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The terms biomimetic and bioinspired are very relevant in the field of bioinorganic chemistry and have been widely applied. Although they were defined by the International Organization for Standardization in 2015, these terms have at times been used rather ambiguously in the literature. This may be due to the inherent complexity of bioinorganic systems where, for example, a structural model of an enzyme active site may not replicate its function. Conversely, the function of an enzyme may be reproduced in a system where the structure does not resemble the enzyme’s active site. To address this, we suggest definitions for the terms biomimetic and bioinspired wherein structure and function have been decoupled. With the help of some representative case studies we have outlined the challenges that may arise and make suggestions on how to apply terminology with careful intention.

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 H2O2generation has hardly been investigated in a systematic manner, and it is unknown if their stability is sufficient for H2O2generation in bulk electrolysis. This study answers these questions using the copper-based Cu(tmpa) (tmpa = tris(2-pyridylmethyl)amine) complex. Since the selectivity of H2O2production originates from the relative rates of oxygen and H2O2reduction, 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 H2O2production with an FEH2O2of more than 50% over 8 h. Additionally, we show that Cu(tmpa) has a great electrochemical stability and is able to generate H2O2in various electrolytes.

Phebe van Langevelde earned her BSc in molecular science and technology from Leiden University and Delft University of Technology (joint degree) in 2017. She completed a master's degree in chemistry with a specialization in energy and sustainability at Leiden University in 2020, working on the development of catalysts for the oxygen reduction reaction, and was a visiting student at the Institute of Chemical Research of Catalonia (ICIQ). Since 2020, she is a PhD candidate in the Catalysis and Surface Chemistry group of Leiden University. Her current research focuses on electrocatalysis for the sustainable production of hydrogen peroxide.

Changes in the electronic structure of copper complexes can have a remarkable impact on the catalytic rates, selectivity, and overpotential of electrocatalytic reactions. We have investigated the effect of the half-wave potential (E1/2) of the CuII/CuIredox couples of four copper complexes with different pyridylalkylamine ligands. A linear relationship was found between E1/2of the catalysts and the logarithm of the maximum rate constant of the reduction of O2and H2O2. Computed binding constants of the binding of O2to CuI, which is the rate-determining step of the oxygen reduction reaction, also correlate with E1/2. Higher catalytic rates were found for catalysts with more negative E1/2values, while catalytic reactions with lower overpotentials were found for complexes with more positive E1/2values. The reduction of O2is more strongly affected by the E1/2than the H2O2rates, resulting in that the faster catalysts are prone to accumulate peroxide, while the catalysts operating with a low overpotential are set up to accommodate the 4-electron reduction to water. This work shows that the E1/2is an important descriptor in copper-mediated O2reduction and that producing hydrogen peroxide selectively close to its equilibrium potential at 0.68 V vs reversible hydrogen electrode (RHE) may not be easy.