(7e) Synthesis, Characterization, and Electrocatalytic Activity Testing of Electrochemically Synthesized PdxGe1-x Intermetallic Alloys

Electrocatalysis offers a sustainable pathway toward decarbonizing chemical industries by enabling chemical transformations to be driven by renewable electricity. Unfortunately, many electrocatalysts exhibit either poor activity or selectivity toward the desired chemical products. Furthermore, many electrocatalysts consist of rare and expensive elements, reducing the commercial viability of many electrocatalytic processes. Thus, there is a need to develop electrocatalysts with superior intrinsic activity and reduced precious metal content. Intermetallics are a specific class of alloy that consists of electronic dissimilar metals. This electronic dissimilarity results in the formation of strong heteronuclear bonds, which in turn yields long-range structural order¹. Furthermore, these strong heteronuclear bonds also induce significant electronic modifications, the magnitude of which is a function of both the alloy formation energy and composition². Unfortunately, intermetallics are susceptible to segregation upon air exposure due to the significant differences in the oxophillicity of the constituent metals³. Recently, electrochemical methods of preparing intermetallics have been devised based on co-electrodeposition⁴. In the present work, repeated underpotential deposition of Ge onto Pd is demonstrated to yield a near-surface Pd_xGe_1-x intermetallic alloy. The incorporation of Ge into the Pd surface significantly improved the electrocatalytic activity for both CO oxidation and oxygen compared to pure Pd, despite significantly reduced the precious metal content of the surface. Subsequent characterization of the resulting near-surface intermetallic alloy suggested the near-surface intermetallic phase is likely Pd₂₅Ge₉ and that the thickness of the intermetallic layer could be directly controlled by varying the number of Ge underpotential deposition cycles. Interestingly, evidence for surface Ge enrichment was observed, indicating that the surface structure of intermetallic alloys can vary significantly from the bulk.