Reversible Control of the Mn Oxidation State in SrTiO3 Bulk Powders

Manganese Defective Clustering: Influence on the Spectroscopic Features of Ceria-Based Nanomaterials

The influence of manganese modification on the spectroscopic features of manganese-doped CeO₂ systems synthesized by the microwave-assisted hydrothermal route and their correlation with the presence of O defective structures were verified, focusing on their interaction with poisonous atmospheres. Raman and electron paramagnetic resonance studies confirmed the presence of defective clusters formed by dipoles and/or quadrupoles. The number of paramagnetic species was found to be inversely proportional to the doping concentration, resulting in an increase in the Mn²⁺ signal, likely due to the reduction of Mn³⁺ species after the interaction with CO. X-ray photoelectron spectroscopy data showed the pure system with 33% of its cerium species in the Ce³⁺ configuration, with an abrupt decrease to 19%, after the first modification with Mn, suggesting that 14% of the Ce³⁺ species are donating one electron to the Mn²⁺ ions, thus becoming nonparamagnetic Ce⁴⁺ species. On the contrary, 58% of the manganese species remain in the Mn²⁺ configuration with five unpaired electrons, corroborating the paramagnetic feature of the samples seen in the electron paramagnetic resonance study.

Parameter space exploration reveals interesting Mn-doped SrTiO3 structures

The rich chemistry of the SrTiO₃ is often modified, intentionally or unintentionally, through the inclusion of defects and dopants. Much computational effort using periodic boundary DFT has been dedicated towards understanding how these observed properties arise from the disordered perovskite structure, but the range of possible defect chemistries arising from different computational modeling choices has not been thoroughly explored. In this study, we calculate the geometric and electronic properties for a systematic range of supercells, from approximately 40 atoms to approximately 320 atoms, with each atomic vacancy and doped with Mn ions to isolate the contribution of supercell size to predicted properties. Our thorough analysis of the electronic and geometric structure of each defected supercell shows high variability, illustrating the need to map the parameter space in order to achieve a comprehensive model of disordered perovskites. Our results additionally reveal fundamental insights into dopant chemistry in SrTiO₃, and we report new potential geometric and electronic structures for Mn dopants that can be used to justify and guide additional experimental investigation into this complex material.

Understanding Degradation at the Lithium-Ion Battery Cathode/Electrolyte Interface: Connecting Transition-Metal Dissolution Mechanisms to Electrolyte Composition

Lithium transition-metal oxides (LiMn₂O₄ and LiMO₂ where M = Ni, Mn, Co, etc.) are widely applied as cathode materials in lithium-ion batteries due to their considerable capacity and energy density. However, multiple processes occurring at the cathode/electrolyte interface lead to overall performance degradation. One key failure mechanism is the dissolution of transition metals from the cathode. This work presents results combining scanning electrochemical microscopy with inductively coupled plasma (ICP) and electron paramagnetic resonance (EPR) spectroscopies to examine cathode degradation products. Our effort employs a LiMn₂O₄ (LMO) thin film as a model cathode to monitor the Mn dissolution process without the potential complications of conductive additive and polymer binders. We characterize the electrochemical behavior of LMO degradation products in various electrolytes, paired with ICP and EPR, to better understand the properties of Mn complexes formed following metal dissolution. We find that the identity of the lithium salt anions in our electrolyte systems [ClO₄^-, PF₆^-, and (CF₃SO₂)₂N^-] appears to affect the Mn dissolution process significantly as well as the electrochemical behavior of the generated Mn complexes. This implies that the mechanism for Mn dissolution is at least partially dependent on the lithium salt anion.

Synthesis, Cytotoxicity Assessment and Optical Properties Characterization of Colloidal GdPO4:Mn2+, Eu3+ for High Sensitivity Luminescent Nanothermometers Operating in the Physiological Temperature Range

Herein, a novel synthesis method of colloidal GdPO4:Mn2+,Eu3+ nanoparticles for luminescent nanothermometry is proposed. XRD, TEM, DLS, and zeta potential measurements confirmed the crystallographic purity and reproducible morphology of the obtained nanoparticles. The spectroscopic properties of GdPO4:Mn2+,Eu3+ with different amounts of Mn2+ and Eu3+ were analyzed in a physiological temperature range. It was found that GdPO4:1%Eu3+,10%Mn2+ nanoparticles revealed extraordinary performance for noncontact temperature sensing with relative sensitivity SR = 8.88%/°C at 32 °C. Furthermore, the biocompatibility and safety of GdPO4:15%Mn2+,1%Eu3+ was confirmed by cytotoxicity studies. These results indicated that colloidal GdPO4 doped with Mn2+ and Eu3+ is a very promising candidate as a luminescent nanothermometer for in vitro applications.

Ag(I) ions working as a hole-transfer mediator in photoelectrocatalytic water oxidation on WO3 film

Ag(I) is commonly employed as an electron scavenger to promote water oxidation. In addition to its straightforward role as an electron acceptor, Ag(I) can also capture holes to generate the high-valent silver species. Herein, we demonstrate photoelectrocatalytic (PEC) water oxidation and concurrent dioxygen evolution by the silver redox cycle where Ag(I) acts as a hole-transfer mediator. Ag(I) enhances the PEC performance of WO₃ electrodes at 1.23 V vs. RHE with increasing O₂ evolution, while forming Ag(II) complexes (Ag^IINO₃⁺). Upon turning off both light and potential bias, the photocurrent immediately drops to zero, whereas O₂ evolution continues over ~10 h with gradual bleaching of the colored complexes. This phenomenon is observed neither in the Ag(I)-free PEC reactions nor in the photocatalytic (i.e., bias-free) reactions with Ag(I). This study finds that the role of Ag(I) is not limited as an electron scavenger and calls for more thorough studies on the effect of Ag(I).

While water splitting catalysis may provide a renewable means to produce fuel, sacrificial reagents are typically employed to assess the water oxidation half reaction. Here, authors find the silver redox cycle to mediate O₂ evolution in photoelectrocatalytic water oxidation with WO₃ electrodes.