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Influence of surface functionalization on thermal transport and thermoelectric properties of MXene monolayers


The newest members of two-dimensional material family, called transition metal carbides and nitrides (MXenes), have garnered increasing attention due to their tunable electronic and thermal properties depending on the chemical composition and functionalization. This flexibility can be exploited to fabricate efficient electrochemical energy storage (batteries) and energy conversion (thermoelectric) devices. In this study, we calculated the Seebeck coefficients and lattice thermal conductivity values of oxygen terminated M$_2$CO$_2$ (where M=Ti, Zr, Hf, Sc) monolayer MXene crystals in two different functionalization configurations (model-II (MD-II) and model-III (MD-III)), using Density Functional Theory and the Boltzmann Transport Theory. We estimated thermoelectric figure-of-merit, $zT$, of these materials by two different approaches, as well. First of all, we found that the structural model (i.e. adsorption site of oxygen atom on the surface of MXene) has a paramount impact on the electronic and thermoelectric properties of MXene crystals, that can be exploited to engineer the thermoelectric properties of these material. The lattice thermal conductivity $\kappa_l$, Seebeck coefficient and $zT$ values may vary 40\% depending on the structural model. The MD-III configuration always has the larger band gap, Seeback coefficient and $zT$, and smaller $\kappa_l$ as compared to the MD-II structure due to larger band gap, highly flat valence band and reduced crystal symmetry in the former. The MD-III configuration of Ti$_2$CO$_2$ and Zr$_2$CO$_2$ has the lowest $\kappa_l$ as compared to the same configuration of Hf$_2$CO$_2$ and Sc$_2$CO$_2$. Among all the considered structures, the MD-II configuration of Hf$_2$CO$_2$ has the highest $\kappa_l$, and Ti$_2$CO$_2$ and Zr$_2$CO$_2$ in MD-III configuration have the lowest one. For instance, while the band gap of MD-II configuration of Ti$_2$CO$_2$ is $0.26$ eV, it becomes $0.69$ eV in MD-III. $zT_{\mathrm{max}}$ value may reach up to 1.1 depending on the structural model of MXene.

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Publication details

The article was received on 08 Dec 2017, accepted on 05 Apr 2018 and first published on 06 Apr 2018

Article type: Paper
DOI: 10.1039/C7NR09144C
Citation: Nanoscale, 2018, Accepted Manuscript
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    Influence of surface functionalization on thermal transport and thermoelectric properties of MXene monolayers

    S. Sarıkurt, D. Cakir, M. Keceli and C. Sevik, Nanoscale, 2018, Accepted Manuscript , DOI: 10.1039/C7NR09144C

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