Rongan Shen

Isolated Single Iron Atoms Anchored on N-Doped Porous Carbon as an Efficient Electrocatalyst for the Oxygen Reduction Reaction

The development of low-cost, efficient, and stable electrocatalysts for the oxygen reduction reaction (ORR) is desirable but remains a great challenge. Herein, we made a highly reactive and stable isolated single-atom Fe/N-doped porous carbon (ISA Fe/CN) catalyst with Fe loading up to 2.16 wt %. The catalyst showed excellent ORR performance with a half-wave potential (E1/2 ) of 0.900 V, which outperformed commercial Pt/C and most non-precious-metal catalysts reported to date. Besides exceptionally high kinetic current density (Jk ) of 37.83 mV cm-2 at 0.85 V, it also had a good methanol tolerance and outstanding stability. Experiments demonstrated that maintaining the Fe as isolated atoms and incorporating nitrogen was essential to deliver the high performance. First principle calculations further attributed the high reactivity to the high efficiency of the single Fe atoms in transporting electrons to the adsorbed OH species.

Synergetic Integration of Cu1.94S-ZnxCd1-xS Heteronanorods for Enhanced Visible-Light-Driven Photocatalytic Hydrogen Production.

In this Communication, we present the integration of synergetic designs into high-quality, well-defined Cu1.94S-ZnxCd1-xS heteronanorods (0 ≤ x ≤ 1) for enhanced photocatalytic hydrogen evolution. These heteronanorods possess two light absorbers, intimate heterointerfaces, tunable band gaps over a wide range, and uniform one-dimensional morphology. As verified by experimental and density functional theory studies, these heteronanorods with continuous composition adjustment fully exploit the benefits of both interfacial charge separation and optimized band alignments. Even without any cocatalysts, Cu1.94S-Zn0.23Cd0.77S heteronanorods exhibit efficient hydrogen production activity (7735 μmol h(-1) g(-1)) under visible-light irradiation (λ > 420 nm), representing a 59-fold enhancement compared with the pristine CdS catalyst. Meanwhile, deposition of a Pt cocatalyst on the Cu1.94S-ZnxCd1-xS surface substantially enhances the hydrogen production performance (13 533 μmol h(-1) g(-1)) with an apparent quantum efficiency of 26.4% at 420 nm, opening up opportunities to promote the overall photocatalytic performance using rationally designed nanostructures.

Hollow N-Doped Carbon Spheres with Isolated Cobalt Single Atomic Sites: Superior Electrocatalysts for Oxygen Reduction

The search for a low-cost, ultrastable, and highly efficient non-precious metal catalyst substitute for Pt in the oxygen reduction reaction (ORR) is extremely urgent, especially in acidic media. Herein, we develop a template-assisted pyrolysis (TAP) method to obtain a unique Co catalyst with isolated single atomic sites anchored on hollow N-doped carbon spheres (ISAS-Co/HNCS). Both the single sites and the hollow substrate endow the catalyst with excellent ORR performance. The half-wave potential in acidic media approaches that of Pt/C. Experiments and density functional theory have verified that isolated Co sites are the source for the high ORR activity because they significantly increase the hydrogenation of OH* species. This TAP method is also demonstrated to be effective in preparing a series of ISAS-M/HNCS, which provides opportunities for discovering new catalysts.

Intermetallic NixMy (M = Ga and Sn) Nanocrystals: A Non-precious Metal Catalyst for Semi-Hydrogenation of Alkynes

Intermetallic Nix My (M = Ga and Sn) nanocrystals with uniform particle size and controlled composition are successfully synthesized via a solution-based co-reduction strategy. The as-obtained nanocrystals are crystalline and structurally ordered. The active-site isolation and modified electronic structure are responsible for the excellent catalytic performance for alkyne semi-hydrogenation of the as-obtained non-precious catalysts.

Water-soluble, highly emissive, color-tunable, and stable Cu-doped ZnSeS/ZnS core/shell nanocrystals

Water-soluble, highly emissive, color-tunable, and stable Cu:ZnSeS/ZnS core/shell doped nanocrystals (d-dots) with pure dopant emission have been synthesized through a simple aqueous synthetic route. The influence of various experimental variables, including introduction of chloride ions, amount of mercaptopropanoic acid (MPA), pH value and Cu-doping concentration, on the optical properties of Cu dopant emission have been systematically investigated. Through epitaxial growth of a ZnS shell on Cu:ZnSeS cores, the fabricated Cu:ZnSeS/ZnS d-dots exhibit a high PL QY of up to 40%, which is the highest ever reported for any type of water-soluble Cu-doped selenide-based II–VI semiconductor nanocrystals (NCs). Moreover, the serious photostability problem of Cu-based d-dots in the presence of air and light is solved and the quenching of the excitonic emission is suppressed as well. The stable testing of these highly luminescent d-dots shows that the Cu:ZnSeS/ZnS d-dots have better photostability and preserve more than ~90% of the initial intensity in the presence of air and light 30 days later. This new class of green emissive material shows their potential applications in biolabeling, bioimaging, and light emitting devices.

Pd-dispersed CuS hetero-nanoplates for selective hydrogenation of phenylacetylene

We have exploited a new and distinctive combination method that “disperses” elemental Pd into CuS nanoplates. Pd was successfully dispersed by means of the concomitant transformation of CuS into an amorphous sulfide, which formed an intimate metal–sulfide contact via cation exchange and underwent a subsequent reduction. A series of such Pd-dispersed CuS hetero-nanoplates were synthesized with tailored proportions and compositions. By efficient utilization of noble metal atoms and stable anchored active sites, the optimal catalytic performance for the semihydrogenation of phenylacetylene, a probe reaction, was achieved with high selectivity, activity, and stability. We believe that the synthetic strategy described in our study is a feasible means of developing effective metal–sulfide catalysts for organic reactions.

Controlled one-pot synthesis of RuCu nanocages and Cu@Ru nanocrystals for the regioselective hydrogenation of quinoline

RuCu nanocages and core–shell Cu@Ru nanocrystals with ultrathin Ru shells were first synthesized by a one-pot modified galvanic replacement reaction. The construction of bimetallic nanocrystals with fully exposed precious atoms and a high surface area effectively realizes the concept of high atom-efficiency. Compared with the monometallic Ru/C catalyst, both the RuCu nanocages and Cu@Ru core–shell catalysts supported on commercial carbon show superior catalytic performance for the regioselective hydrogenation of quinoline toward 1,2,3,4-tetrahydroquinoline. RuCu nanocages exhibit the highest activity, achieving up to 99.6% conversion of quinoline and 100% selectivity toward 1,2,3,4-tetrahydroquinoline.

Facile synthesis of Ag-doped ZnCdS nanocrystals and transformation into Ag-doped ZnCdSSe nanocrystals with Se treatment

High-quality, pure, and color-tunable Ag:ZnCdS quantum dots (d-dots) are prepared by optimization of the experimental conditions including Ag-doping concentration and Zn/Cd precursor ratio. Highly emissive Ag:ZnCdS/ZnS core/shell d-dots with photoluminescence quantum yield (PL QY) as high as 58% are constructed in situ by the growth of a ZnS shell around the crude Ag:ZnCdS solution, which is the highest PL QY reported to date for Ag-based semiconductor d-dots. The emission color of a Ag:ZnCdS d-dot can be tuned toward a larger red region by simple Se treatment at high temperature (220–260 °C). With Se treatment, Ag:ZnCdS alloyed d-dots are transformed into Ag:ZnCdSSe alloyed d-dots, and the corresponding optical changes of d-dots in this process are investigated systematically. This strategy provides a versatile approach for the preparation of other multinary semiconductor nanocrystals.

Fe Isolated Single Atoms on S, N Codoped Carbon by Copolymer Pyrolysis Strategy for Highly Efficient Oxygen Reduction Reaction

Heteroatom-doped Fe-NC catalyst has emerged as one of the most promising candidates to replace noble metal-based catalysts for highly efficient oxygen reduction reaction (ORR). However, delicate controls over their structure parameters to optimize the catalytic efficiency and molecular-level understandings of the catalytic mechanism are still challenging. Herein, a novel pyrrole-thiophene copolymer pyrolysis strategy to synthesize Fe-isolated single atoms on sulfur and nitrogen-codoped carbon (Fe-ISA/SNC) with controllable S, N doping is rationally designed. The catalytic efficiency of Fe-ISA/SNC shows a volcano-type curve with the increase of sulfur doping. The optimized Fe-ISA/SNC exhibits a half-wave potential of 0.896 V (vs reversible hydrogen electrode (RHE)), which is more positive than those of Fe-isolated single atoms on nitrogen codoped carbon (Fe-ISA/NC, 0.839 V), commercial Pt/C (0.841 V), and most reported nonprecious metal catalysts. Fe-ISA/SNC is methanol tolerable and shows negligible activity decay in alkaline condition during 15 000 voltage cycles. X-ray absorption fine structure analysis and density functional theory calculations reveal that the incorporated sulfur engineers the charges on N atoms surrounding the Fe reactive center. The enriched charge facilitates the rate-limiting reductive release of OH* and therefore improved the overall ORR efficiency.

Bimetallic PdCo catalyst for selective direct formylation of amines by carbon monoxide

A highly efficient and selective bimetallic Pd0.88Co0.12 nanoparticle catalyst was developed for the direct N-formylation of amines by carbon monoxide. This catalyst is compatible with a wide range of substrates, affording various synthetically useful formamides under practical and mild reaction conditions.