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1. Highly Efficient Solar‐Driven Carbon Dioxide Reduction on Molybdenum Disulfide Catalyst Using Choline Chloride‐Based Electrolyte

   https://doi.org/10.1002/aenm.201803536  

   Asadi, Mohammad; Motevaselian, Mohammad_Hossein; Moradzadeh, Alireza; Majidi, Leily; Esmaeilirad, Mohammadreza; Sun, Tao_Victor; Liu, Cong; Bose, Rumki; Abbasi, Pedram; Zapol, Peter; et al (January 2019, Advanced Energy Materials)

   Abstract Conversion of CO₂to energy‐rich chemicals using renewable energy is of much interest to close the anthropogenic carbon cycle. However, the current photoelectrochemical systems are still far from being practically feasible. Here the successful demonstration of a continuous, energy efficient, and scalable solar‐driven CO₂reduction process based on earth‐abundant molybdenum disulfide (MoS₂) catalyst, which works in synergy with an inexpensive hybrid electrolyte of choline chloride (a common food additive for livestock) and potassium hydroxide (KOH) is reported. The CO₂saturated hybrid electrolyte utilized in this study also acts as a buffer solution (pH ≈ 7.6) to adjust pH during the reactions. This study reveals that this system can efficiently convert CO₂to CO with solar‐to‐fuel and catalytic conversion efficiencies of 23% and 83%, respectively. Using density functional theory calculations, a new reaction mechanism in which the water molecules near the MoS₂cathode act as proton donors to facilitate the CO₂reduction process by MoS₂catalyst is proposed. This demonstration of a continuous, cost‐effective, and energy efficient solar driven CO₂conversion process is a key step toward the industrialization of this technology. 

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2. The Influence of pH and Electrolyte Concentration on Fractional Protonation and CO ₂ Reduction Activity in Polymer-Encapsulated Cobalt Phthalocyanine

   https://doi.org/10.1021/acs.jpcc.3c01490  

   Soucy, Taylor L.; Dean, William S.; Rivera Cruz, Kevin E.; Eisenberg, Jonah B.; Shi, Lirong; McCrory, Charles C. (July 2023, The Journal of Physical Chemistry C)

   Polymer-encapsulated cobalt phthalocyanine (CoPc) is a model system for studying how polymer-catalyst interactions in the electrocatalytic systems influence performance for the CO2 reduction reaction. In particular, understanding how bulk electrolyte and proton concentration influences polymer protonation, and in turn how the extent of polymer protonation influences catalytic activity and selectivity, is crucial to understanding polymer-catalyst composite materials. We report a study of the dependence of bulk pH and electrolyte concentration on the fractional protonation of poly-4-vinylpyridine and related polymers with both electrochemical and spectroscopic evidence. In addition, we show that the fractional protonation of the polymer is directly related to both the activity of the catalyst and the reaction selectivity for the CO2 reduction reaction over the competitive hydrogen evolution reaction. Of particular note is that the fractional protonation of the film is related to electrolyte concentration, which suggests that the transport of counterions plays an important role in regulating proton transport within the polymer film. These insights suggest that electrolyte concentration and pH play an important in the electrocatalytic performance for polymer-catalyst composite systems, and these influences should be considered in both experimental preparation and analysis. 

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3. Recent advances in CO ₂ capture and reduction

   https://doi.org/10.1039/d2nr02894h  

   Wei, Kecheng; Guan, Huanqin; Luo, Qiang; He, Jie; Sun, Shouheng (August 2022, Nanoscale)

   Given the continuous and excessive CO 2 emission into the atmosphere from anthropomorphic activities, there is now a growing demand for negative carbon emission technologies, which requires efficient capture and conversion of CO 2 to value-added chemicals. This review highlights recent advances in CO 2 capture and conversion chemistry and processes. It first summarizes various adsorbent materials that have been developed for CO 2 capture, including hydroxide-, amine-, and metal organic framework-based adsorbents. It then reviews recent efforts devoted to two types of CO 2 conversion reaction: thermochemical CO 2 hydrogenation and electrochemical CO 2 reduction. While thermal hydrogenation reactions are often accomplished in the presence of H 2 , electrochemical reactions are realized by direct use of electricity that can be renewably generated from solar and wind power. The key to the success of these reactions is to develop efficient catalysts and to rationally engineer the catalyst–electrolyte interfaces. The review further covers recent studies in integrating CO 2 capture and conversion processes so that energy efficiency for the overall CO 2 capture and conversion can be optimized. Lastly, the review briefs some new approaches and future directions of coupling direct air capture and CO 2 conversion technologies as solutions to negative carbon emission and energy sustainability. 

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4. Modifying Copper Local Environment with Electrolyte Additives to Alter CO ₂ Electroreduction vs Hydrogen Evolution

   https://doi.org/10.1021/acscatal.3c00035  

   Sharifi_Golru, Samaneh; May, Andrew S; Biddinger, Elizabeth J (June 2023, ACS Catalysis)

   CO2 electroreduction (CO2ER) by using renewable energy resources is a promising method to mitigate the CO2 level in the atmosphere as well as producing valuable chemicals. Local environment at the electrode-electrolyte interface plays a key role in CO2ER activity and selectivity along with its competing hydrogen evolution reaction (HER). In addition to the catalyst and reactor design, electrolyte has also a significant impact on the interface. Herein, electrolyte additives were used to modify the local environment around the Cu catalyst during CO2ER. To this purpose, 10mM of ionic additives with bis(trifluoromethylsulfonyl)imide ([NTF2]-) and dicyanamide ([DCA]-) as anions and 1-butyl-3-methylimidazolium ([BMIM]+), potassium (K+), or sodium (Na+) as cations have been added to an aqueous potassium bicarbonate solution (0.1 M KHCO3). COMSOL Multiphysics was also used to calculate the local pH and CO2 concentration at electrode-electrolyte interface in different electrolytes. Results showed that the local environment modifications by the electrolyte additives altered the activity and selectivity of Cu in CO2ER. It was found that the CO2ER activity at -0.92 V was enhanced when using anion with high CO2 affinity and high hydrophobicity such as [NTF2]–. Among [NTF2]–-based additives, [BMIM][NTF2] had a higher faradaic efficiency (FE) for formate (38.7%) compared to K[NTF2] (23.2%) and Na[NTF2] (18.5%) at -0.92 V likely due to the presence of imidazolium cation which can further stabilize the intermediates on the surface and enhance CO2ER. Electrolytes containing [DCA]–-based additives with high hydrophilicity and low CO2 affinity had a very high HER selectivity (>90% FEH2) and low CO2ER selectivity regardless of the cation nature. This observation is attributed to the presence of hydrophilic [BMIM][DCA] in the vicinity of the catalyst which impacts the microenvironment around the catalyst. We observed that [DCA]– anions have a high affinity to adsorb on Cu catalysts as soon as the catalyst is submerged in the electrolyte. Although FTIR showed that [DCA]– anions desorb from the surface at negative potentials, it is likely that [DCA]– anions still remain in the proximity of the electrode, next to the adsorbed cations, impacting the transport of H2O and CO2, and altering the product selectivity. COMSOL calculations showed that the local pH is directly proportional to the H2 evolution activity. Also, hydrophilic salts such as those with the [DCA]– anion had a more alkaline local pH which leads to a lower CO2 concentration in the vicinity of the catalyst. 

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5. Direct and continuous generation of pure acetic acid solutions via electrocatalytic carbon monoxide reduction

   https://doi.org/10.1073/pnas.2010868118  

   Zhu, Peng; Xia, Chuan; Liu, Chun-Yen; Jiang, Kun; Gao, Guanhui; Zhang, Xiao; Xia, Yang; Lei, Yongjiu; Alshareef, Husam N.; Senftle, Thomas P.; et al (December 2020, Proceedings of the National Academy of Sciences)

   null (Ed.)

   Electrochemical CO 2 or CO reduction to high-value C 2+ liquid fuels is desirable, but its practical application is challenged by impurities from cogenerated liquid products and solutes in liquid electrolytes, which necessitates cost- and energy-intensive downstream separation processes. By coupling rational designs in a Cu catalyst and porous solid electrolyte (PSE) reactor, here we demonstrate a direct and continuous generation of pure acetic acid solutions via electrochemical CO reduction. With optimized edge-to-surface ratio, the Cu nanocube catalyst presents an unprecedented acetate performance in neutral pH with other liquid products greatly suppressed, delivering a maximal acetate Faradaic efficiency of 43%, partial current of 200 mA⋅cm −2 , ultrahigh relative purity of up to 98 wt%, and excellent stability of over 150 h continuous operation. Density functional theory simulations reveal the role of stepped sites along the cube edge in promoting the acetate pathway. Additionally, a PSE layer, other than a conventional liquid electrolyte, was designed to separate cathode and anode for efficient ion conductions, while not introducing any impurity ions into generated liquid fuels. Pure acetic acid solutions, with concentrations up to 2 wt% (0.33 M), can be continuously produced by employing the acetate-selective Cu catalyst in our PSE reactor. 

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