Municipal Sludge-Derived Activated Carbon as a Highly Efficient and Selective Electrocatalyst for H2O2 Synthesis

Low-cost, efficient, and durable electrocatalysts for two-electron oxygen reduction (2e− ORR) to synthesize hydrogen peroxide (H2O2) are essential for sustainable chemical manufacturing. Herein, we report a sustainable route to prepare activated carbon electrodes (ASC) from municipal sludge via chemical activation and pyrolysis. The electrode activated with 30 wt.% H3PO4 and calcined at 600 °C for 2 h exhibited high catalytic activity. This electrode featured a hierarchical micro-/meso-/macroporous structure with a high BET surface area of 806.20 m2·g−1, abundant carboxyl groups (surface O content of 4.0 at.%), and high hydrophobicity (contact angle of 121.6°). The unique hierarchical porosity, high surface area, hydrophobic surface, and carboxyl functionalities synergistically enhanced O2 mass transfer, exposed abundant accessible active sites, and stabilized the triple-phase interface. Electrochemical evaluation revealed that 30 wt.% H3PO4-ASC achieved a high H2O2 selectivity of 86–92% with an electron transfer number of 2.2, approaching the ideal 2e− ORR pathway. Under optimized conditions (pH = 3, j = 5.0 mA·cm−2), it produced 997.3 mg·L−1 of H2O2 in 90 min, with a current efficiency of 68.8% and an energy consumption of 27.6 kWh·kg−1 H2O2. Moreover, the electrode retained 81.1% of its initial H2O2 production after 15 cycles, demonstrating good reusability and long-term stability. This work offers a sustainable strategy for high-value utilization of municipal sludge and advances the development of efficient electrocatalysts for green H2O2 production.