David N. Abram

New insights into the electrochemical reduction of carbon dioxide on metallic copper surfaces

We report new insights into the electrochemical reduction of CO2 on a metallic copper surface, enabled by the development of an experimental methodology with unprecedented sensitivity for the identification and quantification of CO2 electroreduction products. This involves a custom electrochemical cell designed to maximize product concentrations coupled to gas chromatography and nuclear magnetic resonance for the identification and quantification of gas and liquid products, respectively. We studied copper across a range of potentials and observed a total of 16 different CO2 reduction products, five of which are reported here for the first time, thus providing the most complete view of the reaction chemistry reported to date. Taking into account the chemical identities of the wide range of C1–C3 products generated and the potential-dependence of their turnover frequencies, mechanistic information is deduced. We discuss a scheme for the formation of multicarbon products involving enol-like surface intermediates as a possible pathway, accounting for the observed selectivity for eleven distinct C2+ oxygenated products including aldehydes, ketones, alcohols, and carboxylic acids.

Electrocatalytic Conversion of Carbon Dioxide to Methane and Methanol on Transition Metal Surfaces

Fuels and industrial chemicals that are conventionally derived from fossil resources could potentially be produced in a renewable, sustainable manner by an electrochemical process that operates at room temperature and atmospheric pressure, using only water, CO2, and electricity as inputs. To enable this technology, improved catalysts must be developed. Herein, we report trends in the electrocatalytic conversion of CO2 on a broad group of seven transition metal surfaces: Au, Ag, Zn, Cu, Ni, Pt, and Fe. Contrary to conventional knowledge in the field, all metals studied are capable of producing methane or methanol. We quantify reaction rates for these two products and describe catalyst activity and selectivity in the framework of CO binding energies for the different metals. While selectivity toward methane or methanol is low for most of these metals, the fact that they are all capable of producing these products, even at a low rate, is important new knowledge. This study reveals a richer surface chemistry for transition metals than previously known and provides new insights to guide the development of improved CO2 conversion catalysts.

Synthesis of thin film AuPd alloys and their investigation for electrocatalytic CO2 reduction

We synthesize and investigate AuPd alloys for the electrocatalytic reduction of CO2. Thin films of AuPd were synthesized using an electron-beam co-deposition method, which yields uniform, phase-pure metal alloys with composition control. Scanning electron microscope images show that the thin films are relatively uniform and flat in morphology. X-ray diffraction showed alloying and phase homogeneity within the AuPd thin films. Elemental mapping of Au and Pd with scanning transmission electron microscopy shows that AuPd thin films are uniform in composition on the nanometer scale. X-ray photoelectron spectroscopy characterization indicates that AuPd alloys are slightly Au-rich on the surface and follow a similar trend to the bulk composition as determined by Vegards Law. CO2 reduction activity and selectivity were investigated across the AuPd system. All AuPd alloys were found to be more active and selective for formate production than either of the pure metals, indicating that Au and Pd can act synergistically to yield new electrocatalytic properties.

An X-ray Photoelectron Spectroscopy Study of Surface Changes on Brominated and Sulfur-Treated Activated Carbon Sorbents during Mercury Capture: Performance of Pellet versus Fiber Sorbents

This work explores surface changes and the Hg capture performance of brominated activated carbon (AC) pellets, sulfur-treated AC pellets, and sulfur-treated AC fibers upon exposure to simulated Powder River Basin-fired flue gas. Hg breakthrough curves yielded specific Hg capture amounts by means of the breakthrough shapes and times for the three samples. The brominated AC pellets showed a sharp breakthrough after 170-180 h and a capacity of 585 μg of Hg/g, the sulfur-treated AC pellets exhibited a gradual breakthrough after 80-90 h and a capacity of 661 μg of Hg/g, and the sulfur-treated AC fibers showed no breakthrough even after 1400 h, exhibiting a capacity of >9700 μg of Hg/g. X-ray photoelectron spectroscopy was used to analyze sorbent surfaces before and after testing to show important changes in quantification and oxidation states of surface Br, N, and S after exposure to the simulated flue gas. For the brominated and sulfur-treated AC pellet samples, the amount of surface-bound Br and reduced sulfur groups decreased upon Hg capture testing, while the level of weaker Hg-binding surface S(VI) and N species (perhaps as NH4(+)) increased significantly. A high initial concentration of strong Hg-binding reduced sulfur groups on the surface of the sulfur-treated AC fiber is likely responsible for this sorbents minimal accumulation of S(VI) species during exposure to the simulated flue gas and is linked to its superior Hg capture performance compared to that of the brominated and sulfur-treated AC pellet samples.

Improved CO2 reduction activity towards C2+ alcohols on a tandem gold on copper electrocatalyst

The discovery of materials for the electrochemical transformation of carbon dioxide into liquid fuels has the potential to impact large-scale storage of renewable energies and reduce carbon emissions. Here, we report the discovery of an electrocatalyst composed of gold nanoparticles on a polycrystalline copper foil (Au/Cu) that is highly active for CO2 reduction to alcohols. At low overpotentials, the Au/Cu electrocatalyst is over 100 times more selective for the formation of products containing C–C bonds versus methane or methanol, largely favouring the generation of alcohols over hydrocarbons. A combination of electrochemical testing and transport modelling supports the hypothesis that CO2 reduction on gold generates a high CO concentration on nearby copper, where CO is further reduced to alcohols such as ethanol and n-propanol under locally alkaline conditions. The bimetallic Au/Cu electrocatalyst exhibits synergistic activity and selectivity superior to gold, copper or AuCu alloys, and opens new possibilities for the development of CO2 reduction electrodes exploiting tandem catalysis mechanisms.The electrochemical transformation of CO2 into liquid fuels is a major challenge. Now, Jaramillo, Hahn and co-workers present a Au/Cu catalyst highly active to C2+ alcohols at low overpotentials as a result of a tandem mechanism where CO2 is reduced to CO on Au and further reduced to C2+ alcohols on nearby Cu.