Organic-inorganic hybrid titanophosphite proton conductive membranes with graded monomer conversion

► A membrane with a gradation of monomer conversion by UV absorption was prepared. ► The monomer conversion is high at the top and low at the bottom. ► The membrane was water-durable and thermally stable up to 200 °C. ► The proton conductivity was 6.3 × 10− 4 S cm− 1 at 150 °C under N2 atmosphere.