3 research outputs found
NiTe<sub>2</sub> Nanowire Outperforms Pt/C in High-Rate Hydrogen Evolution at Extreme pH Conditions
Better
hydrogen generation with nonprecious electrocatalysts over Pt is highly
anticipated in water splitting. Such an outperforming nonprecious
electrocatalyst, nickel telluride (NiTe<sub>2</sub>), has been fabricated
on Ni foam for electrocatalytic hydrogen evolution in extreme pH conditions,
viz., 0 and 14. The morphological outcome of the fabricated NiTe<sub>2</sub> was directed by the choice of the Te precursor. Nanoflakes
(NFs) were obtained when NaHTe was used, and nanowires (NWs) were
obtained when Te metal powder with hydrazine hydrate was used. Both
NiTe<sub>2</sub> NWs and NiTe<sub>2</sub> NFs were comparatively screened
for hydrogen evolution reaction (HER) in extreme pH conditions, viz.,
0 and 14. NiTe<sub>2</sub> NWs delivered current densities of 10,
100, and 500 mA cm<sup>–2</sup> at the overpotentials of 125
± 10, 195 ± 4, and 275 ± 7 mV in 0.5 M H<sub>2</sub>SO<sub>4</sub>. Similarly, in 1 M KOH, overpotentials of 113 ±
5, 247 ± 5, and 436 ± 8 mV were required for the same current
densities, respectively. On the other hand, NiTe<sub>2</sub> NFs showed
relatively poorer HER activity than NiTe<sub>2</sub> NWs, which required
overpotentials of 193 ± 7, 289 ± 5, and 494 ± 8 mV
in 0.5 M H<sub>2</sub>SO<sub>4</sub> for the current densities of
10 and 100 mA cm<sup>–2</sup> and 157 ± 5 and 335 ±
6 mV in 1 M KOH for the current densities of 10 and 100 mA cm<sup>–2</sup>, respectively. Notably, NiTe<sub>2</sub> NWs outperformed
the state-of-the-art Pt/C 20 wt % loaded Ni foam electrode of comparable
mass loading. The Pt/C 20 wt % loaded Ni foam electrode reached 500
mA cm<sup>–2</sup> at 332 ± 5 mV, whereas NiTe<sub>2</sub> NWs drove the same current density with 57 mV less. These encouraging
findings emphasize that a NiTe<sub>2</sub> NW could be an alternative
to noble and expensive Pt as a nonprecious and high-performance HER
electrode for proton-exchange membrane and alkaline water electrolyzers
Self-Assembled Molecular Hybrids of CoS-DNA for Enhanced Water Oxidation with Low Cobalt Content
Water oxidation in
alkaline medium was efficiently catalyzed by the self-assembled molecular
hybrids of CoS-DNA that had 20 times lower Co loading than the commonly
used loading. The morphological outcome was directed by varying the
molar ratio of metal precursor CoÂ(Ac)<sub>2</sub> and DNA and three
different sets of CoS-DNA molecular hybrids, viz. CoS-DNA(0.036),
CoS-DNA(0.06), and CoS-DNA(0.084) were prepared. These morphologically
distinct hybrids had shown similar electrocatalytic behavior, because
of the fact that they all contained the same cobalt content. The CoS-DNA(0.036),
CoS-DNA(0.06), and CoS-DNA(0.084) required very low overpotentials
of 350, 364, and 373 mV at a current density of 10 mA cm<sup>–2</sup> (1 M KOH), respectively. The advantages of lower overpotential,
lower Tafel slope (42.7 mV dec<sup>–1</sup>), high Faradaic
efficiency (90.28%), high stability and reproducibility after all,
with a lower cobalt loading, have certainly shown the worth of these
molecular hybrids in large-scale water oxidation. Moreover, since
DNA itself a good binder, CoS-DNA molecular hybrids were directly
casted on substrate electrodes and used after drying. It also showed
minimum intrinsic resistance as DNA is a good ionic and electronic
conductor. Besides, the present method may also be extended for the
preparation of other active electrocatalysts for water splitting
Shrinking the Hydrogen Overpotential of Cu by 1 V and Imparting Ultralow Charge Transfer Resistance for Enhanced H<sub>2</sub> Evolution
Copper
and its oxides are among the best electrocatalysts for the
electrochemical conversion of CO<sub>2</sub> to value-added small
organics because of its high hydrogen overvoltage, making the hydrogen
evolution reaction (HER) a poor side reaction. Here we report an interesting
finding that turned the nature of surface-oxidized Cu upside down
in electrochemical H<sub>2</sub> evolution. It is commonly known that
the electrochemical reactivity of a metal ion is highly sensitive
to the anion to which it is coordinated in the electrolyte. In the
case of Cu, when it is in the form of copper oxide, the hydrogen overvoltage
is huge. Nonetheless, we found that when Cu is in coordination with
Se<sup>2–</sup> ions as Cu<sub>2</sub>Se, the hydrogen overvoltage
was shrunken by ∼1 V, imparting ultralow charge transfer resistance
(<i>R</i><sub>CT</sub>) that varied from 0.32 to 0.61 Ω
depending on the means by which selenization was carried out. Selenization
was done by two different methods. In one method, conventional stirring
was employed to selenize Cu foam in a preheated NaHSe solution at
90 °C for 20 min. In another method, hydrothermal treatment was
employed to selenize Cu foam with NaHSe solution at 120 °C for
1 h. The wet-chemical method yielded honeycomb-like hierarchical arrays
of Cu<sub>2</sub>Se sheets on Cu foam (designated as Cu<sub>2</sub>Se-ch/Cu), and the hydrothermal method yielded a uniform array of
spiky rods of Cu<sub>2</sub>Se (designated as Cu<sub>2</sub>Se-ht/Cu).
The HER electrocatalytic studies carried out in 0.5 M H<sub>2</sub>SO<sub>4</sub> showed that Cu<sub>2</sub>Se-ch/Cu and Cu<sub>2</sub>Se-ht/Cu had similar kinetics, with Tafel slopes of 32 to 35 mV dec<sup>–1</sup>, which is closer to the state-of-the-art Pt/C. Interestingly,
the Cu<sub>2</sub>Se-ch/Cu delivered a total kinetic current density
of −1200 mA cm<sup>–2</sup> when polarized up to −0.85
V vs RHE, whereas Cu<sub>2</sub>Se-ht/Cu delivered a maximum of −780
mA cm<sup>–2</sup> only