Dissolution Stability of Graphene-Modified Pt(111)

Abstract

Pt plays a leading role in electrocatalysis, being the best pure metal catalyst for the oxygen reduction reaction (ORR) taking place at the cathode of the commercial polymer electrolyte membrane fuel cells (PEMFCs). In addition, it is usually used in the cathode to catalyze the hydrogen evolution reaction (HER) in water electrolyzers for hydrogen production. Apart from activity, stability is another critical parameter to consider when evaluating the performance of electrochemical energy conversion devices. Even pure Pt catalysts degrade under real-life conditions due to electro-oxidation and dissolution processes. Fundamental studies with well-defined Pt surfaces are mandatory for understanding these phenomena and developing new electrocatalysts with improved activity and stability.1 Different types of protection on the surface of electrocatalysts, such as carbon layers or ceria surrounding metal nanoparticles,2-4 have been investigated to enhance their stability while maintaining or improving their activity towards a reaction of interest. Here, we propose the modification of Pt(111) single crystal electrode with an adlayer of graphene as a model system to evaluate the protection mechanism of carbon-capped catalysts.In this work, the stability of graphene-modified Pt(111) in 0.1 M HClO4 is studied by on-line inductively coupled plasma mass spectrometry (ICP-MS) measurements using an electrochemical scanning flow cell (SFC). The Pt(111) surface was modified by a fast and easy transfer method of a commercially available chemical vapor deposited (CVD) graphene single-layer. The cyclic voltammetry results are comparable to those previously reported for surfaces prepared by direct CVD on the Pt(111) electrode.5 To test the quality of the graphene adlayer we checked the electrocatalytic activities towards different reactions of interest, such as ORR, HER and hydrogen oxidation reaction (HOR), and compared the results with the previous works.6 The graphene-modified Pt(111) surface presents enhanced stability since no dissolution is detected for a cyclic voltammetry experiment at 10 mV s-1 with an upper potential limit (UPL) of 1.3 V vs. RHE. In contrast, evident Pt dissolution is observed for the unmodified surface. Different accelerated stress test (AST) protocols consisting in groups of 50 cyclic voltammetries at 200 mV s-1 were performed up to three different UPL, namely 1.3 V, 1.5 V and 1.7 V vs. RHE, showing almost no dissolution over the protocol when UPL = 1.3 V, while the integrity of the graphene adlayer was quickly compromised for UPL = 1.7 V as pointed out by the quick increase in Pt dissolution. The degradation of the graphene layer in the different conditions was additionally characterized by Raman spectroscopy and atomic force microscopy (AFM). The results from this work provide useful information about the behavior of carbon capping agents on Pt surfaces, which can help to design new electrocatalytic materials with improved stability. References (1) Fuchs, T.; Briega-Martos, V.; Drnec, J.; Stubb, N.; Martens, I.; Calle-Vallejo, F.; Harrington, D. A.; Cherevko, S.; Magnussen, O. M. Anodic and Cathodic Platinum Dissolution Processes Involve Different Oxide Species. Angew. Chem. Int. Edit. 2023, 62, e202304293.(2) Sgarbi, R.; Doan, H.; Martin, V.; Chatenet, M. Tailoring the Durability of Carbon-Coated Pd Catalysts Towards Hydrogen Oxidation Reaction (HOR) in Alkaline Media. Electrocatalysis 2023, 14 (2), 267-278.(3) Kim, H.; Kwon, G. H.; Han, S. O.; Robertson, A. Platinum Encapsulated within a Bacterial Nanocellulosic-Graphene Nanosandwich as a Durable Thin-Film Fuel Cell Catalyst. ACS Appl. Energy Mater. 2021, 4 (2), 1286-1293.(4) Miller, H. A.; Vizza, F.; Marelli, M.; Zadick, A.; Dubau, L.; Chatenet, M.; Geiger, S.; Cherevko, S.; Doan, H.; Pavlicek, R. K.; et al. Highly active nanostructured palladium-ceria electrocatalysts for the hydrogen oxidation reaction in alkaline medium. Nano Energy 2017, 33, 293-305.(5) Fu, Y. C.; Rudnev, A. V.; Wiberg, G. K. H.; Arenz, M. Single Graphene Layer on Pt(111) Creates Confined Electrochemical Environment via Selective Ion Transport. Angew. Chem. Int. Edit. 2017, 56 (42), 12883-12887.(6) Shih, A. J.; Arulmozhi, N.; Koper, M. T. M. Electrocatalysis under Cover: Enhanced Hydrogen Evolution via Defective Graphene-Covered Pt(111). ACS Catal. 2021, 11 (17), 10892-10901.