将CO2电还原(CO2RR)转化为可再生燃料,如CH4,C2H4,C2H5OH,被认为是实现碳循环和储存可再生能源的有效途径.与其他材料相比,铜(Cu)基催化剂对*CO中间体具有合适的吸附能,能够将CO2还原为多碳产物.但是,Cu基催化剂在高电流密度(大于100 mA cm-2)下的催化活性较低,选择性较差,这是亟待解决的问题.通过Cu0/Cu+界面策略可以提高CO2RR为C2产物的选择性.然而,在H型电解池中,由于传质限制,高质子浓度的溶液容易引起析氢反应(HER),同时催化剂表面发生的HER竞争反应也导致了产物电流密度的降低.随着反应进行,催化剂表面活性位点上CO2浓度逐渐降低,而溶液中的CO2不能及时补充到催化剂表面,进一步加剧了这一问题.本文在CO2气氛下合成了具有高曲率结构的枝晶状Cu/Cu2O.实验结果表明,得到的枝晶状Cu/Cu2O不仅具有较高的C2H4(51.42％)选择性,而且C2类产物(如C2H4,C2H5OH等)的总选择性达到69.82％,同时在H型电解池中具有较高C2H4(95.3 mA cm-2)和C2产物分电流密度(129.5 mA cm-2).有限元模拟计算结果表明,具有高曲率结构的枝晶状Cu/Cu2O表面产生了增强的局部电场,从而提高了催化剂表面局部CO2浓度.结合弛豫时间分布分析结果,发现高曲率的枝晶状结构能够主动吸附催化剂周围溶液环境中的CO2,提高了反应的传质速率,实现了还原过程中产物的高电流密度.在实验过程中,通过改变催化剂表面Cu0/Cu+的原子比,研究电子结构对催化剂性能的影响.在Cu0/Cu+的最佳原子比时,电荷转移电阻最小,中间体的解吸速率慢,更有利于C2产物的生成.密度泛函理论计算结果也表明,在Cu0/Cu+界面处,将CO2还原为C2的关键步骤(即决速步骤)所涉及反应中间体具有较低的吉布斯自由能,从而促进了C2H4形成.Cu/Cu2O催化剂还具有较低的Cu的d能带中心,增强了*CO在催化剂表面的吸附稳定性,促进了C2产物的形成,因此在快速传质条件下,Cu0/Cu+界面获得的是C2产物.最后,利用净现值模型计算了H型电解池工业应用的经济可行性,结果表明,H型电解池是否具有广阔的工业前景,取决于催化剂是否同时具有高选择性和高电流密度的能力.综上所述,将特殊形貌与催化剂成分相结合的设计策略,不仅可以将两者的优势相结合,还实现了单一条件时难以达到的效果,显著提升了CO2RR催化剂的性能.本研究将对CO2RR催化剂的设计和实际应用提供参考.
A dendritic Cu/CU2O structure with high curvature enables rapid and efficient reduction of carbon dioxide to C2 in an H-cell
Electrocatalytic reduction of CO2(CO2RR)to multicarbon products is an efficient approach for ad-dressing the energy crisis and achieving carbon neutrality.In H-cells,achieving high-current C2 products is challenging because of the inefficient mass transfer of the catalyst and the presence of the hydrogen evolution reaction(HER).In this study,dendritic Cu/Cu2O with abundant Cu0/Cu+interfaces and numerous dendritic curves was synthesized in a CO2 atmosphere,resulting in the high selectivity and current density of the C2 products.Dendritic Cu/Cu2O achieved a C2 Faradaic efficiency of 69.8％and a C2 partial current density of 129.5 mA cm-2 in an H-cell.Finite element simulations showed that a dendritic structure with a high curvature generates a strong electric field,leading to a localized CO2 concentration.Additionally,DRT analysis showed that a dendritic struc-ture with a high curvature actively adsorbed the surrounding high concentration of CO2,enhancing the mass transfer rate and achieving a high current density.During the experiment,the impact of the electronic structure on the performance of the catalyst was investigated by varying the atomic ratio of Cu0/Cu+on the catalyst surface,which resulted in improved ethylene selectivity.Under the optimal atomic ratio of Cu0/Cu+,the charge transfer resistance was minimized,and the desorption rate of the intermediates was low,favoring C2 generation.Density functional theory calculations indicated that the Cu0/Cu+interfaces exhibited a lower Gibbs free energy for the rate-determining step,enhancing C2H4 formation.The Cu/Cu2O catalyst also exhibited a low Cu d-band center,which enhanced the adsorption stability of*CO on the surface and facilitated C2 formation.This observa-tion explained the higher yield of C2 products at the Cu0/Cu+interface than that of H2 under rapid mass transfer.The results of the net present value model showed that the H-cell holds promising industrial prospects,contingent upon it being a catalyst with both high selectivity and high current density.This approach of integrating the structure and composition provides new insights for ad-vancing the CO2RR towards high-current C2 products.
Reduction of CO2High currentDendritic structureCu/Cu2OH-cell
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