General Self-Assembly Route toward Sparsely Studded Noble-Metal Nanocrystals inside Graphene Hollow Sphere Network for Ultrastable Electrocatalyst Utilization

Herein, we rationally design and construct a novel type of sparsely studded noble-metal nanocrystals inside graphene hollow sphere network (abbreviated as noble-metal@G HSN) through an electrostatic-attraction-directed self-assembly approach. The formation of Pt@G and Pd@G hollow sphere networks have been illustrated as examples using SiO₂ spheres as templates. Moreover, the electrocatalytic performance of the Pt@G HSN for methanol oxidation reaction has been examined as a proof-of-concept demonstration of the compositional and structural superiorities of noble-metal@G HSN toward electrocatalyst utilization. The as-prepared Pt@G HSN manifests higher catalytic activity and markedly enhanced long-term durability in comparison with commercial Pt/C catalyst

Achieving Highly Electrocatalytic Performance by Constructing Holey Reduced Graphene Oxide Hollow Nanospheres Sandwiched by Interior and Exterior Platinum Nanoparticles

Two-dimensional (2D) graphene nanosheets are considered as an attractive support to load metal nanoparticles for applications in fuel cells due to their extraordinary physicochemical properties arising from the 2D nanostructure. However, fabricating graphene/metal nanoparticle nanohybrids with superior electrochemical performance remains a great challenge to date. In this work, we, for the first time, demonstrate a novel and ingenious approach to fabricate holey reduced graphene oxide hollow nanospheres sandwiched by interior and exterior Pt nanoparticles (denoted as Pt@holey r-GO@Pt hollow nanospheres), using uniform SiO₂ nanospheres as the templates. The Pt@holey r-GO@Pt hollow nanospheres represent a new type of metal/graphene heteroarchitecture due to their rich porosity, abundant active sites, facilitated reaction kinetics, and outstanding structural stability. Thanks to these distinguished merits, the as-prepared Pt@holey r-GO@Pt hollow nanospheres exhibit greatly enhanced electrocatalytic performances toward the oxygen reduction reaction and methanol oxidation reaction as compared with the intact counterparts and commercial Pt/C catalyst, showing great potential in fuel cell devices. The smart strategy outlined here should be readily applicable to rational design of other graphene/metal nanoparticle nanohybrids for energy storage and conversion applications in the future

One-Pot Water-Based Synthesis of Pt–Pd Alloy Nanoflowers and Their Superior Electrocatalytic Activity for the Oxygen Reduction Reaction and Remarkable Methanol-Tolerant Ability in Acid Media

Well-defined and strikingly monomorphic Pt–Pd alloy nanoflowers (Pt–Pd ANFs) with dominant {111} facets were successfully synthesized through a facile cochemical reduction method in a poly­(allylamine hydrochloride) (PAH) based aqueous solution. The detailed morphology, composition, and structure of the Pt–Pd ANFs were investigated by transmission electron microscopy (TEM), selected-area electron diffraction (SAED), energy dispersive spectrum (EDS), nitrogen adsorption–desorption isotherms (SADI), EDS mapping, X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS), demonstrating the Pt–Pd ANFs were highly porous and a self-supported structure. The formation mechanism of the Pt–Pd ANFs were investigated by TEM and Fourier transform infrared (FT-IR), indicating that the existence of PAH and rapid growth of crystal nuclei were essential for the formation of the Pt–Pd ANFs. The electrocatalytic activity and stability of the Pt–Pd ANFs for the oxygen reduction reaction (ORR) were investigated by rotating disk electrode voltammetry in 0.1 M HClO₄ solution. The electrochemical tests indicated the {111}-enclosed Pt–Pd ANFs exhibited superior ORR activity along with satisfactory stability and methanol-tolerant ability under acidic conditions, which made them promising electrocatalysts for the future

Cyanogel-Enabled Homogeneous Sb–Ni–C Ternary Framework Electrodes for Enhanced Sodium Storage

Antimony (Sb) represents an important high-capacity anode material for advanced sodium ion batteries, but its practical utilization has been primarily hampered by huge volume expansion-induced poor cycling life. The co-incorporation of transition-metal (M = Ni, Cu, Fe, <i>etc.</i>) and carbon components can synergistically buffer the volume change of the Sb component; however, these Sb–M–C ternary anodes often suffer from uneven distribution of Sb, M, and C components. Herein, we propose a general nanostructured gel-enabled methodology to synthesize homogeneous Sb–M–C ternary anodes for fully realizing the synergestic effects from M/C dual matrices. A cyano-bridged Sb­(III)–Ni­(II) coordination polymer gel (Sb–Ni cyanogel) has been synthesized and directly reduced to an Sb–Ni alloy framework (Sb–Ni framework). Moreover, graphene oxide (GO) can be <i>in situ</i> immobilized within the cyanogel framework, and after reduction, reduced graphene oxide (rGO) is uniformly distributed within the alloy framework, yielding a homogeneous rGO@Sb–Ni ternary framework. The rGO@Sb–Ni framework with optimal rGO content manifests a high reversible capacity of ∼468 mA h g^–1 at 1 A g^–1 and stable cycle life at 5 A g^–1 (∼210 mA h g^–1 after 500 cycles). The proposed cyanogel-enabled methodology may be extended to synthesize other homogeneous ternary framework materials for efficient energy storage and electrocatalysis

Double-Network Nanostructured Hydrogel-Derived Ultrafine Sn–Fe Alloy in Three-Dimensional Carbon Framework for Enhanced Lithium Storage

Tin-based alloys (Sn–M, M = Fe, Co, Ni, and Cu) have been considered as promising alternatives for graphite anode in advanced Li-ion batteries, but their practical application is hindered by huge volume change-induced poor cycle life. We propose here a facile inorganic–organic double-network nanostructured hydrogel-enabled methodology for uniformly immobilizing ultrafine Sn–M alloys in hierarchical carbon frameworks. The double-network nanostructured gel, consisting of three-dimensional (3D) intertwined cyano-bridged Sn­(IV)–Fe­(II) inorganic gel and chitosan–glutaraldehyde organic polymer gel, can realize 3D space confinement in molecular scale and thus obtain ultrafine Sn–Fe alloy particles (average size ∼2.7 nm) uniformly embedded in hierarchical 1D to 3D carbon framework. These unique structural features enable the Sn–Fe@C framework electrodes to exhibit long cycle life (516 mA h g^–1 after 500 cycles at 0.1 A g^–1) and high rate capability (491 and 270 mA h g^–1 at 1 and 10 A g^–1, respectively). This work provides new insight into controlled synthesis of ultrafine alloys in hierarchical 3D carbon frameworks for improving energy storage properties

Porous AgPt@Pt Nanooctahedra as an Efficient Catalyst toward Formic Acid Oxidation with Predominant Dehydrogenation Pathway

For direct formic acid fuel cells (DFAFCs), the dehydrogenation pathway is a desired reaction pathway, to boost the overall cell efficiency. Elaborate composition tuning and nanostructure engineering provide two promising strategies to design efficient electrocatalysts for DFAFCs. Herein, we present a facile synthesis of porous AgPt bimetallic nanooctahedra with enriched Pt surface (denoted as AgPt@Pt nanooctahedra) by a selective etching strategy. The smart integration of geometric and electronic effect confers a substantial enhancement of desired dehydrogenation pathway as well as electro-oxidation activity for the formic acid oxidation reaction (FAOR). We anticipate that the obtained nanocatalyst may hold great promises in fuel cell devices, and furthermore, the facile synthetic strategy demonstrated here can be extendable for the fabrication of other multicomponent nanoalloys with desirable morphologies and enhanced electrocatalytic performances

Nitrogen-Doped Carbon-Wrapped Porous Single-Crystalline CoO Nanocubes for High-Performance Lithium Storage

Herein, we have designed and synthesized a novel type of nitrogen-doped carbon-supported CoO nanohybrids, i.e., nitrogen-doped carbon-wrapped porous single-crystalline CoO nanocubes (CoO@N–C nanocubes), by using Co₃O₄ nanocubes as precursors. Owing to its unique structural features, the as-synthesized CoO@N–C nanocubes demonstrate markedly enhanced anodic performance in terms of reversible capacity, cycling stability, and rate capability, facilitating its application as a high-capacity, long-life, and high-rate anode for advanced lithium-ion batteries

Novel Hydrogel-Derived Bifunctional Oxygen Electrocatalyst for Rechargeable Air Cathodes

The commercialization of Zn–air batteries has been impeded by the lack of low-cost, highly active, and durable catalysts that act independently for oxygen electrochemical reduction and evolution. Here, we demonstrate excellent performance of NiCo nanoparticles anchored on porous fibrous carbon aerogels (NiCo/PFC aerogels) as bifunctional catalysts toward the Zn–air battery. This material is designed and synthesized by a novel K₂Ni­(CN)₄/K₃Co­(CN)₆-chitosan hydrogel-derived method. The outstanding performance of NiCo/PFC aerogels is confirmed as a superior air-cathode catalyst for a rechargeable Zn–air battery. At a discharge–charge current density of 10 mA cm^–2, the NiCo/PFC aerogels enable a Zn–air battery to cycle steadily up to 300 cycles for 600 h with only a small increase in the round-trip overpotential, notably outperforming the more costly Pt/C+IrO₂ mixture catalysts (60 cycles for 120 h). With the simplicity of the synthetic method and the outstanding electrocatalytic performance, the NiCo/PFC aerogels are promising electrocatalysts for Zn–air batteries

Polyallylamine Functionalized Palladium Icosahedra: One-Pot Water-Based Synthesis and Their Superior Electrocatalytic Activity and Ethanol Tolerant Ability in Alkaline Media

Polyallylamine (PAH) functionalized Pd icosahedra are synthesized through a simple, one-pot, seedless and hydrothermal growth method. Herein, PAH is used efficiently as a complex-forming agent, capping agent, and facet-selective agent. The strong interaction between PAH and Pd atom sharply changes the electronic structure of Pd atom in the Pd icosahedra. The protective function of PAH layers and enhanced antietching capability of Pd atom are responsible for the formation of the Pd icosahedra. Very importantly, the as-prepared PAH functionalized Pd icosahedra exhibit superior electrocatalytic activity and ethanol tolerant ability toward the oxygen reduction reaction (ORR) compared to the commercially available Pt black in alkaline media. At 0.95 V (vs RHE), the ORR specific kinetic current density at the Pd icosahedra is 4.48 times higher than that at commercial Pt black. The fact demonstrates the appropriate surface modification of the Pd nanoparticles by nonmetallic molecules can be regarded as an effective way to enhance the electrocatalytic activity toward the ORR