Thomas Burdyny

CO2 electroreduction to ethylene via hydroxide-mediated copper catalysis at an abrupt interface

A very basic pathway from CO2 to ethylene Ethylene is an important commodity chemical for plastics. It is considered a tractable target for synthesizing renewably from carbon dioxide (CO2). The challenge is that the performance of the copper electrocatalysts used for this conversion under the required basic reaction conditions suffers from the competing reaction of CO2 with the base to form bicarbonate. Dinh et al. designed an electrode that tolerates the base by optimizing CO2 diffusion to the catalytic sites (see the Perspective by Ager and Lapkin). This catalyst design delivers 70% efficiency for 150 hours. Science, this issue p. 783; see also p. 707 Electrode design facilitates reductive coupling of CO2 to ethylene under otherwise inhibitory strongly basic conditions. Carbon dioxide (CO2) electroreduction could provide a useful source of ethylene, but low conversion efficiency, low production rates, and low catalyst stability limit current systems. Here we report that a copper electrocatalyst at an abrupt reaction interface in an alkaline electrolyte reduces CO2 to ethylene with 70% faradaic efficiency at a potential of −0.55 volts versus a reversible hydrogen electrode (RHE). Hydroxide ions on or near the copper surface lower the CO2 reduction and carbon monoxide (CO)–CO coupling activation energy barriers; as a result, onset of ethylene evolution at −0.165 volts versus an RHE in 10 molar potassium hydroxide occurs almost simultaneously with CO production. Operational stability was enhanced via the introduction of a polymer-based gas diffusion layer that sandwiches the reaction interface between separate hydrophobic and conductive supports, providing constant ethylene selectivity for an initial 150 operating hours.

Steering post-C–C coupling selectivity enables high efficiency electroreduction of carbon dioxide to multi-carbon alcohols

AbstractEngineering copper-based catalysts that favour high-value alcohols is desired in view of the energy density, ready transport and established use of these liquid fuels. In the design of catalysts, much progress has been made to target the C–C coupling step; whereas comparatively little effort has been expended to target post-C–C coupling reaction intermediates. Here we report a class of core–shell vacancy engineering catalysts that utilize sulfur atoms in the nanoparticle core and copper vacancies in the shell to achieve efficient electrochemical CO2 reduction to propanol and ethanol. These catalysts shift selectivity away from the competing ethylene reaction and towards liquid alcohols. We increase the alcohol-to-ethylene ratio more than sixfold compared with bare-copper nanoparticles, highlighting an alternative approach to electroproduce alcohols instead of alkenes. We achieve a C2+ alcohol production rate of 126 ± 5 mA cm−2 with a selectivity of 32 ± 1% Faradaic efficiency.The conversion of carbon dioxide into multi-carbon alcohols would enable the synthesis of sustainable liquid fuels with high energy densities. Now, vacancy-engineered core–shell copper-based catalysts are able to shift the selectivity of electrochemical CO2 reduction into alcohols instead of alkenes, as obtained with bare-copper catalysts.

Joint tuning of nanostructured Cu-oxide morphology and local electrolyte programs high-rate CO2 reduction to C2H4

Electrochemical ethylene production rates are enhanced by pushing favourable local electrolyte conditions to occur at higher current densities and lower relative overpotentials. In particular the combined influences of electrode morphology and buffering on electrode pH and CO2 conditions are assessed.

Hydronium-Induced Switching between CO2 Electroreduction Pathways

Over a broad range of operating conditions, many CO2 electroreduction catalysts can maintain selectivity toward certain reduction products, leading to materials and surfaces being categorized according to their products; here we ask, is product selectivity truly a property of the catalyst? Silver is among the best electrocatalysts for CO in aqueous electrolytes, where it reaches near-unity selectivity. We consider the hydrogenations of the oxygen and carbon atoms via the two proton-coupled-electron-transfer processes as chief determinants of product selectivity; and find using density functional theory (DFT) that the hydronium (H3O+) intermediate plays a key role in the first oxygen hydrogenation step and lowers the activation energy barrier for CO formation. When this hydronium influence is removed, the activation energy barrier for oxygen hydrogenation increases significantly, and the barrier for carbon hydrogenation is reduced. These effects make the formate reaction pathway more favorable than CO. Experimentally, we then carry out CO2 reduction in highly concentrated potassium hydroxide (KOH), limiting the hydronium concentration in the aqueous electrolyte. The product selectivity of a silver catalyst switches from entirely CO under neutral conditions to over 50% formate in the alkaline environment. The simulated and experimentally observed selectivity shift provides new insights into the role of hydronium on CO2 electroreduction processes and the ability for electrolyte manipulation to directly influence transition state (TS) kinetics, altering favored CO2 reaction pathways. We argue that selectivity should be considered less of an intrinsic catalyst property, and rather a combined product of the catalyst and reaction environment.

A penalty on photosynthetic growth in fluctuating light

Fluctuating light is the norm for photosynthetic organisms, with a wide range of frequencies (0.00001 to 10 Hz) owing to diurnal cycles, cloud cover, canopy shifting and mixing; with broad implications for climate change, agriculture and bioproduct production. Photosynthetic growth in fluctuating light is generally considered to improve with increasing fluctuation frequency. Here we demonstrate that the regulation of photosynthesis imposes a penalty on growth in fluctuating light for frequencies in the range of 0.01 to 0.1 Hz (organisms studied: Synechococcus elongatus and Chlamydomonas reinhardtii). We provide a comprehensive sweep of frequencies and duty cycles. In addition, we develop a 2nd order model that identifies the source of the penalty to be the regulation of the Calvin cycle – present at all frequencies but compensated at high frequencies by slow kinetics of RuBisCO.

Low pressure supercritical CO 2 extraction of astaxanthin from Haematococcus pluvialis demonstrated on a microfluidic chip

This study demonstrates the efficacy of low pressure supercritical CO2 extraction of astaxanthin from disrupted Haematococcus pluvialis. A microfluidic reactor was employed that enabled excellent control and allowed direct monitoring of the whole process at the single cell level, in real time. Astaxanthin extraction using ScCO2 achieved 92% recovery at 55 °C and 8 MPa applied over 15 h. With the addition of co-solvents, ethanol and olive oil, the extraction rates in both experiments were significantly improved reaching full recovery within a few minutes. Notably, for the ethanol case, the timescales of extraction process are reduced 1800-fold from 15 h to 30 s at 55 °C and 8 MPa, representing the fastest complete astaxanthin extraction at such low pressures.

Copper nanocavities confine intermediates for efficient electrosynthesis of C3 alcohol fuels from carbon monoxide

The electrosynthesis of higher-order alcohols from carbon dioxide and carbon monoxide addresses the need for the long-term storage of renewable electricity; unfortunately, the present-day performance remains below what is needed for practical applications. Here we report a catalyst design strategy that promotes C3 formation via the nanoconfinement of C2 intermediates, and thereby promotes C2:C1 coupling inside a reactive nanocavity. We first employed finite-element method simulations to assess the potential for the retention and binding of C2 intermediates as a function of cavity structure. We then developed a method of synthesizing open Cu nanocavity structures with a tunable geometry via the electroreduction of Cu2O cavities formed through acidic etching. The nanocavities showed a morphology-driven shift in selectivity from C2 to C3 products during the carbon monoxide electroreduction, to reach a propanol Faradaic efficiency of 21 ± 1% at a conversion rate of 7.8 ± 0.5 mA cm−2 at −0.56 V versus a reversible hydrogen electrode.The production of higher alcohols is very valuable because of their high volumetric energy density. Now, Sargent, Sinton and co-workers report the design of copper nanoparticles with tailored nanocavities that promote n-propanol formation by the coupling of C2 and C1 intermediates inside the cavity.

Combined high alkalinity and pressurization enable efficient CO2 electroreduction to CO

The electroreduction of carbon dioxide (CO2) to carbon monoxide (CO) is a promising strategy to utilize CO2 emissions while generating a high value product. Commercial CO2 electroreduction systems will require high current densities (>100 mA cm−2) as well as improved energetic efficiencies (EEs), achieved via high CO selectivity and lowered applied potentials. Here we report a silver (Ag)-based system that exhibits the lowest overpotential among CO2-to-CO electrolyzers operating at high current densities, 300 mV at 300 mA cm−2, with near unity selectivity. We achieve these improvements in voltage efficiency and selectivity via operation in a highly alkaline reaction environment (which decreases overpotentials) and system pressurization (which suppresses the generation of alternative CO2 reduction products), respectively. In addition, we report a new record for the highest half-cell EE (>80%) for CO production at 300 mA cm−2.

A Surface Reconstruction Route to High Productivity and Selectivity in CO2 Electroreduction toward C2+ Hydrocarbons

Electrochemical carbon dioxide reduction (CO2 ) is a promising technology to use renewable electricity to convert CO2 into valuable carbon-based products. For commercial-scale applications, however, the productivity and selectivity toward multi-carbon products must be enhanced. A facile surface reconstruction approach that enables tuning of CO2 -reduction selectivity toward C2+ products on a copper-chloride (CuCl)-derived catalyst is reported here. Using a novel wet-oxidation process, both the oxidation state and morphology of Cu surface are controlled, providing uniformity of the electrode morphology and abundant surface active sites. The Cu surface is partially oxidized to form an initial Cu (I) chloride layer which is subsequently converted to a Cu (I) oxide surface. High C2+ selectivity on these catalysts are demonstrated in an H-cell configuration, in which 73% Faradaic efficiency (FE) for C2+ products is reached with 56% FE for ethylene (C2 H4 ) and overall current density of 17 mA cm-2 . Thereafter, the method into a flow-cell configuration is translated, which allows operation in a highly alkaline medium for complete suppression of CH4 production. A record C2+ FE of ≈84% and a half-cell power conversion efficiency of 50% at a partial current density of 336 mA cm-2 using the reconstructed Cu catalyst are reported.