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...

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The electrochemical conversion of CO 2 into useful chemicals in a microfluidic flow cell (MFC) reactor depends not only on intrinsic electrochemical, physical, and material parameters but also on extrinsic operating conditions and cell design. Variations in these parameters significantly affect the overall performance of the MFC reactor. In this regard, to correlate the cell performance, conversion efficiency, and selectivity of the MFC reactor with the variability of these input parameters, we carry out a Monte Carlo simulation (MCS) based on a mechanistic mathematical model for the electrochemical conversion of CO 2 to CO. The MCS is conducted in two scenarios: first, by varying the stochastic parameters individually (IND), and second, by varying all of the stochastic parameters simultaneously (SIM), at different cell potentials. These parameters are then ranked on the basis of their contributions to the cell performance, the conversion efficiency, and the selectivity, thereby providing insights into optimum ranges of operation. The charge-transfer coefficient toward CO and H 2 formation, catalyst properties, are the most sensitive parameters toward the cell performance and conversion efficiency and the selectivity, respectively, at all cell potentials. The thickness of the catalyst layer has a significant effect on the cell performance and conversion efficiency during the IND scenario, but its relative effect during the SIM scenario is not significant at all cell potentials. Furthermore, we derive reduced regression models based on supervised machine learning algorithms to predict the overall cell performance without having to solve the complete set of equations and also statistically discuss the distribution of overall cell performance at various cell potentials.

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In response to issues raised by modern energy challenges, molecular electrocatalysis is currently attracting a lot of attention to the tailoring of “model” catalysts, notably understanding the mechanisms and kinetic and thermodynamic parameters that occur during a catalytic reaction. In this regard, nature offers extremely efficient enzymes called hydrogenases. These enzymes that catalyze the reversible interconversions between H2 and H+ at high turnover rates are inactivated by O2. This inactivation yields odd cyclic voltammetric responses originating from a chemical inactivation–redox activation process (IAP). Although IAP has been extensively studied for hydrogenases, their catalytic mechanism is not fully understood because of the intricate but necessary electrical wiring, desorption, and complex biochemical environment required. Here, we report a unique example of IAP based on a nonenzymatic catalyst prepared by mixing rhodium-porphyrinic catalyst and an interconnected multiwalled carbon nanotubes matrix which presents an excellent and stable electron transfer. We combined organic synthesis, electrochemistry, mathematical models, and density functional theory calculations to uncover the molecular IAP at the catalytic metallic site. We present a mechanistic analysis of the noncatalytic and catalytic responses exhibited by this complex, enabling a comprehensive understanding of the thermodynamic and kinetic parameters that govern the IAP. These stepwise studies support a mechanism for glucose oxidation that proceeds most likely through an EC′CE scheme with catalytic steps similar to the ones reported for NiFe hydrogenases. The overall mechanism of the molecular IAP was detailed on the basis of our experimentally validated models and compared to NiFe hydrogenase IAP. Our findings offer novel perspectives to design finely optimized catalysts by eliminating the inactivation phenomena.

The operation of electrochemical capacitors depends not only on extrinsic operating and design parameters, but also intrinsic physical, material, and electrochemical parameters. Fluctuations in these stochastic parameters can significantly influence the performance and may lead to quicker degradation of the electrochemical capacitors, thereby affecting their durability and reliability. Thus, it is important to quantify the sensitivities of these extrinsic and intrinsic parameters and correlate them with the performance, to delay the inevitable performance degradation. To achieve this, we perform Monte Carlo simulations (MCS) followed by sensitivity analysis under high and low charge/ discharge current (load) conditions. The MCS is statistically performed by varying all the stochastic parameters simultaneously. We then identify the critical parameters that affect the performance under different load conditions, which provides insights into optimal operation of electrochemical capacitors. The thickness of positive electrode and the radius of active material were identified as the most significant parameters under low and high load conditions, respectively. Furthermore, we derive reduced order surrogate models with at least 95% accuracy using supervised machine learning techniques to predict the performance without solving the full physics-based model.

We report a chemical inactivation/redox reactivation process (IAP) based on the surface-confined rhodium–porphyrinic catalyst on a multi-walled carbon nanotube surface which presents an excellent and stable electron transfer.