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Open access publications by faculty, staff, postdocs, and graduate students from the Center for Catalytic Science and Technology.
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Item Turning Carbon Dioxide into Sustainable Food and Chemicals: How Electrosynthesized Acetate Is Paving the Way for Fermentation Innovation(Accounts of Chemical Research, 2023-06-20) Crandall, Bradie S.; Overa, Sean; Shin, Haeun; Jiao, FengConspectus The agricultural and chemical industries are major contributors to climate change. To address this issue, hybrid electrocatalytic–biocatalytic systems have emerged as a promising solution for reducing the environmental impact of these key sectors while providing economic onboarding for carbon capture technology. Recent advancements in the production of acetate via CO2/CO electrolysis as well as advances in precision fermentation technology have prompted electrochemical acetate to be explored as an alternative carbon source for synthetic biology. Tandem CO2 electrolysis coupled with improved reactor design has accelerated the commercial viability of electrosynthesized acetate in recent years. Simultaneously, innovations in metabolic engineering have helped leverage pathways that facilitate acetate upgrading to higher carbons for sustainable food and chemical production via precision fermentation. Current precision fermentation technology has received much criticism for reliance upon food crop-derived sugars and starches as feedstock which compete with the human food chain. A shift toward electrosynthesized acetate feedstocks could help preserve arable land for a rapidly growing population. Technoeconomic analysis shows that using electrochemical acetate instead of glucose as a fermentation feedstock reduces the production costs of food and chemicals by 16% and offers improved market price stability. Moreover, given the rapid decline in utility-scale renewable electricity prices, electro-synthesized acetate may become more affordable than conventional production methods at scale. This work provides an outlook on strategies to further advance and scale-up electrochemical acetate production. Additional perspective is offered to help ensure the successful integration of electrosynthesized acetate and precision fermentation technologies. In the electrocatalytic step, it is critical that relatively high purity acetate can be produced in low-concentration electrolyte to help ensure that minimal treatment of the electrosynthesized acetate stream is needed prior to fermentation. In the biocatalytic step, it is critical that microbes with increased tolerances to elevated acetate concentrations are engineered to help promote acetate uptake and accelerate product formation. Additionally, tighter regulation of acetate metabolism via strain engineering is essential to improving cellular efficiency. The implementation of these strategies would allow the coupling of electrosynthesized acetate with precision fermentation to offer a promising approach to sustainably produce chemicals and food. Reducing the environmental impact of the chemical and agricultural sectors is necessary to avoid climate catastrophe and preserve the habitability of the planet for future generations.Item Best practices for electrochemical reduction of carbon dioxide(Nature Sustainability, 2023-01-02) Seger, Brian; Robert, Marc; Jiao, FengCarbon capture, utilization and storage, a fundamental process to a sustainable future, relies on a suite of technologies among which electrochemical reduction of carbon dioxide is essential. Here, we discuss the issues faced when reporting performance of this technology and recommend how to move forward at both materials and device levels. Electrochemical reduction of CO2 into value-added chemicals has attracted considerable attention recently1,2,3. However, reporting the performance of a new CO2 electrocatalyst or a new reactor design is not trivial because of the complex nature of the CO2 electroreduction reaction. In many cases, the results are presented in a confusing manner, rendering it difficult to assess the true performance of the catalyst and/or device. In this Comment, we first discuss common problems in reporting the performance of a new electrocatalyst (including both heterogeneous and molecular catalysts) in the literature and then extend the discussion to how the products should be properly measured and quantified. Finally, we comment on the issues associated with full-cell level studies and recommend the best practices for electrochemical CO2 reduction.Item Voltage Loss Diagnosis in CO2 Electrolyzers Using Five-Electrode Technique(ACS Energy Letters, 2022-12-09) Hansen, Kentaro U.; Cherniack, Luke H.; Jiao, FengCO2 electrolysis is a promising carbon utilization technology. Currently, energetic efficiency still requires a significant improvement for commercialization. To rationally design a more efficient CO2 electrolyzer, diagnostic tools are necessary to pinpoint the source of voltage losses across the full cell at work. Here we develop a five-electrode technique to probe voltage drops at the cathode, anode, membrane, and their interfaces in a typical zero-gap cell. We show that the cathode/membrane ionic interface is the major source of overpotential, contributing 720 mV voltage loss at 600 mA cm–2. This loss can be mitigated by coating the catalyst directly onto the membrane to lower ionic resistances, reducing this voltage loss to 80 mV at the same current density. The improved design enables us to achieve a full cell performance of 3.55 V and >95% CO Faradaic efficiency at 800 mA cm–2, representing the highest performance for CO2 electrolysis with a dilute bicarbonate electrolyte. The insights provided by the five-electrode technique may guide the rational design of future membrane-based electrochemical cells.Item A molecular substitutional disorder case study suitable for instruction: L2CrII(THF)/L2[(trimethylsilyl)methyl]CrIII (L is 2,5-bis{[(2,6-diisopropylphenyl)imino]methyl}pyrrol-1-ide)(Acta Crystallographica Section C: Structural Chemistry, 2022-04-06) Salisbury, Brian A.; Young, John F.; Theopold, Klaus H.; Yap, Glenn P. A.A solution of CrII and CrIII complexes, bis(2,5-bis{[(2,6-diisopropylphenyl)imino]methyl}pyrrol-1-ido)(tetrahydrofuran)chromium(II)–bis(2,5-bis{[(2,6-diisopropylphenyl)imino]methyl}pyrrol-1-ido)[(trimethylsilyl)methyl]chromium(III) (0.88/0.12), [Cr(C30H38N3)2(C4H8O)]0.88[Cr(C30H38N3)2(C4H11Si)]0.12 or L2CrII(THF)/L2[(trimethylsilyl)methyl]CrIII (L = 2,5-bis{[(2,6-diisopropylphenyl)imino]methyl}pyrrol-1-ide and THF is tetrahydrofuran), in pentane crystallizes in the monoclinic space group P21/c. The structure obtained shows most of the atoms coincident but with THF disordered with the (trimethylsilyl)methyl ligand. Structures with this disorder, involving more than two or three atoms, seem to appear rarely in the literature; however, in this case, the data set is ideal for the crystallographic instruction of molecular substitution disorder.Item Permethyl Cobaltocenium (Cp* 2Co+) as an Ultra-Stable Cation for Polymer Hydroxide-Exchange Membranes(Nature Publishing Group, 2015-06-29) Gu, Shuang; Wang, Junhua; Kaspar, Robert B.; Fang, Qianrong; Zhang, Bingzi; Coughlin, E. Bryan; Yan, Yushan; Shuang Gu, Junhua Wang, Robert B. Kaspar, Qianrong Fang, Bingzi Zhang, E. Bryan Coughlin & Yushan Yan; Gu, Shuang; Wang, Junhua; Kspar, Robert B.; Fang, Qianrong; Zhang, Bingzi; Yan, YushanHydroxide (OH−)-exchange membranes (HEMs) are important polymer electrolytes enabling the use of affordable and earth-abundant electrocatalysts for electrochemical energy-conversion devices such as HEM fuel cells, HEM electrolyzers, and HEM solar hydrogen generators. Many HEM cations exist, featuring desirable properties, but new cations are still needed to increase chemical stability at elevated temperatures. Here we introduce the permethyl cobaltocenium [(C5Me5)2Co(III)+ or Cp*2Co+] as an ultra-stable organic cation for polymer HEMs. Compared with the parent cobaltocenium [(C5H5)2Co(III)+ or Cp2Co+], Cp*2Co+ has substantially higher stability and basicity. With polysulfone as an example, we demonstrated the feasibility of covalently linking Cp*2Co+ cation to polymer backbone and prepared Cp*2Co+-functionalized membranes as well. The new cation may be useful in designing more durable HEM electrochemical devices.Item Nonaqueous redox-flow batteries: organic solvents, supporting electrolytes, and redox pairs(Royal Society of Chemistry, 2015-08-17) Gong, Ke; Fang, Qianrong; Gu, Shuang; Li, Sam Fong Yau; Yan, Yushan; Ke Gong, Qianrong Fang, Shuang Gu, Sam Fong Yau Li and Yushan Yan; Gong, Ke; Fang, Qianrong; Gu, Shuang; Yan, YushanAs members of the redox-flow battery (RFB) family, nonaqueous RFBs can offer a wide range of working temperature, high cell voltage, and potentially high energy density. These key features make nonaqueous RFBs an important complement of aqueous RFBs, broadening the spectrum of RFB applications. The development of nonaqueous RFBs is still at its early research stage and great challenges remain to be addressed before their successful use for practical applications. As such, it is essential to understand the major components in order to advance the nonaqueous RFB technology. In this perspective, three key major components of nonaqueous RFBs: organic solvents, supporting electrolytes, and redox pairs are selectively focused and discussed, with emphasis on providing an overview of those components and on highlighting the relationship between structure and properties. Urgent challenges are also discussed. To advance nonaqueous RFBs, the understanding of both components and systems is critically needed and it calls for inter-disciplinary collaborations across expertise including electrochemistry, organic chemistry, physical chemistry, cell design, and system engineering. In order to demonstrate the key features of nonaqueous RFBs, herein we also present an example of designing a 4.5 V ultrahigh-voltage nonaqueous RFB by combining a BP/BP˙− redox pair and an OFN˙+/OFN redox pair.Item Cr−Cr Quintuple Bonds: Ligand Topology and Interplay Between Metal−Metal and Metal−Ligand Bonding(American Chemical Society, 2015-10-26) Falceto, Andrés; Theopold, Klaus H.; Alvarez, Santiago; Andrés Falceto, Klaus H. Theopold, and Santiago Alvarez; Theopold, Klaus H.Chromium–chromium quintuple bonds seem to be approaching the lower limit for their bond distances, and this computational density functional theory study tries to explore the geometrical and electronic factors that determine that distance and to find ways to fine-tune it via the ligand choice. While for monodentate ligands the Cr–Cr distance is predicted to shorten as the Cr–Cr–L bond angle increases, with bridging bidentate ligands the trend is the opposite, since those ligands with a larger number of spacers between the donor atoms favor larger bond angles and longer bond distances. Compared to Cr–Cr quadruple bonds, the quintuple bonding in Cr2L2 compounds (with L a bridging bidentate N-donor ligand) involves a sophisticated mechanism that comprises a positive pyramidality effect for the σ and one π bond, but a negative effect for one of the δ bonds. Moreover, the shorter Cr–Cr distances produce a mismatch of the bridging ligand lone pairs and the metal acceptor orbitals, which results in a negative correlation of the Cr–Cr and Cr–N bond distances in both experimental and calculated structures.