Anolyte Selection Framework for Iodide Oxidation Coupled Hydrogen Evolution‐Based Hybrid Electrolysis Process

Hydrogen production via iodide oxidation reaction‐coupled hybrid electrolysis is an emerging approach in which the system‐level role of anolyte composition remains poorly understood. A systematic investigation on the influence of anolyte composition using hydroiodic acid (HI) and iodine (I 2 ) by varying I 2 /HI and HI/H 2 O ratios is presented. The behavior has been examined at both electrode scale (three‐electrode configuration) and device scale (membrane‐separated two‐compartment cell). A mathematical framework is developed to deconvolute the contributions of the overall cell voltage into the overpotential components. Model‐based analysis reveals that, although anolyte composition influences anode kinetics, activation overpotential changes are negligible at the full‐cell level. Instead, the cell voltage is governed by the composition‐dependent open‐circuit voltage and cell resistance. A lower operating cell potential is achieved at lower I 2 /HI ratios and higher HI/H 2 O ratios. While the azeotropic HI/H 2 O ratio (∼0.186) represents a practical upper limit, the optimal I 2 /HI ratio is dictated by the downstream processing requirements of the anolyte. Continuous hydrogen production is demonstrated at three I 2 /HI ratios at the azeotropic HI/H 2 O ratio and two current densities, achieving 0.01–0.015 mL s −1 production rate with a high current efficiency (93.7%–96.8%). The specific energy consumption increases with both I 2 /HI ratio and current density.