Density functional theory was used to study the CO oxidation catalytic activity of CeO 2 -supported Au nanoparticles (NPs). Experimental observations on CeO 2 show that the surface of CeO 2 is enriched with oxygen vacancies. We compare CO oxidation by a Au 13 NP supported on stoichiometric CeO 2 (Au 13 @CeO 2 -STO) and partially reduced CeO 2 with three vacancies (Au 13 @CeO 2 -3VAC). The structure of the Au 13 NP was chosen to minimize structural rearrangement during CO oxidation. We suggest three CO oxidation mechanisms by Au 13 @CeO 2 : CO oxidation by coadsorbed O 2 , CO oxidation by a lattice oxygen in CeO 2 , and CO oxidation by O 2 bound to a Au−Ce 3+ anchoring site. Oxygen vacancies are shown to open a new CO oxidation pathway by O 2 bound to a Au−Ce 3+ anchoring site. Our results provide a design strategy for CO oxidation on supported Au catalysts. We suggest lowering the vacancy formation energy of the supporting oxide, and using an easily reducible oxide to increase the concentration of reduced metal ions, which act as anchoring sites for O 2 molecules.

The Lewis acid-base adduct approach has been widely used to form uniform perovskite films, which has provided a methodological base for the development of high-performance perovskite solar cells. However, its incompatibility with formamidinium (FA)-based perovskites has impeded further enhancement of photovoltaic performance and stability. Here, we report an efficient and reproducible method to fabricate highly uniform FAPbI films via the adduct approach. Replacement of the typical Lewis base dimethyl sulfoxide (DMSO) with N-methyl-2-pyrrolidone (NMP) enabled the formation of a stable intermediate adduct phase, which can be converted into a uniform and pinhole-free FAPbI film. Infrared and computational analyses revealed a stronger interaction between NMP with the FA cation than DMSO, which facilitates the formation of a stable FAI·PbI·NMP adduct. On the basis of the molecular interactions with different Lewis bases, we proposed criteria for selecting the Lewis bases. Owed to the high film quality, perovskite solar cells with the highest PCE over 20% (stabilized PCE of 19.34%) and average PCE of 18.83 ± 0.73% were demonstrated.

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Manipulation of grain boundaries in polycrystalline perovskite is an essential consideration for both the optoelectronic properties and environmental stability of solar cells as the solution-processing of perovskite films inevitably introduces many defects at grain boundaries. Though small molecule-based additives have proven to be effective defect passivating agents, their high volatility and diffusivity cannot render perovskite films robust enough against harsh environments. Here we suggest design rules for effective molecules by considering their molecular structure. From these, we introduce a strategy to form macromolecular intermediate phases using long chain polymers, which leads to the formation of a polymer-perovskite composite cross-linker. The cross-linker functions to bridge the perovskite grains, minimizing grain-to-grain electrical decoupling and yielding excellent environmental stability against moisture, light, and heat, which has not been attainable with small molecule defect passivating agents. Consequently, all photovoltaic parameters are significantly enhanced in the solar cells and the devices also show excellent stability.

To achieve a high reversibility and long cycle life for lithium-oxygen (Li-O) batteries, the irreversible formation of LiO, inevitable side reactions, and poor charge transport at the cathode interfaces should be overcome. Here, we report a rational design of air cathode using a cobalt nitride (CoN) functionalized carbon nanofiber (CNF) membrane as current collector-catalyst integrated air cathode. Brush-like CoN nanorods are uniformly anchored on conductive electrospun CNF papers via hydrothermal growth of Co(OH)F nanorods followed by nitridation step. CoN-decorated CNF (CoN/CNF) cathode exhibited excellent electrochemical performance with outstanding stability for over 177 cycles in Li-O cells. During cycling, metallic CoN nanorods provide sufficient accessible reaction sites as well as facile electron transport pathway throughout the continuously networked CNF. Furthermore, thin oxide layer (<10 nm) formed on the surface of CoN nanorods promote reversible formation/decomposition of film-type LiO, leading to significant reduction in overpotential gap (∼1.23 V at 700 mAh g). Moreover, pouch-type Li-air cells using CoN/CNF cathode stably operated in real air atmosphere even under 180° bending. The results demonstrate that the favorable formation/decomposition of reaction products and mediation of side reactions are hugely governed by the suitable surface chemistry and tailored structure of cathode materials, which are essential for real Li-air battery applications.

We used density functional theory to study CO oxidation catalyzed by TiO 2 (110), in which some Ti atoms on the surface are replaced with V, Cr, Mo, W, or Mn. We find that in the presence of O, V, Cr, Mo, and W dopants at the surface bind an oxygen atom so that the dopant has formula MO (M ) V, Cr, Mo, W). Rutile doped with Mn does not take an oxygen atom from the gas phase. We find that these materials oxidize CO by a Mars-van Krevelen mechanism in which the role of the dopant is to facilitate the formation of oxygen vacancies. The energy of CO reaction with an oxygen atom from the surface layer decays linearly with the energy of vacancy formation ∆E v , whereas the energy of adsorption of O 2 at a vacancy is a linear function of ∆E v . These are the only two reactions in the mechanism whose energy varies from one doped oxide to another. Because they both depend on the energy of oxygen vacancy formation, the latter quantity is a good descriptor of catalytic activity. In deciding which intermediate reactions are most likely from an energetic point of view, we impose a "spin conservation" rule: a reaction that requires "flipping a spin" is too slow for catalysis. Because of this, we only consider reactions that conserve spin. We find that all the dopants studied here lower the energy of vacancy formation; therefore, the doped oxides are better oxidants than the undoped ones.

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