Corrosion-Resistant Precious Metal Coated Oxide Nanoparticles As Supports for Iridium-Based Oxygen Evolution Reaction Catalysts in Proton Exchange Membrane Electrolyzers

Abstract

Presently, the most efficient catalysts chosen for proton exchange membrane water electrolyzers (PEMWE) are platinum group metal (PGM) based, and the required high mass loading of these metals makes the technology expensive at large scale.1 Thus, it is desirable to find alternative catalysts or structures that can lower PGM loading while maintaining efficient PEMWE operation. The anodic oxygen evolution reaction (OER) of a PEMWE suffers from a high catalyst loading as a result of lack of stable catalyst supports that can withstand the highly corrosive electrochemical conditions. These supports would help disperse the PGMs within the catalyst layer. The current practice is to use unsupported iridium based nanoparticles as catalysts since most supports degrade under such harsh conditions. However, only surface atoms participate in electrocatalysis, leaving the bulk of the iridium as an expensive PGM support that functions solely as a conductive matrix. Replacing the core with less expensive and resource constrained materials that can be conductive yet stable under the highly oxidizing OER conditions is very desirable. Unfortunately, doping or defecting oxides to make them conductive hinders their stability, so other tactics must be utilized.2 In this talk we will present our work on materials prepared by coating insulating titanium dioxide nanoparticles (< 100 nm) with small amounts of conductive platinum or gold nanoparticles to prepare supports for iridium catalysts. Under OER conditions, all three materials are stable. In order to synthesize these structures, we identified synthesis routes to prepare well dispersed layers of these precious metal nanoparticles onto the titanium dioxide nanoparticles; making them the optimal substitute metals for an iridium core. These nanostructures were then coated with iridium to prepare supported OER catalysts with the desired activity and stability. Three synthetic procedures were implemented and compared in order to determine the most efficient way to prepare the nanoparticle composites, i.e. wetness impregnation, citric acid reduction, and light catalyzed deposition. X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), and Energy Dispersive X-ray Spectroscopy (EDS) were utilized to characterize the nanoparticles. XRD suggested that the final catalyst material did indeed contain a combination of crystalline titanium dioxide, iridium, and metal gold or platinum nanoparticles. SEM and EDS indicated that the iridium, as well as the gold or platinum nanoparticles, were well distributed upon the larger titanium dioxide nanoparticles. It was determined that the best distribution was found when using platinum nanoparticles and the photo reduction synthesis technique. The complete synthesis methods, characterization of the materials, as well as electrocatalytic performance towards OER using rotating disk electrode in acidic electrolyte, will be presented in this poster.