Jose A. Vega

Recent progress in the electrochemical conversion and utilization of CO2

Over the past several years, there has been a growing interest in the capture of carbon dioxide emissions and either their permanent immobilization or chemical conversion to industrially relevant products. Several processes have been developed and studied; however, many of these methods are quite expensive since they require either ultra high purity CO2 or are energy intensive. Also, many purely chemical methods show low product selectivity. To address these limitations, several researchers have initiated activities using electrochemical processes to increase reaction pathway selectivity and reduce cost since it allows for direct control of the surface free energy through the electrode potential, which has shown promise. This review article focuses on the advantages and disadvantages of current electrochemical, photoelectrochemical and bioelectrochemical processes for CO2 conversion, and future directions for research in this area are discussed.

Electrochemical comparison and deposition of lithium and potassium from phosphonium- and ammonium-tfsi ionic liquids

Two room-temperature ionic liquids, Bu 3 HexP + TFSI - [TFSI = bis(trifluoromethanesulfonyl)imide] and Bu 3 HexN + TFSI - , were synthesized and their electrochemical behavior was investigated using CV. The phosphonium-based ionic liquid (IL) showed improved stability and physical properties compared to the analogous ammonium-based IL. The phosphonium-based IL had higher conductivity (0.43 mS/cm) than the ammonium-based IL (0.28 mS/cm). The lower viscosity and higher stability of the phosphonium-based IL led to higher current density and stability for electrodeposited lithium metal. The addition of LiTFSI to both ILs led to a decrease in conductivity and increase in viscosity. An optimum deposition potential was found that was bounded by the electrochemical stability of each IL. The stability of lithium in the ILs increased at lower temperature due to slower reactivity with the IL. The electrodeposition and reoxidation of potassium was also demonstrated. It was found that a lithium-potassium alloy could be deposited at high current for long times without the occurrence of dendrites.

Hydrogen and Methanol Oxidation Reaction in Hydroxide and Carbonate Alkaline Media

The oxidation of hydrogen and methanol by hydroxide and carbonate anions in low temperature alkaline electrolytes was investigated on a polycrystalline platinum rotating disk electrode. The electron equivalence was experimentally determined as 2.0 and 1.9 for oxidation of hydrogen with hydroxide and carbonate anions, respectively. The exchange current density for hydrogen oxidation was measured as 0.14 mA cm−2 by hydroxide (1 M KOH), while in carbonate electrolytes, the exchange current density was 0.24 mA cm−2 (0.3 M CO3 −2) and 0.32 mA cm−2 (0.5 M CO3 −2). The increased exchange current density through the carbonate pathway was attributed to the ease of bond reorganization between hydrogen and carbonate compared to hydrogen and hydroxide, which results in a more thermodynamically favored process. Also, a more complete methanol oxidation was observed in the presence of hydroxide, though the difference compared to carbonate was not significant.