Temperature promotes selectivity during electrochemical CO2 reduction on NiO:SnO2 nanofibers

Electrolyzers operate over a range of temperatures; hence, it is crucial to design electrocatalysts that do not compromise the product distribution unless temperature can promote selectivity. This work reports a synthetic approach based on electrospinning to produce NiO:SnO2 nanofibers (NFs) for selectively reducing CO2 to formate above room temperature. The NFs comprise compact but disjoined NiO and SnO2 nanocrystals identified with STEM. The results are attributed to the segregation of NiO and SnO2 confirmed with XRD. The NFs are evaluated for the CO2 reduction reaction (CO2RR) over various temperatures (25, 30, 35, and 40 °C). The highest faradaic efficiencies to formate (FEHCOO- ) are reached by NiO:SnO2 NFs containing 50% of NiO and 50% SnO2 (NiOSnO50NF), and 25% of NiO and 75% SnO2 (NiOSnO75NF), at an electroreduction temperature of 40 °C. At 40 °C, product distribution is assessed with in situ differential electrochemical mass spectrometry (DEMS), recognizing methane and other species, like formate, hydrogen, and carbon monoxide, identified in an electrochemical flow cell. XPS and EELS unveiled the FEHCOO- variations due to a synergistic effect between Ni and Sn. DFT-based calculations reveal the superior thermodynamic stability of Ni-containing SnO2 systems towards CO2RR over the pure oxide systems. Furthermore, computational surface Pourbaix diagrams showed that the presence of Ni as a surface dopant increases the reduction of the SnO2 surface and enables the production of formate. Our results highlight the synergy between NiO and SnO2, which can promote the electroreduction of CO2 at temperatures above room temperature.

A nanostructured SnO2/Ni/CNT composite as an anode for Li ion batteries

A SnO₂/Ni/CNT nanocomposite was synthesized using a simple one-step hydrothermal method followed by calcination. A structural study via XRD shows that the tetragonal rutile structure of SnO₂ is maintained. Further, X-ray photoelectron spectroscopy (XPS) and Raman studies confirm the existence of SnO₂ along with CNTs and Ni nanoparticles. The electrochemical performance was investigated via cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and galvanostatic charge–discharge measurements. The nanocomposite has been used as an anode material for lithium-ion batteries. The SnO₂/Ni/CNT nanocomposite exhibited an initial discharge capacity of 5312 mA h g⁻¹ and a corresponding charge capacity of 2267 mA h g⁻¹ during the first cycle at 50 mA g⁻¹. Pristine SnO₂ showed a discharge/charge capacity of 1445/636 mA h g⁻¹ during the first cycle at 50 mA g⁻¹. This clearly shows the effects of the optimum concentrations of CNTs and Ni. Further, the nanocomposite (SnNiCn) shows a discharge capacity as high as 919 mA h g⁻¹ after 210 cycles at a current density of 400 mA g⁻¹ in a Li-ion battery set-up. Thus, the obtained capacity from the nanocomposite is much higher compared to pristine SnO₂. The higher capacity in the nanoheterostructure is due to the well-dispersed nanosized Ni-decorated stabilized SnO₂ along with the CNTs, avoiding pulverization as a result of the volumetric change of the nanoparticles being minimized. The material accommodates huge volume expansion and avoids the agglomeration of nanoparticles during the lithiation and delithiation processes. The Ni nanoparticles can successfully inhibit Sn coarsening during cycling, resulting in the enhancement of stability during reversible conversion reactions. They ultimately enhance the capacity, giving stability to the nanocomposite and improving performance. Additionally, the material exhibits a lower Warburg coefficient and higher Li ion diffusion coefficient, which in turn accelerate the interfacial charge transfer process; this is also responsible for the enhanced stable electrochemical performance. A detailed mechanism is expressed and elaborated on to provide a better understanding of the enhanced electrochemical performance.

SnO₂/Ni/CNT nanocomposite approach has been demonstrated which confers shielding against volume expansion due to the use of optimum % of Ni & CNT exhibiting superior cycling stability and rate capabilities of the stable electrode structure.

Undoped SnO2 as a Support for Ni Species to Boost Oxygen Generation through Alkaline Water Electrolysis

In this study, the synergistic behavior of Ni species and bimodal mesoporous undoped SnO₂ is investigated in oxygen evolution reactions (OERs) under alkaline conditions without any other modification of the compositional phases or using noble metals. An efficient and environmentally friendly hydrothermal method to prepare bimodal mesoporous undoped SnO₂ with a very high surface area (>130 m² g^-1) and a general deposition-precipitation method for the synthesis of well-dispersed Ni species on undoped SnO₂ are reported. The powders were characterized by adsorption-desorption isotherms, TG-DTA, XRD, SEM, TEM, Raman, TPR-H₂, and XPS. The best NiSn composite generates, under certain experimental conditions, a very high TOF value of 1.14 s^-1 and a mass activity higher than 370 A g^-1, which are remarkable results considering the low amount of Ni deposited on the electrode (3.78 ng). Moreover, in 1 M NaOH electrolyte, this material produces more than 24 mA cm^-2 at an overpotential value of approximately +0.33 V, with only 5 wt % Ni species. This performance stems from the dual role of undoped SnO₂, on the one hand, as a support for active and well-dispersed Ni species and on the other hand as an active player through the oxygen vacancies generated upon Ni deposition.

Molybdenum-doped tin oxide nanoflake arrays anchored on carbon foam as flexible anodes for sodium-ion batteries

Tin oxide (SnO₂) has been widely used as an anode material for sodium-ion storage because of its high theoretical capacity. However, it suffers from large volume expansion and poor conductivity. To overcome these limitations, in this study, we have designed and prepared Mo-doped SnO₂ nanoflake arrays anchored on carbon foam (Mo-SnO₂@C-foam with 38.41 wt% SnO₂ and 3.7 wt% Mo content) by a facile hydrothermal method. The carbon foam serves as a three-dimensional conductive network and a buffer skeleton, contributing to improved rate performance and cycling stability. In addition, Mo doping enhances the kinetics of sodium-ion transfer, and the interlaced SnO₂ nanoflake arrays is beneficial to promote the conversion reactions during the charge/discharge process. The as-prepared composite with a unique structure demonstrate a high initial capacity of 1017.1 mAh g^-1 at 0.1 A g^-1, with a capacity retention over three times higher than that of the control sample (SnO₂@C-foam) at 1 A g^-1, indicating a remarkable rate performance.

Novel Silicon Doped Tin Oxide-Carbon Microspheres as Anode Material for Lithium Ion Batteries: The Multiple Effects Exerted by Doped Si

Silicon doped tin oxide embedded porous carbon microspheres (Si_y Sn_1-y O_x @C) are synthesized. It is found that the doped Si not only improves the reversibility of lithiation/delithiation reactions, but also prevents Sn from aggregation. In addition, the doped Si introduces extra defects into the carbon matrix and produces Li⁺ conductive Li₄ SiO₄ , which accelerates Li⁺ diffusion. Together with the conductive, porous carbon matrix that provides void space to accommodate the volume change of Sn during charge/discharge cycling, the novel Si_y Sn_1-y O_x @C exhibits excellent electrochemical performance. It shows a high initial columbic efficiency of 75.9%. A charge (delithiation) capacity of 880.32 mA h g^-1 is retained after 150 cycles, i.e., 91% of the initial capacity. These results indicate that the as-synthesized Si_y Sn_1-y O_x @C is a promising anode material for lithium ion batteries.

Controllable synthesis of micro/nano-structured MnCo2O4 with multiporous core–shell architectures as high-performance anode materials for lithium-ion batteries

Various micro/nano-structured MnCo₂O₄ with excellent lithium storage performance were synthesized controllably.