Janotta Benjamin, Schalenbach Maximilian, Turiaux Marcel, Tempel Hermann, Eichel Rüdiger A
Fundamental Electrochemistry (IET-1), Forschungszentrum Jülich, Institute of Energy Technologies, Wilhelm-Johnen-Straße, 52425, Jülich, Germany.
Institute of Physical Chemistry, RWTH Aachen University, 52062, Aachen, Germany.
Sci Rep. 2025 Sep 12;15(1):32458. doi: 10.1038/s41598-025-18219-z.
In electrochemical processes, the pH values at the electrodes affect their potentials, reaction kinetics, product compositions, etc. However, predicting local pH values is complicated due to multi-ion movement between the electrodes and buffering effects of the electrolyte constituents. Here, local pH values in an electrochemical cell are studied with a combined model and experimental approach, focussing on buffering effects of supporting electrolytes. The simulated ion displacements are evaluated with optically measured pH values using a thymol blue pH indicator in a NaSO-based electrolyte. By including buffering reactions of the pH indicator in the ion transport simulation, the local pH value in the near-neutral area and its temporal change are in precise agreement with the measurements. Without this buffering effect, the simulated propagation velocities of the pH fronts increase as such homogeneous reactions are shown to reduce the ion fluxes and those of the accompanied reaction products. The effect of the ionic strength on the ion transport in multi-ion electrolytes is included by modelling electrolyte transport properties with the Mean Spherical Approximation. Finally, the effects of current density and supporting electrolyte concentration on local pH values are elucidated based on a parameter variation of the simulations presented.
在电化学过程中，电极处的pH值会影响其电位、反应动力学、产物组成等。然而，由于电极之间的多离子移动以及电解质成分的缓冲作用，预测局部pH值很复杂。在此，采用组合模型和实验方法研究了电化学电池中的局部pH值，重点关注支持电解质的缓冲作用。在基于NaSO的电解质中，使用百里酚蓝pH指示剂，通过光学测量的pH值评估模拟的离子位移。通过在离子传输模拟中纳入pH指示剂的缓冲反应，近中性区域的局部pH值及其随时间的变化与测量结果精确吻合。没有这种缓冲作用，pH前沿的模拟传播速度会增加，因为此类均相反应会降低离子通量以及伴随反应产物的通量。通过用平均球近似法对电解质传输特性进行建模，考虑了离子强度对多离子电解质中离子传输的影响。最后，基于所呈现模拟的参数变化，阐明了电流密度和支持电解质浓度对局部pH值的影响。
