Strong Metal-Support Interactions through Sulfur-Anchoring of Metal Catalysts on Carbon Supports.

In supported metal catalysts, the supports would strongly interact with the metal components instead of just acting as a carrier, which greatly affects both of their synthesis and catalytic activity, selectivity, and stability. Carbon is considered as very important but inert support and thus hard to induce strong metal-support interaction (SMSI). This mini-review highlights that sulfur-a documented poison reagent for metal catalysts-when doped in a carbon supports can induce diverse SMSI phenomenon, including electronic metal-support interaction (EMSI), classic SMSI, and reactive metal-support interaction (RMSI). These SMSI between metal and sulfur-doped carbon (S-C) supports enables the catalysts with extraordinary resistance to sintering at high temperatures of up to 1100 °C, which allows the general synthesis of single-atom, alloy cluster, and intermetallic compound catalysts with high dispersion and metal loading for a variety of applications.

Alloying Matters for Ordering: Synthesis of Highly Ordered PtCo Intermetallic Catalysts for Fuel Cells.

Porous carbon-supported atomically ordered intermetallic compounds (IMCs) are promising electrocatalysts in boosting oxygen reduction reaction (ORR) for fuel cell applications. However, the formation mechanism of IMC structures under high temperatures is poorly understood, which hampers the synthesis of highly ordered IMC catalysts with promoted ORR performance. Here, we employ high-temperature X-ray diffraction and energy-dispersive spectroscopic elemental mapping techniques to study the formation process of IMCs, by taking PtCo for example, in an industry-relevant impregnation synthesis. We find that high-temperature annealing is crucial in promoting the formation of alloy particles with a stoichiometric Co/Pt ratio, which in turn is the precondition for transforming the disordered alloys to ordered intermetallic structures at a relatively low temperature. Based on the findings, we accordingly synthesize highly ordered L10-type PtCo catalysts with a remarkable ORR performance in fuel cells.

Non-iridium-based electrocatalyst for durable acidic oxygen evolution reaction in proton exchange membrane water electrolysis.

Iridium-based electrocatalysts remain the only practical anode catalysts for proton exchange membrane (PEM) water electrolysis, due to their excellent stability under acidic oxygen evolution reaction (OER), but are greatly limited by their high cost and low reserves. Here, we report a nickel-stabilized, ruthenium dioxide (Ni-RuO2) catalyst, a promising alternative to iridium, with high activity and durability in acidic OER for PEM water electrolysis. While pristine RuO2 showed poor acidic OER stability and degraded within a short period of continuous operation, the incorporation of Ni greatly stabilized the RuO2 lattice and extended its durability by more than one order of magnitude. When applied to the anode of a PEM water electrolyser, our Ni-RuO2 catalyst demonstrated >1,000 h stability under a water-splitting current of 200 mA cm-2, suggesting potential for practical applications. Density functional theory studies, coupled with operando differential electrochemical mass spectroscopy analysis, confirmed the adsorbate-evolving mechanism on Ni-RuO2, as well as the critical role of Ni dopants in stabilization of surface Ru and subsurface oxygen for improved OER durability.

Phase diagrams guide synthesis of highly ordered intermetallic electrocatalysts: separating alloying and ordering stages.

Supported platinum intermetallic compound catalysts have attracted considerable attention owing to their remarkable activities and durability for the oxygen reduction reaction in proton-exchange membrane fuel cells. However, the synthesis of highly ordered intermetallic compound catalysts remains a challenge owing to the limited understanding of their formation mechanism under high-temperature conditions. In this study, we perform in-situ high-temperature X-ray diffraction studies to investigate the structural evolution in the impregnation synthesis of carbon-supported intermetallic catalysts. We identify the phase-transition-temperature (TPT)-dependent evolution process that involve concurrent (for alloys with high TPT) or separate (for alloys with low TPT) alloying/ordering stages. Accordingly, we realize the synthesis of highly ordered intermetallic catalysts by adopting a separate annealing protocol with a high-temperature alloying stage and a low-temperature ordering stage, which display a high mass activity of 0.96 A mgPt-1 at 0.9 V in H2-O2 fuel cells and a remarkable durability.

A Top-Down Templating Strategy toward Functional Porous Carbons.

Nanostructured carbon materials with high porosity and desired chemical functionalities are of immense interest because of their wide application potentials in catalysis, environment, and energy storage. Herein, a top-down templating strategy is presented for the facile synthesis of functional porous carbons, based on the direct carbonization of diverse organic precursors with commercially available metal oxide powders. During the carbonization, the metal oxide powders can evolve into nanoparticles that serve as in situ templates to introduce nanopores in carbons. The porosity and heteroatom doping of the prepared carbon materials can be engineered by varying the organic precursors and/or the metal oxides. It is further demonstrated that the top-down templating strategy is applicable to prepare carbon-based single-atom catalysts with iron-nitrogen sites, which exhibit a high power density of 545 mW cm-2 in a H2 -air proton exchange membrane fuel cell.

Sulfur-anchoring synthesis of platinum intermetallic nanoparticle catalysts for fuel cells.

Atomically ordered intermetallic nanoparticles are promising for catalytic applications but are difficult to produce because the high-temperature annealing required for atom ordering inevitably accelerates metal sintering that leads to larger crystallites. We prepared platinum intermetallics with an average particle size of <5 nanometers on porous sulfur-doped carbon supports, on which the strong interaction between platinum and sulfur suppresses metal sintering up to 1000°C. We synthesized intermetallic libraries of small nanoparticles consisting of 46 combinations of platinum with 16 other metal elements and used them to study the dependence of electrocatalytic oxygen-reduction reaction activity on alloy composition and platinum skin strain. The intermetallic libraries are highly mass efficient in proton-exchange-membrane fuel cells and could achieve high activities of 1.3 to 1.8 amperes per milligram of platinum at 0.9 volts.

Hydrolyzed seawater pearl tablet modulates the immunity via attenuating Th1/Th2 imbalance in an immunosuppressed mouse model.

OBJECTIVE: To investigate whether Hydrolyzed Seawater Pearl tablet (HSPT) could modulate the Th1/Th2 imbalance in an immunosuppressed mouse model with Th1 to Th2 shift induced by Cyclosporine A (CsA) which can be used in the clinical treatment of Th2 to Th1 shift diseases, and explore the possible mechanism for the adjuvant therapeutic efficacy of HSPT on recurrent respiratory infections (RRI) and acquired immune deficiency syndrome (AIDS). METHODS: The mice were randomly divided into six groups of five animals each, namely normal group, model group, lentinan polysaccharide tablet (LPT) group and three HPST treated groups. HPST treated groups were administered with HPST (0.51, 1.02, 2.04 g/kg) via intragastric gavage (i.g) for 30 consecutive days. LPT used as reference drug for positive control, LPT group was administered with LPT (8.2 mg/kg) for 30 consecutive days. Normal group and model group were received distilled water. The animals in model group, LPT group and HPST treated groups were injected intraperitoneally with CsA (50 mg/kg) to establish the immunosuppressed mice model with Th1 to Th2 shift on the 20th, 22nd and 24th day, one hour after the administration of the respective treatment. Animals were sacrificed one hour after the last administration to collect blood and splenic tissue. The proportion of T cells including CD8+ and CD4+ T cells, Th1 and Th2 in peripheral blood of experimental mice were measured by flow cytometric. The protein level in serum and mRNA level in splenic tissue of experimental mice for interleukin (IL)-2, IL-12, interferon-γ (IFN-γ), IL-4, IL-6, IL-10 and IL-13 were measured by enzyme linked immunosorbent assay and fluorescence quantitative polymerase chain reaction respectively. RESULTS: HSPT elevated the proportion of T cells including both CD8+ and CD4+ T cells, in which the proportion of Th1 and Th2 cells increased, while the ratio of Th1/Th2 cells decreased in peripheral blood of the immunosuppressed mouse model with Th1 to Th2 shift induced by CsA. Furthermore, HSPT elevated both protein and mRNA level of Th1-type cytokines IL-2 and IFN-γ, while had no significant effect on protein and mRNA level of Th1-type cytokine IL-12 and Th2-type cytokines IL-4, IL-6, IL-10, IL- 13 in mouse model. CONCLUSION: Our findings suggest that HSPT can increase proportion of T cells including both CD8+ and CD4+ T cells and induce Th2 to Th1 shift in both cells and cytokines, which probably was the mechanism to account for the adjuvant therapeutic efficacy of HSPT on RRI and AIDS.

Hierarchically Porous Carbons Derived from Nonporous Coordination Polymers.

Hierarchically porous carbons (HPCs) with multimodal pore systems exhibit great technological potentials, especially in the fields of heterogeneous catalysis, energy storage, and conversion. Here, we establish a simple and general approach to HPCs by carbonization of nonporous coordination polymers that are produced by mixing metal salts with polytopic ligands in alkaline aqueous solutions at room temperature. The proposed approach is applicable to a wide scope of ligand molecules (18 examples), thus affording the synthesized HPCs with high diversity in porosity, morphology, and composition. In particular, the prepared HPCs exhibit high specific surface areas (up to 2647 m2 g-1) and large pore volumes (up to 2.39 cm3 g-1). The HPCs-supported atomically dispersed Fe-Nx catalysts show much-improved fuel cell cathode performance over the micropore-dominated carbon black-supported catalysts, demonstrating the structural superiority of the HPCs for enhancing the mass transport properties.

Hierarchically porous carbons as supports for fuel cell electrocatalysts with atomically dispersed Fe-N x moieties.

The development of high-performance non-platinum group metal (non-PGM) catalysts for the oxygen reduction reaction (ORR) is still of significance in promoting the commercialization of proton exchange membrane fuel cells (PEMFCs). In this work, a "hierarchically porous carbon (HPC)-supporting" approach was developed to synthesize highly ORR active Fe-phenanthroline (Fe-phen) derived Fe-N x -C catalysts. Compared to commercial carbon black supports, utilizing HPCs as carbon supports can not only prevent the formation of inactive iron nanoparticles during pyrolysis but also optimize the porous morphology of the catalysts, which eventually increases the amount of reactant-accessible and atomically dispersed Fe-N x active sites. The prepared catalyst therefore exhibits a remarkable ORR activity in both half-cells (half-wave potential of 0.80 V in 0.5 M H2SO4) and H2-air PEMFCs (442 mA cm-2 at a working voltage of 0.6 V), making it among the best non-PGM catalysts for PEMFCs.

A sulfur-tethering synthesis strategy toward high-loading atomically dispersed noble metal catalysts.

Metals often exhibit robust catalytic activity and specific selectivity when downsized into subnanoscale clusters and even atomic dispersion owing to the high atom utilization and unique electronic properties. However, loading of atomically dispersed metal on solid supports with high metal contents for practical catalytic applications remains a synthetic bottleneck. Here, we report the use of mesoporous sulfur-doped carbons as supports to achieve high-loading atomically dispersed noble metal catalysts. The high sulfur content and large surface area endow the supports with high-density anchor sites for fixing metal atoms via the strong chemical metal-sulfur interactions. By the sulfur-tethering strategy, we synthesize atomically dispersed Ru, Rh, Pd, Ir, and Pt catalysts with high metal loading up to 10 wt %. The prepared Pt and Ir catalysts show 30- and 20-fold higher activity than the commercial Pt/C and Ir/C catalysts for catalyzing formic acid oxidation and quinoline hydrogenation, respectively.

Reversing the charge transfer between platinum and sulfur-doped carbon support for electrocatalytic hydrogen evolution.

Metal-support interaction is of great significance for catalysis as it can induce charge transfer between metal and support, tame electronic structure of supported metals, impact adsorption energy of reaction intermediates, and eventually change the catalytic performance. Here, we report the metal size-dependent charge transfer reversal, that is, electrons transfer from platinum single atoms to sulfur-doped carbons and the carbon supports conversely donate electrons to Pt when their size is expanded to ~1.5 nm cluster. The electron-enriched Pt nanoclusters are far more active than electron-deficient Pt single atoms for catalyzing hydrogen evolution reaction, exhibiting only 11 mV overpotential at 10 mA cm-2 and a high mass activity of 26.1 A mg-1 at 20 mV, which is 38 times greater than that of commercial Pt/C. Our work manifests that the manipulation of metal size-dependent charge transfer between metal and support opens new avenues for developing high-active catalysts.

Transition metal-assisted carbonization of small organic molecules toward functional carbon materials.

Nanostructured carbon materials with large surface area and desired chemical functionalities have been attracting considerable attention because of their extraordinary physicochemical properties and great application potentials in catalysis, environment, and energy storage. However, the traditional approaches to fabricating these materials rely greatly on complex procedures and specific precursors. We present a simple, effective, and scalable strategy for the synthesis of functional carbon materials by transition metal-assisted carbonization of conventional small organic molecules. We demonstrate that transition metals can promote the thermal stability of molecular precursors and assist the formation of thermally stable polymeric intermediates during the carbonization process, which guarantees the successful preparation of carbons with high yield. The versatility of this synthetic strategy allows easy control of the surface chemical functionality, porosity, and morphology of carbons at the molecular level. Furthermore, the prepared carbons exhibit promising performance in heterogeneous catalysis and electrocatalysis.