Selective electrochemical H2O2 production by a molecular copper catalyst: A crucial relation between reaction rate and mass transport

Hydrogen peroxide (H2O2) generation via electrochemical oxygen reduction is a sustainable production method for this bulk chemical. However, the selectivity of molecular catalysts for electrochemical H2O2 generation has hardly been investigated in a systematic manner, and it is unknown if their stability is sufficient for H2O2 generation in bulk electrolysis. This study answers these questions using the copper-based Cu(tmpa) (tmpa = tris(2-pyridylmethyl)amine) complex. Since the selectivity of H2O2 production originates from the relative rates of oxygen and H2O2 reduction, we show that substrate availability and catalyst concentration are key descriptors to tune the selectivity. Consequently, we can control the Faradaic efficiency to H2O2 (FEH2O2) in bulk electrolysis, and micromolar concentrations of Cu(tmpa) are sufficient for H2O2 production with an FEH2O2 of more than 50% over 8 h. Additionally, we show that Cu(tmpa) has a great electrochemical stability and is able to generate H2O2 in various electrolytes.