Using nonthermal plasma (NTP) to promote CO2 hydrogenation
is one of the most promising approaches that overcome the limitations
of conventional thermal catalysis. However, the catalytic surface
reaction dynamics of NTP-activated species are still under debate.
The NTP-activated CO2 hydrogenation was investigated in
Pd2Ga/SiO2 alloy catalysts and compared to thermal
conditions. Although both thermal and NTP conditions showed close
to 100% CO selectivity, it is worth emphasizing that when activated
by NTP, CO2 conversion not only improves more than 2-fold
under thermal conditions but also breaks the thermodynamic equilibrium
limitation. Mechanistic insights into NTP-activated species and alloy
catalyst surface were investigated by using in situ transmission infrared spectroscopy, where catalyst surface species
were identified during NTP irradiation. Moreover, in in situ X-ray absorption fine-structure analysis under reaction conditions,
the catalyst under NTP conditions not only did not undergo restructuring
affecting CO2 hydrogenation but also could clearly rule
out catalyst activation by heating. In situ characterizations
of the catalysts during CO2 hydrogenation depict that vibrationally
excited CO2 significantly enhances the catalytic reaction.
The agreement of approaches combining experimental studies and density
functional theory (DFT) calculations substantiates that vibrationally
excited CO2 reacts directly with hydrogen adsorbed on Pd
sites while accelerating formate formation due to neighboring Ga sites.
Moreover, DFT analysis deduces the key reaction pathway that the decomposition
of monodentate formate is promoted by plasma-activated hydrogen species.
This work enables the high designability of CO2 hydrogenation
catalysts toward value-added chemicals based on the electrification
of chemical processes via NTP.
Generally, carbon anode materials used in sodium-ion batteries do not exhibit good electrochemical performance because of low coulombic efficiency (CE).
A hindrance to the practical use of sodium-ion batteries is the lack of adequate anode materials. By utilizing the co-intercalation reaction, graphite, which is the most common anode material of lithium-ion batteries, was used for storing sodium ion. However, its performance, such as reversible capacity and coulombic efficiency, remains unsatisfactory for practical needs. Therefore, to overcome these drawbacks, a new carbon material was synthesized so that co-intercalation could occur efficiently. This carbon material has the same morphology as carbon black; that is, it has a wide pathway due to a turbostratic structure, and a short pathway due to small primary particles that allows the co-intercalation reaction to occur efficiently. Additionally, due to the numerous voids present in the inner amorphous structure, the sodium storage capacity was greatly increased. Furthermore, owing to the coarse co-intercalation reaction due to the surface pore structure, the formation of solid-electrolyte interphase was greatly suppressed and the first cycle coulombic efficiency reached 80%. This study shows that the carbon material alone can be used to design good electrode materials for sodium-ion batteries without the use of next-generation materials.
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