Selectivity Control under Dynamic CO2 Electroreduction Conditions

一氧化碳(CO2RR)在铜基电催化剂上的电还原可以获得大量的多碳(C2+)产物，从而为将其转化为有价值的原料化学品和燃料开辟了一条很有前途的途径。动态(电势脉冲)CO2RR最近受到了极大的关注，因为它允许在原位周期性地产生/恢复不同的催化剂状态和形态基序，为调节产品选择性和再生中毒的催化剂表面提供了新的可能性。然而，催化剂的活性状态及其动态演化仍然不清楚，动态CO2RR的详细机理还有待于阐明，我们将探索利用动态反应条件提高CO2RR对C2+产物的选择性。优化的条件将从广泛的电催化研究中确定，并通过操纵性时间分辨方法进行深入研究。我们的目标是确定动电位特性(脉冲形状、脉冲范围和脉冲周期)对催化剂选择性的影响。通过改变阳极电位(氧化和非氧化条件)和时间范围(从毫秒到小时)，可以对电极状态进行不同的修改，如表面电荷、吸附物种、氧化还原状态和表面形态的变化。除了纯的铜催化剂(Cu2O纳米立方体、铜单晶)外，我们还将研究那些修饰了二次金属纳米颗粒(Ag、Au、Zn)的催化剂用于串联催化。此外，我们还将探索化学物种(碱性阳离子、卤素阴离子)对机械途径的选择性促进/抑制作用。对于这两种情况，在恒电位条件下C2+的选择性都有所增加，我们将把这些研究扩展到动电位情况。为了更好地理解，将研究与电位有关的吸附几何结构、所涉及物种(中间体、抑制剂/促进剂)的表面浓度及其对铜结构的影响。在这些研究中，FHI和CAU团队将利用他们在操作技术方面的互补专业知识，包括各种光谱(拉曼、XAS)和X射线散射(粉末和表面X射线衍射)以及显微(STM/AFM)方法。这将对催化剂的结构、重要反应中间体(CO)和活性旁观者物种的吸附几何结构以及催化剂性能的动态变化提供全面的见解。这些洞察力将直接与催化活性和C2+选择性相关。此外，FHI小组将把所获得的理解转移到类似电解槽的气体流动池中。因此，我们将有助于从根本上理解C2+在CO2RR过程中的形成，特别是在动电位反应条件下。

Electroreduction of carbon monoxide (CO2RR) on Cu-based electrocatalysts can provide significant yields of multi-carbon (C2+) products and thus opens a promising way for its conversion into valuable feedstock chemicals and fuels. Dynamic (potential pulsed) CO2RR has recently received significant attention, as it allows to periodically generate/restore distinct catalyst states and morphological motifs in situ, offering new possibilities for tuning the product selectivity, and regenerating poisoned catalyst surfaces. However, the active catalyst state and its dynamic evolution are still unclear and the detailed mechanisms of dynamic CO2RR require clarification.We will explore enhancing the CO2RR selectivity towards C2+ products using dynamic reaction conditions. Optimized conditions will be identified from extensive electro¬catalytic studies and studied in-depth by operando time-resolved methods. We aim to identify the influence of the potentiodynamic charac¬teris¬tics (pulse shape, range, and period) on the catalyst selectivity. By varying the anodic potential (to oxidizing and non-oxidizing conditions) and time regime (from ms to hours) different modifications of the electrode’s state are possible, such as changes in the surface charge, adsorbed species, redox state, and surface morphology. We will identify how this can improve the evolution of the C2+ selectivity and overcome catalyst poisoning to ensure stable catalyst activitiy and selectivity.Apart from pure Cu catalysts (Cu2O nanocubes, Cu single crystals) we will also study those decorated with secondary metal nanoparticles (Ag, Au, Zn) for tandem catalysis. Further-more, we will explore the selective promotion/inhibition of mechanistic pathways by chemical species (alkali cations, halide anions). For both, an increase in C2+ selectivity under potentiostatic conditions has been shown and we will extend these studies to the potentiodynamic case. For an improved understanding, the potential-dependent adsorption geometries, surface concentrations of the involved species (intermediates, inhibitors/promotors) and their influence on the Cu structure will be studied.For these studies, the FHI and CAU teams will employ their complementary expertise in operando techniques comprising a variety of spectroscopic (Raman, XAS) and X-ray scattering (powder and surface X-ray diffraction) as well as microscopic (STM/AFM) methods. These will provide comprehensive insights into the catalyst structure, adsorption geometry of important reaction intermediates (CO) and active spectator species as well as the dynamic changes of the catalyst’s properties. These insights will be directly correlated to the catalytic activity and C2+ selectivity. Furthermore, the FHI group will transfer the obtained understanding to electrolyzer-like gas-fed flow cells. Thereby, we will significantly contribute to a fundamental understand on the C2+ formation during CO2RR and especially, under potentiodynamic reaction conditions.