Manganese Electrocatalysts with Bulky Bipyridine Ligands: Utilizing Lewis Acids To Promote Carbon Dioxide Reduction at Low Overpotentials
Manganese Electrocatalysts with Bulky Bipyridine Ligands: Utilizing Lewis Acids To Promote Carbon Dioxide Reduction at Low Overpotentials
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DOI：
10.1021/jacs.5b12215
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发表时间：
2016-02-03
影响因子：
15
通讯作者：
Kubiak, Clifford P.
中科院分区：
文献类型：
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作者：
Sampson, Matthew D.;Kubiak, Clifford P.
稀土锰联吡啶（bpy）配合物是质子耦合二氧化碳（CO2）还原为一氧化碳（CO）的分子电催化剂。最近，一个庞大的联吡啶配体，6，6 '-dimesityl-2，2'-bipyridine（mesbpy），用于显着降低所需的潜力，以获得这些锰催化剂的双还原状态，通过消除他们的能力，二聚后的一个电子还原。尽管这种Mn mesbpy催化剂在非常低的电势下结合CO2，但需要在显著更高的负电势下还原所得Mn（I）-COOH络合物以实现快速催化速率。在不还原Mn（I）-COOH的情况下，催化经由Mn（I）-COOH的交替催化途径质子化以形成阳离子四羰基络合物而缓慢发生。我们报道了使用刘易斯酸，特别是Mg 2+阳离子，以在这些低过电位（即，与CO2相同的电势，结合）：CO2的还原发生在分子电催化剂所报道的最低过电势之一（η = 0.3-0.45 V）。在Mg ~（2+）存在下，催化作用通过2CO（2）+2 e（-）-> CO和CO ~（3 2-）的还原性缩合反应进行。通过使用可变浓度循环伏安法，红外光谱电化学，和本体电解研究的催化机理的见解。将添加Mg ~（2+）的[Mn（mesbpy）（CO）（3）（MeCN）]（OTf）的催化Tafel行为（对数转换频率与过电位关系）与其它通常研究的CO_2还原催化剂进行比较。
Earth-abundant manganese bipyridine (bpy) complexes are well-established molecular electrocatalysts for proton-coupled carbon dioxide (CO2) reduction to carbon monoxide (CO). Recently, a bulky bipyridine ligand, 6,6'- dimesityl-2,2'-bipyridine (mesbpy), was utilized to significantly lower the potential necessary to access the doubly reduced states of these manganese catalysts by eliminating their ability to dimerize after one-electron reduction. Although this Mn mesbpy catalyst binds CO2, at very low potentials, reduction of a resulting Mn(I)-COOH complex at significantly more, negative potentials is required to achieve fast catalytic rates. Without reduction of Mn(I)-COOH, catalysis occurs slowly via a alternate catalytic pathway protonation of Mn(I)-COOH to form a cationic tetracarbonyl complex. We report the use of Lewis, acids, specifically Mg2+ cations, to significantly increase the rate of catalysis (by over 10-fold) at these low overpotentials (i.e., the same potential as CO2, binding): Reduction of CO2, occurs at one of the lowest overpotentials ever reported for molecular electrocatalysts (eta = 0.3-0.45 V). With Mg2+, catalysis proceeds via a reductive disproportionation reaction of 2CO(2) + 2e(-) -> CO and CO32-. Insights into the catalytic mechanism were gained by using variable concentration cyclic voltammetry, infrared spectroelectrochemistry, and bulk electrolysis studies. The catalytic Tafel behavior (log turnover frequency vs overpotential relationship) of [Mn(mesbpy)(CO)(3)(MeCN)](OTf) with added Mg2+ is compared with those of other commonly studied CO2, reduction catalysts.