Electrochemical
reduction of carbon dioxide (CO2) to
formate (HCOO–) in aqueous solution is studied using
tin–lead (Sn–Pb) alloys as new electrocatalysts. In
electrochemical impedance spectroscopy (EIS) measurements, lower charge-transfer
resistance is observed for the alloy electrodes when compared to the
single metal electrodes such as Sn and Pb. The results of X-ray photoelectron
spectroscopy (XPS) and cyclic voltammetric (CV) analysis show that
the Sn in the Sn–Pb alloys facilitates the formation of oxidized
tin (SnO
x
) and metallic lead (Pb0) on the alloy surface by inhibiting the formation of low-conductive
lead oxide (PbO) film. The CV analysis confirms that the Sn–Pb
alloys exhibit higher reduction current than the single metal electrodes
under CO2 atmosphere. The Faradaic efficiency (FE) and
the partial current density (PCD) of HCOO– production
on the alloy electrodes is investigated by electroreduction experiments
at −2.0 V (vs Ag/AgCl) in an H-type cell. As results, respectively
more than 16% and 25% higher FE and PCD of HCOO– are obtained from the Sn–Pb alloys compared to the single
metal electrodes. A Sn–Pb alloy including surface composition
of Sn56.3Pb43.7 exhibits the highest FE of 79.8%
with the highest PCD of 45.7 mA cm–2.
Alkyl amines, which have multiple
amino groups, are used as activators
to improve the CO2 absorption performances of aqueous methyldiethanolamine
(MDEA) solutions. The aqueous MDEA blends consisted of 20% (w/w) of
MDEA and 10% (w/w) of activators, which are 3-methylamino propylamine
(MAPA), diethylenetriamine (DETA), triethylene tetramine (TETA), and
tetraethylenepentamine (TEPA). Aqueous solutions of monoethanolamine
(MEA; 30% (w/w)) and MDEA (30% (w/w)) are used as reference absorbents
for comparison. The CO2 absorption performances of aqueous
MDEA blends were investigated by measurements of absorption capacities,
absorption rates, and heats of absorption. The MDEA blends have higher
CO2 absorption capacities than MEA and MDEA. MDEA/TEPA
shows the highest CO2 loading amount of 0.753 mol-CO2·mol-absorbent–1 at 313 K. In addition,
the MDEA blends show high cyclic capacities (0.241–0.330 mol-CO2·mol-absorbent–1), the values of which
are about 3 times higher than that of MEA. All MDEA blends show higher
absorption fluxes than MDEA. The MDEA/MAPA showed the highest overall
mass transfer coefficient of 3.351 × 103 mol·m–2·s–1·kPa–1, 8 times higher than that of MDEA (0.451 × 103 mol·m–2·s–1·kPa–1) and even higher than that of MEA (3.014 × 103 mol·m–2·s–1·kPa–1). The heats of absorption of the MDEA blends (57.21–59.53
kJ·mol-CO2
–1) are about 30% higher
than that of MDEA and about 30% lower than that of MEA.
Nanocomposites of Co3S4 grown on nitrogen‐doped graphene (NG) (Co3S4‐NG) have been prepared at various concentrations of NG. The supercapacitive behaviors of the developed nanocomposites were assessed with cyclic voltammetry and galvanostatic charge discharge techniques. The nanocomposites exhibit excellent capacitive behavior with a high specific capacitance of 2427 F/g at 2 mV/s in Co3S4‐NG‐7 composite (7 indicates the percentage weight ratio of NG). The superior electrochemical performances could be due to synergistic effects between Co3S4 and NG, high charge mobility and good flexibility of graphene structures. These results indicate that the developed hybrid materials are promising candidates for high performance energy applications.
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