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由于量子限域效应和态密度的限制, 石墨烯、硅烯等二维材料的量子电容在费米能级附近趋近于零. 基于密度泛函理论的第一性原理研究发现, 掺杂和吸附使石墨烯等二维电极材料的电子结构得以有效的调制, 它促进狄拉克点附近局域电子态的形成和/或费米能级的移动, 从而使量子电容得到了提高. 比较Ti (Au, Ag, Cu, Al)和3-B (N, P, S)掺杂单空位石墨烯(硅烯, 锗烯)的量子电容, 发现3-N掺杂单空位石墨烯和Ti原子吸附单空位硅烯、锗烯的量子电容明显得到了提升, 量子电容分别为118.42 μF/cm 2, 79.84 μF/cm 2和76.54 μF/cm 2. 另外还研究了3-N掺杂三种烯类的浓度效应, 随掺杂浓度的增加, 量子电容呈增加趋势. 通过研究各掺杂体系的热力学稳定性问题, 发现Ti是最稳定的吸附原子, 因为Ti和C原子之间可以形成强键. 在B, N, P, S掺杂单空位硅烯和锗烯中, S是最稳定的掺杂原子, 而对于石墨烯, N掺杂的形成能最低, 量子电容最高. 上述二维电极材料的理论模拟计算为超级电容器和场效应晶体管中的实际应用做出了探索性的工作.Double electric layer capacitor is a kind of supercapacitor with high power density, but has relatively low energy density. Improving the quantum capacitances of materials will be a new way to increase their total interface capacitances. We design a two-dimensional electrode material with a high specific capacity and stable crystal structure. Due to the quantum confinement effect and the density of states, the quantum capacitances of two-dimensional materials such as graphene and silicene approach to zero when they are near the Fermi level. On the basis of the first principles of density functional theory, doping and adsorption can effectively modulate the electronic structure of two-dimensional electrode material such as graphene. It promotes the formation of the local state of the electrode material near the Dirac point and/or the movement of the Fermi level, thereby improving the quantum capacitance. Compared with the quantum capacitance of Ti (Au, Ag, Cu, Al), and 3-B (N, P, S) doped single-vacancy graphene (silicene, germanene), the quantum capacitance of 3-N doped single-vacancy graphene and of Ti atom adsorbed single-vacancy silicene/germanene are both significantly improved, and their quantum capacitances are as high as 118.42 μF/cm 2, 79.84 μF/cm 2, and 76.54 μF/cm 2. The concentration effects of 3N-doped three kinds of alkenes are studied, and the results show that the quantum capacitance is enhanced with the doping concentration increasing. It is also found by studying the thermodynamic stability of the doped systems that Ti is the most stable adsorbed atom because of the strong bond between Ti atom and C atom. The S is the most stable doping atom in B, N, P, S doped single-vacancy silicene and germanene. For graphene, N doping has the lowest formation energy and the best quantum capacitance. This study intends to clarify the controversy regarding the energy storage enhancement of two-dimensional double-layer supercapacitor materials, and to improve the quantum capacitance. The research results provide the guidance for understanding the quantum effects caused by optimizing the structure of two-dimensional electrode material. The above theoretical calculation of the mentioned two-dimensional electrode material provides some research ideas for improving the low energy density of electric double-layer supercapacitors.
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System
ΔEad(eV)Hill Valley Bridge Hollow H* Graphene Al –0.888 — –0.902 –1.012 –5.399 Ag 0.035 — –0.001 0.011 –1.695 Cu –0.220 — –0.217 –0.057 –3.599 Ti –1.075 — –0.827 –1.544 –8.159 Au –0.096 — –0.082 –0.073 –2.359 Silicene Al –2.794 –2.907 — –2.573 –5.502 Ag –0.991 –1.313 –1.244 –1.616 –3.182 Cu –1.549 –2.368 — –2.764 –4.538 Ti –3.694 –3.907 — –3.893 –6.348 Au –1.843 — –1.933 –2.238 –4.486 Germanene Al –1.815 –2.716 — –2.520 –4.908 Ag –0.984 –1.322 — –1.650 –2.869 Cu –1.377 –2.091 — –2.489 –3.812 Ti –3.569 –3.968 — –4.144 –5.565 Au –1.636 –1.700 –1.818 –2.113 –4.020 
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System ΔEf(eV) B N P S Graphene 4.663 3.735 7.773 3.708 Silicene 7.825 0.503 –0.590 –6.759 Germanene 8.684 5.256 0.575 –6.149 下载:
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