Study On Promoting Oxygen Reduction To Hydrogen Peroxide By Fabricating Hierarchical Pores Electrode

The construction of hierarchical pores structure is beneficial to the mass transfer and electrocatalytic reaction of gas diffusion electrode.In this paper,the cheap and easily available carbon black and graphite are mixed with the common binder PTFE emulsion and the pore-forming agent,and a non-metal carbon base gas diffusion electrode with hierarchical pores structure is prepared,in which the diffusion layer and the reaction layer are combined.The electrode is used for electrocatalytic reduction of O₂ to H₂O₂.Structural characterizations find that PTFE is not only a binder,but also works with pore-forming agents to change the original pore size distribution of carbon materials,increase the number of 20-80nm pores,and form a large number of micron-level pores.An efficient gas transmission and dispersion network system has been formed,and it is conducive to the migration and enrichment of the product H₂O₂.Characterizations also find that PTFE forms a polymer phase of 30nm-1?m in the electrode,and the dispersed polymer phase increases the affinity of the catalyst surface for O₂.Our research shows that after adding PTFE,pore-forming agent and simple processing,the binary phase region and hierarchical pores structure of carbon materials and polymers can be formed at the mesoscopic scale.It has a synergistic effect under electrocatalysis and increases the electrochemically active surface area of the catalyst.While improving O₂ utilization rate,it inhibits the production of by-product H₂.As a result,it exhibits excellent H₂O₂ generation capability on a macro level.Under the self-made H-type H₂O₂ test device and optimized conditions,the electrode prepared at dry weight ratio carbon black:graphite:binder:pore-forming agent=3:3:3:1,pressing pressure 6MPa,calcination temperature 330?has the best performance.The prepared electrode is used for the preparation of H₂O₂.When using Nafion117 proton exchange membrane,a platinum electrode as anode,current density150m A·cm^-2,flow rate of O₂ 30ml·min^-1,the electrolyte solution 0.5mol·L^-1 Na₂SO₄,and p H=1.0,the H₂O₂ generation rate can reach 2.50mmol·cm^-2·h^-1.Faraday efficiency is 79.00%.H₂O₂ concentration can reach 3.25mol·L^-1,that is,mass fraction is about 11.00wt%.We also reasonably simplify and derive the electrode process.The reaction and mass transfer model of the three-phase interface at high current density and the polarization curve equation based on the Bullter-Volmer are established,and the main factors affecting the electrode polarization at different current densities are simulated.It is found that there is an electrochemical polarization process and ohmic polarization caused by the liquid phase resistance in the electrode reaction layer.At the same time,ohmic polarization caused by the resistance of the bulk electrolyte solution consumes more electrical energy.The industrialization process needs to reduce the energy consumption of this part in order to improve economy.Under the premise of stable electrode structure and certain experimental conditions,the decomposition rate of H₂O₂ will increase to be equal to the net generation rate of H₂O₂.At this time,the cumulative concentration of H₂O₂ is not increasing,and the maximum cumulative concentration of H₂O₂ appears,[H₂O₂]_max?136.88p_O2^0.75.It shows that the maximum cumulative concentration of H₂O₂ is controlled by the O₂ delivery volume.This conclusion has guiding significance for engineering applications.