Qiurong Shi

Single-Atom Electrocatalysts

Recent years have witnessed a dramatic increase in the production of sustainable and renewable energy. However, the electrochemical performances of the various systems are limited, and there is an intensive search for highly efficient electrocatalysts by more rational control over the size, shape, composition, and structure. Of particular interest are the studies on single-atom catalysts (SACs), which have sparked new interests in electrocatalysis because of their high catalytic activity, stability, selectivity, and 100 % atom utilization. In this Review, we introduce innovative syntheses and characterization techniques for SACs, with a focus on their electrochemical applications in the oxygen reduction/evolution reaction, hydrogen evolution reaction, and hydrocarbon conversion reactions for fuel cells (electrooxidation of methanol, ethanol, and formic acid). The electrocatalytic performance is further considered at an atomic level and the underlying mechanisms are discussed. The ultimate goal is the tailoring of single atoms for electrochemical applications.

Efficient Synthesis of MCu (M = Pd, Pt, and Au) Aerogels with Accelerated Gelation Kinetics and their High Electrocatalytic Activity

To accelerate hydrogel formation and further simplify the synthetic procedure, a series of MCu (M = Pd, Pt, and Au) bimetallic aerogels is synthesized from the in situ reduction of metal precursors through enhancement of the gelation kinetics at elevated temperature. Moreover, the resultant PdCu aerogel with ultrathin nanowire networks exhibits excellent electrocatalytic performance toward ethanol oxidation, holding promise in fuel-cell applications.

Self-Assembled Fe-N-Doped Carbon Nanotube Aerogels with Single-Atom Catalyst Feature as High-Efficiency Oxygen Reduction Electrocatalysts

Self-assembled M-N-doped carbon nanotube aerogels with single-atom catalyst feature are for the first time reported through one-step hydrothermal route and subsequent facile annealing treatment. By taking advantage of the porous nanostructures, 1D nanotubes as well as single-atom catalyst feature, the resultant Fe-N-doped carbon nanotube aerogels exhibit excellent oxygen reduction reaction electrocatalytic performance even better than commercial Pt/C in alkaline solution.

Synthesis of Monodisperse, Quasi-Spherical Silver Nanoparticles with Sizes Defined by the Nature of Silver Precursors

Monodisperse, quasi-spherical silver nanoparticles (Ag NPs) with controlled sizes have been produced directly in water via adding the aqueous solutions of the mixtures of AgNO3 and sodium citrate to boiling aqueous solutions of ascorbic acid (AA). Different compounds, including NaCl, NaBr, KI, Na2SO4, Na2CO3, Na2S, and Na3PO4, are added to the AgNO3/citrate mixture solutions to form new silver compounds with fairly low solubility in water, which are used as precursors instead of soluble Ag(+) ions to synthesize Ag NPs via AA/citrate reduction. This enables us not only to produce monodisperse, quasi-spherical Ag NPs but also to tune the sizes of the resulting NPs from 16 to 30 nm according to the potential of new silver precursors as well as the concentrations of anions.

Ultrasonic-assisted synthesis of carbon nanotube supported bimetallic Pt–Ru nanoparticles for effective methanol oxidation

In this paper, we demonstrate a facile and one-step ultrasonic method to synthesize a carboxylate functionalized multi-walled carbon nanotube supported bimetallic platinum ruthenium nanoparticle (Pt–Ru/c-MWNT) catalyst. The results show that the atomic Pt–Ru ratio is approximately 1 : 1, and the Pt mass loading in the catalyst is 8%. In addition, Pt–Ru nanoparticles with bimetallic structure, ultrasmall size (1.9 nm), and uniform distribution were well-dispersed onto the surface of c-MWNTs, which exhibit enhanced electrocatalytic performance toward methanol oxidation. It is found that this catalyst has a much higher electrochemically active surface area (ECSA) (133.2 m2 gPt−1) and current density for methanol oxidation (1236.0 mA mgPt−1) than those of commercial Pt/C (20 wt%) (55.6 m2 gPt−1, 214.2 mA mgPt−1). Furthermore, the oxidation current density of the Pt–Ru/c-MWNT catalyst at 10 000 s is 22.5 mA mgPt−1, which indicates a long-term high electrocatalytic activity of the Pt–Ru/c-MWNT catalyst for methanol oxidation in acid media.

One-Pot Fabrication of Mesoporous Core–Shell Au@PtNi Ternary Metallic Nanoparticles and Their Enhanced Efficiency for Oxygen Reduction Reaction

Currently, Pt-based nanomaterials with tailorable shapes, structures, and morphologies are the most popular electrocatalysts for oxygen reduction reaction, which is a significant cathode reaction in fuel cells for renewable energy applications. We have successfully synthesized mesoporous core-shell Au@PtNi ternary metallic nanoparticles through a one-pot reduction method for cathodic materials used as oxygen reduction reaction catalysts. The as-synthesized nanoparticles exhibited superior catalytic activities and long-term stabilities compared with mesoporous core-shell Au@Pt nanoparticles and commercial Pt/C. The unique mesoporous core-shell structures as well as the alloy shells enable the enhanced electrochemical oxygen reduction reaction performances of the Pt-based materials via the electronic effect and geometric effect, holding great promise in fuel cell application.

Water-soluble gold nanoclusters with pH-dependent fluorescence and high colloidal stability over a wide pH range via co-reduction of glutathione and citrate

We present a strategy for the synthesis of water-soluble, monodisperse, highly fluorescent gold nanoclusters (Au NCs) with sizes of 1.8 nm by co-reduction of glutathione and citrate (denoted as GS/C–Au NCs) for 24 h at 50 °C. The high content of Au(I)–thiolate complexes (about 75%) on the surfaces of core–shell structured GS/C–Au NCs is responsible for their strong fluorescence generated by aggregation-induced emission (AIE). The advantages of this method using citrate are as follows: (i) lower reaction temperature; (ii) controlled formation rate of Au(0) cores by selective reduction of Au(III) ions; and (iii) enhanced colloidal stability of GS/C–Au NCs in the wide pH range from 4.1 to 8.6 due to differently stable states of glutathione–citrate complex on the surfaces. In addition, the fluorescence intensity of GS/C–Au NCs obtained is pH-dependent and can be reversibly adjusted in the pH range from 4.1 to 8.6 due to changes in their surface charge density stemming from the transitions among differently stable states of the glutathione–citrate complex. Our preliminary study also demonstrates that the resulting GS/C–Au NCs can be used as fluorescent nanoprobes in bio-imaging.

Highly branched PtCu bimetallic alloy nanodendrites with superior electrocatalytic activities for oxygen reduction reactions

Morphology control is a promising strategy to improve the catalytic performance of Pt-based catalysts. In this work, we reported a facile synthesis of PtCu bimetallic alloy nanodendrites using Brij 58 as a template. The highly branched structures and porous features offer relatively large surface areas, which is beneficial to the enhancement of the catalytic activity for oxygen reduction reactions in fuel cells. In addition, the elimination of carbon supports showed an important effect on the stability of the catalysts. By tuning the ratio of Pt and Cu precursors, PtCu nanodendrites were almost four times more active on the basis of an equivalent Pt mass for oxygen reduction reactions than the commercial Pt/C catalyst.

Mesoporous Pt Nanotubes as a Novel Sensing Platform for Sensitive Detection of Intracellular Hydrogen Peroxide

Controlling the shape, structure, and surface morphology of nanomaterials is of great significance in optimizing sensitivity and catalytic performances in biosensing applications. The main goal of employing Pt-based nanomaterials is to increase their utilization efficiency due to their high cost. Herein, we report the synthesis of mesoporous Pt nanotubes using Pluronic P123 as soft templates and Ag nanowires with 50 nm in diameter as hard templates. The resultant materials with unique structures show high sensitivity and stability toward H2O2 detection with low cellular cytotoxicity. The high sensitivity and catalytic properties are attributed to the mesopores and hollow structures making the inner Pt surfaces accessible to reaction media and enlarging the total surface area and one-dimensional structure facilitating the mass diffusion rate.

Enhanced electrocatalytic activities of three dimensional PtCu@Pt bimetallic alloy nanofoams for oxygen reduction reaction

Finding an approach to synthesize low cost catalysts with high activity and improved durability is the main challenge for the commercialization of proton exchange membrane fuel cells. The electrocatalytic performance of Pt-based catalysts could be improved significantly by accurately controlling the particle size, morphology and composition. In this work, PtCu bimetallic nanofoams, composed of fused nanoparticles with ∼3 nm in diameter, were synthesized using a one-step reduction method. After dealloying with nitric acid, the PtCu@Pt core–shell bimetallic nanofoams were 7-fold more active in terms of mass activity, 14 times more active on the basis of specific activity, and more durable for ORR than the commercial Pt/C catalyst, which hold great promise in fuel cell applications.