Linear Free Energy Relationships in Hydrogen Evolution Catalysis by a Cobalt Tripeptide in Water
Linear Free Energy Relationships in Hydrogen Evolution Catalysis by a Cobalt Tripeptide in Water
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DOI：
10.1021/acsenergylett.1c00680
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发表时间：
2021-05-24
影响因子：
22
通讯作者：
Bren, Kara L.
中科院分区：
文献类型：
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作者：
Alvarez-Hernandez, Jose L.;Han, Ji Won;Bren, Kara L.
水是催化制氢的理想溶剂，但缓冲水中存在多个质子供体，使反应机制的分析变得复杂。在这里，我们确定了在 pK(a) 6.9 至 10.4 的缓冲液存在下，钴三肽 (CoGGH) 电催化析氢的底物依赖性速率常数。缓冲液 (k(HA)) 存在下的催化速率常数比水为唯一质子源时高 2 至 4 个数量级，表明缓冲酸作为质子供体胜过水。研究发现，CoGGH 催化的析氢速率取决于缓冲酸 pK(a)，且与 pH 值无关（从 pH 8 到 10）。发现了 k(HA) 和缓冲液酸 pK(a) 之间的布朗斯台德型线性自由能关系，支持与缓冲液共轭酸质子供体的协同质子耦合电子转移作为所用缓冲液的常见速率决定步骤。
Water is the desired solvent for catalytic hydrogen production, but the presence of multiple proton donors in buffered water complicates analysis of reaction mechanisms. Here, we determine substrate-dependent rate constants for electrocatalytic hydrogen evolution by a cobalt tripeptide (CoGGH) in the presence of buffers of pK(a) 6.9 to 10.4. Catalytic rate constants in the presence of buffer (k(HA)) are 2 to 4 orders of magnitude higher than when water is the sole proton source, indicating that buffer acid outcompetes water as a proton donor. The rate of hydrogen evolution catalyzed by CoGGH is found to be dependent on the buffer-acid pK(a) and independent of pH (from pH 8 to 10). A Bronsted-type linear free energy relationship between k(HA) and buffer-acid pK(a) is found, supporting a concerted proton-coupled electron transfer with a buffer conjugate acid proton donor as a common rate-determining step for the buffers used.