Redox Hopping in Metal-Organic Frameworks through the Lens of the Scholz Model

Initially proposed by Lovric and Scholz to explain redox reactions in solid-phase voltammetry, the Scholz model's applications have expanded to redox reactions in various materials. As an extension of the Cottrell equation, the Scholz model enabled the quantification of electron hopping and ion diffusion with coefficients, D_e and D_i, respectively. Research utilizing the Scholz model indicated that, in most cases, a huge bottleneck results from the ion diffusion which is slower than electron hopping by orders of magnitude. Therefore, electron and ion motion can be tuned and optimized to increase the charge transport and conductivity through systematic investigations guided by the Scholz model. The strategy may be extended to other solid-state materials in the future, e.g., battery anodes/cathodes. In this Perspective, the applications of the Scholz model in different materials will be discussed. Moreover, the limitations of the Scholz model will also be introduced, and viable solutions to those limitations discussed.