Electrosynthesis of Hydrogen Peroxide Enabled by Exceptional Molecular Ni Sites in a Graphene-Supported Nickel...

Electrosynthesis of hydrogen peroxide (H₂O₂) from 2e^- transfer of the oxygen reduction reaction (2e^--ORR) is a potential alternative to the traditional anthraquinone process. Two-dimensional (2D) metal-organic frameworks (MOFs) supported by carbon are frequently reported as promising 2e^--ORR catalysts. Herein, a graphene-supported 2D MOF of Ni₃(2,3,6,7,10,11-hexahydrotriphenylene)₂ is synthesized through a common hydrothermal method, which exhibits high 2e^--ORR performance. It is discovered that except for emerging MOFs, exceptional molecularly dispersed Ni sites coexist in the synthesis that have the same coordination sphere of the NiO₄C₄ moiety as the MOF. The molecular Ni sites are more catalytically active. The graphene support contains a suitable amount of residual oxygen groups, leading to the generation of those molecularly dispersed Ni sites. The oxygen groups exhibit a moderate electron-withdrawing effect at the outer sphere of Ni sites to slightly increase their oxidation state. This interaction decreases overpotentials and kinetically improves the selectivity of the 2e^- reaction pathway.