Quantification on Degradation Mechanisms of Polymer Electrolyte Membrane Fuel Cell Catalyst Layers during an Accelerated Stress Test

Abstract

The long-term durability of the catalyst layers of a lowworking temperature fuel cell such as a polymer electrolyte membrane fuel cell (PEMFC) is of significant scientific interest because of their operation criteria and high initial cost. Identification of degradation mechanisms quantitatively during an accelerated stress test (AST) is essential for assessing and improving the durability of such catalyst layers. In this study, we present a quantitative analysis of the degradation mechanisms such as (i) electronic connectivity loss due to carbon support corrosion, (ii) proton connectivity loss due to ionomer/catalyst interface loss, (iii) catalyst loss due to dissolution or detachment, and (iv) physical surface area loss due to particle growth that is responsible for the electrochemical surface area (ECSA) loss in Pt-based catalyst layers for PEMFCs during an AST performed through potential cycling (linear sweep cyclic voltammetry) between 0.4 and 1.6 V for 7000 cycles in Ar-saturated 1 M H 2 SO 4 . Using a half-membrane electrode assembly (half-MEA), where a gas diffusion electrode with genuine three-phase boundaries is used as a working electrode through a solid electrolyte, we have observed the ECSA loss due to ionomer/catalyst interface loss and identified a catalyst heterogeneous degradation pattern during an AST. Results suggest a significant ECSA loss due to catalyst isolation (∼64% of ECSA loss) from loss of electron and proton connectivities by catalyst support corrosion (∼45%) and ionomer/catalyst interface loss (∼19%), followed by particle growth (∼30%) and dissolution/detachment (6%). Such knowledge and methodology can effectively contribute to catalyst material screening and electrode structure development to advance the PEMFC technology.

Environmentally and Industrially Friendly Recycling of Platinum Nanoparticles Through Electrochemical Dissolution–Electrodeposition in Acid‐Free/Dilute Acidic Electrolytes

“…Although capture of those harmful compounds is an option, it may significantly increase capital cost and also requires a rational disposal plan. Hence, despite the well‐established extraction/recycling processes, alternative approaches for recycling of PGMs are of considerable interest …”

“…During the potentiodynamic dissolution process controlled by using an external potential (Figure a, b), dissolved platinum can redeposit through a well‐known process (Ostwald ripening) where larger particles grow on account of the smaller ones . This leads to significant growth of the Pt nanoparticles, which reduces the efficiency of the dissolution process . Hence, the dissolution efficiency of the nanoparticulate catalysts may be enhanced by reducing the rate of the redeposition process.…”

“…Hence, despite the well-established extraction/recycling processes, alternative approaches for recycling of PGMs are of considerable interest. [16][17][18][19][20] Nanoparticulate PGM (especially Pt) catalysts are of significant strategic importance for applicationsi ncluding catalytic convertors in automobiles, chemicalsynthesis in the petroleum industries, and the fast-growing electrochemical energy conversion devices such as PEMFCs and electrolyzer cells (ECs). [9,11,13] Owing to their high surface-to-volume ratio, PGM nanoparticles exhibit ah ighera ctivity comparedt ot heir bulk counterparts.…”

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

“…The XRD pattern of pristine and HCl treated electrodes show diffraction peaks corresponding to both the graphitic carbon from GDL and the Ptnanoparticles. [31,52] As shown in the inset of Figure 7a, the decreased peak width of the diffraction for the post-dissolution sample suggests an increased average size of crystallites from 2.0 nm for pristine electrode to 2.4 nm for the post-dissolution electrode (~25 % dissolution). The crystallite growth may be attributed to the faster dissolution of the smaller particles and/ or the growth of larger particles (Ostwald ripening).…”

“…4 have also been made in our previous studies. [31,[52][53] Hence, in absence of complexing agents, very little amount of Pt was removed from the WE due to the unstable nature of the Pt-Oxides formed at potentials higher than~1 V at the low pH values of the studied electrolytes [54] and high tendency for redeposition. However, the average Pt-nanoparticle size increases during the electrochemical treatment due to Ostwald ripening.…”