Water Interaction with Iron Oxides

We present a mechanistic study on the interaction of water with a well‐defined model Fe 3 O 4 (111) surface that was investigated by a combination of direct calorimetric measurements of adsorption energies, infrared vibrational spectroscopy, and calculations bases on density functional theory (DFT). We show that the adsorption energy of water (101 kJ mol −1 ) is considerably higher than all previously reported values obtained by indirect desorption‐based methods. By employing 18 O‐labeled water molecules and an Fe 3 O 4 substrate, we proved that the generally accepted simple model of water dissociation to form two individual OH groups per water molecule is not correct. DFT calculations suggest formation of a dimer, which consists of one water molecule dissociated into two OH groups and another non‐dissociated water molecule creating a thermodynamically very stable dimer‐like complex.