Cu纳米针上电场促进C-C耦合增强CO2电还原生成C2产物

电催化CO₂减排技术利用电能将过量的CO₂转化为有附加值的化学品,是解决能源危机、实现碳中和的有效途径之一.电催化CO₂还原反应(CO₂RR)中的多碳产物(C₂),如乙烯和乙醇,因其比C1产物具有更高的能量密度和更广泛的应用而受到较大关注.目前为止,Cu基催化剂被认为是获得C₂产物的独特材料.研究者在提高Cu基催化剂C₂产物的活性和选择性方面做了大量的工作,如催化剂形貌工程、活性位点设计和中间吸附性能调控等.许多理论和实验研究已经证明,Cu基催化剂上的C-C偶联过程是C₂产物生成的速率决定步骤.优化C-C偶联过程的能垒是提高C₂产物活性和选择性的重要而直接的策略.CO₂RR在Cu上是由CO₂还原吸附CO(*CO)并二聚生成C₂产物引起的.C-C偶联过程与*CO的吸附性能密切相关.众所周知,CO是一种典型的极性分子,因此其在催化剂表面的吸附性能可能会受到活性位点周围的局部电场的影响.构建合适的局部电场是调节CO吸附性能和C-C偶联过程的潜在手段之一.前期工作(Nature,2016,537,382-386)证明了高曲率金纳米针可以在尖端产生高的局部电场.高局域电场诱导K+聚集,使活性位点周围CO₂浓度升高,大大促进了Au纳米针上的CO生成.基于Au纳米针的局域电场促进了CO₂RR的CO生成.本文利用Cu纳米针促进并优化C-C偶联反应来提高C₂产物活性和选择性.结果表明,局部电场可以促进C-C偶联过程,进而增强CO₂电还原生成C₂产物.有限元模拟结果表明,高曲率铜纳米针处存在较强的局部电场;密度泛函理论计算结果表明,强电场能促进C-C耦合过程.在此基础上,制备了一系列不同曲率的Cu催化剂,其中,Cu纳米针(CuNNs)的曲率最高,Cu纳米棒(CuNRs)和Cu纳米颗粒(CuNPs)曲率次之.实验测得CuNNs上吸附的K+浓度最高,证明了纳米针上的局部电场最强.同时,CO吸附传感器测试表明,CuNNs对CO的吸附能力最强,原位傅里叶变换红外光谱显示,CuNNs的*COCO和*CO信号最强.由此可见,高曲率铜纳米针可以诱导高局部电场,从而促进C-C耦合过程.催化性能测试结果表明,在低电位(-0.6 V vs.RHE)下,Cu NNs对CO₂RR的生成C₂产物的法拉第效率值为44%,约为Cu NPs的2.2倍.综上,本文为CO₂RR过程中提高多碳产物提供了新的思路.

Electric-field promoted C-C coupling over Cu nanoneedles for CO2 electroreduction to C2 products

Cu-based catalysts are the most promising candidates for electrochemical CO2 reduction (CO2RR) to multi-carbon (C2) products. Optimizing the C-C coupling process, the rate-determining step for C2 product generation, is an important strategy to improve the production and selectivity of the C2 products. In this study, we determined that the local electric field can promote the C-C coupling reaction and enhance CO2 electroreduction to C2 products. First, finite-element simulations indicat-ed that the high curvature of the Cu nanoneedles results in a large local electric field on their tips. Density functional theory (DFT) calculations proved that a large electric field can promote C-C cou-pling. Motivated by this prediction, we prepared a series of Cu catalysts with different curvatures. The Cu nanoneedles (NNs) exhibited the largest number of curvatures, followed by the Cu nanorods (NRs), and Cu nanoparticles (NPs). The Cu NNs contained the highest concentration of adsorbed K+, which resulted in the highest local electric field on the needles. CO adsorption sensor tests indicated that the Cu NNs exhibited the strongest CO adsorption ability, and in-situ Fourier-transform infrared spectroscopy (FTIR) showed the strongest *COCO and *CO signals for the Cu NNs. These experi-mental results demonstrate that high-curvature nanoneedles can induce a large local electric field, thus promoting C-C coupling. As a result, the Cu NNs show a maximum FEC2 of 44％ for CO2RR at a low potential (-0.6 V vs. RHE), which is approximately 2.2 times that of the Cu NPs. This work pro-vides an effective strategy for enhancing the production of multi-carbon products during CO2RR.