Porous Dendrites Research Articles

Porous Ni-Cu Alloy Dendrite Anode Catalysts with High Activity and Selectivity for Direct Borohydride Fuel Cells.

A porous Ni-Cu alloy dendrite catalyst covered by Ni nanoparticles (Ni-np@NC) has been fabricated by an ultrafast and controllable strategy. The research results show that the morphology of the Ni-Cu alloy depends strongly on the Cu2+concentration. Moreover, the Ni-np@NC catalyst demonstrates excellent selectivity and activity toward the borohydride oxidation reaction (BOR). Furthermore, on the Ni-np@NC catalyst electrode, the overpotential merely requires 169 mV at a current density of 10 mA cm-2 for BOR, and the fuel efficiency may reach 70%. The direct borohydride fuel cell using the Ni-np@NC/C anode can export a maximum power density of 218 mW cm-2, much higher than that using the noble-based anode reported in the literature. The remarkable enhancement of Ni-np@NC catalyst performances is on the back of the unique morphology of porous dendrite covered by nanoparticles and the introduction of Cu.

Ion-Enhanced Conversion of CO2 to Formate on Porous Dendrite Bismuth Electrodes with High Efficiency and Durability

Facile synthesis of efficient electrocatalysts that can selectively convert CO2 into value-added chemicals remains a challenge. This study presents the electrochemical synthesis of porous Bi dendrite electrodes and details on their activity toward CO2 conversion to formate in aqueous bicarbonate solutions. The as-synthesized multi-layered porous dendrite Bi electrodes exhibit the faradaic efficiency (FE) of ~100% of formate production. The added halides and cations significantly influence the steady-state partial current density for formate production (J FM) (Cl- > Br- ~ I-; Cs+ > K+ > Li+). Density functional theory calculations have revealed that the reaction pathway involving the species *OCOH occurs predominantly, while co-existence of Cs+ and Cl- changes the overall reactions more spontaneously. A photovoltaic cell-assisted electrocatalysis produces formate with FEs of ~95% (J FM ~10 mA cm-2) at an overall solar conversion efficiency of ~8.5%. The Bi electrodes maintain their activity over 360 h without a change in the surface states. Figure 1

Ion-Enhanced Conversion of CO2 into Formate on Porous Dendritic Bismuth Electrodes with High Efficiency and Durability.

Invited for this month's cover is the group of Prof. Hyunwoong Park at the Kyungpook National University. The image shows the high-efficiency CO2 conversion to formate using multilayered porous dendrite Bi electrocatalysts. The Full Paper itself is available at 10.1002/cssc.201902581.

Development of nanotubes coated with platinum nanodendrites using a virus as a template

We developed a facile method to fabricate platinum (Pt) porous nanotubes coated with interconnected Pt dendrites using the tobacco mosaic virus (TMV) as a template. The surface-exposed arginine residues of the TMV induced the selective deposition of Pt seeds on the TMV outside surface, and poly(sodium-p-styrenesulfonate) (PSS) was chosen to stabilize the dispersity of TMV coated with Pt seeds (TMV/SPt). The limited space between the Pt seeds and their uniform distribution on the TMV exterior confined the growth of Pt dendrites, resulting in continuous dendritic platinum nanotubes (TMV/DPtNT). The synergistic effects of porous dendrites and anisotropic structures of the TMV/DPtNTs provided an increase in the active sites, the enhancement of transport efficiency and long-distance electron transfer, which greatly improved the catalytic activity. We also demonstrated that such nanotubes could be used in the detection of H2O2 with good sensitivity.

C-reactive protein detection based on ISFET structure with gate dielectric SiO2-CeO2

This paper considers a new biosensor based on p-channel ion sensitive field effect transistors (ISFET) as a sensitive platform for low concentration detection of C-reactive protein (CRP). The ISFET structure is fabricated by a standard CMOS technology on a phosphorus-doped Si (111) wafer with ρ = 4.5 Ω.cm. A complex layer of gate dielectric SiO2-CeO2 (dSiO2 = 50 nm, dCeO2 = 10 nm) is chosen since such layers have previously proven their suitability and are technologically simple to manufacture. To improve the antigen binding to the sensitive surface, streptavidin and biotin with and without melanin agents are immobilized on the gate dielectric. Optical microscopy, SEM and AFM results showed that the immobilized streptavidin and biotin agents form porous dendrite structure. The limit of CRP detection is 0.1 mg/L, the range of measuring CRP concentrations is 0.1–2.5 mg/L, the measurement time is about 1 min, and the required amount of solution for analysis - 20 μL. The application of the sensor was evaluated using real samples of human blood serum.

Advanced Cu-Sn foam for selectively converting CO2 to CO in aqueous solution

A tin-modified copper foam for the efficient and selective reduction of CO2 to CO is reported. We employ a cost-efficient electrodeposition route to form a three-dimensional porous dendrite architecture, in which each dendrite possesses a copper core and a copper oxide/tin oxide shell. The sparse tin species on the electrode surface play a key role to achieve excellent faradaic efficiencies for CO formation with a maximum value of 94%. We demonstrate high CO partial current densities of 4.7 mA cm−2 and 7.9 mA cm−2 at applied potentials of -0.8 V and -1.1 V vs. the reversible hydrogen electrode, respectively. The high activity for electrochemical CO2 reduction is attributed to the unique hierarchical porous structure, which offers abundant electrochemically active sites and facilitates mass transport.

In Situ Optical Imaging of Sodium Electrodeposition: Effects of Fluoroethylene Carbonate

The morphologies of sodium electrodeposits and gas evolution were studied in a system comprising a symmetrical Na/Na optical cell, a digital microscope, and an electrochemical workstation. Sodium deposition in ethylene carbonate (EC), diethyl carbonate (DEC), and propylene carbonate (PC) generated large volumes of gas and fragile, porous dendrites. The use of fluoroethylene carbonate (FEC) greatly reduced gassing during deposition and demonstrated superior cycling performance, impedance, and cycling efficiency when it was used as a cosolvent with DEC (1:1 vol); however, porous depositions persisted. Time of flight secondary-ion mass spectrometry revealed that the solid-electrolyte interphase formed in FEC/DEC, in contrast with the EC/DEC electrolyte, is thicker, richer in NaF, and forms a less dense polymer organic layer.

Dendritic Ni(Cu)-polypyrrole hybrid films for a pseudo-capacitor.

Dendritic Ni(Cu)-polypyrrole hybrid films are fabricated for a pseudo-capacitor in a unique morphology using two simple methods: electro-deposition and electrochemical de-alloying. Three-dimensional structures of porous dendrites are prepared by electro-deposition within the hydrogen evolution reaction (HER) at a high cathodic potential; the high-surface-area structure provides sufficient redox reactions between the electrodes and the electrolyte. The dependence of the active-layer thickness on the super-capacitor performance is also investigated, and the 60 μm-thick Ni(Cu)PPy hybrid electrode presents the highest performance of 659.52 F g(-1) at the scan rate of 5 mV s(-1). In the thicker layers, the specific capacitance became smaller due to the diffusion limitation of the ions in an electrolyte. The polypyrrole-hybridization on the porous dendritic Ni(Cu) electrode provides superior specific capacitance and excellent cycling stability due to the improvement in electric conductivity by the addition of conducting polypyrrole in the matrices of the dendritic nano-porous Ni(Cu) layer and the synergistic effect of composite materials.

The Formation of Freckles in Binary Alloys

This paper presents a synopsis of some recent work, still in progress, aimed at elucidating a quantitative explanation of the processes by which flow chimneys form when certain types of alloys are directionally solidified. If (for example) light fluid is released at the liquid—solid “mushy” (dendrite) zone, and cooling is from below, then the intermediate fluid flow undergoes convection through the porous dendrite mass. This can lead to an “instability” of the form of the mushy zone, such that upwelling light fluid flows preferentially in channels within the dendrite mass. What we seek to develop here, is a mathematical basis by which this phenomenon may be properly understood. Accordingly, a mathematical model is developed, simplified, and partially analysed, and as a result we are able to make one specific prediction concerning a criterion for the onset of convection and freckling. This prediction is equivalent to the classical Rayleigh number condition for convective instability.