Electrospun Carbon Nanofibers with Embedded Co-Ceria Nanoparticles for Efficient Hydrogen Evolution and Overall Water Splitting

In this study, simple electrospinning combined with pyrolysis were used to fabricate transition-metal-based-nanoparticle-incorporated carbon nanofiber (CNF) electrocatalysts for a high-efficiency hydrogen evolution reaction (HER) and overall water splitting. Co-CeO2 nanoparticle-incorporated carbon nanofibers (Co-CeO2@CNF) exhibit an outstanding electrocatalytic HER performance with an overpotential and Tafel slope of 92 mV and 54 mV/dec, respectively. For the counterpart, electrolysis, we incorporate the widely used Ni2Fe catalyst with a high oxygen evolution reaction (OER) activity into the carbon nanofiber (Ni2Fe@CNF). To evaluate their electrochemical properties for the overall water splitting, Co-CeO2@CNF and Ni2Fe@CNF were used as the HER and OER electrocatalysts in an alkaline electrolyzer. With the paired Co-CeO2@CNF and Ni2Fe@CNF electrodes, an overall water splitting current density of 10 mA/cm2 was achieved by applying 1.587 V across the electrodes with a remarkably lower overpotential of 257 mV compared to that of an electrolyzer comprised of Pt/C and IrO2 electrodes (400 mV). Owing to the conformal incorporation of nanoparticles into the CNF, the electrocatalysts exhibit significant long-term durability over 70 h of overall water splitting. This study provides rational designs of catalysts with high electrochemical catalytic activity and durability to achieve overall water splitting.

Construction of secondary coordination sphere boosts electrochemical CO2 reduction of iron porphyrins

Iron porphyrins with simple aminophenyl substitution are synthesized and their electrochemical CO[Formula: see text] reduction properties are studied. Fe-1, bearing an amino group in the ortho position of the phenyl ring exhibits an improved catalytic turn over frequency (TOF), lower overpotential and higher selectivity, compared with para-amino-substituted iron porphyrin (Fe-2) and the control iron tetraphenylporphyrin (Fe-3). DFT calculations also support the importance of hydrogen bonds on the reactivity of Fe-1, which facilitates the formation [Fe–CO[Formula: see text]][Formula: see text] adduct by lowering 1.45 kcal mol[Formula: see text].

Lithia/(Ir, Li2IrO3) nanocomposites for new cathode materials based on pure anionic redox reaction

Anionic redox reactions attributed to oxygen have attracted much attention as a new approach to overcoming the energy-density limits of cathode materials. Several oxides have been suggested as new cathode materials with high capacities based on anionic (oxygen) redox reactions. Although most still have a large portion of their capacity based on the cationic redox reaction, lithia-based cathodes present high capacities that are purely dependent upon oxygen redox. Contrary to Li-air batteries, other systems using pure oxygen redox reactions, lithia-based cathodes charge and discharge without a phase transition between gas and condensed forms. This leads to a more stable cyclic performance and lower overpotential compared with those of Li-air systems. However, to activate nanolithia and stabilize reaction products such as Li2O2 during cycling, lithia-based cathodes demand efficient catalysts (dopants). In this study, Ir based materials (Ir and Li2IrO3) were introduced as catalysts (dopants) for nanolithia composites. Oxide types (Li2IrO3) were used as source materials of catalyst because ductile metal (Ir) can hardly be pulverized during the milling process. Two types of Li2IrO3 were prepared and used for catalyst-sources. They were named ‘1-step Li2IrO3’ and ‘2-step Li2IrO3’, respectively, since they were prepared by ‘1-step’ or ‘2-step’ heat treatment. The nanocomposites prepared using lithia & 2-step Li2IrO3 presented a higher capacity, more stable cyclic performance, and lower overpotential than those of the nanocomposites prepared using lithia & 1-step Li2IrO3. The voltage profiles of the nanocomposites prepared using lithia & 2-step Li2IrO3 were stable up to a limited capacity of 600 mAh·g−1, and the capacity was maintained during 100 cycles. XPS analysis confirmed that the capacity of our lithia-based compounds is attributable to the oxygen redox reaction, whereas the cationic redox related to the Ir barely contributes to their discharge capacity.

Aromaticity Driven Electrocatalytic Water Oxidation by a Phosphorus-Nitrogen PN3-Pincer Cobalt Complex

Water oxidation is the primary step in both natural and artificial photosynthesis to convert solar energy in into chemical fuels. Herein, we report the first cobalt-based pincer catalyst for electrolytic water oxidation at neutral pH with high efficiency under electrochemical conditions. Most importantly, ligand (pseudo)aromaticity is identified to play an important role in the electrocatalysis. A significant potential jump (~300 mV) was achieved towards a lower positive value when the aromatized cobalt complex was transformed to a (pseudo)dearomatized cobalt species. This complex catalyzes the water oxidation in its high valent oxidation state at a much lower overpotential (~ 340 mV vs. NHE) based on the onset potential (0.5 mA/cm²) of catalysis at pH 10.5, outperforming all the other literature systems. These observations may provide a new strategy for the design of earth-abundant transition metal-based water oxidation catalysts.

Aromaticity Driven Electrocatalytic Water Oxidation by a Phosphorus-Nitrogen PN3-Pincer Cobalt Complex

Water oxidation is the primary step in both natural and artificial photosynthesis to convert solar energy in into chemical fuels. Herein, we report the first cobalt-based pincer catalyst for electrolytic water oxidation at neutral pH with high efficiency under electrochemical conditions. Most importantly, ligand (pseudo)aromaticity is identified to play an important role in the electrocatalysis. A significant potential jump (~300 mV) was achieved towards a lower positive value when the aromatized cobalt complex was transformed to a (pseudo)dearomatized cobalt species. This complex catalyzes the water oxidation in its high valent oxidation state at a much lower overpotential (~ 340 mV vs. NHE) based on the onset potential (0.5 mA/cm²) of catalysis at pH 10.5, outperforming all the other literature systems. These observations may provide a new strategy for the design of earth-abundant transition metal-based water oxidation catalysts.

A Facile Electrochemical Sensor Labeled by Ferrocenoyl Cysteine Conjugate for the Detection of Nitrite in Pickle Juice

Simple and facile electrochemical sensors for nitrite detection were fabricated by directly depositing ferrocenoyl cysteine conjugates Fc[CO-Cys(Trt)-OMe]2 [Fc(Cys)2] or Fc[CO-Glu-Cys-Gly-OH] [Fc-ECG] on screen-printed electrodes (SPEs). The modified carbon electrodes were characterized by scanning electron microscopy (SEM), cyclic voltammetry (CV) and differential pulse voltammetry (DPV). Results indicated that Fc-ECG/SPE sensor showed enhanced current response and a lower overpotential than Fc(Cys)2/SPE sensor for nitrite detection. Optimal operating conditions were estimated for nitrite detection by DPV. The concentration of nitrite showed a good linear relationship with the current response in the range of 1.0–50 μmol·L−1 and with 0.3 μmol·L−1 as the concentration for limit of detection. There were no interferences from most common ions. The development of this electrochemical sensor was used for nitrite detection in pickled juice with a R.S.D. lower than 2.1% and average recovery lower than 101.5%, which indicated that disposable electrochemical sensor system can be applied for rapid and precise nitrite detection in foods.

Enhanced Electrocatalytic CO2 Reduction at Lower Overpotentials Using Iron (III) Tetra(thienyl)porphyrin

Iron(III) tetra(5,10,15,20-thienyl)porphyrin chloride (FeTThP) is introduced as a new CO₂ reduction catalyst. The optical and electrochemical properties, as well as the CO₂ reduction capabilities of FeTThP are directly compared to those of iron(III) tetra(5,10,15,20-phenyl)porphyrin chloride (FeTPP). Relative to FeTPP, the newly developed FeTThP achieves a higher TON_CO, with comparable faradaic efficiency, using a much lower overpotential.

Engineering the surface atomic structure of FeVO4 nanocrystals for use as highly active and stable electrocatalysts for oxygen evolution

FeVO4 nanobelts bounded by {010} facets exhibit much higher OER activities and lower overpotential than nanosheets enclosed by {010} facets, which were mainly attributed to the favorable atomic arrangements of {010} facets with Fe–V dual-active sites and an open surface structure.

In situ study of the low overpotential “dimer pathway” for electrocatalytic carbon dioxide reduction by manganese carbonyl complexes

In situ VSFG spectroscopy was used to probe the mechanism of the lower overpotential “dimer pathway” for the CO2 reduction by [Mn(bpy)(CO)3]Br.