Freestanding MXene–MnO₂ Films for Li–CO₂ Cathodes with Low Overpotential and Long-Term Cycling

Abstract

The Li−CO 2 battery is a potential energy storage device that not only possesses a theoretical energy density as high as 1876 W h kg −1 but also alleviates the consumption of fossil resources by converting the greenhouse gas CO 2 into electric energy. However, some technique bottlenecks, such as high overpotential, low recyclability, and low energy density, severely prohibit its application rhythm. Here, we prepare a binder-free MXene−MnO 2 composite film using vacuum-assisted filtration and in situ reduction, which can be used as a freestanding cathode for Li−CO 2 batteries. This MXene−MnO 2 film electrode bestows good cycle stability (∼220 cycles), high specific capacity, and lower overpotential (∼0.89 V) in Li−CO 2 batteries. Both experimental tests and first-principles calculations reveal that the enhanced electrochemical properties are associated with three aspects. First, the MXene−MnO 2 film offers a high electrical conductivity and porous structure, which provide fast transport channels for electrons and ions. Then, the replacement of Mn by Ti increases the adsorption of Li ions, which facilitates the rapid decomposition of Li 2 CO 3 . Finally, the synergistic effect of MXene and MnO 2 exposes a large number of active sites, which increases the capacity of Li−CO 2 batteries. Therefore, this self-supporting strategy on the MXene composite paves a way to develop high-performance Li−CO 2 batteries.

Toward an Understanding of Bimetallic MXene Solid‐Solution in Binder‐Free Electrocatalyst Cathode for Advanced Li–CO2 Batteries

“…The cathode peak generated at 2.5 V makes known that CO 2 undergoes a reduction reaction to form Li 2 CO 3 , and then in the scanning anode region, the peak at 3.5 V corresponds to the decomposition of discharge product Li 2 CO 3 to CO 2 . [59] Meanwhile, the CV test (Figure S9, Supporting Information) was carried out in inert gas Ar atmosphere within 2.0-4.5 V. As expected, there was no redox reaction peak appeared on the CV curve, indicating the indispensability of CO 2 , which is consistent with the above test results. Figure 4d was the electrochemical impedance diagram (EIS) of batteries assembled with different electrode sheets.…”

Metal-related electrocatalysts for Li–CO2batteries: an overview of the fundamentals to explore future-oriented strategies

“…MXenes are novel 2D nanomaterials derived from a large family of transition metal carbides, nitrides and carbon nitrides with excellent conductivity and efficient charge transport. [114][115][116] Recently, Wang et al 117 used vacuum-assisted ltration and in situ reduction to prepare MXene-MnO 2 composite membranes as cathode catalysts for Li-CO 2 batteries (Fig. 11a).…”

Long-life reversible Li-CO2batteries with optimized Li2CO3flakes as discharge products on palladium-copper nanoparticles

“…Besides, the catalytic sites have been buried for the incomplete decomposition of Li 2 CO 3 and its accumulation on the cathode. 10–12…”

“…However, Li 2 CO 3 , as a thermodynamically stable insulator, is hard to be reversibly decomposed and consequently needs a high charge potential to overcome the reaction barrier. 7,[10][11][12] The high charge potential will bring a series of adverse issues, like electrolyte decomposition, cathode corrosion, electrode passivation and so on. Besides, the catalytic sites have been buried for the incomplete decomposition of Li 2 CO 3 and its accumulation on the cathode.…”

“…Besides, the catalytic sites have been buried for the incomplete decomposition of Li 2 CO 3 and its accumulation on the cathode. [10][11][12] To conquer these barriers, a lot of effort has been made to explore high-efficiency bifunctional electrochemical catalysts towards both the CO 2 reduction reaction (CRR) and the CO 2 evolution reaction (CER). To date, carbon-based cathodes 5,6 including compounds with transition metal oxides/carbides, [13][14][15] noble metals, 11,13,16 metal-organic frameworks 17,18 and covalent organic frameworks (COFs) 8,19 have achieved a lot of effective and fruitful results in Li-CO 2 batteries.…”