  Metal organic framework (MOF) materials in general, and MOF-74 in particular,
have promising properties for many technologically important processes.
However, their instability under humid conditions severely restricts practical
use. We show that this instability and the accompanying reduction of the CO$_2$
uptake capacity of MOF-74 under humid conditions originate in the water
dissociation reaction H$_2$O$\rightarrow$OH+H at the metal centers. After this
dissociation, the OH groups coordinate to the metal centers, explaining the
reduction in the MOF's CO$_2$ uptake capacity. This reduction thus strongly
depends on the catalytic activity of MOF-74 towards the water dissociation
reaction. We further show that-while the water molecules themselves only have a
negligible effect on the crystal structure of MOF-74-the OH and H products of
the dissociation reaction significantly weaken the MOF framework and lead to
the observed crystal structure breakdown. With this knowledge, we propose a way
to suppress this particular reaction by modifying the MOF-74 structure to
increase the water dissociation energy barrier and thus control the stability
of the system under humid conditions.
