Citation: Rotundo, L.; Barbero, A.; Nervi, C.; Gobetto, R. CO 2 Electroreduction on Carbon-Based Electrodes Functionalized with Molecular Organometallic Complexes—A Mini Review. Catalysts 2022, 12, 1448. https:// doi.org/10.3390/catal12111448 Academic Editor: Ruitao Lv Received: 19 October 2022 Accepted: 14 November 2022 Published: 16 November 2022 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). catalysts Review CO 2 Electroreduction on Carbon-Based Electrodes Functionalized with Molecular Organometallic Complexes—A Mini Review Laura Rotundo 1,2,† , Alice Barbero 1,2 , Carlo Nervi 1,2, * and Roberto Gobetto 1,2, * 1 Department of Chemistry and NIS Center, University of Turin, Via P. Giuria 7, 10125 Turin, Italy 2 Centro Interuniversitario di Reattività Chimica e Catalisi (CIRCC), Via Celso Ulpiani 27, 70126 Bari, Italy * Correspondence: carlo.nervi@unito.it (C.N.); roberto.gobetto@unito.it (R.G.) † Current address: Chemistry Division Brookhaven National Laboratory, Upton, New York, NY 11973-5000, USA. Abstract: Heterogeneous electrochemical CO 2 reduction has potential advantages with respect to the homogeneous counterpart due to the easier recovery of products and catalysts, the relatively small amounts of catalyst necessary for efficient electrolysis, the longer lifetime of the catalysts, and the elimination of solubility problems. Unfortunately, several disadvantages are also present, including the difficulty of designing the optimized and best-performing catalysts by the appropriate choice of the ligands as well as a larger heterogeneity in the nature of the catalytic site that introduces differences in the mechanistic pathway and in electrogenerated products. The advantages of homogeneous and heterogeneous systems can be preserved by anchoring intact organometallic molecules on the electrode surface with the aim of increasing the dispersion of active components at a molecular level and facilitating the electron transfer to the electrocatalyst. Electrode functionalization can be obtained by non-covalent or covalent interactions and by direct electropolymerization on the electrode surface. A critical overview covering the very recent literature on CO 2 electroreduction by intact organometallic complexes attached to the electrode is summarized herein, and particular attention is given to their catalytic performances. We hope this mini review can provide new insights into the development of more efficient CO 2 electrocatalysts for real-life applications. Keywords: CO 2 ; electroreduction; molecular catalysts; covalent immobilization; non-covalent immobilization; electropolymerization; carbon nanotubes; carbon cloth; glassy carbon 1. Introduction Global climate change generated by anthropogenic emission of CO 2 represents a major challenge for our society. Among various approaches, including chemical, electrochemi- cal, and photochemical techniques, the electrochemical conversion of carbon dioxide into added-value chemicals mediated by catalysts using renewable electricity has attracted growing interest in recent years. Particularly interesting is the production of several liquid fuels in which CO 2 and hydrogen can be converted, such as methanol, light hydrocar- bons, formic acid, dimethyl ether, etc. Recent decades have witnessed great advances in the field of electrochemical CO 2 reduction reaction (CO 2 RR), but for applications on an industrial scale, many potential drawbacks should be taken into account: the excessive overpotential, the poor selectivity for the desired products, and, concerning the catalyst, limited efficiency, low stability, and high costs. Different categories of electrocatalysts have been investigated, including metal oxides, chalcogenides, nitrogen-doped carbons, and transition metal complexes [1–12]. The reduction products of CO 2 are generally classified as C 1 ,C 2 , ... ,C n , where n indicates the number of carbon atoms in the product. Derivatives with n = 1 are by far the easiest to obtain in term of faradaic efficiency (FE), turnover number (TON), and turnover Catalysts 2022, 12, 1448. https://doi.org/10.3390/catal12111448 https://www.mdpi.com/journal/catalysts