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 .

Size,m orphology,a nd surface sites of electrocatalysts have amajor impact on their performance.Understanding how, when, and why these parameters change under operating conditions is of importance for designing stable,a ctive,a nd selective catalysts.Herein, we study the reconstruction of aCubased nanocatalysts during the startup phase of the electrochemical CO 2 reduction reaction by combining results from electrochemical in situ transmission electron microscopyw ith operando X-ray absorption spectroscopy. We reveal that dissolution followed by redeposition, rather than coalescence, is the mechanism responsible for the sizei ncrease and morphology change of the electrocatalyst. Furthermore,w e point out the key role played by the formation of copper oxides in the process.U nderstanding of the underlying processes opens apathway to rational design of Cu electro (re)deposited catalysts and to stability improvement for catalysts fabricated by other methods.

The aim of this study is to provide a better understanding of performance degrading mechanisms occurring when a proton exchange membrane water electrolyzer (PEM-WE) is coupled with renewable energies, where times of operation and idle periods alternate. An accelerated stress test (AST) is proposed, mimicking a fluctuating power supply by operating the electrolyzer cell between high (3 A cm −2 geo) and low current densities (0.1 A cm −2 geo), alternating with idle periods during which no current is supplied and the cell rests at open circuit voltage (OCV). Polarization curves, periodically recorded during the OCV-AST, reveal an initial increase in activity (≈50 mV after 10 cycles) followed by a significant decrease in performance during prolonged OCV cycling due to an increasing high frequency resistance (HFR) (≈1.6-fold after 718 cycles). These performance changes can clearly be related to the OCV periods, since they are not observed in a reference experiment where the OCV period is replaced by a potential hold at 1.3 V. The origin of the phenomena, which are responsible for the initial performance gain as well as the subsequent decay are analyzed via detailed electrochemical and physical characterization of the MEAs, and an operating strategy to prevent performance degradation is proposed.

Silicon-graphite electrodes usually exhibit improved cycling stability when limiting the capacity exchanged by the silicon particles per cycle. Yet, the influence of the upper and the lower cutoff potential was repeatedly shown to differ significantly. In the present study, we address this discrepancy by investigating two distinct degradation phenomena occurring in silicon-graphite electrodes, namely (i) the roughening of the silicon particles upon repeated (de-)lithiation which leads to increased irreversible capacity losses, and (ii) the decay in the reversible capacity which mainly originates from increased electronic interparticle resistances between the silicon particles. First, we investigate the cycling stability and polarization of the silicon-graphite electrodes in dependence on different cutoff potentials using pseudo full-cells with capacitively oversized LiFePO 4 cathodes. Further, we characterize postmortem the morphological changes of the silicon nanoparticles by means of scanning transmission electron microscopy (STEM) and energy dispersive spectroscopy (EDS) as a function of the cycle number. To evaluate the degradation of the entire electrode coating, we finally complement our investigation by impedance spectroscopy (EIS) with a gold-wire micro-reference electrode and post-mortem analyses of the electrode structure and coating thickness by cross-sectional SEM. Silicon is among the most promising anode materials for future lithium-ion batteries.1,2 For example, a prismatic hard case cell comprising a silicon-carbon anode with 1000 mAh gand an NMC811 cathode would offer a specific energy of up to ∼280 Wh kgcell . 3 In contrast to state-of-the-art graphite electrodes, where lithium is inserted into the interlayers between the graphene sheets, silicon reacts with lithium and forms Li x Si alloys.4-6 Because the (de-)alloying reaction allows a higher lithium uptake per silicon atom (3579 mAh g −1Si , Li 15 Si 4 ) compared to the intercalation of lithium into the graphite host structure (372 mAh g −1 C , LiC 6 ), silicon offers an about ∼10 times larger theoretical specific capacity. However, while the intercalation chemistry reveals excellent cycling stability with only minor irreversible changes of the graphite's morphology (ca. +10%), 8 the (de-)alloying reaction causes significant morphological and chemical changes to the silicon particles, including (i) a large volume expansion of up to +280% and (ii) repeated breakage and formation of Si-Si bonds, which leads to severe mechanical stress and particle fracturing. [9][10][11][12] Upon continued cycling, these morphological changes cause a rapid capacity decay of silicon-based electrodes, which is largely driven by the electrical isolation of the fractured silicon particles.13-17 Nanometer-sized structures, including nanoparticles and nanowires, were shown to mitigate the mechanical stress which results from volumetric changes during the (de-)alloying reaction.12,18-20 However, there exists a trade-off, because the reduction of the particle size als...

Understanding the interaction between water and oxides is critical for many technological applications, including energy storage, surface wetting/self-cleaning, photocatalysis and sensors. Here, we report observations of strong structural oscillations of BaSrCoFeO (BSCF) in the presence of both HO vapour and electron irradiation using environmental transmission electron microscopy. These oscillations are related to the formation and collapse of gaseous bubbles. Electron energy-loss spectroscopy provides direct evidence of O formation in these bubbles due to the incorporation of HO into BSCF. SrCoO was found to exhibit small oscillations, while none were observed for LaSrCoO and LaCoO. The structural oscillations of BSCF can be attributed to the fact that its oxygen 2p-band centre is close to the Fermi level, which leads to a low energy penalty for oxygen vacancy formation, high ion mobility, and high water uptake. This work provides surprising insights into the interaction between water and oxides under electron-beam irradiation.