Controlling the synthesis of uniform electron-deficient Pd clusters for superior hydrogen production from formic acid

Abstract

Formic acid (FA) has been considered as a safe and convenient hydrogen carrier. Via an efficient catalytic process, hydrogen with the weight percentage of 4.4 wt% can be released in situ for onsite fuel cell applications. Herein, we report the coating of the surface of amino-functionalized SiO₂ by diamine-modified graphene oxide as a superior support of Pd clusters (AP-SiO₂@PDA-NGO@Pd) for robust hydrogen production from formic acid without any additives. The TOF value can reach 8274 mol_H2 mol_Pd⁻¹ h⁻¹ at 323 K and 18 625 mol_H2 mol_Pd⁻¹ h⁻¹ at 338 K with the complete conversion of FA, nearly 100% H₂ selectivity and non-detectable generation of CO, surpassing that of all the heterogeneous catalysts reported to date. Detailed experiments proved that the modification of SiO₂ and graphene oxide with chemicals containing amino groups as a catalyst support was essential for determining the morphology and chemical status of the Pd clusters. Electron-deficient Pd plays an important role in boosting the activity of the catalyst. Accordingly, DFT calculations reveal that the terminal –NH₂ of the PDA functional groups on NGO can serve as proton reservoirs with suitable binding capability towards the H* species, which promotes the dehydrogenation of the FA molecule in addition to being beneficial for H* detachment to form H₂.