SnP nanocrystals as anode materials for Na-ion batteries

Tin monophosphide is a layered material consisting of Sn-P-P-Sn sandwiches that are stacked on top of each other to form a three dimensional crystallographic structure. Its composition and crystal structure makes it an excellent candidate anode material for sodium-ion batteries (SIBs). However, SnP is yet to be explored for such and other applications due to its challenging synthesis. In the present work, we report the synthesis of SnP nanocrystals (NCs) from the reaction of hexamethylphosphorous triamide (HMPT) and a tin phosphonate prepared from tin oxalate and a long chain phosphonic acid. SnP NCs obtained from this reaction displayed a spherical geometry and a trigonal crystallographic phase with a superstructure attributed to ordered diphosphorus pairs. Such NCs were mixed with carbon black and used as anode materials in SIBs. SIBs based on SnP NCs and sodium(i) bis(fluorosulfonyl)imide (NaFSI) electrolyte displayed a high reversible capacity of 600 mA h g at a current density of 100 mA g and cycling stability for over 200 cycles. Their excellent cycling performance is associated with both the small size of the crystal domains and the particular composition and phase of SnP which prevent mechanical disintegration and major phase separation during sodiation and desodiation cycles. These results demonstrate SnP to be an attractive anode material for sodium ion batteries

Controlling the Formation of Conductive Pathways in Memristive Devices

Resistive random-access memories are promising candidates for novel computer architectures such as in-memory computing, multilevel data storage, and neuromorphics. Their working principle is based on electrically stimulated materials changes that allow access to two (digital), multiple (multilevel), or quasi-continuous (analog) resistive states. However, the stochastic nature of forming and switching the conductive pathway involves complex atomistic defect configurations resulting in considerable variability. This paper reveals that the intricate interplay of 0D and 2D defects can be engineered to achieve reproducible and controlled low-voltage formation of conducting filaments. The author find that the orientation of grain boundaries in polycrystalline HfO x is directly related to the required forming voltage of the conducting filaments, unravelling a neglected origin of variability. Based on the realistic atomic structure of grain boundaries obtained from ultra-high resolution imaging combined with first-principles calculations including local strain, this paper shows how oxygen vacancy segregation energies and the associated electronic states in the vicinity of the Fermi level govern the formation of conductive pathways in memristive devices. These findings are applicable to non-amorphous valence change filamentary type memristive device. The results demonstrate that a fundamental atomistic understanding of defect chemistry is pivotal to design memristors as key element of future electronics

Graphene-supported palladium phosphide PdP2 nanocrystals for ethanol electrooxidation

We present a procedure to produce single-phase PdP2 nanocrystals (NCs). The approach involves the reaction of palladium(II) acetylacetonate and hexamethylphosphoroustriamide to nucleate defective Pd5P2 nanoparticles that subsequently, with further phosphorous incorporation, crystallize into PdP2. The synthesized PdP2 NCs were supported on reduced graphene oxide (rGO) and applied as electrocatalysts for ethanol oxidation. The activity of PdP2 toward the ethanol oxidation reaction (EOR) was over a threefold higher than that of Pd NCs prepared under similar conditions. Even better performance was obtained from PdP2 NCs supported on rGO, which showed current densities up to 51.4¿mA cm-2 and mass activities of 1.60¿A mg-1Pd, that is 4.8 and 15 times higher than Pd NCs. Besides, PdP2 NCs and PdP2/rGO catalysts showed improved stability during EOR than Pd NCs and Pd/rGO.Peer ReviewedPostprint (author's final draft

Oxide thickness-dependent resistive switching characteristics of Cu/HfO2/Pt ECM devices

HfO2-based resistive random-access memory devices are promising candidates for new memory and computing applications. Hereby, scaling of the devices is a key issue, where overall fundamental switching and conduction mechanisms can be easily influenced by changes in the oxide layer thickness. This work addresses the oxide thickness-dependent resistive switching characteristics in Cu/HfO2/Pt memory devices through bipolar DC switching characterization. Forming, reset, and set characteristics are investigated depending on the oxide layer thickness, revealing a significant difference for thicker compared to thinner films. Thicker samples tend to show a more abrupt reset behavior and a larger set voltage variance, while for thinner samples, a more gradual reset behavior and a low set variance is found. These phenomena can be explained by a model based on thermally assisted electrochemical metallization. Furthermore, to understand the conduction mechanism of the devices, current–voltage curves of the set process were investigated. The devices are found to have an Ohmic conduction mechanism in the lower voltage region generally, while thinner samples tend to show an additional space-charge-limited current conduction mechanism in a higher voltage region

SnP nanocrystals as anode materials for Na-ion batteries

Tin monophosphide is a layered material consisting of Sn-P-P-Sn sandwiches that are stacked on top of each other to form a three dimensional crystallographic structure. Its composition and crystal structure makes it an excellent candidate anode material for sodium-ion batteries (SIBs). However, SnP is yet to be explored for such and other applications due to its challenging synthesis. In the present work, we report the synthesis of SnP nanocrystals (NCs) from the reaction of hexamethylphosphorous triamide (HMPT) and a tin phosphonate prepared from tin oxalate and a long chain phosphonic acid. SnP NCs obtained from this reaction displayed a spherical geometry and a trigonal crystallographic phase with a superstructure attributed to ordered diphosphorus pairs. Such NCs were mixed with carbon black and used as anode materials in SIBs. SIBs based on SnP NCs and sodium(i) bis(fluorosulfonyl)imide (NaFSI) electrolyte displayed a high reversible capacity of 600 mA h g at a current density of 100 mA g and cycling stability for over 200 cycles. Their excellent cycling performance is associated with both the small size of the crystal domains and the particular composition and phase of SnP which prevent mechanical disintegration and major phase separation during sodiation and desodiation cycles. These results demonstrate SnP to be an attractive anode material for sodium ion batteries

Phosphorous incorporation in Pd₂Sn alloys for electrocatalytic ethanol oxidation

Altres ajuts: CERCA Programme / Generalitat de Catalunya and ICREA Academia program.Direct ethanol fuel cells (DEFCs) show a huge potential to power future electric vehicles and portable electronics, but their deployment is currently limited by the unavailability of proper electrocatalysis for the ethanol oxidation reaction (EOR). In this work, we engineer a new electrocatalyst by incorporating phosphorous into a palladium-tin alloy and demonstrate a significant performance improvement toward EOR. We first detail a synthetic method to produce Pd₂Sn:P nanocrystals that incorporate 35% of phosphorus. These nanoparticles are supported on carbon black and tested for EOR. Pd₂Sn:P/C catalysts exhibit mass current densities up to 5.03 A mg , well above those of Pd₂Sn/C, Pd₂P/C and Pd/C reference catalysts. Furthermore, a twofold lower Tafel slope and a much longer durability are revealed for the Pd₂Sn:P/C catalyst compared with Pd/C. The performance improvement is rationalized with the aid of density functional theory (DFT) calculations considering different phosphorous chemical environments. Depending on its oxidation state, surface phosphorus introduces sites with low energy OH adsorption and/or strongly influences the electronic structure of palladium and tin to facilitate the oxidation of the acetyl to acetic acid, which is considered the EOR rate limiting step. DFT calculations also points out that the durability improvement of Pd₂Sn:P/C catalyst is associated to the promotion of OH adsorption that accelerates the oxidation of intermediate poisoning CO, reactivating the catalyst surface

Integration of labeled 4D-STEM SPED data for confirmation of phase identification

Workflow (jupyter notebook) of integrating a 4D-STEM scanning precession electron diffraction (SPED) dataset by creating the mean of the diffraction patterns for each label created in ASTAR. Subsequently, azimuthal integration is performed. The routine is based on the packages HyperSpy and pandas for file import numpy and OpenCV for azimuthal integration. It is part of the following paper (in review): Tobias Vogel, Alexander Zintler, Nico Kaiser, Nicolas Guillaume, Gauthier Lefèvre, Maximilian Lederer, Anna Lisa Serra, Eszter Piros, Taewook Kim, Philipp Schreyer, Robert Winkler, Déspina Nasiou, Ricardo Revello Olivo, Tarek Ali, David Lehninger, Alexey Arzumanov, Christelle Charpin-Nicolle, Guillaume Bourgeois, Laurent Grenouillet, MarieClaire Cyrille, Gabriele Navarro, Konrad Seidel, Thomas Kämpfe, Stefan Petzold, Christina Trautmann, Leopoldo Molina-Luna, Lambert Alff Structural and electrical response of emerging memories exposed to heavy ion radiation