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.

Electrocatalytic oxidative upgrading of organic molecules is a promising alternative process to water oxidation for clean hydrogen production. Yet, its underlying mechanism is still not fully understood, and suitable low‐cost electrocatalysts with good product selectivity and activity are still sought after. Here, an active NiFeOx‐based catalyst is reported on as a general platform for the electro‐oxidative upgrading of organic molecules through oxygenation and dehydrogenation, with hydrogen coproduction. Detailed mechanistic studies unveil that C–H bond oxidation (with a bond dissociation energy BDEC–H of ≈88–96 kcal mol−1) is involved in the rate‐limiting step, which differs significantly from the oxygen evolution reaction mechanism. These findings show that the oxidation efficacy is linearly correlated with the BDEC–H of the molecule. Thus, the catalyst can be used as a general platform for large‐scale electro‐oxidation of various substrates through oxygenation and dehydrogenation at high current density (25 mA cm−2), with a good Faradaic yield. The platform's generality is further demonstrated by the selective oxidation of 5‐(hydroxymethyl)furfural into 2,5‐furandicarboxylic acid with good efficiency.

Redox-active Metal−Organic Frameworks (MOFs) are considered as promising platforms for assembling high quantities of solutionaccessible molecular catalysts on conductive surfaces, toward their utilization in electrochemical solar fuel related reactions. Nevertheless, slow redox hopping-based conductivity often constitutes a kinetic bottleneck hindering the overall electrocatalytic performance of these systems. In this work, we show that, by a systematic control of MOF defect site density, one can modulate the spatial distribution of post synthetically installed molecular catalyst and hence accelerate charge transport rates by an order of magnitude. Moreover, the improved MOF conductivity also yields an enhancement in its intrinsic electrocatalytic activity. Consequently, these results offer new possibilities for designing efficient MOF-based electrocatalytic systems.

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−organic frameworks (MOFs) have emerged as outstanding electrocatalysts for water oxidation. Commonly, MOFs are utilized for electrocatalytic water oxidation either in pristine or pyrolyzed form. Yet, despite significant advancements in their catalytic performance, further improvement requires new insights on the parameters influencing MOF-based catalysts activity. Here, we have conducted a detailed comparison between the intrinsic electrocatalytic properties of pristine and pyrolyzed Ni−Febased MOFs. Interestingly, although pristine MOF exhibits the maximum overall electrocatalytic performance, apparent turnover frequency (TOF) values (intrinsic activity) of all pyrolyzed MOFs exceeded the one of pristine MOF. Moreover, an upper-limit estimation of TOF was extracted using electrochemical impedance spectroscopy (EIS), by excluding IR-drops linked with the electrochemical cell. By doing so, EISextracted TOF values were 10-times higher compared to the apparent TOFs. Accordingly, a great leap in performance should still be expected for these catalysts, by designing conductive MOF-platforms having larger pore-diameters to reduce masstransport limitations.