High-pressure electrides: From design to synthesis

Electrides are unique ionic compounds that electrons serve as the anions. Many electrides with fascinating physical and chemical properties have been discovered at ambient condition. Under pressure, electrides are also revealed to be ubiquitous crystal morphology, enriching the geometrical topologies and electronic properties of electrides. In this Review,we overview the formation mechanism of high-pressure electrides(HPEs) and outline a scheme for exploring new HPEs from pre-design, CALYPSO assisted structural searches, indicators for electrides, to experimental synthesis. Moreover, the evolution of electronic dimensionality under compression is also discussed to better understand the dimensional distribution of anionic electrons in HPEs.

Single-atom catalysts supported on graphene/electride heterostructures for the enhanced sulfur reduction reaction in lithium-sulfur batteries

Single-atom catalysts(SACs)hold great promise in addressing the sluggish kinetics of the sulfur reduction reaction(SRR)in lithium-sulfur(Li-S)batteries for their unique catalytic activity and maximum atom efficiency.While these SACs must be dispersed on solid substrates,the underlying support is usually limited to carbon materials that have a poor ability to modulate the coordination environment and electronic structures of single atoms,and consequently their catalytic activity toward the SRR is restricted.Here we propose two-dimensional(2D)graphene/electride heterostructu res as substrates to enhance the catalytic activities of SACs for Li-S batteries.2D electrides featuring the anionic electron gas on their surface enable efficient electron transfer to SACs,which alters their electronic structures,resulting in the shifts of the d orbital and Fermi levels.This unique electronic structure decreases the filling of antibonding states such that the bonding with adsorbates at active sites is enhanced.We demonstrate the enhanced catalytic performance of SACs in terms of the Gibbs free energy of SRR and Li_(2)S dissociation.In addition,a universal descriptor for the rapid screening of SACs is established by a linear regression fitting method.This work provides a new design strategy to modulate SAC activity through electrides for Li-S batteries.

Enhanced Oxygen Reduction on Graphene via Y5Si3 Electride Substrate:a First-Principles Study

Manipulating the chemical reactivity of graphene toward oxygen reduced reduction(ORR)is of particular interest for both fundamental research and practical application in fuel cell.Deposing graphene on selected substrate provides a structure-intact strategy to enhance its chemical reactivity due to substrate-induced charge and interface effect.Here,we report the graphene deposited on one-dimensional electride Y5Si3 as an effective ORR catalyst in acidic media.Thermodynamic calculations suggest that depositing graphene on electride materials can facilitate the protonation of O2,which is the rate-determining step based on the four-electron reaction pathway and thus promote the ORR activity.Further electronic calculations reveal that low work function(3.5 eV),superior electrical conductivity and slight charge transfer from substrate to graphene result in the enhanced ORR performance of graphene.These findings shed light on the rational design of ORR catalysts based on graphitic materials and emphasize the critical role of substrates for energy-related electrochemical reactions.

An experimental study on the degradation of the C12A7 hollow cathode

Emitter overheating is by far the greatest problem limiting the performance of novel C12A7 hollow cathodes. To explore the failure operating point and degradation mechanism of the C12A7 hollow cathode, microscopic analyses of a degraded electride emitter after 10 h of thermal electron emission are presented in this paper. The morphology and composition variation of overheated electride emitters by scanning electron microscopy, energy-dispersive spectroscopy and X-ray diffraction indicate the melting and decomposition of electride of the surface layer. The monitored temperature of the electride emitter during the C12A7 hollow cathode operation shows that to avoid overheating the electride emitter, the average current density allowed should be about 64 m A mm^(-2) for the C12A7 hollow cathode in its current configuration. Experimental results of the heaterless C12A7 hollow cathode demonstrate that xenon(Xe) ion bombardment can remove the insulating layer and restore the thermionic emission capability for less degraded emitters. Based on experimental results and microscopic characterization, the depletion and degradation mechanisms of electride emitters during the hollow cathode operation are discussed.

Early experimental investigation of the C12A7 hollow cathode fed on iodine

To fully realize the superiority of the iodine electric propulsion system in streamlining the size and reducing the operating costs, iodine hollow cathode technology must be developed. Considering the corrosiveness of iodine and the possible impurity of the working propellant, the C12A7 hollow cathode with promising chemical ability was developed and tested. The C12A7 hollow cathode with a nominal current of 1–4 A was successfully ignited with iodine from the reservoir outside the vacuum chamber. It was operated at 1 A of anode current with a 1.2 mg s^(-1) iodine mass flow rate.Despite involuntary extinguishment, the C12A7 hollow cathode could be restarted repeatedly with a single operation time of up to 12 min and a total duration of 30 min. The unexpected fluctuation of iodine flow may be the reason for the short operation time. Experimental results and microscopical observation of the electride emitter show the compatibility of the iodine and electride emitter. For the development and demonstration of future single-iodine electric propulsion of Hall thrusters, the iodine storage and supply system with precise control and regulation may be the critical technology.

Enhancing hydrogen evolution reaction performance of transition metal doped two-dimensional electride Ca_(2)N

Two-dimensional electride Ca_(2)N has strong electron transfer ability and low work function,which is a potential candidate for hydrogen evolution reaction(HER)catalyst.In this work,based on density functional theory calculations,we adopt two strategies to improve the HER catalytic activity of Ca_(2)N monolayer:introducing Ca or N vacancy and doping transition metal atoms(TM,refers to Ti,V,Cr,Mn,Fe,Zr,Nb,Mo,Ru,Hf,Ta and W).Interestingly,the Gibbs free energyΔG_(H*)of Ca_(2)N monolayer after introducing N vacancy is reduced to-0.146 e V,showing good HER catalytic activity.It is highlighted that,the HER catalytic activity of Ca_(2)N monolayer can be further enhanced with TM doping,the Gibbs free energyΔG_(H*)of single Mo and double Mn doped Ca_(2)N are predicted to be 0.119 and 0.139 e V,respectively.The present results will provide good theoretical guidance for the HER catalysis applications of two-dimensional electride Ca_(2)N monolayer.