Tunable Cu Enrichment Enables Designer Syngas Electrosynthesis from CO2

Posting date on solidfuturism: February 22th 2024
Published date: June 29th 2017
Authors: Michael B. Ross, Cao Thang Dinh, Yifan Li, Dohyung Kim, Phil De Luna, Edward H. Sargent, and Peidong Yang
DOI: https://dx.doi.org/10.1021/jacs.7b04892
Abstract composer: Seyed Amirhosein Mirsadri
carbon dioxide syngas
Graphical abstract

Nowadays, many scientists have directed their research towards carbon-based syntheses that usually start from the absorption of carbon dioxide gas. This means that we convert carbon dioxide into other good carbon compounds in a way that we can better store or use. This work can have a great impact on atmospheric processes and, in addition to creating clean air, enable access to a new branch of renewable energies. To achieve a process that is both cheap and in normal and calm synthetic conditions, i.e. at ambient temperature and pressure, we need a very precise study of the behavior of materials in synthetic conditions. The electrochemical reduction of carbon dioxide is one of the branches of carbon dioxide synthesis that has attracted much attention today due to its performance at ambient temperature and pressure.

carbon dioxide syngas
Fig.1 | Cu enrichment of Au surfaces enables tuning the composition of electrosynthesized syngas. (a) Scheme depicting the relationship between Cu-enriched Au surface, in situ characterization of CO* coordination, and syngas composition. (b) Calculated d-band electronic states for increasingly Cu-enriched Au surfaces.

. In this article, an attempt has been made to change the structure of the gold electrode with copper to a structure for better conversion of carbon dioxide to carbon monoxide and also hydrogen. The gases synthesized from carbon dioxide are called synthetic gases or 'Syngas'. Since the electrochemical conversion of carbon dioxide can be converted into various carbon products, we need more selective processes and the study of this issue is one of the most important topics. Scientists have concluded that changing the gold electrode with copper in the electrochemical process can affect the conversion efficiency and selectivity of carbon monoxide and hydrogen resulting from the reduction of carbon dioxide. Not that we want to make an alloy of gold and copper metals, but we only get there by single-layer deposition by deposition and electrochemical underpotential deposition. In this method, we can deposit layers of less noble atoms such as copper on a more noble metal such as gold.

carbon dioxide syngas
| Figure 2. In situ spectroscopic and theoretical characterization of CO* binding. (a) Scheme depicting in situ SERS during CO electrosynthesis. (b) Waterfall plot of typical SER spectra as a function of potential for the fully Cu enriched Au electrode (V vs RHE). (c) Waterfall plot of SER spectra for different Cu UPD coverages at −0.3 V vs RHE. (d) Calculated vibrational frequencies for CO bound on Cu-enriched Au slab models (from Figure 1). Solid lines indicate CO* at Cu sites, dashed lines indicate CO* at Au sites, and the narrow dashed trace (bottom) is for gas-phase CO at the same level of theory. (e) Renderings of optimized slab geometries for the different CO* adsorption sites. (f) Calculated adsorption energies for CO* at Au sites (blue squares) and Cu sites (red circles) as well as for H* (gray diamonds).

Also, this method can improve the Raman spectroscopy identification method for better tracking the production and creation of carbon monoxide and hydrogen. By controlling the synthetic conditions, layers with ratios of 1 to 3, 2 to 3 and 1 were obtained for the placement of copper atoms next to gold. In the meantime, the studies showed that carbon monoxide molecules can interact better with the orbital d of the copper metal from the oxygen head. Although carbon monoxide can bond with gold metal, the studies indicated that the deposition of copper atoms on gold can create better electronic coordination structures on the gold surface for better absorption of carbon monoxide and hydrogen molecules. This important information was obtained from the Raman spectrum study, which was taken directly from the electrode during the reaction, which was the result of diagrams that showed that when the molecular interaction between carbon monoxide and the orbital bond of the copper and gold atoms occurs, the red shift becomes more and stronger. All these studies were performed on the electrolysis of a half-molar solution of potassium hydrogen carbonate and all the results were confirmed by calculations (DFT).

carbon dioxide syngas
| Figure 3. Cu enrichment enables control over syngas composition on high-performance Au nanostructured electrocatalysts. (a) Scanning electron micrographs of Au nanostructured needle electrodes (scale bars: 1 μm, top, and 5 μm, bottom). (b) Cyclic voltammograms for increasingly wide Cu underpotential deposition windows (no Cu, yellow; 1/3 of the window, orange; 2/3 blue; and 3/3 purple). (c) Partial current densities (left axis) and production rates (right axis) at −0.65 V vs RHE for CO (red circles) and H2 (black squares) as a function of Cu monolayer deposition. (d) Controlling syngas (H2:CO faradaic efficiencies) composition as a function of both Cu deposition (yellow squares, no Cu; orange circles, 1/3 Cu UPD window; blue triangles, 2/3 Cu UPD window; purple inverted triangles, 3/3 Cu UPD window) and applied potential.

To better understand the absorption of carbon monoxide, the Gibbs free energy for surface absorption was studied, which showed that the absorption of hydrogen and carbon monoxide gas on the surface of the gold electrode compared to copper (1,1,1) is performed at high and positive energies, indicating non-spontaneity and reluctance. Also, all the tests indicated better absorption and desorption and reaction of carbon monoxide and hydrogen on the electrode surface. Therefore, the gold electrode covered by copper atoms with a ratio of 3 to 3 (i.e. a complete layer of copper atoms) showed a high yield of 70% for converting carbon dioxide to carbon monoxide. These reactions were investigated by Raman device, electron microscope, XPS and cyclic voltammetry.