Alkaline-Induced Structural Evolution of Na3MnPO4CO3-g-C3N4 to Mn3O4-g-C3N4: Unlocking Superior Electrocatalytic Activity in Water Splitting and Ethylene Glycol Oxidation

Abstract

The alkaline activation of Na3MnPO4CO3-g-C3N4 results in a Mn3O4-g-C3N4 nanocomposite. The leaching of Na+, PO43−, and CO32− from the Na3MnPO4CO3-g-C3N4 framework destabilizes the original structure, facilitating a rearrangement of the Mn−O framework into Mn3O4 alongside g-C3N4. This rapid ion removal and subsequent lattice reorganization can create a surface rich in defects. The presence of g-C3N4 in conjunction with defect-rich Mn3O4 enhances the electrochemically accessible surface area, thereby increasing the reaction rate for both ethylene glycol electrooxidation reactions (EGEOR) and ethylene glycol-assisted water splitting reactions (EG-WSR). The nanocomposite achieves a current density of 10 mA/cm2 at 1.32 V vs RHE for EGEOR. It also shows superior mass activity (66.6 A/g), specific activity (0.380 mA/cm2), and turnover frequency (0.0796 s−1) compared to oxygen evolution reaction (OER), indicating favorable kinetics for water splitting. In a two-electrode single-stack configuration, the nanocomposite requires only 1.30 V at 10 mA/cm2 for ethylene glycol-assisted water splitting, achieving 91.2% faradaic efficiency in converting ethylene glycol to glycolic acid and 95% for hydrogen production. The electrical energy consumption for hydrogen production, both with and without ethylene glycol, indicates that the EG-WSR reduces energy consumption by 14.7%, demonstrating its efficiency in hydrogen production. Additionally, the catalyst maintains stability, sustaining a current density of 2 A for over 24 h with minimal degradation. These results emphasize the effectiveness of the reconstruction strategy for transition metal-based electrocatalysts and offer insights for designing high-performance electrocatalysts for water splitting and organic molecule electrooxidation.