Fabrication, Electrocatalytic Water Splitting, And Carbon Dioxide Reduction Of Nanoporous Electrodes

The energy crisis and global warming greenhouse effect are two major problems in our human society.Electrochemical conversion of H₂O and greenhouse gas CO₂ into H₂,CO,HCOOH and other molecules,and the energy is transferred to these clean,high energy density fuels to be stored for recycling.On the one hand,energy conversion can be realized to meet the growing demand for energy for human.On the other hand,realizing water cycle and carbon cycle through electrochemical method is of great significance for solving energy and environmental problems.However,the electrochemical conversion of H₂O and CO₂ to the available energy molecules is still many problems:（1）the high overpotential of the catalytic reaction makes the electrochemical reaction not easy to occur;（2）precious metal materials with high catalytic activity have high cost and poor stability,（3）the current utilization ratio is low with more side effects,and the electrocatalytic selectivity and efficiency of CO₂ is not high.The study shows that among the numerous catalysts,the earth-abundant porous materials based transition-metals have unique advantages in the field of electrocatalytic conversion.For electrolysis water,hydroxide and phosphide of transition metals（such as Cu,Fe,Ni）show a high activity and good stability;as to the electrochemical reduction of CO₂,transition-metal Sn-based materials show the advantages of high activity,high selectivity,and high conversion efficiency.In view of the above problems,this thesis is explored as follows:Here,we utilized copper weaving mesh to in-situ fabricate homologous integrated electrodes for high performance water splitting,including NiFe-LDH electrode for oxygen evolution reaction（OER）and Cu₃P nanoarrays electrode for hydrogen evolution reaction（HER）.Compared with the powder catalyst materials,the arrays catalysts prepared by metal weaving mesh have the advantages of large electrochemical surface area,fast bubble diffusion,favorable charge transfer and good conductivity.Electrochemical tests result showed that NiFe-LDH and Cu₃P have an onset potential of 1.52 and-0.2 V（vs.RHE）,a current density of 100mA cm^-2 under an overpotentials of 300 and 365 mV,respectively.Immediately,the assembled NiFe-LDH||Cu₃P electrolyser exhibits a small cell working voltage of 1.72 V under the current density of 10 mA cm^-2 in 1 M KOH,and a high Faraday efficiency（FE）¹00%.In addtion,nanoporous tin oxide（NP-SnO₂）with high porosity was uniformly grown on the tin substrate by anodic oxidation method and was applied for electroreduction CO₂ in 0.5M KHCO₃ electrolyte.The gas product（CO）and liquid product（HCOOH）were quantitatively analyzed by gas chromatography（GC）and nuclear magnetic resonance（NMR）,respectively.The results showed that NP-SnO₂/C has an onset potential of-0.6 V（vs.RHE）,and FE of products（HCOOH,CO）at-0.7,-0.8,0.9,-1.0,-1.1 and-1.2 V（vs RHE）is（55%,30%）,（73%,19%）,（76%,13%）,（56%,12%）,（50%,4%）and（42%,2%）,respectively.The highest carbon conversion rate was over 90%at-0.8 V,as well as very good catalytic stability for 180 min.