Computational Discovery of Active and Selective Metal-Nitrogen-Graphene Catalysts for Electrooxidation of Water to H₂O₂

A direct electrosynthesis of H2O2 from either O-2 or H2O is an attractive strategy to replace the energy-intensive industrial anthraquinone process. Two-electron water oxidation reaction (2e-WOR) offers several advantages over the oxygen reduction reaction such as better mass transfer due to the absence of gas-phase reactants. However, 2e-WOR is a more challenging and less studied process with only a handful of metal oxides exhibiting reasonable activity/selectivity properties. Herein, we employ density-functional-theory calculations to screen a variety of metal-nitrogen-graphene structures for 2e-WOR. As a consequence of scaling between the adsorption energies of reaction intermediates, we determine a linear relation between selectivities for the first and second reaction steps of 2e-WOR, viz. that if selectivity toward adsorbed OH is improved, then selectivity toward H2O2 at the subsequent step is decreased. We also find that selectivity and activity are linearly scaled in such a way that a higher activity (i. e., a lower overpotential) leads to a lower selectivity for the H2O2 formation step. Based on the obtained results several chemistries, e. g., containing NiNx-C moieties, are predicted to rival the best-performing metal oxides such as ZnO and CaSnO3 in terms of combination of their activity/selectivity characteristics for 2e-WOR.