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SnSb binary alloy induced heterogeneous nucleation within the confined nanospace: Toward dendrite-free, flexible and energy/power dense sodium metal batteries

Dou Du, Yujie Liu, Min Zhang

Rechargeable sodium (Na) metal batteries (SMBs) provide an alternative energy-dense, low-cost energy storage system beyond prevailing Li-ion technologies. However, their practical deployment requires the performance evaluation of Na anodes on the device level and mitigation of safety hazards, i.e., mechanical stress, electrode pulverization and dynamic interfacial properties. Here, we propose a lightweight N-doped carbon nanofiber substrate with SnSb nanocrystallites monodispersed within the mesopores (SnSb@NCNF). The alloying-induced Na15Sn4 and Na3Sb intermediates act as the heterogeneous sodiophilic "magnets" to homogenize Na ion flux and confine Na deposits within the nanospace. Additionally, the nucleation theory of metal solidification bridges the density functional theory calculations, elucidating the oriented Na propagation that maximizes the anode utilization. With the proper Na plating regulation, the SnSb@NCNF substrate (pre-stored 1 x excess Na) integrates with the NaVPO4F cathode in 5 mA h single-layer pouch cell, the prototype of which exhibits the cycling endurance (96.3% capacity retention for 500 cycles) and high specific energy/power densities even upon the repetitive mechanical flexing scenarios. The nanoconfinement of the heterogeneous nucleation process affords a feasible approach to mitigate the dendrite formation upon the geometry deformation or high areal-capacity loading, which enlightens the further exploration of the energy-dense, mechanical flexible battery system.

ELSEVIER2021

Efficient Base-Metal NiMn/TiO2 Catalyst for CO2 Methanation

Wei Chen, Emanuele Moioli, Min Zhang, Andreas Züttel

Energy storage solutions are a vital component of the global transition toward renewable energy sources. The power-to-gas (PtG) concept, which stores surplus renewable energy in the form of methane, has therefore become increasingly relevant in recent years. At present, supported Ni nanoparticles are preferred as industrial catalysts for CO2 methanation due to their low cost and high methane selectivity. However, commercial Ni catalysts are not active enough in CO2 methanation to reach the high CO2 conversion (>99%) required by the specifications for injection in the natural gas grid. Herein we demonstrate the promise of promotion of Ni by Mn, another low-cost base metal, for obtaining very active CO2 methanation catalysts, with results comparable to more expensive precious metal-based catalysts. The origin of this improved performance is revealed by a combined approach of nanoscale characterization, mechanistic study, and density functional theory calculations. Nanoscale characterization with scanning transmission electron microscopy-energy- dispersive X-ray spectroscopy (STEM-EDX) and X-ray absorption spectroscopy shows that NiMn catalysts consist of metallic Ni particles decorated by oxidic Mn2+ species. A mechanistic study combining IR spectroscopy of surface adsorbates, transient kinetic analysis with isotopically labeled CO2, density functional theory calculations, and microkinetics simulations ascertains that the MnO clusters enhance CO2 adsorption and facilitate CO2 activation. A macroscale perspective was achieved by simulating the Ni and NiMn catalytic activity in a Sabatier reactor, which revealed that NiMn catalysts have the potential to meet the demanding PtG catalyst performance requirements and can largely replace the need for expensive and scarce noble metal catalysts.

2019

Effect of Sensitizer Adsorption Temperature on the Performance of Dye-Sensitized Solar Cells

Pascal Comte, Jean-David Décoppet, Michael Graetzel, Mohammad Khaja Nazeeruddin, Peng Wang, Shaik Mohammed Zakeeruddin, Min Zhang

Employing a mesoscopic titania photoanode whose bilayer structure was judiciously selected to fit the optoelectronic characteristics of the Ru-based heteroleptic complex Na-cis-Ru(4,4'-(5-hexyltiophen-2-yl)-2,2'-bipyridine)(4-carboxylic-acid-4'-carboxylate-2,2'-bipyridine)(thiocyanate)(2), coded as C101, we investigated the effect of temperature for dye adsorption on the photovoltaic performance of dye-sensitized solar cells (DSCs). We found a significant efficiency enhancement upon lowering the temperature applied during the sensitizer uptake from solution. When the dye adsorption was performed at 4 degrees C, the photovoltaic performance parameters measured under standard reporting conditions (AM1.5 G sunlight at 1000 W/m(2) intensity and 25 degrees C), i.e., the open circuit voltage (V-oc), the short circuit photocurrent density (J(sc)), the fill factor (FF), and consequently the power conversion efficiency (PCE), improved in comparison to cells stained at 20 and 60 degrees C.Results from electrochemical impedance spectroscopy (EIS) and attenuated total reflection Fourier-transform infrared spectroscopy (ATR-FTIR) show that the self-assembled layer of C101 formed at lower temperature impairs the back-electron transfer from the TiO2 conduction band to the triiodide ions in the electrolyte more strongly than the film produced at 60 degrees C. Profiting from the favorable influence that the low-temperature dye uptake exerts on photovoltaic performance, we have realized DSCs showing a power conversion efficiency of 11.5%.

2011