Lead-tannin Complex And N-doped Carbon Nanotube Arrays:Chemical Conversion And Electrocatatlytic Performance Toward CO₂ Reduction

The use of electricity to reduce carbon dioxide to low-carbon fuels and other small organic molecules is expected to alleviate the energy crisis,greenhouse effect and other problems caused by the use of fossil.There are many paths of electrocatalytic reduction of carbon dioxide and the products are complex.The products of one carbon reduction include formate,methane,carbon monoxide and so on.Among them,formate is one of the basic organic chemical raw materials and an important intermediate in drug molecular organic synthesis,which is widely used in medicine,dyes,textiles,pesticides and other industrial production.At the same time,the mixed gas of carbon monoxide and hydrogen(syngas)is an important raw material for Fischer-Tropsch synthesis and plays an important role in the industrial preparation of multi-carbon hydrocarbons.Therefore,it is necessary to design and synthesize efficient electrocatalysts to achieve high selectivity of carbon dioxide reduction to formate and carbon monoxide.Based on this,two inexpensive electrocatalysts including lead complex and nitrogen-doped carbon nanotube array were prepared with the goal of developing an efficient and highly selective electrocatalytic carbon dioxide reduction catalyst.This article systematically characterizes its morphology,structure and composition,and studies in detail their electrochemical performance and the conversion mechanism of catalyst during the reduction process to explore the active species.The main research contents are as follows:(1)Polyphenolic hydroxyl metal complexes were prepared with tannic acid as ligand and divalent lead ion as central atom.The catalyst showed excellent performance of carbon dioxide reduction to formate and the Faraday efficiency of formate was up to 96.4±0.9%at-0.92 V(RHE).In addition,combined with XPS,XRD,SEM,TEM to characterize the structure and composition of the catalytic material.In-situ Raman spectroscopy and EXAFS spectroscopy reveals the in situ transformation of TA-Pb to cerussite,and sequentially to hydrocerussite,which finally serves as a stable and active phase.It is also verified that hydrocerussite can effectively suppress self-reduction and become a stable active phase while efficient carbon dioxide electroreduction to formate.(2)We present the controllable electrochemical CO₂reduction to syngas over Ar-plasma-treated N-doped carbon nanotube arrays.With different treatment conditions,the CO/H₂ratio ranges from 0.55 to 3.03,which is suitable for Fischer-Tropsch synthesis.The highest CO Faradaic efficiency under optimal condition is 75%with excellent stability for over 10 h.Our results show that pyridinic N is advantageous for the formation of CO,while pyrrolic N and carbon outside the sp²plane are in favor of hydrogen generation.And the percentage of the above components can be manipulated by plasma treatment conditions to control the ratio of CO/H₂in the product.This strategy paves a new avenue to regulate the structure of the electrocatalysts for the preparation of syngas with a controllable CO/H₂ ratio.