On-line Inductively Coupled Plasma Mass Spectrometry Reveals Material Degradation Dynamics of Au and Cu Catalysts during Electrochemical CO₂ Reduction

Abstract

A significant challenge in commercializing electrochemical CO₂ reduction (CO₂R) is achieving catalyst durability. In this study, online inductively coupled mass spectrometry (ICP-MS) was used to investigate catalyst degradation via nanoparticle detachment and/or dissolution into metal ions under CO₂R operating conditions in 0.1 M KHCO₃. We developed an experimental framework with <i>ex situ</i> characterization to validate the online ICP-MS method for <i>in situ</i> evaluation of degradation from metal foils. By varying the applied potential and microenvironment (CO₂ vs N₂-saturated electrolyte), we gained insights into the degradation of Au and Cu foils under CO₂R and hydrogen evolution reaction (HER) conditions. While both Au and Cu foils were observed to be stable to dissolution in these regimes, degradation via nanoparticle detachment from the foil surface at the femtogram scale was observed as a function of reaction conditions, providing new insights into material degradation mechanisms. When applying potential steps at -0.1 and -1.0 V vs the reversible hydrogen electrode (RHE), Au was found to degrade via nanoparticle detachment under CO₂R operating conditions more than under HER conditions, while Cu was found to degrade via nanoparticle detachment in similar amounts during both reactions. Au lost ∼1.8× more mass and ∼7.5× more nanoparticles than Cu under CO₂R operating conditions. This study demonstrates the use of online ICP-MS to gain insight into the degradation of Au and Cu, the importance of studying unconventional degradation mechanisms such as nanoparticle detachment, and that online ICP-MS can be further utilized to gain fundamental understanding of catalyst durability for a variety of reaction systems.