## 3 Results and Discussion  
### Experimental Quantification of the Water Dissociation Reaction Rate  
To determine the impact of guest molecules on the water dissociation rate through chemical interactions, we studied this reaction in the presence of alcohol molecules inside the MOF as a function of temperature and time. After MOF activation, the alcohol/D\({}_{2}\)O mixture was introduced into the cell at room temperature and IR absorption spectra were subsequently recorded with the sample at 180 \({}^{\circ}\)C, monitoring the above-mentioned O-D bending vibration at \(\sim\)970 cm\({}^{-1}\), which is the product of the D\({}_{2}\)O dissociation [3]. The IR spectra were recorded until the intensity of the 970 cm\({}^{-1}\) peak stabilized. In this manner, the kinetics of methanol/D\({}_{2}\)O and isopropanol/D\({}_{2}\)O mixtures could be compared for different alcohol pressures with previously reported data with either pure D\({}_{2}\)O or inert gas/D\({}_{2}\)O mixtures [14], using the integrated area of the 970 cm\({}^{-1}\) peak as a quantification of D\({}_{2}\)O dissociation. Results with pure methanol and pure deuterated methanol are also presented for comparison in the supplementary information (see Figure S2). Figure 1a shows the representative water dissociation fingerprint at 970 cm\({}^{-1}\) after 8 h of reaction at 180 \({}^{\circ}\)C for the different mixtures analyzed inside the MOF, which is sufficient time for the reaction to stabilize in all environments. All spectra are normalized to the quantity (weight) of the MOF powder. The feature at 1003 cm\({}^{-1}\), only observed for the mixture with 8 Torr MeOH, will be discussed shortly. Figure 1b shows the kinetic evolution of the tested reactions. It is clear that water dissociation rates strongly depend on the environment: the D\({}_{2}\)O \(\rightarrow\) 2D + O reaction is faster in the presence of methanol and slower in the presence of isopropanol or inert gases such as He. Experimentally, we find that the water reaction rates inside MOF-74 are fastest to slowest as follows: 8 Torr MeOH > 4 Torr MeOH > Pure D\({}_{2}\)O > 8 Torr IPA > 950 Torr He. Table 1 reports the percent of dissociated water molecules, as compared with pure water (100%), as function of guest molecules. These data can be used to examine the dependence on the alcohol pressure, for instance in the case of methanol. The dependence is clearly not linear, but can be well fitted with a quadratic fit, \(y~{}=~{}25.5x^{2}-149.5x~{}+~{}219\), where \(y\) is the percentdissociation and \(x\) the pressure, pointing to the importance of the local environment. Indeed, water dissociation is faster when there are more MeOH molecules inside the MOF pore, i.e., when a network can be formed. Methanol is interesting, namely because of its small size that minimizes steric hindrance within the MOF pore. Different pressures of methanol were tested while keeping the D\({}_{2}\)O pressure at 8 Torr for all experiments. The infrared spectra measured after introduction of a MeOH/D\({}_{2}\)O mixture as a function of temperature and time are presented in Figure 2. After introducing a methanol/D\({}_{2}\)O mixture into Zn-MOF-74 at room temperature, the C-O stretch mode of methanol gas phase was observed at 1033 cm\({}^{-1}\) (see Figure S3). As the temperature increases, this band red-shifts to 1010 cm\({}^{-1}\) at 170 \({}^{\circ}\)C and to 1003 cm\({}^{-1}\) at 180 \({}^{\circ}\)C, which suggests a strong interaction of methanol with the MOF metal center [40]. Water dissociation only proceeds at 180 \({}^{\circ}\)C, as evidenced by the appearance of the 970 cm\({}^{-1}\) peak. At that point, the peak at 1003 cm\({}^{-1}\) weakens, indicating that C-O dissociation occurs. The synergistic dissociation of methanol and D\({}_{2}\)O results in a faster D\({}_{2}\)O dissociation reaction. In fact, the increased dissociation with MeOH pressure described earlier suggests that the presence of methanol fosters the reaction, mediated by the metal site, almost doubling the reaction yield in 8 Torr MeOH.