  Every time a chemical reaction occurs, an energy exchange between reactants
and environment exists, which is defined as the enthalpy of the reaction. In
the last decades, research has resulted in an increasing number of devices at
the micro- or nano-scale. Sensors, catalyzers, and energy storage systems are
more and more developed as nano-devices which represent the building blocks for
commercial "macroscopic" objects. A general method for the direct evaluation of
the energy balance of such systems is not available at present. Calorimetry is
a powerful tool to investigate energy exchange, but it usually needs
macroscopic sample quantities. Here we report on the development of an original
experimental setup able to detect temperature variations as low as 10 mK in a
sample of 10 ng using a thermometer device having physical dimensions of 5x5
mm2. The technique has been utilized to measure the enthalpy release during the
adsorption process of H2 on a titanium decorated monolayer graphene. The
sensitivity of these thermometers is high enough to detect a hydrogen uptake of
10^(-10) moles, corresponding to 0.2 ng, with an enthalpy release of about 23
uJ. The experimental setup allows, in perspective, the scalability to even
smaller sizes.
