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Ultra-high electrochemical catalytic activity of MXenes

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ABSTRACT

Cheap and abundant electrocatalysts for hydrogen evolution reactions (HER) have been widely pursued for their practical application in hydrogen-energy technologies. In this work, I present systematical study of the hydrogen evolution reactions on MXenes (Mo2X and W2X, X = C and N) based on density-functional-theory calculations. I find that their HER performances strongly depend on the composition, hydrogen adsorption configurations, and surface functionalization. I show that W2C monolayer has the best HER activity with near-zero overpotential at high hydrogen density among all of considered pure MXenes, and hydrogenation can efficiently enhance its catalytic performance in a wide range of hydrogen density further, while oxidization makes its activity reduced significantly. I further show that near-zero overpotential for HER on Mo2X monolayers can be achieved by oxygen functionalization. My calculations predict that surface treatment, such as hydrogenation and oxidization, is critical to enhance the catalytic performance of MXenes. I expect that MXenes with HER activity comparable to Pt in a wide range of hydrogen density can be realized by tuning composition and functionalizing, and promotes their applications into hydrogen-energy technologies.

No MeSH data available.


Calculated H-adsorption energy at different sites on M2X monolayers: (a) one-side H-coverage and (b) two-side H-coverage.
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f2: Calculated H-adsorption energy at different sites on M2X monolayers: (a) one-side H-coverage and (b) two-side H-coverage.

Mentions: where E(M2XHm) and E(M2X) are the total energies of MXene unit cell with and without H atoms (m), and E(H2) is the energy of hydrogen molecule (H2). m is 1 for H-coverage on one side of monolayer or 2 for H-coverage on its both sides. Our calculations shows that the adsorption energies are negative at all of three possible sites (Fig. 2), indicating that all of the sites may be possible to host hydrogen atoms. It is found that HC is the most stable site to host hydrogen atom, followed by TX, and then by TM because the adsorption energy (negative) increases as the adsorption site changing from HC → TX → TM (Fig. 2). It is also found that the adsorption energy difference between two sites on W2C monolayer is the smallest among all of the considered MXenes. The variation of adsorption energy may affect the HER ability of MXenes.


Ultra-high electrochemical catalytic activity of MXenes
Calculated H-adsorption energy at different sites on M2X monolayers: (a) one-side H-coverage and (b) two-side H-coverage.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5015052&req=5

f2: Calculated H-adsorption energy at different sites on M2X monolayers: (a) one-side H-coverage and (b) two-side H-coverage.
Mentions: where E(M2XHm) and E(M2X) are the total energies of MXene unit cell with and without H atoms (m), and E(H2) is the energy of hydrogen molecule (H2). m is 1 for H-coverage on one side of monolayer or 2 for H-coverage on its both sides. Our calculations shows that the adsorption energies are negative at all of three possible sites (Fig. 2), indicating that all of the sites may be possible to host hydrogen atoms. It is found that HC is the most stable site to host hydrogen atom, followed by TX, and then by TM because the adsorption energy (negative) increases as the adsorption site changing from HC → TX → TM (Fig. 2). It is also found that the adsorption energy difference between two sites on W2C monolayer is the smallest among all of the considered MXenes. The variation of adsorption energy may affect the HER ability of MXenes.

View Article: PubMed Central - PubMed

ABSTRACT

Cheap and abundant electrocatalysts for hydrogen evolution reactions (HER) have been widely pursued for their practical application in hydrogen-energy technologies. In this work, I present systematical study of the hydrogen evolution reactions on MXenes (Mo2X and W2X, X = C and N) based on density-functional-theory calculations. I find that their HER performances strongly depend on the composition, hydrogen adsorption configurations, and surface functionalization. I show that W2C monolayer has the best HER activity with near-zero overpotential at high hydrogen density among all of considered pure MXenes, and hydrogenation can efficiently enhance its catalytic performance in a wide range of hydrogen density further, while oxidization makes its activity reduced significantly. I further show that near-zero overpotential for HER on Mo2X monolayers can be achieved by oxygen functionalization. My calculations predict that surface treatment, such as hydrogenation and oxidization, is critical to enhance the catalytic performance of MXenes. I expect that MXenes with HER activity comparable to Pt in a wide range of hydrogen density can be realized by tuning composition and functionalizing, and promotes their applications into hydrogen-energy technologies.

No MeSH data available.