Tuning the Composition of Silicon Oxide Overlayers to Control the Performance of Platinum Electrocatalysts

Abstract

Membrane coated electrocatalyst (MCEC) architectures have been demonstrated to be an attractive approach for improving the activity, stability, and selectivity of electrocatalysts. However, little is known how overlayer structure impacts different electrocatalytic properties. By analyzing the impact that overlayer composition has on electrochemical behavior, the relationship between MCEC structure and performance can be better understood. For a silicon oxide (SiOx)|Pt MCEC, limiting the conversion of polydimethyl-siloxane (PDMS) to SiOx during synthesis can result in varied concentrations of carbon and silicon-oxygen coordination in the overlayer film, allowing these factors to be manipulated and studied directly. These changes in composition are shown to affect the hydrophobic character of the overlayers, as well as impact the performance of electrochemical reactions that require water as a reactant. Specifically, platinum electrodes with partially converted SiOxCy overlayers showed decreased permeability for both water and protons when studying hydrogen evolution. Partially converted samples also exhibit clear shifts in CO oxidation potential compared to unencapsulated Pt, however, these shifts do not directly improve activity for the methanol oxidation reaction. Instead, samples that had the lowest extent of conversion showed the highest degree of current enhancement for methanol oxidation, despite these samples demonstrating a higher CO oxidation potential than samples with longer curing times. These observations offer insights into how the composition and properties of MCEC overlayers can affect different factors in an electrochemical system and offer an additional level of design for the development of future electrocatalyst architectures.