Studies On Applied Technologies Of The Proton Exchange Membrane Water Electrolysis

The development of society bears a huge consumption of energy.However,the issue of the daily-shorted fossil resource and greenhouse effect forces us to seek the clean and renewable green energy,such as hydrogen energy.Compared with the traditional alkaline electrolysis water and solid oxide electrolysis water technologies,proton exchange membrane(PEM)electrolysis water technology has been widely concerned for the advantages of the low energy consumption,high safety and high purity of gas production.While the disadvantages are also obvious,the high cost and the instability related to ion contamination.So,it is urgent to reduce the cost of PEM water electrolysis,as well as understand the influence of impurity ions on the electrolyzer and put forward effective countermeasures.For this purpose,some technical researches on PEM water electrolysis have been carried out.The main contents and results are as follows:1?It is the first time that powdered fluorinated acetylene black(CFx)is adopted to replace with polytetrafluoroethylene(PTFE),a typical hydrophobic component of the first generation of gas diffusion electrode,and prepare the hydrogen evolution electrode by the ink electrode preparation method.CFx electrode shows a better electrochemical performance at low temperature and high current density with the same Pt loading,comparing with the PTFE electrode,which is fabricated by the spraying method.The results indicate the surface of CFx electrode is more smooth to build a more connective proton transfer passage with the membrane.The pore analysis shows that the particles in CFx electrode stack more regularly,providing a larger pore area in the catalytic layer,which means CFx electrodes have more reaction sites.The electrochemical surface area test also confirms.The performance of CFx electrode with different ratio and different thickness of catalyst layer is also different.When the thickness of catalyst layer is thin and the content of CFx is high,the three-phase structure of electrode is more effective,which can reduce the Pt load to0.03mg/cm².2?Commercial WC is directly used as non-precious hydrogen evolution catalyst.The results show that the small-sized WC is not stable.And the performance differs greatly during the operation and an interrupted electrolysis.Compared with Pt electrode,the performance of WC electrode is greatly affected by the operation parameters and an interrupted electrolysis,and it is more competitive when running at low temperature and high current.However,it also suffers a unrecoverable performance if the electrolyzer goes through a long-time interrupted operation,which related to the easily-oxidized WC.Due to the oxidization,the proportion of catalytic carbon carbide on the surface decreases seriously.Luckily,this problem can be effectively and economically solved by the measurement of a timely water seal water in the cathode chamber.Loading nanosized WC on fluorinated acetylene black can significantly improve the stability of the WC catalyst.This method of improving the stability of the catalyst by changing the chemical environment of the catalyst may provide a practical and significance solution for expanding the application range of non-precious metal catalysts.3?The impurity ion poisoning mechanism and solution of PEM water electrolyzer have been systematically studied,and the poisoning mechanism of Na⁺,Ca²⁺,Fe³⁺and Ti⁴⁺has been investigated with emphasis.The results show that for Na⁺poisoning,which does not create a cover and has a weak affinity with Nafion,even1000ppm Na⁺contamination can be removed or controlled by maintaining the cathode p H at 1;For Ca²⁺and Ti⁴⁺impurities,which can generate oxide coverings and have a strong affinity with Nafion,it is difficult to remove high-concentration ion poisoning in the same way,because the dissociation of impurity ions and Nafion requires a higher concentration of protons at the cathode.So the oxide formed in the water electrolyzer will cause the electronic impedance to increase significantly.Fe³⁺contamination is not serious.This is because a certain amount of protons are generated by the Fe³⁺hydrolysis,no under-potential deposition will occur on the cathode side,neither the insoluble coverings,so the influence of Fe³⁺poisoning is weakened.The mechanism of acid treatment to restore the influence of impurity ions can be described as:when the electrolyzer is contaminated by impurity ions,the higher affinity of the impurity ions and the membrane causes the proton transfer to be blocked and the cell pressure rises.Providing sufficient protons outside the membrane can promote the impurity Nafion dissociates and releases the occupied proton sites,which in turn reduces the electrolyzer cell pressure and restores its performance.Based on the understanding of impurity ion poisoning,when using tap water for electrolysis,only need to control the cathode p H to 1 to achieve long-term stable operation.