Hydrogen production from formic acid decomposition in the liquid phase using Pd nanoparticles supported on CNFs with different surface properties

The development of safe and efficient H-2 generation/storage materials toward a fuel-cell-based H-2 economy as a long-term solution has recently received much attention. Herein we report the development of preformed Pd nanoparticles supported on carbon nanofibers (CNFs) via sol-immobilisation and impregnation techniques as efficient catalysts for the liquid phase decomposition of formic acid to H-2. We used CNFs as the preferred choice of support and treated at three different temperatures for the deposition of Pd nanoparticles. They were thoroughly characterised using XRD, XPS, SEM-EDX, TEM, Raman spectroscopy and BET. We observed that the Pd particle size, metal exposure and CNF graphitisation grade play an important role in catalytic performance. We found that Pd/CNFs prepared by the sol-immobilisation method displayed higher catalytic performance than those prepared by the impregnation method, due to the smaller Pd particles and high Pd exposure of the catalysts prepared by the first method. Moreover, we have shown that the best results have been obtained using CNFs with a high graphitisation degree (HHT). DFT studies have been performed to gain insights into the reactivity and decomposition of formic acid along two-reaction pathways on Pd(111), Pd(011) and Pd(001) surfaces.