W Doping in Ni12P5 as a Platform to Enhance Overall Electrochemical Water Splitting.

Bifunctional electrocatalysts for efficient hydrogen generation from water splitting must overcome both the sluggish water dissociation step of the alkaline hydrogen evolution half-reaction (HER) and the kinetic barrier of the anodic oxygen evolution half-reaction (OER). Nickel phosphides are a promising catalysts family and are known to develop a thin active layer of oxidized Ni in an alkaline medium. Here, Ni12P5 was recognized as a suitable platform for the electrochemical production of γ-NiOOH─a particularly active phase─because of its matching crystallographic structure. The incorporation of tungsten by doping produces additional surface roughness, increases the electrochemical surface area (ESCA), and reduces the energy barrier for electron-coupled water dissociation (the Volmer step for the formation of Hads). When serving as both the anode and cathode, the 15% W-Ni12P5 catalyst provides an overall water splitting current density of 10 mA cm-2 at a cell voltage of only 1.73 V with good durability, making it a promising bifunctional catalyst for practical water electrolysis.

Metal-organic framework derived nanomaterials for electrocatalysis: recent developments for CO2 and N2 reduction.

In recent years, we are witnessing a substantially growing scientific interest in MOFs and their derived materials in the field of electrocatalysis. MOFs acting as a self-sacrificing template offer various advantages for the synthesis of carbon-rich materials, metal oxides, and metal nanostructures containing graphitic carbon-based materials benefiting from the high surface area, porous structure, and abundance of metal sites and organic functionalities. Yet, despite recent advancement in the field of MOF-derived materials, there are still several significant challenges that should be overcomed, to obtain better control and understanding on the factors determining their chemical, structural and catalytic nature. In this minireview, we will discuss recently reported advances in the development of promising methods and strategies for the construction of functional MOF-derived materials and their application as highly-active electrocatalysts for two important energy-related reactions: nitrogen reduction to produce ammonia, and CO2 reduction into carbon-based fuels. Moreover, a discussion containing assessments and remarks on the possible future developments of MOF-derived materials toward efficient electrocatalysis is included.

Active-Site Modulation in an Fe-Porphyrin-Based Metal-Organic Framework through Ligand Axial Coordination: Accelerating Electrocatalysis and Charge-Transport Kinetics.

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.

Pristine versus Pyrolyzed Metal-Organic Framework-based Oxygen Evolution Electrocatalysts: Evaluation of Intrinsic Activity Using Electrochemical Impedance Spectroscopy.

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-Fe-based 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, EIS-extracted 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 mass-transport limitations.

Redox-active, pyrene-based pristine porous organic polymers for efficient energy storage with exceptional cyclic stability.

A novel class of pyrene-based conjugated porous organic polymers having an N-containing network was developed by employing Buchwald-Hartwig coupling for supercapacitor energy storage. The pristine polymer was found to exhibit a specific capacitance of 456 F g-1 at 0.5 A g-1 current density with excellent long-term cyclic stability.

Nano "Koosh Balls" of Mesoporous MnO2 : Improved Supercapacitor Performance through Superior Ion Transport.

Manganese dioxide nanomaterials with "Koosh-ball"-like morphology (MnO2 -KBs) as well as worm-like nanotubes (MnO2 -NWs) are obtained by employing Tween 20 as the reducing and structure-directing agent, and KMnO4 as a MnO2 precursor. Whereas the MnO2 -KBs are interconnected through tubular extensions, the MnO2 -NWs are largely disconnected. Both MnO2 -KBs and MnO2 -NWs have large BET surface areas (>200 m2 g-1 ), and are thermally robust up to 300 °C. Electrochemical studies reveal that the highest specific capacitance (Csp ) obtained for MnO2 -KBs (272 F g-1 ) is significantly higher than that of MnO2 -NWs (129 F g-1 ). The Csp values correlate well with the electroactive surface areas of the materials: MnO2 -KBs have a significantly higher electrolyte-accessible surface area. Electrochemical impedance spectroscopy (EIS) reveals a higher electron-transfer rate at the electrode/electrolyte interface for MnO2 -KBs than for MnO2 -NWs. The multiple tubular interconnections between individual MnO2 -KBs allow improved ion penetration and act as conduits for their propagation, shortening the diffusion distances of the ions from external electrolytes to the interior of the MnO2 framework. Thus, this work exemplifies the importance of interconnections for enhancing the electrochemical performance of nanomaterials employed for energy storage.

Correction: Proton conduction through oxygen functionalized few-layer graphene.

Correction for 'Proton conduction through oxygen functionalized few-layer graphene' by Chanderpratap Singh et al., Chem. Commun., 2016, 52, 12661-12664.

Proton conduction through oxygen functionalized few-layer graphene.

The first report of oxygen functionalized few-layer graphene (OFG) having an interlayer distance of 3.6 Å as an excellent proton conductor (8.7 × 10-3 S cm-1 at 80 °C, 95% RH) utilizing hydrophilic oxygen functionalities present at sheet edges bypassing the theoretical limitation of proton conduction through a basal plane. The synthesized OFG also exhibited excellent supercapacitor performance (296 F g-1).