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

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/CexZr1‑xO2, where Pt particles are anchored on the CexZr1‑xO2 support. Adapting a one-pot polyol method, Pt/CexZr1‑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 °C 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/Ce0.5Zr0.5O2 and 5‑Pt/Ce0.5Zr0.5O2, 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/Ce0.5Zr0.5O2, compared to the blank measurement. The results confirm the bi-functionality of this synthesized catalyst, demonstrating its novel application for gas recombination and radical scavenging.