An In Situ Surface-Enhanced Infrared Absorption Spectroscopy Study of Electrochemical CO2 Reduction: Selectivity Dependence on Surface C-Bound and O-Bound Reaction Intermediates
An In Situ Surface-Enhanced Infrared Absorption Spectroscopy Study of Electrochemical CO2 Reduction: Selectivity Dependence on Surface C-Bound and O-Bound Reaction Intermediates
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DOI：
10.1021/acs.jpcc.8b09598
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发表时间：
2019-03-14
影响因子：
3.7
通讯作者：
Shao-Horn, Yang
中科院分区：
文献类型：
--
作者：
Katayama, Yu;Nattino, Francesco;Shao-Horn, Yang
二氧化碳电还原反应(CO2RR)除了是一种有吸引力的间歇性可再生能源储存方法外，还是一种将温室气体转化为高价值燃料和化学品的有前途的途径。尽管长期以来，多晶铜表面在催化二氧化碳转化为碳氢化合物(CH4、C2H4等)等更高阶的C1和C2燃料方面一直被认为是独一无二的。和醇(CH3OH、C2H5OH)，产品的选择性仍然是一个挑战。合理设计更具选择性的催化剂将极大地受益于从机理上理解二氧化碳的复杂、多质子和多电子转化。在本研究中，我们选择了三种金属催化剂(铂、金、铜)，应用原位表面增强红外吸收光谱(SEIRAS)和常压X射线光电子能谱(APXPS)，结合密度泛函理论(DFT)计算，对CO2RR的反应途径进行了深入的研究。我们提出了CO2RR的综合反应机理，并从金属-碳(M-C)和金属-氧(M-O)亲和力的角度对优先反应途径进行了合理化。结果表明，最终产物由初始中间体C-键和O-键的构型决定，这两个中间体分别可以从CO2和(H)CO3中得到。C1烃是通过OCH3生产的，从O-键CO3和Ad获得的中间体，需要对O-键中间体具有相对高亲和力的催化剂。此外，C2烃的生成是由于C-键Coad和(H)Coad之间的C-C偶联，这需要对C-键物种有最佳的亲和力，因此可以在不毒化催化剂表面的情况下进一步还原(H)Coad。结果表明，C_1醇(CH3OH)的生成是最具挑战性的优化过程，因为O-键物种的稳定既会加速关键中间体(OCH3，ad)的形成，同时也会抑制它们从催化剂表面脱附。我们的发现为基于已确定的实验/理论反应机理的具有更高选择性的CO2RR催化剂的设计策略铺平了道路。这些结果还表明，设计催化剂的电子结构并不是实现高选择性CO2RR催化的唯一决定因素；相反，调整额外的实验反应条件，如电解液-中间体相互作用也变得至关重要。
The CO2 electroreduction reaction (CO2RR) is a promising avenue to convert greenhouse gases into high-value fuels and chemicals, in addition to being an attractive method for storing intermittent renewable energy. Although polycrystalline Cu surfaces have long been known to be unique in their capabilities of catalyzing the conversion of CO2 to higher-order C1 and C2 fuels, such as hydrocarbons (CH4, C2H4, etc.) and alcohols (CH3OH, C2H5OH), product selectivity remains a challenge. Rational design of more selective catalysts would greatly benefit from a mechanistic understanding of the complex, multiproton, and multielectron conversion of CO2. In this study, we select three metal catalysts (Pt, Au, Cu) and apply in situ surface enhanced infrared absorption spectroscopy (SEIRAS) and ambient-pressure X-ray photoelectron spectroscopy (APXPS), coupled to density-functional theory (DFT) calculations, to get insight into the reaction pathway for the CO2RR We present a comprehensive reaction mechanism for the CO2RR and show that the preferential reaction pathway can be rationalized in terms of metal-carbon (M-C) and metal-oxygen (M-O) affinity. We show that the final products are determined by the configuration of the initial intermediates, C-bound and O-bound, which can be obtained from CO2 and (H)CO3, respectively. C1 hydrocarbons are produced via OCH3,ad intermediates obtained from O-bound CO3,ad and require a catalyst with relatively high affinity for O-bound intermediates. Additionally, C2 hydrocarbon formation is suggested to result from the C-C coupling between C-bound COad and (H)COad, which requires an optimal affinity for the C-bound species, so that (H)COad can be further reduced without poisoning the catalyst surface. It is suggested that the formation of C1 alcohols (CH3OH) is the most challenging process to optimize, as stabilization of the O-bound species would both accelerate the formation of key intermediates (OCH3,ad) but also simultaneously inhibit their desorption from the catalyst surface. Our findings pave the way toward a design strategy for CO2RR catalysts with improved selectivity, based on the experimental/theoretical reaction mechanisms that have been identified. These results also suggest that designing the electronic structure of the catalyst is not the sole determining factor to achieve highly selective CO2RR catalysis; rather, tuning additional experimental reaction conditions such as electrolyte-intermediate interactions also become critical.