Alexander Robertson

© 2018 Elsevier Inc. Nitrogen fixation under ambient conditions remains a significant challenge. Here, we report nitrogen fixation by Ru single-atom electrocatalytic reduction at room temperature and pressure. In contrast to Ru nanoparticles, single Ru sites supported on N-doped porous carbon greatly promoted electroreduction of aqueous N2 selectively to NH3, affording an NH3 formation rate of 3.665 mgNH3h−1mgRu−1 at −0.21 V versus the reversible hydrogen electrode. Importantly, the addition of ZrO2 was found to significantly suppress the competitive hydrogen evolution reaction. An NH3 faradic efficiency of about 21% was achieved at a low overpotential (0.17 V), surpassing many other reported catalysts. Experiments combined with density functional theory calculations showed that the Ru sites with oxygen vacancies were major active centers that permitted stabilization of *NNH, destabilization of *H, and enhanced N2 adsorption. We envision that optimization of ZrO2 loading could further facilitate electroreduction of N2 at both high NH3 synthesis rate and faradic efficiency.

Discovering highly efficient, environmentally friendly, and low-cost exfoliating media that can both disperse and protect black phosphorus (BP) remains a challenge. Herein, we demonstrate such a new molecule, N,N'-dimethylpropyleneurea (DMPU), for effective exfoliation and dispersion of two-dimensional BP nanosheets. A very high exfoliation efficiency of up to 16% was achieved in DMPU, significantly surpassing other good solvents. Exfoliated flakes are free from structural disorder or oxidation. Nanosheets retain high stability in DMPU even after addition of 25 vol% of common solvents. The solvation shell appears to protect the nanosheets from reacting with water and air, more remarkably than the best solvent N-cyclohexyl-2-pyrrolidone reported so far. Molecular dynamics simulations of the exfoliation process show that DMPU is among the effective solvents, although energetically it does not appear as favorable as some other amides. We also demonstrate that our exfoliated BP nanosheets exhibit excellent antimicrobial activities against both Escherichia coli and Staphylococcus aureus, outperforming other common two-dimensional materials of graphene and MoS2, suggesting promise in biomedical applications.

© 2018 The Royal Society of Chemistry. In this study, we demonstrate dual roles for graphene, as both a platform for large-area, fully-wetted growth of two-dimensional Pt films that are one monolayer to several multilayers thick, while also serving as a 'chemically transparent' barrier to catalytic deactivation wherein graphene does not restrict the access of the reactants but does block Pt from dissolution or agglomeration. Using these architectures, we show that it is possible to simultaneously achieve enhanced catalytic activity and unprecedented stability, retaining full activity beyond 1000 cycles, for the canonical oxygen reduction reaction (ORR). Using high resolution TEM, AFM, X-ray photoemission/absorption spectroscopy (XPS/XAS), Raman, and electrochemical methods, we show that, due to intimate graphene-Pt epitaxial contact, Pt-ML/GR hybrid architectures are able to induce a compressive strain on the supported Pt adlayer and increase catalytic activity for ORR. With no appreciable Pt loss or agglomeration observed with the GR/Pt-ML catalysts after 1000 ORR cycles, our results open the door to using similar graphene-templated/graphene-capped hybrid catalysts as means to improve catalyst lifetime without a necessary compromise to their activity. More broadly, the epitaxial growth made possible by the room-temperature, wetted synthesis approach, should allow for efficient transfer of charge, strain, phonons and photons, impacting not just catalysis, but also electronic, thermoelectric and optical materials.

© 2018 The Royal Society of Chemistry. Developing selective and efficient catalysts is highly desirable for electrochemical CO 2 reduction (ECR) to fuels and chemicals. Pd can strongly bind ∗COOH but weakly bind ∗CO, thus resulting in CO as a product. However, proton reduction also occurs severely on the surface of Pd, leading to low CO selectivity. Here we found that the ECR to CO can be greatly enhanced by controlling the Pd-ceria interface and doping with tellurium atoms. Notably, a very high mass activity of 92 mA mg Pd-1 (at 1.0 V vs. reversible hydrogen electrode) for CO formation was achieved, significantly surpassing previously reported Pd catalysts (35 mA mg Pd-1 at -1.0 V). The Pd catalysts comprising CeO x displayed more positive onset potentials than the Pd catalysts in the absence of CeO x , enabling ECR to CO at -0.6 V (vs. RHE). The modified Pd catalyst also afforded an unprecedented CO faradaic efficiency of over 84% at a low Pd loading (<3 wt%). Density functional theory calculations revealed that the Pd atoms located between the Te dopant and CeO 2 promoted CO formation, thus improving CO 2 conversion efficiency.