Diyong Tang

Capture and electrochemical conversion of CO2 to value-added carbon and oxygen by molten salt electrolysis

A molten salt electrochemical system comprising a eutectic mixture of Li–Na–K carbonates, a Ni cathode, and a SnO2 inert anode is proposed for the capture and electrochemical conversion of CO2. It is demonstrated that CO2 can be effectively captured by molten carbonates, and subsequently electrochemically split into amorphous carbon on the cathode, and oxygen gas at the anode. The carbon materials generated at the cathode exhibit high BET surface areas of more than 400 m2 g−1 and as such, represent value-added products for a variety of applications such as energy storage and pollutant adsorption. In the carbonate eutectic (500 °C), the presence of Li2CO3 is shown to be required for the deposition of carbon from the melt, wherein O2− or Li2O serves as the intermediate for CO2 capture and electrochemical conversion. SnO2 proved to be an effective anode for the electrochemical evolution of oxygen. Electrochemical reactions were found to proceed at relatively high current efficiencies, even though the current densities exceed 50 mA cm−2. The intrinsic nature of alkaline oxides for CO2 capture, the conversion of CO2 to value-added products, and the ability to drive the process with renewable energy sources such as solar power, enables the technology to be engineered for high flux capture and utilization of CO2.

Harvesting capacitive carbon by carbonization of waste biomass in molten salts.

Conversion of waste biomass to value-added carbon is an environmentally benign utilization of waste biomass to reduce greenhouse gas emissions and air pollution caused by open burning. In this study, various waste biomasses are converted to capacitive carbon by a single-step molten salt carbonization (MSC) process. The as-prepared carbon materials are amorphous with oxygen-containing functional groups on the surface. For the same type of waste biomass, the carbon materials obtained in Na2CO3-K2CO3 melt have the highest Brunauer-Emmett-Teller (BET) surface area and specific capacitance. The carbon yield decreases with increasing reaction temperature, while the surface area increases with increasing carbonization temperature. A working temperature above 700 °C is required for producing capacitive carbon. The good dissolving ability of alkaline carbonate molten decreases the yield of carbon from waste biomasses, but helps to produce high surface area carbon. The specific capacitance data confirm that Na2CO3-K2CO3 melt is the best for producing capacitive carbon. The specific capacitance of carbon derived from peanut shell is as high as 160 F g(-1) and 40 μF cm(-2), and retains 95% after 10,000 cycles at a rate of 1 A g(-1). MSC offers a simple and environmentally sound way for transforming waste biomass to highly capacitive carbon as well as an effective carbon sequestration method.

Preparation of CeNi2 intermetallic compound by direct electroreduction of solid CeO2-2NiO in molten LiCl

Abstract Electrochemical reduction of solid CeO 2 -2NiO to produce CeNi 2 was conducted in molten LiCl at 650 °C. The electrochemical reduction behaviors of NiO, CeO 2 and their mixture were investigated by cyclic voltammetric measurements. Moreover, a series of electrolysis experiments of different electrolysis cell voltages and electrolysis duration were performed to evaluate the reduction mechanism of the mixed oxides pellet cathode as well as the energy efficiency of the process. Homogeneous CeNi 2 was prepared by electrolysis at the constant cell voltage of 3.5 V with a graphite anode. The results demonstrated that the NiO was preferentially reduced to Ni and it subsequently promoted the reduction of CeO 2 . The electrolysis energy consumption for preparation of the CeNi 2 could be as low as 6.5 kWh/kg-CeNi 2 .

Electrolytic calcium hexaboride for high capacity anode of aqueous primary batteries

The use of lightweight elements/compounds and the employment of multi-electron reaction (MER) chemistry are two approaches used to develope high energy density materials for batteries. In this work, nanoscaled calcium hexaboride (CaB6) was prepared in one-step by the electro-reduction of solid calcium borate (CaB2O4) in molten CaCl2–NaCl. CaB2O4 was synthesized by a simple co-precipitation method. It was revealed that the electrolytic CaB6 delivers a specific capacity of 2400 mA h g−1 in 30% KOH solution though a multi-electron reaction mechanism. Its practical gravimetric energy is three times that of Zn. Decrease of particle size substantially improves both the electrochemical activity and discharge capacity of CaB6. The electrolysis of CaB2O4 in molten salt provides a straightforward and sustainable way to prepare high-capacity CaB6 using low-cost and environmentally friendly boron and calcium resources, which can be recycled from the used CaB6 primary batteries.

Coating titanium on carbon steel by in-situ electrochemical reduction of solid TiO2 layer

Abstract Ti coating on A3 steel was successfully prepared by direct electrochemical reduction of high-velocity oxy-fuel (HVOF) thermally sprayed and room-temperature dip-coating titanium dioxide coating on A3 steel in molten CaCl 2 at 850 °C. The interfacial microstructure and mutual diffusion between coating and steel substrate were investigated using scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) spectroscopy. The results show that the precursory TiO 2 coating prepared by HVOF has closer contact and better adhesion with the A3 steel substrate. After electrolysis, all of the electro-generated Ti coatings show intact contact with the substrates, regardless of the original contact situation between TiO 2 layer and the steel substrate in the precursors. The inter-diffusion between the iron substrate and the reduced titanium takes place at the interface. The results demonstrate the possibility of the surface electrochemical metallurgy (SECM) is a promising surface engineering and additive manufacturing method.