Changeover of the thermodynamic behavior for hydrogen storage in Rh with increasing nanoparticle size

We first report the hydrogen storage properties of Rh nanoparticles having a diameter over 10nm and the change in the temperature dependences of hydrogen storage based on particle sizes of Rh nanoparticles. Hydrogen storage was investigated by hydrogen pressurecomposition isotherm and solid-state ²HNMR measurements. We demonstrate that Rh nanoparticles with dimensions of ca. 10nm absorb hydrogen similar to smaller Rh nanoparticles; however, the enthalpy of hydrogen storage in Rh nanoparticles is changed from exothermic to endothermic with increasing particle size, with a critical size between 7.1 and 10.5 nm. The thermodynamics of hydrogen storage in Rh can be tuned by controlling the particle size.