Pt/CexZr1–xO2 Bi-Functional Catalyst for Gas Recombination and Radical Scavenging in PEM Water Electrolysis Cells

Abstract

Incorporating platinum (Pt) as a gas recombination catalyst in proton exchange membranes (PEMs) effectively addresses the challenge of pronounced hydrogen crossover in PEM water electrolysis cells, particularly when thin membranes are employed. However, the Pt-catalyzed formation of reactive oxygen species, including hydroxyl radicals (HO^•), can accelerate membrane degradation, requiring the use of a radical scavenger such as cerium–zirconium oxide. Given the short diffusion length of HO^• in the PEM, it is necessary to position the cerium–zirconium oxide close to the Pt sites where radicals are catalytically produced, for timely scavenging. To address this issue, we propose the use of a bi-functional catalyst Pt/Ce_xZr_1–xO₂, where Pt particles are anchored on the Ce_xZr_1–xO₂ support. Adapting a one-pot polyol method, Pt/Ce_xZr_1–xO₂ catalysts were synthesized with Ce contents of x = 0.25, 0.5, 0.75 and 1, and two Pt-to-oxide loadings of 0.5 and 5 wt %. The catalysts were then calcined at either 500 or 900 °C, and the resulting phases were characterized by high resolution X-ray diffraction with Rietveld refinement, nitrogen physisorption and transmission electron microscopy. It was observed that the cubic fluorite structure of ceria tends to be maintained with a higher Ce content, a lower Pt-to-oxide loading and a lower calcination temperature. Otherwise, the formation of tetragonal phase is favored. Pt was found to be mainly dispersed ionically when calcined at 500 °C, and to largely segregate into particles at 900 °C. Two selected compositions, namely 0.5-Pt/Ce_0.5Zr_0.5O₂ and 5-Pt/Ce_0.5Zr_0.5O₂, were incorporated into the membrane for PEM water electrolysis cell measurements. A reduced content of H₂ in O₂ in the anode product gas and a lower fluoride release rate were observed using the composite membrane containing 5-Pt/Ce_0.5Zr_0.5O₂, compared to the blank measurement. The results confirm the bi-functionality of this synthesized catalyst, demonstrating its application for concurrent gas recombination and radical scavenging.