Interrogating Steady-State Multi-electron and Multi-step Reactions Mediated by an Electrocatalytic Heterogeneous Film

The development of new types of heterogeneous catalysts for fuel-forming electrochemical reactions has been a subject of research focus over the past decade. Despite recent huge progress in preparations of electrocatalytic materials, such as metal organic framework (MOF) and redox polymer, understanding the underlying microscopic mechanisms at play and the key rate-limiting step is still poor due to a lack of electrochemical analysis tools. Here, complete electrokinetic models for multi-electron redox reactions for heterogeneous electrocatalysis, including a monolayer (2D) and porous 3D film, are developed to comprehensively interrogate all relevant kinetic parameters, charge transport, substrate diffusion and catalysis. Therefore, the effects of these parameters on the resulting voltammograms can be analyzed and then the characteristic properties of electrocatalytic voltammograms are identified. In addition, the foot of the wave analysis, widely used to evaluate the catalytic performance of molecular catalysts in the homogeneous system, is also applied and found to be a useful tool to characterize the kinetic mechanism of the chemical steps. Based on these electrochemical methods and analysis, the MOF systems are evaluated to address the discrepancy among these kinetic parameters reported in the literature. Further design principles for catalytic MOF films and their theoretical performance are provided. Overall, these electrochemical methods presented here provide useful and feasible tools to benchmark heterogeneous electrocatalysts and characterize the key step that limits the electrocatalytic performance of MOFs and other heterogeneous systems.