Kinetic and thermodynamic studies of hydrogen adsorption on titanate nanotubes decorated with a Prussian blue analogue

In this paper, the kinetic and thermodynamic hydrogen adsorption characteristics of a novel composite comprising TiNT decorated with the Prussian blue analogue Cd3FeIII are investigated at high pressures and different temperatures. It is shown that boundary-layer (film) diffusion does not play a limiting role in the mass transport of hydrogen inside the composite material. The diffusion coefficient and time constant at different temperatures and pressures are calculated using an intra-particle diffusion model. The results suggest that molecular diffusion dominates Knudsen diffusion in the composite material. There are clear improvements in the mass transport characteristics compared to bulk Cd3FeIII. The Gibbʹs free energy is estimated by fitting isotherm equilibrium data to the Dubinin–Astakhov model and is used to calculate the enthalpy and the entropy of adsorption. The calculated value of enthalpy is characteristic of a physisorption process and is considerably higher than the activation energy for intraparticle diffusion, suggesting that the rate-limiting step of hydrogen is not mass transport to the adsorption sites.