Electrochemical Stability and Degradation of Commercial Pd/C Catalyst in Acidic Media

Milutin Smiljanić,Martin Šala,Marjan Bele,Francisco Ruiz-Zepeda,Nejc Hodnik,Leonard Moriau

doi:10.1021/acs.jpcc.1c08496

Abstract

Palladium has attracted significant attention as a catalyst or co-catalyst for many electrochemical reactions in energy conversion devices. We have studied electrochemical stability of a commercial Pd/C sample in an acidic electrolyte by exposing it to an accelerated stress test (AST) to mimic potential spikes in fuel cells and electrolyzers during start/stop events. AST consisted of extensive rapid potential cycling (5000 cycles, 1 V/s) in two potential regions, namely AST1 was performed between 0.4 and 1.4 VRHE, while AST2 was performed between 0.05 and 1.4 VRHE. Degradation of Pd/C was monitored by the changes in Pd electrochemical surface area, while the hydrogen evolution reaction (HER) was used as a test reaction to observe the corresponding impact of the degradation on the activity of Pd/C. Significant Pd/C degradation and HER activity loss were observed in both potential regions. Coupling of the electrochemical flow cell with an inductively coupled plasma mass spectrometry device showed substantial Pd dissolution during both ASTs. Identical location scanning electron microscopy revealed that Pd dissolution is followed by redeposition during both ASTs, resulting in particle size growth. Particle size growth was seen as especially dramatic in the case of AST2, when particularly large Pd nanostructures were obtained on top of the catalyst layer. According to the results presented in this work, (in)stability of Pd/C and other Pd-based nanocatalysts should be studied systematically as it may present a key factor limiting their application in energy conversion devices.

Highlights

Palladium has attracted significant attention over the past decades as a catalytic material in energy conversion devices
If Pd loadings are kept low, selectivity during oxygen reduction reaction (ORR) can be tuned from 4e− to 2e− reduction and H2O2 production, which means that Pd is a promising catalyst for small scale on-site electrochemical synthesis of this valuable compound.[10−12] Another example of diverse Pd application is emerging electrochemical CO2 reduction, where Pd nanoparticles were reported as efficient catalysts with high selectivity toward CO and formate production.[13]
SEM imaging of Pd/C catalyst deposited on glassy carbon in the thin films (TFs)-Rotating disc electrodes (RDEs) setup, Figure 1c, confirm the properties observed in TEM imaging

Summary

Introduction

Palladium has attracted significant attention over the past decades as a catalytic material in energy conversion devices. Interest in Pd was initially driven by its chemical and physical similarities with Pt coupled with notably higher abundance in the Earth’s crust and high electrocatalytic activity for different reactions. All together, these motivations highlighted Pd as a perfect substitute for scarce Pt. Pd-based materials were widely explored as catalysts for hydrogen evolution/oxidation reactions (HER/HOR).[1,2] HER has been studied on Pd nanoparticles loaded on various supports, Pd-alloys, Pdbimetallics and Pd-intermetallics, as nicely reviewed in ref 1. Pd/C is a better catalyst for formic acid oxidation than Pt/C due to favorable reaction pathways that lead to the formation of minor amounts of CO, which acts as strongly adsorbed poisoning species and Received: September 27, 2021 Revised: November 9, 2021 Published: December 10, 2021

Methods

Results

Conclusion