Electrocatalytic reactions, such as oxygen reduction/evolution reactions and CO2 reduction reaction that are pivotal for the energy transition, are multi-step processes that occur in a nanoscale electric double layer (EDL) at a solid-liquid interface. Conventional analyses based on the Sabatier principle, using binding energies or effective electronic structure properties such as the d-band center as descriptors, are able to grasp overall trends in catalytic activity in specific groups of catalysts. However, thermodynamic approaches often fail to account for a plethora of electrolyte effects that arise in the EDL, including pH, cation, and anion effects. These effects have been observed to exert strong impacts on electrocatalytic reactions. There is growing consensus that the local reaction environment (LRE) in the EDL is the key to deciphering these complex and hitherto perplexing electrolyte effects. Increasing attention is thus paid to designing appropriate electrolytes, positioning the LRE at center stage. To this end, unraveling the LRE is becoming a new channel of delivering needed breakthroughs in electrochemical energy science. Theory and modeling are getting more and more important and powerful in addressing this multifaceted problem that involves physical phenomena at different scales and interacting in a multidimensional parametric space. Theoretical models developed for this purpose should treat intrinsic multistep kinetics of electrocatalytic reactions, EDL effects from sub-nm scale to the scale of 10 nm, and mass transport phenomena bridging scales from < 0.1 to 100 μm. Given the diverse physical phenomena and scales involved, it is evident that the challenge at hand surpasses the capabilities of any single theoretical or computational approach. In this thesis, I present a hierarchical theoretical framework to address the above challenge. It seamlessly integrates several modules: (i) microkinetic modelling that accounts for various reaction pathways; (ii) an LRE model that describes the interfacial region extending from the nanometric EDL continuously to the solution bulk; (iii) first-principles calculations that provide parameters, e.g., adsorption energies, activation barriers and EDL parameters. The microkinetic model considers all elementary steps without designating an a priori rate-determining step. The kinetics of these elementary steps are expressed in terms of local concentrations, potential, and electric field that are co-determined by EDL charging and mass transport in the LRE model. This framework has been applied to several crucial reactions, including electrochemical CO2 reduction, oxygen reduction/evolution reaction, and formic acid oxidation reaction, which has yielded vital insights on electrode kinetic phenomena, i.e., potential-dependent Tafel slopes, cation effects, and pH effects. This thesis provides means to navigate the intricate couplings among processes occurring across a wide spectrum of time constants and lengths, and is expected to contribute to a comprehensive understanding of the influence of multistep kinetics and local reaction conditions on electrocatalytic reactions.
Xinwei Zhu (Thu,) studied this question.