Co-assembly of a nafion-mesoporous zirconium phosphate composite membrane for PEM fuel cells

Abstract

Synthesis of mesoporous zirconium phosphate (MZP) by co-assembly of a tri-block copolymer, namely pluronic-F127, as a structure-directing agent, and a mixture of zirconium butoxide and phosphorous trichloride as inorganic precursors is reported. MZP with a specific surface area of 84m²g^-1, average pore diameter of about 17 nm and pore volume of 0.35cm³g^-1 has been prepared, and characterised by X-ray diffraction (XRD) and transmission electron microscopy. Nafion-MZP composite membrane is obtained by employing MZP as a surface-functionalised solid-super-acid-proton-conducting medium as well as an inorganic filler with high affinity to absorb water and fast proton-transport across the electrolyte membrane even under low relative humidity (RH) conditions. The composite membranes have been evaluated in H₂/O₂ polymer electrolyte fuel cells (PEFCs) at varying RH values between 18 and 100%; a peak power density of 355mWcm^-2 at a load current density of 1,100mAcm^-2 is achieved with the PEFC employing Nafion-MZP composite membrane while operating at optimum temperature (70° C) under 18% RH and ambient pressure. On operating the PEFC employing Nafion-MZP membrane electrolyte with hydrogen and air feeds at ambient pressure and a RH value of 18%, a peak power density of 285mWcm^-2 at the optimum temperature (60° C) is achieved. In contrast, operating under identical conditions, a peak power density of only ~170mWcm^-2 is achieved with the PEFC employing Nafion-1135 membrane electrolyte.