Development, Electrochemical Characterization, and Statistical Optimization of a Low-Cost Membraneless Tubular Flow-By Alkaline Electrolyzer for Green Hydrogen Production.

Hydrogen production by alkaline water electrolysis is a promising pathway for sustainable energy systems; however, conventional electrolyzers rely on membranes or diaphragms that increase cost, electrical resistance, and maintenance requirements. This study reports the development and experimental evaluation of a low-cost, membrane-less, flow-by tubular alkaline electrolyzer integrated with a dedicated gas-liquid separation and volumetric gas-measurement system. The electrolyzer was designed, constructed, experimentally validated, and electrochemically characterized using polarization curves. The effects of KOH concentration (0.50-2.00 mol L-1), electrolyte flow rate (1.00-4.00 L min-1), and applied voltage (2.20-3.20 V) on hydrogen production were investigated through a full factorial 33 experimental design combined with analysis of variance, response surface methodology, and numerical optimization using the desirability function. The applied voltage was identified as the dominant operating variable, followed by KOH concentration and electrolyte flow rate, while significant interactions involving voltage were also observed. The quadratic regression model showed excellent predictive performance (R2 = 0.9614), and within the investigated operating domain, the highest hydrogen production rate was obtained at 2.00 mol L-1 KOH, 1.00 L min-1 electrolyte flow rate, and 3.20 V, resulting in an experimental hydrogen production rate of 0.4395 mL s-1. These findings demonstrate the potential of the proposed membrane-less flow-by electrolyzer as a simplified, low-cost, and experimentally validated platform for investigating and optimizing membrane-less alkaline water electrolysis under the evaluated operating conditions.