The supplementary materials for the study "Decoupled supercapacitive electrolyzer for membrane-free water splitting" include figures and references. Figures S1 to S18 provide detailed information on the cell assembly, electrode morphology, X-ray photoelectron spectroscopy (XPS) analysis, and performance of the electrolyzer. Figure S1 shows the cell assembly and balance of plant setup. Figure S2 presents the morphology of Pt/C electrodes. Figure S3 details the XPS analysis of Pt/C electrodes, showing the binding energies of various functional groups. Figures S4 to S7 describe the morphology of nickel foam, cobalt phosphide, and iron phosphide electrodes. Figures S8 to S14 provide information on the thickness of cobalt iron phosphide films, XPS analysis of electrodeposited electrodes, and the performance of activated carbon cloth. Figures S15 to S18 show cyclic voltammograms, gas separation during electrolysis, energy consumption profiles, and impedance measurements. The references list key studies on hydrogen production, water splitting, and electrocatalysts. The study highlights the development of a decoupled supercapacitive electrolyzer for membrane-free water splitting, focusing on the performance and stability of cobalt iron phosphide and activated carbon cloth electrodes. The results demonstrate the efficiency and potential of this system for sustainable hydrogen production.The supplementary materials for the study "Decoupled supercapacitive electrolyzer for membrane-free water splitting" include figures and references. Figures S1 to S18 provide detailed information on the cell assembly, electrode morphology, X-ray photoelectron spectroscopy (XPS) analysis, and performance of the electrolyzer. Figure S1 shows the cell assembly and balance of plant setup. Figure S2 presents the morphology of Pt/C electrodes. Figure S3 details the XPS analysis of Pt/C electrodes, showing the binding energies of various functional groups. Figures S4 to S7 describe the morphology of nickel foam, cobalt phosphide, and iron phosphide electrodes. Figures S8 to S14 provide information on the thickness of cobalt iron phosphide films, XPS analysis of electrodeposited electrodes, and the performance of activated carbon cloth. Figures S15 to S18 show cyclic voltammograms, gas separation during electrolysis, energy consumption profiles, and impedance measurements. The references list key studies on hydrogen production, water splitting, and electrocatalysts. The study highlights the development of a decoupled supercapacitive electrolyzer for membrane-free water splitting, focusing on the performance and stability of cobalt iron phosphide and activated carbon cloth electrodes. The results demonstrate the efficiency and potential of this system for sustainable hydrogen production.