Highly Active and Durable Pt-Doped Nanoporous Au-Cu Catalysts for Formic Acid Oxidation

Abstract

A substantial work has been done in the field of electrocatalysis to address all known drawbacks of Pt-based catalysts and to ultimately improve their activity and durability in the formic acid oxidation (FAO) process. Among the entertained approaches, alloying of Pt with other metals has been key for achieving better performance. Bi-metallic catalysts such as Pt-Ru, Pt-Cu, Pt-Au, Bi decorated Pt, Pt-Pd and Pt-Ag were synthesized in order to achieve better activity by suppressing the dehydration pathway. Alternatively, some researchers focused on studying the application of Pd nanoparticles or Pd based nano-alloys due to palladium’s preference for supporting oxidative formic-acid dehydrogenation to form CO2 instead of CO. However, most of Pd based catalysts feature substantially poorer durability in comparison with Pt based ones. Therefore, in order to tune the electronic surface structure of feasible alloy catalysts and obtain better overall performance, some research groups resorted to the investigation of tri-metallic catalysts like Pd-Cu-Co, Pt-Au-Ru, Pt-Pd-Cu, and Pt-Au-Cu with tunable composition.Inspired by the recent developments of de-alloying in ternary systems, we report herein on the synthesis, characterization and testing of a nanoporous (np) Au-Cu-Pt alloy catalyst with ultralow-Pt loading. Our catalyst has been synthesized by a two-step process including Cu de-alloying from previously co-electrodeposited Au0.27Cu0.70Pt0.03 alloy. As-synthesized np Au-Cu-Pt catalysts have been assessed for overall surface area by Pb underpotential deposition (PbUPD), and for Pt surface content using HUPD paralleled with CO stripping work. Scanning electron microscopy has been employed to image the morphology of as-synthesized and catalytically tested np Au-Cu-Pt films. Energy dispersive spectroscopy has been applied to confirm the synthesized alloy's atomic composition before and after catalytic testing. FAO tests have been conducted by cyclic voltammetry (CV) and chronoamperometry (CA). The CV testing provides information about the mass activity of the alloy catalyst, its overall propensity to CO poisoning and passivation with cycling. The durability of np Au-Cu-Pt catalysts has been assessed by long-term experiments including CA at constant potential (CP) and harsh potential cycling.In the main body of this talk we discuss in detail activity tests showing excellent catalytic performance of prepared catalysts manifested by more than 200 times higher mass activity than commercial Pt/GC counterparts along with remarkable durability in both harsh CV cycling and constant potential (CP) long-term tests. An unique, no-passivation cycling behavior retained for up to either 60 harsh CV cycles or 12 hours of CP testing indicates that our np Au-Cu-Pt catalysts exhibit outstanding CO-poisoning tolerance as well as unseen to date resistance to anodic passivation. Results from the testing runs have been compared critically with best performing Pt and binary Pt-alloy counterpart catalysts. The optimal electronic structure, high surface-to-volume ratio, synergistic effects, ensemble effects, strain effects, and d-band center shift are deemed responsible for the outstanding catalytic properties of the np Au-Cu-Pt catalyst developed in this work.