Cooperative electrocatalytic alcohol oxidation with electron-proton-transfer mediators
Cooperative electrocatalytic alcohol oxidation with electron-proton-transfer mediators
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DOI：
10.1038/nature18008
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发表时间：
2016-07-21
期刊：
影响因子：
64.8
通讯作者：
Stahl, Shannon S.
中科院分区：
文献类型：
--
作者：
Badalyan, Artavazd;Stahl, Shannon S.
醇的电化学氧化是能量和化学转化工作的主要焦点，其潜在应用范围从燃料电池到生物质利用和精细化学合成（1-7）。用于这类工艺的小分子电催化剂是有希望进一步开发的目标（8），如用于电化学生产和氢氧化的镍催化剂的最新进展所证明的（9-11）。类似于氢化酶活性位点的具有束缚胺的复合物（12）已经显示出以远远超过这些酶的速率催化氢产生（从质子和电子）（11，13），并且以酶样性能介导可逆电催化氢产生和氧化（14）。电催化醇氧化的进展较为温和。镍络合物类似于用于氢氧化的那些，已被证明可以介导苯甲醇的有效电化学氧化，其周转频率为每秒2.1次。然而，这些化合物与乙醇和甲醇的反应性较差（15）。有机硝酰基，例如克里思（2，2，6，6-四甲基-1-哌啶N-氧基），是用于醇氧化的最广泛研究的电催化剂（5- 7，16 -19）。这些催化剂对各种醇表现出良好的活性（每秒1-2次转换）（18），并且在电有机合成中具有很大的前景（7）。然而，它们在能量转换应用中的使用受到产生反应性氧代铵物质所需的高电极电位的限制。在这里，我们报告（2，2 '-联吡啶）铜/硝酰基的电化学醇氧化的助催化剂系统，进行更快的速度，同时在电极电位比用于TEMPO的过程中使用的半伏低。（2，2 '-联吡啶）Cu（II）和克里思氧化还原配偶体表现出协同反应性，并利用低电位、质子耦合的克里思/TEMPO H氧化还原过程，而不是高电位的克里思/克里思+过程。结果表明，如何电子-质子转移介质，如克里思，可用于与第一行过渡金属，如铜，以实现有效的双电子电化学过程，从而引入一个新的概念，为非贵金属电催化剂的发展。
The electrochemical oxidation of alcohols is a major focus of energy and chemical conversion efforts, with potential applications ranging from fuel cells to biomass utilization and fine-chemical synthesis(1-7). Small-molecule electrocatalysts for processes of this type are promising targets for further development(8), as demonstrated by recent advances in nickel catalysts for electrochemical production and oxidation of hydrogen(9-11). Complexes with tethered amines that resemble the active site of hydrogenases(12) have been shown both to catalyse hydrogen production (from protons and electrons) with rates far exceeding those of such enzymes(11,13) and to mediate reversible electrocatalytic hydrogen production and oxidation with enzyme-like performance(14). Progress in electrocatalytic alcohol oxidation has been more modest. Nickel complexes similar to those used for hydrogen oxidation have been shown to mediate efficient electrochemical oxidation of benzyl alcohol, with a turnover frequency of 2.1 per second. These compounds exhibit poor reactivity with ethanol and methanol, however(15). Organic nitroxyls, such as TEMPO (2,2,6,6-tetramethyl-1-piperidine N-oxyl), are the most widely studied electrocatalysts for alcohol oxidation(5-7,16-19). These catalysts exhibit good activity (1-2 turnovers per second) with a wide range of alcohols(18) and have great promise for electro-organic synthesis(7). Their use in energy-conversion applications, however, is limited by the high electrode potentials required to generate the reactive oxoammonium species. Here we report (2,2'-bipyridine) Cu/nitroxyl co-catalyst systems for electrochemical alcohol oxidation that proceed with much faster rates, while operating at an electrode potential a half-volt lower than that used for the TEMPO-only process. The (2,2'-bipyridine) Cu(II) and TEMPO redox partners exhibit cooperative reactivity and exploit the low-potential, proton-coupled TEMPO/TEMPOH redox process rather than the high-potential TEMPO/TEMPO+ process. The results show how electron-proton-transfer mediators, such as TEMPO, may be used in combination with first-row transition metals, such as copper, to achieve efficient two-electron electrochemical processes, thereby introducing a new concept for the development of non-precious-metal electrocatalysts.