Fabrication Of Co-Based Nano Materials And Their Electrocatalytic Activity In Water Oxidation

Water splitting is considered a perfect reaction for the production of hydrogen chemical fuels.Water splitting is hindered by the oxygen evolution reaction（OER）due to the complex four-electron transfer process,which results in a large overpotential for power-driven water splitting.Consequently,it is necessary to use catalysts to reduce the reaction energy consumption and overpotential of the OER process.Traditional noble metal-oxide catalysts,such as IrO₂ and RuO₂,are not suitable for large-scale applications because of their high cost and low earth abundance.Development of high efficiency and low cost electrocatalysts is significant for developing sustainable energy system,and transition metal compounds meet this requirement.In this paper,the main research objects were cobalt-based hydroxides and oxides.We focused on exploring the methods to enhance OER activity of the materials.The preparation strategy,characterization and catalytic acticity of the as-prepared Co-based materials were discussed and analyzed.The research contents of this paper are as follows:（1）Facile and novel strategy to fabricate 2Dα-Co（OH）₂ nanosheets for efficient oxygen evolution reaction application:2D ultrathinα-Co（OH）₂ nanosheets with a large surface area of 237.7 m²/g were synthesized via a reduction-oxidation strategy.The thickness of the 2D nanosheets is about 2 nm and the transverse dimension is about several microns.The as-preparedα-Co（OH）₂ nanosheets showed an overpotential as low as 278 m V at the current density of 10 m A/cm².This is related to the larger specific surface area of the material,which provides more active sites for electrocatalytic reaction.（2）Composition controllable fabrication of ultrathin 2D CoMn-LDHs for highly efficient electrocatalytic oxygen evolution:The 2D CoMn-LDHs were prepared by the reduction-oxidation method.CoMn-LDHs with different components can be prepared by adjusting the proportion of Co/Mn elements.The electrochemical test results indicated that the OER activity of CoMn-LDHs was highly dependent on the content of Mn.The Co₈Mn₂-LDH showed the highest OER activity among all the samples.（3）Remarkably improved oxygen evolution reaction activity of cobalt oxides by an Fe ion solution immersion process:The Co₃O₄ and CoO nanoparticles were obtained by calcining theα-Co（OH）₂ nanoflowers.And the Fe-Co₃O₄ and Fe-CoO were obtained after soaking with Fe SO₄ solution.The OER activity of cobalt oxides was significantly increased after Fe ion treatment,and the Fe-Co₃O₄ and Fe-CoO showed the overpotentials of only 280 m V and 296 m V respectively,which were much lower than those of Co₃O₄ and CoO.Not only that,the OER activity of Fe-Co₃O₄ and Fe-CoO was also higher than that of RuO₂.In addition,the OER activity of the Fe ion-treated cobalt oxides was increased slightly after 1000 CV scans,which is due to Fe ion escaping from the crystal lattice,forming an amorphous layer on the surface of the material.In addition,the DFT calculation results indicated that the theoretical overpotentials of Co₃O₄,Fe-Co₃O₄,CoO and Fe-CoO were 0.45 V、0.37 V、0.68 V and 0.63 V respectively,which were highly consistent with the experimental results.（4）Pulsed laser deposited Cr-doped CoFe₂O₄ thin film as highly efficient oxygen evolution reaction electrode.Squama-like Cr-doped CoFe₂O₄ thin film electrode was deposited on Ni foam substrate by pulsed laser deposition.By comparing the OER activity of the Cr-doped CoFe₂O₄ and undoped CoFe₂O₄ thin film electrode,it was found that the Cr doping led to the electrode highly effective for OER.The OER performance analysis of the corresponding powder materials showed that the powder catalyst was inferior to the thin film electrode.This proves that the thin film electrode has more advantages in electrocatalysis.