# Sustainable Additives for the Production of Hydrogen via Sodium Borohydride Hydrolysis
## 3 Results
### Hydrogen Generation Rates  
In order to understand NaBH4 hydrolysis, it is essential to monitor hydrogen generation over time. In this regard, this section discusses the evolution of hydrogen release in the batch reactor in the presence of the four different additives employed in the previous section and compares the results with values provided in the literature so far. Figure 2: Hydrogen generation yield (%) achieved in a batch reactor using different additives. Figure 3 depicts the evolution of hydrogen generation curves for CMC, PAM, SDS, and BCD, including the results of the control test. Figure 3a shows the pressure variation inside the reactor over time until it stabilized. According to Section 3.1, PAM offered the highest hydrogen yield, however, it also required a longer period of time until a plateau was reached. The stabilization of the pressure for PAM was seen after 4000 s, representing up to four times the stabilization time required for the rest of the additives and the control test. This suggests that this admixture could be used when low and controlled quantities of hydrogen are required. On the other hand, when CMC was added, the final pressure was obtained in the shortest time. In this case, only 300 s were required to achieve the maximum volume of hydrogen. As seen before, CMC reported a hydrogen yield of 85% (the second-best value). Consequently, considering both the release time and yield, CMC could be among the most prominent options to control NaBH\({}_{4}\) hydrolysis. The tests with SDS and the system without precursor showed similar stabilization times, 450 and 500 s, respectively. Finally, despite the bad performance provided by BCD, Figure 3 demonstrates that this additive offers rapid kinetics before stabilization of the hydrogen release (app. 300 s). Figure 3b shows the slopes of the curves, which lead to the hydrogen rates. Table 1 includes the calculated release velocities with regard to the mass of the catalyst and the comparison with results previously reported working with 10 wt% of NaBH\({}_{4}\) in the presence of NaOH and operating at room temperature, as in this work. \begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Additive**} & \multicolumn{2}{c}{**H\({}_{2}\) Rate**} & \multirow{2}{*}{**Conditions**} & \multirow{2}{*}{**Ref**} \\  & **(mL-min\({}^{-1}\).geat\({}^{-1}\))** & & \\ \hline Control & 1000 \(\pm\) 500 & 10 wt\% NaBH\({}_{4}\), 7 wt\% NaOH, 1 wt\% additive & \\  & & & Catalyst: Ni-Ru & \\ \hline CMC & 1374 \(\pm\) 40 & 10 wt\% NaBH\({}_{4}\), 7 wt\% NaOH, 1 wt\% additive & \\  & & & Catalyst: Ni-Ru & \\ \hline PAM & 721 \(\pm\) 62 & 10 wt\% NaBH\({}_{4}\), 7 wt\% NaOH, 1 wt\% additive & \\  & & & Catalyst: Ni-Ru & \\ \hline SDS & 688 \(\pm\) 66 & 10 wt\% NaBH\({}_{4}\), 7 wt\% NaOH, 1 wt\% additive & \\  & & & Catalyst: Ni-Ru & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Hydrogen generation rates. Figure 3: (**a**) Hydrogen generation plots obtained for the reaction of NaBH\({}_{4}\) hydrolysis at room temperature. \(\bullet\) Control, \(\bullet\) BCD additive, \(\bullet\) SDS additive, \(\bullet\) CMC additive, \(\bullet\) PAM additive. (**b**) Zoom of subfigure (**a**) to show slopes differences. Among the additives tested, CMC provided promising values in terms of kinetics and stability in hydrogen production, specifically 1374 \(\pm\) 40 mL\(\cdot\)min\({}^{-1}\cdot\)gcat\({}^{-1}\), showing a clear positive effect of its use for NaBH\({}_{4}\) hydrolysis. The rest of the additives offered lower generation rates in comparison to the control test. In detail, the velocity of SDS was almost half the value obtained with CMC, achieving rates of 688 \(\pm\) 66 mL\(\cdot\)min\({}^{-1}\cdot\)gcat\({}^{-1}\), but with high reproducibility (error lower than 9%). A similar trend was observed with BDC, which accomplished values of 788 \(\pm\) 120 mL\(\cdot\)min\({}^{-1}\cdot\)gcat\({}^{-1}\). In contrast, when the control test was studied, the results showed higher values of hydrogen generation rates compared to PAM, SDS, and BCD additives.