Interrogating Steady-State\nMultielectron and Multistep\nReactions Mediated by an Electrocatalytic Heterogeneous Film

The development of\nnew types of heterogeneous electrocatalysts,\nsuch as metal–organic frameworks (MOFs) and redox polymers,\noffers a promising approach for promoting sustainable fuel-forming\nelectrochemical reactions. Despite advancements in the preparations\nof these electrocatalytic materials, understanding the underlying\nmicroscopic mechanisms at play and the key rate-limiting step is still\npoor due to a lack of suitable electrochemical analysis tools. Here,\ncomplete electrokinetic models for multielectron redox reactions for\nheterogeneous electrocatalysis, including a monolayer (2D) and a 3D\nfilm, are developed to comprehensively interrogate all relevant kinetic\nparameters, including charge transport, substrate diffusion, chemical\ncatalysis, and interfacial charge transfer. Therefore, the impacts\nof these parameters on the resulting steady-state voltammograms can\nbe analyzed systematically, and then the characteristic features of\ndifferent scenarios are identified for understanding the nature of\nthe rate-limiting step. In addition, the foot of the wave analysis,\nwidely used to evaluate the catalytic performance of molecular catalysts\nin the homogeneous system, is also applied and is found to be a useful\ntool to elucidate the kinetic mechanism of the chemical steps. Finally,\nthe design principles for catalytic MOF films and their theoretical\nperformance based on literature results are further re-evaluated.\nOverall, these electrokinetic methods presented here provide useful\nand feasible tools to benchmark heterogeneous electrocatalysts and\ncharacterize the key step that limits the electrocatalytic performance\nof MOFs and other heterogeneous systems.