Study On Hydrogen Evolution Reaction Performance Of Composite Based On Cobalt And Nickel In Seawater Electrolysis

Hydrogen production from water electrolysis is not only an industrialized hydrogen production technology,but also an important and potential technical for the production of"green hydrogen"in the future.However,the hydrogen production process though water electrolysis is an electrocatalytic reaction process with high energy consumption,and the efficiency of water electrolysis is not high enough today.It is an urgent requirement for the basic research of electrochemistry and electrocatalysis materials to develop novel catalyst for hydrogen evolution reaction（HER）with improving the efficiency and keeping the cost down.In addition,most of electrolyte in current studies is used in alkaline solution based on fresh water.However,seawater,as the most abundant water resource on earth,has potentially harmful to HER.So,important directions of basic research to study the electrocatalysts’characteristics of HER in seawater and explore how to overcome the shortcomings of seawater electrolyte have been developed.In this regard,this paper mainly carried out the preparation of Co and Ni-based electrocatalytic hydrogen evolution materials,and discussed their performance in various electrolytes using electrochemical technology and theory.The main contents include:（1）Based on the electrochemical HER kinetics theory,the equivalent circuit model（ECM）of the HER process was reviewed and simplified appropriately to form a simpler ECM as R_s（C_aR_f）,and the circuit analysis was carried out.The current-voltage polarization curves are firstly simulated on the assumption that all electrical components are unchanged under linear voltage excitation.Then,the Kalman filter（KF）algorithm was used to solve the electrical component values from the polarization curve,which proved the algorithm’s ability to solve the ECM.Furthermore,the current-voltage polarization curve under electrochemical polarization is simulated,and the values of this time-varying ECM electrical component are solved by using the KF algorithm and the extended Kalman filter（EKF）algorithm.The results of this study show that the KF or EKF algorithm can be used to solve the ECM electrical components of the simple HER process,which provides a methodological basis for the actual polarization curve solution in the follow-up research.（2）Dissolve inorganic cobalt/nickel salt in the melamine resin prepolymer to form a homogeneous liquid following polymerization to form organic-inorganic polymeric material.The complex polymer was used as a precursor to obtain nitrogen-doped carbon-supported cobalt phosphide/nickel（Co_xP_y/Ni_xP_y-NPC）with uniform composition and structure after calcination following gas-solid reaction in phosphorus vapor.The material conversion process was studied using X-ray powder diffraction（XRD）technology,and it was confirmed that these processes underwent several main reactions,including inorganic decomposition,in-situ reduction to metal element,and phosphating.Scanning electron microscopy（SEM）and X-ray photoelectron spectroscopy（XPS）revealed the structure and composition of the material in more details.Using Co_xP_y/Ni_xP_y-NPC as HER catalyst in 1.0 M KOH solution,alkaline seawater and natural seawater,the overpotentials(η₁₀)at 10 m A?cm^-2 current density were obtained as 138 m V,222 m V and 490 m V,respectively.It shows that seawater has negative influence on HER process.Co_xP_y/Ni_xP_y-NPC exhibits good long-cycle HER stability in both KOH and seawater electrolytes.The study also shows that the HER performance of the Co-Ni hybrid material is better than that of Co or Ni alone,indicating the interpromotion between heterogeneous metals.（3）BN-doped carbon support（BN-C）was prepared by using waste tires as carbon source and calcining with B（OH）₃.Co P composites（Co P/BN-C）were prepared by loading Co salt on this carrier and phosphating.The composition of the composites was proved by XRD,XPS and EDS.The material exhibitsη₁₀ of 154 m V and 545 m V for hydrogen evolution in 1.0 M KOH and seawater,respectively.Based on this test data,KF algorithm was used to solve the ECM for the polarization curves of Pt/C and Co P/BN-C.The results show that the Faradaic process resistance（R_f）of Co P/BN-C is significantly higher than that of Pt/C,and R_f in seawater is higher than that in KOH.By analyzing the power of R_f,it is found that when the external input power is 0.5 m W,the current density of Co P/BN-C in KOH is 4.4 times that of its corresponding value in seawater,and maintain the trend of expansion at high current density.Pt/C also showed similar phenomenon.This results show that the decline of the hydrogen evolution electrolysis efficiency in seawater cannot be ignored.（4）La was used as an auxiliary agent to improve the HER catalytic activity of Ni-based catalysts.Ni-La-Ni N/CNT was prepared by carbon nanotubes loading with La doping and reduction of nickel salts in ammonia gas.Characterization analysis shows that the loaded components contain La₂O₃,Ni N and Ni.The presence of La₂O₃ improve the dispersion of Ni,and existence of Ni N improve the HER activity of Ni.Theη₁₀ of Ni-La-Ni N/CNT in 1.0 M KOH is 157 m V,which is significantly higher than that of the control sample of Ni-Ni N/CNT without La addition(η₁₀=292 m V).Subsequently,the HER performance of the material was tested in various electrolytes including PBS buffer,Na Cl-added alkaline solution,alkaline seawater and seawater,and the exchange current density（j°）value was fitted by the electrode process kinetic equation.It shows that the saline concentration and p H value have a great influence on the HER activity.The j°value of Ni-La-Ni N/CNT in alkaline seawater(2.188×10^-4 A?cm^-2)is close to that in 1.0 M KOH(2.420×10^-4 A?cm^-2).This phenomenon shows that adding alkali into seawater is indeed an effective method to improve catalytic activity.The R_f solved by EKF algorithm and its power analysis also proved that the energy consumption of Ni-La-Ni N/CNT in alkaline seawater is closest to its energy consumption in KOH.（5）The Ni salt was modified with Zr as the auxiliary agent and supported on the carbon nanotube carrier,and then reduced with ammonia gas to obtain the Zr-Ni/CNT composite material.XRD and other analysis show that Zr-Ni/CNT is a catalytic material mainly composed of Ni and Zr O₂.Theη₁₀ of Zr-Ni/CNT in 1.0 M KOH is 169m V for HER,and theη₁₀ for oxygen evolution reaction（OER）is 249 m.The addition of Zr has a great effect on improving the overpotential of HER and OER,and the C_dland R_ct values change coincided.Zr-Ni/CNT maintained good performance in the stability test for more than 10 h.