Recently, many experimental and theoretical efforts are being intensified to develop high-performance catalysts for electrochemical CO 2 conversion. Beyond the catalyst material screening, it is also critical to optimize the surrounding reaction medium. From vast experiments, inclusion of room-temperature ionic liquid (RTIL) in the electrolyte is found to be beneficial for CO 2 conversion; however, there is no unified picture of the role of RTIL, prohibiting further optimization of the reaction medium. Using a state-of-the-art multiscale simulation, we here unveil the atomic origin of the catalytic promotion effect of RTIL during CO 2 conversion. Unlike the conventional belief, which assumes a specific intermolecular coordination by the RTIL component, we find that the promotion effect is collectively manifested by tuning the reaction microenvironment. This mechanism suggests the critical importance of the bulk properties (e.g., resistance, gas solubility and diffusivity, viscosity, etc.) over the detailed chemical variations of the RTIL components in designing the optimal electrolyte components, which is further supported by our experiments. This fundamental understanding of complex electrochemical interfaces will help in the development of more advanced electrochemical CO 2 conversion catalytic systems in the future.
We review recent advances in the DNA sequencing based on the measurement of transverse electrical currents. Device configurations proposed in the literature are classified according to whether the molecular fingerprints appear as the major (Mode I) or perturbing (Mode II) current signals. Scanning tunneling microscope and tunneling electrode gap configurations belong to the former category, while the nanochannels with or without an embedded nanopore belong to the latter. The molecular sensing mechanisms of Modes I and II roughly correspond to the electron tunneling and electrochemical gating, respectively. Special emphasis will be given on the computer simulation studies, which have been playing a critical role in the initiation and development of the field. We also highlight low-dimensional nanomaterials such as carbon nanotubes, graphene, and graphene nanoribbons that allow the novel Mode II approach. Finally, several issues in previous computational studies are discussed, which points to future research directions toward more reliable simulation of electrical current DNA sequencing devices.
Based on first-principles nonequilibrium Green's function calculations, we demonstrate quantum interference (QI) effects on the tunneling conductance of deoxyribonucleic acid bases placed between zigzag graphene nanoribbon electrodes. With the analogy of QI in hydrocarbon ring structures, we hypothesize that QI can be well preserved in the p-p coupling between the carbon-based electrode and a single DNA base. We demonstrate indications of QI, such as destructively interfered anti-resonance or Fano-resonance, that affect the variation of tunneling conductance depending on the orientation of a base. We find that guanine, with a 10-fold higher transverse conductance, can be singled out from the other bases. V
It was recently shown that nitrogen-doped graphene (NG) can exhibit both p- and n-type characters depending on the C-N bonding nature, which represents a significant bottleneck for the development of graphene-based electronics. Based on first-principles calculations, we herein scrutinize the correlations between the atomic and electronic structures of NG and particularly explore the feasibility of converting p-type NG with pyridinic, pyrrolic, and nitrilic N atoms into n- or bipolar type by introducing an additional dopant atom. Of the nine candidates B, C, O, F, Al, Si, P, S, and Cl, we find that B-, Al-, and P-codoping can anneal even relatively large vacancy defects in p-type NG. It will be also shown that, while the NG with pyridinic N can be converted into the n-type via codoping, only a bipolar type conversion can be achieved for the NG with nitrilic or pyrrolic N. The amount of work function reduction was up to 0.64 eV for the pyridinic N next to a monovacancy. The atomistic origin of such diverse type changes is analyzed based on Mulliken and crystal orbital Hamiltonian populations, which provide us with a framework to connect the local bonding chemistry with the macroscopic electronic structure in doped and/or defective graphene. Moreover, we demonstrate that the proposed codoping scheme can recover the excellent charge transport properties of pristine graphene. Both the electronic type conversion and conductance recovery in codoped NG should have significant implications for the electronic and energy device applications.
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