Photoreduction of CO2 into sustainable and green solar fuels is generally believed to be an appealing solution to simultaneously overcome both environmental problems and energy crisis. The low selectivity of challenging multi-electron CO2 photoreduction reactions makes it one of the holy grails in heterogeneous photocatalysis. This Review highlights the important roles of cocatalysts in selective photocatalytic CO2 reduction into solar fuels using semiconductor catalysts. A special emphasis in this review is placed on the key role, design considerations and modification strategies of cocatalysts for CO2 photoreduction. Various cocatalysts, such as the biomimetic, metal-based, metal-free, and multifunctional ones, and their selectivity for CO2 photoreduction are summarized and discussed, along with the recent advances in this area. This Review provides useful information for the design of highly selective cocatalysts for photo(electro)reduction and electroreduction of CO2 and complements the existing reviews on various semiconductor photocatalysts.

Cocatalysts for Selective Photoreduction of CO2 into Solar Fuels.

In view of the climate changes caused by the continuously rising levels of atmospheric CO2 , advanced technologies associated with CO2 conversion are highly desirable. In recent decades, electrochemical reduction of CO2 has been extensively studied since it can reduce CO2 to value-added chemicals and fuels. Considering the sluggish reaction kinetics of the CO2 molecule, efficient and robust electrocatalysts are required to promote this conversion reaction. Here, recent progress and opportunities in inorganic heterogeneous electrocatalysts for CO2 reduction are discussed, from the viewpoint of both experimental and computational aspects. Based on elemental composition, the inorganic catalysts presented here are classified into four groups: metals, transition-metal oxides, transition-metal chalcogenides, and carbon-based materials. However, despite encouraging accomplishments made in this area, substantial advances in CO2 electrolysis are still needed to meet the criteria for practical applications. Therefore, in the last part, several promising strategies, including surface engineering, chemical modification, nanostructured catalysts, and composite materials, are proposed to facilitate the future development of CO2 electroreduction.

Recent Advances in Inorganic Heterogeneous Electrocatalysts for Reduction of Carbon Dioxide

The gradually increased concentration of carbon dioxide (CO2 ) in the atmosphere has been recognized as the primary culprit for the rise of the global mean temperature. In recent years, development of routes for highly efficient conversion of CO2 has received much attention. This Review describes recent progress on the design and synthesis of solid-state catalysts for the electrochemical reduction of CO2 . The significance of this catalytic conversion is presented, followed by the general parameters for CO2 electroreduction and a summary of the reaction apparatus. We also discuss various types of solid catalysts based on their CO2 conversion mechanisms. We summarize the crucial factors (particle size, surface structure, composition, etc.) determining the performance for electroreduction.

Nanostructured Materials for Heterogeneous Electrocatalytic CO2 Reduction and their Related Reaction Mechanisms

The electrochemical reduction of CO2 to multi-carbon products has attracted much attention because it provides an avenue to the synthesis of value-added carbon-based fuels and feedstocks using renewable electricity Unfortunately, the efficiency of CO2 conversion to C2 products remains below that necessary for its implementation at scale Modifying the local electronic structure of copper with positive valence sites has been predicted to boost conversion to C2 products Here, we use boron to tune the ratio of Cuδ+ to Cu0 active sites and improve both stability and C2-product generation Simulations show that the ability to tune the average oxidation state of copper enables control over CO adsorption and dimerization, and makes it possible to implement a preference for the electrosynthesis of C2 products We report experimentally a C2 Faradaic efficiency of 79 ± 2% on boron-doped copper catalysts and further show that boron doping leads to catalysts that are stable for in excess of ~40 hours while electrochemically reducing CO2 to multi-carbon hydrocarbons

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Dopant-induced electron localization drives CO 2 reduction to C 2 hydrocarbons

Advances in CO2 capture technology: A patent review

Electrochemical reduction of carbon dioxide (CO2) to formate (HCOO–) in aqueous solution is studied using tin–lead (Sn–Pb) alloys as new electrocatalysts. In electrochemical impedance spectroscopy (EIS) measurements, lower charge-transfer resistance is observed for the alloy electrodes when compared to the single metal electrodes such as Sn and Pb. The results of X-ray photoelectron spectroscopy (XPS) and cyclic voltammetric (CV) analysis show that the Sn in the Sn–Pb alloys facilitates the formation of oxidized tin (SnOx) and metallic lead (Pb0) on the alloy surface by inhibiting the formation of low-conductive lead oxide (PbO) film. The CV analysis confirms that the Sn–Pb alloys exhibit higher reduction current than the single metal electrodes under CO2 atmosphere. The Faradaic efficiency (FE) and the partial current density (PCD) of HCOO– production on the alloy electrodes is investigated by electroreduction experiments at −2.0 V (vs Ag/AgCl) in an H-type cell. As results, respectively more than 16% an...

Electrochemical Reduction of Carbon Dioxide to Formate on Tin–Lead Alloys

Electrochemical reduction of carbon dioxide at low overpotential on a polyaniline/Cu2O nanocomposite based electrode

Nanocomposites of Co3S4 grown on nitrogen-doped graphene (NG) (Co3S4-NG) have been prepared at various concentrations of NG. The supercapacitive behaviors of the developed nanocomposites were assessed with cyclic voltammetry and galvanostatic charge discharge techniques. The nanocomposites exhibit excellent capacitive behavior with a high specific capacitance of 2427 F/g at 2 mV/s in Co3S4-NG-7 composite (7 indicates the percentage weight ratio of NG). The superior electrochemical performances could be due to synergistic effects between Co3S4 and NG, high charge mobility and good flexibility of graphene structures. These results indicate that the developed hybrid materials are promising candidates for high performance energy applications.

Facile Synthesis and Electrochemical Properties of Co3S4-Nitrogen-Doped Graphene Nanocomposites for Supercapacitor Applications

Alkyl amines, which have multiple amino groups, are used as activators to improve the CO2 absorption performances of aqueous methyldiethanolamine (MDEA) solutions. The aqueous MDEA blends consisted of 20% (w/w) of MDEA and 10% (w/w) of activators, which are 3-methylamino propylamine (MAPA), diethylenetriamine (DETA), triethylene tetramine (TETA), and tetraethylenepentamine (TEPA). Aqueous solutions of monoethanolamine (MEA; 30% (w/w)) and MDEA (30% (w/w)) are used as reference absorbents for comparison. The CO2 absorption performances of aqueous MDEA blends were investigated by measurements of absorption capacities, absorption rates, and heats of absorption. The MDEA blends have higher CO2 absorption capacities than MEA and MDEA. MDEA/TEPA shows the highest CO2 loading amount of 0.753 mol-CO2·mol-absorbent–1 at 313 K. In addition, the MDEA blends show high cyclic capacities (0.241–0.330 mol-CO2·mol-absorbent–1), the values of which are about 3 times higher than that of MEA. All MDEA blends show higher abs...

Carbon Dioxide Absorption into Aqueous Blends of Methyldiethanolamine (MDEA) and Alkyl Amines Containing Multiple Amino Groups

A recent class of porous materials, viz., metal–organic frameworks (MOFs), finds applications in several areas. In this work, Cu-based MOFs (Cu–benzene-1,3,5-tricarboxylic acid) along with graphene...

Song Yi Choi

Papers

Electrochemical Reduction of Carbon Dioxide to Formate on Tin–Lead Alloys

Electrochemical reduction of carbon dioxide at low overpotential on a polyaniline/Cu2O nanocomposite based electrode

Facile Synthesis and Electrochemical Properties of Co3S4-Nitrogen-Doped Graphene Nanocomposites for Supercapacitor Applications

Carbon Dioxide Absorption into Aqueous Blends of Methyldiethanolamine (MDEA) and Alkyl Amines Containing Multiple Amino Groups

Investigation on Electroreduction of CO2 to Formic Acid Using Cu3(BTC)2 Metal–Organic Framework (Cu-MOF) and Graphene Oxide