Green modification of water-soluble phenolic resin-based carbon fiber paper with waterborne alkyd resin for high-performance PEMFC gas diffusion layers

• Proposes a green waterborne alkyd resin blend to modify phenolic resin for carbon paper. • Achieves 42% lower resistivity and 120% higher tensile strength simultaneously. • Optimized GDL shows 1664 mW/cm 2 peak power density, 160% higher than commercial. • Exhibits inherent superhydrophobicity (contact angle >132°) without post-treatment. • Unveils enhancement via continuous carbon network and nano-filaments formation. Proton exchange membrane fuel cells (PEMFCs) require gas diffusion layers (GDLs) with balanced electrical conductivity, mechanical robustness, and efficient mass transfer for optimal performance and durability.While water-soluble phenolic resin (WPF) offers an environmentally friendly processing route, carbon fiber paper (CFP) derived solely from WPF often suffers from insufficient conductivity and brittleness, limiting its practical application.To bridge this performance gap while preserving green processing advantages, this study proposes a facile blending modification strategy by introducing waterborne alkyd resin (WAR) into the WPF matrix.</mark > Composite carbon papers were prepared via impregnation, hot-pressing, carbonization, and graphitization. The effects of WAR addition amount (with fixed WPF concentration at 10 wt%) and the proportion of WAR in the mixed resin (with total concentration fixed at 10 wt%) on the microstructure, fundamental physicochemical properties, and single-cell performance were systematically investigated. Results indicate that the introduction of WAR significantly optimizes the microstructure of the resin carbon, forming a continuous, dense network and promoting the growth of nano-carbon filaments. When the WAR addition amount was 7.5 wt%, the resistivity of the carbon paper decreased to 3.98 mΩ·cm 2 (a 42% reduction compared to pure WPF), and the tensile strength increased to 33.07 MPa (a 120% improvement). Single-cell tests demonstrated that all self-made GDLs exhibited inherent superhydrophobicity (contact angle > 132°) and could be directly applied without post-hydrophobic treatment. Notably, when the proportion of WAR in the mixed resin was 4.29 wt% (WPF:WAR = 4:3), the prepared GDL exhibited the best overall performance, achieving a maximum power density of 1664 mW/cm 2 (over 160% higher than commercial Toray carbon paper at 639 mW/cm 2 ) and a limiting current density exceeding 3300 mA/cm 2 , attributed to the optimal synergy between its excellent mass transfer capability and conductivity. This study provides a new pathway for developing green, high-performance gas diffusion layers for fuel cells.