Boris Shvartsev

Aluminum–air battery based on an ionic liquid electrolyte

Metal–air batteries, and particularly aluminum–air (Al–air) batteries, draw a major research interest nowadays due to their high theoretical energy content of Al (gravimetric and volumetric). Nevertheless, the implementation of Al–air batteries as a sustainable energy storage device is hampered by severe hurdles. Al anode high corrosion rate in aqueous alkaline solution is of major concern in terms of Al usage and safety. In non-aqueous electrolytes adverse Al surface activation substantially limits any power output. This study presents a novel non-aqueous Al–air battery. This battery utilizes 1-ethyl-3-methylimidazolium oligo-fluoro-hydrogenate (EMIm(HF)2.3F) room temperature ionic liquid (RTIL). Al–air batteries can sustain current densities up to 1.5 mA cm−2, producing capacities above 140 mA h cm−2, thus utilizing above 70% of the theoretical Al capacity. This is equivalent to an outstanding energy densities of 2300 W h kg−1 and 6200 W h L−1. We detected Al2O3 at the air electrode as the battery discharge product of the oxygen reduction coupled with Al ions migrated to the air electrode.

Reference electrode assembly and its use in the study of fluorohydrogenate ionic liquid silicon electrochemistry

Silicon electrochemistry in fluorohydrogenate ionic liquids is partly hampered owing to the incapability of producing an accurate and reproducible potential measurement due to a lack of appropriate reference electrodes. This research work describes a simple assembly of a stable external reference electrode enabling accurate studies of silicon electrochemistry in fluorohydrogenate ionic liquids. The electrode configuration is based on the ferrocene/ferrocenium (Fc|Fc(+)) couple dissolved in the EMIm(HF)(2.3)F (1-ethyl-3-methyl-imidazolium fluorohydrogenate)/Carbopol 941 gel. A stable potential of 2.5 wt% Carbopol-based electrode was measured versus a calomel reference electrode at 250 ± 3 mV. By utilizing the constructed electrode, an intensive electrochemical investigation on n-type silicon in EMIm(HF)(2.3)F was conducted. Flat-band and open circuit potentials were measured, along with Si-air half- and full-cell electrochemical measurements. A suggested mechanism for the n-type Si dissolution process in the EMIm(HF)(2.3)F electrolyte, without illumination, is discussed as well.

Influence of Solution Volume on the Dissolution Rate of Silicon Dioxide in Hydrofluoric Acid

Experimental data and modeling of the dissolution of various Si/SiO2 thermal coatings in different volumes of hydrofluoric acid (HF) are reported. The rates of SiO2 -film dissolution, measured by means of various electrochemical techniques, and alteration in HF activity depend on the thickness of the film coating. Despite the small volumes (0.6-1.2 mL) of the HF solution, an effect of SiO2 -coating thickness on the dissolution rate was detected. To explain alterations detected in HF activity after SiO2 dissolution, spectroscopic analyses (NMR and FTIR) of the chemical composition of the solutions were conducted. This is associated with a modification in the chemical composition of the HF solution, which results in either the formation of an oxidized species in solution or the precipitation of dissolution products. HF2 (-) accumulation in the HF solution, owing to SiO2 dissolution was identified as the source of the chemical alteration.

Challenges and Prospect of Non-aqueous Non-alkali (NANA) Metal–Air Batteries

Non-aqueous non-alkali (NANA) metal–air battery technologies promise to provide electrochemical energy storage with the highest specific energy density. Metal–air battery technology is particularly advantageous being implemented in long-range electric vehicles. Up to now, almost all the efforts in the field are focused on Li–air cells, but other NANA metal–air battery technologies emerge. The major concern, which the research community should be dealing with, is the limited and rather poor rechargeability of these systems. The challenges we are covering in this review are related to the initial limited discharge capacities and cell performances. By comprehensively reviewing the studies conducted so far, we show that the implementation of advanced materials is a promising approach to increase metal–air performance and, particularly, metal surface activation as a prime achievement leading to respectful discharge currents. In this review, we address the most critical areas that need careful research attention in order to achieve progress in the understanding of the physical and electrochemical processes in non-aqueous electrolytes applied in beyond lithium and zinc air generation of metal–air battery systems.