Modifying Ionic Membranes with Carbon Dots Enables Direct Production of High-Purity Hydrogen through Water Electrolysis.

Traditional electrolysis of water produces hydrogen with a purity of ∼98%. Using ion transport membranes to prevent the migration of oxygen (O2) from the anode to the cathode, the purity of H2 can be increased to ∼99.8%, but it still cannot fulfill the requirement for use in fuel cells (>99.97%). Here, we report that modifying a commercial ionic membrane (Nafion) with carbon dots (CDs) can further inhibit O2 permeation across the membrane, while effectively improving its ion transportability. The key to achieve these effects is the rational design and proper loading of the CDs, which narrows the pore size of the membrane from ∼4 nm to <2 nm and alters its surface functionality. Using the CDs-modified Nafion membrane in an H-type electrolysis cell, we demonstrate that H2 with a purity of up to 99.98%, which meets the standards of hydrogen fuel cells, can be directly produced without any additional purification process. Our study provides a new route for the low-cost electrolysis of water to produce high-purity hydrogen.