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.

Alloying elements with strong and weak adsorption properties can produce a catalyst with optimally tuned adsorbate binding. A full understanding of this alloying effect, however, is not well-established. Here, we use density functional theory to study the ensemble, ligand, and strain effects of closepacked surfaces alloyed by transition metals with a combination of strong and weak adsorption of H and O. Specifically, we consider PdAu, RhAu, and PtAu bimetallics as ordered and randomly alloyed (111) surfaces, as well as randomly alloyed 140-atom clusters. In these alloys, Au is the weak-binding component and Pd, Rh, and Pt are characteristic strong-binding metals. In order to separate the different effects of alloying on binding, we calculate the tunability of Hand O-binding energies as a function of lattice constant (strain effect), number of alloy-substituted sublayers (ligand effect), and randomly alloyed geometries (ensemble effect). We find that on these alloyed surfaces, the ensemble effect more significantly tunes the adsorbate binding as compared to the ligand and strain effects, with the binding energies predominantly determined by the local adsorption environment provided by the specific triatomic ensemble on the (111) surface. However, we also find that tuning of adsorbate binding from the ligand and strain effects cannot be neglected in a quantitative description. Extending our studies to other bimetallics (PdAg, RhAg, PtAg, PdCu, RhCu, and PtCu), we find similar conclusions that the tunability of adsorbate binding on random alloys is predominately described by the ensemble effect.

Nitrate (NO 3 − ) is a ubiquitous contaminant in groundwater that causes serious public health issues around the world. Though various strategies are able to reduce NO 3 − to nitrite (NO 2 − ), a rational catalyst design strategy for NO 2 − removal has not been found, in part because of the complicated reaction network of nitrate chemistry. In this study, we show, through catalytic modeling with density functional theory (DFT) calculations, that the performance of mono-and bimetallic surfaces for nitrite reduction can be rapidly screened using N, N 2 , and NH 3 binding energies as reactivity descriptors.With a number of active surface atomic ensembles identified for nitrite reduction, we have designed a series of "metal-on-metal" bimetallics with optimized surface reactivity and a maximum number of active sites. Choosing Pd-on-Au nanoparticles (NPs) as candidate catalysts, both theory and experiment find that a thin monolayer of Pd-on-Au NPs (size: ∼4 nm) leads to high nitrite reduction performance, outperforming pure Pd NPs and the other Pd surface compositions considered. Experiments show that this thin layer of Pd-on-Au has a relatively high selectivity for N 2 formation, compared to pure Pd NPs. More importantly, our study shows that a simple model, based upon DFTcalculated thermodynamic energies, can facilitate catalysts design relevant to environmental issues.

We have developed a recombinant live oral vaccine using the ice-nucleation protein (Inp) from Pseudomonas syringae to display viral antigens on the surface of Salmonella spp. Fusion proteins containing viral antigens were expressed in the oral vaccine strain, Salmonella typhi Ty21a. Surface localization was verified by immunoblotting and fluorescence-activated cell sorting. The immunogenicity of surface-displayed viral antigens on the recombinant live vaccine strain was assessed in mice inoculated intranasally and intraperitoneally. Inoculation resulted in significantly higher serum antibody level than those induced by viral antigens expressed intracellularly. Thus, this multivalent mucosal live vaccine may provide an effective means for inducing mucosal or systemic immune responses against multiple viral antigens.

Included among the many challenges regarding renewable energy technology are improved electrocatalysts for the oxygen evolution reaction (OER). In this study, we report a novel bifunctional electrocatalyst based on a highly dense CoO x catalyst by introducing CeO x . The CoO x catalyst is fabricated by two-step electrodeposition, including Co seed formation, to obtain a very dense, layered structure, and CeO x is also successfully deposited on the CoO x catalyst. CoO x is an active catalyst showing good activity (η = 0.331 V at 10 mA cm–2) and also stability for the OER. Higher activity is observed with the CeO x /CoO x electrocatalyst (η = 0.313 V at 10 mA cm–2). From mechanistic studies conducted with synchrotron-based photoemission electron spectroscopy and DFT calculations, Ce promotes a synergistic effect by perturbing the electronic structure of surface Co species (facile formation to CoOOH) on the CoO x catalyst and optimizes the binding energy of intermediate oxygenated adsorbates.