Upcycling CO2 into energy-rich long-chain compounds via electrochemical and metabolic engineering

Scaling-Free Cathodes: Enabling Electrochemical Extraction of High-Purity Nano-CaCO3 and -Mg(OH)2 in Seawater

For electrochemical application in seawater or brine, continuous scaling on cathodes will form insulation layers, making it nearly impossible to run an electrochemical reaction continuously. Herein, we report our discovery that a cathode consisting of conical nanobundle arrays with hydrophobic surfaces exhibits a unique scaling-free function. The hydrophobic surfaces will be covered with microbubbles created by electrolytic water splitting, which limits scale crystals from standing only on nanotips of conical nanobundles, and the bursting of large bubbles formed by the accumulation of microbubbles will cause a violent disturbance, removing scale crystals automatically from nanotips. Benefiting from the scaling-free properties of the cathode, high-purity nano-CaCO3 (98.9%) and nano-Mg(OH)2 (99.5%) were extracted from seawater. This novel scaling-free cathode is expected to eliminate the inherent limitations of electrochemical technology and open up a new route to seawater mining.

Upcycling CO2 into succinic acid via electrochemical and engineered Escherichia coli

Converting CO2 into value-added chemicals still remains a grand challenge. Succinic acid has long been considered as one of the top building block chemicals. This study reported efficiently upcycling CO2 into succinic acid by combining between electrochemical and engineered Escherichia coli. In this process, the Cu-organic framework catalyst was synthesized for electrocatalytic CO2-to-ethanol conversion with high Faradaic efficiency (FE, 84.7 %) and relative purity (RP, 95 wt%). Subsequently, an engineered E. coli with efficiently assimilating CO2-derived ethanol to produce succinic acid was constructed by combining computational design and metabolic engineering, and the succinic acid titer reached 53.8 mM with the yield of 0.41 mol/mol, which is 82 % of the theoretical yield. This study effort to link the two processes of efficient ethanol synthesis by electrocatalytic CO2 and succinic acid production from CO2-derived ethanol, paving a way for the production of succinic acid and other value-added chemicals by converting CO2 into ethanol.

A Novel Sustainable and Self-Sufficient Biotechnological Strategy for Directly Transforming Sewage Sludge into High-Value Liquid Biochemicals

Sewage sludge, as a carbon-rich byproduct of wastewater treatment, holds significant untapped potential as a renewable resource. Upcycling this troublesome waste stream represents great promise in addressing global escalating energy demands through its wide practice of biochemical recovery concurrently. Here, we propose a biotechnological concept to gain value-added liquid bioproducts from sewage sludge in a self-sufficient manner by directly transforming sludge into medium-chain fatty acids (MCFAs). Our findings suggest that yeast, a cheap and readily available commercial powder, would involve ethanol-type fermentation in chain elongation to achieve abundant MCFA production from sewage sludge using electron donors (i.e., ethanol) and acceptors (i.e., short-chain fatty acids) produced in situ. The enhanced abundance and transcriptional activity of genes related to key enzymes, such as butyryl-CoA dehydrogenase and alcohol dehydrogenase, affirm the robust capacity for the self-sustained production of MCFAs. This is indicative of an effective metabolic network established between yeast and anaerobic microorganisms within this innovative sludge fermentation framework. Furthermore, life cycle assessment and techno-economic analysis evidence the sustainability and economic competitiveness of this biotechnological strategy. Overall, this work provides insights into sewage sludge upgrading independent of additional carbon input, which can be applied in existing anaerobic sludge fermentation infrastructure as well as to develop new applications in a diverse range of industries.

Selective and stable CO2 electroreduction at high rates via control of local H2O/CO2 ratio

Controlling the concentrations of H2O and CO2 at the reaction interface is crucial for achieving efficient electrochemical CO2 reduction. However, precise control of these variables during catalysis remains challenging, and the underlying mechanisms are not fully understood. Herein, guided by a multi-physics model, we demonstrate that tuning the local H2O/CO2 concentrations is achievable by thin polymer coatings on the catalyst surface. Beyond the often-explored hydrophobicity, polymer properties of gas permeability and water-uptake ability are even more critical for this purpose. With these insights, we achieve CO2 reduction on copper with Faradaic efficiency exceeding 87% towards multi-carbon products at a high current density of -2 A cm-2. Encouraging cathodic energy efficiency (>50%) is also observed at this high current density due to the substantially reduced cathodic potential. Additionally, we demonstrate stable CO2 reduction for over 150 h at practically relevant current densities owning to the robust reaction interface. Moreover, this strategy has been extended to membrane electrode assemblies and other catalysts for CO2 reduction. Our findings underscore the significance of fine-tuning the local H2O/CO2 balance for future CO2 reduction applications.

Solid Electrolytes for Low-Temperature Carbon Dioxide Valorization: A Review

One of the most promising approaches to address the global challenge of climate change is electrochemical carbon capture and utilization. Solid electrolytes can play a crucial role in establishing a chemical-free pathway for the electrochemical capture of CO2. Furthermore, they can be applied in electrocatalytic CO2 reduction reactions (CO2RR) to increase carbon utilization, produce high-purity liquid chemicals, and advance hybrid electro-biosystems. This review article begins by covering the fundamentals and processes of electrochemical CO2 capture, emphasizing the advantages of utilizing solid electrolytes. Additionally, it highlights recent advancements in the use of the solid polymer electrolyte or solid electrolyte layer for the CO2RR with multiple functions. The review also explores avenues for future research to fully harness the potential of solid electrolytes, including the integration of CO2 capture and the CO2RR and performance assessment under realistic conditions. Finally, this review discusses future opportunities and challenges, aiming to contribute to the establishment of a green and sustainable society through electrochemical CO2 valorization.

Bi/CeO2-Decorated CuS Electrocatalysts for CO2-to-Formate Conversion

The electrocatalytic carbon dioxide (CO2) reduction reaction (CO2RR) is extensively regarded as a promising strategy to reach carbon neutralization. Copper sulfide (CuS) has been widely studied for its ability to produce C1 products with high selectivity. However, challenges still remain owing to the poor selectivity of formate. Here, a Bi/CeO2/CuS composite was synthesized using a simple solvothermal method. Bi/CeO2-decorated CuS possessed high formate selectivity, with the Faraday efficiency and current density reaching 88% and 17 mA cm-2, respectively, in an H-cell. The Bi/CeO2/CuS structure significantly reduces the energy barrier formed by OCHO*, resulting in the high activity and selectivity of the CO2 conversion to formate. Ce4+ readily undergoes reduction to Ce3+, allowing the formation of a conductive network of Ce4+/Ce3+. This network facilitates electron transfer, stabilizes the Cu+ species, and enhances the adsorption and activation of CO2. Furthermore, sulfur catalyzes the OCHO* transformation to formate. This work describes a highly efficient catalyst for CO2 to formate, which will aid in catalyst design for CO2RR to target products.

State of Play of Critical Mineral-Based Catalysts for Electrochemical E-Refinery to Synthetic Fuels

The pursuit of decarbonization involves leveraging waste CO2 for the production of valuable fuels and chemicals (e.g., ethanol, ethylene, and urea) through the electrochemical CO2 reduction reactions (CO2RR). The efficacy of this process heavily depends on electrocatalyst performance, which is generally reliant on high loading of critical minerals. However, the supply of these minerals is susceptible to shortage and disruption, prompting concerns regarding their usage, particularly in electrocatalysis, requiring swift innovations to mitigate the supply risks. The reliance on critical minerals in catalyst fabrication can be reduced by implementing design strategies that improve the available active sites, thereby increasing the mass activity. This review seeks to discuss and analyze potential strategies, challenges, and opportunities for improving catalyst activity in CO2RR with a special attention to addressing the risks associated with critical mineral scarcity. By shedding light onto these aspects of critical mineral-based catalyst systems, this review aims to inspire the development of high-performance catalysts and facilitates the practical application of CO2RR technology, whilst mitigating adverse economic, environmental, and community impacts.

Development of Multifunctional Catalysts for the Direct Hydrogenation of Carbon Dioxide to Higher Alcohols

The direct hydrogenation of greenhouse gas CO2 to higher alcohols (C2+OH) provides a new route for the production of high-value chemicals. Due to the difficulty of C-C coupling, the formation of higher alcohols is more difficult compared to that of other compounds. In this review, we summarize recent advances in the development of multifunctional catalysts, including noble metal catalysts, Co-based catalysts, Cu-based catalysts, Fe-based catalysts, and tandem catalysts for the direct hydrogenation of CO2 to higher alcohols. Possible reaction mechanisms are discussed based on the structure-activity relationship of the catalysts. The reaction-coupling strategy holds great potential to regulate the reaction network. The effects of the reaction conditions on CO2 hydrogenation are also analyzed. Finally, we discuss the challenges and potential opportunities for the further development of direct CO2 hydrogenation to higher alcohols.

Artificial photosynthesis: Promising approach for the efficient production of high-value bioproducts by microalgae

Recently, microalgae had received extensive attention for carbon capture and utilization. But its overall efficiency still could not reach a satisfactory degree. Artificial photosynthesis showed better efficiency in the conversion of carbon dioxide. However, artificial photosynthesis could generally only produce C1-C3 organic matters at present. Some studies showed that heterotrophic microalgae can efficiently synthesize high value organic matters by using simple organic matter such as acetate. Therefore, the combination of artificial photosynthesis with heterotrophic microalgae culture showed great potential for efficient carbon capture and high-value organic matter production. This article systematically analyzed the characteristics and challenges of carbon dioxide conversion by microalgae and artificial photosynthesis. On this basis, the coupling mode and development trend of artificial photosynthesis combined with microalgae culture were discussed. In summary, the combination of artificial photosynthesis and microalgae culture has great potential in the field of carbon capture and utilization, and deserves further study.

CO electrolysis to multicarbon products over grain boundary-rich Cu nanoparticles in membrane electrode assembly electrolyzers

Producing valuable chemicals like ethylene via catalytic carbon monoxide conversion is an important nonpetroleum route. Here we demonstrate an electrochemical route for highly efficient synthesis of multicarbon (C2+) chemicals from CO. We achieve a C2+ partial current density as high as 4.35 ± 0.07 A cm-2 at a low cell voltage of 2.78 ± 0.01 V over a grain boundary-rich Cu nanoparticle catalyst in an alkaline membrane electrode assembly (MEA) electrolyzer, with a C2+ Faradaic efficiency of 87 ± 1% and a CO conversion of 85 ± 3%. Operando Raman spectroscopy and density functional theory calculations reveal that the grain boundaries of Cu nanoparticles facilitate CO adsorption and C - C coupling, thus rationalizing a qualitative trend between C2+ production and grain boundary density. A scale-up demonstration using an electrolyzer stack with five 100 cm2 MEAs achieves high C2+ and ethylene formation rates of 118.9 mmol min-1 and 1.2 L min-1, respectively, at a total current of 400 A (4 A cm-2) with a C2+ Faradaic efficiency of 64%.

Scanning the active center of formolase to identify key residues for enhanced C1 to C3 bioconversion

BACKGROUND

Formolase (FLS) is a computationally designed enzyme that catalyzes the carboligation of two or three C1 formaldehyde molecules into C2 glycolaldehyde or C3 dihydroxyacetone (DHA). FLS lays the foundation for several artificial carbon fixation and valorization pathways, such as the artificial starch anabolic pathway. However, the application of FLS is limited by its low catalytic activity and product promiscuity.

FINDINGS

FLS, designed and engineered based on benzoylformate decarboxylase from Pseudomonas putida, was selected as a candidate for modification. To evaluate its catalytic activity, 25 residues located within an 8 Å distance from the active center were screened using single-point saturation mutagenesis. A screening approach based on the color reaction of the DHA product was applied to identify the desired FLS variants. After screening approximately 5,000 variants (approximately 200 transformants per site), several amino acid sites that were not identified by directed evolution were found to improve DHA formation. The serine-to-phenylalanine substitution at position 236 improved the activity towards DHA formation by 7.6-fold. Molecular dynamics simulations suggested that the mutation increased local hydrophobicity at the active site, predisposing the cofactor-C2 intermediate to nucleophilic attack by the third formaldehyde molecule for subsequent DHA generation.

CONCLUSIONS

This study provides improved FLS variants and valuable information into the influence of residues adjacent to the active center affecting catalytic efficiency, which can guide the rational engineering or directed evolution of FLS to optimize its performance in artificial carbon fixation and valorization.

Long-Chain Hydrocarbons from Nonthermal Plasma-Driven Biogas Upcycling

The burgeoning necessity to discover new methodologies for the synthesis of long-chain hydrocarbons and oxygenates, independent of traditional reliance on high-temperature, high-pressure, and fossil fuel-based carbon, is increasingly urgent. In this context, we introduce a nonthermal plasma-based strategy for the initiation and propagation of long-chain carbon growth from biogas constituents (CO2 and CH4). Utilizing a plasma reactor operating at atmospheric room temperature, our approach facilitates hydrocarbon chain growth up to C40 in the solid state (including oxygenated products), predominantly when CH4 exceeds CO2 in the feedstock. This synthesis is driven by the hydrogenation of CO2 and/or amalgamation of CHx radicals. Global plasma chemistry modeling underscores the pivotal role of electron temperature and CHx radical genesis, contingent upon varying CO2/CH4 ratios in the plasma system. Concomitant with long-chain hydrocarbon production, the system also yields gaseous products, primarily syngas (H2 and CO), as well as liquid-phase alcohols and acids. Our finding demonstrates the feasibility of atmospheric room-temperature synthesis of long-chain hydrocarbons, with the potential for tuning the chain length based on the feed gas composition.

Random mutagenesis and transcriptomics-guided rational engineering in Zygosaccharomyces rouxii for elevating D-arabitol biosynthesis

D-arabitol, a versatile compound with applications in food, pharmaceutical, and biochemical industries, faces challenges in biomanufacturing due to poor chassis performance and unclear synthesis mechanisms. This study aimed to enhance the performance of Zygosaccharomyces rouxii to improve D-arabitol production. Firstly, a mutant strain Z. rouxii M075 obtained via atmospheric and room temperature plasma-mediated mutagenesis yielded 42.0 g/L of D-arabitol at 96 h, with about 50 % increase. Transcriptome-guided metabolic engineering of pathway key enzymes co-expression produced strain ZR-M3, reaching 48.9 g/L D-arabitol after 96 h fermentation. Finally, under optimized conditions, fed-batch fermentation of ZR-M3 in a 5 L bioreactor yielded an impressive D-arabitol titer of 152.8 g/L at 192 h, with a productivity of 0.8 g/L/h. This study highlights promising advancements in enhancing D-arabitol production, offering potential for more efficient biomanufacturing processes and wider industrial applications.

Engineering a solar formic acid/pentose (SFAP) pathway in Escherichia coli for lactic acid production

Microbial CO2 fixation into lactic acid (LA) is an important approach for low-carbon biomanufacturing. Engineering microbes to utilize CO2 and sugar as co-substrates can create efficient pathways through input of moderate reducing power to drive CO2 fixation into product. However, to achieve complete conservation of organic carbon, how to engineer the CO2-fixing modules compatible with native central metabolism and merge the processes for improving bioproduction of LA is a big challenge. In this study, we designed and constructed a solar formic acid/pentose (SFAP) pathway in Escherichia coli, which enabled CO2 fixation merging into sugar catabolism to produce LA. In the SFAP pathway, adequate reducing equivalents from formate oxidation drive glucose metabolism shifting from glycolysis to the pentose phosphate pathway. The Rubisco-based CO2 fixation and sequential reduction of C3 intermediates are conducted to produce LA stoichiometrically. CO2 fixation theoretically can bring a 20% increase of LA production compared with sole glucose feedstock. This SFAP pathway in the integration of photoelectrochemical cell and an engineered Escherichia coli opens an efficient way for fixing CO2 into value-added bioproducts.

Local CO Generator Enabled by a CO-Producing Core for Kinetically Enhancing Electrochemical CO2 Reduction to Multicarbon Products

CO plays a crucial role as an intermediate in electrochemical CO2 conversion to generate multicarbon (C2+) products. However, optimizing the coverage of the CO intermediate (*CO) to improve the selectivity of C2+ products remains a great challenge. Here, we designed a hierarchically structured double hollow spherical nanoreactor featuring atomically dispersed nickel (Ni) atoms as the core and copper (Cu) nanoparticles as the shell, which can greatly improve the catalytic activity and selectivity for C2+ compounds. Within this configuration, CO generated at the active Ni sites on the inner layer accumulates in the cavity before spilling over neighboring Cu sites on the outer layer, thus enhancing CO dimerization within the cavity. Notably, this setup achieves a sustained faradaic efficiency of 74.4% for C2+ production, with partial current densities reaching 337.4 mA cm-2. In situ Raman spectroscopy and finite-element method (FEM) simulations demonstrate that the designed local CO generator can effectively increase the local CO concentration and restrict CO evolution, ultimately boosting C-C coupling. The hierarchically ordered architectural design represents a promising solution for achieving highly selective C2+ compound production in the electroreduction of CO2.

Tandem Acidic CO2 Electrolysis Coupled with Syngas Fermentation: A Two-Stage Process for Producing Medium-Chain Fatty Acids

The tandem application of CO2 electrolysis with syngas fermentation holds promise for achieving heightened production rates and improved product quality. However, the significant impact of syngas composition on mixed culture-based microbial chain elongation remains unclear. Additionally, effective methods for generating syngas with an adjustable composition from acidic CO2 electrolysis are currently lacking. This study successfully demonstrated the production of medium-chain fatty acids from CO2 through tandem acidic electrolysis with syngas fermentation. CO could serve as the sole energy source or as the electron donor (when cofed with acetate) for caproate generation. Furthermore, the results of gas diffusion electrode structure engineering highlighted that the use of carbon black, either alone or in combination with graphite, enabled consistent syngas generation with an adjustable composition from acidic CO2 electrolysis (pH 1). The carbon black layer significantly improved the CO selectivity, increasing from 0% to 43.5% (0.05 M K+) and further to 92.4% (0.5 M K+). This enhancement in performance was attributed to the promotion of K+ accumulation, stabilizing catalytically active sites, rather than creating a localized alkaline environment for CO2-to-CO conversion. This research contributes to the advancement of hybrid technology for sustainable CO2 reduction and chemical production.

Carbon Dioxide Electroreduction and Formic Acid Oxidation by Formal Nickel(I) Complexes of Di-isopropylphenyl Bis-iminoacenaphthene

Processing CO2 into value-added chemicals and fuels stands as one of the most crucial tasks in addressing the global challenge of the greenhouse effect. In this study, we focused on the complex (dpp-bian)NiBr2 (where dpp-bian is di-isopropylphenyl bis-iminoacenaphthene) as a precatalyst for the electrochemical reduction of CO2 into CH4 as the sole product. Cyclic voltammetry results indicate that the realization of a catalytically effective pattern requires the three-electron reduction of (dpp-bian)NiBr2. The chemically reduced complexes [K(THF)6]+[(dpp-bian)Ni(COD)]- and [K(THF)6]+[(dpp-bian)2Ni]- were synthesized and structurally characterized. Analyzing the data from the electron paramagnetic resonance study of the complexes in solutions, along with quantum-chemical calculations, reveals that the spin density is predominantly localized at their metal centers. The superposition of trajectory maps of the electron density gradient vector field∇ ρ r ${\nabla \rho \left({\bf r}\right)}$ and the electrostatic force density fieldF e s r ${{{\bf F}}_{{\rm e}{\rm s}}\left({\bf r}\right)}$ per electron, as well as the atomic charges, discloses that, within the first coordination sphere, the interatomic charge transfer occurs from the metal atom to the ligand atoms and that the complex anions can thus be formally described by the general formulae (dpp-bian)2-Ni+(COD) and (dpp-bian)2 -Ni+. It was also shown that the reduced nickel complexes can be oxidized by formic acid; resulting from this reaction, the two-electron and two-proton addition product dpp-bian-2H is formed.

Current trends and possibilities of typical microbial protein production approaches: a review

Global population growth and demographic restructuring are driving the food and agriculture sectors to provide greater quantities and varieties of food, of which protein resources are particularly important. Traditional animal-source proteins are becoming increasingly difficult to meet the demand of the current consumer market, and the search for alternative protein sources is urgent. Microbial proteins are biomass obtained from nonpathogenic single-celled organisms, such as bacteria, fungi, and microalgae. They contain large amounts of proteins and essential amino acids as well as a variety of other nutritive substances, which are considered to be promising sustainable alternatives to traditional proteins. In this review, typical approaches to microbial protein synthesis processes were highlighted and the characteristics and applications of different types of microbial proteins were described. Bacteria, fungi, and microalgae can be individually or co-cultured to obtain protein-rich biomass using starch-based raw materials, organic wastes, and one-carbon compounds as fermentation substrates. Microbial proteins have been gradually used in practical applications as foods, nutritional supplements, flavor modifiers, and animal feeds. However, further development and application of microbial proteins require more advanced biotechnological support, screening of good strains, and safety considerations. This review contributes to accelerating the practical application of microbial proteins as a promising alternative protein resource and provides a sustainable solution to the food crisis facing the world.

Solar-driven sugar production directly from CO2 via a customizable electrocatalytic-biocatalytic flow system

Conventional food production is restricted by energy conversion efficiency of natural photosynthesis and demand for natural resources. Solar-driven artificial food synthesis from CO2 provides an intriguing approach to overcome the limitations of natural photosynthesis while promoting carbon-neutral economy, however, it remains very challenging. Here, we report the design of a hybrid electrocatalytic-biocatalytic flow system, coupling photovoltaics-powered electrocatalysis (CO2 to formate) with five-enzyme cascade platform (formate to sugar) engineered via genetic mutation and bioinformatics, which achieves conversion of CO2 to C6 sugar (L-sorbose) with a solar-to-food energy conversion efficiency of 3.5%, outperforming natural photosynthesis by over three-fold. This flow system can in principle be programmed by coupling with diverse enzymes toward production of multifarious food from CO2. This work opens a promising avenue for artificial food synthesis from CO2 under confined environments.

Surface coating combined with in situ cyclic voltammetry to enhance the stability of gas diffusion electrodes for electrochemical CO2 reduction

Electrochemical CO2 reduction (CO2RR), fueled by clean and renewable energy, presents a promising method for utilizing CO2 effectively. The electrocatalytic reduction of CO2 to CO using a gas diffusion electrode (GDE) has shown great potential for industrial applications due to its high reaction rate and selectivity. However, guaranteeing its long-term stability still poses a significant challenge. In this study, we conducted a comprehensive investigation into various strategies to enhance the stability of the GDE. These strategies involved modifying the structure of the substrate, such as the gas diffusion layer (GDL) and the back side of the GDL (macroporous layer side). Additionally, we explored modifications to the catalyst layer (CL) and the front of the CL. To address these stability concerns, we proposed a practical approach that involved surface coating using carbon black in combination with in situ cyclic voltammetry (CV) cycles on Ag/Ag300/polytetrafluoroethylene (PTFE). The partial Faradaic efficiency exceeded 80 % within a span of 70 h. Electron microscopy and electrochemical characterization revealed that the implementation of in situ CV led to a reduction in catalyst particle size and the formation of a porous surface structure. By enhancing the stability of the GDE, this research opens up possibilities for the advancement of hybrid systems that focus on the production and utilization of syngas.

Mid-Long Chain Dicarboxylic Acid Production via Systems Metabolic Engineering: Progress and Prospects

Mid-to-long-chain dicarboxylic acids (DCAi, i ≥ 6) are organic compounds in which two carboxylic acid functional groups are present at the terminal position of the carbon chain. These acids find important applications as structural components and intermediates across various industrial sectors, including organic compound synthesis, food production, pharmaceutical development, and agricultural manufacturing. However, conventional petroleum-based DCA production methods cause environmental pollution, making sustainable development challenging. Hence, the demand for eco-friendly processes and renewable raw materials for DCA production is rising. Owing to advances in systems metabolic engineering, new tools from systems biology, synthetic biology, and evolutionary engineering can now be used for the sustainable production of energy-dense biofuels. Here, we explore systems metabolic engineering strategies for DCA synthesis in various chassis via the conversion of different raw materials into mid-to-long-chain DCAs. Subsequently, we discuss the future challenges in this field and propose synthetic biology approaches for the efficient production and successful commercialization of these acids.

Cascade Electrocatalytic and Thermocatalytic Reduction of CO2 to Propionaldehyde

Electrochemical CO2 reduction can convert CO2 to value-added chemicals, but its selectivity toward C3+ products are very limited. One possible solution is to run the reactions in hybrid processes by coupling electrocatalysis with other catalytic routes. In this contribution, we report the cascade electrocatalytic and thermocatalytic reduction of CO2 to propionaldehyde. Using Cu(OH)2 nanowires as the precatalyst, CO2 /H2 O is reduced to concentrated C2 H4 , CO, and H2 gases in a zero-gap membrane electrode assembly (MEA) reactor. The thermochemical hydroformylation reaction is separately investigated with a series of rhodium-phosphine complexes. The best candidate is identified to be the one with the 1,4-bis(diphenylphosphino)butane diphosphine ligand, which exhibits a propionaldehyde turnover number of 1148 under a mild temperature and close-to-atmospheric pressure. By coupling and optimizing the upstream CO2 electroreduction and downstream hydroformylation reaction, we achieve a propionaldehyde selectivity of ~38 % and a total C3 oxygenate selectivity of 44 % based on reduced CO2 . These values represent a more than seven times improvement over the best prior electrochemical system alone or over two times improvement over other hybrid systems.

Tandem Dual-Site PbCu Electrocatalyst for High-Rate and Selective Glycine Synthesis at Industrial Current Densities

Direct electrosynthesis of high-value amino acids from carbon and nitrogen monomers remains a challenge. Here, we design a tandem dual-site PbCu electrocatalyst for efficient amino acid electrosynthesis. Using oxalic acid (H2C2O4) and hydroxylamine (NH2OH) as the raw reactants, for the first time, we have realized the flow-electrosynthesis of glycine at the industrial current density of 200 mA cm-2 with Faradaic efficiency over 78%. In situ ATR-FTIR spectroscopy characterizations reveal a favorable tandem pathway on the dual-site catalyst. Specifically, the Pb site drives the highly selective electroreduction of H2C2O4 to form glyoxylic acid, and the Cu site accelerates the fast hydrogenation of oxime to form a glycine product. A glycine electrosynthesis (GES)-formaldehyde electrooxidation (FOR) assembly is further established, which synthesizes more valuable chemicals (HCOOH, H2) while minimizing energy consumption. Altogether, we introduce a new strategy to enable the one-step electrosynthesis of high-value amino acid from widely accessible monomers.

Engineering extracellular electron transfer pathways of electroactive microorganisms by synthetic biology for energy and chemicals production

The excessive consumption of fossil fuels causes massive emission of CO2, leading to climate deterioration and environmental pollution. The development of substitutes and sustainable energy sources to replace fossil fuels has become a worldwide priority. Bio-electrochemical systems (BESs), employing redox reactions of electroactive microorganisms (EAMs) on electrodes to achieve a meritorious combination of biocatalysis and electrocatalysis, provide a green and sustainable alternative approach for bioremediation, CO2 fixation, and energy and chemicals production. EAMs, including exoelectrogens and electrotrophs, perform extracellular electron transfer (EET) (i.e., outward and inward EET), respectively, to exchange energy with the environment, whose rate determines the efficiency and performance of BESs. Therefore, we review the synthetic biology strategies developed in the last decade for engineering EAMs to enhance the EET rate in cell-electrode interfaces for facilitating the production of electricity energy and value-added chemicals, which include (1) progress in genetic manipulation and editing tools to achieve the efficient regulation of gene expression, knockout, and knockdown of EAMs; (2) synthetic biological engineering strategies to enhance the outward EET of exoelectrogens to anodes for electricity power production and anodic electro-fermentation (AEF) for chemicals production, including (i) broadening and strengthening substrate utilization, (ii) increasing the intracellular releasable reducing equivalents, (iii) optimizing c-type cytochrome (c-Cyts) expression and maturation, (iv) enhancing conductive nanowire biosynthesis and modification, (v) promoting electron shuttle biosynthesis, secretion, and immobilization, (vi) engineering global regulators to promote EET rate, (vii) facilitating biofilm formation, and (viii) constructing cell-material hybrids; (3) the mechanisms of inward EET, CO2 fixation pathway, and engineering strategies for improving the inward EET of electrotrophic cells for CO2 reduction and chemical production, including (i) programming metabolic pathways of electrotrophs, (ii) rewiring bioelectrical circuits for enhancing inward EET, and (iii) constructing microbial (photo)electrosynthesis by cell-material hybridization; (4) perspectives on future challenges and opportunities for engineering EET to develop highly efficient BESs for sustainable energy and chemical production. We expect that this review will provide a theoretical basis for the future development of BESs in energy harvesting, CO2 fixation, and chemical synthesis.

Probing efficient microbial CO2 utilisation through metabolic and process modelling

Acetogenic gas fermentation is increasingly studied as a promising technology to upcycle carbon-rich waste gasses. Currently the product range is limited, and production yields, rates and titres for a number of interesting products do not allow for economically viable processes. By pairing process modelling and host-agnostic metabolic modelling, we compare fermentation conditions and various products to optimise the processes. The models were then used in a simulation of an industrial-scale bubble column reactor. We find that increased temperatures favour gas transfer rates, particularly for the valuable and limiting H2 , while furthermore predicting an optimal feed composition of 9:1 mol H2 to mol CO2 . Metabolically, the increased non-growth associated maintenance requirements of thermophiles favours the formation of catabolic products. To assess the expansion of the product portfolio beyond acetate, both a product volatility analysis and a metabolic pathway model were implemented. In-situ recovery of volatile products is shown to be within range for acetone but challenging due to the extensive evaporation of water, while the direct production of more valuable compounds by acetogens is metabolically unfavourable compared to acetate and ethanol. We discuss alternative approaches to overcome these challenges to utilise acetogenic CO2 fixation to produce a wider range of carbon negative chemicals.

Catalysts and electrolyzers for the electrochemical CO2 reduction reaction: from laboratory to industrial applications

To cope with the urgent environmental pressure and tight energy demand, using electrocatalytic methods to drive the reduction of carbon dioxide molecules and produce a variety of fuels and chemicals, is one of the effective pathways to achieve carbon neutrality. In recent years, many significant advances in the study of the electrochemical carbon dioxide reduction reaction (CO2RR) have been made, but most of the works exhibit low current density, small electrode area and poor long-term stability, which are not suitable for large-scale industrial applications. Herein, combining the research achievements obtained in laboratories and the practical demand of industrial production, we summarize recent frontier progress in the field of the electrochemical CO2RR, including the fundamentals of catalytic reactions, catalyst design and preparation, and the construction of electrolyzers. In addition, we discuss the bottleneck problem of industrial CO2 electrolysis, and further present the prospect of the essential issues to be solved by the available technology for industrial electrolysis. This review can provide some basic understanding and knowledge accumulation for the development and practical application of electrochemical CO2RR technology.

Compositional and temporal division of labor modulates mixed sugar fermentation by an engineered yeast consortium

Synthetic microbial communities have emerged as an attractive route for chemical bioprocessing. They are argued to be superior to single strains through microbial division of labor (DOL), but the exact mechanism by which DOL confers advantages remains unclear. Here, we utilize a synthetic Saccharomyces cerevisiae consortium along with mathematical modeling to achieve tunable mixed sugar fermentation to overcome the limitations of single-strain fermentation. The consortium involves two strains with each specializing in glucose or xylose utilization for ethanol production. By controlling initial community composition, DOL allows fine tuning of fermentation dynamics and product generation. By altering inoculation delay, DOL provides additional programmability to parallelly regulate fermentation characteristics and product yield. Mathematical models capture observed experimental findings and further offer guidance for subsequent fermentation optimization. This study demonstrates the functional potential of DOL in bioprocessing and provides insight into the rational design of engineered ecosystems for various applications.

Organic Semiconducting Polymers for Augmenting Biosynthesis and Bioconversion

Solar-driven biosynthesis and bioconversion are essential for achieving sustainable resources and renewable energy. These processes harness solar energy to produce biomass, chemicals, and fuels. While they offer promising avenues, some challenges and limitations should be investigated and addressed for their improvement and widespread adoption. These include the low utilization of light energy, the inadequate selectivity of products, and the limited utilization of inorganic carbon/nitrogen sources. Organic semiconducting polymers offer a promising solution to these challenges by collaborating with natural microorganisms and developing artificial photosynthetic biohybrid systems. In this Perspective, we highlight the latest advancements in the use of appropriate organic semiconducting polymers to construct artificial photosynthetic biohybrid systems. We focus on how these systems can enhance the natural photosynthetic efficiency of photosynthetic organisms, create artificial photosynthesis capability of nonphotosynthetic organisms, and customize the value-added chemicals of photosynthetic synthesis. By examining the structure-activity relationships and emphasizing the mechanism of electron transfer based on organic semiconducting polymers in artificial photosynthetic biohybrid systems, we aim to shed light on the potential of this novel strategy for artificial photosynthetic biohybrid systems. Notably, these coupling strategies between organic semiconducting polymers and organisms during artificial photosynthetic biohybrid systems will pave the way for a more sustainable future with solar fuels and chemicals.

Tandem Electro-Thermo-Catalysis for the Oxidative Aminocarbonylation of Arylboronic Acids to Amides from CO2 and Water

Direct CO2 electroreduction to valuable chemicals is critical for carbon neutrality, while its main products are limited to simple C1 /C2 compounds, and traditionally, the anodic O2 byproduct is not utilized. We herein report a tandem electrothermo-catalytic system that fully utilizes both cathodic (i.e., CO) and anodic (i.e., O2 ) products during overall CO2 electrolysis to produce valuable organic amides from arylboronic acids and amines in a separate chemical reactor, following the Pd(II)-catalyzed oxidative aminocarbonylation mechanism. Hexamethylenetetramine (HMT)-incorporated silver and nickel hydroxide carbonate electrocatalysts were prepared for efficient coproduction of CO and O2 with Faradaic efficiencies of 99.3 % and 100 %, respectively. Systematic experiments, operando attenuated total reflection surface-enhanced Fourier transform infrared spectroscopy characterizations and theoretical studies reveal that HMT promotes *CO2 hydrogenation/*CO desorption for accelerated CO2 -to-CO conversion, and O2 inhibits reductive deactivation of the Pd(II) catalyst for enhanced oxidative aminocarbonylation, collectively leading to efficient synthesis of 10 organic amides with high yields of above 81 %. This work demonstrates the effectiveness of a tandem electrothermo-catalytic strategy for economically attractive CO2 conversion and amide synthesis, representing a new avenue to explore the full potential of CO2 utilization.

Co-NC@Co-NP hierarchical nanoforest steering charge exchange efficiency at biotic-abiotic interface for microbial electrochemical carbon reduction

Converting anthropogenic carbon dioxide (CO2) to value-added products using bio-electrochemical conversions represents a promising strategy for producing sustainable fuel. However, the reaction kinetics are hindered by insufficient attachment of microorganisms and limited charge extraction at the bioinorganic interface. A hierarchical nanoforest with doped cobalt‑nitrogen-doped carbon covering cobalt nanoparticle (Co-NC@Co-NP) was integrated with a CO2-to-CH4 conversion microbiome for methane production to address these shortcomings. In-situ nanoforests were developed on the nanosheet by chemical vapor deposition with Co nanoparticles catalyzed. The bio-nanowire-like carbon nanotubes enhanced the electrostatic force for microbe enrichment via the tip effect, providing a maximum of 3.6-fold electron-receiving microbes to utilize reducing equivalents. The Co-NC@Co-NP enhanced the direct electron transfer between microbes and electrodes, reducing the adoption of energy barriers for heme-like proteins. Thus, the optimized electron transfer pathway improved selectivity by a factor of 2.0 compared to the pristine nanosheet biohybrid. Furthermore, the adjusted microbial community structure provided sufficient methanogenesis genes to match the strong electron flow, achieving maximal methane production rates (311.1 mmol/m2/day at -0.9 V vs. Ag/AgCl), 8.62 times higher than those of the counterpart nanosheet biohybrid (36.06 mmol/m2/day). This work demonstrates a comprehensive assessment of biotic-abiotic energy transfer, which may serve as a guiding principle for designing efficient bio-electrochemical systems.

Coupling chemistry and biology for the synthesis of advanced bioproducts

Chemical and biological syntheses can both lead to a myriad of compounds. Biology enables us to harness the metabolism of microbial cell factories to produce key target molecules from renewable biomass-derived substrates. Although bio-based feedstocks are sustainably sourced and more benign than the rapidly depleting fossil fuels that chemical processes have historically relied on, limiting pathways solely to biological reactions may not equate to a greener process overall. In fact, bioreactors rely on substantial quantities of water and can be inefficient since organisms typically operate around ambient conditions and are sensitive to perturbations in their environment. Hybridizing biosynthetic pathways with green chemistry can instead be a more potent strategy to reduce our net manufacturing footprint. Emerging chemistries have demonstrated considerable success in performing complex transformations on biological feedstocks without significant solvent use. Many of these transformations would be too slow to perform enzymatically or infeasible altogether. Here, we put forth the concept that by carefully considering the merits and drawbacks of synthetic biology and chemistry as well as one's own use case, there exist many opportunities for coupling the two. Merging these syntheses can unlock a wider suite of functional group transformations, thereby enabling future manufacturing processes to sustainably access a larger space of valuable, platform chemicals.

Advanced Catalyst Design and Reactor Configuration Upgrade in Electrochemical Carbon Dioxide Conversion

Electrochemical carbon dioxide reduction reaction (CO2 RR) driven by renewable energy shows great promise in mitigating and potentially reversing the devastating effects of anthropogenic climate change and environmental degradation. The simultaneous synthesis of energy-dense chemicals can meet global energy demand while decoupling emissions from economic growth. However, the development of CO2 RR technology faces challenges in catalyst discovery and device optimization that hinder their industrial implementation. In this contribution, a comprehensive overview of the current state of CO2 RR research is provided, starting with the background and motivation for this technology, followed by the fundamentals and evaluated metrics. Then the underlying design principles of electrocatalysts are discussed, emphasizing their structure-performance correlations and advanced electrochemical assembly cells that can increase CO2 RR selectivity and throughput. Finally, the review looks to the future and identifies opportunities for innovation in mechanism discovery, material screening strategies, and device assemblies to move toward a carbon-neutral society.

Super-fast Charging Biohybrid Batteries through a Power-to-formate-to-bioelectricity Process by Combining Microbial Electrochemistry and CO2 Electrolysis

Extensive study on renewable energy storage has been sparked by the growing worries regarding global warming. In this study, incorporating the latest advancements in microbial electrochemistry and electrochemical CO2 reduction, a super-fast charging biohybrid battery was introduced by using pure formic acid as an energy carrier. CO2 electrolyser with a slim-catholyte layer and a solid electrolyte layer was built, which made it possible to use affordable anion exchange membranes and electrocatalysts that are readily accessible. The biohybrid battery only required a 3-minute charging to accomplish an astounding 25-hour discharging phase. In the power-to-formate-to-bioelectricity process, bioconversion played a vital role in restricting both the overall Faradaic efficiency and Energy efficiency. The CO2 electrolyser was able to operate continuously for an impressive total duration of 164 hours under Gas Stand-By model, by storing N2 gas in the extraction chamber during stand-by periods. Additionally, the electric signal generated during the discharging phase was utilized for monitoring water biotoxicity. Functional genes related to formate metabolism were identified in the bioanode and electrochemically active bacteria were discovered. On the other hand, Paracoccus was predominantly found in the used air cathode. These results advance our current knowledge of exploiting biohybrid technology.

Gerhardtite as a Precursor to an Efficient CO-to-Acetate Electroreduction Catalyst

Carbon-carbon coupling electrochemistry on a conventional copper (Cu) catalyst still undergoes low selectivity among many different multicarbon (C2+) chemicals, posing a grand challenge to achieve a single C2+ product. Here, we demonstrate a laser irradiation synthesis of a gerhardtite mineral, Cu2(OH)3NO3, as a catalyst precursor to make a Cu catalyst with abundant stacking faults under reducing conditions. Such structural perturbation modulates electronic microenvironments of Cu, leading to improved d-electron back-donation to the antibonding orbital of *CO intermediates and thus strengthening *CO adsorption. With increased *CO coverage on the defect-rich Cu, we report an acetate selectivity of 56 ± 2% (compared to 31 ± 1% for conventional Cu) and a partial current density of 222 ± 7 mA per square centimeter in CO electroreduction. When run at 400 mA per square centimeter for 40 h in a flow reactor, this catalyst produces 68.3 mmol of acetate throughout. This work highlights the value of a Cu-containing mineral phase in accessing suitable structures for improved selectivity to a single desired C2+ product.

Poly-3-hydroxybutyrate production from acetate by recombinant Pseudomonas stutzeri with blocked L-leucine catabolism and enhanced growth in acetate

Acetate is a low-cost feedstock for the production of different bio-chemicals. Electrochemical reduction of CO2 into acetate and subsequent acetate fermentation is a promising method for transforming CO2 into value-added chemicals. However, the significant inhibitory effect of acetate on microbial growth remains a barrier for acetate-based biorefinery. In this study, the deletion of genes involved in L-leucine degradation was found to be beneficial for the growth of Pseudomonas stutzeri A1501 in acetate. P. stutzeri (Δpst_3217), in which the hydroxymethylglutaryl-CoA lyase catalyzing β-hydroxy-β-methylglutaryl-CoA into acetyl-CoA and acetoacetate was deleted, grew faster than other mutants and exhibited increased tolerance to acetate. Then, the genes phbCAB from Ralstonia eutropha H16 for poly-3-hydroxybutyrate (PHB) biosynthesis were overexpressed in P. stutzeri (∆pst_3217) and the recombinant strain P. stutzeri (∆pst_3217-phbCAB) can accumulate 0.11 g L-1 PHB from commercial acetate. Importantly, P. stutzeri (∆pst_3217-phbCAB) can also use CO2-derived acetate to produce PHB and the accumulated PHB accounted for 5.42% (w/w) of dried cell weight of P. stutzeri (∆pst_3217-phbCAB).

Directing the Selectivity of CO Electrolysis to Acetate by Constructing Metal-Organic Interfaces

Electrochemically converting CO2 to valuable chemicals holds great promise for closing the anthropogenic carbon cycle. Owing to complex reaction pathways and shared rate-determining steps, directing the selectivity of CO2 /CO electrolysis to a specific multicarbon product is very challenging. We report here a strategy for highly selective production of acetate from CO electrolysis by constructing metal-organic interfaces. We demonstrate that the Cu-organic interfaces constructed by in situ reconstruction of Cu complexes show very impressive acetate selectivity, with a high Faradaic efficiency of 84.2 % and a carbon selectivity of 92.1 % for acetate production, in an alkaline membrane electrode assembly electrolyzer. The maximum acetate partial current density and acetate yield reach as high as 605 mA cm-2 and 63.4 %, respectively. Thorough structural characterizations, control experiments, operando Raman spectroscopy measurements, and density functional theory calculation results indicate that the Cu-organic interface creates a favorable reaction microenvironment that enhances *CO adsorption, lowers the energy barrier for C-C coupling, and facilitates the formation of CH3 COOH over other multicarbon products, thus rationalizing the selective acetate production.

Electrical-biological hybrid system for carbon efficient isobutanol production

We have developed an electrical-biological hybrid system wherein an engineered microorganism consumes electrocatalytically produced formate from CO2 to supplement the bioproduction of isobutanol, a valuable fuel chemical. Biological CO2 sequestration is notoriously slow compared to electrochemical CO2 reduction, while electrochemical methods struggle to generate carbon-carbon bonds which readily form in biological systems. A hybrid system provides a promising method for combining the benefits of both biology and electrochemistry. Previously, Escherichia coli was engineered to assimilate formate and CO2 in central metabolism using the reductive glycine pathway. In this work, we have shown that chemical production in E. coli can benefit from single carbon substrates when equipped with the RGP. By installing the RGP and the isobutanol biosynthetic pathway into E. coli and by further genetic modifications, we have generated a strain of E. coli that can consume formate and produce isobutanol at a yield of >100% of theoretical maximum from glucose. Our results demonstrate that carbon produced from electrocatalytically reduced CO2 can bolster chemical production in E. coli. This study shows that E. coli can be engineered towards carbon efficient methods of chemical production.

Design and Construction of Artificial Biological Systems for One-Carbon Utilization

The third-generation (3G) biorefinery aims to use microbial cell factories or enzymatic systems to synthesize value-added chemicals from one-carbon (C1) sources, such as CO2, formate, and methanol, fueled by renewable energies like light and electricity. This promising technology represents an important step toward sustainable development, which can help address some of the most pressing environmental challenges faced by modern society. However, to establish processes competitive with the petroleum industry, it is crucial to determine the most viable pathways for C1 utilization and productivity and yield of the target products. In this review, we discuss the progresses that have been made in constructing artificial biological systems for 3G biorefineries in the last 10 years. Specifically, we highlight the representative works on the engineering of artificial autotrophic microorganisms, tandem enzymatic systems, and chemo-bio hybrid systems for C1 utilization. We also prospect the revolutionary impact of these developments on biotechnology. By harnessing the power of 3G biorefinery, scientists are establishing a new frontier that could potentially revolutionize our approach to industrial production and pave the way for a more sustainable future.

De novo artificial synthesis of hexoses from carbon dioxide

Developing artificial "CO2-sugar" platforms is meaningful for addressing challenges posed by land scarcity and climate change to the supply of dietary sugar. However, upcycling CO2 into complex polyoxygenated carbohydrates involves several major challenges, including achieving enantioselective and thermodynamically driven transformation and expanding product repertoires while reducing energy consumption. We present a versatile chemoenzymatic roadmap based on aldol condensation, iso/epimerization, and dephosphorylation reactions for asymmetric CO2 and H2 assembly into sugars with perfect stereocontrol. In particular, we developed a minimum ATP consumption and the shortest pathway for bottom-up biosynthesis of the fundamental precursor, fructose-6-phosphate, which is valuable for synthesizing structure-diverse sugars and derivatives. Engineering bottleneck-associated enzyme catalysts aided in the thermodynamically driven synthesis of several energy-dense and functional hexoses, such as glucose and D-allulose, featuring higher titer (63 mmol L-1) and CO2-product conversion rates (25 mmol C L-1 h-1) compared to established in vitro CO2-fixing pathways. This chemical-biological platform demonstrated greater carbon conversion yield than the conventional "CO2-bioresource-sugar" process and could be easily extended to precisely synthesize other high-order sugars from CO2.

Designs of Tandem Catalysts and Cascade Catalytic Systems for CO2 Upgrading

Upgrading CO2 into multi-carbon (C2+) compounds through the CO2 reduction reaction (CO2 RR) offers a practical approach to mitigate atmospheric CO2 while simultaneously producing high value chemicals. The reaction pathways for C2+ production involve multi-step proton-coupled electron transfer (PCET) and C-C coupling processes. By increasing the surface coverage of adsorbed protons (*Had ) and *CO intermediates, the reaction kinetics of PCET and C-C coupling can be accelerated, thereby promoting C2+ production. However, *Had and *CO are competitively adsorbed intermediates on monocomponent catalysts, making it difficult to break the linear scaling relationship between the adsorption energies of the *Had /*CO intermediate. Recently, tandem catalysts consisting of multicomponents have been developed to improve the surface coverage of *Had or *CO by enhancing water dissociation or CO2 -to-CO production on auxiliary sites. In this context, we provide a comprehensive overview of the design principles of tandem catalysts based on reaction pathways for C2+ products. Moreover, the development of cascade CO2 RR catalytic systems that integrate CO2 RR with downstream catalysis has expanded the range of potential CO2 upgrading products. Therefore, we also discuss recent advancements in cascade CO2 RR catalytic systems, highlighting the challenges and perspectives in these systems.

Atomic high-spin cobalt(II) center for highly selective electrochemical CO reduction to CH3OH

In this work, via engineering the conformation of cobalt active center in cobalt phthalocyanine molecular catalyst, the catalytic efficiency of electrochemical carbon monoxide reduction to methanol can be dramatically tuned. Based on a collection of experimental investigations and density functional theory calculations, it reveals that the electron rearrangement of the Co 3d orbitals of cobalt phthalocyanine from the low-spin state (S = 1/2) to the high-spin state (S = 3/2), induced by molecular conformation change, is responsible for the greatly enhanced CO reduction reaction performance. Operando attenuated total reflectance surface-enhanced infrared absorption spectroscopy measurements disclose accelerated hydrogenation of CORR intermediates, and kinetic isotope effect validates expedited proton-feeding rate over cobalt phthalocyanine with high-spin state. Further natural population analysis and density functional theory calculations demonstrate that the high spin Co2+ can enhance the electron backdonation via the dxz/dyz-2π* bond and weaken the C-O bonding in *CO, promoting hydrogenation of CORR intermediates.

Electrochemical Reversible Reforming between Ethylamine and Acetonitrile on Heterostructured Pd-Ni(OH)2 Nanosheets

Rational design of electrocatalysts is essential to achieve desirable performance of electrochemical synthesis process. Heterostructured catalysts have thus attracted widespread attention due to their multifunctional intrinsic properties, and diverse catalytic applications with corresponding outstanding activities. Here, we report an in situ restoration strategy for the synthesis of ultrathin Pd-Ni(OH)2 nanosheets. Such Pd-Ni(OH)2 nanosheets exhibit excellent activity and selectivity towards reversible electrochemical reforming of ethylamine and acetonitrile. In the acetonitrile reduction process, Pd acts as reaction center, while Ni(OH)2 provide proton hydrogen through promoting the dissociation of water. Also ethylamine oxidation process can be achieved on the surface of the heterostructured nanosheets with abundant Ni(II) defects. More importantly, an electrolytic cell driven by solar cells was successfully constructed to realize ethylamine-acetonitrile reversible reforming. This work demonstrates the importance of heterostructure engineering in the rational synthesis of multifunctional catalysts towards electrochemical synthesis of fine chemicals.

Alkaline Ionic Liquid Microphase Promotes Deep Reduction of CO2 on Copper

Electrochemical reduction of CO2 to multicarbon (C2+) products using renewable energy sources is an important route to storing sustainable energy and achieving carbon neutrality. It remains a challenge to achieve high C2+ product faraday efficiency (FE) at ampere-level current densities. Herein, we propose the immobilization of an alkaline ionic liquid on copper for promoting the deep reduction of CO2. By this strategy, a C2+ FE of 81.4% can be achieved under a current density of 0.9 A·cm-2 with a half-cell energy conversion efficiency of 47.4% at -0.76 V vs reversible hydrogen electrode (RHE). Particularly, when the current density is as high as 1.8 A·cm-2, the C2+ FE reaches 71.6% at an applied potential of -1.31 V vs RHE. Mechanistic studies demonstrate that the alkaline ionic liquid plays multiple roles of improving the accumulation of CO2 molecules on the copper surface, promoting the activation of the adsorbed CO2, reducing the energy barrier of CO dimerization, stabilizing intermediates, and facilitating the C2+ product formation.

Developing Catalysts Integrated in Gas-Diffusion Electrodes for CO2 Electrolyzers

ConspectusAs the demand for a carbon-neutral society grows rapidly, research on CO2 electrolysis has become very active. Many catalysts are reported for converting CO2 into value-added products by electrochemical reactions, which have to perform at high Faradaic and energy efficiency to become commercially viable. Various types of CO2 electrolyzers have been used in this effort, such as the H-cell, flow cell, and zero-gap membrane-electrode assembly (MEA) cell. H-cell studies are conducted with electrodes immersed in CO2-saturated electrolyte and have been used to elucidate reaction pathways and kinetic parameters of electrochemical CO2 reduction on many types of catalytic surfaces. From a transport phenomenological perspective, the low solubility and diffusion of CO2 to the electrode surface severely limit the maximum attainable current density, and this metric has been shown to have significant influence on the product spectrum. Flow and MEA cells provide a solution in the form of gas-diffusion electrodes (GDEs) that enable gaseous CO2 to closely reach the catalyst layer and yield record-high current densities. Because GDEs involve a complicated interface consisting of the catalyst surface, gaseous CO2, polymer overlayers, and liquid electrolyte, catalysts with high intrinsic activity might not show high performance in these GDE-based electrolyzers. Catalysts showing low overpotentials at low current densities may suffer from poor electron conductivity and mass transfer limitations at high current densities. Furthermore, the stability of the GDE-based catalysts is often compromised as CO2 electrolysis is pursued with high activity, most notoriously by electrolyte flooding.In this Account, we introduce recent examples where the electrocatalysts were integrated in GDEs, achieving high production rates. The performance of such systems is contingent on both GDE and cell design, and various parameters that affect the cell performance are discussed. Gaseous products, such as carbon monoxide, methane, and ethylene, and liquid products, such as formate and ethanol, have been mainly reported with high partial current density using the flow or MEA cells. Different strategies to this end are described, such as controlling microenvironments by the use of polymers mixed within the catalyst layer or the functionalization of catalyst surfaces with ligands to increase local concentrations of intermediates. Unique CO2 electrolyzer designs are also treated, including the incorporation of light-responsive plasmonic catalysts in the GDE, and combining the electrolyzer with a fermenter utilizing a microbial biocatalyst to synthesize complex multicarbon products. Basic conditions which the catalyst should satisfy to be adapted in the GDEs are listed, and our perspective is provided.

Multiscale CO2 Electrocatalysis to C2+ Products: Reaction Mechanisms, Catalyst Design, and Device Fabrication

Electrosynthesis of value-added chemicals, directly from CO2, could foster achievement of carbon neutral through an alternative electrical approach to the energy-intensive thermochemical industry for carbon utilization. Progress in this area, based on electrogeneration of multicarbon products through CO2 electroreduction, however, lags far behind that for C1 products. Reaction routes are complicated and kinetics are slow with scale up to the high levels required for commercialization, posing significant problems. In this review, we identify and summarize state-of-art progress in multicarbon synthesis with a multiscale perspective and discuss current hurdles to be resolved for multicarbon generation from CO2 reduction including atomistic mechanisms, nanoscale electrocatalysts, microscale electrodes, and macroscale electrolyzers with guidelines for future research. The review ends with a cross-scale perspective that links discrepancies between different approaches with extensions to performance and stability issues that arise from extensions to an industrial environment.

Polarized Active Pairs at Grain Boundary Boost CO2 Chemical Fixation

The chemical fixation of CO2 as a C1 feedstock is considered one of the most promising ways to obtain long-chain chemicals, but its efficiency was limited by the ineffective activation of CO2. Herein, we propose a grain boundary engineering strategy to construct polarized active pairs with electron poor-rich character for effective CO2 activation. By taking CeO2 as a model system, we illustrate that the polarized "Ce4+-Ce3+-Ce4+" pairs at the grain boundary can simultaneously accept and donate electrons to coordinate with O and C, respectively, in CO2. By the combination of synchrotron radiation in situ technique and density functional theory calculations, the mechanism of the catalytic reaction has been systematically investigated. As a result, the CeO2 nanosheets with a rich grain boundary show a high DMC yield of 60.3 mmol/gcat with 100% atomic economy. This study provides a practical way for the chemical fixation of CO2 to high-value-added chemicals via grain boundary engineering.

Surface passivation for highly active, selective, stable, and scalable CO2 electroreduction

Electrochemical conversion of CO2 to formic acid using Bismuth catalysts is one the most promising pathways for industrialization. However, it is still difficult to achieve high formic acid production at wide voltage intervals and industrial current densities because the Bi catalysts are often poisoned by oxygenated species. Herein, we report a Bi3S2 nanowire-ascorbic acid hybrid catalyst that simultaneously improves formic acid selectivity, activity, and stability at high applied voltages. Specifically, a more than 95% faraday efficiency was achieved for the formate formation over a wide potential range above 1.0 V and at ampere-level current densities. The observed excellent catalytic performance was attributable to a unique reconstruction mechanism to form more defective sites while the ascorbic acid layer further stabilized the defective sites by trapping the poisoning hydroxyl groups. When used in an all-solid-state reactor system, the newly developed catalyst achieved efficient production of pure formic acid over 120 hours at 50 mA cm-2 (200 mA cell current).

Zn-induced electron-rich Sn catalysts enable highly efficient CO2 electroreduction to formate

Renewable-energy-driven CO2 electroreduction provides a promising way to address the growing greenhouse effect issue and produce value-added chemicals. As one of the bulk chemicals, formic acid/formate has the highest revenue per mole of electrons among various products. However, the scaling up of CO2-to-formate for practical applications with high faradaic efficiency (FE) and current density is constrained by the difficulty of precisely reconciling the competing intermediates (*COOH and HCOO*). Herein, a Zn-induced electron-rich Sn electrocatalyst was reported for CO2-to-formate with high efficiency. The faradaic efficiency of formate (FEformate) could reach 96.6%, and FEformate > 90% was maintained at formate partial current density up to 625.4 mA cm-1. Detailed study indicated that catalyst reconstruction occurred during electrolysis. With appropriate electron accumulation, the electron-rich Sn catalyst could facilitate the adsorption and activation of CO2 molecules to form a intermediate and then promoted the carbon protonation of to yield a HCOO* intermediate. Afterwards, the HCOO* → HCOOH* proceeded via another proton-coupled electron transfer process, leading to high activity and selectivity for formate production.

Bioconversion of C1 feedstocks for chemical production using Pichia pastoris

Bioconversion of C1 feedstocks for chemical production offers a promising solution to global challenges such as the energy and food crises and climate change. The methylotroph Pichia pastoris is an attractive host system for the production of both recombinant proteins and chemicals from methanol. Recent studies have also demonstrated its potential for utilizing CO2 through metabolic engineering or coupling with electrocatalysis. This review focuses on the bioconversion of C1 feedstocks for chemical production using P. pastoris. Herein the challenges and feasible strategies for chemical production in P. pastoris are discussed. The potential of P. pastoris to utilize other C1 feedstocks - including CO2 and formate - is highlighted, and new insights from the perspectives of synthetic biology and material science are proposed.

Electrochemical transformations catalyzed by cytochrome P450s and peroxidases

Cytochrome P450s (Cyt P450s) and peroxidases are enzymes featuring iron heme cofactors that have wide applicability as biocatalysts in chemical syntheses. Cyt P450s are a family of monooxygenases that oxidize fatty acids, steroids, and xenobiotics, synthesize hormones, and convert drugs and other chemicals to metabolites. Peroxidases are involved in breaking down hydrogen peroxide and can oxidize organic compounds during this process. Both heme-containing enzymes utilize active Fe^IVO intermediates to oxidize reactants. By incorporating these enzymes in stable thin films on electrodes, Cyt P450s and peroxidases can accept electrons from an electrode, albeit by different mechanisms, and catalyze organic transformations in a feasible and cost-effective way. This is an advantageous approach, often called bioelectrocatalysis, compared to their biological pathways in solution that require expensive biochemical reductants such as NADPH or additional enzymes to recycle NADPH for Cyt P450s. Bioelectrocatalysis also serves as an ex situ platform to investigate metabolism of drugs and bio-relevant chemicals. In this paper we review biocatalytic electrochemical reactions using Cyt P450s including C-H activation, S-oxidation, epoxidation, N-hydroxylation, and oxidative N-, and O-dealkylation; as well as reactions catalyzed by peroxidases including synthetically important oxidations of organic compounds. Design aspects of these bioelectrocatalytic reactions are presented and discussed, including enzyme film formation on electrodes, temperature, pH, solvents, and activation of the enzymes. Finally, we discuss challenges and future perspective of these two important bioelectrocatalytic systems.