One-Step High-Temperature Electrodeposition of Fe-Based Films as Efficient Water Oxidation Catalysts.

Electrolysis of water to produce hydrogen requires an efficient catalyst preferably made of cheap and abundant metal ions for the improved water oxidation reaction. An Fe-based film has been deposited in a single step by electrochemical deposition at temperatures higher than the room temperature. Until now, the electrodeposition of iron oxide has been carried out at 298 K or at lower temperatures under a controlled atmosphere to prohibit atmospheric oxidation of Fe2+ of the iron precursor. A metal inorganic complex, ferrocene, and non-aqueous electrolyte medium propylene carbonate have been used to achieve electrodeposition of iron oxide without the need of any inert or controlled atmosphere. At 298 K, the amorphous film was formed, whereas at 313 K and at higher temperatures, the hematite film was grown, as confirmed by X-ray diffraction. The transformation of iron of the ferrocene into a higher oxidation state under the experimental conditions used was further confirmed by X-ray photoelectron spectroscopy, ultraviolet-visible, and electron paramagnetic resonance spectroscopic methods. The films deposited at 313 K showed the best performance for water oxidation with remarkable long-term electrocatalytic stability and an impressive turnover frequency of 0.028 s-1 which was 4.5 times higher than that of films deposited at 298 K (0.006 s-1). The observed overpotential to achieve a current density of 10 mA cm-2 was found to be 100 mV less for the film deposited at 313 K compared to room-temperature-derived films under similar experimental conditions. Furthermore, electrochemical impedance data revealed that films obtained at 313 K have the least charge transfer resistance (114 Ω) among all, supporting the most efficient electron transport in the film. To the best of our knowledge, this is the first-ever report where the crystalline iron-based film has been shown to be electrodeposited without any post-deposition additional treatment for alkaline oxygen evolution reaction application.

Bioinspired Design of an Uncharged Ambipolar Helical Scaffold To Achieve Efficient Solid-State Proton Conduction.

This work demonstrates highly efficient solid-state proton conduction in helical organic scaffolds inspired by the biomolecule gramicidin A. The scaffold, 1, derived from a pyridine-2,6-dicarboxamide (PDC) residue adopts a helical conformation that is stabilized by a network of strong bifurcated intramolecular H-bonds between the polar residues that align the inner (concave) face of the molecule, while the aromatic units in 1 are oriented outwards. As a result, the helix attains an ambipolar nature just like gramicidin A. Two different solid forms of 1 could be isolated: a yellow solid from high-polarity solvents and an orange solid from low-polarity solvents. Single-crystal X-ray diffraction (SCXRD) studies showed that in the former, molecules of 1 are stacked in a homochiral fashion, while in the latter heterochiral stacks of 1 were present. The yellow form exhibited an almost ∼300-fold higher conductivity (of up to 0.12 mS cm-1 at 95 °C and 95 % relative humidity) than the orange form as a result of closer intermolecular proximity and lower activation energy of 0.098 eV, thus indicating a Grotthus mechanism of proton transport. This study establishes the key role of bioinspired design and controlled stereo-organization of such discrete uncharged organic molecules in achieving efficient solid-state proton conduction.

Decoding Carbon-Based Materials' Properties for High CO2 Capture and Selectivity.

Carbon-based materials are well established as low-cost, easily synthesizable, and low regeneration energy adsorbents against harmful greenhouse gases such as CO2. However, the development of such materials with exceptional CO2 uptake capacity needs well-described research, wherein various factors influencing CO2 adsorption need to be investigated. Therefore, five cost-effective carbon-based materials that have similar textural properties, functional groups, and porous characteristics were selected. Among these materials, biordered ultramicroporous graphitic carbon had shown an excellent CO2 capture capacity of 7.81 mmol/g at 273 K /1 bar with an excellent CO2 vs N2 selectivity of 15 owing to its ultramicroporous nature and unique biordered graphitic morphology. On the other hand, reduced graphene revealed a remarkable CO2 vs N2 selectivity of 57 with a CO2 uptake of 2.36 mmol/g at 273 K/1 bar. In order to understand the high CO2 capture capacity, important properties derived from adsorption/desorption, Raman spectroscopy, and X-ray photoelectron spectroscopy were correlated with CO2 adsorption. This study revealed that an increase in ultramicropore volume and sp2 carbon (graphitic) content of nanomaterials could enhance CO2 capture significantly. FTIR studies revealed the importance of oxygen functionalities in improving CO2 vs N2 selectivity in reduced graphene due to higher quadruple-dipole interactions between CO2 and oxygen functionalization of the material. Apart from high CO2 adsorption capacity, biordered ultramicroporous graphitic carbon also offered low regeneration energy and excellent pressure swing regeneration ability for five consecutive cycles.