Optimization of Pd–Co–M (M= Cu, Au, Ni) Catalysts for the Oxidation of Formic Acid Using Scanning Electrochemical Microscopy

Abstract

Formic acid, a versatile substance with applications as both a fuel and hydrogen storage material, emerges as a promising energy source. When utilized as a hydrogen storage material, a single liter of formic acid yields an impressive 590 liters of hydrogen gas under ambient conditions. Furthermore, as a fuel, the Direct Formic Acid Fuel Cell (DFAFC) stands out as a potential energy solution due to its elevated open-circuit voltage, low toxicity, and reduced permeability of high molecular weight membranes. Efficient catalysts play a pivotal role in enhancing the formic acid oxidation reaction, thereby diminishing the anode overpotential and amplifying the hydrogen production efficiency of DFAFC. The conventional method of manually testing each catalyst for optimal formic acid oxidation performance is both time-consuming and resource-intensive. Consequently, this study employs a substrate collection method based on a scanning electrochemical microscope (SECM) microelectrode for catalyst screening. A ternary catalyst array, primarily comprising PdCo with supplementary elements (Au, Cu, Ni), was crafted using the innovative concept of compositional assembly. The SECM facilitated the determination of the catalyst's surface morphology, energy-dispersive spectroscopy gauged the catalyst composition, and X-ray diffraction, along with X-ray photoelectron spectroscopy, confirmed the crystalline structure composition. To delve into the kinetic aspects of the catalyst for formic acid oxidation, a comprehensive analysis was carried out using cyclic voltammetry, stripping voltammetry, electrochemical impedance spectroscopy, and Tafel slope analysis. The outcomes unveiled that the optimal proportions for the ternary catalysts were Pd2Co6Au2, Pd2Co6Cu2, and Pd2Co6Ni2, with Pd2Co6Au2 exhibiting superior attributes such as lower overpotential, heightened resistance to CO poisoning, and enhanced catalytic activity for formic acid oxidation.