and hydrolysis techniques. However, all these methods suffer some drawbacks such as low efficiency, high cost of components, highly acidic or highly alkaline, toxic environments, low durability, nonefficient photocatalytic material, production and emission of CO2 as a byproduct in the use of fossil fuels, need for excellent corrosion resistance in nuclear reactions, requirement of a large reactor, or high cost for biomass conversion.

[0007] Among the proposed approaches, metal hydrolysis, also loosely referred to as corrosion, has a great advantage owing to its simplicity, being spontaneous due to its exothermic nature, effectiveness, and environmental safety requiring the use of only water-based media while

[0008] 1

[0009] 184086148.1 releasing large amounts of H2 produced at ambient temperature. However, the H2 release performance from the hydrolysis of metal-based materials is frequently blocked by the formation of surface passivation layers, resulting in sluggish reaction kinetics and low H2 yield.

[0010] Hydrogen production based on the corrosion of light metals such as Magnesium (Mg) or Aluminum (Al) in aqueous solutions can be considered as a promising alternative route. While Mg exhibits a spontaneous reaction in water forming magnesium-hydroxide and hydrogen, aluminum is inert to corrosion in water due to a self-passivating AI2O3 oxide layer. Various approaches have been attempted to remove the AI2O3 layer and thereby overcome the passivation of Al. One representative method is to corrode Al in a strong acidic (HC1, HNO3, H2SO4, or H3PO4) or strong basic (NaOH / KOH) aqueous solution at extreme pH about 1.0 or below, or about 13.0 and above, respectively, which effectively dissolves the AI2O3 oxide layer, enabling the H2 generation reaction to proceed. However, these acidic or alkaline aqueous solutions can be exceedingly corrosive, thus difficult to handle and require highly corrosion resistant equipment with high maintenance costs. In addition to the inherently corrosive nature of strong mineral acids and alkalis, these are consumed during the corrosion reaction with Al and must be replenished with each reaction. Also, corrosion reactions using strong mineral acids or alkalis require stringent control of the solution pH throughout the reaction for effectiveness.

[0011] When pure Al or Al alloy is reacted with weak organic acids having pH values significantly greater than 1.0, either no H2 is generated or the generation rate is exceedingly sluggish to be of any practical interest. This is due primarily to the inability of these weak acids to destroy the passivating oxide layer over the reactive Al metal surface.

[0012] Since aluminum and aluminum alloys are abundant and relatively inexpensive, for example in form of metal scrap, it was previously considered to corrode aluminum or aluminum alloys to obtain hydrogen as an alternative method to the more expensive methods of splitting of water by electrolysis or reforming of methane gas. As described above, the drawback of corroding aluminum using strong acids or strong bases is that the chemicals employed are highly corrosive and problematic if they are released into the environment. Moreover, this method is costly as acids or bases are consumed in the reaction. When using mineral acids like HC1, HNO3, H2SO4, or H3PO4, undesirable byproducts like AICI3, Al(NOs)3, A12(SC>4)3, or AIPO4 are formed, which are environmentally problematic in themselves.

[0013] 2

[0014] 184086148.1 Nevertheless, the corrosion of aluminum (Al) and its alloys is as a method to generate hydrogen holds promise as the reaction is exothermic and therefore energetically favorable, the high abundance, low density, and therefore low price of aluminum and its alloys. Due to its relatively low density, aluminum has high capacity to generate hydrogen through a redox reaction with water. The theoretical yield is -11.2% in wt.% of H2 (2.016 g / mol) generated per wt.% of input Al metal (26.982 g / mol), for the following corrosion reaction (Equation 1):

[0015] One gram of aluminum can produce about 1.36 liters of hydrogen at normal condition, i.e. 298K and atmospheric pressure of 1013 mbar, as the redox reaction does not require extremes of either temperature or pressure. However, as stated above, a several-nanometer-thick passive oxide layer is formed on the surface of Al that interferes with the contact between Al and water, resulting in an infinitely slow reaction rate. Therefore, the metal aluminum has to be activated by the disturbance and / or removal of the layer of aluminum oxide in order to use it in the reaction.

[0016] Recently, it was shown that gallium, a liquid metal above about 30°C, can be used as an activating agent, enabling the reaction between aluminum and water, eliminating the need for acids or bases. In this method, gallium reacts with the aluminum first, embrittling the aluminum, which then is corroded by water. The gallium is reclaimed as a product after the corrosion reaction forming aluminum oxide and hydrogen. The problem is that while a reaction is enabled in water, the rate is still too low for practical applications, and the problem remains that acids or bases are consumed and form environmentally harmful byproducts.

[0017] The techniques described in the published references, for generating hydrogen from the reaction between aluminum and water, either employ hazardous and ecologically undesirable mineral acids or bases, or provide an unacceptably low hydrogen generation rate. There remains a need for an environmentally sound, highly efficient method to generate useful quantities of hydrogen in a scalable system. The invention described herein provides such a solution and further attendant benefits.

[0018] 184086148.1 Brief Description of the Drawings

[0019] Fig. 1 shows the reactor set-up for quantifying the generation of hydrogen from reaction between Ga-Al composite and various aqueous-based media.

[0020] Fig. 2 shows complexation of aluminum with different salts formed upon corrosion with various weak organic acids, (a) 5-member ring formed by oxalic acid; (b) 7-member ring formed by malic, tartaric, and succinic acid; (c) ring structure formed by citric acid; (d) 6-member ring structure formed by malonic acid; (e) coordination formed by monoprotic acids such as acetic, formic, lactic, and glyoxylic acid (no ring structure is formed).

[0021] Fig- 3 shows the formation and collection of alumina (AI2O3) byproduct at the end of the corrosion reaction between citric acid and Al in the presence of liquid Ga metal.

[0022] Fig. 4 shows the formation of aluminum oxalate precipitate at the end of the corrosion reaction between oxalic acid and Ga-Al.

[0023] Fig- 5 is a process flow diagram for the generation of hydrogen from an organic acid solution and aluminum-gallium mixture.

[0024] Fig. 6 shows a commercial model for on-demand generation of hydrogen via controlled corrosion of scrap Al / Al alloys using gallium and non-toxic organic acid.

[0025] Fig- 7 shows the reaction between Al granules and liquid Ga in 10:90 wt.% ratio to generate Ga- Al composite.

[0026] Fig. 8 shows the variation of hydrogen induction time with different Ga content (wt.%) for corrosion reaction of Al in 1.0 M citric acid solution.

[0027] Fig. 9 shows the variation of 100% hydrogen yield time with different Ga content (wt.%) for corrosion reaction of Al in 1.0 M citric acid solution.

[0028] Fig. 10 shows the variation of initial hydrogen generation rate with different Ga content (wt.%) for reaction of Al in 1.0 M citric acid solution.

[0029] Fig. 11 shows hydrogen generation curves obtained for reaction of aqueous corrosion medium (1 M citric acid) and 1.0 g of Ga-Al composite material with different Ga content (wt.%) at 70°C.

[0030] 4

[0031] 184086148.1 The dashed line indicates the theoretical volume (136 mL) of H2 expected from reaction with 0.1 g of Al metal.

[0032] Fig. 12 shows hydrogen generation curves obtained for reaction between 1 M citric acid solution and 1.0 g Ga-Al composite material with Al of different grain sizes.

[0033] Fig. 13 shows the variation of initial reaction rate of H2 generation for reaction between Ga-Al composite with various aqueous based organic media. The concentration of all organic acids is 1 M except 0.65 M for succinic, 0.45 M for glutaric acid, and 0.09 M for gallic acid due to their lower solubility limits. Monoprotic organic acids are shown in plain text, diprotic and triprotic organic acids are shown in bold text.

[0034] Fig. 14 shows hydrogen generation curves obtained for reaction between 1 M lactic acid solution and 1.0 g of Ga-Al composite material and 0.1 g of Al granules at 70°C.

[0035] Fig. 15 shows hydrogen generation curves obtained for reaction between 1 M succinic acid solution and 1 .0 g of Ga-Al composite material and 0.1 g of Al granules at 70°C.

[0036] Fig. 16 shows hydrogen generation curves obtained for reaction between 1 M tartaric acid solution and 1.0 g of Ga-Al composite material and 0.1 g of Al granules at 70°C.

[0037] Fig. 17 shows hydrogen generation curves obtained for reaction between 1 M glutaric acid solution and 1.0 g of Ga-Al composite material and 0. 1 g of Al granules at 70°C.

[0038] Fig. 18 shows hydrogen generation curves obtained for reaction between 1 M malic acid solution and 1.0 g of Ga-Al composite material and 0.1 g of Al granules at 70°C.

[0039] Fig. 19 shows hydrogen generation curves obtained for reaction between 1 M oxalic acid solution and 1.0 g of Ga-Al composite material and 0.1 g of Al granules at 70°C.

[0040] Fig. 20 shows hydrogen generation curves obtained for reaction between 25 mM 2,5- furandicarboxylic acid (FDCA) solution and 1.0 g of Ga-Al and Ga-Al 2011 alloy composite materials at 70°C.

[0041] Fig. 21 shows hydrogen generation curves obtained for reaction between 1 M citric acid solution and 1.0 g of Ga-Al composite material and 0.1 g of Al granules at 70°C.

[0042] 5

[0043] 184086148.1 Fig. 22 shows hydrogen generation curves obtained for reactions between 0.34 M aconitic acid and 1 M citric acid solutions and 1.0 g of Ga-Al composite material and 0.1 g of Al granules at 70°C.

[0044] Fig. 23 shows hydrogen generation curves obtained for reaction between 1 M malic acid and 1.0 g of Ga-Al 6061 alloy composite and 0.1 g of Al 6061 alloy at 70°C.

[0045] Fig. 24 shows hydrogen generation curves obtained for reaction between 1 M malic acid and 1.0 g of Ga-Al 6101 alloy composite and 0.1 g of Al 6101 alloy at 70°C.

[0046] Fig. 25 shows hydrogen generation curves obtained for reaction between 0.5 M oxalic acid and 1.0 g of Ga-Al 6061 alloy composite and 0.1 g of Al 6061 alloy at 70°C.

[0047] Fig. 26 shows hydrogen generation curves obtained for reaction between 0.5 M oxalic acid and 1.0 g of Ga-Al 6101 alloy composite and 0.1 g of Al 6101 alloy at 70°C.

[0048] Fig. 27 shows hydrogen generation curves obtained for reaction between 1 M citric acid and 1.0 g of Ga-Al 6061 alloy composite and 0.1 g of Al 6061 alloy at 70°C.

[0049] Fig. 28 shows hydrogen generation curves obtained for reaction between 1 M citric acid and 1.0 g of Ga-Al 6101 alloy composite and 0.1 g of Al 6101 alloy at 70°C.

[0050] Fig. 29 shows hydrogen generation curves obtained for reaction between 1 M malic acid and 1.0 g of Ga-Al 5005 alloy composite, 1.0 g of Ga-Al 5052 alloy composite, and 1.0 g of Ga-Al composite material at 70°C.

[0051] Fig. 30 shows hydrogen generation curves obtained for reaction between 0.5 M oxalic acid and 1.0 g of Ga-Al 5052 alloy composite, 0.1 g of Al 5052 alloy, and 0.1 g of Al at 70°C.

[0052] Fig. 31 shows hydrogen generation curves obtained for reaction between 1 M citric acid and 1.0 g of Ga-Al 5052 alloy composite, 1.0 g of Ga-Al composite, and 0.1 g of Al 5052 alloy.

[0053] Fig. 32 shows hydrogen generation curves obtained for reaction between 1 M malic acid and 1.0 g of Ga-Al 2024 alloy composite, 1.0 g of Ga-Al 2011 alloy composite, and 1.0 g of Ga-Al composite material at 70°C.

[0054] Fig. 33 shows hydrogen generation curves obtained for reaction between 1 M tartaric acid and 1.0 g of Ga-Al 2024 alloy composite, 1.0 g of Ga-Al 2011 alloy composite, and 1.0 g of Ga-Al composite material at 70°C.

[0055] 6

[0056] 184086148.1 Fig. 34 shows hydrogen generation curves obtained for reaction between 0.5 M oxalic acid and 1.0 g of Ga-Al 2024 alloy composite, 1.0 g of Ga-Al 2011 alloy composite, and 1.0 g of Ga-Al composite material at 70°C.

[0057] Fig. 35 shows hydrogen generation curves obtained for reaction between 1 M citric acid and 1.0 g of Ga-Al 2024 alloy composite, 1 .0 g of Ga-Al 201 1 alloy composite, and 1 .0 g of Ga-Al composite material at 70°C.

[0058] Fig. 36 shows hydrogen generation curves obtained for reaction between 1 M malic acid and 1.0 g of Ga-Al 7075 alloy composite, 1.0 g of Ga-Al 2024 alloy composite, 1.0 g of Ga-Al 5052 alloy composite, and 1.0 g of Ga-Al composite material at 70°C.

[0059] Fig. 37 shows hydrogen generation curves obtained for reaction between 1 M tartaric acid and 1.0 g of Ga-Al 7075 alloy composite, 1.0 g of Ga-Al 2024 alloy composite, 1.0 g of Ga-Al 5052 alloy composite, and 1.0 g of Ga-Al composite material at 70°C.

[0060] Fig. 38 shows hydrogen generation curves obtained for reaction between 0.5 M oxalic acid and 1.0 g of Ga-Al 7075 alloy composite, 1.0 g of Ga-Al 2024 alloy composite, 1.0 g of Ga-Al 5052 alloy composite, and 1.0 g of Ga-Al composite material at 70°C.

[0061] Fig. 39 shows hydrogen generation curves obtained for reaction between 1 M citric acid and 1.0 g of Ga-Al 7075 alloy composite, 1.0 g of Ga-Al 2024 alloy composite, 1.0 g of Ga-Al 5052 alloy composite, and 1.0 g of Ga-Al composite material at 70°C.

[0062] Fig. 40 shows combined hydrogen generation curves obtained for reaction between 1 M malic acid and mixtures of (A) 2.0 g Ga-Al / Al 5052 in 25:75 wt.% ratio and 2.0 g Ga-Al / Al 5005 in 25:75 wt.% ratio; (B) 2.0 g Ga-Al / Al 5052 in 50:50 wt.% ratio and 2.0 g Ga-Al / Al 5005 in 50:50 wt.% ratio; and (C) 2.0 g Ga-Al / Al 5052 in 75:25 wt.% ratio and 2.0 g Ga-Al / Al 5005 in 75:25 wt.% ratio at 70°C.

[0063] Fig. 41 shows combined hydrogen generation curves obtained for reaction between 1 M tartaric acid and mixtures of (A) 2.0 g Ga-Al / Al 5052 in 25:75 wt.% ratio and 2.0 g Ga-Al / Al 5005 in 25:75 wt.% ratio; (B) 2.0 g Ga-Al / Al 5052 in 50:50 wt.% ratio and 2.0 g Ga-Al / Al 5005 in 50:50 wt.% ratio; and (C) 2.0 g Ga-Al / Al 5052 in 75:25 wt.% ratio and 2.0 g Ga-Al / Al 5005 in 75:25 wt.% ratio at 70°C.

[0064] 7

[0065] 184086148.1 Fig. 42 shows combined hydrogen generation curves obtained for reaction between 1 M citric acid and mixtures of (A) 2.0 g Ga-Al / Al 5052 and 2.0 g Ga-Al / Al 5005 in 25:75 wt.% ratio, and 1.0 g Ga-Al 5052 and 1.0 g Ga-Al 5005 alloy composites; (B) 2.0 g Ga-Al / Al 5052 and 2.0 g Ga-Al / Al 5005 in 50:50 wt.% ratio, and 1.0 g Ga-Al 5052 and 1.0 g Ga-Al 5005 alloy composites; (C) 2.0 g Ga-Al / Al 5052 and 2.0 g Ga-Al / Al 5005 in 75:25 wt.% ratio, and 1.0 g Ga-Al 5052 and 1.0 g Ga-Al 5005 alloy composites at 70°C.

[0066] Fig. 43 shows recovered Ga metal (~1 g) after reaction of Ga-Al composite with 1 M citric acid solution.

[0067] Fig. 44 shows hydrogen generation curves obtained for four consecutive reactions between 1 M citric acid solution and Ga-Al composite material at 70°C.

[0068] Detailed Description

[0069] The present invention provides a method in which certain aliphatic diprotic or triprotic carboxylic acids are used in the presence of gallium as an activating agent to accelerate the corrosion reaction of aluminum or aluminum alloys to generate hydrogen (H2) in gaseous form as a reaction product. The acids used in the present method are all environmentally friendlier than strong mineral acids such as HC1, HNO3, H2SO4, H3PO4, etc., or strong bases such as NaOH, KOH, etc. as they are derived from natural food resources.

[0070] The method of the invention allows naturally occurring, environmentally benign organic acids dissolved in water, to be used as corrosion media for Al and Al alloys. Liquid gallium (Ga) is used as an activating agent in contact with the Al and / or Al alloys, to generate hydrogen with 100% theoretical yield at initial rates similar to those observed with strong acids and bases. In particular, preferable organic acids form intermediate organic aluminum salts upon reaction with aluminum, which are soluble in water, and will revert to form the original organic acid along with hydrolyzed aluminum products such as Al(0H)3 or A10(0H), which may be dehydrated to AI2O3.

[0071] Moreover, unlike highly corrosive mineral acids and strong bases with extreme pH values that are completely consumed when reacted with Al, the organic acid used in the present method is only marginally consumed and is regenerated during the corrosion reaction without the addition

[0072] 8

[0073] 184086148.1 of an oxidizing agent, such as hydrogen peroxide (H2O2), pure oxygen, or ozone. Consequently, the only byproduct of the corrosion reaction of Al or Al alloy using the organic acid in aqueous media is hydrolyzed aluminum Al(0H)3, and A10(0H), or AI2O3 (alumina) after partial or full dehydration, respectively, instead of undesirable aluminum salts such as AlCh, A1(NC> ) , Ah(SO4)3, or AIPO4. Alumina is a useful material for various industrial and consumer applications. Thus, after separation of the solid alumina byproduct, both the liquid gallium metal and the organic acid medium can both be recovered and reused for further H2 generation reaction with Al and Al alloys, which is not possible with conventional mineral acids and strong bases.

[0074] The inventors have discovered a method in which the corrosion reaction of Al and Al alloys to generate hydrogen can be promoted using liquid Ga metal (or eutectic) as an activating agent, in combination with aqueous solutions of certain organic acids as corrosion media. At the end of the reaction, the Ga metal or Ga eutectic is recovered for reuse and the organic acid corrosion medium is regenerated for reuse in the corrosion reaction.

[0075] The method comprises the steps of (a) combining aluminum (Al) or an aluminum alloy with gallium (Ga) or a gallium eutectic, which acts as an activating agent for the aluminum, to form a compound; (b) reacting the resulting compound with a selected aliphatic diprotic or triprotic carboxylic acid to generate hydrogen; (c) collecting hydrogen as a reaction product, and (d) recovering the organic acid.

[0076] The method optionally comprises the further steps of (e) isolating and recovering the hydrolyzed aluminum byproduct, and (f) collecting the gallium or gallium eutectic for reuse in step (a).

[0077] In one embodiment, one or more of pure Al and Al alloy is first brought into contact or pre-treated with liquid Ga metal (or a Ga eutectic) for a period between 24 - 72 hours at a temperature at or above 29.8°C (temperature above which Ga metal remains in liquid state), typically and preferably around 40-45°C. This ensures that the liquid Ga penetrates into the grains and / or segregates to the grain boundaries of the Al or Al alloy(s), triggering the process of embrittlement of the Al-based metal, and preventing the formation of an oxide layer on its surface. The resulting activated Al / Al alloy can undergo a spontaneous corrosion reaction in aqueous solutions of naturally occurring, environmentally benign organic acids at temperatures at or above 29.8°C, to generate hydrogen.

[0078] 9

[0079] 184086148.1 The aluminum and / or Al alloy(s) used in the invented method may be in any of a number of forms, or a combination of forms. For example, the Al or Al alloy(s) may be in the form of sheet, foil, bar, rod, wire, particles, irregular pieces, or any combination of these forms. The invented method is particularly well-suited for utilizing scrap aluminum in various forms as the source of reactive materials, because all types of aluminum can be activated by combining with gallium, and as will be shown in the Examples, many varieties of Al alloys can be used to generate hydrogen via the invented method.

[0080] If a lower treatment temperature is desired, a gallium-tin eutectic (Ga9iSn9) with a melting temperature of 20.5°C or a gallium-indium eutectic (Gavsl s) with a melting temperature of 15.7°C, or a gallium-tin-indium eutectic (Galinstan) with a melting temperature of -19°C may be used instead of pure gallium. In the following embodiments and illustrative examples, and without loss of generality or narrowing the scope of the invention, the method herein is described with the use of gallium (Ga) metal.

[0081] While the preferred Ga:Al ratio is 90: 10 weight percent (wt.%) for removing the passive oxide layer and promoting embrittlement of the Al metal, the Ga:Al ratio can be between 95:5 wt.% and 10:90 wt.%. Other Ga:Al compositions such as 75:25, 66:34, and 50:50 wt.% are also effective. Using Ga concentrations < 50 wt.% will still eventually remove the passive oxide layer on the Al surfaces, but will take a longer time than with higher Ga concentrations, resulting in a longer reaction time to attain 100% yield of hydrogen than for higher Ga:Al ratios.

[0082] The inventors have discovered that the use of certain aliphatic diprotic and triprotic carboxylic acids as corrosion media with Al or Al alloys results in 100% stochiometric yield of hydrogen. Conversely, monoprotic organic acids react considerably slower and do not provide 100% H2 yield. Furthermore, certain, diprotic and triprotic acids are especially attractive for use in hydrogen generation via Al corrosion reaction, because they are regenerated during the corrosion reaction, and not consumed as are mineral acids such as HC1.

[0083] Diprotic aliphatic organic acids malic, tartaric, malonic, succinic, and glutaric acids are especially attractive because these acids react with Al to first generate an intermediate Al-acid anion complex, which is converted to the more favorable Al(0H)3 complex and regenerates the starting acid in the process. For example, malic acid reacts with Al to generate Al-malate complex,

[0084] 10

[0085] 184086148.1 which is converted to Al(0H)3 complex, regenerating malic acid for continued use in the corrosion reaction.

[0086] Citric acid, the triprotic carboxylic acid naturally occurring in lemons, behaves similarly.

[0087] Consequently, the promoted corrosion reactions in above mentioned acids generate hydrogen primarily through consumption of water, yielding solid Al(0H)3 as byproduct.

[0088] The advantages of the present method over corrosion of Al metal using mineral acids and / or alkalis for hydrogen generation include (i) the absence of strongly corrosive media resulting in simplification of reactor design, (ii) replenishment of organic acid corrosion medium without addition of oxidizing media resulting in cost savings through reuse of reagents, and (iii) the formation of non-toxic aluminum hydroxide as reaction product, instead of toxic aluminum salts such as AlCh, A1(NO3)3, Ah(SO4)3, or AIPO4. At the end of the corrosion reaction, the liquid Ga metal can be recovered for reuse in repeated Al / Al alloy corrosion reactions for hydrogen generation.

[0089] A) Reaction setup

[0090] An example of a suitable reactor setup is shown in Fig. 1 for the corrosion reaction between the Ga-Al composite and aqueous-based media for generation of hydrogen. A constant temperature bath is used to maintain a constant temperature environment at > 30°C, for example at 70°C to ensure Ga metal remains in the liquid state for the reaction. H2 generation systems based on Al corrosion do not need to be warmed up externally since the reaction is highly exothermic. Consequently, Al corrosion can be achieved under mild conditions of temperature and pressure using standard glassware and reactor apparatus.

[0091] The corrosion reaction starts when the Ga-Al composite and aqueous medium are placed into contact with each other. For example, the Ga-Al composite may be placed into a reactor vessel, and the organic acid poured over it. Alternatively, the organic acid may be placed into a vessel, and the Ga-Al composite then submerged in the acid.

[0092] In one embodiment, the reactor is connected to a displacer (inverted measuring cylinder immersed in water) through plastic tubing. H2 generation is measured using a water displacement

[0093] 11

[0094] 184086148.1 method, wherein the volume of H2 generated is measured by the volume change in the gas capture cylinder connected to the closed glass reactor.

[0095] Theoretically, the consumption of 1 g of Al can produce about 1.36 L of H2 at a temperature near room temperature according to the following reaction:

[0096] The H2 productivity, i.e. the ratio of the actual volume of H2 generated (i.e., H2 yield) to the theoretical H2 generation for the Ga-Al composite can be calculated and plotted as a function of reaction time.

[0097] B) Organic Acid Corrosion Media

[0098] Hydrogen generation from the corrosion reaction of Al and Al alloys typically employs aqueous acidic or alkaline corrosion media with extremes of pH, for example, hydrochloric acid (HC1) solution with pH < 1.0 or sodium hydroxide (NaOH) solution with pH > 13.0. Corrosion reactions in such strong media are dependent on maintaining stringent pH control.

[0099] In the present disclosed method, certain organic acids are used as the corrosion media for Al and Al alloys to generate hydrogen. An organic acid is an organic compound with acidic characteristics that does not dissociate completely in water and donates hydrogen ions to water molecules. Mineral acids such as HC1 are stronger than organic acids because of their complete dissociation in water. Consequently, organic acids are referred to as weak acids.

[0100] Organic acids in general have weaker acidic properties than mineral acids. The acidity of carboxylic acids, a certain category of organic acid, is associated with one or more carboxylic groups (-COOH). These can be classified as mono-, di-, or tri-protic acids based on having one, two, or three carboxylic groups in the structure. The lower reactivity and weak acidity make organic acids usable at higher temperatures and for a longer time.

[0101] The reactivity / strength of acids is characterized by the value of the acid-dissociation constant (Ka). This constant is used to measure the acid-ionization strength. The logarithmic values of Kaare referred to as pKaand are commonly used for acid-strength comparisons. A higher value of pKadenotes a relatively weaker acid and a lower value indicates a relatively stronger acid.

[0102] 12

[0103] 184086148.1 Alpha (a)-hydroxy acids (AHAs) are a subgroup of carboxylic acids, where the a-carbon (the carbon next to the carboxyl group) also bears a hydroxyl (-OH) group. In general, a-hydroxy acids (AHAs) are usually stronger acids than their parent carboxylic acids (without the a-OH) since the a-OH group exerts an inductive effect that stabilizes the conjugate base (carboxylate anion), making deprotonation of the COOH group easier resulting in lower pKa.

[0104] The following Tables 1 - 3 show the chemical structures, some properties, and hazard ratings of certain monoprotic, diprotic, and triprotic carboxylic acids sorted by their pKavalues. The inventors have evaluated these acids for (i) their ability to corrode Al and Al-alloys for the generation of H2 reaching close to 100% yield, practically above 98% yield, (ii) whether the acid is capable of substantially restoring itself after the corrosion reaction is completed, and (iii) that the reaction product is Al(OH)s instead of an aluminum salt. Acids that provide a >98% hydrogen yield and substantially restore themselves, resulting in a substantially unchanged pH, and with Al(0H)3 as reaction product are identified in Tables 1 - 3 as being suitable for the invented method.

[0105] Table 1 shows the chemical structures, some properties, and hazard ratings of certain monoprotic carboxylic acids. Glyoxylic acid is a naturally occurring compound found in plants. It can be isolated from many natural sources, including banana peels, citrus fruits, sugarcane, beets, and pineapple. Formic acid is the simplest organic acid and occurs naturally in fruits and vegetables such as pineapples, apples, kiwis, onions, eggplants, and cucumbers. Lactic acid is a natural organic acid that is formed by natural fermentation in products such as cheese, yogurt, soy sauce, meat products, pickled vegetables, beer, and wine. Gallic acid is found in many plants, including gallnuts, sumac, witch hazel, tea leaves, oak bark, grapes, and lemons. Acetic acid is a natural organic acid found in most fruits that is produced by bacterial fermentation. None of the listed monoprotic acids are suitable for the method of the invention, because they generally do not provide close to 100% yield of hydrogen when used in the corrosion reaction with Al or Al alloy.

[0106] 13

[0107] 184086148.1 Table 1. Chemical structures, properties, and hazard ratings of monoprotic carboxylic acids. For NFPA ratings, H = Health, F = Flammability, R = Reactivity. Solubility limits are provided at room temperature.

[0108] Table 2 shows the chemical structures, properties, and hazard ratings of certain diprotic carboxylic acids. Oxalic acid occurs naturally in leafy vegetables such as spinach, kale, Swiss chard, and rhubarb. Malonic acid occurs naturally in various fruits, vegetables, and fungi, including citrus fruits, red beetroots, corn, scarlet beans, and mushrooms such as shiitake. Tartaric acid (an AHA) occurs naturally in a wide diversity of fruits such as grapes, bananas, tamarinds, apples, and citrus fruits. Malic acid (an AHA) is a natural acid found in, for example, apples, apricots, bananas, cherries, grapes, mangos, nectarines, oranges, papayas, pineapples, prunes, strawberries, broccoli, carrots, olives, peas, potatoes, and tomatoes. Succinic acid, also known as butanedioic acid, is naturally occurring in many foods such as broccoli, rhubarb, sugar beets, fresh meat extracts, cheeses, and sauerkraut. Glutaric acid is naturally produced in the body during the metabolism of some amino acids, including lysine and tryptophan, but is also found in green sugar beets. Adipic acid is a natural acid found in, for example, beets and sugar cane. 2,5- Furandicarboxylic acid (FDCA) can be produced by the dehydration of hexose sugars such as glucose and fructose naturally occurring in sugar cane or sugar beet, and in other fruits. Among

[0109] 14

[0110] 184086148.1 these diprotic acids, malonic, tartaric, malic, succinic, and glutaric acids are suitable media for the invented method.

[0111] Oxalic acid, adipic acid, and FDC A are not suitable media for the invented method. Oxalic acid reacts with aluminum and provides >98% H2 yield, but forms aluminum oxalate (CeAhOn), which precipitates out of the acid solution. Therefore, the acid is not self-restoring.

[0112] Adipic acid has a favorable pKai, and a solubility that, while lower than the other listed diprotic acids, should still be sufficient to be used in the invented method. However, adipic acid is unsuitable for the invented method because it does not provide efficient corrosion of aluminum (in the presence of Ga), so the attendant hydrogen generation is slow and does not approach 100% yield.

[0113] FDCA, which is an aromatic organic acid, has a very low solubility of only about 6 mM, and does not provide a hydrogen yield of >98%, but rather only about 37%.

[0114] Table 2. Chemical structures, properties, and hazard ratings of certain diprotic carboxylic acids. For NFPA ratings, H = Health, F = Flammability, R = Reactivity. Solubility limits are at room temperature

[0115] 15

[0116] 184086148.1

[0117] Table 3 shows the chemical structure, properties, and hazard rating of certain aliphatic triprotic carboxylic acids. Aconitic acid (propene- 1,2, 3 -tricarboxylic acid) accumulates in sugarcane and sweet sorghum. Citric acid is a naturally occurring organic acid found in many fruits and vegetables, with citrus fruits such as lemons and limes having the highest concentrations. Aconitic acid is not a suitable medium for the invented method as it has a very low solubility limit.

[0118] Table 3. Chemical structure, properties, and hazard rating of triprotic aliphatic organic acids. For NFPA ratings, H = Health, F = Flammability, R = Reactivity. Solubility limits are at room temperature.

[0119] C) Corrosion reactions using organic acids and Al for hydrogen generation

[0120] The inventors have discovered that aqueous solutions of certain aliphatic diprotic and triprotic carboxylic acids are especially effective corrosion media for generating hydrogen (H2) from their reaction with Al and Al alloys, in the presence of liquid Ga metal, while other diprotic, triprotic, and monoprotic carboxylic acids are ineffective and therefore not suitable. Monoprotic carboxylic acids generally react sluggishly with Al in the presence of liquid Ga metal, with variable initial corrosion reaction rates ranging from 0.002 - 0.12 dm3H2 min’1g’1Al. Moreover, the corrosion reaction of Al in monoprotic organic acids does not generate 100% yield of hydrogen.

[0121] 16

[0122] 184086148.1 On the contrary, initial corrosion rates of at least 0.14 dm3H2 min1g'1Al and close to 100% yield of H2 are achieved in corrosion reactions using certain aliphatic diprotic and triprotic carboxylic acids such as malic, tartaric, malonic, succinic, glutaric, and citric acid.

[0123] The inventors have discovered that the aluminum corrosion rate in the organic acid media is generally inversely correlated with the length of the main carbon chain and number and relative positions of OH and COOH groups on the main carbon chain, as these determine the type of aluminum complexation. In any case, Al prefers to be coordinated with three oxygen atoms as next neighbors due to its valence of 3.

[0124] In one embodiment of the invented method, a solution of a selected aliphatic diprotic or triprotic carboxylic acid with a carbon chain length of 3, 4, or 5 is used as a medium for the corrosion of aluminum or an Al alloy to generate hydrogen. Examples of such acids include malic, tartaric, malonic, succinic, glutaric, and citric acid. The inventors have discovered that certain aliphatic carboxylic acids with carbon chain lengths of 3, 4, or 5 are more favorable for chelating with Al during corrosion reactions to form stable 6-, 7-, or 8-membered intermediate ring structures, respectively. Aliphatic organic acids with carbon chain lengths greater than 5 are not capable of forming stable ring structures with Al. Moreover, such high molecular weight organic acids have severe solubility limitations in water.

[0125] In one embodiment of the invented method, an aliphatic diprotic or triprotic carboxylic acid selected from among malic, tartaric, malonic, succinic, glutaric, and citric acids is used to generate hydrogen via corrosion of aluminum.

[0126] In another embodiment of the invented method, an aliphatic diprotic carboxylic acid selected from among malic, tartaric, malonic, succinic, and glutaric acids is used to generate hydrogen via corrosion of aluminum.

[0127] In another embodiment of the invented method, an aliphatic diprotic carboxylic acid selected from among malic, tartaric, malonic, and glutaric acids is used to generate hydrogen via corrosion of aluminum.

[0128] In yet another embodiment of the invented method, a selected aliphatic diprotic or triprotic carboxylic acid that is not citric acid, is used to generate hydrogen via corrosion of aluminum.

[0129] 17

[0130] 184086148.1 Chelation is a type of coordination in which a single ligand binds to a metal with two or more donor atoms to form a ring structure. The strength of the chelation depends on the number of donor atoms, the length, and the geometry of the donor ligand. If the ligand is too short, the donors cannot reach the metal; if it is too long, the ring structure becomes too pliant and unstable. Five- and six-membered rings are the most stable. Diprotic and triprotic carboxylic acids chelate through the deprotonation of two or three carboxyl groups. A few example ring structures formed by chelation of aluminum with organic acids of various chain lengths are shown in Fig. 2(a-d).

[0131] Aluminum oxalate, formed from oxalic acid having a 2-carbon chain, comprises an extremely stable 5-member ring structure with Al3+binding to the two deprotonated oxygens as shown in Fig. 2(a). It is due to its extreme stability that aluminum-oxalate precipitates out of solution. Oxalic acid is therefore unsuitable for the invented method.

[0132] Aluminum tartrate, aluminum malate, and aluminum succinate comprise a stable 7- member ring structure by Al3+binding to two deprotonated oxygens, as shown in Fig. 2(b). The a-OH groups in malic acid and tartaric acids add extra stability to the ring structure.

[0133] Aluminum citrate forms a more complex, but stable double-ring structure as shown in Fig. 2(c).

[0134] Aluminum malonate comprises a highly stable 6-member ring structure by Al3+binding to the two deprotonated oxygens as shown in Fig. 2(d).

[0135] Aromatic carboxylic acids such as FDCA will not chelate due to steric hindrance. Monoprotic acids generally will not chelate but rather coordinate as they only have one donor group, as shown in Fig. 2(e).

[0136] Aluminum glutarate comprises an 8-member ring structure by Al3+binding to the two carboxylate oxygens (not shown).

[0137] The inventors discovered that chelation is critical for corroding the aluminum or aluminum alloy and regenerating the acid. For that reason, the monoprotic acids listed in Table 1 and the aromatic acid FDCA listed in Table 2 are not suitable for use in the invented method because they are inefficient at generating hydrogen and / or do not regenerate themselves.

[0138] To obtain high yield a suitable acid molarity needs to be used. If the molarity is too low, the acid solution will not provide sufficient free protons to corrode all aluminum; conversely, if

[0139] 18

[0140] 184086148.1 the molarity is too high, chelation will slow down and eventually stop, and precipitation will occur as gel-like films of Al(OH)s adhere to the aluminum surface inhibiting mass transfer. Moreover, a highly concentrated acid may become too viscous, which also inhibits mass transfer.

[0141] Apart from the type of acid, the initial corrosion rate for hydrogen generation generally increases with increasing concentration of the selected acid. Tn one embodiment of the invented method, the selected aliphatic diprotic or triprotic carboxylic acid has a solubility limit at room temperature of not less than 0.1 M. In another embodiment, the organic acid has a room temperature solubility limit of not less than 0.4 M.

[0142] In one embodiment of the invented method, the concentration of the selected aliphatic diprotic or triprotic carboxylic acid solution is at least 0.1 M. The rate of the corrosion reaction and attendant hydrogen generation trends higher with higher acid solution concentration. Therefore, the concentration of the acid solution is preferably not less than 0.4 M, or not less than 0.5 M, or about 1 M. Naturally, the solubility limit of the selected acid may impact the maximum possible concentration of the acid solution.

[0143] Certain acids that chelate and regenerate themselves have a relatively low solubility limit in water resulting in a slow reaction rate and / or low H2 yield. For example, under certain reaction conditions, corrosion takes about 3 hours in succinic acid at a solubility limit of 0.68 M, and 9 hours in glutaric acid at a solubility limit of 0.45-0.53 M to achieve 100% H2 yield. Hence, succinic and glutaric acids are less preferred than malic, tartaric, malonic, or citric acid with higher solubility limits and stronger chelating properties. Aconitic acid, although a triprotic acid, is not able to fully corrode aluminum due to its low solubility limit.

[0144] Reviewing the lowest protonation constants pKai of the preferred carboxylic acids, succinic and glutaric acid, and the more preferred malic, tartaric, malonic, and citric acids a pKai range of 2 to 5 is preferred, and a range of 2.5 to 4.5 is more preferred, and a range of 2.8 to 3.8 is most preferred.

[0145] From the above description of chelation, and the Examples presented below, it is evident that the formation of a stable ring structure is related to higher aluminum corrosion reaction rates, while the lack of formation of a ring structure is related to lower aluminum corrosion rates and / or less than 100% yield.

[0146] 19

[0147] 184086148.1 Conversely, if the formed ring structure is too stable, as in the case of oxalic acid, the reaction rate and yield can be high, yet oxalic acid is unsuitable as a corrosion medium in the invented method because oxalic acid is consumed during the corrosion reaction without being replenished, due to formation of the highly stable oxalate.

[0148] The change in pH of the acid solution between the beginning and the completion of the corrosion reaction with aluminum is a clear indicator of whether the acid is being regenerated or consumed. If the final pH after the reaction has not changed significantly compared with the initial pH, it means that the acid solution is relatively intact, i.e. the acid has regenerated, and can be reused for a subsequent reaction cycle. Conversely, if the final pH after the reaction has increased significantly, this is a clear sign that the acid has been largely consumed and the solution cannot be reused without adding more acid. In the case of oxalic acid, the consumption of the acid is also indicated by the formation of oxalate precipitate.

[0149] In certain embodiments of the invented method, the molar concentration or molarity of the diprotic or triprotic carboxylic acid solution, and the volume of solution, are chosen to ensure that the number of moles of acid is sufficient to generate 100% hydrogen yield upon completion of the corrosion reaction. From Equations 3 and 4 below, for a diprotic acid such as malic acid, the number of moles of acid needed to ensure 100% hydrogen yield is at least 1.5 times the number of moles of aluminum or Al alloy reagents. For a triprotic acid such as citric acid, the number of moles of acid needed to ensure 100% yield is at least 1.0 times (i.e., at least equal to) the number of moles of aluminum or Al alloy reagents. Based on the acid’s solubility and the volume of solution needed to completely immerse the aluminum, the volume of acid solution to be used is then determined. For the corrosion reactions, the acid solution is selected to function as excess reagent.

[0150] In an embodiment of the invented method, in which the chosen number of moles of diprotic or triprotic carboxylic acid is sufficient to generate 100% hydrogen yield, the acid regenerates during the reaction, and the pH will increase by not more than about 0.2 between the beginning and completion of the reaction, i.e., while hydrogen is being generated. Conversely, when an aluminum corrosion reaction causes the acid to be consumed, such as in the case of oxalic acid, the pH will increase by more than 0.2 between the beginning and end of the reaction.

[0151] 20

[0152] 184086148.1 D) Mechanism of hydrogen generation from corrosion reaction between Al and weak organic acid (for example, malic acid)

[0153] For corrosion reactions using Al in a preferred carboxylic acid solution such as malic acid (H2(Ma)), Al malate (Al2(Ma)3) is initially formed as an intermediate complex. This intermediate complex then diffuses into solution and dissolves with water to regenerate malic acid while forming Al-hydroxide (Al(0H)3) as a byproduct. The regeneration of acid substantially maintains the pH of the solution over the course of the hydrogen generating reaction. The Al-hydroxide may convert to A10(0H) and alumina (AI2O3) once it is collected and dehydrated, as shown in Fig. 3. Equations 3 - 6 summarize the mechanistic reactions.

[0154] 2A1 + 3H2(Ma) Al2(Ma)3+ 3H2(3)

[0155] Al2(Ma)3+ 6H2O 3H2(Ma) + 2A1(OH)3(4)

[0156] A1(OH)3A10(0H) + H2O (5)

[0157] 2A1(OH)3A12O3+ 3H2O (6)

[0158] The aluminum-containing precipitates after the reaction are a mixture of Al(0H)3, A10(0H), A12O3. Once dried, the collected byproduct converts mostly or entirely to AhOs. This can be confirmed by analysis using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD) phase analysis.

[0159] E) Mechanism of hydrogen generation from corrosion reaction between Al and strong organic acid (oxalic acid)

[0160] For corrosion reactions using Al in oxalic acid solution, Al oxalate is formed as a final complex that precipitates out as shown in Fig. 4. Equations 7 and 8 summarize the mechanistic reactions.

[0161] 2A1 + 3H2(Oxa) Al2(Oxa)3+ 3H2(7)

[0162] 2A1(OH)3+ 3H2(Oxa) Al2(Oxa)3+ 6H2O (8)

[0163] 21

[0164] 184086148.1 The aluminum-containing precipitate produced as a byproduct of the corrosion reaction is Al-oxalate. This is confirmed by analysis using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD) phase analysis.

[0165] F) Process Flow for Hydrogen Generation from Organic Acid Solution and Aluminum in the Presence of Gallium

[0166] Fig- 5 shows a flow chart for an exemplary batch process 100. At 101 aluminum or aluminum alloy and gallium are weighed out separately, to attain a preferred ratio, for example 10 parts of aluminum or Al alloy by weight and 90 parts of gallium by weight. The weighed aluminum or Al alloy and the weighed gallium are then mixed at a preferred temperature above the melting point of gallium, for example at 40°C.

[0167] At 102 a preferred organic acid solution is obtained or prepared having a preferred molarity, for example citric acid at 1 .0 M concentration or malic acid at 1 .0 M concentration or tartaric acid at 1.0 M concentration. At 103, the aluminum (alloy)-gallium mixture obtained at 101 is then immersed in the preferred organic acid at preferred molarity obtained at 102, and at a preferred temperature. This may be accomplished, for example, by placing the Al-Ga mixture into the acid, or by pouring the acid over the Al-Ga mixture, or by any other suitable technique. The mixture is then heated to the preferred temperature. Since gallium may take up some contaminants such as silicon or magnesium from the mixing with Al or Al alloy, the melting temperature of gallium may increase slightly and thus the temperature of the organic acid may be adjusted above the melting point of pure gallium, for example to 70° C.

[0168] Hydrogen is collected as it evolves at 104. In a batch process, once the preferred yield of hydrogen is reached, for example 99% or greater, the remaining reaction products are collected separately. This can be accomplished simply by gravity-induced sedimentation as the densities of the organic acid, aluminum hydroxide particles, and gallium are sufficiently different to enable this technique. Moreover, the acid is liquid, the aluminum hydroxide particles are solid, and the gallium is liquid, however with much higher density than the organic acid and aluminum hydroxide, so gallium collects at the bottom. At 105 the organic acid is collected and removed, at 106 gallium is collected and removed, and at 107 the aluminum hydroxide is collected and removed.

[0169] 22

[0170] 184086148.1 At 108 the molarity of collected organic acid is optionally adjusted as necessary, for example, by adding more acid to obtain a 1.0 M solution. At 109 the collected gallium is optionally refined, i.e. contaminants can be removed by a standard metallurgical refining process. After 105 and optional 108 the recovered organic acid is reused for the next batch. After 106 and optional 109 the recovered gallium is also reused for the next batch.

[0171] The above batch process can be turned into a continuous process by continuously removing reaction products, hydrogen in particular, and adding new reactants such as organic acid, aluminum or aluminum alloys, and gallium.

[0172] G) On-demand generation of hydrogen from corrosion of Al / Al alloy waste using Ga metal and organic acid

[0173] Fig- 6 illustrates a commercial model for on-demand generation of hydrogen via controlled corrosion of scrap Al / Al alloys using non-toxic organic acid.

[0174] Aluminum scrap, gallium, and non-toxic organic acid are transported to public hydrogen generation stations or small-scale household hydrogen production installations, where the aluminum scrap is converted to hydrogen by controlled corrosion reaction. This can be an effective hydrogen production and consumption model for "local production for local consumption". Furthermore, this model can utilize the supply networks of existing gas and logistics companies to create a virtuous cycle of material supply and recovery. The aluminum-hydroxide byproduct can be recovered and reused in applications such as ceramics and pharmaceuticals.

[0175] To determine if the generated rate of H2 is sufficient to fuel a mid-sized vehicle on the road, the diesel fuel model is used as a comparison.

[0176] Diesel fuel model

[0177] • It takes 2 minutes to fill a vehicle containing a 15-gallon fuel tank with Diesel (equivalent to 620 kWh)

[0178] • Assume that pumps are occupied 5% of the time

[0179] Hydrogen fuel model

[0180] • To attain the same 620 kWh energy requires 15.7 kg of H2 (High Heating Value)

[0181] 23

[0182] 184086148.1 • Targeting a similar 2-minute fill time as diesel (7.9 kg of H2 / minute)

[0183] • Assume that pumps are also occupied 5% of the time

[0184] • Assume 1kg of Al yields 112 g of H2

[0185] • Requirement: need to react 3.53 kg of Al / min to obtain 395 g of H2 / min

[0186] Thus, from the above determination, 3.53 kg of Al metal is needed to generate 395 g of hydrogen per minute for a hydrogen fuel station to obtain an efficiency equivalent to that of a diesel fuel station.

[0187] The invention is illustrated further by the following examples that are not to be construed as limiting the invention in scope to the specific procedures or products described therein.

[0188] Examples

[0189] 1. Generation of activated Al metal

[0190] Pure Al granules (for example, Al 99.7 also designated as alloy 1070) or other Al alloy particles (0.1 g) were separately weighed on a sheet of weighing paper. Liquid Ga (0.9 g) of purity > 99.0% was introduced onto the Al granules / Al alloy on the weighing paper using a syringe. The weighing paper was folded into fourths, and the metals were pressed from the outside edges to the center to keep the Ga from spilling. The Ga was continuously pressed into the Al for 24 hours at 40°C using a metal weight. A typical immersion time of Al in Ga is 16 hours (overnight), although longer immersion times can be used to generate reactive Al. The resulting Ga-Al composite, shown in Fig. 7, was dull gray in color when hardened.

[0191] This process was repeated several times with varying amounts of Ga, while keeping the amount of Al constant at 0.1 g, to obtain various Ga:Al mixtures having weight ratios between 90: 10 and 10:90, as shown in Table 4.

[0192] 2. Corrosion of Al in citric acid with varying Ga:Al ratio

[0193] Each Ga:Al composite prepared in Example 1, and pure Al granules, were reacted in turn in 1.0 M citric acid, using a reaction setup similar to that shown in Fig. 1.

[0194] 24

[0195] 184086148.1 The quantity and rate of H2 generated from each reaction using the Ga-Al composite were compared to the reaction using 0.1 g of pure Al granules without Ga. Table 4 shows the impact of varying the Ga wt.% on hydrogen generation kinetics of the corrosion reaction of Al using 1.0 M citric acid. Figs. 8, 9, and 10 show the trends in induction time (time before H2 evolution), 100% H2 yield time, and initial hydrogen generation rate respectively, as a function of Ga content in the Ga-Al immersion mix.

[0196] Table 4. Effect of Ga content on corrosion reaction kinetics of Al in 1.0 M citric acid solution. NR

[0197] = no reaction.

[0198] Combining Al with liquid Ga at increasing wt.% resulted in exponential reduction of induction time from 30 minutes to < 10 minutes at Ga content > 66 wt.%, achieving immediate hydrogen generation upon contact with the citric acid solution for the Ga:Al 90:10 wt.% composition (Fig. 8). The time to achieve 100% yield of H2 also decayed exponentially with Ga content, reaching < 1 hour at > 75 wt. % (Fig. 9).

[0199] The initial corrosion rate increased to > 0.10 dm3H2 min’1g’1Al at Ga content > 75 wt.%, with the Ga:Al 90: 10 wt.% composition achieving the highest rate of 0.25 dm3H2 min’1g’1Al (Fig. 10). Higher corrosion rates with higher Ga content are consistent with the findings of Amberchan et al. (ACS AppL Nano Mater. 2022, 5, 2636-2643) who demonstrated this trend for corrosion in water.

[0200] Typical hydrogen generation curves for reaction of Ga-Al composites (containing different wt.% of Ga metal) in 1.0 M citric acid corrosion medium are shown in Fig. 11.

[0201] The volume of hydrogen collected by water displacement was plotted as a function of corrosion reaction time. The initial corrosion rate of the reaction was calculated from the slope of the initial linear portion of the generation curve and expressed in units of dm3H2 min’1g’1Al. Using 0.1 g of Al metal and taking the theoretical volume of 136 mb of generated hydrogen as

[0202] 25

[0203] 184086148.1 100% yield, the secondary y-axis in Fig. 11 shows the yield percent over time for the Ga-Al composites with different Ga amounts.

[0204] The initial corrosion rate for hydrogen generation generally increased with smaller grain size of Al metal. This was observed for corrosion reactions of Ga-treated Al metals possessing significantly different grain sizes, one with grain size around 50 m versus Al metal possessing average grain size in the range of 5-10 pm, using citric acid as corrosion media. Fig. 12 shows the hydrogen generation profiles. While corrosion of both Al metals generates 100% stoichiometric yield of hydrogen, the Al metal with finer grains achieves 100% yield of H2 in < 5 minutes compared to 60 minutes for the Al metal possessing larger grains. Initial corrosion rates were 0.67 dm3l inin'1g'1Al versus 0.25 dm3Ho min'1g'1Al, respectively, with more than 2.5x increase in initial corrosion rate for the Al metal with finer grain size.

[0205] 3. Corrosion of Al in various organic acids

[0206] Fig. 13 plots the variation in initial reaction rate of Al corrosion in the presence of liquid gallium to generate hydrogen when reacted with different organic acid media at 1.0 M concentration. Aliphatic diprotic and triprotic acids shown in bold clearly show higher aluminum corrosion rates than monoprotic acids and, in contrast to monoprotic acids, always yield 100% H2.

[0207] The highest reaction rate was observed for corrosion of Al in 1.0 M oxalic acid, generating 1.1 dm3Ho min'1g'1Al. This can be explained by oxalic acid’s low pKai value of 1.27. However, as explained above, oxalic acid is unsuitable as it was consumed during the corrosion reaction and not regenerated.

[0208] 4. Corrosion reaction of Al with Ga and monoprotic organic acid solutions (Comparative)

[0209] Among the investigated classes of organic acids, it was found that the monoprotic acids generally reacted sluggishly with Al in the presence of liquid Ga metal, with variable initial corrosion reaction rates ranging from 0.002 - 0.12 dm3H2 min1g1Al. Moreover, the corrosion reaction of Al in monoprotic organic acids does not generate 100%> yield of hydrogen.

[0210] Fig. 14 shows representative hydrogen generation profiles for the reaction of 0.1 g Al without and with the use of liquid Ga metal (90: 10 Ga:Al wt.%) in aqueous lactic acid solution

[0211] 26

[0212] 184086148.1 (1.0 M). The theoretical yield of hydrogen from this quantity of Al is 136 mL, indicated as 100% yield on the graph. There was a lengthy induction period of 45 minutes prior to the generation of H2 with the lactic acid reaction. The initial reaction rate after the induction period was 0.002 dm3Tbmin'1g-1Al. The reaction yield of H2 was 75% after close to 30 h (1800 min). Pure Al without Ga showed no reaction with lactic acid.

[0213] Table 5 compares the respective initial corrosion reaction rates among different monoprotic organic acids. In addition to having low initial corrosion rates, none of the monoprotic acids realized a 100% yield of hydrogen with Al in the presence of Ga.

[0214] Table 5. Initial corrosion reaction rates for Ga-Al 90:10 wt.% composite reacting with different monoprotic organic acid solutions at 1.0 M concentration.

[0215] 5. Corrosion reaction of Al with liquid Ga and diprotic organic acid solutions

[0216] In all of the following examples 35 mL of organic acids were used for the reaction with 0.1 g Al, ALalloy or 1 g of ALGa, or ALalloy-Ga composites to keep the acid reagent well in excess for all reactions described below in order to achieve the theoretical yield of 136 mL equivalent to 100% hydrogen under STP conditions.

[0217] Succinic acid

[0218] Ga-Al composite (90: 10 wt.%) and Al granules without Ga were both separately reacted with a volume of 35 mL of 0.65 M succinic acid solution with a pH of 1.54, which was introduced into the reactor flask containing either 1.0 g of Ga-Al composite or 0.1 g of Al granules and immersed in a water bath at a constant temperature of 70°C. A magnetic stirrer was used to stir the reactor contents during the reaction.

[0219] 27

[0220] 184086148.1 Fig. 15 shows the representative H2 generation curves. Similar to the reaction of Al granules with the monoprotic organic acids, there was no generation of H2 upon reacting Al granules without Ga with succinic acid solution. In contrast, the reaction between Ga-Al composite and succinic acid generated immediate evolution of H2, with a measured initial reaction rate of 0.14 dm3H2 min'1g'1Al. This rate was higher than the initial rates previously measured for the reaction of Ga-Al composite with all investigated monoprotic organic acid solutions. The reaction generated 100% yield of H2 after -190 min, whereby the pH of the solution remained substantially unchanged, indicating that the acid was mostly restored during the reaction achieving 100% H2 yield.

[0221] Tartaric acid

[0222] H2 generation curves for the reaction between Ga-Al composite (90: 10 wt.%) and Al granules without Ga with a volume of 35 mL of 1.0 M tartaric acid solution with a pH of 1.53, which was introduced into the reactor flask containing either 1.0 g of Ga-Al composite or 0.1 g of Al granules and immersed in a water bath at a constant temperature of 70°C. A magnetic stirrer was used to stir the reactor contents during the reaction.

[0223] Fig. 16 shows the representative H2 generation curves. Al granules showed no reaction with this diprotic organic acid. The addition of liquid Ga metal to the Al granules to promote corrosion by embrittlement resulted in the instantaneous generation of H2. The measured initial reaction rate was 0.21 dm3IL min'1g'1Al. The rate with tartaric acid and Ga-Al was higher than that measured with succinic acid. The reaction between Ga-Al and tartaric acid generated 100% yield of H2 after -50 minutes, whereby the pH of the solution remained substantially unchanged, indicating that the acid was mostly restored during the reaction achieving 100% H2 yield.

[0224] Glutaric acid

[0225] Ga-Al composite (90: 10 wt.%) and Al granules without Ga were separately reacted with a volume of 35 mL of 0.45 M glutaric acid solution with a pH of 2.15, which was introduced into the reactor flask containing either 1.0 g of Ga-Al composite or 0.1 g of Al granules and immersed in a water bath at a constant temperature of 70°C. A magnetic stirrer was used to stir the reactor contents during the reaction.

[0226] 28

[0227] 184086148.1 Fig. 17 shows the representative H2 generation curves. As previously observed for the reaction of Al granules without Ga with organic acids, there was no generation of H2 upon reacting Al with glutaric acid solution. In contrast, the reaction between Ga-Al composite and glutaric acid generated immediate evolution of H2, with a measured initial reaction rate of 0.15 dm3H2 min-1g1Al. This rate was similar to the initial reaction rate measured for H2 generation using succinic acid (0.14 dm3Fb min'1g'1Al). The reaction generated 100% yield of H2 after 565 min (~9.5 h), whereby the pH of the solution remained substantially unchanged, indicating that the acid was mostly restored during the reaction achieving 100% H2 yield.

[0228] Malic acid

[0229] Ga-Al composite (90: 10 wt.%) and Al granules without Ga were separately reacted with a volume of 35 mb of 1.0 M malic acid solution with a pH of 1.80, which was introduced into the reactor flask containing either 1.0 g of Ga-Al composite or 0.1 g of Al granules and immersed in a water bath at a constant temperature of 70°C. A magnetic stirrer was used to stir the reactor contents during the reaction.

[0230] Fig. 18 plots the H2 generation curves for the reaction between Ga-Al composite and Al granules with the malic acid solution. Similar to what was previously observed with succinic, glutaric, and tartaric acids, Al without Ga does not react with malic acid to generate any H2. In contrast, the reaction between Ga-Al and malic acid generated immediate bubbling of H2, with an initial reaction rate of 0.26 dm3H2 min1g'1Al. This reaction rate was higher than the initial rate previously measured for the reaction of Ga-Al composite with 1.0 M tartaric acid (0.21 dm3H2 min'1g'1Al) and with 1.0 M succinic acid (0.14 dm3ft min'1g'1Al). Also, the reaction between Ga-Al composite and malic acid solution generated 100% yield of H2 after 115 min (~ 2 h) of reaction, whereby the pH of the solution remained substantially unchanged, indicating that the acid was mostly restored during the reaction achieving 100% H2 yield.

[0231] Oxalic acid (Comparative)

[0232] Ga-Al composite (90: 10 wt.%) and Al granules without Ga were separately reacted with a volume of 35 mb of 1.0 M oxalic acid solution with a pH of 1.20, which was introduced into the reactor flask containing either 1.0 g of Ga-Al composite or 0.1 g of Al granules and immersed in a water bath at a constant temperature of 70°C. A magnetic stirrer was used to stir the reactor

[0233] 29

[0234] 184086148.1 contents during the reaction. Fig. 19 plots the H2 generation curves for the reaction between the Ga-Al composite and Al granules with the oxalic acid solution.

[0235] Unlike the reactions with the other diprotic organic acids in which Al did not react with any of these acids to generate H2, Al without Ga reacted with oxalic acid after a 5-minute induction period to generate H2. The initial reaction rate was very slow, 0.005 dm3Ffc min'1g’1Al, which resulted in a yield of 74% of H2 after more than 11 h of reaction. The reaction between Ga-Al and oxalic acid generated immediate and rapid bubbling of H2, with an initial reaction rate of 1.1 dm3Fhmin'1g’1Al. This reaction rate was the highest measured corrosion rate among all investigated aqueous-based media, more than 3.5x higher than the initial rate measured for the reaction of Ga- Al composite with 1.0 M HC1 acid (0.3 dm3H2 min’1g’1Al). The reaction between Ga-Al composite and oxalic acid solution generated 100% yield of H2 after only 2 minutes of reaction, confirming that it was the fastest generation of H2 among all tested organic acids. However, as discussed before, aluminum-oxalate precipitated out and the pH of the reaction medium increased from 1.2 to 2.25 at the end of the reaction, indicating that the acid was not regenerated as it was with tartaric, malonic, malic, succinic, glutaric, and citric acids.

[0236] 2,5-Furaiidicarboxylic acid (Comparative)

[0237] 2,5-Furandicarboxylic acid (FDCA) is an organic aromatic chemical compound consisting of two carboxylic acid groups attached to a central furan ring. FDCA has very limited solubility in water, about 6 mM, and consequently, only very low concentrations of acid solutions can be prepared using FDCA. Al and Al 2024 alloy were each first separately reacted with liquid Ga metal as described previously (90: 10 wt.% Ga:Al). The pH of this FDCA acid solution was 1.74 as measured using a pH meter. A volume of 35 mL of 6 mM FDCA solution was added to a reactor flask containing either 1.0 g of Ga-Al composite or 1.0 g of Ga-Al 2024 composite granules and immersed in a deionized water bath at a constant temperature of 70°C.

[0238] Fig. 20 plots the H2 generation curves for reaction between Ga-Al and Ga-Al 2024 alloy composites with the FDCA acid solution. For the corrosion of Al in the presence of Ga, the initial corrosion rate in FDCA acid solution was 0.25 dm3H2 min’1g’1Al, and similar to the initial corrosion rate of 0.23 dm3IC min’1g’1Al for corrosion of Al 2024 alloy in FDCA acid solution. For both Al and Al 2024 alloy, the respective corrosion reactions in FDCA acid solution generated less than 100% yield of H2 due to the solubility limit of FDCA acid in water.

[0239] 30

[0240] 184086148.1 Table 6 compares the respective initial corrosion reaction rates among different diprotic organic acids. In contrast to corresponding reactions using monoprotic organic acid solutions, Ga- activated Al corrosion reactions using all tested diprotic organic acid solutions yielded 100% stoichiometric equivalent of hydrogen with initial corrosion rates > 0.12 dm3H2 min-1g'1Al. The very high corrosion rate of 1.1 dm3H2 min1g'1Al achieved with 1.0 M oxalic acid is due to its strong acidic nature (pKai = 1.27). Performing the Al corrosion reaction using a more dilute 0.5 M oxalic acid solution resulted in a corrosion rate of 0.25 dm3H2 min'1g'1Al. However, unlike the behavior of the suitable diprotic and triprotic organic acids, oxalic acid was consumed during the corrosion reaction and moreover the oxalic acid was not regenerated during the Al corrosion reaction.

[0241] In the case of FDCA, the solubility limit of the acid in water prevented a yield of 100% stoichiometric equivalent of hydrogen.

[0242] Table 6. Initial corrosion reaction rates for Ga-Al 90:10 wt.% composite reacting with different diprotic organic acid solutions at 1.0 M concentration.

[0243] 6. Corrosion reaction of Al with gallium and triprotic organic acid solution

[0244] Citric acid

[0245] Both Ga-Al composite (90: 10 wt.%) and Al granules without Ga were separately reacted with a volume of 35 mb 1.0 M solution of citric acid with a pH of 1.73, which was introduced into the reactor flask containing either 1.0 g of Ga-Al composite or 0.1 g of Al granules and immersed in a water bath at a constant temperature of 70°C. A magnetic stirrer was used to stir the reactor contents during the reaction. Fig. 21 shows the representative H2 generation curves. Al granules showed no reaction with the triprotic organic acid. Extending the reaction time period out to 48 h

[0246] 31

[0247] 184086148.1 did not generate any H2, indicating that the weak organic acid was not effective in promoting corrosion of the Al metal. However, once liquid Ga metal was introduced with the Al to enable corrosion by embrittlement, the reaction with citric acid proceeded instantaneously with the rapid evolution of H2. The measured initial reaction rate was 0.25 dm3H2 min’1g’1Al, which was higher than reaction rates measured for Ga-Al reacting with 0.1 M NaOH (0.22 dm3H2 min’1g’1Al) or 0.1 M KOH (0.19 dm3H2 min’1g’1Al). The reaction between Ga-Al and citric acid generated 100% yield of H2 after ~50 minutes.

[0248] Aconitic acid (Comparative)

[0249] Pure Al (A199.7) was first combined with liquid Ga metal as described previously (Ga:Al 90: 10 wt.%), and then immersed in aconitic acid solution for hydrogen generation.

[0250] Fig. 22 plots the H2 generation curve for the corrosion reaction between Ga-Al with 0.34 M aconitic acid solution. For comparison, the H2 generation curve for Al corrosion in the presence of Ga using citric acid solution is also included in the plot. The initial corrosion rate in aconitic acid solution was 0.09 dm3H2 min’1g’1Al, about 3 times lower than that measured in citric acid solution (0.25 dm3H2 min’1g’1Al). Moreover, due to the limited solubility of aconitic acid in water, the corrosion reaction with Al did not generate ~ 100% yield of H2 as is observed with citric acid solution.

[0251] 7. Corrosion reaction of Al 6xxx alloys with gallium and diprotic organic acid solutions

[0252] Two commercial aluminum 6xxx series alloys, Al 6061 and Al 6101, were obtained from McMaster Carr as rods. The chemical composition of each alloy is shown in Table 7. Al 6061 is widely used for the fabrication of automotive and aerospace parts. Al 6101 is primarily used as a lightweight and economical alternative to copper in electrical applications such as busbars.

[0253] Table 7 Chemical composition of Al 6061 and Al 6101 commercial alloys.

[0254] 32

[0255] 184086148.1 Both Al 6xxx alloys were first combined with liquid Ga metal as described previously (Ga:Al 90: 10 wt.%), then introduced into organic acid solutions for hydrogen generation.

[0256] Malic acid

[0257] A volume of 35 mb of 1.0 M malic acid solution with a pH of 1.80 was introduced into the reactor flask containing either 1.0 g of Ga-Al (90: 10) 6061 alloy composite or 0.1 g of Al 6061 alloy particles and immersed in a water bath at a constant temperature of 70°C. A magnetic stirrer was used to stir the reactor contents during the reaction. Fig. 23 plots the H2 generation curves for the reaction between Ga-Al 6061 alloy composite and Al 6061 alloy with the malic acid solution. For reference, the hydrogen generation curve obtained with Ga-Al composite is also included. Similar to what was previously observed with Al granules, Al 6061 alloy did not react with malic acid to generate any H2. In contrast, the reaction between Ga-Al 6061 alloy composite and malic acid generated immediate bubbling of H2, with an initial reaction rate of 0.43 dm3H2min-1g'1Al. This reaction rate was 1.7x higher than the initial rate previously measured for reaction of Ga-Al composite with 1.0 M malic acid (0.26 dm3H2 min-1g'1Al). Also, the reaction between Ga-Al 6061 alloy composite and malic acid solution generated 100% yield of H2 after ~ 10 minutes of reaction. This represents lOx reduction in reaction time for 100% yield compared to reaction with Ga-Al composite (100 minutes). The pH of the malic acid solution at the end of the reaction with Ga-Al 6061 alloy composite remained substantially unchanged, indicating that the acid was mostly restored during the reaction achieving 100% H2.

[0258] The malic acid reaction was repeated using 1.0 g of Ga-Al (90: 10) 6101 alloy composite. Fig. 24 plots the corresponding H2 generation curves. As before, the hydrogen generation curve obtained with Ga-Al composite is also included for reference. Like its counterpart alloy composite, the reaction between Ga-Al 6101 alloy composite and malic acid generated immediate bubbling of H2, with an initial reaction rate of 0.67 dm3H2 min'1g'1Al, or more than 50% higher corrosion rate compared with the reaction using Ga-Al 6061 alloy composite. This reaction rate was 2.6x higher than the initial rate previously measured for the reaction of Ga-Al composite with 1.0 M malic acid

[0259] (0.26 dm3H2 min'1g'1Al). The reaction between Ga-Al 6101 alloy composite and malic acid solution also generated 100% yield of H2 after ~ 10 minutes of reaction, whereby the pH of the

[0260] 33

[0261] 184086148.1 solution remained substantially unchanged, indicating that the acid was mostly restored during the reaction achieving 100% H2 yield . Like the Al alloy 6061, there was no hydrogen generated when malic acid was reacted in the presence of Al alloy 6101.

[0262] Oxalic acid (Comparative)

[0263] A volume of 35 mL of 0.5 M oxalic acid solution with a pH of 1.30 was introduced into the reactor flask containing either 1.0 g of Ga-Al 6061 alloy composite or 0.1 g of Al 6061 alloy particles and immersed in a water bath at constant temperature of 70°C. A magnetic stirrer was used to stir the reactor contents during the reaction. Fig. 25 plots the H2 generation curves for reaction between Ga-Al 6061 alloy composite and Al 6061 alloy with the oxalic acid solution. For reference, the hydrogen generation curve obtained with Ga-Al composite is also included.

[0264] Unlike the reactions between Al 6061 alloy and both malic and citric (see below) acids which generated no hydrogen, Al 6061 did react with oxalic acid to liberate a small volume (~ 10 mL) of H2. This confirms the stronger acidic nature of oxalic acid compared to malic and citric acids.

[0265] The reaction between Ga-Al 6061 alloy composite and oxalic acid generated a steep reaction curve with no induction period, producing > 80% yield of H2 after only 2 minutes of reaction. The initial rate of generation of H2 was calculated as 1.0 dm3H2min-1g'1Al. This reaction rate was 4x higher than the initial rate previously measured for the reaction of Ga-Al composite with 0.5 M oxalic acid (0.24 dm3H2 min'1g'1Al). The reaction between Ga-Al 6061 alloy composite and oxalic acid solution generated 100% yield of H2 after ~ 20 minutes of reaction, slower than the 12 minutes required for 100% yield reaction with Ga-Al composite. The pH of the oxalic acid solution at the end of the reaction with Ga-Al 6061 alloy composite was measured at 2.45. The substantial pH change of the oxalic acid medium from 1.30 at the start of the corrosion reaction to 2.45 at the end signifies consumption of a significant quantity of oxalic acid. The quantity of oxalic acid consumed during this corrosion reaction, as calculated from NaOH titration analyses, was determined to be ~ 45% of oxalic acid.

[0266] The oxalic acid reaction was repeated using 1.0 g of Ga-Al 6101 alloy composite. Fig. 26 plots the corresponding H2 generation curves. Similar to that observed with its counterpart Al 6061 alloy, Al 6101 alloy also reacted with oxalic acid to generate a small volume of H2.

[0267] 34

[0268] 184086148.1 The reaction between Ga-Al 6101 alloy composite and oxalic acid also generated a steep reaction curve without any induction period, producing > 80% yield of H2 after 3 minutes of reaction. The initial rate of generation of H2 was calculated as 0.56 dm3Ho min'1g’1Al, about 2x lower than the corresponding rate calculated for Ga-Al 6061 reaction and 2x higher than the initial rate previously measured for the reaction of Ga-Al composite with 0.5 M oxalic acid (0.24 dm3H2 min’1g’1Al). The reaction between Ga-Al 6101 alloy composite and the oxalic acid solution generated 100% yield of H2 after ~ 20 minutes of reaction. The pH of the oxalic acid solution at the end of the reaction with Ga-Al 6101 alloy composite was measured at 2.45. The substantial pH change of the oxalic acid medium from 1.30 at the start of the corrosion reaction to 2.45 at the end signifies consumption of a significant quantity of oxalic acid.

[0269] 8. Corrosion reaction of Al 6xxx alloys with gallium and triprotic organic acid solution

[0270] A volume of 35 mL of 1.0 M citric acid solution with a pH of 1.73 was introduced into the reactor flask containing either 1.0 g of Ga-Al 6061 alloy composite (Ga:Al 90: 10 wt.%) or 0.1 g of Al 6061 alloy particles and immersed in a water bath at a constant temperature of 70°C. A magnetic stirrer was used to stir the reactor contents during the reaction. Fig. 27 plots the H2 generation curves for the reaction between Ga-Al 6061 alloy composite and Al 6061 alloy with the citric acid solution. For reference, the hydrogen generation curve obtained with Ga-Al composite is also included.

[0271] As previously observed with Al granules, Al 6061 alloy did not react with citric acid to generate any H2. The reaction between Ga-Al 6061 alloy composite and citric acid generated a sigmoidal reaction curve, suggesting a 2-stage corrosion reaction mechanism, proceeding sluggishly for the first 50 minutes and generating a consistent but slow stream of H2. Then, after 50 minutes of reaction, the rate of generation of H2 progressed significantly faster at 0.10 dm3H2 min’1g’1Al. This reaction rate was still 2.5x lower than the initial rate previously measured for the reaction of Ga-Al composite with 1.0 M citric acid (0.25 dm3Fh min’1g’1Al). Despite the reduced corrosion rate, the reaction between Ga-Al 6061 alloy composite and citric acid solution generated 100% yield of H2 after ~60 minutes of reaction, and not significantly different from the 100% yield reaction time measured with Ga-Al composite (50 minutes). The pH of the citric acid solution at

[0272] 35

[0273] 184086148.1 the end of the reaction with Ga-Al 6061 alloy composite remained substantially unchanged, indicating that the acid was mostly restored during the reaction achieving 100% H2 yield.

[0274] The citric acid reaction was repeated using 1.0 g of Ga-Al 6101 alloy composite (Ga:Al 90: 10 wt.%). Fig. 28 plots the corresponding H2 generation curves. As before, the hydrogen generation curve obtained with Ga-Al composite (90: 10 wt.%) is also included for reference. Like its counterpart alloy composite, the reaction between Ga-Al 6101 alloy composite and citric acid also displayed a sigmoidal profile. The first stage of the reaction generated H2 at a slow rate. After 35 minutes, there was an increase in bubbling of H2, with an initial reaction rate of 0.16 dm3H2 min’1g’1Al, or more than 50% higher corrosion rate compared with the corresponding reaction using Ga-Al 6061 alloy composite. Still, the reaction rate was ~ 1.5x lower than the initial rate previously measured for the reaction of Ga-Al composite with 1.0 M citric acid (0.25 dm3Fhmin’1g’1Al). The reaction between Ga-Al 6101 alloy composite and citric acid solution also generated 100% yield of H2 after ~40 minutes of reaction, reaching 100% H2 yield at faster times than both Ga-Al 6061 alloy composite and Ga-Al materials. The pH of the citric acid solution at the end of the reaction with Ga-Al 6101 alloy composite was substantially unchanged, indicating no significant consumption of citric acid during the corrosion reaction. Like the Al alloy 6061, there was no hydrogen generated when Al alloy 6101 was reacted in citric acid.

[0275] 9. Corrosion reaction of Al 5xxx alloys with gallium and diprotic organic acid solutions

[0276] Two commercial aluminum 5xxx series alloys, Al 5005 and Al 5052, were obtained from Online Metals and McMaster Carr, respectively, in 0.125-in and 0.5-in thick sheet form. The chemical composition of each alloy is shown in Table 8. Aluminum alloy 5005 is a lean aluminum magnesium alloy which can be hardened by cold work, it is not heat treatable to higher strength. It has medium strength, good weldability, and good corrosion resistance in marine atmospheres. It also has low density and excellent thermal conductivity common to all aluminum alloys. It is the most commonly used grade of aluminum in sheet and plate form. Aluminum alloy 5052 has ~2% Mg alloy content and is the strongest non-heat-treatable sheet and plate in common use. Among the benefits of Al 5052 are good weldability, very good corrosion resistance against, seawater and salt spray, and high fatigue strength.

[0277] 36

[0278] 184086148.1 Table 8: Chemical composition of Al 5005 and Al 5052 commercial alloys.

[0279] The Al 5xxx alloys were first combined with liquid Ga metal as described previously (90: 10 wt.% Ga:Al), then immersed in organic acid solutions for hydrogen generation.

[0280] Malic acid

[0281] A volume of 35 mb of 1.0 M malic acid solution with a pH of 1.80 was introduced into the reactor flask containing either 1.0 g of Ga-Al (90:10) 5005 alloy composite or 1.0 g of Ga-Al (90: 10) 5052 alloy composite particles and immersed in a water bath at a constant temperature of 70°C. A magnetic stirrer was used to stir the reactor contents during the reaction.

[0282] Fig. 29 plots the H2 generation curves for the reaction between the two Ga-Al 5xxx alloy composites with 1.0 M malic acid solution. For reference, the hydrogen generation curve obtained with Ga-Al composite is also included. Similar to what was previously observed with pure Al, both Al 5xxx alloys did not react with malic acid to generate H2. The reaction between Ga-Al 5052 alloy composite and malic acid generated a steep reaction curve with no induction period, producing 100% yield of H2 after only 3 minutes of reaction. The initial rate of generation of H2 was calculated as 0.73 dm3H2 min’1g’1Al. This reaction rate was ~3x higher than the initial rate previously measured for the reaction of Ga-Al composite with 1.0 M malic acid (0.26 dm3H2min’1g’1Al). Two corrosion rates were observed for the reaction between Ga-Al 5005 alloy composite and malic acid solution. Within the first 5 minutes of the corrosion reaction, the hydrogen generation rate gradually increased to a constant high value of 0.91 dm3ftmin’1g’1Al. This was the highest measured corrosion rate among the Ga-Al 5xxx composites in malic acid, 3.5x higher initial rate than that of Ga-Al composite in malic acid. The remainder of the corrosion reaction with Ga-Al 5005 proceeded at this high rate to give 100% yield of H2 after 8 minutes. The pH remained substantially unchanged, indicating that the acid was mostly restored during the reaction achieving 100% H2 yield.

[0283] Oxalic acid (Comparative)

[0284] 37

[0285] 184086148.1 A volume of 35 mL of 0.5 M oxalic acid solution with a pH of 1.30 was introduced into the reactor flask containing either 0.1 g Al 5052 granules or 1.0 g of Ga-Al (90: 10) 5052 alloy composite particles and immersed in a water bath at a constant temperature of 70°C. A magnetic stirrer was used to stir the reactor contents during the reaction.

[0286] Fig. 30 plots the H2 generation curves for the reaction between Ga-Al 5052 alloy composite and Al 5052 alloy with 0.5 M oxalic acid solution. For reference, the hydrogen generation curve obtained with pure Al is also included. Like pure Al, particles of Al 5052 alloy reacted with oxalic acid with no initial induction period to generate hydrogen. While the reactions between oxalic acid and Al and Al 5052 alloy particles both resulted in the same H2 yield of 75% over a significant accumulation time of ~15 h, the initial rate of H2 generation measured for Al 5052 alloy, 0.007 dm3H2 min'1g'1Al, was ~3x higher than the initial rate measured for Al, 0.0023 dm3H2 min'1g'1Al. The reaction between Ga-Al 5052 alloy composite and oxalic acid generated a steep reaction curve with no induction period, producing 95% yield of H2 after only 2.5 minutes. The initial rate of generation of H2 was calculated as 0.65 dm3Fk min'1g'1Al. This was ~2.7x higher than the initial rate previously measured for the reaction of Ga-Al composite with 0.5 M oxalic acid (0.24 dm3H2 min'1g'1Al). The reaction between Ga-Al 5052 alloy composite and oxalic acid solution generated 100% yield of H2 after 5 minutes, approximately 2x faster than the 12 minutes required for 100% reaction yield with Ga-Al composite. However, unlike the behavior of the suitable diprotic and triprotic organic acids, the pH increased substantially to 2.50, indicating that oxalic acid was consumed during the corrosion reaction of Al 5052 alloy and was not regenerated.

[0287] 10. Corrosion reaction of Al 5052 alloy with gallium and triprotic citric acid solution

[0288] The Al 5052 alloy was first reacted with liquid Ga metal as described previously for Al particles, then introduced into citric acid solution for hydrogen generation. A volume of 35 mL of 1 .0 M citric acid solution with a pH of 1 .74 was introduced into the reactor flask containing either 0.1 g of Al 5052 granules or 1.0 g of Ga-Al (90:10) 5052 alloy composite particles and immersed in a water bath at a constant temperature of 70°C. A magnetic stirrer was used to stir the reactor contents during the reaction.

[0289] Fig. 31 plots the H2 generation curves for the reaction between Ga-Al 5052 alloy composite and Al 5052 alloy with 1.0 M citric acid solution. For reference, the hydrogen generation curve

[0290] 38

[0291] 184086148.1 obtained with Ga-Al is also included. As seen with pure Al, Al 5052 alloy did not react with citric acid to generate any H2. The reaction between Ga-Al 5052 alloy composite and citric acid generated a steep initial reaction curve with no induction period. The initial rate of generation of H2 was calculated as 0.36 dm3H2 min'1g'1Al. This reaction rate was ~1 ,4x higher than the initial rate previously measured for the reaction of Ga-Al composite with 1.0 M citric acid (0.25 dm3H2 min'1g'1Al). Similar to the reaction with Ga-Al composite, the reaction between Ga-Al 5052 alloy composite and citric acid solution generated 100% yield of H2 after 35 minutes of reaction. The pH remained substantially unchanged, indicating that the acid was mostly restored during the reaction achieving 100% H2 yield.

[0292] 11. Corrosion reaction of Al 2xxx alloys with gallium and diprotic organic acid solutions

[0293] Commercial aluminum 2xxx series alloys Al 2011 and Al 2024 were obtained from McMaster Carr. The chemical composition of each Al 2xxx alloy is shown in Table 9.

[0294] Table 9. Chemical composition of Al 2011 and Al 2024 commercial alloys.

[0295] The Al 2xxx alloys were first reacted with liquid Ga metal as described previously for Al particles, then introduced into organic acid solutions for hydrogen generation.

[0296] Malic acid

[0297] A volume of 35 mb of 1.0 M malic acid solution with a pH of 1.8 was introduced into a reactor flask containing either 1.0 g of Ga-Al (90: 10) 2024 alloy composite particles or 1.0 g of Ga-Al (90: 10) 2011 alloy composite particles and immersed in a water bath at a constant temperature of 70°C. A magnetic stirrer was used to stir the reactor contents during the reaction.

[0298] Fig. 32 plots the H2 generation curves for reactions between the two Ga-Al 2xxx alloy composites with 1.0 M malic acid solution. For reference, the hydrogen generation curve obtained with Ga-Al composite in malic acid is also included. The initial corrosion rate for Ga-Al 2011

[0299] 39

[0300] 184086148.1 reaction in malic acid corrosion medium was faster than for both Ga-Al 2024 and Ga-Al. Both Ga- A1 2xxx alloy composites achieved 100 % yield of H2 in shorter times than the reference Ga-Al. Corrosion of Ga-Al 2024 in malic acid proceeded to yield H2 in 25 minutes, fastest among the three investigated Al species. The pH remained substantially unchanged, indicating that the acid was mostly restored during the reaction achieving 100% H2 yield.

[0301] Tartaric acid

[0302] A volume of 35 mL of 1.0 M citric acid solution with a pH of 1.53 was introduced into a reactor flask containing either 1.0 g of Ga-Al (90: 10) 2024 alloy composite particles or 1.0 g of Ga-Al (90: 10) 2011 alloy composite particles and immersed in a water bath at a constant temperature of 70°C. A magnetic stirrer was used to stir the reactor contents during the reaction.

[0303] Fig. 33 plots the H2 generation curves for reactions between the two Ga-Al 2xxx alloy composites with 1.0 M tartaric acid solution. For reference, the hydrogen generation curve obtained with Ga-Al composite is also included. As was consistently observed with other weakly acidic corrosion media, the Ga-Al 2024 composite reacted with tartaric acid to give 100 % yield of H2 in shorter time than similar reaction with Ga-Al 2011. The pH remained substantially unchanged, indicating that the acid was mostly restored during the reaction achieving 100% H2 yield.

[0304] Oxalic acid (Comparative)

[0305] A volume of 35 mL of 0.5 M oxalic acid solution with a pH of 1.3 was introduced into a reactor flask containing either 1.0 g of Ga-Al (90: 10) 2024 alloy composite particles or 1.0 g of Ga-Al (90: 10) 2011 alloy composite particles and immersed in a water bath at a constant temperature of 70°C. A magnetic stirrer was used to stir the reactor contents during the reaction.

[0306] Fig. 34 plots the H2 generation curves for reactions between the two Ga-Al 2xxx alloy composites with 0.5 M oxalic acid solution. For reference, the hydrogen generation curve obtained with Ga-Al composite is also included. There is a marked difference in H2 generation profdes between Ga-Al 2024 and 2011 composites with respect to yield time. While both show similar initial corrosion rates in oxalic acid, the time to attain 100 % yield of H2 was significantly accelerated for Ga-Al 2024 at ~20 minutes compared to >300 minutes for Ga-Al 2011. However, unlike the behavior of the suitable diprotic and triprotic organic acids, the pH increased

[0307] 40

[0308] 184086148.1 substantially to about 2.60, indicating that oxalic acid was consumed during the corrosion reaction of Al 2xxx alloys and was not regenerated.

[0309] 12. Corrosion reaction of Al 2xxx alloys with gallium and triprotic citric acid solution

[0310] The Al 2xxx alloys were first reacted with liquid Ga metal as described previously for Al particles, then introduced into 1.0 M citric acid solution for hydrogen generation. A volume of 35 mL of 1.0 M citric acid solution with a pH of 1.7 was introduced into a reactor flask containing either 1.0 g of Ga-Al (90: 10) 2024 alloy composite particles or 1.0 g of Ga-Al (90:10) 2011 alloy composite particles and immersed in a water bath at a constant temperature of 70°C. A magnetic stirrer was used to stir the reactor contents during the reaction.

[0311] Fig. 35 plots the H2 generation curves for reactions between the two Ga-Al 2xxx alloy composites with 1.0 M citric acid solution. For reference, the hydrogen generation curve obtained with the Ga-Al composite is also included. There is a marked difference in H2 generation profiles between Ga-Al 2024 and 2011 composites. While both show similar initial corrosion rates in citric acid, the time to attain 100% yield of H2 was significantly accelerated for Ga-Al 2024 at -35 minutes compared to 600 minutes for Ga-Al 2011. The yield time for Ga-Al 2024 was even faster than that measured for Ga-Al at 85 minutes. The pH remained substantially unchanged, indicating that the acid was mostly restored during the reaction achieving 100% H2 yield.

[0312] 13. Corrosion reaction of Al 7075 alloy with gallium and diprotic organic acid solutions

[0313] A high strength Al 7075 bar (1.25 in thick x 1.25 in wide) was sourced from McMaster Carr that contains -5% Zn, 2% Cu, and 2.5% Mg alloying elements (Table 10). The Al 7075 alloy was first reacted with liquid Ga metal as described previously (Ga:Al 90: 10 wt.%), then immersed in organic acid solutions for hydrogen generation.

[0314] Table 10. Composition of commercial Al 7075 alloy (wt.%'

[0315] Malic acid

[0316] 41

[0317] 184086148.1 A volume of 35 mL of 1.0 M malic acid solution with a pH of 1.8 was introduced into a reactor flask containing either 1.0 g of Ga-Al (90: 10) 7075 alloy composite particles or 1.0 g of Ga-Al (90: 10) composite particles and immersed in a water bath at a constant temperature of 70°C. A magnetic stirrer was used to stir the reactor contents during the reaction.

[0318] Fig. 36 plots the H2 generation curves for the corrosion reaction between the Ga-Al 7075 alloy composite with 1.0 M malic acid solution. For reference, the hydrogen generation curves obtained with Ga-Al 2024, Ga-Al 5052, and Ga-Al composite are also included. In the malic acid corrosion medium Ga-Al 7075 alloy composite is fully corroded to yield 100% H2 in < 10 minutes, which was 2x faster than the corresponding corrosion reaction with Ga-Al 2024 (20 minutes), but slower than the corresponding corrosion reaction with Ga-Al 5052 (3 minutes). Compared to the corrosion reaction using Ga-Al in malic acid, which took 115 minutes to attain 100% yield of H2, corrosion of Ga-Al 7075 proceeded at a lOx faster time to generate 100% yield of H2. The initial corrosion rate of Ga-Al 7075 was determined as 0.28 H2 min’1g’1Al, which was very similar to that for Ga-Al (0.26 dm3H2 min’1g’1Al). Compared to the corrosion rate of Ga-Al 2024 in malic acid (0.13 dm3H2 min’1g’1Al), the corrosion of Ga-Al 7075 proceeded at 2x higher rate, but was 2.6x lower than the measured corrosion rate for Ga-Al in the same medium (0.73 dm3H2 min’1g’ ' Al).

[0319] Tartaric acid

[0320] A volume of 35 mL of 1.0 M tartaric acid solution with a pH of 1.53 was introduced into a reactor flask containing either 1.0 g of Ga-Al (90: 10) 7075 alloy composite particles or 1.0 g of Ga-Al (90: 10) composite particles and immersed in a water bath at a constant temperature of 70°C. A magnetic stirrer was used to stir the reactor contents during the reaction.

[0321] Fig. 37 plots the H2 generation curves for the corrosion reaction between the Ga-Al 7075 alloy composite with 1.0 M tartaric acid solution. For reference, the hydrogen generation curves obtained with Ga-Al 2024, Ga-Al 5052 and Ga-Al composites (all Ga:Al 90: 10 wt.%) are included. In tartaric acid corrosion medium, Ga-Al 7075 alloy composite was fully corroded to yield 100% H2 in 14 minutes, very similar to the time to 100% yield measured for Ga-Al 2024 alloy composite (12 minutes), and faster than both Ga-Al 5052 (20 minutes) and Ga-Al (53 minutes) 100% yield times in the same acid medium. Similar to that observed in citric acid corrosion medium, the initial corrosion rate of Ga-Al 7075 at 0.4 dm3H2 min’1g’1Al was highest measured corrosion rate among

[0322] 42

[0323] 184086148.1 the investigated Al alloys with Ga; 3x higher than the initial corrosion rate calculated for Ga-Al 2024 (0.125 dm3H2 min'1g'1Al), and 1.6x higher than that for Ga-Al 5052 (0.25 dm3H2 min'1g'1Al). Compared to corrosion of Ga-Al (0.21 dm3H2 min'1g'1Al), the corrosion of Ga-Al 7075 proceeded at 2x faster rate.

[0324] Oxalic acid (Comparative)

[0325] A volume of 35 mL of 0.5 M oxalic acid solution with a pH of 1.3 was introduced into a reactor flask containing either 1.0 g of Ga-Al (90: 10) 7075 alloy composite particles or 1.0 g of Ga-Al (90: 10) composite particles and immersed in a water bath at a constant temperature of 70°C. A magnetic stirrer was used to stir the reactor contents during the reaction.

[0326] Fig. 38 plots the H2 generation curves for the corrosion reaction between the Ga-Al 7075 alloy composite with 0.5 M oxalic acid solution. For reference, the hydrogen generation curves obtained with Ga-Al 2024, Ga-Al 5052 and Ga-Al composite are also included. In oxalic acid corrosion medium Ga-Al 7075 alloy composite was fully corroded to yield 100% H2 in 60 minutes, which was the slowest among the investigated group, compared with oxalic acid corrosion of Ga- Al 2024 in 20 minutes, corrosion of Ga-Al 5052 in 5 minutes and corrosion of Ga-Al in 10 minutes to yield 100% H2. Due to the greater acidic strength of oxalic acid, the initial corrosion rate of Ga- Al 7075 was calculated at 0.77 dm3H2 min'1g'1Al which was lower than the corrosion rate measured for both Ga-Al 2024 (0.86 dm3H2 min'1g'1Al) and Ga-Al 5052 (0.91 dm3H2 min'1g'1Al) in oxalic acid. In spite of having a lower corrosion rate than the alloy composites, Ga-Al 7075 corroded at 3x higher rate than Ga-Al corrosion in the same medium (0.24 dm3H2 min'1g'1Al). However, unlike the behavior of the suitable diprotic and triprotic organic acids, the pH increased substantially to about 2.75, indicating that oxalic acid was consumed during the corrosion reaction of Al 7075 alloy and was not regenerated, and is therefore unsuitable for the invented method.

[0327] 14. Corrosion reaction of Al 7075 alloy with gallium and triprotic citric acid solution

[0328] The Al 7075 alloy was first reacted with liquid Ga metal as described previously for Al particles, then introduced into citric acid solution for hydrogen generation. A volume of 35 mL of 1.0 M citric acid solution with a pH of 1.73 was introduced into a reactor flask containing either 1.0 g of Ga-Al (90: 10) 7075 alloy composite particles or 1.0 g of Ga-Al (90: 10) composite particles

[0329] 43

[0330] 184086148.1 and immersed in a water bath at a constant temperature of 70°C. A magnetic stirrer was used to stir the reactor contents during the reaction.

[0331] Fig. 39 plots the H2 generation curve for the corrosion reaction between the Ga-Al 7075 alloy composite with 1.0 M citric acid solution. For reference, the hydrogen generation curves obtained with Ga-Al 2024, Ga-Al 5052, and Ga-Al composite are also included. In citric acid corrosion medium, Ga-Al 7075 alloy composite is fully corroded to yield 100% H2 in ~30 minutes, similar to corrosion reactions with Ga-Al 2024 (33 minutes) and Ga-Al 5052 (36 minutes), and faster than Ga-Al (60 minutes) composite materials in the same acid medium. The initial corrosion rate of Ga-Al 7075 was calculated from the slope of the initial H2 generation profile and determined as 0.49 dm3H2 min’1g’1Al. This rate was highest among the investigated Al alloys with Ga; 8x higher than the initial corrosion rate calculated for Ga-Al 2024 (0.06 dm3H2 min’1g’1Al), and 1.4x higher than that for Ga-Al 5052 (0.357 dm3H2 min’1g’1Al). Compared to corrosion of Ga-Al (0.25 dm3H2 min’1g’1Al), the corrosion of Ga-Al 7075 proceeded at 2x faster rate.

[0332] 15. Changes in pH of various carboxylic acids after aluminum corrosion reaction

[0333] Table 11 lists the initial and final pH values and the overall change in pH units for several 1.0 M diprotic and triprotic carboxylic acid solutions used to corrode aluminum (Al) in the presence of gallium (Ga) (Ga:Al 90:10 wt.%) to generate hydrogen, as described in Examples 5 and 6. Final pH values were measured after hydrogen generation had reached 100% theoretical yield. All solutions showed only a slight increase in pH (+0.05 - 0.10) with the exception of oxalic acid solution which showed a substantially larger increase from 1.20 to 2.25.

[0334] Table 11: Initial and final pH values of acid solutions used for corrosion of Al in the presence of Ga, for H2 generation.

[0335] 44

[0336] 184086148.1 The relatively small pH increase of the majority of the solutions is indicative of the acids regenerating during the corrosion reaction. These acid solutions can be reused for subsequent aluminum corrosion reactions. The large increase in pH of the oxalic acid solution indicates the acid was consumed by the reaction due to the formation and precipitation of aluminum oxalate.

[0337] Table 12 lists the initial and final pH values and the overall change in pH units for 1.0 M diprotic and triprotic carboxylic acid solutions used to corrode Al 6101 alloy in the presence of gallium (Ga) (Ga:Al 90: 10 wt.%) to generate hydrogen, as described in Examples 7 and 8. Final pH values were measured after hydrogen generation had reached 100% theoretical yield. Diprotic malic acid and triprotic citric acid solutions showed only slight increases in pH (+0.11 and +0.03, respectively), whereas oxalic acid solution showed a substantially larger pH increase from 1.30 to 2.45 (+1.15). Similar to pure Al, malic and citric acid solutions were regenerated during the corrosion reaction with Al 6101 and can be reused, but oxalic acid was consumed and formed Al oxalate precipitate during the reaction.

[0338] Table 12: Initial and final pH values of acid solutions used for corrosion of Al 6101 alloy in the presence of Ga, for H2 generation.

[0339] Table 13 lists the initial and final pH values and the overall change in pH units for 1.0 M diprotic and triprotic carboxylic acid solutions used to corrode Al 5052 alloy in the presence of gallium (Ga) (Ga:Al 90:10 wt.%) to generate hydrogen, as described in Examples 9 and 10. Final pH values were measured after hydrogen generation had reached 100% theoretical yield. Diprotic malic acid and triprotic citric acid solutions showed only slight increases in pH (+0.08 and +0.09, respectively), whereas oxalic acid solution showed a substantially larger pH increase from 1.30 to 2.50 (+1.20). Similar to pure Al, malic and citric acid solutions were regenerated during the corrosion reaction with Al 5052 and can be reused, but oxalic acid was consumed and formed Al oxalate precipitate during the reaction.

[0340] 45

[0341] 184086148.1 Table 13: Initial and final pH values of acid solutions used for corrosion of Al 5052 alloy in the presence of Ga, for H2 generation.

[0342] Table 14 lists the initial and final pH values and the overall change in pH units for 1.0 M diprotic and triprotic carboxylic acid solutions used to corrode Al 2024 alloy in the presence of gallium (Ga) (Ga:Al 90: 10 wt.%) to generate hydrogen, as described in Examples 11 and 12. Final pH values were measured after hydrogen generation had reached 100% theoretical yield. Diprotic malic and tartaric, and triprotic citric acid solutions showed only slight increases in pH (+0.11, +0.10, and +0.09, respectively), whereas oxalic acid solution showed a substantially larger pH increase from 1.30 to 2.60 (+ 1.30). Similar to pure Al, malic, tartaric, and citric acid solutions were regenerated during their corrosion reaction with Al 2024 and can be reused, but oxalic acid was consumed and formed Al oxalate precipitate during the reaction.

[0343] Table 14: Initial and final pH values of acid solutions used for corrosion of Al 2024 alloy in the presence of Ga, for H2 generation.

[0344] Table 15 lists the initial and final pH values and the overall change in pH units for 1.0 M diprotic and triprotic carboxylic acid solutions used to corrode Al 7075 alloy in the presence of gallium (Ga) (Ga:Al 90:10 wt.%) to generate hydrogen, as described in Examples 13 and 14. Final pH values were measured after hydrogen generation had reached 100% theoretical yield. Diprotic malic and tartaric, and triprotic citric acid solutions showed only slight increases in pH (+0.09, +0.10, and +0.09, respectively), whereas oxalic acid solution showed a substantially larger pH increase from 1.30 to 2.75 (+1.45). Similar to pure Al, malic, tartaric, and citric acid solutions were

[0345] 46

[0346] 184086148.1 regenerated during their corrosion reaction with Al 7075 and can be reused, but oxalic acid was consumed and formed Al oxalate precipitate during the reaction.

[0347] Table 15: Initial and final pH values of acid solutions used for corrosion of Al 7075 alloy in the presence of Ga, for H2 generation.

[0348] 16. Corrosion reaction of mixtures of Al and Al 5xxx alloys with gallium and diprotic organic acid solutions

[0349] The corrosion reactions of mixtures of pure Al (A199.7) with Al 5xxx alloys in the presence of Ga metal were performed to evaluate the effectiveness of Ga-promoted corrosion of Al mixtures using organic acids as corrosion media. The compositions are shown in Table 16.

[0350] Table 16. Al-Al 5xxx mixtures evaluated for Ga-promoted corrosion in organic acids.

[0351] Mixtures of Al and Al 5xxx alloys were first combined with liquid Ga metal as described previously (Ga:Al 90: 10 wt.%), then immersed in organic acid solutions for hydrogen generation.

[0352] Malic acid

[0353] Fig. 40 plots the H2 generation curves for the reaction between the various Al-Al 5xxx alloy mixtures with 1.0 M malic acid solution in the presence of Ga. The influence of pure Al addition to Al 5005 and Al 5052 alloys in the Ga-assisted corrosion reactions using malic acid was noticeably different. While all Al-Al 5xxx mixtures achieved 100% stoichiometric yield of H2 in the malic acid corrosion medium using Ga, the initial corrosion rates varied among the mixtures. The corrosion reaction rates for mixtures of Al-Al 5005 alloy were all higher than the

[0354] 47

[0355] 184086148.1 corresponding corrosion rates for mixtures of Al-Al 5052 alloy. The highest initial rate of ~0.4 dm3Fbmin’1g’1Al was achieved with the addition of 50 wt.% Al to Al 5005 alloy. This was 2.5x the rate measured for the corresponding 50:50 Al-Al 5052 mixture in malic acid (0.158 dm3H2 min’1g’1Al). The 75:25 and 25:75 Al-Al 5005 mixtures exhibited initial corrosion rates that were 4x and 5x higher than rates measured for corresponding mixtures of Al-Al 5052. This trend of higher reaction rates observed for mixtures of Al-Al 5005 material compared to mixtures of Al-Al 5052 in malic acid followed a similar behavior observed for Al 5005 vs. Al 5052 in citric acid, in which Al 5005 displayed the higher initial corrosion rate (0.91 vs. 0.73 dm3Homin’1g’1Al).

[0356] Tartaric acid

[0357] Fig. 41 plots the H2 generation curves for the reaction between the various Al-Al 5xxx alloy mixtures with 1.0 M tartaric acid solution in the presence of Ga. The H2 generation profiles for corrosion reactions of mixtures of Al metal with Al 5005 and Al 5052 alloys were quite similar at each investigated ratio. Each Al-Al 5xxx mixture generated 100% yield of H2 in 150 minutes or less in tartaric acid. As shown in Table 17, this was generally the fastest time measured to 100% reaction completion among all Al-Al 5xxx mixes using the three investigated organic acid corrosion media - citric acid, malic acid, and tartaric acid.

[0358] 17. Corrosion reaction of mixtures of Al and Al 5xxx alloys with gallium and triprotic citric acid solution

[0359] Mixtures of Al and Al 5xxx alloys, as shown in Table 16, were first combined with liquid Ga metal as described previously (Ga:Al 90: 10 wt.%), then immersed in citric acid solution for hydrogen generation.

[0360] Fig. 42 plots the H2 generation curves for the reaction between the various Ga-Al-Al 5xxx alloy composites with 1.0 M citric acid solution. For reference, the hydrogen generation curves obtained with the unmixed Al 5xxx alloys in citric acid are also included in each plot (green and blue profiles). The influence of pure Al addition to Al 5005 and Al 5052 alloys in the Ga-assisted corrosion reactions using citric acid was noticeably different. While all Al-Al 5xxx mixtures with Ga achieved 100% stoichiometric yield of H2 in citric acid, the initial corrosion rates varied among the mixtures. In the case of Ga-assisted corrosion of Al-Al 5005 (25:75) mixture, the highest

[0361] 48

[0362] 184086148.1 corrosion rate of

[0363] 0.6 dm3H2 min'1g'1Al occurred with the addition of 25 wt.% Al. The addition of 25 wt.% Al to Al 5005 alloy resulted in 4x higher corrosion rate than that of Al 5005 (0.147 dm3H2 min'1g'1Al). In contrast, the corrosion of Al-Al 5052 (25:75) mixture proceeded at the lowest initial rate of 0.01 dm3Fb min'1g'1Al. The addition of 25 wt.% Al to Al 5052 alloy resulted in 36x lower corrosion rate than that of Al 5052 (0.357 dm3Tb min'1g'1Al). Table 17 compares the respective times for the Al-Al 5xxx alloy mixtures to achieve 100% yield of H2 gas using different organic acid corrosion media.

[0364] Table 17: Reaction time to achieve 100% yield of H2 from mixtures of Al-Al 5xxx alloys in the presence of Ga using various organic acid solutions.

[0365] 18. Recyclability of recovered gallium

[0366] The recovery and recyclability of the Ga metal for reaction with Al particles to form Ga- A1 composite and subsequently generate hydrogen in 1.0 M citric acid solution were demonstrated. About 1.0 g of liquid Ga metal was first combined with 0. 1 g of Al granules for 24 hours at 1 atm, 40°C to form the Ga-Al (~90: 10) composite. The Ga-Al composite was then placed into 35 mb of 1.0 M citric acid solution maintained at 70°C, and the initial rate and yield of H2 generation were measured. At the end of the reaction, liquid Ga metal was recovered and reacted with a fresh batch of Al granules as before. The recovered gallium is shown in Fig. 43.

[0367] The Ga-Al composite produced from the recovered Ga metal was subsequently introduced into a fresh 1.0 M citric acid solution for additional hydrogen generation. This sequence of reactions was repeated three times. Fig. 44 shows the resulting hydrogen generation profiles from the Ga recycling experiments using 1.0 M citric acid solution as corrosion medium.

[0368] 49

[0369] 184086148.1 All hydrogen generation profiles were superimposed with similar initial reaction rate values around 0.25 dm3Ho min'1g'1Al and 100% yield of H2. These results demonstrate the recyclability of the liquid Ga metal to repeatedly generate hydrogen in citric acid solutions without loss of corrosion efficiency. The same procedure was applied to mixtures of gallium and Al 6061 alloy, and gallium and Al 6101 alloy in the same ratio of 90: 10. Similar results were observed.

[0370] Chemical analysis by X-ray fluorescence spectroscopy (XRF) was performed on the recovered gallium metal from corrosion reactions using Ga-Al, Ga-Al 6061, and Ga-Al 6101 alloy composites with organic acid to determine the purity of the recovered gallium specimens. Table 18 shows the chemical analysis results.

[0371] Table 18. Elemental analysis of samples of recovered gallium at the end of respective reactions involving Ga-Al 6061 and Ga-Al 6101 alloy composites with 0.5 M oxalic acid. Included for reference is analysis data for recovered gallium at the end of a reaction using Ga-Al composite and 0.5 M oxalic acid (Ga:Al 90: 10 wt.% for all).

[0372] The recovered metals comprise -99% Ga, followed by < 1% Al leached from the Al-based reactants. The next most abundant chemical detected in the recovered metals is phosphorus. This

[0373] 50

[0374] 184086148.1

Claims

contaminant is the second most abundant chemical impurity present in commercially available pure Ga (4 ppm). The presence of Si, Fe, and Cu in the recovered metals from both Ga-Al 6061 and Ga-Al 6101 alloy reactions most likely originates from the Al 6101 and Al 6061 alloys, while a small amount of Cr detected specifically in the recovered metal from Ga-Al 6061 reaction could account for the presence of leached Cr from Al 6061 alloy.Although several embodiments of the invention have been described in the Examples given above, those of ordinary skill in the art will appreciate that various modifications can be made without departing from the scope of the invention. Accordingly, other embodiments are within the scope of the following claims.51184086148.1What is Claimed:

1. A method of generating hydrogen, comprising the steps of(a) combining aluminum (Al) or an aluminum alloy with liquid gallium or gallium eutectic to form a compound;(b) placing the compound in contact with a solution comprising an aliphatic diprotic or triprotic carboxylic acid to corrode the aluminum or aluminum alloy, and generating hydrogen and hydrolyzed aluminum as a byproduct;(c) collecting the generated hydrogen; and(d) recovering the solution for reuse.

2. The method according to claim 1, further comprising a step (e) collecting and separating the hydrolyzed aluminum byproduct.

3. The method according to claim 1, further comprising a step (f) recovering the gallium or gallium eutectic for reuse.

4. The method according to claim 1, wherein the aliphatic diprotic or triprotic carboxylic acid is malonic, malic, tartaric, succinic, or glutaric acid.

5. The method according to claim 1, wherein the aliphatic diprotic or triprotic carboxylic acid is malic acid.

6. The method according to claim 1, wherein the aliphatic diprotic or triprotic carboxylic acid is tartaric acid.

7. The method according to claim 1, wherein the aliphatic diprotic or triprotic carboxylic acid is succinic acid.

8. The method according to claim 1, wherein the aliphatic diprotic or triprotic carboxylic acid is malonic acid.52184086148.

19. The method according to claim 1, wherein the aliphatic diprotic or triprotic carboxylic acid is glutaric acid.

10. The method according to claim 1, wherein the aliphatic diprotic or triprotic carboxylic acid is citric acid.

11. The method according to claim 1, wherein the aliphatic diprotic or triprotic carboxylic acid has a pKai between 2 and 5.

12. The method according to claim 1, wherein the aliphatic diprotic or triprotic carboxylic acid has a pKai between 2.5 and 4.5.

13. The method according to claim 1, wherein the aliphatic diprotic or triprotic carboxylic acid has a pKai between 2.8 and 3.8.

14. The method according to claim 1, wherein the aliphatic diprotic or triprotic carboxylic acid has a solubility of at least 0.1 M in water at room temperature.

15. The method according to claim 1, wherein the concentration of the aliphatic diprotic or triprotic carboxylic acid in the solution is at least 0.1 M.

16. The method according to claim 1, wherein the solution comprises an aliphatic diprotic carboxylic acid, the molar amount of the acid is at least 1.5 times that of the aluminum or aluminum alloy, and the pH of the acid solution increases by no more than 0.2 while the hydrogen is being generated.

17. The method according to claim 1, wherein the solution comprises an aliphatic triprotic carboxylic acid, the molar amount of the acid is at least 1.0 times that of the aluminum or aluminum alloy, and the pH of the acid solution increases by no more than 0.2 while the hydrogen is being generated.53184086148.

118. The method according to claim 1, wherein the aluminum is a 1070 aluminum alloy.

19. The method according to claim 1, wherein the aluminum alloy is a 2000 series alloy comprising Cu.

20. The method according to claim 1, wherein the aluminum alloy is a 5000 series alloy comprising Mg.

21. The method according to claim 1, wherein the aluminum alloy is a 6000 series alloy comprising Mg and Si.

22. The method according to claim 1, wherein the aluminum alloy is a 7000 series alloy comprising Zn.

23. The method according to claim 1, wherein the aluminum or aluminum alloy is a mixture of aluminum and aluminum alloys.

24. The method according to claim 1, wherein the aluminum is in a form of sheet, foil, bar, rod, wire, particles, irregular pieces, or any combination of these forms.

25. The method according to claim 1, wherein the aluminum comprises pure aluminum, one or more aluminum alloys, or a mixture of pure aluminum and one or more aluminum alloys.

26. The method according to claim 1, wherein the gallium is a eutectic alloy comprising gallium and one or more elements selected from the group of In and Sn.

27. The method according to claim 1, wherein the gallium content is between 10 wt.% and 95 wt.% based on the total combined weight of aluminum, aluminum alloys, and gallium.54184086148.1

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