Sorbonne Paris Cité, Laboratoire d'Electrochimie Moléculaire, Unité Mixte de Recherche Université - CNRS no. 7591, Université Paris Diderot , Bâtiment Lavoisier, 15 rue Jean de Baïf, 75205 Paris Cedex 13, France.
IC2MP UMR-CNRS 7285, Université de Poitiers , 4 rue Michel Brunet, TSA 51106, 86073 Poitiers Cedex 9, France.
J Am Chem Soc. 2017 Oct 4;139(39):13922-13928. doi: 10.1021/jacs.7b08028. Epub 2017 Sep 25.
In the framework of modern energy challenges, the reduction of CO into fuels calls for electrogenerated low-valent transition metal complexes catalysts designed with considerable ingenuity and sophistication. For this reason, the report that a molecule as simple as protonated pyridine (PyH) could catalyze the formation of methanol from the reduction of CO on a platinum electrode triggered great interest and excitement. Further investigations revealed that no methanol is produced. It appears that CO is not really reduced but rather participates, on the basis of its aquation into carbonic acid, in hydrogen evolution. Actually, the situation is not that straightforward, as revealed by scrutinizing what happens at the platinum electrode surface. The present study confirms the lack of methanol formation upon bulk electrolysis of PyH solutions at Pt and provides a detailed account of the Faradaic yield for H production as a function of the electrode potential, but the main finding is that CO reduction is accompanied by a strong inhibition of the electrode process taking place when it is carried out in the presence of acids such as PyH and AcOH. Cyclic voltammetry and in situ infrared spectroscopy were closely combined to investigate and understand the nature and consequences of the inhibition process. Constant comparison between the two acids was required to decipher the course of the reaction owing to the fact that the IR responses are perturbed by PyH adsorption. It finally appears that inhibition is caused by the reduction of CO into CO, whose high affinity with platinum triggers the formation of a Pt-CO film that prevents the reaction process. Thus, a paradoxical situation develops in which the high affinity of Pt for CO helps to decrease the overpotential for the reduction of CO and therefore blocks the electrode, preventing the reaction process.
在现代能源挑战的框架下，将 CO 还原为燃料需要设计具有相当巧妙性和复杂性的电生成低价过渡金属配合物催化剂。出于这个原因，当报道称像质子化吡啶（PyH）这样简单的分子可以在铂电极上通过 CO 的还原来催化甲醇的形成时，引起了极大的兴趣和兴奋。进一步的研究表明并没有甲醇生成。似乎 CO 并没有真正被还原，而是在其水合形成碳酸的基础上，参与了析氢反应。实际上，如在铂电极表面进行仔细观察所揭示的那样，情况并非如此简单。本研究证实了在 Pt 上进行 PyH 溶液的批量电解时没有甲醇形成，并详细说明了电极电位对 H 生产的法拉第产率的影响，但主要发现是 CO 还原伴随着在存在像 PyH 和 AcOH 这样的酸时进行电极过程的强烈抑制。循环伏安法和原位红外光谱紧密结合，以研究和理解抑制过程的性质和后果。由于 IR 响应受到 PyH 吸附的干扰，需要对两种酸进行恒定比较，以解析反应过程。最终表明，抑制是由 CO 还原为 CO 引起的，CO 与铂的高亲和力引发了 Pt-CO 膜的形成，从而阻止了反应过程。因此，一种自相矛盾的情况出现了，即 Pt 对 CO 的高亲和力有助于降低 CO 还原的超电势，从而阻止了电极，阻止了反应过程。
