## 3 Results and Discussion
### Thermogravimetric Analysis
\(\alpha_{red}\) = 0.8: \(t_{red2-wc1}\) = 18 min, \(t_{red5-wc1}\) \(\approx\) 21,min, and \(t_{rd6-wc1}\) \(\approx\) 25 min). A similar behavior can be observed during the oxidation reactions (cf. \(\alpha_{ox}\)=0.8: \(t_{ox2-wc1}\) \(\approx\) 10 min, \(t_{ox5-wc1}\) \(\approx\) 14 min, and \(t_{ox6-wc1}\) \(\approx\) 18 min). It is also observable that samples P1 and P2 cannot reach the complete oxidation conversion of \(\alpha_{ox}\) = 1 in 60 min. In addition, the reaction kinetics of both samples P1 and P2 during the sixth redox cycle is clearly slower than those of the samples with higher water contents during the ninth redox cycle (cf. \(\alpha_{ox}\) = 0.8: \(t_{ox9-wc2}\) \(\approx\) 15 min, and \(t_{ox9-wc3}\) \(\approx\) 13 min). Thus, no further cycles have been measured for P1 and P2. In Figure 4c,d, the time-dependent conversion rates for the reduction and oxidation reactions of the samples P5, P6, and P7 (wc\({}_{2}\)) during the second, fifth, and ninth cycles are illustrated. For those samples, the conversion rates during the second and the fifth reduction cycles are approximately the same (\(\alpha_{red}\) = 0.8: \(t_{rd2-wc2}\) \(\approx\)\(t_{rd5-wc2}\) = 16 min). In case of sample P5, \(\alpha\) = 0.8 can be reached about 1 min faster during the second cycle. Between the fifth and the ninth cycle, the time needed for \(\alpha_{red}\) to reach 0.8 increases by 7 min. Additionally, for the samples P5, P6, and P7, the kinetics of the oxidation reactions were notably faster compared to the reduction reactions. Strictly speaking, the required time for the oxidation to reach \(\alpha_{ox}\) = 0.8 during the second, fifth, and ninth oxidation cycles is about 8 min, 10 min and 15 min, respectively. In comparison to samples with the water contents wc\({}_{1}\) and wc\({}_{2}\), the conversion rates of samples P8, P9, and P10 (wc\({}_{3}\) in Figure 4e,f) exhibit a smaller decrease over the nine redox cycles, which is attributed to less aging effects. During the second redox cycle, the average reaction time to reach a conversion level of 80% is about 15 min for reduction and 8 min for oxidation, respectively. The time required to achieve an 80% conversion rate during the fifth redox cycle of the reaction is about 1 min longer for the reduction and 2 min longer for the oxidation reactions. Sample P10 is, on average, 3 min slower than P8 and P9 (cf. \(\alpha_{red}\) = 0.8: \(t_{rd9-P10}\) \(\approx\) 22 min). Additionally, sample P10 cannot reach the complete conversion to \(\alpha_{red}\) = 1 in 60 min. However, during the ninth oxidation, sample P10 shows a comparable reaction behavior to P8 and P9 (\(\alpha_{ox}\) = 0.8: \(t_{ox9-P8}\) \(\approx\) 14 min, \(t_{ox9-P9}\) \(\approx\) 14 min, and \(t_{ox9-P10}\) \(\approx\) 12 min). The discussed results so far indicate that the samples with a higher water content (wc\({}_{3}\) \(\approx\) 33 wt-\(\%\)) have a higher cycle stability. To illustrate this conclusion more clearly, the conversion rates of sample P3 (wc = 21 wt-\(\%\)), P6 (wc = 27 wt.-\(\%\)), P2 (wc = 20 wt.-\(\%\)), and P9 (wc = 33 wt.-\(\%\)) are compared in Figure 5.  
In the following, the relative increase in reaction time during the redox cycles (illustrated in Figure 5) is discussed. Concerning sample P2, the time needed to reach \(\alpha\) = 0.8  
Figure 4: **(a)** Reduction of samples P1 and P2 (wc\({}_{1}\)\(\leq\) 20 wt.-\(\%\)). **(b)** Oxidation of samples P1 and P2 (wc\({}_{1}\)\(\leq\) 20 wt.-\(\%\)). **(c)** Reduction of samples P5, P6, and P7 (wc\({}_{2}\) = 26–27 wt.-\(\%\)). **(d)** Oxidation of samples P5, P6, and P7 (wc\({}_{2}\) = 26–27 wt.-\(\%\)). **(e)** Reduction of samples P8, P9, and P10 (wc\({}_{3}\) = 33 wt.-\(\%\)). **(f)** Oxidation of samples P8, P9, and P10 (wc\({}_{3}\) = 33 wt.-\(\%\)).