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Cooperative electrocatalytic alcohol oxidation with electron-proton-transfer mediators

机译：电子质子转移介体的协同电催化醇氧化

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摘要

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) Cuitroxyl 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.
机译：醇的电化学氧化是能源和化学转化努力的重点，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）。这种类型的方法的小分子电催化剂是有希望进一步发展的目标（8），如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）。已显示与束缚胺类似的加氢酶活性位点的配合物（12）催化氢的产生（由质子和电子产生）的速率远超过此类酶（11,13）的速率，并介导可逆的电催化氢产生和氧化具有类似酶的性能（14）。电催化醇氧化的进展较为温和。已显示与用于氢氧化的那些类似的镍配合物可介导苯甲醇的有效电化学氧化，周转频率为每秒2.1。这些化合物与乙醇和甲醇的反应性较差（15）。有机硝基氧基，例如TEMPO（2,2,6,6-四甲基-1-哌啶N-氧基），是最广泛研究的醇氧化电催化剂（5-7,16-19）。这些催化剂在多种醇中均表现出良好的活性（每秒1-2次转换）（18），并有望用于有机合成（7）。然而，它们在能量转换应用中的使用受到产生反应性氧铵盐类物质所需的高电极电位的限制。在这里，我们报告了用于电化学醇氧化的（2,2'-联吡啶）铜/硝基甲苯助催化剂体系，其速率要快得多，而电极电位比仅TEMPO工艺所用的电位低半伏。 （2,2'-联吡啶）Cu（II）和TEMPO氧化还原伙伴表现出协同反应性，并利用低电势，质子耦合的TEMPO / TEMPOH氧化还原过程，而不是高电势的TEMPO / TEMPO +过程。结果表明，电子质子转移介体（如TEMPO）可与第一行过渡金属（如铜）结合使用，以实现高效的双电子电化学过程，从而为开发非质子交换体系引入了新概念。 -贵金属电催化剂。

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  • 来源
    《Nature》 |2016年第7612期|406-410|共5页
  • 作者

    Badalyan Artavazd; Stahl Shannon S.;

  • 作者单位

    Univ Wisconsin, Dept Chem, 1101 Univ Ave, Madison, WI 53706 USA;

    Univ Wisconsin, Dept Chem, 1101 Univ Ave, Madison, WI 53706 USA;

  • 收录信息 美国《科学引文索引》(SCI);美国《工程索引》(EI);美国《生物学医学文摘》(MEDLINE);美国《化学文摘》(CA);
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  • 正文语种 eng
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