# Perspectives of Hydrogen Generation in Cavitation-Jet Hydrodynamic Reactor
## 3 Results and Discussions
### Hydrogen from Al in Cavitation-Jet Apparatus
Reactions involving active OH radicals: \[\text{Al}+\text{H}_{2}\text{O}_{2} \rightarrow\text{Al}^{+}+\dot{\text{OH}}+\text{OH}^{-}\] \[\text{Al}^{+}+\text{H}_{2}\text{O}_{2} \rightarrow\text{Al}^{+2}+\dot{\text{OH}}+\text{OH}^{-}\] \[\text{Al}^{+2}+\text{H}_{2}\text{O}_{2} \rightarrow\text{Al}^{+3}+\dot{\text{OH}}+\text{OH}^{-}\] \[\text{Al}+3\dot{\text{OH}}+2\text{H}_{2}\text{O} \rightarrow\text{Al}(\text{OH})_{3}\downarrow+\text{H}_{2}+2\text{OH}^{-}\] 2. Reactions in alkali solution: \[ \begin{gathered} 2\text{Al}+2\text{NaOH}+6\text{H}_{2}\text{O} \rightarrow 2\text{NaAl}(\text{OH})_{4}+3\text{H}_{2}\\ 2\text{NaAl}(\text{OH})_{4}\rightarrow 2\text{NaOH}+2\text{Al}(\text{OH})_{3} \end{gathered} \]
3. Reaction in water: \[2\text{Al}+6\text{H}_{2}\text{O}\rightarrow 2\text{Al}(\text{OH})_{3}+3\text{H}_{2}\]  
These reactions directly confirm the formation of molecular hydrogen. The Na\({}^{+}\) ion acts as a catalyst, and the recovered aluminum hydroxide from the compound serves as a useful by-product, potentially used to produce hydrated sodium aluminate [29]. Electroplating aluminum with metals like copper, iron, and zinc is not feasible due to the lack of direct contact necessary to establish a potential difference. Figure 5 illustrates that raising the concentration of the four metals, which are utilized in the construction of the cavitation-jet reactor, varies with temperature over time. The data show that the highest accumulation of aluminum ions, crucial for the formation of  
molecular hydrogen, occurs during the cavitation-jet processing of demineralized water and aqueous alkaline solutions. Hydrogen production involves redox reactions with materials such as aluminum, which is used in the screw of the Venturi tube, as \(\mathrm{s}\) liquid flow splitter in the confuser, and as a reflector in the diffuser of the Laval nozzle. It has been observed that using 0.1 wt.% sodium hydroxide to generate hydrogen results in a significantly higher yield of H\({}_{2}\) compared to demineralized water. Additionally, cavitation-jet processing in both moving and stationary cavitation-jet chambers leads to the formation of various solid sediments, each with unique compositions and structures. During the cavitation-jet processing of liquids, the resulting vapor and gas mixture is condensed using a water cooler situated beyond the receiver. This dehydrated mixture subsequently flows through calcium chloride and carbon adsorbents to eliminate any remaining water vapor completely. Excess oxygen is captured using a nitrogen trap, after which the gas mixture undergoes quantitative analysis via a multi-channel gas detector and gas chromatography. Figure 6 illustrates the formation of gaseous products in a 0.1% NaOH aqueous solution during cavitation-jet processing. The primary gases formed are hydrogen, carbon monoxide, and methane. Oxygen and CO\({}_{2}\) are not accounted for, as they may originate from the environment or be present in the initial domestic hot water or NaOH solution. Moreover, the dissolution of gases in water prevents excessive numbers of cavitation nuclei and improves the conditions for bubble collapse when the temperature rises during water compression. During the CJR operation gas in the cavitation-jet chamber can leak into the discharge zone of the Laval nozzle from the surrounding air. Notably, the concentrations of hydrogen and carbon monoxide in the gas mixture increase at temperatures exceeding 55 \({}^{\circ}\)C. This rise in carbon monoxide levels may result from the reduction in carbon dioxide in the surrounding water and air. At a temperature of 75 \({}^{\circ}\)C, the cavitation of liquid methane occurs, resulting in the production and stabilization of the H\({}_{2}\) and CO content. It is important to note that the data in Figure 7 do not represent the precise quantities of these gases in the mixture, as their concentrations surpass the detection limits of the gas detector.