Fig. 5: Gradient wettability and structural hierarchy promote directional transport and enhance electrode performance.

a Cross-sectional EDS mapping results of PPE-D featuring a dense hydrophobic bottom layer and a particulate-packed top layer, forming a structural and wettability gradient. b H₂O₂ yield and corresponding Faraday efficiency (FE) for different GDEs (1 mol L^–1 Na₂SO₄, pH = 6.92 ± 0.06, mass loadings: PPE, 6 mg cm^–2; PPE-D and PPE-T, 8 mg cm^–2). Values are means, and error bars indicate standard deviation (n  =  3 replicates). Source data are provided as a Source Data file. c Correlation between FE and the resistance impulse (RI) (1 mol L^–1 Na₂SO₄, pH = 6.92 ± 0.06). Values are means (n = 3). Full statistical information, including standard deviations and raw data, is provided in the Source Data file. d Molecular dynamics rendering of H₂O₂ diffusion trajectories within gradient versus non-gradient CLs. e Time-resolved spatial density distributions of H₂O₂ molecules, showing preferential migration toward regions with larger pores and lower PTFE content in the gradient structure. f Mean square displacement (MSD) of H₂O₂ and O₂ molecules in gradient and non-gradient CLs, indicating enhanced directional transport in the presence of wettability gradients. g Schematic of the microfluidic device designed to visualize directional H₂O₂ flow in biomimetic CL channels. h Experimental visualization of H₂O₂ transport in microfluidic chips with hydrophobic and hydrophilic gradients. The H₂O₂ solution (mixed with potassium titanyl oxalate) appears pink and is injected from the central region. Pores are shown in blue and the solid skeleton in white. The observed capillary-driven directional transport is consistent with the CL gradient design (See Supplementary Videos 3 and 4 for experimental details).