A Study Of Non-noble Anode Catalysts And Cell Stability Of Alkaline Polymer Electrolyte Water Electrolysis

Water electrolysis is an important technology for building a"hydrogen economy"and achieving"carbon peaking and carbon neutrality".Among them,alkaline water electrolysis（AWE）is the primary choice for industrial water electrolysis due to its mature technology and low cost.However,AWE requires using a high-concentration KOH solution,and it is difficult to produce H₂ with high purity and high output pressure.Benefiting from the needs of the application in the military industry,proton exchange membrane water electrolysis（PEMWE）has achieved rapid development in the past 70years.The membrane electrode assembly（MEA）structure allows PEMWE to break free from the reliance on liquid electrolytes and enables it to rapidly response to load changes in the renewable energy grid.However,the stronge acidic reaction environment of PEMWE results in a dependence on noble metal catalysts.Alkaline polymer electrolyte water electrolysis（APEWE）,which combines the advantages of PEMWE and AWE,has received extensive attention in recent years.The development of efficient non-noble anode catalysts is an important way to improve the energy conversion efficiency of APEWE.In the first three chapters of this work,a series of Ni-based catalysts were studied,including Ni@NC,NiFe-LDH/ATO,NiFeCo,etc.The study of Ni@NC catalysts revealed the electronic control mechanism of Co on Niand the electrochemical activation phenomenon of oxygen evolution reaction（OER）catalysts.It demonstrated that carbon-containing catalysts were not stable in the high-potential of OER.To avoid the decrease of catalyst utilization caused by the electrochemical corrosion of carbon supports,antimony tin oxide（ATO）,a more corrosion-resistant conductive oxide,was used as the catalyst support.Although the electrochemical activity of NiFe-LDH/ATO was lower than NiFe-LDH,the improvement in conductivity made NiFe-LDH/ATO better performance in pure water-fed APEWE.When NiFe was used as the anode catalyst,a current density of 2 A cm^-2was achieved at a cell voltage of 1.84 V and 1.71 V under pure water-fed and 1 M KOH-fed APEWE.Given that Co can enhance the intrinsic activity of Ni-based catalysts,a NiFeCo anode catalyst was synthesized,and the pure water-fed APEWE reached the near the-state-of-art performance of 3 A cm^-2@1.92 V.Based on the high-efficiency NiFeCo anode catalyst,electrochemical impedance spectroscopy（EIS）was used to investigate the properties of APEWE under the working conditions,and the EIS data was analyzed by the distribution of relaxation time（DRT）.The anode reaction resistance,cathode reaction resistance,and mass transfer resistance of APEWE were identified by EIS-DRT,which provided the case for the performance diagnosis and the stability research of APEWE.With the improvement of the properties of key materials such as APE and catalysts and the design optimization of the MEA,the performance of APEWE was improved,and comparable to PEMWE at high current densities.At present,stability is the main factor limiting the application of APEWE.It lacks research on the stability and the deactivation mechanism of APEWE.The last chapter of this work focused on the research of APEWE stability.We found that ionomer degradation,mass transfer resistance increase,and anode catalyst reconstruction were important reasons for the degradation of APEWE performance by combining in-situ EIS,offline XPS,SEM and ICP-MS,etc.Furthermore,we indicated that anode deactivation was the main cause of the degradation of APEWE performance.Based on these understandings,we optimized the anode catalytic layer ionomer content and the electrode preparation process.The pure water-fed APEWE was operated at 200 m A·cm^-2 for 190 h under the condition of pulsed intermittent electrolysis.Finally,this work tried to reveal the scientific nature of the phenomenon that the improvement of APEWE stability by the addition of electrolytes.The electrochemical behavior of the electrolyzer and the off-line test results was compared before and after the stability test when pure water and 10 m M KOH solution were used as the anolyte.We found that the reconstruction of the anode NiFeCo would lead to a decrease in the contact interface of the catalyst/ionomer,resulting in a decrease in the utilization of the catalyst and the deactivation of pure water-fed APEWE.The catalyst/solution interface formed by alkaline solution maintained the utilization of the catalyst after reconstruction,which was an important reason for the improved stability of APEWE.By adding a dilute alkaline solution（50 or 100 m M KOH）to maintain the utilization of the catalyst,the stability of 1000 h@200 m A cm^-2 was achieved,and there is no such long-stability data under this condition that has been reported in the literature.Moreover,we found that NiFeCo can maintain the initial morphology when using a buffer solution as an anolyte.This result indicated that the local p H drop at the anode reaction site under OER conditions may be the main reason for catalyst reconstruction.This work deepened the understanding of the APEWE inactivation process and indicated the important influence of the dimensional stability of the catalyst on the stability of pure water-fed APEWE.