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.

The conversion of metal-organic frameworks (MOFs) into inorganic nanomaterials is considered as an attractive means to produce highly efficient electrocatalysts for alternative-energy related applications. Yet, traditionally employed MOF-conversion conditions (e.g., pyrolysis) commonly involve multiple complex high-temperature reaction processes, which often make it challenging to control the composition, pore structure, and active-sites of the MOF-derived catalysts. Herein, a general, simple, room-temperature method is presented for a controlled electrochemical conversion of MOF (EC-MOF) films into porous, amorphous metal sulfides (a-MS x ). Detailed X-ray photoelectron spectroscopy analysis and control over independent EC-MOF parameters (e.g., scan-rate and potential window) enable to gain insights on the MOFconversion mechanisms, and in turn to fine-tune the porosity and composition of the obtained MS x . As a result, a highly active amorphous cobalt sulfide (a-CoS x ) electrocatalyst can be designed for hydrogen evolution reaction in neutral pH. Furthermore, the adjustable nature of the EC-MOF method allows to draw conclusions about the correlation between the concentration of catalytically active species (S 2 2sites) and the hydrogen evolution properties of the a-CoS x . Given the method's generality and the diversity of available MOF structures, EC-MOF provides a compelling platform for a rational design of a wide variety of active electrocatalytic materials.

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.

We show that a MOF-converted compound can act as highly active co-catalyst in a water splitting photo-electrochemical cell.

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.