No abstract

Zinc anode-based batteries have been widely studied due to their low cost, high capacity and high energy density. However, the formation of dendrites on the zinc anode during cycling severely affects the stability and safety of this type of battery. In this work, a series of electrolyte additives with potential to counter this problem were studied. We found that lithium chloride (LiCl) additive can suppress the growth of dendrites and stabilize the Zn metal anode, on which the cations (Li + ) preferentially form Li2O/Li2CO3 upon the Zn surface and provide a shielding effect to suppress dendritic deposition, while a moderate amount of anions (Cl -) decrease the Zn polarization and facilitate ion transport.Asymmetric cells with LiCl additives in the electrolyte showed notably higher stability during the long cycling process.

Phosphorene is a mono-elemental two-dimensional (2D) material with outstanding, highly directional properties and a thickness-tuneable band gap 1-8. Nanoribbons combine the flexibility and unidirectional properties of 1D nanomaterials, the high surface area of 2D nanomaterials and the electron-confinement and edge effects of both. Their structures can thus offer exceptional control over electronic bandstructure, lead to the emergence of novel phenomena and present unique architectures for applications 5,6,9-24. Motivated by phosphorene's intrinsically anisotropic structure, theoretical predictions of the extraordinary properties of phosphorene nanoribbons (PNRs) have been rapidly emerging in recent years 5,6,12-24. However to date, discrete PNRs have not been produced. Here we present a method for creating quantities of high quality, individual PNRs via ionic scissoring of macroscopic black phosphorus crystals. The top-down process results in stable liquid dispersions of PNRs with typical widths of 4 to 50 nm, predominantly single layer thickness, measured lengths up to 75 μm and aspect ratios of up to ~1000. The nanoribbons are atomically-flat single crystals, aligned exclusively in the zigzag crystallographic orientation. The ribbon widths are remarkably uniform along their entire length and they display extreme flexibility. These properties, in conjunction with the ease of downstream manipulation via liquidphase methods, now enable the search for predicted exotic states 6,12-14,17-19,21 and an array of applications where PNRs have been widely predicted to offer transformative advantages, ranging from thermoelectric devices to high-capacity fast-charging batteries and integrated high-speed electronic circuits 6,14-16,20,23,24. Phosphorene's anisotropic properties, including for electron, thermal and ionic transport, derive from its atomic structure where the atoms are arranged in corrugated sheets with two different P-P bond lengths (Fig. 1a) 1-8. Calculations predict that PNRs can possess enhanced characteristics compared with phosphorene and that their electronic structure, carrier mobilities and optical and mechanical properties can be tuned by varying the ribbon width, thickness, edge passivation, and by introducing strain or functionalization 6,12-14,20,22-24. Additionally, there have been numerous predictions of exotic effects in PNRs, including the spin-dependent Seebeck effect 17 , room temperature magnetism 6,21 , topological phase transitions 18 , large exciton splitting 14 and spin density waves 19. These results have led to suggestions of unique capabilities of PNRs in a number of applications such as thermoelectric devices 6,23 , photocatalytic water splitting 15 , solar cells 14 , batteries 6,24 , electronics 6,20,22 and quantum information technologies 14 .

The electro-oxidation of dopamine (DA) is investigated on the unmodified surfaces of five different classes of carbon electrodes: glassy carbon (GC), oxygen-terminated polycrystalline boron-doped diamond (pBDD), edge plane pyrolytic graphite (EPPG), basal plane pyrolytic graphite (BPPG), and the basal surface of highly oriented pyrolytic graphite (HOPG), encompassing five distinct grades with step edge density and coverage varying by more than 2 orders of magnitude. Surfaces were prepared carefully and characterized by a range of techniques, including atomic force microscopy (AFM), field emission scanning electron microscopy (FE-SEM), and Raman spectroscopy. Although pBDD was found to be the least susceptible to surface fouling (even at relatively high DA concentrations), the reaction showed sluggish kinetics on this electrode. In contrast, DA electro-oxidation at pristine basal plane HOPG at concentrations ≤100 μM in 0.15 M PBS, pH 7.2, showed fast kinetics and only minor susceptibility toward surface fouling from DA byproducts, although the extent of HOPG surface contamination by oxidation products increased substantially at higher concentrations (with the response similar on all grades, irrespective of step edge coverage). EPPG also showed a fast response, with little indication of passivation with repeated voltammetric cycling but a relatively high background signal due to the high capacitance of this graphite surface termination. Of all five carbon electrode types, freshly cleaved basal plane HOPG showed the clearest signal (distinct from the background) at low concentrations of DA (<10 μM) as a consequence of the low capacitance. Studies of the electrochemical oxidation of DA in the presence of the common interferents ascorbic acid (AA) and serotonin (5-HT), of relevance to neurochemical analysis, showed that the signals for DA were still clearly and easily resolved at basal plane HOPG surfaces. In the presence of AA, repetitive voltammetry caused products of AA electro-oxidation to adsorb onto the HOPG surface, forming a permselective film that allowed the electrochemical oxidation of DA to proceed unimpeded, while greatly inhibiting the electrochemical response of AA itself. The studies presented provide conclusive evidence that the pristine surface of basal plane HOPG is highly active for the detection of DA, irrespective of the step edge density and method of cleavage, and adds to a growing body of evidence that the basal plane of HOPG is a much more active electrode for many classes of electrode reactions than previously believed.

We demonstrate a novel and versatile pipetbased approach to study the landing of individual nanoparticles (NPs) on various electrode materials without any need for encapsulation or fabrication of complex substrate electrode structures, providing great flexibility with respect to electrode materials. Because of the small electrode area defined by the pipet dimensions, the background current is low, allowing for the detection of minute current signals with good time resolution. This approach was used to characterize the potential-dependent activity of Au NPs and to measure the catalytic activity of a single NP on a TEM grid, combining electrochemical and physical characterization at the single NP level for the first time. Such measurements open up the possibility of studying the relation between the size, structure and activity of catalyst particles unambiguously.