Reaction Kinetics of CO2 Carbonation with Mg-Rich Minerals

Substrate Effect of Platinum-Decorated Carbon on Enhanced Hydrogen Oxidation in PEMFC

Environmentally sustainable fuel cells with high efficiency have attracted much attention as a promising approach to resolving future energy problems. However, some obstacles must be overcome, such as corrosion, water control, and long-term degradation. Herein, we investigated the improved electrochemical performance and hydrogen oxidation reaction (HOR) mechanism of platinum loaded on carbon nanotube (Pt/CNT) catalyst by conducting experimental and theoretical studies. The Pt/CNT catalyst had a larger active area than the Pt/C (platinum loaded on carbon black) catalyst and also exhibited improved performance due to its long-term stability. In addition, the charge-transfer resistance of Pt/CNT (61.2 Ω cm2) is much smaller than that of Pt/C (90.2 Ω cm2), indicating that the CNT support offers good electron transfer. To further understand the hydrogen dissociation mechanisms of Pt/CNT and Pt/C, we investigated the adsorption characteristics and electron transfer of the catalysts with optimized geometry using the density functional theory (DFT). Pt/CNT exhibited higher adsorption energy and electron transfer than Pt/C, which leads to improved HOR. The integrated experimental and theoretical study conducted here suggests that Pt/CNT is a promising candidate for maintaining the performance of cathode catalysts in the polymer electrolyte membrane fuel cell.

Carbon dioxide mineralization process design and evaluation: concepts, case studies, and considerations

Numerous carbon dioxide mineralization (CM) processes have been proposed to overcome the slow rate of natural weathering of silicate minerals. Ten of these proposals are mentioned in this article. The proposals are described in terms of the four major areas relating to CM process design: pre-treatment, purification, carbonation, and reagent recycling operations. Any known specifics based on probable or representative operating and reaction conditions are listed, and basic analysis of the strengths and shortcomings associated with the individual process designs are given in this article. The processes typically employ physical or chemical pseudo-catalytic methods to enhance the rate of carbon dioxide mineralization; however, both methods have its own associated advantages and problems. To examine the feasibility of a CM process, three key aspects should be included in the evaluation criteria: energy use, operational considerations as well as product value and economics. Recommendations regarding the optimal level of emphasis and implementation of measures to control these aspects are given, and these will depend very much on the desired process objectives. Ultimately, a mix-and-match approach to process design might be required to provide viable and economic proposals for CM processes.

Optimized carbonation of magnesium silicate mineral for CO2 storage

The global ambition of reducing the carbon dioxide emission makes sequestration reactions attractive as an option of storing CO2. One promising environmentally benign technology is based on forming thermodynamically stable carbonated minerals, with the drawback that these reactions usually have low conversion rates. In this work, the carbonation reaction of Mg rich olivine, Mg2SiO4, under supercritical conditions has been studied. The reaction produces MgCO3 at elevated temperature and pressure, with the addition of NaHCO3 and NaCl to improve the reaction rates. A sequestration rate of 70% was achieved within 2 h, using olivine particles of sub-10 μm, whereas 100% conversion was achieved in 4 h. This is one of the fastest complete conversions for this reaction reported to date. The CO2 sequestration rate is found to be highly dependent on the applied temperature and pressure, as well as the addition of NaHCO3. In contrast, adding NaCl was found to have limited effect on the reaction rate. The roles of NaHCO3 and NaCl as catalysts are discussed and especially how their effect changes with increased olivine particle size. The products have been characterized by Rietveld refinement of powder X-ray diffraction, scanning electron microscopy (SEM), and energy-dispersive X-ray (EDX) spectroscopy revealing the formation of amorphous silica and micrometer-sized magnesium carbonate crystals.