Single-atom catalysis, which utilizes single atoms as active sites, is one of the most promising ways to enhance the catalytic activity and to reduce the amount of precious metals used. Platinum atoms deposited on graphene are reported to show enhanced catalytic activity for some chemical reactions, e.g. methanol oxidation in direct methanol fuel cells. However, the precise atomic structure, the key to understand the origin of the improved catalytic activity, is yet to be clarified. Here, we present a computational study to investigate the structure of platinum adsorbed on graphene with special emphasis on the edges of graphene nanoribbons. By means of density functional theory based thermodynamics, we find that single platinum atoms preferentially adsorb on the substitutional carbon sites at the hydrogen terminated graphene edge. The structures are further corroborated by the core level shift calculations. Large positive core level shifts indicate the strong interaction between single Pt atoms and graphene. The atomistic insight obtained in this study will be a basis for further investigation of the activity of single-atom catalysts based on platinum and graphene related materials.

Two-dimensional bismuth (Bi) layer, known as bismuthene, exhibits $Z2$ topological bulk states due to large spin-orbit coupling that inverts the bands. Using the tight-binding method, we calculate the band structure of buckled bismuthene to understand its topological and trivial phases. We determine the thermoelectric properties for some considered phases, incorporating the edge states contribution, by using the linearized Boltzmann transport equation with a constant relaxation time approximation. It is shown that the thermoelectric figure of merit, $ZT$, actually drops in undoped topological bismuthene due to the edge effects. Surprisingly, the topological edge states enhance $ZT$ at large doping with the Fermi energy near the bottom of bulk bands when bismuthene is nearly metallic.

The adsorption of CO on ${\mathrm{Pt}}_4$ clusters supported on graphene with lattice vacancies is studied theoretically using the first-principles calculation. Our results show that the electronic structure of the graphene-supported ${\mathrm{Pt}}_4$ clusters is significantly modified by the interaction with carbon dangling bonds. As a result the adsorption energy of CO at a Pt site decreases almost linearly with the lowering of the Pt $d$-band center, in analogy with the linear law previously reported for CO adsorption on various Pt surfaces. An exceptional behavior is found for ${\mathrm{Pt}}_4$ supported on graphene with a tetravacancy, where CO adsorption is noticeably weaker than predicted by the shift in the $d$-band center. Detailed electronic structure analyses reveal that the deviation from the linear scaling can be attributed to lack of Pt $d$ states near the Fermi level that hybridize with CO molecular orbitals. The weakening of CO adsorption on the ${\mathrm{Pt}}_4$ clusters is considered as a manifestation of the support effect of graphene, and leads to the enhancement of CO poisoning tolerance that is crucial for developing high-performance Pt cluster catalysts.

Electronic, optical, and thermoelectric properties of germanium tellurides (GeTe) were investigated through a series of first-principles calculations of band structures, absorption coefficients, and thermoelectric transport coefficients. We consider bulk GeTe to consist of cubic and rhombohedral phases, while the two-dimensional (2D) GeTe monolayers can form as a 2D puckered or buckled honeycomb crystals. All of the GeTe variants in the bulk and monolayer shapes are excellent light absorbers in a wide frequency range: (1) bulk cubic GeTe in the near-infrared regime, (2) bulk rhombohedral GeTe and puckered monolayer GeTe in the visible-light regime, and (3) buckled monolayer GeTe in the ultraviolet regime. We also found specifically that the buckled monolayer GeTe exhibits remarkable thermoelectric performance compared to the other GeTe phases due to a combination of electronic band convergence, a moderately wide band gap, and unique 2D density of states from the quantum confinement effect.

Historically, finding two-dimensional (2D) magnets is well known to be a difficult task due to the instability against thermal spin fluctuations. Metals are also normally considered poor thermoelectric (TE) materials. Combining intrinsic magnetism in two dimensions with conducting properties, one may expect to get the worst for thermoelectrics. However, we will show this is not always the case. Here, we investigate the spin-dependent TE properties of monolayer chromium pnictides ($\mathrm{Cr}X$, where $X=\text{P}$, As, Sb, and Bi) using first-principles calculations of electron- and phonon-energy dispersion, along with the Boltzmann transport formalism under an energy-dependent relaxation time approximation. All the $\mathrm{Cr}X$ monolayers are dynamically stable and they also exhibit half metallicity with ferromagnetic ordering. Using the spin-valve setup with an antiparallel spin configuration, the half metallicity and ferromagnetism in monolayer $\mathrm{Cr}X$ enable the manipulation of spin degrees of freedom to tune the TE figure of merit $\left(ZT\right)$. At an optimized chemical potential and operating temperature of 500 K, the maximum $ZT$ values ($\approx 0.22$, 0.12, and 0.09) with the antiparallel spin-valve setup in CrAs, CrSb, and CrBi improve up to almost twice the original values ($ZT\approx 0.12$, 0.08, and 0.05) without the spin-valve configuration. Only in CrP, which is the lightest species and less spin polarized among $\mathrm{Cr}X$, the maximum $ZT$ $(\approx 0.34)$ without the spin-valve configuration is larger than that $(\approx 0.19)$ with the spin-valve one. We also find that, at 500 K, all the $\mathrm{Cr}X$ monolayers possess exceptional TE power factors of about 0.02–0.08 W/m ${\mathrm{K}}^2$, which could be one of the best values among 2D conductors.