Tailoring the electronic structure of the NaTi₂(PO₄)₃ anode for high-performing sodium-ion batteries via defect engineering

Abstract

NASICON-type electrode materials suffer poor intrinsic electronic conductivity, which significantly limits their capacity and rate capability for further application in sodium-ion batteries. Herein, we aim to address this issue by...

Ir Nanoparticles Supported on Oxygen-Deficient Vanadium Oxides Prepared by a Polyoxovanadate Precursor for Enhanced Electrocatalytic Hydrogen Evolution

“…Under alkaline conditions, the electrocatalytic HER consists of the following steps: H 2 normalO + e − + normalM = normalM normalH normala normald normals + normalO normalH − 2 normalM normalH normala normald normals + e − + H 2 normalO = H 2 + 2 normalO normalH − + 2 normalM (M represents the catalytic site of the catalyst and H ads represents adsorbed hydrogen). , In the reaction process, H + (OH – ) first binds to the iridium catalytic site to form H ads , followed by dehydrogenation. Due to the interleaving of various vanadium oxide compounds in V x O y /C atoms and the presence of simultaneous oxygen vacancies, electron enrichment occurs at the Ir–V x O y active site. , During the reaction process, more electrochemically accessible Ir active sites are effectively added, which is conducive to accelerating the initial hydrolytic ionization, accelerating the formation of adsorbed hydrogen atoms (H ads ) by H + (OH – ), and weakening the binding strength of hydrogen with the Ir catalytic site due to charge sharing, thus facilitating rapid desorption of hydrogen. This process promotes the Volmer and Tafel processes, achieving a good balance between the catalyst’s adsorption and desorption capabilities toward hydrogen atoms, thereby successfully reducing the activation energy and hydrogen evolution overpotential of the HER. − The XPS spectra of Ir/V x O y /C after the HER test are shown in Figure e–h.…”

“…The oxygen defect structures derived from V x O y particles can also enhance charge separation , and thus improve the kinetic ability of charge transfer. In the process of HER, the free charge on the surface of oxygen vacancy can reduce the initial hydrolysis of adjacent catalytic sites and the adsorption energy of H*, thus promoting the release of H 2 from the surface of the catalytic site and greatly improving HER activity. ,,, In the O 1s spectrum, the defective oxygen peak still exists, indicating that the defected structure is stable in a strong acid and alkali environment.…”

“…Under alkaline conditions, the electrocatalytic HER consists of the following steps: ­(M represents the catalytic site of the catalyst and H ads represents adsorbed hydrogen). , In the reaction process, H + (OH – ) first binds to the iridium catalytic site to form H ads , followed by dehydrogenation. Due to the interleaving of various vanadium oxide compounds in V x O y /C atoms and the presence of simultaneous oxygen vacancies, electron enrichment occurs at the Ir–V x O y active site. , During the reaction process, more electrochemically accessible Ir active sites are effectively added, which is conducive to accelerating the initial hydrolytic ionization, accelerating the formation of adsorbed hydrogen atoms (H ads ) by H + (OH – ), and weakening the binding strength of hydrogen with the Ir catalytic site due to charge sharing, thus facilitating rapid desorption of hydrogen. This process promotes the Volmer and Tafel processes, achieving a good balance between the catalyst’s adsorption and desorption capabilities toward hydrogen atoms, thereby successfully reducing the activation energy and hydrogen evolution overpotential of the HER. − The XPS spectra of Ir/V x O y /C after the HER test are shown in Figure e–h.…”

CNT Composite β-MnO2 with Fiber Cable Shape as Cathode Materials for Aqueous Zinc-Ion Batteries

“…24,25 Although a manganese-based positive electrode material in AZIBs has become the most widely used positive electrode material because of its high energy density, large capacity as well as long life, its actual application is restricted due to its poor conductivity, relatively low energy density, and incomplete understanding of the electrochemical reaction mechanism. 26,27 Therefore, the methods to strengthen the properties of manganese-based positive materials include carbon coating, 28 metal element doping, 29 morphology refinement, 30 defect engineering, 31 nanostructure engineering, 32 and conductive polymer coatings. 33 For example, Wang et al obtained PVP-MnO 2 , which possesses a steady long life cycle of 210 mA h g −1 at 0.3 A g −1 in 180 cycles and a capacity retention of 84% at 1 A g −1 in 850 cycles.…”

“…At present, the materials widely used in AZIBs mainly include: (1) vanadium-based materials that can promote the insertion and removal of Zn 2+ attributed to it having an open layered structure during charging/discharging processes. Nevertheless, they have poor conductivity and low operating voltage. , (2) Prussian blue analogues that possess a high output voltage and stable structure but low theoretical capacity, poor conductivity, and poor rate capability. , (3) Transition metal sulfides that have a high specific area and abundant interior defects, but instability of the material structure affects their electrochemical properties during charging and discharging. , (4) Manganese-based materials that have multiple valence states, adjustable structure, a high operating voltage, and theoretical capacity, but their structures are unstable and tend to collapse in long-term cycles. , Although a manganese-based positive electrode material in AZIBs has become the most widely used positive electrode material because of its high energy density, large capacity as well as long life, its actual application is restricted due to its poor conductivity, relatively low energy density, and incomplete understanding of the electrochemical reaction mechanism. , Therefore, the methods to strengthen the properties of manganese-based positive materials include carbon coating, metal element doping, morphology refinement, defect engineering, nanostructure engineering, and conductive polymer coatings . For example, Wang et al.…”