Investigation of electrocatalytic trends of palladium-based bimetallic surfaces for formic acid oxidation in direct formic acid fuel cells

Shuozhen Hu

This work is focused on investigating the relationship between the electronic perturbation and the electrocatalytic performance for Pd-based bimetallic surfaces for formic acid oxidation (FAO) in direct formic acid fuel cells (DFAFCs). The starting point of this research was to improve the performances and reduce the cost of DFAFCs by modifying the anode materials, Pd-based catalysts. Previous studies demonstrated that combining Pd with other transition metals (TMs) could improve the electrochemical activity and stability of Pd in FAO, and improve the DFAFC performance. However, there is a lack of understanding of how these TMs interact with Pd, namely influencing their electronic structure (d-band center) and electrochemical property toward FAO. Thus, the goal of this research is to fill this knowledge gap by experimentally determining the electronic interactions between Pd and various TMs, and understanding how they influence the catalytic property of Pd towards FAO. Additionally, using non-expensive 3d TMs for the bimetallic catalyst design will reduce the required amount of Pd for DFAFCs. Thus, their fabrication cost will be significantly reduced. To achieve these goals and only focus on the electronic interactions between Pd and the additional TMs, layered Pd-based bimetallic samples were first fabricated and tested. We found that the d-band center of the layered Pd-based samples shifts away from the Fermi level either by decreasing the thickness of Pd layer deposited over TM layer or changing the substrate TMs with following order: Co < Cu < Ag < Au. Such d-band center shift resulted in a drastic increase in activity and stability for FAO, and gained a volcano-shape relationship. In the volcano-shape relationship, Pd-Cu combination provided the best activity at the d-band center of 2.7 eV. Furthermore, we proved that the layered Pd-Cu sample with 3.8 nm thickness of Pd remains Cu free surface even after annealed at 350 K and maintained high electrochemical activity towards FAO. Finally, to apply the Pd-based bimetallic surfaces in real DFAFCs, nanoparticles with both alloy and core@shell structures were synthesized. Similarly, a volcano relationship was also found. PdNiCu/C alloy shows the best activity with the d-band center of 2.64 ± 0.10 eV.

Investigation of electrocatalytic trends of palladium-based bimetallic surfaces for formic acid oxidation in direct formic acid fuel cells

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