Acidic media enables oxygen-tolerant electrosynthesis of multicarbon products from simulated flue gas.

Renewable electricity powered electrochemical CO2 reduction (CO2R) offers a valuable method to close the carbon cycle and reduce our overreliance on fossil fuels. However, high purity CO2 is usually required as feedstock, which potentially decreases the feasibility and economic viability of the process. Direct conversion of flue gas is an attractive option but is challenging due to the low CO2 concentration and the presence of O2 impurities. As a result, up to 99% of the applied current can be lost towards the undesired oxygen reduction reaction (ORR). Here, we show that acidic electrolyte can significantly suppress ORR on Cu, enabling generation of multicarbon products from simulated flue gas. Using a composite Cu and carbon supported single-atom Ni tandem electrocatalyst, we achieved a multicarbon Faradaic efficiency of 46.5% at 200 mA cm-2, which is ~20 times higher than bare Cu under alkaline conditions. We also demonstrate stable performance for 24 h with a multicarbon product full-cell energy efficiency of 14.6%. Strikingly, this result is comparable to previously reported acidic CO2R systems using pure CO2. Our findings demonstrate a potential pathway towards designing efficient electrolyzers for direct conversion of flue gas to value-added chemicals and fuels.

High-Rate and Selective CO2 Electrolysis to Ethylene via Metal-Organic-Framework-Augmented CO2 Availability.

High-rate conversion of carbon dioxide (CO2 ) to ethylene (C2 H4 ) in the CO2 reduction reaction (CO2 RR) requires fine control over the phase boundary of the gas diffusion electrode (GDE) to overcome the limit of CO2 solubility in aqueous electrolytes. Here, a metal-organic framework (MOF)-functionalized GDE design is presented, based on a catalysts:MOFs:hydrophobic substrate materials layered architecture, that leads to high-rate and selective C2 H4 production in flow cells and membrane electrode assembly (MEA) electrolyzers. It is found that using electroanalysis and operando X-ray absorption spectroscopy (XAS), MOF-induced organic layers in GDEs augment the local CO2 concentration near the active sites of the Cu catalysts. MOFs with different CO2 adsorption abilities are used, and the stacking ordering of MOFs in the GDE is varied. While sputtering Cu on poly(tetrafluoroethylene) (PTFE) (Cu/PTFE) exhibits 43% C2 H4 Faradaic efficiency (FE) at a current density of 200 mA cm- 2 in a flow cell, 49% C2 H4 FE at 1 A cm- 2 is achieved on MOF-augmented GDEs in CO2 RR. MOF-augmented GDEs are further evaluated in an MEA electrolyzer, achieving a C2 H4 partial current density of 220 mA cm-2 for CO2 RR and 121 mA cm-2 for the carbon monoxide reduction reaction (CORR), representing 2.7-fold and 15-fold improvement in C2 H4 production rate, compared to those obtained on bare Cu/PTFE.

Chloride-mediated selective electrosynthesis of ethylene and propylene oxides at high current density.

Chemicals manufacturing consumes large amounts of energy and is responsible for a substantial portion of global carbon emissions. Electrochemical systems that produce the desired compounds by using renewable electricity offer a route to lower carbon emissions in the chemicals sector. Ethylene oxide is among the world's most abundantly produced commodity chemicals because of its importance in the plastics industry, notably for manufacturing polyesters and polyethylene terephthalates. We applied an extended heterogeneous:homogeneous interface, using chloride as a redox mediator at the anode, to facilitate the selective partial oxidation of ethylene to ethylene oxide. We achieved current densities of 1 ampere per square centimeter, Faradaic efficiencies of ~70%, and product specificities of ~97%. When run at 300 milliamperes per square centimeter for 100 hours, the system maintained a 71(±1)% Faradaic efficiency throughout.

Enhanced Nitrate-to-Ammonia Activity on Copper-Nickel Alloys via Tuning of Intermediate Adsorption.

Electrochemical conversion of nitrate (NO3-) into ammonia (NH3) recycles nitrogen and offers a route to the production of NH3, which is more valuable than dinitrogen gas. However, today's development of NO3- electroreduction remains hindered by the lack of a mechanistic picture of how catalyst structure may be tuned to enhance catalytic activity. Here we demonstrate enhanced NO3- reduction reaction (NO3-RR) performance on Cu50Ni50 alloy catalysts, including a 0.12 V upshift in the half-wave potential and a 6-fold increase in activity compared to those obtained with pure Cu at 0 V vs reversible hydrogen electrode (RHE). Ni alloying enables tuning of the Cu d-band center and modulates the adsorption energies of intermediates such as *NO3-, *NO2, and *NH2. Using density functional theory calculations, we identify a NO3-RR-to-NH3 pathway and offer an adsorption energy-activity relationship for the CuNi alloy system. This correlation between catalyst electronic structure and NO3-RR activity offers a design platform for further development of NO3-RR catalysts.

A spongy nickel-organic CO2 reduction photocatalyst for nearly 100% selective CO production.

Solar-driven photocatalytic conversion of CO2 into fuels has attracted a lot of interest; however, developing active catalysts that can selectively convert CO2 to fuels with desirable reaction products remains a grand challenge. For instance, complete suppression of the competing H2 evolution during photocatalytic CO2-to-CO conversion has not been achieved before. We design and synthesize a spongy nickel-organic heterogeneous photocatalyst via a photochemical route. The catalyst has a crystalline network architecture with a high concentration of defects. It is highly active in converting CO2 to CO, with a production rate of ~1.6 × 104 µmol hour-1 g-1. No measurable H2 is generated during the reaction, leading to nearly 100% selective CO production over H2 evolution. When the spongy Ni-organic catalyst is enriched with Rh or Ag nanocrystals, the controlled photocatalytic CO2 reduction reactions generate formic acid and acetic acid. Achieving such a spongy nickel-organic photocatalyst is a critical step toward practical production of high-value multicarbon fuels using solar energy.