Fig. 6: NO₃RR performance and theoretical analysis of the bilayer-EM.

a Effect of electrified operation modes, including flow-by (left, grey shading), single-layer flow-through (middle, blue shading), and bilayer flow-through (right, pink shading) modes, on the distribution of nitrogen species in the permeate (left axis) and N₂ selectivity (right axis) using the membrane. Black bars indicate the residual nitrogen concentration (i.e., the sum of NO₃⁻, NO₂⁻, and NH₃) in the permeate. The voltages were not iR corrected (membrane electrode surface area = 12.6 cm², resistance value = 23 Ω). CFD simulating the NO₃⁻ concentration distributions under (b₁) flow-through and (b₂) flow-by modes and (b₃) the concentration changes with flow distance. c Generation of free chlorine by the TiO_2-x-EM as a function of current density using a feed solution with 5 mM Na₂SO₄ and 10 mM NaCl under a permeate flow rate of 1.2 mL min⁻¹. d NO₃⁻ removal performance of the bilayer-EM when treating different feed solutions containing 10 mg-N L⁻¹ NaNO₃ in 10 mM Na₂SO₄, 1 mM Na₂SO₄, or simulated surface water (containing 2 mM Cl⁻, other constituents listed in Table S2). The data in (a) and (b) are presented as mean values ± s.d. (n = 3). e NO₃⁻ removal efficiency and loss of Sn of the bilayer-EM as a function of filtration cycles. After operating for 1.5 h, the membrane was rinsed and dried and then used for the next cycle. f Sn FT-EXAFS spectra of the Sn₂/NCB-EM before and after long-term operation. Source data are provided as a Source Data file.