Electroreduction of CO 2 (eCO 2 RR) is a potentially sustainable approach for carbon-based chemical production. Despite significant progress, performing eCO 2 RR economically at scale is challenging. Here we report meeting key technoeconomic benchmarks simultaneously through electrolyte engineering and process optimization. A systematic flow electrolysis studyperforming eCO 2 RR to CO on Ag nanoparticles as a function of electrolyte composition (cations, anions), electrolyte concentration, electrolyte flow rate, cathode catalyst loading, and CO 2 flow rate -resulted in partial current densities of 417 and 866 mA/cm 2 with faradaic efficiencies of 100 and 98 % at cell potentials of À 2.5 and À 3.0 V with full cell energy efficiencies of 53 and 43 %, and a conversion per pass of 17 and 36 %, respectively, when using a CsOH-based electrolyte. The cumulative insights of this study led to the formulation of system design rules for high rate, highly selective, and highly energy efficient eCO 2 RR to CO.[a] S.

The electrochemical reduction of CO 2 (ECO 2 R) is a promising method for reducing CO 2 emissions and producing carbonneutral fuels if long-term durability of electrodes can be achieved by identifying and addressing electrode degradation mechanisms. This work investigates the degradation of gas diffusion electrodes (GDEs) in a flowing, alkaline CO 2 electrolyzer via the formation of carbonate deposits on the GDE surface. These carbonate deposits were found to impede electrode performance after only 6 h of operation at current densities ranging from −50 to −200 mA cm −2 . The rate of carbonate deposit formation on the GDE surface was determined to increase with increasing electrolyte molarity and became more prevalent in K + -containing as opposed to Cs + -containing electrolytes. Electrolyte composition and concentration also had significant effects on the morphology, distribution, and surface coverage of the carbonate deposits. For example, carbonates formed in K + -containing electrolytes formed concentrated deposit regions of varying morphology on the GDE surface, while those formed in Cs + -containing electrolytes appeared as small crystals, well dispersed across the electrode surface. Both deposits occluding the catalyst layer surface and those found within the microporous layer and carbon fiber substrate of the electrode were found to diminish performance in ECO 2 R, leading to rapid loss of CO production after ∼50% of the catalyst layer surface was occluded. Additionally, carbonate deposits reduced GDE hydrophobicity, leading to increased flooding and internal deposits within the GDE substrate. Electrolyte engineering-based solutions are suggested for improved GDE durability in future work.

The renewable electricity-powered electrolysis of CO 2 could be a viable carbon-neutral method for producing carbon-based value-added chemicals like carbon monoxide, formic acid, ethylene, and ethanol. A typical CO 2 electrolyzer suffers, however, from the high power requirements, mainly due to the energy-intense anode reaction. In this work, we decrease the anode overpotential and thus reduce the overall cell energy consumption by using a NiFe-based bimetallic catalyst at the anode and applying a magnetic field. For a CO 2 electrolysis process producing CO in a gas diffusion electrode-based flow electrolyzer, we demonstrate that power savings in the range from 7% to 64% can be achieved at CO partial current densities exceeding −300 mA/cm 2 using a NiFe catalyst at the anode and/or by using a magnetic field at the anode. We achieve a maximum CO partial current density of −565 mA/cm 2 at a full cell energy efficiency of 45% with 2 M KOH as the electrolyte.

Indium phosphide core/shell nanocrystals hold promise to replace heavy-metal-based emissive materials for bioimaging and optoelectronic applications. Uniformity of the shell passivation and the interfacial defects are critical for achieving improved optical properties. A combination of Fourier-transform infrared spectroscopy (FTIR) and liquid and solid-state NMR spectroscopy revealed a strong correlation between interfacial oxidation and photoluminescence of InP-based core/shell quantum dots. Using an automated sequential shell growth approach enabled efficient flow synthesis of InP/ZnSe/ZnS quantum dots, exhibiting high-quantum yields and narrow emission line widths. Feeding individual precursors into the reactor channel in a sequential fashion combined with inline reaction monitoring enabled precise control over layer-by-layer shell passivation of the core particles. Our findings suggest that an unintentional aminolytic reaction between oleylamine and carboxylates (two most commonly used starting materials for colloidal synthesis) introduces oxidative defects during the shelling process, thus limiting their optical properties.

Indium phosphide (InP) nanocrystals have emerged as a viable alternative to heavy metal-based colloidal quantum dots for optoelectronic applications. Traditionally, the presence of trace amounts of water during the synthesis of colloidal quantum dots is considered an undesired impurity because it prevents or slows down colloidal growth and alters the surface properties. Here, we report that fine-tuning the amount of trace water is the key for achieving sizefocused growth of monodisperse InP nanocrystals synthesized using aminophosphine precursors. Using solid-state and solution nuclear magnetic resonance, we investigated the role of trace amounts of water in surface oxidation and precursor conversion reactions. Molecular insights from UV−vis spectroscopy and NMR revealed a profound contrast between the growth rates of the nanocrystals upon the addition of water to the reaction system. We demonstrate that by addition of a specific amount of water, the reactivity of the phosphorous precursor can be tuned to enable a constant supply of monomer throughout the reaction. Under an optimal precursor conversion rate, a size-focused growth behavior that is rare for InP nanocrystals is observed, suggesting the presence of an artificial LaMer-like growth regime.

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The electrochemical reduction of CO2 (CO2RR) holds promise for the reduction of environmentally taxing CO2 emissions, for the carbon-neutral production of valuable fuels and chemicals, and for storage of excess renewable energy from intermittent sources such as wind and solar in chemical products. Durability of cathodes used in high-throughput CO2RR systems is of paramount importance for the commercial readiness of the CO2RR technology. In this study, we investigate the durability of silver-coated gas diffusion electrode cathodes under potential cycling conditions to simulate the impact of repeated cycles of startup and shutdown as might be experienced in connection with a variable renewable power source. We determine that cycling can impact the cathode via two distinct degradation mechanisms: (1) carbonate formation at negative potentials and (2) catalyst layer restructuring and loss in the relatively positive “oxide formation” potential range. We also explore tailored potential cycling as a mechanism for inhibiting carbonate formation by interrupting the high concentration of OH– at the catalyst layer. The findings from this work lend insight into the types of variable potential operating conditions under which CO2RR systems can deliver continuous, robust performance.

The Cover Feature illustrates how mechanistic insights can used to engineer the electrolyte composition and formulate system design rules for intensified electroreduction of CO2 to CO. More information can be found in the Aricle by S. S. Bhargava et al.