Simultaneously deposited Pt-alloy nanoparticles over graphene nanoplatelets via supercritical carbon dioxide deposition for PEM fuel cells

Abstract

One of the main barriers to the commercialization of polymer electrolyte membrane fuel cell (PEMFC) systems is the cost, which is largely due to the need of platinum (Pt)-containing catalysts. In order to overcome this issue, several methods have been developed. One of them is the supported electrocatalysts prepared by combining a low cost second metal with Pt. Motivated by this idea, in this study, nano-sized Pt-M (M = Ni, Fe, Cu) binary electrocatalysts were synthesized on the graphene nanoplatelets (GNPs) via supercritical fluid deposition (SFD) technique in order to decrease the cost and increase the activity of the catalysts. Because, the unusual properties of supercritical fluids (SFs), including tunable solvent strength, high diffusivity, low viscosity, and low surface tension, offer significant advantages over conventional techniques for materials processing. In this regard, compared to the other SFs, carbon dioxide (CO2) has received much more attention due to its easy accessibility to the supercritical state, relative benignity to the environment, chemical inertness, low toxicity, low cost. The supercritical carbon dioxide (scCO2) deposition technique involves firstly the dissolution of the metal precursor onto the support material, and then conversion of the metal precursor to its metallic form by means of thermal or chemical conversion. Synthesis of supported bimetallic nanoparticles (NPs) via scCO2 can be sequentially or simultaneously. Herein, we investigated the development of Pt-M (PtCu, PtNi, PtFe) alloy NPs on GNPs by scCO2 deposition via simultaneous addition of metal precursors. Subsequently, these catalysts were characterized by employing various characterization techniques and systems such as X-Ray Diffaction (XRD), Thermogravimetric Analysis (TGA), Inductively Coupled Plasma Mass Spectrometer (ICP-MS), Transmission Electron Microscopy (TEM), Raman Spectroscopy, Cyclic Voltammetry (CV), Rotating Disk Electrode (RDE) and PEM Fuel Cell performance tests. The obtained results revealed the formation of bimetallic catalysts within the size ranges from 1.6 to 2.1 nm. Furthermore, CV results demonstrate that PtNi/GNPs catalyst exhibit significantly high catalytic activity toward the PEM fuel cell reaction in comparison with the PtFe/GNPs and PtCu/GNPs. Also, PtNi/GNPs catalyst show about 2–4 times higher durability than the PtFe/GNPs and PtCu/GNPs catalysts in the accelerated degradation tests (ADTs). All results suggested that the PtNi/GNPs catalyst has great potential for PEM fuel cell applications.