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.

A simple oleylamine-based thermal decomposition process using different time steps for precursor injection was used to obtain bimetallic Ag−Cu nanoparticles with a narrow size distribution. Experimental and theoretical studies were carried out to demonstrate that these bimetallic nanoparticles are less prone to oxidation. The calculated energy trends for O 2 adsorption on the nanoparticles show that the adsorption energy declines rapidly when more than six O 2 molecules are present, indicating that O 2 is rarely adsorbed on Ag−Cu nanoparticles. Electron transfer from Cu to Ag within these bimetallic nanoparticles allows far better resistance to oxidation than monometallic Cu nanoparticles.

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.

electrolyzers and rechargeable metal-air batteries. [1] This complex four-electron reaction involves multiple reaction intermediates and in situ catalyst structural changes, requiring considerable energy input. Ir and Ru oxides show relatively high catalytic activity for OER; however, their high cost and poor stability severely limit their applications. Recent studies show that some first-row earth-abundant transition metal (oxy)hydroxides are promising catalyst candidates for OER. [2] Among them, cobalt (Co) (oxy)hydroxides have drawn intensive interest because Co in (oxy)hydroxides exhibits an intermediate t e g g 2 5 1 electron configuration which interacts with O intermediates (e.g., OH*, O*, and OOH*) favorably for the OER. [3] Co species undergo redox transitions, that is, Co 2+ /Co 3+ and Co 3+ /Co 4+ , during OER and the high valence Co species (Co 3+δ , 1 > δ > 0) have been recognized as active catalytic centers. [4] This process requires significant transformation energy. Lowering this transformation energy may improve the catalytic activity. For example, W 6+ with entirely vacant d-orbitals can accept electrons from Co and promote the transformation from Co 2+ to Co 3+ in a ternary Co-FeW catalyst, resulting in one of the best OER catalysts reported recently. [4d] The similar effect by Mo has been demonstrated as well. [5] Further, experimental and computational studies suggest that modifying Co sites′ local environment can optimize their interactions with O intermediates and improve catalytic activity. [6] Several approaches have been explored, such as creating O or metal vacancies, [7] substituting O with B, N, P, or S, [8] or doping other transition metals, such as Fe, Mn, and Ni. [9] Chromium (Cr) is in the same group as W on the periodic table. Cr 6+ may also promote the catalytic activity of Co. The abundance of Cr is 127 times more than W in the earth's crust, and it is much cheaper than W; thus, it may enable more cost-effective Co (oxy)hydroxide catalysts. Although several studies have explored using Cr to promote the OER activity of Co, [10] the exact role of Cr played has not been fully understood, and the optimal catalytic elemental composition is still unknown. Here, we first used density functional theory (DFT) calculations to predict the Co site's structural transformation energy requirements in ternary Co-Fe-Cr (oxy)hydroxides. The sitespecific catalytic activity for OER was estimated based on the

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