Defective Carbon Electrocatalysts with Accessible Mesopores for Hydrogen Peroxide Synthesis

The growing demand for green synthesis of hydrogen peroxide (H₂O₂) has fueled great interest in electrochemical synthesis via the oxygen reduction reaction (ORR). Carbon-based materials are an appealing class of electrocatalysts, offering the promise of tunable defects, heteroatom dopants, and controllable pore structures. However, increasing the accessibility of mesopores in carbon-based materials is challenging due to the restricted diffusion depth. In this study, we report the synthesis of a mesoporous carbon hollow shell with a big surface opening (C-750) and the nonhollow control material (C-750C). The hollow structure with a big surface opening facilitates rapid diffusion and transport of reactants and products through both its exterior and interior surfaces. This structure enables prompt reactant access to active sites and efficient product desorption, thereby yielding exceptional electrocatalytic ORR performance. In contrast, nonhollow mesoporous carbon materials rely solely on external surface diffusion, resulting in longer transport pathways, restricted accessibility to active sites, and product accumulation that diminishes reaction efficiency. In the rotating ring-disk electrode, C-750 demonstrates a higher diffusion-limited current density and higher H₂O₂ selectivity than C-750C, highlighting its superior mass transport efficiency due to the hollow structure as well as the large opening on the shell. In the flow cell, C-750 shows an industrial-level current density of ∼ -244 mA cm^-2 at 0.28 V vs RHE, and the production rate of H₂O₂ is over 14.6 mol h^-1 g_cat^-1. The density of edge defects, tailored by changing the carbonization temperature, works synergistically with oxygen dopants to enhance the catalytic performance, as confirmed by both theoretical simulations and experimental results.