Recent Trends, Benchmarking, and Challenges of Electrochemical Reduction of CO₂ by Molecular Catalysts

Abstract

provides a promising alternative to hydrocarbon sources for petrochemical feedstock. Thanks to the electrochemical nature of the CO 2 conversion to fuels and chemicals, the electrical energy invested to convert CO 2 in the form of a chemical fuel can be stored and redistributed using established supply chains for future use. Additionally, the integration of renewable energy systems (green electricity) into the grid can potentially create a carbon neutral energy cycle, and when driven by solar energy, offers a completely renewable energy cycle or negative carbon technology. Converting CO 2 electrochemically into compounds with high energy densities, such as alcohols (methanol, ethanol), formates, and CO, represents a form of energy storage and is also adaptable to demand response or energy arbitrage technologies. [3][4][5][6][7] The recoverable energy density of the chemicals that can be converted from CO 2 is substantially higher than most battery technologies.Given CO 2 electroreduction's immense economic and environmental potential, it has been the subject of much research activity over the past decades. [8][9][10][11] One of the greatest challenges of reducing CO 2 in an electrochemical cell is overcoming the immense energy barrier required to do so; the single electron reduction of CO 2 to CO 2 −˙, a common step in many CO 2 reduction mechanisms, requires an applied potential of −1.97 V measured versus standard hydrogen electrode (SHE). To alleviate this problem, many catalytic cathodes have been developed to avoid this intermediate and to reroute the reduction mechanism through alternate pathways requiring much lower applied potentials (a necessity if CO 2 electroreduction is to be implemented at industrial scale). [12][13][14] However, despite the low potentials offered by catalytic electrodes, the cost of electrodes is not always viable when upscaled to industrial levels. [15,16] Therefore, recent research trends in electrocatalytic reduction of CO 2 have been shifting toward the development of molecular catalysts that can exist as either solutes in electrolytes or can be surface-confined on electrodes. [13,16] The tunable nature and electronic characteristics of molecular catalysts give access to a large variety of catalysts with high activity, selectivity, and durability, as well as their ability to be integrated into sophisticated nanoassemblies. [17][18][19] Thanks to the aforementioned proprieties, performing CO 2 reduction using molecularly defined compounds offer several advantages compared to classical solid-state counterparts. Molecular catalysts usually exhibit well-defined homogeneous and/or CO 2 reduction using molecular catalysts is a key area of study for achieving electrical-to-chemical energy storage and feedstock chemical synthesis. Compared to classical metallic solid-state catalysts, these molecular catalysts often result in high performance and selectivity, even under unfavorable aqueous environments. This review considers the recent state-of-the-art molecular catalysts for CO 2 electro...

Transition metal-based catalysts for the electrochemical CO2reduction: from atoms and molecules to nanostructured materials

“…3a, right). 112 A comparable effect but opposite in sign was observed by replacing the trimethylanilinium substituents with negatively charged sulfonate groups (19), owing to unfavorable electrostatic interactions. Furthermore, the derivative bearing the quaternary ammonium groups in ortho positions (compound 20) exhibited a significant decrease of the catalytic overpotential while dramatically increasing the TOF (Fig.…”

“…about 0.03 M in common aqueous electrolytes, 0.31 M in CH 3 CN and 0.19 M in DMF 15 ) must be also carefully assessed. In the last decades, a plethora of transition metal-based catalysts have been reported for efficient CO 2 RR, ranging from molecular catalysts [16][17][18][19][20][21][22] to metal nanoparticles 23,24 and bulk heterogeneous materials. [25][26][27] In parallel, the increasing interest for in situ and operando microscopic and spectroelectrochemical (SEC) techniques applied to both, the homogeneous and heterogeneous systems has led to a strong improvement in the fundamental understanding of the factors governing the CO 2 RR process.…”

Heterostructured Catalysts for Electrocatalytic and Photocatalytic Carbon Dioxide Reduction

“…[ 5,7–9 ] The challenge exists in relieving dependence on fossil fuels and instead utilizing other alternative cleaner energy sources entirely, such as wind, solar, hydropower, and geothermal energy, which result in little or no carbon footprints. [ 1,2,10–13 ] Although active steps have been taken in this direction, such alternative sources are often transient in nature, inconsistent, and unpredictable, depending substantially on a large number of variables, such as location, timing, and environmental conditions [5] …”

Light‐driven catalysis with engineered enzymes and biomimetic systems

“…(4-7)]. TiO 2 nanoparticles and other heterogeneous catalysts have been used to directly reduce CO 2 , along with a variety of metal-based catalysts and metal-organic frameworks [198][199][200][201][202][203]. However, selectivity for desired products is difficult to achieve.…”