Linker‐Modulated Peroxide Electrosynthesis Using Metal‐Organic Nanosheets**

Abstract

The electrochemical synthesis of hydrogen peroxide (H 2 O 2 ), a widely used oxidant, is emerging as a green alternative to the conventional anthraquinone method. In this work, Ni-based metal-organic nanosheet (NiÀ MON) catalysts constructed using a variety of linkers were studied as oxygen reduction catalysts. Using a host of analytical techniques, we reveal how modulating the terephthalic acid linker with hydroxy, amine, and fluorine groups impacts the resulting physical and electronic structure of the Ni catalytic sites. These changes further impact the catalysts' Faradaic Efficiency for H 2 O 2 , with the NiÀ AmineÀ MON reaching near 100 % FE at minimal overpotential for the 2e À H 2 O 2 pathway in alkaline electrolyte. Finally, we translate the NiÀ AmineÀ MON catalyst to a gasdiffusion reaction geometry and demonstrate a H 2 O 2 partial current density of 200 mA/cm 2 while maintaining 85 % Faradaic efficiency. In all, this study puts forth a simple route to catalyst modulation for highly effective H 2 O 2 electrosynthesis.

Electrocatalysis with molecules and molecular assemblies within gas diffusion electrodes

“…The effect of linkers was also used to modulate the reactivity of Ni-based 2D sheets used for oxygen reduction to peroxide, a widely used chemical oxidant. 88 A hypothesis was that amine-functionalized linkers weakened the binding of *OOH on the Ni active sites and thereby promoted the desorption of the desired product (partial current densities of up to 200 mA cm −2 ) instead of over-reduction to H 2 O in a GDE alkaline flow cell setup.…”

Thousand-fold increase in O2 electroreduction rates with conductive MOFs

“…Electrically conductive metal–organic frameworks (MOFs) offer a way to bridge this gap, as they are molecularly defined and are both intrinsically porous and conductive . They are fundamentally distinct from electrocatalysts made from sacrificial MOF precursors (such as single-atom catalysts accessed via thermolysis or electrolytic degradation of MOFs), because they retain their molecular definition. ,,,,− As such, the structure space available to conductive MOFs renders them an ideal platform to tune the atomic structure for performance. We and others have previously shown that a family of 2D MOFs with the general formula M 3 (HITP) 2 (HITP = 2,3,6,7,10,11-hexaiminotriphenylene, M = Co, Cu, Ni) (Figure A) are active for the O 2 electroreduction reaction (ORR), a transformation central to H 2 O 2 electrosynthesis, metal/air batteries, and fuel cells. ,, These and other conductive MOFs typically exhibit intrinsic surface areas (∼300–900 m 2 g –1 ) at least 10 times larger than that of dense metallic nanoparticles and conductivities comparable to that of graphite, yet their geometric current densities for ORR rarely exceed −1 mA cm –2 , implying a surprisingly low intrinsic electrocatalytic activity. ,,,,− …”