Preparation Of Non-noble Metal-based Catalysts And Their Performance In Electrocatalytic Ammonia Synthesis

The synthesis of ammonia in industry mainly depends on the Haber-Bosch process,which has high energy consumption and high pollution.Electrocatalytic ammonia synthesis is considered as a sustainable alternative to the Haber-Bosch process.And non-precious metal catalysts with good catalytic performance and low price can effectively promote the development of electrochemical ammonia synthesis.Therefore,in this paper,we prepared ZnCo bimetallic catalysts,cerium-zirconium series catalysts,bismuth oxyhalide catalysts,and studied their electrocatalytic ammonia synthesis(NRR)performance in 0.1 mol·L-1 Na2SO4 electrolyte.First,ZIF(ZnxCoy)catalysts were synthesized by coprecipitates at room temperature with 2-methylimidazole,Co(NO3)2·6H2O and Zn(NO3)2·6H2O as raw materials in this paper.Then,the ZIF(ZnxCoy)materials were calcined at 650? for 2 hours to synthesize ZIF(ZnxCoy)/NCN catalysts with nitrogen-doped carbon nanotube structure.It was found that the catalytic activity of ZIF(ZnxCoy)/NCN was significantly higher than that of ZIF(ZnxCoy)catalysts,and ZIF(Zn3Co7)/NCN had the best electrocatalytic ammonia synthesis performance.At-1.0 V vs.Ag/AgCl,the NH3 synthesis rate and Faraday efficiency of ZIF(Zn3Co7)/NCN achieved the maximum,which were 9.23×10-11 mol s-1 cm-2 and 15.58%,respectively.The main reason was that the nitrogen-doped carbon nanotubes in ZIF(Zn3Co7)/NCN can avoid the agglomeration of internal nano-junction particles,thereby providing more electrocatalytic active sites,and the pore structure generated by the volatilization of Zn at high temperature can enhance the adsorption of N2 and the transfer of ions.In addition,ZIF-67(Co)/NC-acid synthesized by calcining the precursor ZIF-67 at 750? for 4 hours and immersed in sulfuric acid solution also exhibited excellent electrocatalytic ammonia synthesis performance.At-0.9 V vs.Ag/AgCl,the ammonia synthesis rate and Faraday efficiency reached the maximum,respectively 1.57×10-10 mol s-1 cm-2 and 21.79%.Mainly because the surface of ZIF-67(Co)/NC-acid after pickling can expose more unsaturated nitrogen and Co-Nx to form active sitesIn addition,the precursors were synthesized by hydrothermal method with CeCl3·7H2O,ZrCl4 and urea as raw materials in this paper.Then,the precursors were calcined at 500? for 3 h to synthesize cerium-zirconium series catalysts.Among them,Ce0.25Zr0.75O2 solid solution with tetragonal phase structure showed excellent electrocatalytic ammonia synthesis performance.And its highest NH3 synthesis rate was achieved at-0.7 V vs.Ag/AgCl,which was 1.03×10-10 mol s-1 cm-2;its highest Faraday efficiency was achieved at-0.6 V vs.Ag/AgCl,which was 64%.It was mainly because the change of the lattice structure and the formation of highly defective structure in Ce0.25Zr0.75O2 were conducive to enhancing its catalytic activity.Finally,the bismuth oxyhalide catalysts were synthesized by hydrothermal method with Bi(NO3)3.5H2O,KX(X=Cl,Br,I)as raw materials in this paper.Among them,BiOBr showed the best catalytic activity.At-0.8 V vs.Ag/AgCl,the NH3 synthesis rate was the largest,achieving 8.28×10-11 mol s-1 cm-2,and the Faraday efficiency was 14.9%;At-0.6 V vs.Ag/AgCl,the Faraday efficiency was the largest,achieving 28.3%,and the ammonia synthesis rate was 5.99×10-11 mol s-cm-2.It is mainly because the oxygen vacancy of nanometer BiOBr maked it has a high defect level,which was beneficial to the electrochemical NRR.