Bulk bismuth anodes for wide-temperature sodium-ion batteries enabled by electrolyte chemistry modulation

Sodium ion batteries (SIBs) are considered reliable supplies for next-generation energy devices. However, there is a limited understanding of strategies to prevent the performance deterioration of SIBs under extreme temperature conditions. This study aimed to address this challenge by developing modified electrolyte chemistry to achieve stable wide-temperature SIBs. Weakly Na+-solvating solvent 2-methyltetrahydrofuran (MeTHF) was used to promote the kinetics of Na+ de-solvation. Moreover, 1,2-dimethoxyethane (DME) was introduced as a co-solvent because of the high solubility for Na salts and the coupling reaction mechanism with the Bi electrode. The formulated electrolyte not only endows an anion-dominated NaF-rich solid electrolyte interface (SEI) layer, but also reduces the energy required for the Na+ across the SEI layer (from 291.2 to 89.6 meV). Consequently, Na||Bi half batteries achieve stable cycles at 400 mA g-1 at -20, 20 and 60 °C, respectively. Meanwhile, the extreme operating temperature of the batteries can be extended to -40 and 80 °C, which exceeds those of most current lithium/sodium-based batteries. Furthermore, full batteries employing Na3V2(PO4)3 as the cathode material exhibit stable operation over a wide temperature range of -20 to 60 °C. This electrolyte design strategy presented in this study shows significant promise for enabling wide-temperature SIBs with improved performance.

Fabrication of wide temperature FexCe1-xVO4 modified TiO2-graphene catalyst with excellent NH3-SCR performance and strong SO2/H2O tolerance

Selective catalytic reduction of NO with NH₃ (NH₃-SCR) is one of the most common technique for elimination of NO_x. The promotional effect of Fe additive on the NH₃-SCR activity of the CeVO₄/TiO₂-graphene (GE) is systematically studied. The results exhibited that the low-temperature NO_x conversion could be enhanced dramatically via the addition of Fe and Fe_0.5Ce_0.5VO₄/TiO₂-GE displayed the highest conversion of NO_x in the wide temperature window (200-400 °C). It is because that Fe³⁺ + Ce³⁺ ↔ Fe²⁺ + Ce⁴⁺ facilitated the oxidization of NO to NO₂ at low temperature and led to the "Fast SCR," thereby raising the SCR performance. What is more, the introduction of Fe enhanced redox ability, the surface relative percentage of Ce³⁺, V⁵⁺ and the chemical adsorbed oxygen. Furthermore, the high surface concentration of Ce³⁺ species can produce more active oxygen and leads to the "Fast SCR" reaction. In addition, the Fe_0.5Ce_0.5VO₄/TiO₂-GE catalyst showed excellent H₂O/SO₂ tolerance, which may be due to the decomposition of ammonium bisulphite under high temperature and the hydrophobicity of graphene. What is more, it displayed outstanding the stability. This work would provide theoretical reference for the practical application of NO_x abatement via NH₃-SCR.

Brønsted acid enhanced hexagonal cerium phosphate for the selective catalytic reduction of NO with NH3: In situ DRIFTS and DFT investigation

The possible effect of optimized acid sites on NH₃-SCR performance and the fundamental mechanism are barely illustrated. In this work, we report two model catalysts of hexagonal (h-CPO) and monoclinic (m-CPO) cerium phosphate with disparate acidity that show different NH₃-SCR activities under the same reaction conditions. Brønsted acid sites were found to be crucial for NH₃-SCR performance at both low and high temperature. The electron localization discrepancy of h-CPO was more pronounced as compared with m-CPO, leading to the enrichment of P-OH (Brønsted acid site) which could strongly absorb NH₃ and then generate NH₄⁺ to participate in fast SCR via Langmuir-Hinshelwood mechanism, resulting in good activity at low temperature. The zeolitic water stored in the open channels of h-CPO could be released as supplement for P-OH sites which prevent the depletion and non-selective oxidation of NH₃ thus maintaining its high activity at high temperature via the Eley-Rideal mechanism. Meanwhile, as DFT calculation revealed, cerium is the electron deficient center which can easily fix NO and NO₂ from the intake, generating active NO_2(ad) or nitrites and facilitating fast SCR by reacting with NH₄⁺ species. Hence, the superior protonation ability to form P-OH and low energy barrier to generate active nitrites of h-CPO led its T₈₀ NO_x conversion to a broaden temperature of 150-450 ^oC under high GHSV of 177,000 h^-1. Furthermore, experimental and DFT calculation also demonstrated that the enriched Brønsted acid sites over h-CPO have largely suppressed SO₂ adsorption_, thus significantly reducing the formation of metal sulfates and achieving great SO₂ resistance. The ammonium sulfate deposits can be storage of NH₃, supplying additional reductant to promote high temperature activity and selectivity.

Self-Standing combined covalent-organic-framework membranes for subzero conductivity assisted by ionic liquids

The development of proton-conducting materials in cold regions is still at the initial stage due to the challenge in breaking the subzero temperature limit, especially in covalent organic frameworks (COFs). Herein, we fabricated a series of proton-conductive COFs as self-standing, highly flexible combined membranes (ssc-COFMs) composed of a processable TpBD-Me₂ and a conductive Tp-TG_Cl, in-situ encapsulated proton-conducting ionic liquids (PCILs) as additional proton sources into backbones. Compositions and microstructures of ssc-COFMs are monitored by XRD, FTIR, nitrogen adsorption and elemental analysis. Comparison to other porous organic conductors, a great advance propelled renders the combined COF membranes to have a high protonic conductivities at medium and subzero temperatures (243 to 353 K), owing to the resultant multifaceted synergistic effect of multiple proton units. Specifically, the proton conductivities of the ssc-COFMs loaded with -SO₄H functionalized PCILs reaches 2.87 × 10^-4 S cm^-1 (~58% RH) and 9.93 × 10^-4 S cm^-1 (~98% RH) at 243 K, together with 6.84 × 10^-2 S·cm^-1 under 353 K and ~ 98% RH.