Injection-Molded Carbon Fiber/Carbon Nanotube-Reinforced Polypropylene Composite Electrodes: Processing–Structure–Property Relationships and Aqueous Electrochemical Applications

Conductive polymer composites offer a scalable route to self-supporting electrochemical electrodes, but electrical performance must be balanced against processability at high filler loadings. Fifteen polypropylene (PP)-based carbon-filler formulations were melt-compounded and injection-molded, and their electrical resistivity and moldability were evaluated. PP/CF20/CNT20 was selected, exhibiting a mean volume resistivity of 0.1409 Ω·cm with complete mold filling, no visible surface defects, and good moldability. SEM and synchrotron X-ray CT revealed multiscale carbon-filler morphology and spatially heterogeneous CF organization. Perforated PP/CF20/CNT20 disks were assembled into a ten-electrode parallel stack. At 12 V, the voltage sweep reached approximately 7.1 A in 1 M KOH and 2.1 A in tap water; during 20 h fixed-voltage operation, currents stabilized at approximately 5.2–5.5 A and 2.1 A, respectively. In 1 M KOH, estimated H2 flow reached approximately 42.9 sccm at 7 A. Prolonged tap-water electrolysis produced Ca-dominated surface scale. At 12 V in 0.3 wt.% NaCl, no Escherichia coli colonies were detected under the applied plating conditions from 15 min onward. These results demonstrate the feasibility of injection-molded PP/CF/CNT composites as functional electrodes for aqueous electrochemical applications.