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Molten salt electrochemistry is cited as one of the most efficient ways to convert stable but unwanted CO2 into value-added chemical fuels and functional materials, in particular carbon nanotubes (CNTs). In this work, we report the high yield and scalable CO2-deriving CNTs by adding ZnO to molten carbonate electrolyte. The physicochemical properties such as crystal structure, morphology and element composition of the carbon products were characterized by scanning electron microscope (SEM), transmission electron microscope (TEM), energy dispersive spectroscopy (EDS), X-ray diffractometer (XRD) and Raman spectrometer (Raman). It is demonstrated that an appropriate amount of ZnO additives can greatly increase the content of CNTs in carbon products. However, the micromorphology and microstructure of the carbon products are found to be significantly changed when the ZnO content is insufficient or excessive. Compared with molten salt electrolyte without ZnO, ZnO-included electrolyte endows CNTs with a higher degree of graphitization and crystallinity. This work demonstrates the feasibility of improving CNTs content in carbon products and lowering required energy for CNTs production by adding ZnO as a promoter.

The first experimental evidence of a solar driven thermal electrochemical process (STEP) for wastewater treatment with synergetic co-generation of hydrogen is presented. The co-generation of hydrogen, a useful product, decreases the energy consumption to remove phenol, and increases the oxidation rate of persistent organics (exemplifed by phenol removal). Concentrated solar thermal heat elevates the temperature of the wastewater to be treated. Higher temperature decreases the thermodynamic energy required to drive phenol oxidation, and improves kinetics to sustain higher rates. Solar thermal energy decreases the requisite electrolysis potential, while visible sunlight on a photovoltaic generates this potential to drive the electrolysis.

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 CO2 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 CO2 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.

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STEP, the Solar Thermal Electrochemical Production of energetic molecules uses the whole spectrum of sunlight to produce useful chemicals, rather than electricity. The STEP process powers a high temperature molten electrolysis to produce useful chemicals including metals, such as iron and magnesium, fuels and bleach. Utilizing molten salts, the system has the potential to operate 24/7 without interruption from lack of sunlight. High temperature decreases the chemical production voltage to a small fraction of the room temperature electrolysis potential through the absorption of solar thermal energy. As one example, carbon dioxide is converted from its 0.03% concentration in air, directly to carbonate, which is reduced to form fuels at 50% solar energy conversion efficiency. The lithiated oxide/carbonate electrolyte spontaneously absorbs CO2. Carbonate is the reactant, which is renewed through CO2 absorption, and is efficiently reduced at high rate, low electrolysis potential, and high solar efficiency.