Shichun Mu

Polyaniline-functionalized carbon nanotube supported platinum catalysts.

Electrocatalytically active platinum (Pt) nanoparticles on a carbon nanotube (CNT) with enhanced nucleation and stability have been demonstrated through introduction of electron-conducting polyaniline (PANI) to bridge the Pt nanoparticles and CNT walls with the presence of platinum-nitride (Pt-N) bonding and π-π bonding. The Pt colloids were prepared through ethanol reduction under the protection of aniline, the CNT was dispersed well with the existence of aniline in the solution, and aniline was polymerized in the presence of a protonic acid (HCl) and an oxidant (NH(4)S(2)O(8)). The synthesized PANI is found to wrap around the CNT as a result of π-π bonding, and highly dispersed Pt nanoparticles are loaded onto the CNT with narrowly distributed particle sizes ranging from 2.0 to 4.0 nm due to the polymer stabilization and existence of Pt-N bonding. The Pt-PANI/CNT catalysts are electroactive and exhibit excellent electrochemical stability and therefore promise potential applications in proton exchange membrane fuel cells.

A New Core/Shell NiAu/Au Nanoparticle Catalyst with Pt-like Activity for Hydrogen Evolution Reaction.

We report a general approach to NiAu alloy nanoparticles (NPs) by co-reduction of Ni(acac)2 (acac = acetylacetonate) and HAuCl4·3H2O at 220 °C in the presence of oleylamine and oleic acid. Subject to potential cycling between 0.6 and 1.0 V (vs reversible hydrogen electrode) in 0.5 M H2SO4, the NiAu NPs are transformed into core/shell NiAu/Au NPs that show much enhanced catalysis for hydrogen evolution reaction (HER) with Pt-like activity and much robust durability. The first-principles calculations suggest that the high activity arises from the formation of Au sites with low coordination numbers around the shell. Our synthesis is not limited to NiAu but can be extended to FeAu and CoAu as well, providing a general approach to MAu/Au NPs as a class of new catalyst superior to Pt for water splitting and hydrogen generation.

Porous polyaniline-derived FeNxC/C catalysts with high activity and stability towards oxygen reduction reaction using ferric chloride both as an oxidant and iron source

A non-precious metal catalyst (NPMC), with nano-porous structure and high BET surface area, is prepared by pyrolyzing the polyaniline on carbon nanospheres using ferric chloride both as an oxidant and iron source. Electrochemical test results show that the catalyst has a high activity and much better stability than that of commercial Pt/C in acid medium.

Highly Active Platinum Nanoparticles on Graphene Nanosheets with a Significant Improvement in Stability and CO Tolerance

Graphene nanosheets (GNS) supporting Pt nanoparticles (PNs) are prepared using perfluorosulfonic acid (PFSA) as a functionalization and anchoring agent. Transmission electron microscope (TEM) results indicate that the prepared Pt NPs are uniformly deposited on GNS with a narrow particle size ranging from 1 to 4 nm in diameter. A high catalytic activity of this novel catalyst is observed by both cyclic voltammetry and oxygen reduction reaction (ORR) measurements due to the increasing of proton (H(+)) transmission channels. Significantly, this novel PFSA-functionalized Pt/GNS (PFSA-Pt/GNS) catalyst reveals a better CO oxidation and lower loss rate of electrochemical active area in comparison with that of the plain Pt/GNS and conventional Pt/C catalysts, indicating our PFSA-Pt/GNS catalysts hold much higher stability and CO tolerance by virtue of introduction of PFSA.

Bifunctional effect of reduced graphene oxides to support active metal nanoparticles for oxygen reduction reaction and stability

Highly active and stable Pt/reduced graphene oxide (RGO) electrocatalysts for the application of proton exchange membrane fuel cells were developed by tuning the O/C atom ratio of RGO supports. The results showed that Pt nanoparticles with a narrow distribution of particle sizes were well dispersed on RGO, and an increased conductivity and stability of RGO were achieved when the Pt/RGO was deoxidized with an increased graphitization degree of RGO during hydrogen reduction. The highest activity of oxygen reduction reaction (ORR) and stability of Pt/RGO was obtained by hydrogen heat treatment Pt/RGO for 1 hour, in which the O/C atom ratio was 0.14. However, with increment of the reaction time, the atom ratio of O/C decreased to 0.11, the performance dropped sharply due to the further removal of the oxygenated groups on RGO, resulting in a serious aggregation of Pt nanoparticles. This study strongly suggested a bifunctional effect of both graphitization and the oxygenated groups on the catalytic activity and stabilization of metal (such as Pt) nanoparticles on RGO. This will open a door to apply graphene in fuel cells and other fields.

Graphene/carbon nanospheres sandwich supported PEM fuel cell metal nanocatalysts with remarkably high activity and stability

A new strategy to synthesize novel nano-sandwiched graphene/carbon/graphene (GCG) composites is described, employing the aqueous dispersion of low cost carbon nanospheres (CNS) in graphene oxide layers with subsequent thermal reduction. This 3D GCG sandwich shows a particular exfoliated graphene morphology, with CNS regularly embedded into the graphene nanosheets (GNS), from SEM and high-resolution TEM observations. The incorporation of CNS not only increases the Brunauer–Emmett–Teller (BET) surface area due to the effective expansion of the graphene interlayer, but also enhances the electrochemically accessible surface area and the charge transfer speed at the GCG–electrolyte interfaces due to a high density of between-plane electrolyte diffusion channels, that facilitate the reaction species transport and electron transport at high rates. As a result, this unique GCG nanoarchitecture with highly dispersed Pt particles exhibits a very high electrocatalytic activity for the oxygen reduction reaction (ORR). The half cell ORR mass activity of the Pt/GCG catalyst (17.7 A g−1) is 2.2 times of that of Pt/GNS (8.2 A g−1), and 3.8 times that of commercial Pt/C catalysts (4.6 A g−1). Moreover, the Pt/GCG catalyst also shows excellent electrochemical stability. Therefore our new catalyst holds tremendous promise for potential applications in proton exchange membrane (PEM) fuel cells.

Synthesis of Capsule-like Porous Hollow Nanonickel Cobalt Sulfides via Cation Exchange Based on the Kirkendall Effect for High-Performance Supercapacitors.

To construct a suitable three-dimensional structure for ionic transport on the surface of the active materials for a supercapacitor, porous hollow nickel cobalt sulfides are successfully synthesized via a facile and efficient cation-exchange reaction in a hydrothermal process involving the Kirkendall effect with γ-MnS nanorods as a sacrificial template. The formation mechanism of the hollow nickel cobalt sulfides is carefully illustrated via the tuning reaction time and reaction temperature during the cation-exchange process. Due to the ingenious porous hollow structure that offers a high surface area for electrochemical reaction and suitable paths for ionic transport, porous hollow nickel cobalt sulfide electrodes exhibit high electrochemical performance. The Ni(1.77)Co(1.23)S4 electrode delivers a high specific capacity of 224.5 mAh g(-1) at a current density of 0.25 A g(-1) and a high capacity retention of 87.0% at 10 A g(-1). An all-solid-state asymmetric supercapacitor, assembled with a Ni(1.77)Co(1.23)S4 electrode as the positive electrode and a homemade activated carbon electrode as the negative electrode (denoted as NCS//HMC), exhibits a high energy density of 42.7 Wh kg(-1) at a power density of 190.8 W kg(-1) and even 29.4 Wh kg(-1) at 3.6 kW kg(-1). The fully charged as-prepared asymmetric supercapacitor can light up a light emitting diode (LED) indicator for more than 1 h, indicating promising practical applications of the hollow nickel cobalt sulfides and the NCS//HMC asymmetric supercapacitor.

All-solid-state high performance asymmetric supercapacitors based on novel MnS nanocrystal and activated carbon materials.

All-solid-state high-performance asymmetric supercapacitors (ASCs) are fabricated using γ-MnS as positive electrode and porous eggplant derived activated carbon (EDAC) as negative electrode with saturated potassium hydroxide agar gel as the solid electrolyte. The laminar wurtzite nanostructure of γ-MnS facilitates the insertion of hydroxyl ions into the interlayer space, and the manganese sulfide nanowire offers electronic transportation channels. The size-uniform porous nanostructure of EDAC provides a continuous electron pathway as well as facilitates short ionic transportation pathways. Due to these special nanostructures of both the MnS and the EDAC, they exhibited a specific capacitance of 573.9 and 396 F g−1 at 0.5 A g−1, respectively. The optimized MnS//EDAC asymmetric supercapacitor shows a superior performance with specific capacitance of 110.4 F g−1 and 89.87% capacitance retention after 5000 cycles, a high energy density of 37.6 Wh kg−1 at a power density of 181.2 W kg−1 and remains 24.9 Wh kg−1 even at 5976 W kg−1. Impressively, such two assembled all-solid-state cells in series can light up a red LED indicator for 15 minutes after fully charged. These impressive results make these pollution-free materials promising for practical applications in solid aqueous electrolyte-based ASCs.

Nanocrystalline-Li2FeSiO4 synthesized by carbon frameworks as an advanced cathode material for Li-ion batteries

The P21/n structured nanocrystalline-Li2FeSiO4 is prepared by a confinement effect of three-dimensional conductive carbon frameworks, which are formed through a chelating reaction and subsequent pyrolysis. As a benefit of enhanced electronic conductivity by carbon frameworks and Li-ion diffusion kinetics by nanocrystalline-Li2FeSiO4 architectures, the novel nanocomposite shows a 1.28 Li-ion storage capacity (211.3 mA h g−1) at 0.1 C, corresponding to two successive steps of oxidation and reduction of Fe2+/Fe3+/Fe4+. Furthermore, the discharge capacity is 189.8, 175.6, 148.9, 125.7 and 106.6 mA h g−1 at a variable rate of 0.5, 1, 2, 5 and 10 C, respectively, and then easily returns to 175 mA h g−1 at 1 C. It is a surprise that the initial capacity is 90.9 mA h g−1 at 10 C, and 97.7% is retained after 1000 cycles. Thus, we believe that the nanocrystalline-Li2FeSiO4 with carbon frameworks, possessing high-capacity and high-rate performance, is a promising next-generation cathode material for high-power lithium-ion batteries.

RuP2-Based Catalysts with Platinum-like Activity and Higher Durability for the Hydrogen Evolution Reaction at All pH Values

Highly active, stable, and cheap Pt-free catalysts for the hydrogen evolution reaction (HER) are under increasing demand for future energy conversion systems. However, developing HER electrocatalysts with Pt-like activity that can function at all pH values still remains as a great challenge. Herein, based on our theoretical predictions, we design and synthesize a novel N,P dual-doped carbon-encapsulated ruthenium diphosphide (RuP2 @NPC) nanoparticle electrocatalyst for HER. Electrochemical tests reveal that, compared with the Pt/C catalyst, RuP2 @NPC not only has Pt-like HER activity with small overpotentials at 10 mA cm-2 (38 mV in 0.5 m H2 SO4 , 57 mV in 1.0 m PBS and 52 mV in 1.0 m KOH), but demonstrates superior stability at all pH values, as well as 100 % Faradaic yields. Therefore, this work adds to the growing family of transition-metal phosphides/heteroatom-doped carbon heterostructures with advanced performance in HER.