4 research outputs found
MnO2-Ir Nanowires: Combining Ultrasmall Nanoparticle Sizes, O-Vacancies, and Low Noble-Metal Loading with Improved Activities towards the Oxygen Reduction Reaction
"Although clean energy generation utilizing the Oxygen Reduction Reaction (ORR) can
be considered a promising strategy, this approach remains challenging by the dependence on high
loadings of noble metals, mainly Platinum (Pt). Therefore, efforts have been directed to develop
new and efficient electrocatalysts that could decrease the Pt content (e.g., by nanotechnology tools or
alloying) or replace them completely in these systems. The present investigation shows that high
catalytic activity can be reached towards the ORR by employing 1.8 ± 0.7 nm Ir nanoparticles (NPs)
deposited onto MnO2 nanowires surface under low Ir loadings (1.2 wt.%). Interestingly, we observed
that the MnO2
-Ir nanohybrid presented high catalytic activity for the ORR close to commercial
Pt/C (20.0 wt.% of Pt), indicating that it could obtain efficient performance using a simple synthetic
procedure. The MnO2
-Ir electrocatalyst also showed improved stability relative to commercial Pt/C,
in which only a slight activity loss was observed after 50 reaction cycles. Considering our findings,
the superior performance delivered by the MnO2
-Ir nanohybrid may be related to (i) the significant
concentration of reduced Mn3+ species, leading to increased concentration of oxygen vacancies at its
surface; (ii) the presence of strong metal-support interactions (SMSI), in which the electronic effect
between MnOx and Ir may enhance the ORR process; and (iii) the unique structure comprised by Ir
ultrasmall sizes at the nanowire surface that enable the exposure of high energy surface/facets, high
surface-to-volume ratios, and their uniform dispersion.
MnO2-Ir Nanowires: Combining Ultrasmall Nanoparticle Sizes, O-Vacancies, and Low Noble-Metal Loading with Improved Activities towards the Oxygen Reduction Reaction
Although clean energy generation utilizing the Oxygen Reduction Reaction (ORR) can be considered a promising strategy, this approach remains challenging by the dependence on high loadings of noble metals, mainly Platinum (Pt). Therefore, efforts have been directed to develop new and efficient electrocatalysts that could decrease the Pt content (e.g., by nanotechnology tools or alloying) or replace them completely in these systems. The present investigation shows that high catalytic activity can be reached towards the ORR by employing 1.8 ± 0.7 nm Ir nanoparticles (NPs) deposited onto MnO2 nanowires surface under low Ir loadings (1.2 wt.%). Interestingly, we observed that the MnO2-Ir nanohybrid presented high catalytic activity for the ORR close to commercial Pt/C (20.0 wt.% of Pt), indicating that it could obtain efficient performance using a simple synthetic procedure. The MnO2-Ir electrocatalyst also showed improved stability relative to commercial Pt/C, in which only a slight activity loss was observed after 50 reaction cycles. Considering our findings, the superior performance delivered by the MnO2-Ir nanohybrid may be related to (i) the significant concentration of reduced Mn3+ species, leading to increased concentration of oxygen vacancies at its surface; (ii) the presence of strong metal-support interactions (SMSI), in which the electronic effect between MnOx and Ir may enhance the ORR process; and (iii) the unique structure comprised by Ir ultrasmall sizes at the nanowire surface that enable the exposure of high energy surface/facets, high surface-to-volume ratios, and their uniform dispersion
Zn‐doped MnOx nanowires displaying plentiful crystalline defects and tunable small cross-sections for an optimized volcano-type performance towards supercapacitors
Abstract MnOx-based nanomaterials are promising large-scale electrochemical energy storage devices due to their high specific capacity, low toxicity, and low cost. However, their slow diffusion kinetics is still challenging, restricting practical applications. Here, a one-pot and straightforward method was reported to produce Zn-doped MnOx nanowires with abundant defects and tunable small cross-sections, exhibiting an outstanding specific capacitance. More specifically, based on a facile hydrothermal strategy, zinc sites could be uniformly dispersed in the α-MnOx nanowires structure as a function of composition (0.3, 2.1, 4.3, and 7.6 wt.% Zn). Such a process avoided the formation of different crystalline phases during the synthesis. The reproducible method afforded uniform nanowires, in which the size of cross-sections decreased with the increase of Zn composition. Surprisingly, we found a volcano-type relationship between the storage performance and the Zn loading. In this case, we demonstrated that the highest performance material could be achieved by incorporating 2.1 wt.% Zn, exhibiting a remarkable specific capacitance of 1082.2 F.g−1 at a charge/discharge current density of 1.0 A g−1 in a 2.0 mol L−1 KOH electrolyte. The optimized material also afforded improved results for hybrid supercapacitors. Thus, the results presented herein shed new insights into preparing defective and controlled nanomaterials by a simple one-step method for energy storage applications
Facile Gram-Scale Synthesis of NiO Nanoflowers for Highly Selective and Sensitive Electrocatalytic Detection of Hydrazine
The design and development of efficient and electrocatalytic
sensitive
nickel oxide nanomaterials have attracted attention as they are considered
cost-effective, stable, and abundant electrocatalytic sensors. However,
although innumerable electrocatalysts have been reported, their large-scale
production with the same activity and sensitivity remains challenging.
In this study, we report a simple protocol for the gram-scale synthesis
of uniform NiO nanoflowers (approximately 1.75 g) via a hydrothermal
method for highly selective and sensitive electrocatalytic detection
of hydrazine. The resultant material was characterized by scanning
electron microscopy, X-ray photoelectron spectroscopy, and X-ray diffraction.
For the production of the modified electrode, NiO nanoflowers were
dispersed in Nafion and drop-cast onto the surface of a glassy carbon
electrode (NiO NF/GCE). By cyclic voltammetry, it was possible to
observe the excellent performance of the modified electrode toward
hydrazine oxidation in alkaline media, providing an oxidation overpotential
of only +0.08 V vs Ag/AgCl. In these conditions, the peak current
response increased linearly with hydrazine concentration ranging from
0.99 to 98.13 μmol L–1. The electrocatalytic
sensor showed a high sensitivity value of 0.10866 μA L μmol–1. The limits of detection and quantification were
0.026 and 0.0898 μmol L–1, respectively. Considering
these results, NiO nanoflowers can be regarded as promising surfaces
for the electrochemical determination of hydrazine, providing interesting
features to explore in the electrocatalytic sensor field