Investigation On Fabrication And Electrocatalytic CO₂ Reduction Performance Of Bi-based Nanostructured Materials

Electrochemical CO2 reduction(CO2ER)is an attractive CO2 reuse technology using electric energy to convert CO2 into high-value chemicals.CO2ER is considered as an effective strategy to store abundant intermittent renewable energy which provides a practical solution to the current environmental issues.However,it is challenging to achieve efficient and stable CO2ER in practical applications due to the slow dynamic process,high overpotentials and multiple reaction paths.In this thesis,a series of Bi-based catalysts with excellent electrocatalytic performances were prepared by dealloying and high temperature pyrolysis.Their micromorphology,phase composition and electrocatalytic performance were investigated in sequence.The main research contents of this thesis are described as follows.Firstly,nanoporous Bi(np-Bi)catalyst prepared by dealloying exhibits a threedimensional interconnected ligament-channel network structure.In the H cell,np-Bi can efficiently convert CO2 to formate in a wide potential range.Compared with commercial Bi powder,the selectivity,activity and stability of formate of np-Bi are significantly improved.The highest FE of formate reaches 94%,and the partial current density of formate(j of formate)reaches 62 mA cm-2 at-1.2 V vs.RHE.Moreover,the FE of formate and morphology of np-Bi can remain stable after the stability test.In addition,np-Bi delivers a high j of formate of～500 mA cm-2 at a low overpotential of 420 mV in the flow cell.Secondly,we developed three Bi nanoparticle(NP-Bi)catalysts(NP-Bi1000,NP-Bi2000 and NP-Bi3500)via rapid solidification with different rotating speeds(1000,2000 and 3500 revolutions per minute(rpm),respectively).The particle sizes decrease with the increase of rotating speed.In the H cell,the three NP-Bis exhibit similar CO2ER properties in general.Specifically,compared with commercial Bi powder,the catalytic performances of NP-Bi are significantly improved.For NP-Bi,the maximum FE of formate can reach 92%,and the j of formate can reach 42 mA cm-2.Furthermore,in the flow cell,NP-Bi2000 can achieve a high FE of～95%at the current density of 100～600 mA cm-2 and an industry-level current density of 574.7 mA cm-2 for formate production at a low overpotential of 484.6 mV.Finally,we prepared Bi@C,BiSn@C and Sn@C by high temperature pyrolysis.Compared with dealloying,the efficiency of material preparation was significantly improved.The three materials are all carbon coated and the morphology of carbon layers are slightly different.In these three composites,most of the metal or alloy components are confined in their carbon layer,and a small fraction of metal or alloy particles anchor onto the material surface.In H cell,Bi@C,BiSn@C and Sn@C show impressive selectivity and activity for formate formation with the highest FE of formate of 93.2%,80.2%and 82.2%,respectively.At-1.2 V vs.RHE,the j of formate reaches 73 mA cm-2,37.5 mA cm-2 and 30.2 mA cm-2 respectively.Additionally,Bi@C achieves a remarkable current density of 531.3 mA cm-2 in the flow cell.