Fig. 3: Scaled-up mesoscale device enabling quantitative analysis of hydrogen and freshwater production.

a Schematic diagram of the 3D mesoscale device, scaled-up from the geometry of the microfluidic device, employing the same strategy for simultaneous hydrogen gas and freshwater production. The device comprises a purification chamber and a hydrogen chamber, separated by a Nafion sheet. Fin-type structures within the purification chamber stabilize the IDZ and guide the separation of purified water and brine streams. b Cross-sectional diagram of the 3D mesoscale device. The device operates via same mechanism as the microfluidic device shown in Fig. 2b but is extended along the z-axis to form a scaled-up structure. c Actual image of the 3D-printed mesoscale device, showing the separation of streams and gas production. Saltwater and rinsing water are introduced into the purification and hydrogen chambers, respectively, and hydrogen gas is produced at the cathode in the hydrogen chamber. d Quantitative results for hydrogen gas production and Na⁺ ion concentration in purified water at 20 mM feed concentration under various applied currents (4, 10, 15 and 20 mA). Hydrogen production increased linearly with the current, while Na⁺ concentration in purified water plateaued, indicating diminishing returns in purification performance. Data are presented as the mean ± standard deviation from measurements on 4 different devices. e Ratio of Na⁺ ions transported to each stream at 20 mM feed concentration. Higher currents increased the fraction of Na⁺ ions in the hydrogen chamber, while decreasing the fractions in the purified water and brine streams. f Quantitative results for hydrogen gas production and Na⁺ ion concentration in purified water at 200 mM feed concentration under various applied currents (40, 100, 150 and 200 mA). Hydrogen production and Na⁺ concentration have similar trends of (c). Data are presented as the mean ± standard deviation from measurements on 4 different devices. g Ratio of Na⁺ ions transported to each stream at 200 mM feed concentration. Higher currents increased the fraction of Na⁺ ions in the hydrogen chamber, while decreasing the fractions in the purified water and brine streams.