Electrocatalytic Reduction NO_x^- For Ammonia Synthesis With Cobalt-based Phosphides

Electrocatalytic nitrogen fixation for ammonia synthesis can be used to replace the haber reaction of traditional industrial ammonia production,which can reduce carbon dioxide emissions and energy waste.It is a green and efficient process for ammonia synthesis.In recent years,the method of indirect ammonia synthesis（NO _x^-→NH₃）has received extensive attention.Compared with the traditional method of direct synthesis of ammonia（N2→NH₃）,the indirect method of ammonia synthesis overcomes the problems of large nitrogen-nitrogen triple bond energy,low N2 solubility in water,low faradaic efficiency,and low ammonia yield.Indirect electrocatalytic ammonia synthesis（NO _x^-→NH₃）has the advantages of high faradaic efficiency and high ammonia yield,but most of the current catalysts are expensive precious metals（Pt,Pd,Ir and alloys with other metals）,moreover,the faradaic efficiency,selectivity and stability of ammonia generation also need to be improved.It is crucial to develop a catalyst capable of selectively converting NO _x^-to NH3 with high efficiency.Transition metal cobalt phosphide has the characteristics of reversible adsorption of active H and charge separation and selective adsorption of species,and it is expected to be an ideal catalyst for electrocatalysis NO _x^-to generate ammonia.Therefore,in this thesis,transition metal cobalt phosphide and bimetallic doped cobalt phosphide with transition metal cobalt as the main body and carbon cloth（CC）as the carrier were designed and synthesized,Its catalytic performance was also studied.The main research contents are as follows:（1）CoP/CC was synthesized in an oven at 120°C using a hydrothermal reaction.SEM shows that CoP/CC forms a nanowire structure with a large electrocatalytic area;electrochemical performance tests show that the faradaic efficiency of CoP/CC in NO ₂^-was91.55%,the yield of ammonia was 362.56μg·h^-1·cm^-2;the faradaic efficiency of CoP/CC in NO₃^–was 65.37%,and the yield of ammonia was 188.15μg·h^-1·cm^-2;the catalyst remained high for 10 consecutive catalytic cycles stability.（2）Bimetallic doped cobalt phosphide（NiCoP 400°C/CC,NiCoP 600°C/CC,Cu CoP/CC）was synthesized by hydrothermal reaction.SEM shows that the synthesized bimetallic doped cobalt phosphide is different in morphology,but all have a large electrocatalytic area;electrochemical performance tests show that they all show a good effect of ammonia synthesis,electrochemical performance tests show that the faradaic efficiency of NiCoP 400℃/CC in NO ₂^-was 89.83%,the yield of ammonia was 290.74μg·h^-1·cm^-2;the faradaic efficiency of NiCoP 400℃/CC in NO₃^–was 64.79%,and the yield of ammonia was 193.71μg·h^-1·cm^-2;the faradaic efficiency of NiCoP 600℃/CC in NO ₂^-was 86.08%,the yield of ammonia was258.25μg·h^-1·cm^-2;the faradaic efficiency of NiCoP 600℃/CC in NO₃^–was 84.08%,and the yield of ammonia was 250.99μg·h^-1·cm^-2;the faradaic efficiency of Cu CoP/CC in NO ₂^-was92.91%,the yield of ammonia was 99.66μg·h^-1·cm^-2;the faradaic efficiency of Cu CoP/CC in NO₃^–was 90.84%,and the yield of ammonia was 265.10μg·h^-1·cm^-2.All bimetallic doped cobalt phosphide catalysts maintained high stability for 10 consecutive catalytic cycles.In conclusion,cobalt phosphating catalyst shows high performance as an electrocatalyst for ammonia synthesis,which proves that transition metal cobalt phosphide supported by carbon cloth is effective in electrocatalytic NO_x^–for efficient ammonia synthesis huge potential.