Identifying and Breaking Scaling Relations in Molecular Catalysis of Electrochemical Reactions
Identifying and Breaking Scaling Relations in Molecular Catalysis of Electrochemical Reactions
复制标题
DOI：
10.1021/jacs.7b05642
复制
发表时间：
2017-08-16
影响因子：
15
通讯作者：
Mayer, James M.
中科院分区：
文献类型：
--
作者：
Pegis, Michael L.;Wise, Catherine F.;Mayer, James M.
改进重要的电化学质子耦合电子转移（PCET）反应的分子催化，例如H+/H-2、O-2/H2O、CO2/CO和N-2/NH3的相互转化，是一个持续的挑战。对分子催化剂的合成改性是有价值的，但通常显示出转换频率（TOF）和引发催化所需的有效过电位（eta（eff））之间的权衡。在这里，我们得到了一个新的方法来提高效率-更高的飞行时间在较低的eta（eff）-通过改变反应物和产品的浓度和性质，而不是通过修改催化剂。TOF对eta（eff）的依赖性显示出在改变例如酸HA的pK（a）对反应物或产物的浓度或分压时相当不同。以DMF中铁卟啉催化的分子氧的电化学还原为例，[HA]降低10倍会使eta（eff）降低59 mV，TOF降低10倍。或者，K-a（HA）降低10倍也会使eta（eff）降低59 mV，但TOF仅降低2倍。这种方法已被用来提高催化TOF的10（4）与以前报道的缩放关系，通过合成改性的催化剂。该分析有可能预测任何分子PCET催化剂的效率和产物选择性的提高，基于其机理和速率定律。
Improving molecular catalysis for important electrochemical proton-coupled electron transfer (PCET) reactions, such as the interconversions of H+/H-2, O-2/H2O, CO2/CO, and N-2/NH3, is an ongoing challenge. Synthetic modifications to the molecular catalysts are valuable but often show trade-offs between turnover frequency (TOF) and the effective overpotential required to initiate catalysis (eta(eff)). Herein, we derive a new approach for improving efficiencies-higher TOF at lower eta(eff)-by changing the concentrations and properties of the reactants and products, rather than by modifying the catalyst. The dependence of TOF on eta(eff) is shown to be quite different upon changing, for instance, the pK(a) of the acid HA versus the concentration or partial pressure of a reactant or product. Using the electrochemical reduction of dioxygen catalyzed by iron porphyrins in DMF as an example, decreasing [HA] 10-fold lowers eta(eff) by 59 mV and decreases the TOF by a factor of 10. Alternatively, a 10-fold decrease in K-a(HA) also lowers eta(eff) by 59 mV but only decreases the TOF by a factor of 2. This approach has been used to improve a catalytic TOF by 10(4) vs the previously reported scaling relationship developed via synthetic modifications to the catalyst. The analysis has the potential to predict improved efficiency and product selectivity of any molecular PCET catalyst, based on its mechanism and rate law.