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The reduction of CO2 on tin cathodes was studied using in situ attenuated total reflectance infrared spectroscopy (ATR-IR). Thin films of a mixed Sn/SnO x species were deposited onto a single-crystal ZnSe ATR crystal. Peaks centered at about 1500, 1385, and 1100 cm–1, attributed to a surface-bound monodentate tin carbonate species, were consistently present under conditions at which CO2 reduction takes place. It was shown that these peaks are only present at potentials where CO2 reduction is observed. Moreover, these peaks disappear if the pH of the reaction is too low or if the tin surface is chemically etched to remove surface oxide. Sn6O4(OH)4 and SnO2 nanoparticles were shown to be catalytically active for CO2 reduction, and insights into the oxidation state of the catalytically active species are gained from a comparison of the catalytic behavior of the two nanoparticle species. From these experiments, a mechanism governing the reduction of CO2 on tin electrodes is proposed.

The role of metastable surface oxides in the reduction of CO 2 on lead, bismuth, tin, and indium electrodes was probed using in situ attenuated total reflectance infrared (ATR-IR) spectroelectrochemistry. The effect of the surface oxide on the Faradaic efficiency of CO 2 reduction to formic acid was studied by etching and anodizing the electrodes, and the results were correlated with respect to the observed spectroscopic behavior of the catalysts. A metastable oxide is observed on lead, tin, and indium cathodes under the electrochemical conditions necessary for CO 2 reduction. Spectroscopic evidence suggests that bismuth electrodes are fully reduced to the metal under the same conditions. The dynamics of the electroreduction of CO 2 at lead and bismuth electrodes appears to be different from that on on tin and indium electrodes, which suggests that these catalysts act through different mechanistic pathways. The post-transition-metal block can be divided into three classes of materials: oxide-active materials, oxide-buffered materials, and oxide-independent materials, and the mechanistic differences are discussed.

Global climate change and energy concerns have led to a surge of interest in the electrochemical conversion of carbon dioxide (CO2) to fuels such as methane and ethanol. Metals such as copper, tin, gold, and others have proven effective as catalysts for reducing CO2 to a wide spectrum of products. Interestingly, it has recently been shown that oxidizing some of these metals further enhances their catalytic activities and selectivities. Oxidation seems to play a fundamental, but poorly understood, role in modulating the reactivity of these catalysts. In this Review, recent progress towards understanding the effect of oxygen, surface morphologies, and local pH gradients on the catalysis of CO2 reduction is discussed.

This work discusses how to best perform experiments and report data for the electrochemical reduction of carbon dioxide.

A facile electropolymerization process was utilized to prepare electrodes modified with thin films of cobalt protoporphyrin IX. These thin films exhibited a high Faradaic efficiency (84±2 %) for the reduction of CO2 to CO in aqueous solutions near neutral pH with 450 mV of overpotential and a turnover frequency at zero overpotential (log(TOF0)) of −5.9. The production of CO was stable over several hours at these modest potentials. The use of a 13CO2 reactant led exclusively to 13CO as the product. Polymeric films of the unmetalated porphyrin did not demonstrate catalysis for CO2 reduction. UV/Vis spectroelectrochemical experiments indicate that the parent CoII complex is reduced to CoI at the electrode surface before interaction with CO2. It is proposed that the rate‐determining step in the reduction of CO2 is the initial reduction of the CoII moiety to CoI, which binds CO2 and then undergoes a proton‐coupled electron transfer and a loss of water to form CO. Additionally, a new metric for the evaluation of electrocatalysts, the catalytic efficiency, is proposed. The catalytic efficiency is the ratio of the power stored to power consumed for a given electrochemical reaction and can be used to describe both the kinetics and overpotential considerations of a given system.

We provide compelling evidence showing that the morphology of a lead cathode is very important in determining its selectivity and activity towards CO2 reduction to formate.

A recently proposed mechanism for electrochemical CO 2 reduction on Pt (111) catalyzed by aqueous acidic pyridine solutions suggests that the observed redox potential of ca. −600 mV vs. SCE is due to the one-electron reduction of pyridinium through proton coupled electron transfer (PCET) to form H atoms adsorbed on the Pt surface (H ads ). The initial pyridinium reduction was probed isotopically via deuterium substitution. A combined experimental and theoretical analysis found equilibrium isotope effects (EIE) due to deuterium substitution at the acidic pyridinium site. A shift in the cathodic cyclic voltammetric half wave potential of −25 mV was observed, consistent with the theoretical prediction of −40 mV based on the recently proposed reaction mechanism where pyridinium is essential to establish a high concentration of Brønsted acid in contact with the substrate CO 2 and with the Pt surface. A prefeature in the cyclic voltammogram was examined under isotopic substitution and indicated an H ads intermediate in pyridinium reduction. Theoretical prediction and observation of an EIE supported the assignment of the cathodic wave to the proposed reduction of pyridinium through PCET forming H ads and eventually H 2 on the Pt surface.