The storage of multiple electrons per molecule provides opportunities to greatly enhance electrochemical energy capacity. VB 2 releases, via electrochemical oxidation, 11 electrons per molecule at a favorable, electrochemical potential. Coupled with an air cathode, this 4060 mAh=g intrinsic capacity anode, has energy capacity greater than that of gasoline. Nanochemical improvements of VB 2 are probed to facilitate charge transfer and discharge voltage. Nanoparticle formation is accomplished with a planetary ball mill media (tungsten carbide) with hardness comparable to that of VB 2 (8-9 Mohs 2 ). Mechanochemical synthesized, VB 2 nanorods, exhibit higher voltage, sustain higher rate, and depth of discharge than macroscopic VB 2 .Transformative advances are needed to increase the battery energy density for devices ranging from hearing aids to electric cars. The storage of multiple electrons per molecular site provides opportunities to greatly enhance electrochemical energy capacity. Hence, we have studied, or introduced, a range of multiple electron per molecule redox materials for charge storage. These range from the two electron redox chemistry of solid sulfur, 1 to the three electron redox chemistry of hexavalent super irons 2,3 or aluminium, 4 as well as multiple electron per molecule transfer in peroxides, 5 polyiodides, 6 permanganates, 7 metal chalcogenides, 8 iodates, 9 and stannates; 10 selective examples are cited in the references.The most compelling case to date for high energy density multielectron charge storage is the multiple electron oxidation of a vanadium boride anode 11,12 which when coupled with air as a cathode (as used in Zn-Air batteries), delivers greater energy storage capacity than gasoline. 13 VB 2 undergoes an extraordinary 11 electron per molecule oxidation, and provides an intrinsic 11 faraday, per 72.6 g mol À1 molecular weight, which is an anode capacity of 4060 mAh=g. With a density, d ¼ 5.10 kg=l, it has a capacity 20,700 Ah=l. This is respectively 10-fold or 3.5-fold higher than the volumetric capacity of lithium or zinc. Discharge of all 11 electrons per molecule occurs at a singular, favorable anodic potential, which includes oxidation of the tetravalent transition metal ion, V(þ4 þ5), and each of the two boron's 2xB(À2 þ3). 12,13 Borides are prone to decomposition in the alkaline media which passivates anodic discharge. 14 This is overcome with a zirconia coating, which sustains effective alkaline discharge and stabilizes the borides in contact with the alkaline electrolyte. 11,13,15 Recently, a series of VB x (x ¼ 0.25, 0.5 and 1) were prepared by a mechanochemical synthesis and observed to deliver an anodic capacity twice higher than the theoretical capacity of Zn. 16 Based on experimental discharge, we had previously estimated that the discharge potential of the high capacity VB 2 =air battery was 1.3 V. An improved estimate of the potential for the VB 2 =air discharge is attained here from available enthalpy and entropy of the reaction components. 17,18 These allow us to ...
The Solar Thermal Electrochemical Production of energetic molecules converts solar energy at high efficiency. Rather than electricity, a variety of useful chemicals, including solar fuels and iron without CO 2 emission, are produced by this STEP process. A synergy of solar thermal and solar-electric and other renewable energy electronic charge transfer, forms an alternative higher efficiency solar energy conversion process. For example, STEP can split CO 2 with >50% solar efficiency. Previously, we demonstrated STEP carbon capture, STEP fuels and STEP iron. Here we expand the STEP process portfolio to include the solar production of magnesium and bleach. IntroductionSTEP, the Solar Thermal Electrochemical Production of energetic molecules is an efficient process for converting solar energy. In STEP, the product of the solar energy conversion is useful chemicals, rather electricity. The STEP approach for solar energy conversion (1) is based on our theory and experimental observation, that even a semiconductor with bandgap smaller than the water splitting potential (E(H 2 O)=1.23V at 25°C) can split water at elevated temperature (2-4). Hence, silicon (bandgap 1.1 eV) was used to directly form hydrogen fuel from water at elevated temperature in a novel molten alkali hydroxide electrolyzer. As represented in Fig. 1 STEP generalizes the advantage of this energy conversion process to the endothermic formation of all useful, energetic molecules (1), is and includes STEP cost effective production of hydrogen (5), iron (6,7) fuels and carbon capture (8,9).The STEP process uses solar thermal energy to heat and decrease the energy of enodothermic electrolysis reactions (Figure 1), and applies the low requisite, remaining energy, by non-fossil fuel electronic charge. This process captures sunlight with conversion efficiency greater than either photovoltaic or solar thermal electric processes, through the use of the global (visible + thermal) sunlight. For example, energy sufficient, visible, sunlight drives photovoltaic charge transfer, and available heat, infrared sunlight, and excess visible sunlight, heats, and decreases the energy of, an electrolysis reaction (1). Figure 1. Left: A conventional, efficient photovoltaic generates a voltage too low to drive many useful electrochemical reactions, such as water or carbon dioxide splitting, or the indicated generic redox transfer, at ambient temperature. Right: The STEP process uses solar thermal energy to drive down the required electrolysis. This forms an energetically allowed pathway to drive charge transfer, as detailed in (1). Figure 2. CO 2 is easily captured as solid carbon at 750°C, or at 950°C as carbon monoxide using a molten Li 2 CO 3 electrolysis cell powered by sunlight, as detailed in (7).In the STEP process, rather than electrical generation, solar energy directly provides the chemical products needed by society. This original process is derived for the solar generation of energetically rich chemicals, including chlorine, metals, hydrogen and to ECS Transactions...
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