Electrochemical reduction of CO₂ by graphitized carbon nitride composite anion exchange membranes: potential for high CO selectivity

A series of crosslinked poly(norbornene)-based composite anion exchange membranes, PHMNHD@CN-X, with different graphitized carbon nitride (g-C₃N₄) contents were prepared by synthesizing new norbornene-like monomers and using g-C₃N₄ as filler. These membranes were utilized for CO₂ reduction reaction (CO₂RR). The analysis indicates that PHMNHD@CN-1, a composite membrane containing 1% g-C₃N₄, has a hydroxide conductivity of 51.29 mS cm⁻¹, which is significantly higher than the hydroxide conductivity of the commercial membrane called Sustainion Grade RT, which is 30.88 mS cm⁻¹. Meanwhile, the anion exchange membrane with filler modification, PHMNHD@CN-1, demonstrated superior electrolytic performance in a homemade membrane electrode assembly (MEA) electrolyzer, achieving a current density of 83.89 mA cm⁻² at the cell voltage of 3 V. At current densities of 100 to 130 mA cm⁻², PHMNHD@CN-1 displayed a higher CO Faraday efficiency (FE_CO%) of 92.41%. These results suggest that the modified anion exchange membrane has a promising potential for CO₂RR.