A Selective Copper Based Oxygen Reduction Catalyst for the Electrochemical Synthesis of H₂O₂ at Neutral pH

Abstract

H₂O₂ is a bulk chemical used as "green" alternative in a variety of applications, but has an energy and waste intensive production method. The electrochemical O₂ reduction to H₂O₂ is viable alternative with examples of the direct production of up to 20% H₂O₂ solutions. In that respect, we found that the dinuclear complex Cu₂(btmpa) (6,6'-bis[[bis(2-pyridylmethyl)amino]methyl]-2,2'-bipyridine) reduces O₂ to H₂O₂ with a selectivity up to 90 % according to single linear sweep rotating ring disk electrode measurements. Microbalance experiments showed that complex reduction leads to surface adsorption thereby increasing the catalytic current. More importantly, we kept a high Faradaic efficiency for H₂O₂ between 60 and 70 % over the course of 2 h of amperometry by introducing high potential intervals to strip deposited copper (^depCu). This is the first example of extensive studies into the long term electrochemical O₂ to H₂O₂ reduction by a molecular complex which allowed to retain the high intrinsic selectivity of Cu₂(btmpa) towards H₂O₂ production leading to relevant levels of H₂O₂.