Novel Platinum–Cobalt Alloy Nanoparticles Dispersed on Nitrogen‐Doped Graphene as a Cathode Electrocatalyst for PEMFC Applications

A novel synthesis procedure is devised to obtain nitrogen‐doping in hydrogen‐exfoliated graphene (HEG) sheets. An anionic polyelectrolyte–conducting polymer duo is used to form a uniform coating of the polymer over graphene sheets. Pyrolysis of graphene coated with polypyrrole, a nitrogen‐containing polymer, in an inert environment leads to the incorporation of nitrogen atoms in the graphene network with simultaneous removal of the polymer. These nitrogen‐doped graphene (N‐HEG) sheets are used as catalyst support for dispersing platinum and platinum–cobalt alloy nanoparticles synthesized by the modified‐polyol reduction method, yielding a uniform dispersion of the catalyst nanoparticles. Compared to commercial Pt/C electrocatalyst, Pt–Co/N‐HEG cathode electrocatalyst exhibits four times higher power density in proton exchange membrane fuel cells, which is attributed to the excellent dispersion of Pt–Co alloy nanoparticles on the N‐HEG support, the alloying effect of Pt–Co, and the high electrocatalytic activity of the N‐HEG support. A stability study shows that Pt/N‐HEG and Pt–Co/N‐HEG cathode electrocatalysts are highly stable in acidic media. The study shows two promising electrocatalysts for proton exchange membrane fuel cells, which on the basis of performance and stability present the possibility of replacing contemporary electrocatalysts.     

Nanoscale Graphene Doped with Highly Dispersed Silver Nanoparticles: Quick Synthesis,Facile Fabrication of 3D Membrane‐Modified Electrode,and Super Performance for Electrochemical Sensing

The performance of graphene‐based hybrid materials greatly depends on the dispersibility of nanoscale building blocks on graphene sheets. Here, a quick green synthesis of nanoscale graphene (NG) nanosheets decorated with highly dispersed silver nanoparticles (AgNPs) is demonstrated, and then the electrospinning technique to fabricate a novel nanofibrous membrane electrode material is utilized. With this technique, the structure, mechanical stability, biochemical functionality, and other properties of the fabricated membrane electrode material can be easily controlled. It is found that the orientations of NG and the dispersity of AgNPs on the surface of NG have significant effects on the properties of the fabricated electrode. A highly sensitive H₂O₂ biosensor is thus created based on the as‐prepared polymeric NG/AgNP 3D nanofibrous membrane‐modified electrode (MME). As a result, the fabricated biosensor has a linear detection range from 0.005 to 47 × 10^?3m (R = 0.9991) with a supralow detection limit of 0.56 × 10^?6m (S/N = 3). It is expected that this kind of nanofibrous MME has wider applications for the electrochemical detection and design of 3D functional nanomaterials in the future.     

Growth of Metal–Metal Oxide Nanostructures on Freestanding Graphene Paper for Flexible Biosensors

Flexible biosensors are of considerable current interest for the development of portable point‐of‐care medical products, minimally invasive implantable devices, and compact diagnostic platforms. A new type of flexible electrochemical sensor fabricated by depositing high‐density Pt nanoparticles on freestanding reduced graphene oxide paper (rGOP) carrying MnO₂ nanowire networks is reported. The triple‐component design offers new possibilities to integrate the mechanical and electrical properties of rGOP, the large surface area of MnO₂ networks, and the catalytic activity of well‐dispersed and small‐sized Pt nanoparticles prepared via ultrasonic‐electrodeposition. The sensitivity and selectivity that the flexible electrode demonstrates for nonenzymatic detection of H₂O₂ enables its use for monitoring H₂O₂ secretion by live cells. The strategy of structurally integrating metal, metal oxide, and graphene paper will provide new insight into the design of flexible electrodes for a wide range of applications in biosensing, bioelectronics, and lab‐on‐a‐chip devices.     

Enhanced Electrochemical CO2 Reduction of Cu@CuxO Nanoparticles Decorated on 3D Vertical Graphene with Intrinsic sp3‐type Defect

Defective 3D vertical graphene (VG) with a relatively large surface area, high defect density, and increased surface electrons is synthesized via a scalable plasma enhanced chemical vapor deposition method, together with a postsynthesis Ar‐plasma treatment (VG‐Ar). Subsequently, Cu@Cu_xO nanoparticles are deposited onto VG‐Ar (Cu/VG‐Ar) through a galvanostatic pulsed electrodeposition method. These Cu@Cu_xO nanocatalyst systems exhibit a superior electrochemical CO₂ reduction performance when compared to Cu‐based catalysts supported on commercial graphene paper or pristine VG without postsynthesis Ar‐plasma treatment. The Cu/VG‐Ar achieves the highest CO₂ reduction Faradaic efficiency of 60.6% (83.5% of which are attributed to liquid products, i.e., formate, ethanol, and n‐propanol) with a 5.6 mA cm^?2 partial current density at ?1.2 V versus reversible hydrogen electrode (RHE). The improved CO₂ reduction performance of Cu/VG‐Ar originates from the well‐dispersed Cu@Cu_xO nanoparticles deposited on the defective VG‐Ar. The intrinsic carbon defects on VG‐Ar can suppress the hydrogen evolution reaction as well as tune the interaction between VG and Cu@Cu_xO, thus impeding the excessive oxidation of Cu₂O species deposited on VG‐Ar. The defective VG‐Ar and stabilized Cu@Cu_xO enhances CO₂ adsorption and promotes electron transfer to the adsorbed CO₂ and intermediates on the catalyst surface, thus improving the overall CO₂ reduction performance.     

Photochemical Deposition of Highly Dispersed Pt Nanoparticles on Porous CeO2 Nanofibers for the Water‐Gas Shift Reaction

Ceria (CeO₂) nanofibers with high porosity are fabricated using an approach involving sol–gel, electrospinning, and calcination. Specifically, cerium(III) acetylacetonate and polyacrylonitrile (PAN) are dissolved in N,N‐dimethylformamide (DMF) and then electrospun into nanofibers. The PAN matrix plays a critical role in stabilizing the porous structure from collapse during calcination in air up to 800 °C. CeO₂ porous nanofibers comprising an interconnected network of single crystalline and fully oxidized CeO₂ nanoparticles about 40 nm in size are obtained. The hierarchically porous structure of the CeO₂ nanofibers enables the facile deposition of Pt nanoparticles via heterogeneous nucleation in a photochemical method. When conducted in the presence of poly(vinyl pyrrolidone) (PVP) and 4‐benzyolbenzoic acid, uniform Pt nanoparticles with an average diameter of 1.7 nm are obtained, which are evenly dispersed across the entire surface of each CeO₂ nanofiber. The high porosity of CeO₂ nanofibers and the uniform distribution of Pt nanoparticles greatly improve the activity and stability of this catalytic system toward the water‐gas shift reaction. It is believed that this method could be extended to produce a variety of catalysts and systems sought for various industrial applications.     

High‐Performance Sodium‐Ion Hybrid Supercapacitor Based on Nb2O5@Carbon Core–Shell Nanoparticles and Reduced Graphene Oxide Nanocomposites

Sodium‐ion hybrid supercapacitors (Na‐HSCs) have potential for mid‐ to large‐scale energy storage applications because of their high energy/power densities, long cycle life, and the low cost of sodium. However, one of the obstacles to developing Na‐HSCs is the imbalance of kinetics from different charge storage mechanisms between the sluggish faradaic anode and the rapid non‐faradaic capacitive cathode. Thus, to develop high‐power Na‐HSC anode materials, this paper presents the facile synthesis of nanocomposites comprising Nb₂O₅@Carbon core–shell nanoparticles (Nb₂O₅@C NPs) and reduced graphene oxide (rGO), and an analysis of their electrochemical performance with respect to various weight ratios of Nb₂O₅@C NPs to rGO (e.g., Nb₂O₅@C, Nb₂O₅@C/rGO‐70, ‐50, and ‐30). In a Na half‐cell configuration, the Nb₂O₅@C/rGO‐50 shows highly reversible capacity of ≈285 mA h g^?1 at 0.025 A g^?1 in the potential range of 0.01–3.0 V (vs Na/Na⁺). In addition, the Na‐HSC using the Nb₂O₅@C/rGO‐50 anode and activated carbon (MSP‐20) cathode delivers high energy/power densities (≈76 W h kg^?1 and ≈20 800 W kg^?1) with a stable cycle life in the potential range of 1.0–4.3 V. The energy and power densities of the Na‐HSC developed in this study are higher than those of similar Li‐ and Na‐HSCs previously reported.