Design And Construction Of Nickel Cobalt Based Integrated Electrode And The Application In Seawater Electrolysis

Due to its advantages of high energy density and carbon-free emission,H₂ is considered as one of the most promising alternative to fossil fuels.Compared with traditional industrial hydrocarbon steam reforming methods,water electrolysis is an efficient and clean method for H₂ produce.To date,most water electrolysis systems have used pure water as electrolyte.With the increasing scarcity of pure water,electrolysis of seawater to produce H₂ has a more promising development prospect.Due to the presence of Cl^-in seawater,high voltage can lead to serious chloride oxidation reactions（the voltage difference between alkaline seawater chloride oxidation reaction and OER is 480 m V）and electrode corrosion reaction.In the face of the high energy consumption problem of seawater electrolysis,the development of efficient,economical,and stable electrocatalysts for hydrogen evolution reaction（HER）and oxygen evolution reaction（OER）is the primary task.In the past decade,the catalytic activity of electrocatalysts has even exceeded the most advanced commercial Pt/C and Ru O₂ electrodes.However,what needs to be urgently addressed is the serious side reactions and high energy consumption.Therefore,this thesis takes the nickel-cobalt based integrated electrodes as examples to inhibit the occurrence of chlorine oxidation reactions by improving the activity of catalysts for OER and HER.At the same time,multi-level structure is constructed on the electrode to adapt to the catalytic reaction under high current density,facing the process of industrial seawater electrolysis.The main research contents are as follows:（1）Hydrazine oxidation assisting seawater splitting is a promising strategy to achieve chlorine-free energy-saving hydrogen production.Herein,Fe-doped Ni₂P/Co P encapsulated by ultrathin nitrogen-doped carbon layers（Fe Co Ni P@NC）with unique nanosheet structure grown on Ni foam are synthesized,which was used as highly efficient and durable bifunctional catalyst for both hydrazine oxidation reaction（Hz OR）and hydrogen evolution reaction（HER）.For the two-electrode system toward overall hydrazine splitting（OHz S）in alkaline seawater,Fe Co Ni P@NC reveals a low cell voltage of 0.56 V at 1000 m A cm^-2,stable operation for 100 h to keep～500 m A cm^-2,and nearly 100%Faraday efficiency.Compared to the N₂H₄-free seawater system,the OHz S system can save 4.03 k Wh for producing 1.0 m³ of H₂,realizing energy-saving H₂ production.（2）Under the condition of industrial ampere-level current density seawater splitting,the electrocatalyst for hydrogen production needs two characteristics of superb activity and long-term durability.In this work,P vacancies enriched Co_xP_v@NC with unique multilevel structure was synthesized and applied to ampere-level current density for seawater splitting process.The coupled Co_xP_v@NC seawater electrolyzer requires low voltages of 1.88 and 1.74 V to provide 1.0 A cm^-2in 1.0 M KOH seawater solution at room temperature and 6.0 M KOH seawater solution at 60 ^oC,respectively,exhibiting no obvious decline over 100 h test at 1.0 A cm^-2.In-situ Raman spectra and density functional theory（DFT）calculations uncover that the outstanding catalytic performance originates from the P vacancy induced optimization of intermediate adsorption energy for HER and rapid reconstruction of active species for OER.The electrocatalyst devised in this work supplies an effective way to settle the insufficient of ampere-level current-density-tolerant bifunctional electrocatalysts in industrial seawater splitting.（3）Recently,hydrogen spillover based binary（HSBB）catalysts have received widespread attention due to the sufficiently utilized reaction sites.However,the specific regulation mechanism of spillover intensity is still unclear.At the same time,the mechanism of hydrogen spillover in seawater electrolyte is unknown.Herein,we have fabricated oxygen vacancies enriched Ru/Ni Mo O_4-x to investigate the internal relationship between electron supply and mechanism of hydrogen spillover enhancement.Experiment results shown that a large number of ions in seawater can promote the hydrogen adsorption step in the hydrogen spillover process.The DFT calculations cooperates with in-situ Raman spectrum to uncover that the H*spillover from Ni Mo O_4-x to Ru.Meanwhile,oxygen vacancies weakened the electron supply from Ru to Ni Mo O_4-x,which contributes to dilute the resistance of built-in electric field（BEF）for hydrogen spillover.Benefiting from the unique catalytic mechanism,the Ru/Ni Mo O_4-x exhibits a low overpotential of 206 m V at3.0 A cm^-2,a small Tafel slope of 28.8 m V dec^-1,and an excellent durability of 110 h at the current density of 1.5 A cm^-2 for HER.