Abstract:

Quasi-spherical carbon nano-onions（CNOs） with a size of ca.5 nm were synthesized via thermal annealing of nanodiamonds. Subsequent oxidation using concentrated H₂SO₄/HNO₃ introduced —COOH groups， yielding carboxylated CNOs（C-CNOs）. Further functionalization through acylation and nucleophilic substitution produced highly phosphorylated CNOs（P-CNOs）. High-resolution transmission electron microscopy（HRTEM）， X-ray diffraction（XRD） and X-ray photoelectron spectroscopy（XPS） confirmed the successful introduction of —COOH and —PO₃H₂ groups， with P-CNOs exhibiting an ion exchange capacity（IEC） of 1.85 mmol/g. Homogeneous， intact， and dense SPAES/P-CNOs composite membranes were prepared via solution casting by blending P-CNOs with sulfonated poly（arylene ether sulfone）（SPAES）. Compared to pristine SPAES， the composite membranes show enhanced properties including water uptake/swelling， oxidative stability， and proton conductivity. This improvement stems from hydrogen-bonding networks between the —COOH/—PO₃H₂ groups in P-CNOs and the —SO₃H groups in SPAES， forming a more stable network structure that bolsters mechanical properties and chemical stability while facilitating proton transfer. The SPAES/P-CNOs-1.5 membrane achieves a high proton conductivity of 220 mS/cm at 90 °C. At 80 °C and 100% relative humidity（RH）， its maximum power density reaches 650 mW/cm²， 36% higher than that of SPAES. It also shows excellent mechanical property and high thermal-dimensional-chemical stability， indicating significant application potential.

Key words: Sulfonated poly（aryl ether sulfone）, Phosphorylated carbon nano-onions, Organic-inorganic composite, Proton exchange membrane, Fuel cell