Iron-iron oxide supported palladium catalyst for the interconversion of formate and carbon dioxide

• Fe@FeO x /Pd catalyst synthesized via the successive salt reduction method. • Electronic property a major contributor for improvement of this catalyst. • Enhancement of both the eCO 2 R to formate and the FO. • Promise for the development of a single sustainable and regenerative energy source. Synthesized palladium-coated iron-iron oxide (Fe@FeO x /Pd) nanoparticles (NPs) using the successive salt reduction method are tested for their activity and stability toward formate oxidation (FO) and electrochemical CO 2 reduction to formate (eCO 2 RF). The experimental results for FO show a current density at 0.12 V vs. Ag/AgCl of 1.65 mA/cm 2 over 1 h, which is 16 times higher than that for Pd NPs. Furthermore, the same catalyst displays a higher current density with a faradaic efficiency (FE) of 95.6 % toward the eCO 2 RF, and exhibits a lower degree of CO adsorption. The iron-iron oxide interaction with the overlayer palladium is characterized by TEM/EDX, XPS/UPS, Mössbauer spectroscopy, and electrochemical techniques such as cyclic voltammetry (CV) and chronoamperometry (CA). NMR is used to estimate the amount of formate produced by the eCO 2 RF. A positive binding energy shift of the Pd 3d peak and the upshift of the d-band center as measured by XPS compared to monometallic homemade Pd NPs confirm that the electronic perturbation of the catalyst surface plays a major role in enhancing the performance of Fe@FeO x /Pd for both FO and eCO 2 RF. Furthermore, the work function as measured by UPS for the Fe@FeO x /Pd material is lower than that for monometallic Pd confirming a change in chemical properties of the catalyst surface. Finally, Mössbauer spectroscopy is used to determine the composition, structure and nature of all sites of the Fe@FeO x substrate before use and the perturbation of their intrinsic properties by the Pd overlayer. This change in intrinsic properties of the Pd coated material provides additional explanations for the electrochemical improvement measured for this catalyst toward both FO and eCO 2 RF