Electrochemical oxygen reduction to peroxide has garnered significant interest as a green alternative to the conventional anthraquinone production process. Electrochemical synthesis offers potentially economical and environmentally friendly route to peroxide (H2O2) synthesis. The significant challenge in electrochemical oxygen reduction reaction is to have selectivity for peroxide production vs oxygen reduction to water by modulating the binding strength of intermediates. Herein linker modulated Ni-based metal-organic nanosheets (Ni-MONs) catalysts were investigated as catalysts for peroxide synthesis. The electronic structure of the Ni active sites was tuned by constructing analogous Ni-MONs with electron-withdrawing groups - fluorine (Ni-F-MON) and electron-donating groups such as (hydroxyl, amine) (Ni-OH-MON, Ni-Amine-MON) grafted onto their linkers. The electronic structure of the Ni active sites of the MONs was investigated through a series of electrochemical experiments and X-ray photoelectron spectroscopy measurements. Amongst the Ni-MONs studied, the Ni-MONs with an electron-donating group –hydroxyl and amine have demonstrated higher activity and selectivity. In a gas diffusion electrode set up with Ni-Amine-MON partial current density of 21.7 mAcm-2 were obtained. Subsequently the system is scaled up to obtain the higher partial current density. Our interpretation is that modifying the Ni electronic structure modulates the binding energy to the *OOH intermediate and is thus the determining factor for H2O2 vs. H2O selectivity in this system and electron-donating groups (hydroxyl and amine) linkers regulated the Ni catalytic activity. This study puts forward design principles towards attaining higher selectivity of electrosynthesis of H2O2 through rational modulation of catalytic sites.

Linker modulated peroxide electrosynthesis using metal-organic nanosheets

ACS Spring 2022

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