Electrochemical reactions catalyzed by carbon dots from computational investigations: functional groups, dopants, and defects

Carbon dots (CDs) have attracted increasing attention due to their unique properties. Consequently, they have been demonstrated to be excellent multi-functional metal-free electrocatalysts, exhibiting an extraordinary catalytic performance compared with their conventional metal-based counterparts. In this review, we present a summary of the progress on electrochemical reactions, including hydrogen evolution reaction (HER), oxygen evolution reaction (OER), oxygen reduction reaction (ORR), carbon dioxide reduction reaction (CO2RR) and nitrogen reduction reaction (NRR) catalyzed by CDs or CD-derived materials based on computational simulations. The in-depth analysis establishes the correlation among electronic structure, catalyst geometry, and catalytic performance and provides possible strategies to tune the performance of these catalysts. For each investigated electrochemical reaction, DFT results are collected and analyzed to demonstrate the effects of functional groups, heteroatom dopants, and defects. In some cases, experimental studies will be discussed to complement the outcome from calculations. Functional groups such as oxygen ubiquitously exist on CDs, and thus the relation between functional group configuration and catalytic performance is examined and a possible solution for the calibration of different group properties simultaneously is suggested. The doping strategy as a common effective method to modulate the electrocatalytic performance of CDs mainly employs non-metals, transition metals, noble metals and their oxides as dopants. The general principle for the doping strategy is concluded based on available reports. Furthermore, due to the unsaturated coordination of CDs, defective sites including vacancies, edges, and dislocations are often very reactive during electrochemical reactions. Different from the previous experimental-oriented reviews, the focus of the current work is the nature of the active sites, the reaction pathway, and the description of the mechanism of catalytic reactions on CDs, which are fundamental for their rational optimization. The current review provides not only a timely account of the progress on CDs in key electrochemical reactions but also unique insights from theoretical computations for future optimization.