The utilization of CO₂ via electrochemical reduction constitutes a promising approach toward production of value-added chemicals or fuels using intermittent renewable energy sources. For this purpose, molecular electrocatalysts are frequently studied and the recent progress both in tuning of the catalytic properties and in mechanistic understanding is truly remarkable. While in earlier years research efforts were focused on complexes with rare metal centers such as Re, Ru, and Pd, the focus has recently shifted toward earth-abundant transition metals such as Mn, Fe, Co, and Ni. By application of appropriate ligands, these metals have been rendered more than competitive for CO₂ reduction compared to the heavier homologues. In addition, the important roles of the second and outer coordination spheres in the catalytic processes have become apparent, and metal–ligand cooperativity has recently become a well-established tool for further tuning of the catalytic behavior. Surprising advances have also been made with very simple organocatalysts, although the mechanisms behind their reactivity are not yet entirely understood. Herein, the developments of the last three decades in electrocatalytic CO₂ reduction with homogeneous catalysts are reviewed. A discussion of the underlying mechanistic principles is included along with a treatment of the experimental and computational techniques for mechanistic studies and catalyst benchmarking. Important catalyst families are discussed in detail with regard to mechanistic aspects, and recent advances in the field are highlighted.

中文翻译：

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二氧化碳的均相催化电还原—方法，机理和催化剂

通过电化学还原利用CO ₂构成了一种使用间歇性可再生能源生产增值化学品或燃料的有前途的方法。为此目的，经常研究分子电催化剂，并且在催化性质的调节和机理理解上的最新进展确实是非常显着的。早些年，虽然研究工作集中在稀土金属中心（例如Re，Ru和Pd）的配合物上，但最近的工作重点已转移到了富含稀土的过渡金属（例如Mn，Fe，Co和Ni）上。通过使用适当的配体，这些金属已具有超过CO ₂竞争性的优势。与较重的同系物相比减少。此外，第二和外部配位球在催化过程中的重要作用已经变得很明显，并且金属-配体的协同作用最近已成为一种完善的工具，可用于进一步调节催化性能。尽管尚未完全理解其反应性背后的机理，但非常简单的有机催化剂也取得了令人惊讶的进展。本文中，近三十年来电催化CO _2的发展审查了均相催化剂的还原反应。包括对基本机械原理的讨论，以及对用于机械研究和催化剂基准测试的实验和计算技术的处理。关于机械方面，对重要的催化剂家族进行了详细讨论，并着重指出了该领域的最新进展。