Preparation And Electrocatalytic Performance Of Self-supporting Metal Phosphide Complex Electrode For Water Decomposition

Hydrogen,as an ideal clean energy,holds great potential to replace fossil fuels in the future.Hydrogen produced from electrolyzed water is simple and efficient,and it is crucial to design suitable electrocatalysts.Pt and Pd are the state-of-the-art electrocatalysts for hydrogen evolution reaction?HER?,while RuO₂ and IrO₂ show outstanding performance for oxygen evolution reaction?OER?.However,it is not conducive to practical application owing to the high cost of these precious metals.Recently,transition-metal compounds,especially transition-metal phosphides?TMPs?,have been recognized as efficient catalysts for the HER and OER.Although there are a few reports on the synergic effect between different metals,there are still needs to be improved in preparation methods,performance,stability,and self-supportability.Based on the above problems,we have studied the multi-metal phosphide.In this thesis,a self-supporting transition metal phosphide electrode was prepared by solvothermal-low temperature phosphating or one-step calcination phosphating method,which has the characteristics of high catalytic efficiency and good stability.The main contents and results of this thesis are as follows:?1?Iron-nickel alloy foam?NIF?was employed as the growth substrate.Cobalt nitrate was used as the source of cobalt and terephthalic acid was used as ligand.A metal phosphide electrode?MIL-P?was synthesized by a method of solvothermal followed by low temperature calcination phosphating.The optimum reaction conditions were as follows:the amount of the reactant was 0.2 mmol,and the solvothermal time was 36 h.The SEM results show that MIL-P has a napoleon crisp-like structure,and XRD and XPS indicate that the main components of the material are CoP and FeNi₂P.EDX shows that Fe,Co,Ni,P,C are homogeneously distributed.The gas contact angle test showed that the contact angle was 116.8°,indicating that the surface of the material was aerophobicity.MIL-P has excellent performance for OER,which shows a low overpotential of 237 mV at 10 mA·cm^-2 and a tafel slope of 84 mV·dec^-1 for OER.The double layer capacitor(C_dl)is 37.84 mF·cm^-2,indicating electrochemical surface area?ECSA?is 946 cm²,which exceeds most of the currently reported non-precious metal catalysts.The charge transfer resistance is only 0.463?.After 2000 cycles of CV,the material still maintains stability.?2?Iron-cobalt-nickel alloy?NICF?was used as the growth substrate and the source of Co,Ni and Fe,and sodium hypophosphite was used as a phosphorus source,and NiFe-CoP_x was synthesized by one-step calcination phosphating.The optimum reaction conditions were as follow:phosphating for 3 h and temperature at 400°C.The SEM characterization results show that NiFe-CoP_x has a mulberry-like structure.XRD,TEM and XPS prove that the main components of the material are Co₂P,Ni₂P and Fe₂P.EDX shows that the various elements are homogeneously distributed.The gas contact angle test showed that the contact angle was 151.3°,indicating that the surface of the material was superaerophobicity,which facilitates the discharge of the generated bubbles.The electrochemical test results show that the HER overpotential is 120 mV at a current density of 10 mA·cm^-2,and the Tafel slope is 95 mV·dec^-1,which is equivalent to Pt/C.The OER overpotential at a current density of 20 mA·cm^-2 is 274 mV,and the Tafel slope is 151 mV·dec^-1,which exceeds the performance of IrO₂.The C_dl is 3.53 mF·cm^-2,indicating ECSA is 88.25 cm².The charge transfer resistance is 4.501?.When NiFe-CoP_x was further used for overall water splitting,and the cell voltage at a current density of 10 mA·cm^-2 was only 1.53 V,which exceeded most of the current reports and after 10hours of stability test,it still has good stability.The reasons for the superior electrocatalytic performance of the as-prepared materials can be summarized as follows:?a?there is a synergetic effect between the metal elements in the material.?b?The materials have large double layer capacitor,which has a large electrochemical surface area and a large number of active sites.?c?The materials are grown on a 3D porous metal substrate to facilitate the discharge of bubbles.