Enhancing the Electrocatalytic Activity and Stability of Prussian Blue Analogues Through the Introduction of Au Nanoparticles in a Core@shell Heterostructure

Prussian blue analogues (PBAs) have shown to be useful as earth-abundant electrocatalysts for the Oxygen Evolution Reaction (OER) in acidic, neutral and alkaline media. Still, further improvements can be achieved by increasing their electrical conductivity. In this work, we have obtained and fully characterized a variety of monodisperse core@shell hybrid nanoparticles of Au@PBA (PBA of NiIIFeII and CoIIFeII) with different shell sizes. Their electrocatalytical activity is evaluated by studying the OER, which is compared to the pristine PBA and other Au-PBA heterostructures. It was observed that the introduction in a core@shell of 5-10 % of Au in weight leads to an increment in the electroactive mass able to be reduced or oxidized and thus, to a higher number of sites capable to take part in the OER. This larger amount of electroactive sites leads to a significant decrease in the onset potential (a reduction of the onset potential up to 100 mV and an increase up to 420 % of the current density recorded at an overpotential of 350 mV), while the Tafel slope remains unchanged, suggesting that Au reduces the limiting potential of the catalyst with no variation in the reaction kinetics. These effects are not experimented in the other Au-PBA nanostructures mainly due to the lower contact between both compounds and the oxidation of Au. Hence, an Au core activates the PBA shell and increases the conductivity of the resulting hybrid while the PBA shell prevents Au oxidation. These improvements come from the strong synergistic effect existing in the core@shell structure and evidence the importance of the chemical design for preparing PBA-based nanostructures displaying better electrocatalytic performances and higher electrochemical stabilities.