Tuning the Products of CO₂Electroreduction on a Ni₃Ga Catalyst Using Carbon Solid Supports

Abstract

Certain alloys of nickel have recently been shown to reduce CO 2 to multi-carbon products electrochemically without the need for copper. Here we show that Ni 3 Ga thin film electrocatalysts on carbon electrodes discriminate between CO 2 reduction pathways and products based on their surface morphologies, which are controlled by catalyst-carbon support interactions. It is also observed that unsupported, bulk Ni 3 Ga reduces CO but not CO 2 . With this understanding, a tandem electrocatalyst utilizing two variants of the Ni 3 Ga material-one supported and one unsupported-was developed. In this two-electrode system, CO is generated from CO 2 on an electrode optimized for this process, and the CO is then further reduced to methanol in the same reactor. It appears that choice of carbon support impacts the morphology of Ni 3 Ga during the synthesis of the catalyst, thereby influencing the electrolysis product distribution. The discovery or design of CO 2 reduction catalysts has been a focus of current electrochemical studies due to the rising concentration of CO 2 in the atmosphere coupled with global challenges accompanying such a phenomenon.1,2 Materials that facilitate the transformation of CO 2 are wide-ranging, but a deficiency in our understanding of how they function is exemplified by several recent studies reporting on what is nominally the same electrode material after modifying the structure, morphology, or composition and eliciting a new or improved response toward CO 2 reduction. 3-10When a known CO 2 -reducing material is altered to include novel structures or morphologies, it is anticipated that the newly introduced characteristic may change the base material's activity by increasing the concentration of surface active sites or improving intermediate stability, thereby impacting catalysis. As an example, the Kanan group has reported that copper catalyst morphology influences the distribution and faradaic efficiencies of CO 2 reduction products. 11 The importance of morphology is one reason why nanoparticles and thin films have garnered attention. Selection of heterogeneous catalysts in non-bulk form involves immobilizing nanoparticles, thin films, and other specialty structures on electrodes, and thus a second material, the solid support, is added to the electrochemical system.It is well-established that solid support identity can directly impact material or catalytic properties. For example, Rakhi et al. grew Co 3 O 4 nanowires on carbon fiber paper and planar graphitized carbon paper and achieved startlingly different morphologies, 12 while other authors witnessed similar morphological impacts for different systems. 13,14 Superconductivity, 15,16 material hardness, 17 and especially catalytic efficacy in the oxygen reduction reaction [18][19][20][21] have been attributed to solid supports interacting with or changing properties of surface materials that are typically the focus of the study. These works suggest that properties such as catalyst morphology, which is important for CO 2 electrocatalysis, ma...

Using Light and Electrons to Bend Carbon Dioxide: Developing and Understanding Catalysts for CO2 Conversion to Fuels and Feedstocks

“…This result is ascribed to a catalyst deposition effect influenced by the solid support, in which the use of different supports led to altered surface morphologies and electrochemical behaviors. 10 Specifically, Ni 3 Ga on HOPG has a distinct rough surface in comparison to Ni 3 Ga on glassy carbon, which has a flat and more uniform structure, shown in Figure 2. It is hypothesized that C−C coupling is possible because the high surface area of the Ni 3 Ga promoted by the HOPG allows surface-bound intermediates to be in close proximity.…”

“…Given this finding, it is not quite as surprising that different product yields are observed using a Ni 3 Al catalyst distributed on glassy carbon versus a CIGS (copper, indium, gallium, selenium) based ptype photoelectrode. 10,12,13 In contrast to the above approach, we have also explored the chemistry involved in the homogeneous electroreduction of CO 2 . Presently, our main vehicle for doing this is complexes based on a MnXbpy(CO) 3 motif, which is highly selective for the conversion of CO 2 to CO.…”

Manganese-Based Catalysts with Varying Ligand Substituents for the Electrochemical Reduction of CO2 to CO

“…Electrochemical measurements were performed on a Model CHI 760D electrochemical workstation (CH Instruments, Austin, TX). Nuclear magnetic resonance (NMR) spectra were recorded on a Bruker AVANCE spectrometer (500 MHz for 1 H nuclei and 125 MHz for 13 C nuclei). Chemical shifts are reported in parts per million (ppm) downfield of tetramethylsilane and are referenced to the solvent residual peak.…”

“…1 H NMR (500 MHz, DMSO-d 6 ): δ 9.02 (d, 2H), 8.57 (s, 2H), 7.59 (d, 2H), 2.84 (q, 4H), 1.31 (t, 6H). 13 Preparation of Mn(4,4′,5,5′-tetraMe)(CO) 3 Br. A mixture of Mn(CO) 5 Br (0.20 g, 0.73 mmol) and 4,4′,5,5′-tetramethyl-2,2′bipyridine (0.161 g, 0.76 mmol) in diethyl ether (40 mL) was refluxed for 3 h in the dark.…”

“…The use of fossil fuels as an energy source continues to increase the global levels of carbon dioxide (CO 2 ) in our environment. , This continuing emission of CO 2 has highlighted the importance of determining ways in which CO 2 can be removed from the environment and utilized. , One attractive way to accomplish this is the electrochemical reduction of CO 2 , which has been studied extensively through the use of metal electrodes − and surface-modified electrodes, − as well as soluble transition-metal catalysts. − Reduction of CO 2 to CO is attractive, since this provides a route to renewable syngas generation …”