We studied ion concentration profiles and the charge density gradient caused by electrode reactions in weak electrolytes by using the Poisson–Nernst–Planck equations without assuming charge neutrality. In weak electrolytes, only a small fraction of molecules is ionized in bulk. Ion concentration profiles depend on not only ion transport but also the ionization of molecules. We considered the ionization of molecules and ion association in weak electrolytes and obtained analytical expressions for ion densities, electrostatic potential profiles, and ion currents. We found the case that the total ion density gradient was given by the Kuramoto length which characterized the distance over which an ion diffuses before association. The charge density gradient is characterized by the Debye length for 1:1 weak electrolytes. We discuss the role of these length scales for efficient water splitting reactions using photo-electrocatalytic electrodes.

我们通过使用Poisson-Nernst-Planck方程研究了弱电解质中电极反应引起的离子浓度分布和电荷密度梯度，而没有假设电荷中性。在弱电解质中，只有一小部分分子被大量电离。离子浓度分布不仅取决于离子传输，还取决于分子的电离。我们考虑了弱电解质中分子的电离和离子缔合，并获得了离子密度，静电势分布和离子电流的解析表达式。我们发现了总离子密度梯度由仓本长度给出的情况，仓本长度表征了离子在缔合之前扩散的距离。电荷密度梯度的特征在于1：1弱电解质的德拜长度。