This supplementary materials section provides detailed experimental data and supporting information for the decoupled supercapacitive electrolyzer for membrane-free water splitting. It includes figures and references that cover various aspects of the research, such as: 1. **Figures S1 to S18**: - **Schematic representation of cell assembly and balance of plant** (Fig. S1). - Morphology and X-ray photoelectron spectroscopy (XPS) analysis of Pt/C electrodes (Figs. S2, S3). - Morphology of pristine nickel foam and electrode preparation configuration (Figs. S4, S5). - XPS study of cobalt phosphide (CoP), iron phosphide (FeP), and cobalt iron phosphide (CoFeP) electrodes (Figs. S9, S10). - Water splitting overpotentials and double-layer capacitance of electrodeposited phosphide electrodes (Figs. S10, S11). - Overall water splitting activity and stability of cobalt iron phosphide (Figs. S12, S13). - XPS study of activated carbon cloth (ACC) capacitive electrode (Fig. S14). - Cyclic voltammogram and gas separation during decoupled electrolysis (Figs. S15, S16). - Energy consumption profile and impedance measurement of a half-cell SCE assembly (Figs. S17, S18). 2. **References**: - A comprehensive list of references that support the experimental and theoretical aspects of the research, including studies on 2D nanomaterials, photoelectrochemical hydrogen production, and decoupled electrochemical water splitting. These materials provide a comprehensive overview of the experimental setup, electrode materials, characterization, and performance metrics, contributing to the understanding and validation of the decoupled supercapacitive electrolyzer for membrane-free water splitting.This supplementary materials section provides detailed experimental data and supporting information for the decoupled supercapacitive electrolyzer for membrane-free water splitting. It includes figures and references that cover various aspects of the research, such as: 1. **Figures S1 to S18**: - **Schematic representation of cell assembly and balance of plant** (Fig. S1). - Morphology and X-ray photoelectron spectroscopy (XPS) analysis of Pt/C electrodes (Figs. S2, S3). - Morphology of pristine nickel foam and electrode preparation configuration (Figs. S4, S5). - XPS study of cobalt phosphide (CoP), iron phosphide (FeP), and cobalt iron phosphide (CoFeP) electrodes (Figs. S9, S10). - Water splitting overpotentials and double-layer capacitance of electrodeposited phosphide electrodes (Figs. S10, S11). - Overall water splitting activity and stability of cobalt iron phosphide (Figs. S12, S13). - XPS study of activated carbon cloth (ACC) capacitive electrode (Fig. S14). - Cyclic voltammogram and gas separation during decoupled electrolysis (Figs. S15, S16). - Energy consumption profile and impedance measurement of a half-cell SCE assembly (Figs. S17, S18). 2. **References**: - A comprehensive list of references that support the experimental and theoretical aspects of the research, including studies on 2D nanomaterials, photoelectrochemical hydrogen production, and decoupled electrochemical water splitting. These materials provide a comprehensive overview of the experimental setup, electrode materials, characterization, and performance metrics, contributing to the understanding and validation of the decoupled supercapacitive electrolyzer for membrane-free water splitting.