Alloying strategies for tuning product selectivity during electrochemical CO2 reduction over Cu.

Excessive reliance on fossil fuels has led to the release and accumulation of large quantities of CO2 into the atmosphere which has raised serious concerns related to environmental pollution and global warming. One way to mitigate this problem is to electrochemically recycle CO2 to value-added chemicals or fuels using electricity from renewable energy sources. Cu is the only metallic electrocatalyst that has been shown to produce a wide range of industrially important chemicals at appreciable rates. However, low product selectivity is a fundamental issue limiting commercial applications of electrochemical CO2 reduction over Cu catalysts. Combining copper with other metals that actively contribute to the electrochemical CO2 reduction reaction process can selectively facilitate generation of desirable products. Alloying Cu can alter surface binding strength through electronic and geometric effects, enhancing the availability of surface confined carbon species, and stabilising key reduction intermediates. As a result, significant research has been undertaken to design and fabricate copper-based alloy catalysts with structures that can enhance the selectivity of targeted products. In this article, progress with use of alloying strategies for development of Cu-alloy catalysts are reviewed. Challenges in achieving high selectivity and possible future directions for development of new copper-based alloy catalysts are considered.

Hydrophobicity Graded Gas Diffusion Layer for Stable Electrochemical Reduction of CO2.

To mitigate flooding associated with the gas diffusion layer (GDL) during electroreduction of CO2 , we report a hydrophobicity-graded hydrophobic GDL (HGGDL). Coating uniformly dispersed polytetrafluoroethylene (PTFE) binders on the carbon fiber skeleton of a hydrophilic GDL uniformizes the hydrophobicity of the GDL and also alleviates the gas blockage of pore channels. Further adherence of the PTFE macroporous layer (PMPL) to one side of the hydrophobic carbon fiber skeleton was aided by sintering. The introduced PMPL shows an appropriate pore size and enhanced hydrophobicity. As a result, the HGGDL offers spatial control of the hydrophobicity and hence water and gas transport over the GDL. Using a nickel-single-atom catalyst, the resulting HGGDL electrode provided a CO faradaic efficiency of over 83 % at a constant current density of 75 mA cm-2 for 103 h operation in a membrane electrode assembly, which is more than 16 times that achieved with a commercial GDL.

Electrochemical Hydrogenation of Furfural in Aqueous Acetic Acid Media with Enhanced 2-Methylfuran Selectivity Using CuPd Bimetallic Catalysts.

Herein, we report a series of CuPd catalysts for electrochemical hydrogenation (ECH) of furfural to 2-methylfuran (MF or FurCH3 where Fur=furyl) in aqueous 0.1 M acetic acid (pH 2.9). The highest faradaic efficiency (FE) for MF reached 75 % at -0.58 V vs. reversible hydrogen electrode with an average partial current density of 4.5 mA cm-2 . In situ surface-enhanced Raman spectroscopic and kinetic isotopic experiments suggested that electrogenerated adsorbed hydrogen (Hads ) was involved in the reaction and incorporation of Pd enhanced the surface coverage of Hads and optimized the adsorption pattern of furfural, leading to a higher FE for MF. Density functional theory calculations revealed that Pd incorporation reduced the energy barrier for the hydrogenation of FurCH2 * to FurCH3 *. Our study demonstrates that catalyst surface structure/composition plays a crucial role in determining the selectivity in ECH and provides a new strategy for designing advanced catalysts for ECH of bio-derived oxygenates.

CdS-Enhanced Ethanol Selectivity in Electrocatalytic CO2 Reduction at Sulfide-Derived Cu-Cd.

The development of Cu-based catalysts for the electrochemical CO2 reduction reaction (eCO2 RR) is of major interest for generating commercially important C2 liquid products such as ethanol. Cu is exclusive among the eCO2 RR metallic catalysts in that it facilitates the formation of a range of highly reduced C2 products, with a reasonable total faradaic efficiency but poor product selectivity. Here, a series of new sulfide-derived copper-cadmium catalysts (SD-Cux Cdy ) was developed. An excellent faradaic efficiency of around 32 % but with a relatively low current density of 0.6 mA cm-2 for ethanol was obtained using the SD-CuCd2 catalyst at the relatively low overpotential of 0.89 V in a CO2 -saturated aqueous 0.10 m KHCO3 solution with an H-cell. The current density increased by an order of magnitude under similar conditions using a flow cell where the mass transport rate for CO2 was greatly enhanced. Ex situ spectroscopic and microscopic, and voltammetric investigations pointed to the role of abundant phase boundaries between CdS and Cu+ /Cu sites in the SD-CuCd2 catalyst in enhancing the selectivity and efficiency of ethanol formation at low potentials.