Synergistic enhancement of hydrogen evolution reaction by bio-surfactant and visible light in alkaline water electrolysis

This study presents a green and scalable strategy to enhance hydrogen evolution in alkaline water electrolysis by integrating a natural bio-surfactant, Sapindus rarak, with visible light irradiation. Electrolysis experiments were conducted using 30 vol% KOH electrolyte supplemented with 0.5 M Sapindus rarak extract under red, green, and blue LED illumination (700 lumens). After 10 min of electrolysis at 9 V and 1.5 A, hydrogen yields increased significantly compared to the dark condition: from 8.3 mL (control) to 16.5 mL (red), 23.6 mL (green), and 29.1 mL (blue). These enhancements are attributed to the synergistic effects of reduced surface tension by the saponin-based surfactant and photothermal activation from high-energy photons. Blue light, having the highest photon energy (∼2.75 eV), induced the greatest temperature rise and HER acceleration. The system exhibited improved mass transfer, smaller bubble diameters, elevated pH, and increased current density under combined treatments. FTIR and UV–Vis analyses confirmed the amphiphilic and photoresponsive nature of the bio-surfactant. The findings demonstrate that combining renewable additives and light energy offers a cost-effective pathway to boost hydrogen production, aligning with sustainable energy goals.