Influence of the metal center of metalloprotoporphyrins on the electrocatalytic CO2 reduction to formic acid
Influence of the metal center of metalloprotoporphyrins on the electrocatalytic CO2 reduction to formic acid
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DOI：
10.1016/j.cattod.2017.02.046
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发表时间：
2017-06-15
期刊：
影响因子：
5.3
通讯作者：
Koper, Marc T. M.
中科院分区：
文献类型：
--
作者：
Birdja, Yuvraj Y.;Shen, Jing;Koper, Marc T. M.
二氧化碳的电催化转化在高附加值化学品和太阳能燃料的合成中得到了广泛的关注。重要的问题，如高过电位和竞争的析氢仍然需要克服更深入地了解反应机理，以引导对特定产品的选择性。在本文中，我们报道了几种固定在热解石墨电极上的金属原卟啉，用于将二氧化碳选择性还原为甲酸。在pH 3的高氯酸溶液中，Cr-、Mn-、Co-和Fe-原卟啉上没有检测到甲酸，而Ni-、Pd-、Cu-和Ga-原卟啉上只有少量甲酸。Rh、In和Sn金属中心产生显著量的甲酸。然而，法拉第效率从1%到70%变化，这取决于金属中心、电解质的pH和施加的电势。甲酸对这些金属原卟啉的法拉第效率的分化与卟啉的析氢反应活性密切相关。Rh-原卟啉上的CO2还原被示出强烈耦合到析氢反应，而Sn-和In-原卟啉上的两个反应之间的这种强烈耦合是不存在的。析氢活性以In < Sn < Rh金属中心的顺序增加，导致甲酸的法拉第效率以Rh < Sn < In金属中心的顺序增加。铟原卟啉是最稳定的，并显示出高的法拉第效率的ca。70%，在9.6的pH和相对于RHE的-1.9V的电势下。在碳酸氢盐电解质中进行实验，试图定性研究碳酸氢盐在甲酸形成中的作用。(C)2017作者（S）由爱思唯尔公司出版
Electrocatalytic conversion of carbon dioxide has gained much interest for the synthesis of value-added chemicals and solar fuels. Important issues such as high overpotentials and competition of hydrogen evolution still need to be overcome for deeper insight into the reaction mechanism in order to steer the selectivity towards specific products. Herein we report on several metalloprotoporphyrins immobilized on a pyrolytic graphite electrode for the selective reduction of carbon dioxide to formic acid. No formic acid is detected on Cr-, Mn-, Co- and Fe-protoporphyrins in perchloric acid of pH 3, while Ni-, Pd-, Cu and Ga-protoporphyrins show only a little formic acid. Rh, In and Sn metal centers produce significant amounts of formic acid. However, the faradaic efficiency varies from 1% to 70% depending on the metal center, the pH of the electrolyte and the applied potential. The differentiation of the faradaic efficiency for formic acid on these metalloprotoporphyrins is strongly related to the activity of the porphyrin for the hydrogen evolution reaction. CO2 reduction on Rh-protoporphyrin is shown to be coupled strongly to the hydrogen evolution reaction, whilst on Sn-and In-protoporphyrin such strong coupling between the two reactions is absent. The activity for the hydrogen evolution increases in the order In < Sn < Rh metal centers, leading to faradaic efficiency for formic acid increasing in the order Rh < Sn < In metal centers. In-protoporphyrin is the most stable and shows a high faradaic efficiency of ca. 70%, at a pH of 9.6 and a potential of -1.9V vs RHE. Experiments in bicarbonate electrolyte were performed in an attempt to qualitatively study the role of bicarbonate in formic acid formation. (C) 2017 The Author(s). Published by Elsevier B.V.