Experimental evidence for Pd-based structure modification of electrocatalysts with hydrogen during their chemical synthesis is still missing. Therefore, insitu X-ray diffraction (XRD) techniques were as used to investigate hydrogen insertion into the lattice of Pd nanomaterials during their preparation. It was shown that the use of NaBH4 as reducing agent led to PdHx whereas L-ascorbic acid gave Pd nanoparticles. The subsequent influence of hydrogen insertion on the catalytic properties of Pd nanostructures was demonstrated by using carbon monoxide and glucose as probing molecules. High active surface areas and catalytic activities were found for the unmodified Pd nanostructures through electrochemical studies. Notably, the reducing agent has a significant effect on the size distribution of the nanoparticles. Its use can precisely and effectively tune their catalytic properties. Consequently, the remarkable behavior uncovered herein provides new strategic routes that can be used for the preparation of Pd-based nanomaterials.