Huayi Yin

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.

Verification and implications of the dissolution–electrodeposition process during the electro-reduction of solid silica in molten CaCl2

With the verification of the existence of the dissolution-electrodeposition mechanism during the electro-reduction of solid silica in molten CaCl2, the present study not only provides direct scientific support for the controllable electrolytic extraction of nanostructured silicon in molten salts but it also opens an avenue to a continuous silicon extraction process via the electro-deposition of dissolved silicates in molten CaCl2. In addition, the present study increases the general understanding of the versatile material extraction route via the electro-deoxidization process of solid oxides in molten salts, which also provokes reconsiderations on the electrochemistry of insulating compounds.

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 .

Preparation of a porous nanostructured germanium from GeO2via a “reduction–alloying–dealloying” approach

We present here a controllable and affordable preparation of porous nanostructured germaniums with interesting photo-responsive properties from GeO2 powder through an electrochemical reduction–alloying process in molten salt (reduction and alloying) and post zero-energy-consumption water etching (dealloying).

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.

Ionic liquids assisted formation of an oil/water emulsion stabilised by a carbon nanotube/ionic liquid composite layer

Assisted by ionic liquids, a facile way of preparing size controllable emulsions stabilised by a CNT/IL composite has been demonstrated. The functionally and structurally tunable CNT/IL composite layer will potentially enhance the application of emulsion in template synthesis, biphase catalysis and interface electron/charge transfer.

One-step molten salt carbonization (MSC) of firwood biomass for capacitive carbon

Capacitive carbons are prepared by a molten salt carbonization (MSC) process from Chinese firwood biomass, and the effect of the biomass size (lengths ranging from 0.09 to 2 cm) on the carbon yield and the electrochemical capacitive performance of the carbonized samples is investigated. The mechanism of carbon treatment and structure–activity correlations are discussed. Compared with carbon prepared without the assistance of MS, MSC-derived carbon prepared from the same precursor size (i.e. 0.09 cm) shows a higher specific capacitance (189 vs. 165 F g−1 at 0.2 A g−1) and enhanced high-rate capability (85% vs. 70% capacitance retention upon increasing the charge–discharge current density from 0.2 to 2.0 A g−1). Upon decreasing the precursor size from 2.0 to 0.09 cm, the specific capacitance increases from 142 to 189 F g−1, with the high-rate capacitance retention increasing from 70% to 85%. These improvements highlight the merits of the MSC method and engineering the precursor sizes for the preparation and modification of enhanced capacitive carbon, which is promising for practical applications. It is also found that the production yield of the MSC method decreases upon decreasing the precursor size. Therefore, the precursor size should be prudently tailored to ensure a balance between the capacitive properties and production yield.