Molten air – a new, highest energy class of rechargeable batteries

The electrochemical discharge of VB 2 is a unique process that involves the multiple electron per molecule oxidation of the tetravalent transition metal ion, V (+4 → +5), and each of the two borons 2×B (−2 → +3), corresponding to a net 11 electron discharge mechanism of the VB 2 /air cell as described by the overall cell reaction: VB 2 + 11/4O 2 → B 2 O 3 + 1 2 V 2 O 5 . However, in the presence of alkaline electrolytes, the discharge products include alkali salts associated with vanadaic and boric acid. In this study, we used FTIR, XRD, and coulombic efficiency measurements to probe the discharge products of high capacity cells and isolate KVO 3 as the principal vanadium discharge product. Additionally, we show that K 2 B 4 O 7 is the probable borate product. From FTIR analysis in KOH electrolyte, it is evident that the alkaline VB 2 /air discharge reaction is: VB 2 + 11/4O 2 + 2KOH → 1 2 K 2 B 4 O 7 + KVO 3 + H 2 O. XPS shows that the surface structure of nanoscopic VB 2 is very different from macroscopic VB 2 , which may contribute to the improved electrochemical properties of the nanoscopic material. The understanding of the discharge process and factors affecting performance contribute to furthering the development of extremely high capacity VB 2 /air batteries that utilize multi-electron processes. Metallic zinc has been used as an anode material in the majority of aqueous primary systems due to zinc metal's high two-electron oxidation capacity and effective discharge. The zinc-carbon battery, known as the Leclanché cell, was first introduced in the 19 th century as a low-cost solution for early energy storage needs. The zinc cell, which produced approximately 65 Wh kg −1 , was ideal only for low-rate discharges.1,2 Until the development of the zinc/alkaline/manganese dioxide battery and the zinc/air cell, there was little improvement in primary batteries. The alkaline Zn/MnO 2 cell has since dominated primary electrochemical storage, providing 145 Wh kg −1 . Although more expensive than the zinc-carbon battery, the alkaline cell improved performance by increasing energy densities and power capabilities. The zinc/air battery, using external O 2 as the battery active cathode reactant further improves the energy density of primary battery systems. It would be useful for electronic devices to have even higher energy storage densities than that available with zinc/air batteries.3 Most metal/air batteries to date have been unsuccessful in reaching the high-energy densities that are made possible by multi-electron oxidations, due to material passivation or chemical instabilities. 4 To provide high energy density cells, there has been an effort to develop high-capacity multi-electron per molecule charge storage processes.5-21 Vanadium diboride (VB 2 ) undergoes a multiple electron oxidation process, which to its completion involves an extraordinary 11 electron per molecule oxidation, including oxidation of the tetravalent transition metal ion, V(+4 → +5), and each of the two borons 2xB(−2 → +3). VB 2 has an intri...

show abstract

“…We are also exploring molten electrolytes to transition VB 2 /air from a primary to a rechargeable battery. 25,26 …”

Section: Discussionmentioning

confidence: 99%

The Net Discharge Mechanism of the VB₂/Air Battery

Stuart

Hohenadel

et al. 2014

J. Electrochem. Soc.

Self Cite

View full text Add to dashboard Cite

show abstract

“…The carbonates, Li 2 CO 3 , Na 2 CO 3 , and K 2 CO 3 , have respective melting points of 723 °C, 851 °C, and 891 °C. [5][6][7]25,26 ] At temperatures below 800 °C, the only observed cathode product is solid carbon, formed by an effi cient 4e − reduction of carbonate (or CO 2 dissolved in carbonate). [ 23 ] Higher conductivity is desired as it leads to lower electrolysis ohmic losses.…”

mentioning

confidence: 99%

A One‐Pot Synthesis of Hydrogen and Carbon Fuels from Water and Carbon Dioxide

Liu

Cui

et al. 2014

Advanced Energy Materials

Self Cite

View full text Add to dashboard Cite

fuels. [5][6][7] Lubomirsky and co-workers [ 16 ] have also probed the electrolysis of lithium molten carbonates to produce carbon monoxide, and Chen and co-workers [ 17 ] have also probed electrolysis of mixed lithium, potassium molten carbonates to carbon.We have previously delineated the solar, optical, and electronic components of STEP. [ 6,13 ] In this study, we focus on the electrolysis component for STEP fuel. Specifi cally, we present the fi rst molten electrolyte sustaining electrolytic co-production of both hydrogen and carbon products in a single cell. Solid carbon (as coal) is used as the starting point to generate CO and hydrogen for the Fischer-Tropsch generation of a variety of fuels, such as synthetic diesel. [ 18 ] However, that process is carbon dioxide emitting intensive. Here, hydrogen and graphitic carbon are produced without carbon dioxide emissions and instead produced from water and carbon dioxide.This communication recounts our successful attempt to simultaneously co-generate hydrogen and solid carbon fuels from a mixed hydroxide/carbonate electrolyte in a "single-pot" electrolytic synthesis at temperatures below 650 °C. The alternative co-generated hydrogen and gaseous carbon monoxide fuel synthesis will be pursued in a later study as the high temperature (over 900 °C) currently required to form CO in molten carbonates is a challenge to make compatible with the lower temperature range we have succeeded for hydrogen in the hydroxide electrolyses. We demonstrate here the functionality of new lithium-barium-calcium hydroxide carbonate electrolytes to co-generate hydrogen and carbon fuel in a single electrolysis chamber at high current densities of several hundreds of mA/cm 2 , at low electrolysis potentials, and from water and CO 2 starting points, which provides a signifi cant step towards the development of renewable fuels.Molten hydroxides are important as conductive, high-current, low-electrolysis-potential electrolytes for water splitting to generate hydrogen that have not been widely explored. [ 3,6,19,20 ] The pure anhydrous akali hydroxides melt only at temperatures >300 °C: LiOH ( T mp = 462 °C), NaOH ( T mp = 318 °C), KOH ( T mp = 406 °C), CsOH ( T mp = 339 °C). The mixed hydroxides have lower melting point. With molar ratios of 0.3:0.7 LiOH/NaOH, 0.3:0.7 LiOH/KOH, 0.5:0.5 NaOH/KOH, 0.44:0.56 KOH/CsOH, respectively, these melt at 215 °C, 225 °C, 170 °C, and 195°C, and the melting point is even lower when hydrated hydroxide salts are used. A eutectic 0.45:0.55 mix of LiOH/Ba(OH) 2 melts at 320 °C, compared to 407 °C for anhydrous Ba(OH) 2 , and 300 °C for the monohydrate Ba(OH) 2 ·H 2 O. [ 21 ] Low temperature enhances electrolytic H 2 formation in molten hydroxides. The coulombic effi ciency of electrolytic water splitting, η H2 (moles H 2 generated per 2 Faraday of applied charge),

show abstract

“…The portfolio of STEP processes continues to grow and develop [103][104][105][106][107][108][109][110], iron, a basic commodity, currently accounts for the release of one-quarter of worldwide CO 2 emissions by industry, which may be eliminated by replacement with the STEP iron process. The unexpected solubility of iron oxides in lithium carbonate electrolytes, coupled with facile charge transfer and a sharp decrease in iron electrolysis potentials with increasing temperature, provides a new route for iron production.…”

Section: Discussionmentioning

confidence: 99%

Molten air – a new, highest energy class of rechargeable batteries

Cited by 41 publications

References 30 publications

The Net Discharge Mechanism of the VB₂/Air Battery

The Net Discharge Mechanism of the VB₂/Air Battery

A One‐Pot Synthesis of Hydrogen and Carbon Fuels from Water and Carbon Dioxide

High‐Solar‐Efficiency Utilization of CO₂: the STEP (Solar Thermal Electrochemical Production) of Energetic Molecules

Contact Info

Product

Resources

About

Molten air – a new, highest energy class of rechargeable batteries

Cited by 41 publications

References 30 publications

The Net Discharge Mechanism of the VB2/Air Battery

The Net Discharge Mechanism of the VB2/Air Battery

A One‐Pot Synthesis of Hydrogen and Carbon Fuels from Water and Carbon Dioxide

High‐Solar‐Efficiency Utilization of CO2: the STEP (Solar Thermal Electrochemical Production) of Energetic Molecules

Contact Info

Product

Resources

About

The Net Discharge Mechanism of the VB₂/Air Battery

The Net Discharge Mechanism of the VB₂/Air Battery

High‐Solar‐Efficiency Utilization of CO₂: the STEP (Solar Thermal Electrochemical Production) of Energetic Molecules