Electroreduction of carbon dioxide (CO ₂ ) or carbon monoxide (CO) toward C ₂₊ hydrocarbons such as ethylene, ethanol, acetate and propanol represents a promising approach toward carbon-negative electrosynthesis of chemicals. Fundamental understanding of the carbon─carbon (C-C) coupling mechanisms in these electrocatalytic processes is the key to the design and development of electrochemical systems at high energy and carbon conversion efficiencies. Here, we report the investigation of CO electreduction on single-atom copper (Cu) electrocatalysts. Atomically dispersed Cu is coordinated on a carbon nitride substrate to form high-density copper─nitrogen moieties. Chemisorption, electrocatalytic, and computational studies are combined to probe the catalytic mechanisms. Unlike the Langmuir-Hinshelwood mechanism known for copper metal surfaces, the confinement of CO adsorption on the single-copper-atom sites enables an Eley-Rideal type of C-C coupling between adsorbed (*CO) and gaseous [CO(g)] carbon moxide molecules. The isolated Cu sites also selectively stabilize the key reaction intermediates determining the bifurcation of reaction pathways toward different C ₂₊ products.

The electrocatalytic reduction of CO₂coupled with the oxidation of 5-hydroxymethylfurfural in a single cell based on molecular catalysts was successfully conducted with high faradaic efficiency, which could successfully be driven by solar energy.

Metal–organic frameworks (MOFs) are used in catalysis due to their high specific surface area and porous structure. The dispersed active sites and limited reaction space that render MOFs have the potential for highly selective electrocatalytic CO₂ reduction reaction (ECO₂RR). Meanwhile, formic acid (HCOOH) is attracting attention as a liquid product with high economic benefits. This review summarizes the MOFs and their derivatives applied for ECO₂RR into HCOOH products. The preparation methods of MOFs as electrocatalysts and their unique advantages are discussed. A series of MOFs and MOF derivatives obtained by electrochemical reduction or carbonization processes are highlighted, including metal nanomaterials, carbon-based nanocomposites, single-atom catalysts, and bimetallic nanocomposites. Depending on the MOF building units (metal ions and organic linkers) and the reaction conditions of derivatization, MOF-based catalysts exhibit rich diversity and controllable modulation of catalytic performance. Finally, the challenges encountered at this stage and the future research directions of MOF-based catalysts are proposed.

A novel member of the metal porphyrinoids family, cobalt 5,15-diazaporphyrin, as a molecular catalyst immobilized onto carbon nanotubes, was developed for highly efficient ECO ₂ R to CO.