The construction of artificial solar
fuel generating systems requires
the heterogenization of large quantities of catalytically active sites
on electrodes. In that sense, metal–organic frameworks (MOFs)
have been utilized to assemble unpreceded concentration of electrochemically
active molecular catalysts to drive energy-conversion electrocatalytic
reactions. However, despite recent advances in MOF-based electrocatalysis,
so far no attempt has been made to exploit their unique chemical modularity
in order to tailor the electrocatalytic function of MOF-anchored active
sites at the molecular level. Here, we show that the axial coordination
of electron-donating ligands to active MOF-installed Fe-porphyrins
dramatically alters their electronic properties, accelerating the
rates of both redox-based MOF conductivity and the electrocatalytic
oxygen reduction reaction (ORR). Additionally, electrochemical characterizations
show that in multiple proton-coupled electron transfer reactions MOF-based
redox hopping is not the only factor that limits the overall electrocatalytic
rate. Hence, future efforts to enhance the efficiency of electrocatalytic
MOFs should also consider other important kinetic parameters such
as the rate of proton-associated chemical steps as well as mass-transport
rates of counterions, protons, and reactants toward catalytically
active sites.
Rhodium, nickel and iridium are introduced into polycyclooctadiene to generate organometallic nanoparticles with different ratios of metals and catalytic properties.
Electrochemically active Metal-Organic Frameworks (MOFs) have been progressively recognized for their use in solar fuel production schemes. Typically, they are utilized as platforms for heterogeneous tethering of exceptionally large concentration of molecular electrocatalysts onto electrodes. Yet so far, the potential influence of their extraordinary chemical modularity on electrocatalysis has been overlooked. Herein, we demonstrate that, when assembled on a solid Ag CO 2 reduction electrocatalyst, a non-catalytic UiO-66 MOF acts as a porous membrane that systematically tunes the active sites immediate chemical environment, leading to a drastic enhancement of electrocatalytic activity and selectivity. Electrochemical analysis shows that the MOF membrane improves catalytic performance through physical and electrostatic regulation of reactants delivery towards the catalytic sites. The MOF also stabilizes catalytic intermediates via modulation of active sites secondary coordination sphere. This concept can be expanded to a wide range of proton-coupled electrochemical reactions, providing new means for precise, molecularlevel manipulation of heterogeneous solar fuels systems.
Metal oxides or sulfides are considered to be one of the most promising CO2 reduction reaction (CO2RR) precatalysts, owing to their electrochemical conversion in situ into highly active electrocatalytic species. However, further improvement of the performance requires new tools to gain fine control over the composition of the active species and its structural features [e.g., grain boundaries (GBs) and undercoordinated sites (USs)], directly from a predesigned template material. Herein, we describe a novel electrochemically driven cation exchange (ED‐CE) method that enables the conversion of a predesigned CoS2 template into a CO2RR catalyst, Cu2S. By means of ED‐CE, the final Cu2S catalyst inherits the original 3 D morphology of CoS2, and preserves its high density of GBs. Additionally, the catalyst's phase structure, composition, and density of USs were precisely tuned, thus enabling rational design of active CO2RR sites. The obtained Cu2S catalyst achieved a CO2‐to‐formate Faradaic efficiency of over 87 % and a record high activity (among reported Cu‐based catalysts). Hence, this study opens the way for utilization of ED‐CE reactions to design advanced electrocatalysts.
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