Similarly, Botti et al. have shown that by increasing NaOH concentration, the first neighboring water layer remains unaltered but the second neighboring layer contracts, which confirms that the water H-bonding network extends as the NaOH concentration increases. In these electrolytes, KOH/NaOH/RbOH dissociates to K + /Na + /Rb + and OH  ions, where they act as monovalent charge centers generating an electric field. This electric field forces polarize the water moleculesresulting in more H-bonding between them. Hence, more tetrahedrally coordinated water molecules are formed with increasing KOH/NaOH/RbOH concentrations. This has been attributed to the increase in the percentage of hydrogen-bond free water content. On the contrary, in the present study the increase in KOH concentration from 0M to 6M, results in a progressive down-field chemical shift of the NMR signal of H2O with increasing KOH concentration from 4.7 ppm (pure water) to 4.8 ppm (6 M KOH), as shown in Figure (A). According to Oka et al., the downfield shift of water proton peak can be due to strong hydrophilic interactions in water clusters. To further verify this observed 1 H NMR shift, we have performed ATR-FTIR spectroscopy was performed in electrolytes with increasing NaOH/KOH/RbOH concentration (Figure ). With increasing the concentration, the H-OH bending frequency is found to be blue-shifted from ~ 1634 cm  (for DI water) to ~ 1641 cm  (for 6 M NaOH and 6 M KOH) and ~ 1638 cm  (for 6 M RbOH), indicating that with increasing NaOH or KOH or RbOH, the H-bonding network increases as H-OH bending mode is a powerful indicator of the strength of H-bonding. Increasing the concentration of KOH results in a broadening of the -OH stretching region below 3000 cm -1 , an effect also observed in NaOH and RbOH solutions (Figure ), suggesting that the concentration of tetrahedrally coordinated water increases with increasing concentration of KOH, NaOH or RbOH. Further to check the population of different types (coordinations) of water molecules, the H-OH stretching region of ATR-FTIR spectra are deconvoluted with four gaussian peaks : namely, quasi-crystalline water ([(H 2 O) n OH]  ) (~ 3000 cm 1 ), solid-like water or tetrahedrally coordinated water (~ 3200 cm 1 ), liquid-like water or trihedrally coordinated water (~ 3400 cm 1 ) and H-bonding free water (~ 3600 cm 1 ). The population of four different types of water is shown in Table in supporting info. It is clear from Table , that in 6 M NaOH or KOH or RbOH, the populations of quasi-crystalline water and tetrahedrally coordinated water are higher than pure DI water which is in line with our ex situ Raman as well as 1 H NMR observations. The interfacial water and its structure play a significant role in HER kinetics. To check the structural changes of interfacial water with changing potential as well as changing the concentration of KOH, we have employed an in situ shell-isolated nanoparticle enhanced Raman spectroscopy (SHINERS) using thin SiO 2 coated Au nanoparticles (Figure ) drop casted over the Pt electrode. Unlike in ex situ Raman study, with in situ SHINERS, the HOH bending mode at ~ 1600 cm -1 can be seen due to the plasmon enhanced Raman scattering effect, Figure ). The vibration mode at ~1330 cm -1 is commonly observed in metals deposited on SiO 2 corresponding to Si-O stretching mode. With increasing concentration, the bending mode of water becomes more prominent. This can be attributed to the fact that with increasing KOH concentration water becomes more ordered (similar observation can be found in NaOH , Figure ). No clear effect of KOH concentration or electrode potential can be observed on the bending mode of water (Figure ). At sufficiently negative potentials, a peak, which is more intense in more concentrated solutions, appears around ~2028-2021 cm -1 (Fig. and), corresponding to the Pt-H stretching of the H adsorbed on-top on Pt, usually known as H OPD . The PtH stretch appears at a considerably lower frequency than that observed by Nichols and Bewick , and Kunimatsu et al. (~2090 cm -1 ) due to the negative shift of the potential window of water with increasingly alkaline pH. This is intense in alkaline medium as one expects a full coverage of hydrogen over Pt unlike in case of acidic medium, as discussed before and seen by others. The PtH bond is very sensitive towards the applied potential. With increasing the potential from 0.005V to 0.035V in 6M KOH, the PtH bond red shifted from ~ 2023 cm -1 to ~ 2021 cm -1 . From Figure , it is observed that with increasing potential from OCP (shown in Table ) to 0.035V, the tetrahedrally coordinated water gradually converted to trihedrally coordinated water in all the electrolytes (1 M, 3 M and 6 M KOH) but minimum effect was observed in 0.1 M KOH. Similar in situ SHINERS spectra are also observed for different concentrations of NaOH and RbOH too, as shown in Figure and S14, respectively. According to Shinagawa et al., the increment in the Tafel slope in Figure can happen not only due to the change in the rate determining step but also due to the increase in the hydrogen coverage of the catalyst during the course of the electrolysis. It is apparent from the in situ SHINERS experiments that with increasing concentration of KOH/NaOH, the H OPD peak of Pt increases. We further extended the in situ SHINERS experiment to the oxidative potential range, from OCP (shown in Table ) to 1.92 V vs RHE in 3M KOH, and the data is shown in Figure . A broad peak at around 570 cm -1 appears due to PtO x formation. With increasing the potential from OCP to 1.92 V, the PtO x formation (intensity) increases, as seen in Figure . But the corresponding water peak remains unaltered, unlike in the negative potential region. This indicates that water structure is not playing a significant role in the OER process, while PtO x formation does. The mechanism of OER alone needs further investigation and will be reported later. Nevertheless, it is evident from Figure (B) that the PtO x intensity increases as the concentration increases while the concentration or potential did not affect the structure of the water in OER process. To elucidate the experimental observations, and to check if the assumed order of water dissociation energy in three different coordination of water molecules is correct, we have calculated this quantity using first principles DFT. To the best of our knowledge, dependence of water dissociation energy on coordination of water molecules have not been calculated from first principles yet. We have considered the Pt (111) surface as the model catalyst (detailed calculation method is in supporting info).