CeO_(2)担载Cu纳米粒子电催化CO_(2)还原产乙烯:CeO_(2)不同暴露晶面对催化性能的影响

Electrocatalytic CO_(2) Reduction to Ethylene over CeO_(2)-Supported Cu Nanoparticles:Effect of Exposed Facets of CeO_(2)

化石燃料在未来几十年仍然是主要的能量来源,但是这种不可再生资源的燃烧释放出大量的CO_(2)(主要的温室气体),空气中CO_(2)的浓度每年仍然持续增加。使用间歇性可再生能源转化的电能驱动电化学CO_(2)还原生成高附加值产品为其减排提供了一种有前景、CO_(2)“零排放”的方法。本文通过利用Cu和不同形状的CeO_(2)纳米晶之间的相互作用,即分别暴露(100)、(110)、(111)晶面的立方体、棒状和八面体CeO_(2),实现了对电化学CO_(2)还原产乙烯的有效调控。研究发现,电化学CO_(2)还原的选择性和活性与CeO_(2)暴露的晶面密切相关,生成乙烯的法拉第效率和偏电流密度在1.00到1.15 V(相对于可逆氢电极)的施加电势范围内呈现出Cu/CeO_(2)(111)<Cu/CeO_(2)(100)<Cu/CeO_(2)(110)的趋势。在H-型电解池中,以0.1 mol·L^(−1)KHCO_(3)溶液为电解质,Cu/CeO_(2)(110)电催化CO_(2)还原的法拉第效率为56.7%,这与纯碳纸、CeO_(2)(100)、CeO_(2)(110)、CeO_(2)(111)纳米颗粒上只发生析氢副反应形成了鲜明对比,并且Cu/CeO_(2)(110)可在较温和的过电势下(1.13 V)电催化CO_(2)还原产乙烯,其法拉第效率达到39.1%,和文献报道的很多Cu-基材料的性能相当,而Cu/CeO_(2)(100)与Cu/CeO_(2)(111)产乙烯的法拉第效率分别为31.8%和29.6%。此外,经过6 h的持续电解后,乙烯的法拉第效率基本保持稳定。Cu/CeO_(2)(110)还原CO_(2)产乙烯的活性可能与CeO_(2)(110)表面的亚稳态性质有关,其不仅能有效促进CO_(2)的吸附,还能有效稳定Cu^(+),从而促进了CO_(2)还原为乙烯。本工作为增强电化学CO_(2)还原提供了晶面工程途径。

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 CO_(2),the primary greenhouse gas.Notably,the concentration of CO_(2) in the atmosphere is increasing annually at an astounding rate.Electrochemical CO_(2) reduction(ECR)to value-added fuels and chemicals using electricity from intermittent renewable energy sources is a carbon-neutral method to alleviate anthropogenic CO_(2) emissions.Despite the steady progress in the selective generation of C1 products(CO and formic acid),the production of multi-carbon species still suffers from low selectivity and efficiency.As an ECR product,ethylene(C_(2)H_(4))has a higher energy density than do C1 species and is an important industrial feedstock in high demand.However,the conversion of CO_(2)to C_(2)H_(4) is plagued by low productivity and large overpotential,in addition to the severe competing hydrogen evolution reaction(HER)during the ECR.To address these issues,the design and development of advanced electrocatalysts are critical.Here,we demonstrate fine-tuning of ECR to C_(2)H_(4) by taking advantage of the prominent interaction of Cu with shape-controlled CeO_(2) 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 CeO_(2).The overall ECR Faradaic efficiency(FE)over Cu/CeO_(2)(110)(FE≈56.7%)surpassed that of both Cu/CeO_(2)(100)(FE≈51.5%)and Cu/CeO_(2)(111)(FE≈48.4%)in 0.1 mol·L^(−1)KHCO_(3) solutions with an H-type cell.This was in stark contrast to the exclusive occurrence of the HER over pure carbon paper,CeO_(2)(100),CeO_(2)(110),and CeO_(2)(111).In particular,the FE toward C_(2)H_(4) formation and the partial current density increased in the sequence Cu/CeO_(2)(111)<Cu/CeO_(2)(100)<Cu/CeO_(2)(110)within applied bias potentials from−1.00 to−1.15 V(vs.the reversible hydrogen electrode),reaching 39.1%over Cu/CeO_(2)(110)at a mild overpotential(1.13 V).The corresponding values for Cu/CeO_(2)(100)and Cu/CeO_(2)(111)were FEC_(2)H_(4)≈31.8%and FEC_(2)H_(4)≈29.6%,respectively.The C_(2)H_(4) selectivity was comparable to that of many reported Cu-based electrocatalysts at similar overpotentials.Furthermore,the FE for C_(2)H_(4) remained stable even after 6 h of continuous electrolysis.The superior ECR activity of Cu/CeO_(2)(110)to yield C_(2)H_(4) was attributed to the metastable(110)surface,which not only promoted the effective adsorption of CO_(2)but also remarkably stabilized Cu^(+),thereby boosting the ECR to produce C_(2)H_(4).This work offers an alternative strategy to enhance the ECR efficiency by crystal facet engineering.