Avoiding a bang! Electrochemical reduction of O2 in an H2/O2 fuel cell with a three‐phase boundary (gaseous O2, aqueous electrolyte, solid cathode) produces concentrated aqueous solutions of H2O2. Even air can serve as the oxygen source.

Knallgasfrei und ökonomisch: Die elektrochemische Reduktion von O2 in einer H2/O2‐Brennstoffzelle mit Dreiphasen‐Grenzfläche (gasförmiges O2, wässrige Elektrolytlösung, feste Kathode) liefert konzentrierte wässrige H2O2‐Lösungen. Luft kann bei diesem Verfahren als Sauerstoffquelle dienen.

Heat-treated MnCl−porphyrin supported on activated carbon (AC) catalyzed electrochemical reduction of O 2 to H 2 O 2 using an H 2 /O 2 fuel cell reactor. Suitable preparation conditions for an Mn−porphyrin electrocatalyst were studied for the H 2 O 2 formation, such as types of porphyrin rings, heat-treatment temperatures in He, and Mn loadings. The effects of reaction conditions, H 2 SO 4 concentration, P(O 2 ), P(H 2 ), and electrolyte flow on the H 2 O 2 formation were studied. Then, 0.5 wt % MnCl−TPP/AC heat treated at 823 K and 0.3 wt % MnCl−OEP/AC heat treated at 723 K showed good electrocatalytic activities for the H 2 O 2 formation (TPP: 5,10,15,20-tetrakis-(phenyl)-21H,23H-porphyrin, OEP: 2,3,7,8,12,13,17,18-octaethyl-21H,23Hporphyrin). A maximum H 2 O 2 concentration of 1.0 mol dm −3 with 47% current efficiency (CE) was obtained under suitable conditions. The heattreated MnCl−TPP/AC and MnCl−OEP/AC electrocatalysts were characterized using temperature-programmed desorption, X-ray absorption near-edge structure spectroscopy, elemental analysis, cyclic voltammetry, and rotating ring-disk electrode voltammetry. Elimination of Cl from MnCl−TPP and MnCl−OEP supported on AC was essential to generate an active site for the H 2 O 2 formation. A model of the Mn active site was proposed.

Mn–porphyrin supported on active carbon, which was activated by heat-treatment in Ar, electrochemically catalyzed reduction of O2 to H2O2 by the H2/O2 fuel cell method. The electrocatalytic activities were strongly dependent on the heat-treatment temperatures. The maximum H2O2 concentration of 3.5 wt % with 47% current efficiency was obtained for the catalyst treated at 450 °C, and a TON (Mn) for the H2O2 formation was over 1000 h−1.