Study Of Cu-Zn,Cu-Sn,and Zn-Sn Bimetallic Catalysts For Electrochemical Reduction Of CO₂

Electrochemical reduction of CO2 to energy fuels driven by renewable energy is a promising technology for the conversion and utilization of CO2 resources.Cheap,abundant and easy-to-prepare catalysts are the main research point in this field.Non-noble metals,such as Cu,Zn and Sn are abundant,cheap and easy to obtain,which also have good catalytic performance for CO2 electro-reduction.The catalytic performance of the materials can be effectively controlled by adjusting the surface morphology of the nletal materials,constructing nanostructured materials and modifying to bimetallic alloys.This study is focousing on the preparation of bimetallic catalytic laterials and the evaluation of catalytic performance for reduction CO2 electro-reduction.The surface of bimetallic materials was modified by simple and easy-to-operate method of annealing treatment oxidation followed by electrochelically reduction to improve or control their catalytic performance.Combineing with the characterization results of the morphology,structure,composition and crystal formation,the intrinsic mechanisms of catalytic performance regulation were analyzed.In addition,to evaluate the catalytic performance of unknown powder materials quickly and preliminarily,an evaluation method based on rotating ring-disk electrode(RRDE)system was established to analyze the main catalytic performance.The main contents and results of this paper are as follows:(1)Electrochemical reduction of CO2 by modified brass(Cu-Zn alloy)Among the bimetallic materials composed of Cu and Zn,commercial brass H62(Cu-Zn alloy)is the cheapest and most available material at present.The modified Cu-Zn allpy(donated as Cu-Zn AR)was prepared by annealing treatment oxidation at 500? for 1 h followed by electrochemical reduction in 0.5 M KHCO3 solution.Carbon dioxide electrochemical reduction electrolysis experiments were carricd out to evaluate the catalytic activity,product selectivity and catalytic stability.The electrolysis results showed that the hydrogen evolution reaction was suppressed a lot after the modification of Cu-Zn alloy.The faraday efficiency of HZ decreases from 86.5%to 27.6%at potential of-1.6 V(vs.SCE),and the productions of CO and HCOOH are increased by 4 times and 6 times,respectively.Surface characterizations showed that the improvement of catalytic performance was due to the formation of nanoporous Zn layer on the surface of Cu-Zn AR.The study also provides a possible way to prepare metal nanoporous materials.(2)Electrochemical reduction of CO2 by modified bronze(Cu-Sn alloy)Similar to brass,bronze is a kind of large-scale commercial copper alloy made up of Cu and Sn.CuSn6 bronze(Cu-Sn alloy)bimetallic material was selected in the experiment to obtain modified Cu-Sn alloy(Cu-Sn AR)by annealing treatment oxidation at 300°C followed by electrochemically reduction.The obtained Cu-Sn AR showed the ability to convert CO to C2/C3 products under lower overpotential than Cu-Sn alloy.According to the surface characterization results,the change of the catalytic activity is due to the formation of abundant Cu nanoparticles and some Cu nanowires during the modification process through the oxidation-reduction of Cu.The nano-scale surface provided more active sites and defects,which could enhance the adsorption capacity of the intermediate products during the catalytic synthesis of C2 and C3 products.Then,the selectivity of products is adjusted.(3)Electrochemical reduction of CO2 by Zn-Sn alloyZn-Sn bimetallic materials with different Zn/Sn compositions were prepared by melting method and chemical substitution method,respectively.The influence mechanism of different Zn/Sn compositions on the catalytic performance of Zn-Sn alloy was studied.Zn-Sn alloy with uniform distribution of Zn and Sn on the surface can be prepared by mc lting method,however,the Zn@Sn alloy prepared by chemical replacement method with low energy consumption showed a surface of uneven distribution of Zn and Sn.The results of CO2 electrochemical reduction electrolysis showed that Sn combined with Zn inhibited the hydrogen evolution reaction on the surface of Zn.With the increase of Sn content,the inhibition of hydrogen evolution became more obvious,and the Faraday efficiency of CO and HCOOH products increased gradually.The reason is that the combination of Sn and Zn results in the reduction of the peak strength of Zn(101)which is conducive to hydrogen evolution,and the increase of the peak strength of Zn(002)promotes the formation of CO,and more protons are used for the formation of HCOOH.This part of the study shows that the catalytic performance of materials can be regulated by controlling the composition of bimetallic materials,which affects the surface morphology of materials(4)Evaluation methodology of performance of catalytic materials for CO2 electro-reduction based on RRDEBased on the rotating ring disk electrode test system,a method was developed for preliminary analysis of the catalytic performance of a small number of unknown powder samples for CO2 electro-reduction.The powder samples were uniformly dripped onto the disk surface of the ring-disk electrode.In the CO2 saturated KHCO3 solutions,the potential of the disk electrode was controlled.The CO2 reduction products on the disk surface were overflowed to the surface of the Pt ring under condition of high-speed rotation of the electrode.By analyzing the cyclic voltammetry curves of the Pt ring,the catalytic performance of the material could be quickly identified,such as initial potential,catalytic stability,and the competition between the hydrogen evolution reaction and CO2 electro-reduction reaction by varying the disk potential.