Copper-based Composites For Electrochemical CO₂ Reduction And Their Properties

Fossil fuels are expected to be the major source of energy for the next few decades.However,combustion of nonrenewable resources leads to the release of large quantities of CO2(the primary greenhouse gas).Notably,the concentration of CO2 in the atmosphere is increasing annually at an astounding rate.Excessive emission of CO2 causes a series of environmental problems such as global warming and climate change.Electrochemical CO2 reduction(ECR)to value-added fuels and chemicals using green and clean electricity from intermittent renewable energy sources is a carbon-neutral method to alleviate anthropogenic CO2 emissions.The development of low-cost,highly active and highly selective catalysts for efficient ECR remains an ongoing challenge.Indeed,the past few years have witnessed enormous effort in the search and design of various electrocatalysts for CO2 reduction.In particular,noble metals such as Au,Ag,Pd,and Pt have been reported for ECR to yield CO during ECR.However,their high cost and scarcity impose unfavorable limitations on the prospects of their practical application in ECR.Copper-based catalysts have attracted significant attention and have been extensively investigated,since they exhibit good selectivity and efficiency for the reduction of CO2 to hydrocarbons and alcohols.Studies show that polycrystalline copper foils generate more than 16 different species,which represents a huge challenge for their separation.Therefore,to improve the selectivity of ECR single product by modifying copper-based composites is conducive to its further application in ECR field.In this paper,the activity and selectivity of ECR single product were improved by surface interface modification of copper-based composites.Specific research contents are as follows:(1)By a simple wet chemical method,Cu and In bimetallic oxides were synthesized and loaded onto N-doped carbon nanotubes(NCNTs)in one step.The interaction between CuO and In2O3 was used to achieve efficient ECR.The results of XRD,XPS and TPR confirmed the interaction between Cu and In,and the electron transfer occurred between Cu and In,which changed the electronic structure of Cu.We can adjust the catalytic performance of the composite catalyst by controlling the composition of metal oxides,and realize the transformation of the main product from HCOOH to CO.In contrast to pure CuO and In2O3 that both catalyze ECR with CO FEs of less than 32.0%,the metal oxide composite catalyst can deliver a CO FE as high as 93.0%at-0.7 V vs.reversible hydrogen electrode(RHE)with a CO partial current density of 4.3 mA cm-2,outperforming many previously reported metal-based electrocatalysts.(2)We report on the stabilization of Cu+by controlling the interplay between lattice-mismatched CuO and CeO2,and effectively electrochemically reduce CO2 to ethylene.Both XPS and Raman spectra confirmed the presence of Cu+.Tuning the CuO/CeO2 interfacial interaction permits dramatic suppression of proton reduction and enhancement of CO2 reduction,with an ethylene faradaic efficiency(FE)as high as 50.0%at-1.1 V(vs.RHE),in stark contrast to 22.6%over pure CuO immobilized on carbon black(CB).The composite catalyst presents a 2.6-fold improvement in ethylene current compared to that of CuO/CB at similar overpotentials,which also exceeds many recently reported Cubased materials.The FE of C2H4 remained at over 48.0%even after 9 h of continuous polarization.Furthermore,density functional theory(DFT)calculations revealed that CeO2 changes the oxidation state of Cu atoms to Cu+at the CuO-CeO2 interface.(3)We demonstrate fine-tuning of ECR to C2H4 by taking advantage of the prominent interaction of Cu with shape-controlled CeO2 nanocrystals,that is,cubes,rods,and octahedra predominantly covered with(100),(110),and(111)surfaces,respectively.We found that the selectivity and activity of the ECR depended strongly on the exposed crystal facets of CeO2.In particular,the FE toward C2H4 formation and the partial current density increased in the sequence Cu/CeO2(111)<Cu/CeO2(100)<Cu/CeO2(110)within applied bias potentials from-1.00 to-1.15 V(vs the reversible hydrogen electrode).The superior ECR activity of Cu/CeO2(110)to yield C2H4 was attributed to the metastable(110)surface,which not only promoted the effective adsorption of CO2 but also remarkably stabilized Cu+,thereby boosting the ECR to produce C2H4.This work offers an alternative strategy to enhance the ECR efficiency by crystal facet engineering.