| Electrolysis of sodium carbonate plays an important role in the process of producing alumina by alkaline digestion-carbonation precipitation and desorption of CO2. Compared with electrolysis of H2O, not only H2 and O2 were produced, but also could obtain NaHCO3 and NaOH at the anode and cathode, respectively. Wherein CO2 can be used in digestion-carbonation process to prepare aluminum hydroxide or separate out high concentration CO2, and NaOH can be used for the dissolution of bauxite and capture the low concentration CO2. Moreover, H2 will also play important role in the future hydrogen era. However, compared with strong alkaline solution, it usually requires a higher oxygen evolution reaction (OER) potential in sodium carbonate solution due to the slow kinetics of OER, thus increasing the energy consumption. Therefore, it is very important to design and fabricate a high active OER anode and reduce the energy consumption of sodium carbonate electrolysis. In this thesis, Ni-Fe composite hydroxide nanosheets with high OER activity were prepared by in-situ precipitation method and electrodeposition method on conductive carbon and nickel foam substrates and applied in electrolysis of sodium carbonate.Firstly, NiFe(OH)x/C/Nifoam were prepared by in-situ precipitation method and the OER performance was studied in 1 M KOH solution. We mainly studied the effect of the proportion of nickel metal precursor salt, calcination temperature and metal loadings on OER performance. The results show that the electrode with the salt proportion of 5:3, the calcination temperature of 150? and metal salt and carbon mass ratio of 7:5 exhibits superb OER performance.Additionly, we fabricated ultrathin NiFe(OH)x on high conductivity nickel foam substrate (NiFe(OH)x/NifOam) electrocatalyst by fast electrodeposition method and investigated the impact of electrodeposition parameters such as current density, electrodeposition time and electricity quantity in sulfate solution and the electrodeposition solution such as pH and anions (nitrate, chloride) of the solution on the performance of NiFe(OH)x/Nifoam for OER. The results show that, NiFe(OH)x/Nifoam prepared in sulfate solution with pH value of 4 and electrodeposited under current density of 200 mA cm-2 for 360 s have optimum performance for OER. SEM results show multicellular nanoflowers structure assembled by ultra NiFe(OH)x nanosheet (2-4 nm) are formed on the surface of nickel foam which not only greatly increases the amount of active sites for OER but also are beneficial to the evolution of oxygen. In 0.5 M Na2CO3/NaHCO3 solution, the OER potential with NiFe(OH)x/Nifoam electrode significantly reduces 290 mV as compared with commercial RuO2/Ti electrode at operating current density of 100 mA cm-2. In 1 M NaOH solution, Tafel slope of NiFe(OH)x/Nifoam electrode is only 28 mV dec-1, and only need an overpential of 254 mV to deliver the operating current density of 10 mA cm-2 which is comparable to the best results reported in the literature. NiFe(OH)x/Nifoam electrode electrodeposited under 200 mA cm-2 for 60 s in chloride solution exhibits the best performance for OER, which is comparable to the NiFe(OH)x/Nifoam electrodeposited in sulfate solution.Finally, the above NiFe(OH)x/Nifoam electrode is used as an OER anode in the electrolysis of sodium carbonate, which significantly reduces the cell voltage and saves the energy consumption. In the electrolysis of 1.5 M Na2CO3 solution, the cell voltage with NiFe(OH)x/Nifoam anode is reduced by 230 mV as compared with the commercial RuO2/Ti anode. In the electrolysis of 0.75 M Na2CO3/NaHCO3 solution, the cell voltage of electrolysis with NiFe(OH)x/Nifoam anode is 2.52V,280 mV lower than that with commercial RuO2/Ti anode. The acid-base titration average analysis results indicate thatthe anodic acidification efficiency and cathodic alkalization efficiency of electrolysis with NiFe(OH)x/Nifoam anode are 93.6% and 87.8%, respectively. |
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