An Integrated Approach to Controlling the Al/H₂O Reaction in Hydrogen Generation

Abstract

The reaction of aluminum with water is a promising method for producing hydrogen on demand for autonomous energy systems. However, its practical implementation faces the challenge of process control due to high exothermicity, leading to particle sintering and thermal instability, especially when using highly reactive nanopowders. The goal of this study is to implement an integrated approach to controlling this reaction, aimed at minimizing these risks. The approach is based on the principle of spatial and temporal distribution of reactants to ensure uniform heat release. Two process management methods were investigated: electrostatic application of aluminum powder to the reactor walls with its gradual release and pre-treatment of a nanopowder-ice mixture. Using a macrokinetic mathematical model, calculations of the conversion kinetics and heat release were performed and compared with experimental data. The results showed that both methods prevent slurry self-heating and achieve uniform hydrogen generation at a constant rate. In particular, the use of a pre-frozen mixture ensured stable hydrogen production over a long period of time without additional heating or stirring. The proposed approaches can be used in the design of safe and efficient hydrogen generators for autonomous power plants.

1. Introduction

Hydrogen is considered a key energy source for decentralized and autonomous energy systems due to its high energy density and the environmental friendliness of its combustion products [1]. However, its widespread use is hampered by problems with safe storage and transportation. In this context, the reaction of aluminum with water (Al + H₂O) is attracting increasing attention as a promising method for producing hydrogen on demand [2,3]. Aluminum is an affordable, lightweight, and energy-intensive material (the theoretical H₂ yield is 1.24 L/g), and the reaction byproduct, aluminum hydroxide, is environmentally safe and recyclable [1,4].

Despite its thermodynamic advantages, the practical implementation of the Al/H₂O reaction faces two fundamental barriers. The first is the presence of a dense oxide film on the aluminum surface, which passivates it and prevents interaction with water under normal conditions [5,6]. The second barrier, particularly relevant for highly dispersed powders, is the extremely high exothermicity and reaction rate after initiation, making the process difficult to control [7,8].

To overcome the barriers to reaction, various activation methods have been developed: the use of alkaline media (NaOH, KOH) to dissolve the oxide layer [9,10], mechanochemical activation with metal salts and oxides [11,12], alloying with low-melting metals (Ga, In, Sn) [13,14], as well as plasma and thermal treatment of particles [15,16]. These approaches successfully solve the problem of starting the reaction and achieving a high (up to 96–99%) hydrogen yield [17].

However, as rightly noted in a number of recent reviews and experimental works, the next critical challenge is process controllability [7,8,18]. The high reactivity of nanoaluminum, due to its huge specific surface area, leads to a rapid process even at room temperature [19]. The released heat (≈15.2 MJ/kg Al) can cause local overheating, water boiling, particle sintering and uneven gas evolution [20]. In the worst case, this can lead to uncontrolled acceleration of the reaction (thermal explosion) and premature termination of the reaction due to blocking of the reactants by a layer of products, which sharply reduces the yield of hydrogen [7,21]. For integration with low-temperature fuel cells (LTE-FCs), which are sensitive to fluctuations in pressure and hydrogen flow rate, a stable, predictable and adjustable gas flow, free from peak loads, is precisely what is needed [20,22]. This is critical for integration with low-temperature fuel cells, which are sensitive to even short-term pressure and flow peaks.

Thus, a contradiction arises: the material must be sufficiently active to react, yet the reaction must proceed “gently” enough to avoid thermal instability and sintering. Traditional rate control approaches, such as varying the alkali concentration or water temperature [10,23], are not always effective for highly reactive nanopowders and do not solve the problem of localized overheating. Clearly, reliable and safe generator operation requires not just an activated powder, but a comprehensive approach combining reagent preparation methods and interaction management, aimed at reducing heat generation and ensuring a uniform process.

The aim of this study is to implement an integrated approach to controlling the reaction of nanoaluminum with water, aimed at minimizing the risks of particle sintering and thermal instability. In this study, we demonstrate that a controlled reaction requires a gradual introduction of powder particles into water at a limited rate. We consider two methods for organizing the process: electrostatic powder deposition on the reactor walls with gradual release and pre-mixing of the nanopowder with ice. The common goal of these methods is the spatial and temporal distribution of the reactants to ensure uniform heat release, prevent local overheating, and achieve high hydrogen yields.

The novelty of this work lies in the transition from externally controlled reaction systems to approaches where the rate of interaction is governed by the internal structure of the reactant system itself. Unlike conventional methods based on mechanical feeding or chemical activation, the proposed strategies rely on the spatial and temporal distribution of reactants, enabling their gradual involvement in the reaction without additional hardware. This allows achieving a stable and controlled hydrogen evolution regime while maintaining high conversion efficiency. A comparison of the proposed methods with conventional approaches is presented in

Table 1. Comparison of reaction control strategies in Al/H₂O systems.

Approach	Control Principle	Implementation	Advantages	Limitations
External feeding systems (pumps, injectors)	Controlled reactant supply	Complex hardware	High controllability; stable flow; high yield	System complexity; limited portability
Chemical activation (alkali, alloys)	Increased intrinsic reactivity	Additives (NaOH, Ga, In, Sn)	Fast initiation; high conversion	Thermal instability; poor control
Electrostatic deposition (this work)	Gradual particle release from surfaces	Pre-treatment of reactor walls	Smooth hydrogen evolution; reduced overheating	Requires pre-processing
Ice pre-mixing (this work)	Phase-transition-controlled reactant availability	Pre-mixed Al + ice	Long-term stability; ΔT < 9 K; no hardware	Long initiation time (can be reduced)

.

The article presents theoretical calculations based on the developed macrokinetic mathematical model, as well as experimental results demonstrating the effectiveness of the proposed approaches compared to the traditional direct mixing scheme. The obtained data can be used in the design of hydrogen generation systems for autonomous power plants, including ground power stations for unmanned vehicles and portable energy sources.

2. Materials and Methods

2.1. Reaction of Aluminum Powder with Water

The object of the study is the reaction of aluminum powder particles with water. Aluminum reacts with water to form aluminum oxide or hydroxide.

The equation for the reaction of aluminum with water is as follows:

2Al + 6H₂O = 2Al(OH)₃ ↓ + 3H₂ ↑

(1)

According to stoichiometric calculations, the reaction of 54 g of aluminum with water produces 67.2 L of hydrogen (6 g at 0 °C and 1 atm) and 156 g of aluminum hydroxide. The oxide film prevents the interaction of aluminum with water at room temperature. However, with increasing temperature, as well as in the presence of alkalis, acids, and salts, the reaction rate increases significantly.

Aluminum nanopowder interacts with water differently from finer powders. This is due to the large surface area of the particles, their structural defects, and their accumulated energy [24]. The rate of H₂ evolution increases with the specific surface area of the aluminum powder (0.91 m²/g), which reacts significantly faster than foil (0.63 m²/g) in a NaOH/H₂O solution [8]. Finer powders with a larger initial specific surface area yield higher instantaneous rates of the Al–H₂O reaction [19].

2.2. Materials: Finely Dispersed Aluminum Powders

In this study, aluminum powders of varying degrees of dispersion, obtained by melt atomization, were used to produce hydrogen. Aluminum nanopowder, created by exploding conductors in an argon atmosphere, was also used. Distilled water, both liquid and frozen, served as oxidizers. The specific surface area of the particles was measured using the BET method based on low-temperature argon adsorption. The dispersion characteristics of the powders were determined using an OLYMPUS OMEC DC130 optical particle analyzer (Olympus Corporation, Tokyo, Japan).

The characteristic particle sizes (D₅₀) are 0.1–12.5 μm (Table 1, according to the author’s work [25]).

Table 2. Dispersion characteristics and kinetic parameters of the reaction of finely dispersed aluminum powders in water.

Brand	D50, µm	Ssp., m2/g	ti, s	αmax	n	E, kJ/mol	k, 1/s (293 K)
ASD-6	2.5	0.58	30	0.22	2.4	67	1.3 × 10−9
ASD-10	2.2	0.94	30	0.61	2.7	67	2.2 × 10−9
Alex	1.8	1.2	10	0.98	6	64	9.4 × 10−8

also presents some kinetic characteristics of the materials, and Figure 1 shows the SEM images of the particles. For aluminum nanopowder, the initiation temperature and time t_i decrease and the conversion degree increases, reaching αmax ~100%. The conversion degree increases approximately linearly with increasing specific surface area of the particles S_sp. [25]: from 0.22 for S_sp. = 0.58 m²/g to 0.98 S_sp. = 1.2 m²/g. With increasing specific surface area, the reaction rate also increases, and the temperature threshold decreases. The linear dependence of the activation energy E (kJ/mol) on the particle diameter D (μm) was approximated based on the experimental data of [26,27]: E = 0.889D + 64.552.

In this case, the observed induction period t_i should be interpreted as an apparent macroscopic parameter that depends on the rate of particle supply (V_m), rather than solely on intrinsic surface activation processes. So, in systems with distributed reactant supply, the induction period loses its purely physicochemical meaning and becomes a macrokinetic characteristic governed by heat and mass distribution in time.

Thus, aluminum nanopowder allows for maximum conversion (and hydrogen yield) when reacting with water, at lower temperatures, and even in the absence of catalysts. However, controlling this reaction poses challenges. Self-heating and particle sintering must be prevented, and a uniform reaction rate and maximum hydrogen production must be achieved.

2.3. Reaction Kinetics. Single-Stage and Gradual Introduction of Aluminum into the Reactor

The interaction of finely dispersed aluminum particles with water is an example of a topochemical reaction that occurs in a limited region at the phase boundary. The Avrami-Erofeev equation [28] is used to analyze the rate of such reactions:

$$\alpha ={\alpha }_{max}(1-\exp (-k{t}^n)),$$

(2)

where α is the degree of aluminum conversion (relative value), t is time, k is the rate constant, and n is the kinetic parameter (Table 1). The reaction rate constant depends on the temperature in accordance with the Arrhenius law and is also proportional to the specific surface area of the particles [25]:

$$k=S_{sp.}\cdot k_0\cdot \exp \left(-{\displaystyle \frac{E}{RT}}\right),$$

(3)

where R is the universal gas constant, k₀ ~ 2000 1/(s · m²).

If the powder is not loaded into the reactor with water at one time, but is fed into the volume of water gradually (using some technological method), then at each moment in time, the degree of conversion is expressed by the average integral value over time:

$${\alpha }_{av}={\displaystyle \frac{V_m}{m_{\max }}}{\displaystyle {\displaystyle \underset{0}{\overset{t}{\int }}}\alpha (t)dt}.$$

(4)

Figure 2a shows the calculated conversion rate of Alex grade nanoaluminum powder at 293 K over time, with a single loading of m_max = 9 g of powder and with gradual addition of powder to water at a rate of V_m = 0.25–0.75 g/s. With the gradual addition of powder, the reaction proceeds more smoothly, with a rate close to linear. This is preferable for practical implementation in hydrogen generators. The higher the powder feed rate, the faster and more abruptly the complete reaction of the mixture is achieved. At a rate of V_m = 0.75 g/s, the reaction dynamics are close to those corresponding to a single powder loading.

The dependence on ambient temperature is determined by the Arrhenius law (2). In the temperature range T = 283–303 K, the temperature dependence is not very pronounced (Figure 2b). However, at higher temperatures, the reaction proceeds more rapidly and begins earlier than at lower temperatures.

To ensure a uniform reaction, it is necessary to gradually introduce particles into the reaction chamber. This can be achieved, for example, by batchwise feeding of powder through the reactor wall. However, this method creates additional technological challenges, including potential reactor leaks, particle agglomeration in the feeder, and the inability to evenly distribute the particles throughout the reactor. Therefore, we will consider two other methods that allow the particles to be pre-loaded into the reactor but released gradually, reacting with water. These methods are:

• Electrostatic powder deposition on the reactor walls;
• Pre-treatment of a powder-ice mixture.

Thus, the idea is to introduce the particles into the reactor early, but gradually, rather than immediately, allowing them to react.

2.4. Experimental Setup

This study examined the reaction between aluminum powder and water using a pilot setup. The setup consists of a high-pressure reactor with a magnetic stirrer and optional heating: a TOP INDUSTRIE FR—77013 Vaux Le Penil Cedex autoclave (Top Industrie: Vaux-le-Pénil, France) (Figure 3). During the experiment, the reaction pressure and temperature were measured over time using a UT323 pyrometer and a UT-T12 type K temperature sensor. When the system pressure exceeds 25 bar, an Air Tek relief valve with a 1/2” thread and a VS1225 manual reset ring is activated.

The required amount of reagents is loaded into a reactor with a diameter of 78 mm with a volume of V_r = 0.8 L. The reactor is then connected to a magnetic stirrer. The autoclave control system monitors and controls the pressure, temperature, and stirrer speed.

The hydrogen evolution rate and the completeness of aluminum conversion (α) are estimated by measuring the reactor pressure. Under excess water conditions (i.e., when the amount exceeds the stoichiometric requirement) in a constant-volume reactor at temperature T:

$$\alpha ={\displaystyle \frac{2M_{Al}(P-P_0)V_r}{3RTm}},$$

(5)

where M_Al is the molar mass of aluminum (27 g/mol), m is the mass of the powder, and P₀ is the initial reactor pressure (atmospheric pressure). The mass of hydrogen produced is determined as follows:

$$m_{H2}={\displaystyle \frac{M_{H2}(P-P_0)V_r}{RT}}=\alpha {\displaystyle \frac{3m}{2}}{\displaystyle \frac{M_{H2}}{M_{Al}}},$$

(6)

where M_H2 is the molar mass of hydrogen. Thus, by analyzing experimental data on reactor pressure as a function of time, we can determine the conversion depth and mass of hydrogen.

3. Results

We present the results of calculations and experiments on controlling the reaction of nanoaluminum powder with water in the proposed methods.

3.1. Electrostatic Powder Deposition on Reactor Walls

To ensure that the aluminum powder reacts gradually with water, it is first applied to the reactor walls using an electrostatic sprayer. This method has two key advantages:

First, electrostatic spraying breaks up agglomerates, which is especially important for powders that have been stored for a long time and have become agglomerated. The finer the powder, the more complete the reaction is.

Second, the powder particles adhere to the reactor walls due to van der Waals forces. They are gradually released from the walls, ensuring a uniform process, similar to how a gradual addition of particles to water can be controlled.

It should be emphasized that the role of electrostatic charging is not to modify the intrinsic chemical reactivity of aluminum, but to control the temporal availability of the reactive surface. The particles deposited on the reactor walls are gradually released into the liquid phase, effectively introducing a finite “feed rate” V_m into the system. As a result, the induction period (t_i) becomes a function of particle involvement kinetics rather than solely surface activation. Compared to instantaneous powder loading, this leads to a delayed but more stable onset of reaction due to the suppression of local overheating and rapid oxide layer disruption.

To implement this idea, a START-50-combi electrostatic spray gun was used. It was used to spray ASD-10 and ASD-6 powders onto the walls and bottom of the reactor. A mixture of distilled water and aluminum powder at a ratio of 100 mL of water to 9 g of powder was used as the aqueous solution. After spraying the walls, the required amount of water was added to the reactor. In a control experiment, all the powder was poured onto the bottom of the reactor. Fine powders were used for the experiment, but not Alex nanopowder, as it may ignite due to spark discharge during spraying.

Figure 4 shows the dependence of the aluminum conversion degree and temperature in the reactor on time. The calculation was performed according to Equations (2) and (3). The slight discrepancy between the calculated and experimental data may be due to the influence of agglomerate size, which is not taken into account in the model. These agglomerates may be wetted and separated from the wall differently than individual particles.

The calculations assumed a powder “feed” rate into the water (i.e., particle separation from the vessel walls and reaction) of V_m = 3 mg/s to ensure consistency with the experimental data. This value is a free parameter of the model but can be further estimated based on the degree of particle adhesion to the vessel walls. Thus, within ~25 min, the powder will separate from the vessel walls and enter the water, reacting to the maximum conversion. The calculated and experimental results show that the reaction proceeds somewhat more uniformly in the case of preliminary electrostatic spraying, eliminating self-heating of the suspension.

3.2. Pre-Preparation of the Powder-Ice Mixture

Another method for gradually introducing particles into the reaction is to pre-mix them with ice at temperatures below 0 °C, when aluminum does not react with water. Gradually heating the powder-ice mixture will initiate the reaction.

We will describe the experiment presented in the author’s paper [29]. Alex brand aluminum nanoparticles and frozen distilled water were used to prepare the mixture. At temperatures below zero degrees Celsius, the water was crushed into ice chips and thoroughly mixed with the aluminum nanoparticles. The ratio of water to aluminum in the mixture exceeds the stoichiometric value. This pre-treatment ensures a homogeneous mixture that can be stored for extended periods at sub-zero temperatures without changing the properties of its components or causing aggregation or sedimentation of the particles in the suspension. Using this mixture eliminates the need for additional stirring or heating.

Using pre-prepared starting materials in this manner guarantees a self-sufficient hydrogen production process. The mixture, placed in the reactor at room temperature, heats up and gradually begins to react, releasing hydrogen. There is no risk of self-heating or particle sintering. The reaction occurs gradually as the suspension heats up. It should be noted that the particles are uniformly distributed throughout the water beforehand. Using nanopowder ensures the maximum amount of hydrogen, corresponding to the volume of powder used.

Let us present a mathematical description of the process. For the reaction to begin, the ice must heat up from its initial temperature (Ti) to T_ml = 0 °C and melt. This will require a time that can be estimated as follows:

$$t_{ml}={\displaystyle \frac{{\rho }_i{V}_r}{a_t{S}_r}}{c}_i\ln {\displaystyle \frac{T_0-T_i}{T_0-T_{ml}}}+{\displaystyle \frac{Q_{ml}}{T_0-T_{ml}}},$$

(7)

where Q_ml is the heat of fusion of ice, T₀ is the ambient temperature, S_r is the heat transfer area, ρ_i is the suspension density, c_i is the heat capacity, and a_t is the heat transfer coefficient [W/(m² K)]. The oxidation reaction of the powder particles will then begin in accordance with the kinetic Equation (2). The particles will not react immediately, but gradually, as they thaw and heat up (taking into account the temperature gradient in the reactor). The gradual nature of the particles’ entry into the reaction can be tentatively determined using the particle “feed” rate V_m, as was done above when modeling particles pre-applied to the reactor walls.

It should be noted that the formation of aluminum hydroxide (Al(OH)₃) during the reaction does not lead to the development of a significant diffusion barrier under the conditions studied. Unlike conventional systems with instantaneous particle immersion, the gradual melting of ice results in progressive wetting of particles and limits the local reaction rate. As a consequence, the hydroxide layer forms slowly and remains relatively loose and permeable, without blocking access of water to the aluminum surface. In this regime, the overall process is controlled primarily by the phase transition (ice melting) and heat transfer, rather than by solid-state diffusion through the reaction products.

Since the reaction will initially proceed slowly, it is necessary to account for heat exchange with the surrounding environment throughout the entire time from the onset of natural heating of the suspension until the end of the reaction. The heat conduction equation can be written in integral form, including the term for heat input from the chemical reaction and heat exchange from the reactor walls $W=a_t{\displaystyle \frac{T_0–T}{L}},$ where L is the characteristic dimension (reactor diameter).

$$T={\displaystyle {\displaystyle \underset{0}{\overset{t}{\int }}}\left(\frac{W}{c_i{\rho }_i}+\frac{Q}{c_i}{\alpha }_{\max }k\cdot n\cdot t^{n-1}\left(1-\frac{\alpha }{{\alpha }_{\max }}\right)\right)dt}$$

(8)

where Q is the thermal effect of the reaction. Equations (2)–(4) will be solved jointly from the moment of ice melting t = t_ml, when the temperature T(t_ml) = T_ml = 0 °C.

The results of the calculation using Equation (8) and the experiment (based on data from [29]) are shown in Figure 5.

At room temperature (20 °C), the mixture, naturally heated from 0 °C, began to react after 7 h. During this time, hydrogen evolution occurred at a constant rate of approximately 1 mL/s. The rate of hydrogen evolution gradually decreased by 20–21 h, and the reaction ceased. The temperature of the mixture increased slightly during the reaction (9 K), after which it stabilized at ambient temperature. The use of a pre-prepared mixture of nanoaluminum and ice allows for uniform hydrogen generation without additional manipulations such as forced heating, stirring, or the addition of catalysts.

This method is distinguished by its simple reactor design, as it does not require external heating or stirring. It is suitable for stand-alone systems without access to external power sources. However, it does have a drawback: a long preparation time prior to reaction. This process can be accelerated by artificially heating the mixture. Furthermore, the reaction rate can be increased by using catalysts. For example, a slightly alkaline solution can be used instead of distilled water to prepare the ice.

4. Discussion

To evaluate the extent of particle sintering, the morphology of the reaction products was analyzed. While optical microscopy does not resolve nanoscale features, it is sufficient to detect macroscopic sintering and agglomeration effects. Figure 6 shows the microstructure and particle size distribution of the dried powder after reaction. The products consist of dispersed micro-sized particles (D₅₀ ≈ 2–3 μm) without the formation of large agglomerates or dense structures. This suggests that the reaction proceeds under conditions that prevent particle coalescence and sintering.

The observed morphology is consistent with the low ΔT (< 9 K) and gradual reaction regime, which suppresses thermal runaway and associated particle fusion processes. In conventional rapid reactions, sintering is driven by local overheating and partial melting at particle contacts. In the present system, such conditions are not reached due to controlled heat release.

To evaluate the predictive capability of the proposed macrokinetic model, a parametric analysis was performed for key variables, including temperature, particle size, and effective reactant supply rate. The model has been validated within the range of parameters covered by available experimental data.

The model accounts for particle size through the specific surface area and activation energy, which were determined experimentally in previous work [25]. The calculated results are consistent with experimental observations presented in this study, confirming the validity of the model across different powders.

The temperature dependence is described by the Arrhenius equation. Calculations show that increasing temperature reduces the induction period and increases the reaction rate, in agreement with known experimental trends.

The effect of reactant loading is represented through the effective particle supply rate (V_m). The results demonstrate that, under excess water conditions, the reaction regime is governed primarily by the rate of particle involvement rather than total reactant quantity.

A significant limitation of the ice pre-mixing approach is the relatively long induction period associated with natural thawing (up to several hours). This latency can be substantially reduced by applying controlled triggering methods. In particular, the addition of a small amount of alkaline solution at room temperature (e.g., 4 mL of 10 wt.% NaOH per 1 g of mixture) leads to rapid initiation of hydrogen evolution (within ~2 min) and complete melting of ice within several minutes. (These values were obtained in a separate set of exploratory experiments). This effect is attributed to a combination of accelerated heat input, enhanced wetting of particles, and partial removal of the oxide layer.

Importantly, due to the initially low temperature and homogeneous distribution of particles within the ice matrix, this approach does not lead to thermal runaway and preserves a relatively uniform reaction regime.

Alternatively, controlled external heating (e.g., mild heating of reactor walls to 30–40 °C) can be used to reduce thawing time while maintaining low thermal gradients.

The proposed methods can be viewed as a form of intrinsic macrokinetic control, where the reaction rate is not imposed externally but emerges from the system organization. The system behaves as a “self-regulating reactor”, in which reactant availability, heat release, and reaction rate are inherently coupled.

To place the proposed approaches in context, a comparison with conventional methods of reaction control is presented in

Table 3. Comparison of different approaches to controlling the Al/H₂O reaction.

Method	Hydrogen Yield (L/g Al)	Conversion (αmax)	Stability of H2 Evolution	Thermal Effect (ΔT)	Limiting Factor
Direct mixing (water)	0.5–1.0	0.2–0.6	Seconds–minutes (unstable)	High (>50 K)	Thermal runaway, sintering
Alkali activation (NaOH, KOH)	~1.0–1.2	0.8–0.95	Minutes (moderate stability)	High	Rapid kinetics, heat release
Alloying (Ga, In, Sn)	~1.1–1.24	0.9–1.0	Minutes	Moderate–high	Surface activation
Electrostatic deposition (this work)	~1.0–1.2	~0.9–1.0	Tens of minutes	Low	Particle release rate
Ice pre-mixing (this work)	~1.2–1.24	~0.95–1.0	Hours (quasi-constant)	<9 K	Ice melting (phase control)

. Unlike chemical activation strategies (alkali solutions or alloying), which primarily accelerate the reaction, the present approach focuses on controlling the rate of reactant interaction. This results in a fundamentally different regime characterized by low thermal gradients and long-term stability of hydrogen evolution. The conversion efficiency of the Alex nanopowder in the ice pre-mixing regime approaches unity (α ≈ 0.95–1.0), indicating that the gentle reaction conditions do not compromise the total hydrogen yield but instead ensure its more complete realization by preventing sintering and premature reaction termination.

Unlike conventional approaches that intensify the reaction, the proposed methods shift the system into a different macrokinetic regime governed by controlled reactant availability. The proposed approach decouples reactivity from reaction rate, allowing highly reactive nanopowders to be used under controlled conditions.

5. Conclusions

In this study, we propose and experimentally validate an integrated approach to controlling the highly exothermic reaction of nanoaluminum with water, aimed at overcoming key issues associated with thermal instability and particle sintering. Unlike traditional methods, which focus primarily on process initiation (e.g., mechanochemical activation or the use of alkaline media), we shifted our focus to orchestrating the interaction itself. The results confirm our initial hypothesis: to ensure process controllability and safety, not only is activated powder required, but also a spatial and temporal distribution of reactants that ensures uniform heat generation.

The study allows the following key conclusions to be drawn:

• It has been shown that the instantaneous mixing of highly dispersed aluminum with water, especially in the case of nanopowders, leads to rapid, uncontrolled heating. The proposed methods—electrostatic deposition on the reactor walls and pre-mixing with ice—allow the process to be transformed from explosive to stable and linear.
• Experimental and theoretical results (based on a macrokinetic model) confirm that the pre-freezing method ensures the most “gentle” reaction regime. Natural thawing of the mixture at room temperature ensures gradual entry of the particles into the reaction, eliminating localized overheating (the temperature increase did not exceed 9 K) and ensuring a constant gas evolution rate over many hours.
• The electrostatic spraying method, in addition to ensuring a gradual supply of reagent due to the desorption of particles from the walls, solves the important technological problem of powder disaggregation, which is especially important for materials subjected to long-term storage.

A comparison with the work of other authors, where the primary focus is on achieving maximum conversion at any cost [17,26], demonstrates a shift in research focus toward practical feasibility. Our data correlate well with the findings of recent studies [7,8,18], which point to the need for thermal control for integrating hydrogen generators with low-temperature fuel cells. The proposed approach enables achieving high hydrogen yields (characteristic of nanoaluminum), but in a form factor suitable for practical application. Thus, the proposed approach resolves the contradiction between the need for high nanopowder activity for maximum hydrogen yield and the requirement for a smooth, controlled reaction to ensure safety and stability.

The obtained results open up prospects for further research. In particular, it is of interest to study the possibility of intensifying the process in ice without losing its stability—for example, by using weakly alkaline solutions instead of distilled water or gentle external heating. Furthermore, an important area for future research is the scaling up of the proposed technical solutions and adapting them to specific types of power plants (ground power stations for drones, portable power sources), where both compactness and predictability of operation are critical.

6. Patents

Kudryashova O.B., Morozova O.N., Titov S.S. Method for obtaining hydrogen. RU Patent RU2853862C1, 17 June 2025.