Department of Chemistry, University of Rochester, Rochester, New York 14627-0216, United States.
Inorg Chem. 2020 Jun 15;59(12):8061-8069. doi: 10.1021/acs.inorgchem.0c00362. Epub 2020 May 21.
The effect of buffer p on the mechanism of electrochemical hydrogen evolution catalyzed by a cobalt porphyrin peptide (CoMP11-Ac) at constant pH is presented. The addition of buffer to CoMP11-Ac in water and KCl leads to an enhancement of the catalytic current of up to 200-fold relative to its value in the absence of a buffer. Two distinct catalytic regimes are identified as a function of the buffer p. In the presence of buffers with p ≤ 7.4, a fast catalysis regime limited by diffusion of buffer is reached. The catalytic half-wave potential () shifts anodically (from -1.42 to -1.26 V vs Ag/AgCl/KCl) as the buffer p decreases from 7.4 to 5.6, proposed to result from fast Co(III)-H formation following the catalysis-initiating Co(II/I) reduction. With higher-p buffers (p > 7.7), an = -1.42 V, proposed to reflect the Co(II/I) couple, is maintained independent of the buffer p, consistent with rate-limiting Co(III)-H formation under these conditions. We conclude that the buffer species p impacts catalytic current and potential and the rate-determining step of the reaction.
在恒 pH 条件下，研究了缓冲剂 p 对钴卟啉肽（CoMP11-Ac）电化学析氢催化机制的影响。在水中和 KCl 中加入缓冲剂会使 CoMP11-Ac 的催化电流相对于没有缓冲剂时增强 200 倍。随着缓冲剂 p 值的降低（从 7.4 降至 5.6），确定了两个不同的催化区。在 p 值≤7.4 的缓冲剂存在下，达到了受缓冲扩散限制的快速催化区。催化半波电位（）向阳极移动（从-1.42 至-1.26 V vs Ag/AgCl/KCl），这是由于在催化起始的 Co(II/I)还原后，快速形成 Co(III)-H。对于更高 p 值的缓冲剂（p＞7.7），= -1.42 V，这被认为反映了 Co(II/I)对，与缓冲 p 无关，与这些条件下 Co(III)-H 形成的速率限制步骤一致。我们得出结论，缓冲剂种类 p 会影响催化电流和电位以及反应的速率决定步骤。
