Sustainable Platinum Recycling through Electrochemical Dissolution of Platinum Nanoparticles from Fuel Cell Electrodes

Abstract

Recycling of the platinum group metals (PGMs) containing industrial wastes obtained from proton exchange membrane fuel cells (PEMFCs), electrolyzers, catalytic convertors and others is of high strategical importance for industrial sustainability. In this work, a highly efficient and environmentally friendly platinum recycling method through potentiodynamic cycling in dilute acidic chloride solutions is demonstrated and optimized to recover platinum from fuel cell electrodes. The process parameters such as upper and lower potential limits are optimized to be 1.6 and 0.4 V vs. RHE. Both the dilute acidic and the acid free Cl− containing electrolytes may be used for the dissolution. Moreover, parameters such as protocol reliability, quantification method and comparison, electrode interface structure, dissolution product and mechanisms etc. are discussed. A study in 1 M HCl shows Pt dissolution rates as high as ∼30 μg/cycle for potential cycling between 0.4 and 1.6 V (scan rate: 100 mV/s) for a PEMFC electrode with initial Pt loading of ∼470 μg. The approach demonstrates a methodology for fast parameter screening on electrocatalyst dissolution and a proof of concept industrial recycling of spent electrocatalysts.

Platinum Recovery Techniques for a Circular Economy

“…Incineration of the fluoropolymers from carbon support with Teflon ® causes the formation of extremely harmful hydrogen fluoride (HF) [72]. On the other hand, the hydrometallurgy process has also been used for MEA recycling, but a high concentration of strong acids and oxidants used, such as HCl, H 2 SO 4 , HNO 3 , and H 2 O 2 , can react with fluorinated compounds and end with highly toxic vapors [73].…”

“…During the last years, Pt electrochemical dissolution has been thoroughly studied by different groups to understand the degradation mechanisms of Pt electrocatalysts [73][74][75][76][77][78][79][80][81][82]. Pourbaix diagram (see Figure 3 [83]) suggests that platinum dissolves when exposed to an anodic polarization at potential above 1 V (vs RHE) in strong acidic electrolytes.…”

“…This treatment triggers a repetitive change in platinum surface oxidation state and ends with Pt dissolution. Raghunandan Sharma et al [73] developed a highly efficient and environmentally friendly platinum recycling method through potentiodynamic cycling in dilute acidic solutions from fuel cell electrodes. They employed a potential window between 0.4-1.6 V vs. RHE to recover 30 µg Pt/cycle with a scan rate of 100 mV/s in 1 M HCl.…”

“…The main challenge from the end-of-life electrode in PEMFCs recycling is the complete recycling of all components of the MEAs, Pt catalyst, In summary, electrochemical dissolution allows the recovery of high purity Pt catalyst at mild conditions in terms of pH, temperature, and voltage, offering a suitable techno-environmental performance. The main challenge from the end-of-life electrode in PEMFCs recycling is the complete recycling of all components of the MEAs, Pt catalyst, carbon support, and ionomer used for both membrane and catalyst layer [73,89]. Further efforts are needed to optimize this relatively unexplored recovery process, which gives the opportunity to recover Pt at a small scale and affordable cost for many research groups using Pt materials.…”

Recovery of Pt and Ru from Spent Low-Temperature Polymer Electrolyte Membrane Fuel Cell Electrodes and Recycling of Pt by Direct Redeposition of the Dissolved Precursor on Carbon

“…The electrode samples were placed unglued on the stainless-steel holders meant for powdered samples. Furthermore, the catalyst loadings/areas on the delaminated components of the MEA, i.e., the cathode, anode, and PEM, were measured by using a portable X-ray fluorescence (XRF) spectrometer (Thermo Scientific Niton XL3t GOLDD+), calibrated for such electrodes, using linear variation of the XRF intensity corresponding to L α emission from Pt (∼9.4 keV) with the Pt loading on the electrode. From XRF measurements, the area specific loadings of Pt and Ru ( W A (pt, Ru) ) were determined to be ∼0.7 mg Pt/cm 2 and 0.1 mg Ru/cm 2 , while the total active area of the MEA ( A ) was measured to be ∼150 cm 2 .…”