  Comparative evaporation rate testing in the absence of solar irradiation is a
widely adopted method for establishing and characterizing a reduced
vaporization enthalpy of water within an interfacial solar evaporator. However,
the assumption of equal energy input between cases is not generally valid, and
renders this characterization method misleading. Larger evaporation rates
result from interfacial evaporators in dark conditions, mostly due to expanded
surface areas. This causes greater evaporation rates, more evaporative cooling,
and larger temperature differentials with the environment. We provide
theoretical and experimental evidence to prove that these temperature
differences cause large differences in environmental energy input, such that
equal energy input cannot be assumed. Evaluation of our data within a transient
analytical model enables quantification of the energy input differences and
calculation of the vaporization enthalpy. This shows that differences in
evaporation rate correspond to differences in energy input, and that
vaporization enthalpy is not reduced below the theoretical value. The magnitude
of increased energy input also agrees well with the increase of dark
environment evaporation rates typically reported for interfacial evaporators,
providing an alternative explanation for previous literature results. Further,
we exemplify that the results of this characterization method contradict
differential scanning calorimetry results, which are often used to make
conclusions about vaporization enthalpy reduction and water state modification
within evaporator materials. Thus, we conclude that this method should not be
used to make conclusions about vaporization enthalpy reductions within
interfacial evaporator materials. These results emphasize that the current
understanding of vaporization enthalpy reduction within evaporator materials
requires re-evaluation.
