Toru Hatsukade

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.

Engineering Cu surfaces for the electrocatalytic conversion of CO2: Controlling selectivity toward oxygenates and hydrocarbons

Significance Anthropogenic global warming necessitates the development of renewable carbon-free and carbon-neutral technologies for the future. Electrochemical CO2 reduction is one such technology that has the potential to impact climate change by enabling sustainable routes for the production of fuels and chemicals. Whereas the field of CO2 reduction has attracted great interest, current state-of-the-art electrocatalysts must be improved in product selectivity and energy efficiency to make this pathway viable for the future. Here, we investigate how controlling the surface structure of copper electrocatalysts can guide CO2 reduction activity and selectivity. We show how the coordination environment of Cu surfaces influences oxygenate vs. hydrocarbon formation, providing insights on how to improve selectivity and energy efficiency toward more valuable CO2 reduction products. In this study we control the surface structure of Cu thin-film catalysts to probe the relationship between active sites and catalytic activity for the electroreduction of CO2 to fuels and chemicals. Here, we report physical vapor deposition of Cu thin films on large-format (∼6 cm2) single-crystal substrates, and confirm epitaxial growth in the <100>, <111>, and <751> orientations using X-ray pole figures. To understand the relationship between the bulk and surface structures, in situ electrochemical scanning tunneling microscopy was conducted on Cu(100), (111), and (751) thin films. The studies revealed that Cu(100) and (111) have surface adlattices that are identical to the bulk structure, and that Cu(751) has a heterogeneous kinked surface with (110) terraces that is closely related to the bulk structure. Electrochemical CO2 reduction testing showed that whereas both Cu(100) and (751) thin films are more active and selective for C–C coupling than Cu(111), Cu(751) is the most selective for >2e− oxygenate formation at low overpotentials. Our results demonstrate that epitaxy can be used to grow single-crystal analogous materials as large-format electrodes that provide insights on controlling electrocatalytic activity and selectivity for this reaction.

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.