Investigation of Proton Diffusion Mechanisms in a Porous Phosphate Material Using Muon Spin Relaxation

Porous materials with high proton conductivity are garnering significant attention due to their potential applications in proton-exchange membrane fuel cells (PEMFCs), a crucial technology in achieving global 'Net Zero' targets. We recently studied a porous phosphate material (Ni-Phos) that demonstrated a proton conductivity of 1.15 × 10⁻³ S·cm⁻¹ at 90 °C and 99% relative humidity (RH). Remarkably, exposure of this material to toxic air pollutants such as NO₂ and SO₂ significantly enhanced its conductivity. After gas capture, the conductivity increased by 29-fold for NO₂@Ni-Phos (3.36 × 10⁻² S·cm⁻¹) and 12-fold for SO₂@Ni-Phos (1.40 × 10⁻² S·cm⁻¹) under the same conditions. Importantly, the conductivity of NO₂@Ni-Phos approaches that of commercially used Nafion (7.8 × 10⁻² S·cm⁻¹). We seek 3 days of beamtime on the EMU instrument to probe the proton transport mechanism within these materials using muon spectroscopy. This study will provide valuable insights into the development of robust proton-conducting materials and demonstrate the application of muon spectroscopy as a powerful tool for characterizing proton diffusion in these systems.