Stabilization of Pt Nanoparticles Due to Electrochemical Transistor Switching of Oxide Support Conductivity

Abstract

Polymer electrolyte fuel cells (PEFCs) offer an efficient way of chemical-to-electrical energy conversion that could drastically reduce the environmental footprint of the mobility and stationary energy supply sectors, respectively. However, PEFCs can suffer from severe degradation during start/stop events, when the cathode catalyst is transiently exposed to very high potentials. In an attempt to mitigate corrosion of conventional carbon support materials for Pt catalyst nanoparticles under these conditions, conductive metal oxides like antimony-doped tin oxide (ATO) are considered alternative support materials with improved corrosion resistance. A combined in situ anomalous small-angle X-ray scattering and post mortem transmission electron microscopy study reveals PEFC-relevant degradation properties of ATO-supported Pt in comparison to carbon-supported Pt catalysts. Against expectation, the superior stability of ATO-supported Pt nanoparticles cannot be merely explained by improved support corrosion resistance. Instead, the dominant loss mechanism of electrochemical Ostwald ripening is strongly suppressed on ATO support, which can be explained with a potential-dependent switching of support oxide surface conductivity. This electrochemical transistor effect represents an important design principle for the development of optimized metal oxide support materials that protect supported Pt nanoparticles at high potentials, where careful consideration of the metal oxide flat-band potential is required in order to maintain high catalyst performance at normal PEFC cathode operation conditions at the same time.

Combining SAXS and XAS To Study the Operando Degradation of Carbon-Supported Pt-Nanoparticle Fuel Cell Catalysts

“…PSDs upon potential cycling is displayed in Figures 5a and 5b (for Pt/BP-g and Pt/V, respectively); in agreement with previous studies in which the changes in the Pt-NPs distribution were assessed using in situ A-SAXS [50][51][52]56,57 or post mortem TEM, [29][30][31][32] the PSDs for both Pt/C materials become broader and shift towards larger average diameters as the number of potential cycles increases -a result of the potential-induced dissolution of surface Pt atoms in smaller NPs and their re-deposition onto larger ones, often referred to as electrochemical Ostwald ripening. 23,26 Moreover, upon comparing the cycle-dependent evolution of the <D> values extracted from these PSDs and plotted in Fig.…”

Capacitive electronic metal-support interactions: Outer surface charging of supported catalyst particles

“…Predictions of the classical electrostatic model were further investigated by density functional theory (DFT). Platinum nanoparticles supported on a Sb-doped SnO 2 (110) surface were chosen for this purpose, because this system has attracted substantial attention in recent research on electrocatalysts for the oxygen reduction reaction [23,24]. Periodic DFT computations were performed using the Vienna ab initio simulation package (VASP).…”

Highly Durable and Active Pt/Sb-Doped SnO2 Oxygen Reduction Reaction Electrocatalysts Produced by Atomic Layer Deposition

“…ATO has been extensively examined as a promising stable and conductivity metal oxide support at the PEMFC cathode. ATO has demonstrated significant oxidative stability in PEMFC operating conditions while also exhibiting loss of electrochemical activity due to Sb dissolution and redeposition. − Herein, Pt deposited using ALD on ATO is shown to be an extremely stable ORR catalyst with high surface area and high electric conductivity. ALD was shown to yield significantly more uniform Pt dispersion and catalyst stability compared to standard wet chemical methods.…”