Synthesis And Catalytic Properties Of Nanoarrays As Electrodes For Water Splitting

Hydrogen from electrolyzed water has many advantages,such as high efficiency,simple process,no pollution,etc.,and its sources are extensive.The process of electrolyzed water reaction is formed by the combination of hydrogen evolution reaction?HER?and oxygen evolution reaction?OER?.The performance of the catalytic electrode directly determines the efficiency of the hydrogen from electrolyzed water.At present,most of the HER and OER reactions use Pt,IrO₂ as catalytic electrodes,but the price of precious metals determines that they cannot achieve large-scale industrial application.Therefore,research and development of non-precious metal-based catalytic electrode materials with catalytic activity comparable to that of noble metals have become the focus of research in the field of hydrogen production from electrolyzed water.In this dissertation,transition metal phosphides with high catalytic activity and strong acid and alkali resistance were the main research objects.A series of tran-sition metals were successfully prepared on the highly conductive carbon cloth substrate by hydrothermal reaction,electrodeposition and low-temperature phosphating.The phosphide nano-array structure was used as a catalytic electrode to carry out the research on the catalytic performance of electrolyzed water.The specific research is as follows:?1?Firstly,a Co_0.5Fe_0.5P/CC monolithic catalytic electrode with a nanowire array struc-ture was prepared by hydrothermal synthesis and low-temperature phosphating using a highly conductive carbon cloth?CC?as a growth substrate.The catalytic electrode exhibited good electrolyzed water catalytic performance in the alkaline electrolyte?1 M KOH solution?.In the catalytic reaction of HER and OER,it required only 108 mV and 280 mV respectively to reach the current density of 10 mA/cm².?2?Based on the Co_0.5Fe_0.5P/CC nanowire array catalyst in?1?,a catalyst with core-shell heterostructure Co_0.5Fe_0.5P@Mn₂P/CC was prepared by a controlled constant current electro-deposition method.?Denoted as CM-X/CC,X is electrodeposition time?.In this way,the con-trollable adjustment of the core-shell ratio of the active material is achieved,and CM-5/CC has the best hydrogen evolution performance.The catalytic electrode has a certain hydrogen evolution performance and stability in the whole pH range from 0-14.In the 0.5 M H₂SO₄solution,a hydrogen evolution current density of 10 mA/cm² was achieved with overpotential of only 37 mV;71 mV and 83 mV were needed in 1 M KOH alkaline electrolyte and 1 M PBS neutral electrolyte,respectively.The overpotential reaches a hydrogen evolution current density of 10 mA/cm².?3?Based on the above experiments,a catalyst with core-shell heterostructure Co_0.5Fe_0.5P@Ni₂P/CC?remembered as CN-X/CC,X is the electrodeposition time?was still prepared using controlled constant current electrodeposition.When the electrodeposition time is 20 min,the catalytic performance of CN-20/CC electrode obtained is the best,and it can achieve a HER current of 10 mA/cm² with overpotential of only 68 mV in 1 M KOH alkaline electrolyte.At the same time,the OER current of 100 mA/cm² can be reached with only 320mV overpotential in 1 M KOH alkaline,which is obviously better than Co_0.5Fe_0.5P/CC?520mV?.?4?The high-HER catalytic performance of CM-5/CC obtained in?2?is used as a cath-ode active material,and CN-20/CC with high OER catalytic performance obtained in?3?is used as an anode active material to construct a two-electrode electrolyzed water system?CM-5/CC||CN-20/CC?.In the alkaline electrolyte,a current density of 10 mA/cm² can be achieved in the electrolyzed water with only a voltage of 1.540 V.