Potentiostatic and Potential Cycling Dissolution of Polycrystalline Platinum and Platinum Nano-Particle Fuel Cell Catalysts

Abstract

The dissolution of Pt in aqueous electrolytes has been studied for over forty years, most recently in the context of understanding the observed loss in electrochemically-active surface area (ECA) of cathode electrocatalysts in polymer electrolyte fuel cells. Despite extensive research, there are many unresolved issues regarding the dissolution of nano-particle Pt, such as the source of the observed potential dependence of potentiostatic and potential cycling dissolution rates. To help resolve these issues, in this paper we present results of measurements of the concentration of dissolved Pt and Pt dissolution rates for carbon-supported platinum nano-particles (Pt/C) in dilute perchloric acid, as a mimic of the PEFC cathode environment, as a function of potential and upper potential limit of potential cycling. Also presented, for comparison, are results of similar studies on polycrystalline platinum. In situ Pt L III X-ray absorption spectroscopy was used to determine the extent of oxidation, the coordination environment, and loss of Pt from the Pt nano-particles to elucidate the mechanism of Pt dissolution. Based on the correlation of these studies with those presented in the literature, mechanisms for Pt dissolution under potentiostatic and potential cycling conditions are proposed.

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

“…The approach provides much faster dissolution compared to the potentiostatic dissolution by direct contact of the corrosive liquids with the metal surface held at a constant potential . During electrochemical potential cycling, Pt dissolves primarily through formation of a Pt‐oxide layer and its subsequent dissolution to form soluble Pt species . For spent PEMFC and EC electrocatalysts, which are supported on an electronically conducting material (e.g., high‐surface‐area carbon) providing connectivity of individual Pt nanoparticles to the external circuit, the potentiodynamic dissolution using an external potential control is particularly suitable.…”

“…potentialc ycling, Pt dissolves primarily through formation of a Pt-oxide layer andi ts subsequentd issolution to form soluble Pt species. [8,21,[28][29][30][31][32] For spent PEMFC and EC electrocatalysts, which are supported on an electronically conducting material (e.g.,h igh-surface-area carbon) [33][34][35][36] providing connectivity of individual Pt nanoparticles to the external circuit, the potentiodynamic dissolution using an externalp otentialc ontroli sp articularly suitable.…”

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

“…In recent years, platinum electrochemical dissolution phenomenon has been intensively studied by several groups, aiming either to understand the degradation mechanisms of Pt electrocatalysts through Pt dissolution under potentiostatic and/or potentiodynamic conditions, [17][18][19][20][21][22][23][24][25][26][27][28] which lead to serious catalyst durability issues, or to develop a process for recovery of PGMs from the end-of-life electrocatalysts. [16,[29][30][31][32] Significant understanding of the dissolution mechanisms under different conditions has been developed recently through the studies using a combination of electrochemical potential controlling systems and highly sensitive analytical instrumentation, such as the quartz crystal microbalance (QCM), [33] inductively coupled plasma -mass spectrometry (ICP-MS), [18,24,28,34] X-ray absorption spectroscopy [25] , etc. The direct evidence on potentiodynamic dissolution through both anodic and cathodic sweep [21,25,27] is one of the most significant contributions in this area.…”

“…[16,[29][30][31][32] Significant understanding of the dissolution mechanisms under different conditions has been developed recently through the studies using a combination of electrochemical potential controlling systems and highly sensitive analytical instrumentation, such as the quartz crystal microbalance (QCM), [33] inductively coupled plasma -mass spectrometry (ICP-MS), [18,24,28,34] X-ray absorption spectroscopy [25] , etc. The direct evidence on potentiodynamic dissolution through both anodic and cathodic sweep [21,25,27] is one of the most significant contributions in this area.…”

“…However, the emphasis of most of such pioneering works is the durability of Pt electrocatalysts under fuel cell or electrolyzer related operation conditions, [18,21,[24][25][35][36] which does not directly serve the purpose of complete Pt-dissolution or recycling. Nevertheless, comparatively faster degradation of the Pt electrocatalysts in presence of Cl À has motivated to employment of the electrochemical potential cycling to recover Pt from the spent catalysts.…”