(438h) Simple, Cost-Effective Synthesis Method of Electrocatalysts for Electrified Hydrocarbon Production

The decarbonization of industrial chemical processes is imperative if humans are going to continue to improve their overall quality of life while simultaneously reducing their impact on the environment. Electrification coupled with a renewable energy supply can facilitate lower emissions through several pathways, though two in particular have been gaining wide popularity in recent years: 1) replacing thermal heating (e.g. burning fuels) with alternative methods (resistive, microwave, etc.); and 2) by replacing thermochemical conversion with electrochemical conversion, where electrical energy can be used directly to drive new chemical reactions. One attractive option that both opens new mechanistic pathways and removes CO₂ from the atmosphere is the electrochemical reduction of carbon dioxide (CO2RR) to hydrocarbons [1].

CO2RR occurs through a complex reaction mechanism that consists of multiple proton and electron transfer steps along a variety of reaction paths to produce mostly C1 and C2 hydrocarbons (carbon monoxide, formate, methane, ethylene, etc.). Because most bulk metals (e.g., Au, Ag, Zn, Pd, Pb, In, and Sn) have lower affinity for important CO2RR intermediates, namely carbon monoxide, the resulting transformations tend to yield some ratio of carbon monoxide and formate only. In contrast, copper catalysts have gained increasing attention due to their ability to more optimally bind CO2RR intermediates to form a litany of products, but competition with the HER and poor selectivity between the multitude of reaction pathways have limited the proliferation of the technology [2].

Single atom catalysts (SACs) have an inherent advantage over bulk metal and metal nanoparticle catalysts because they maximize metal active site utilization for minimal metal loadings. Along with maximizing dispersion, SACs have also been shown to increase the activity of metals for certain reactions, including CO2RR. Lighter transition metals like Fe, Co, and Ni tend to be active mainly for HER and poisoned by carbon monoxide. However, SACs of these metals change their properties and open the door for cheaper and more abundant catalyst materials [2]. There have been numerous techniques developed to synthesize single atom catalysts, but many use high temperatures and specialized chemicals that make them expensive especially when applied to industrial scale [3].

This presentation will report the synthesis and characterization of Cu and other transition metal SACs on high surface area carbon supports for CO2RR. Results from a wide array of physical characterization techniques will be presented, including powder Xray diffraction and STEM imaging, showing the presence of the SACs. The activity and product selectivity for the SACs will be reported in both batch and flow-through electrochemical reactors and linked to the catalyst structure and Cu dispersion. For all catalysts, the product profile, faradaic efficiency, selectivity, and carbon efficiencies will be reported – determined through a combination of integrated gas chromatograph-mass spectrometry and nuclear magnetic resonance.

References:

[1] Xia, R.; Overa, S.; Jiao, F. Emerging Electrochemical Processes to Decarbonize the Chemical Industry. JACS Au 2022, 2 (5), 1054–1070. https://doi.org/10.1021/jacsau.2c00138.

[2] Johnson, D.; Qiao, Z.; Djire, A. Progress and Challenges of Carbon Dioxide Reduction Reaction on Transition Metal Based Electrocatalysts. ACS Applied Energy Materials 2021, 4 (9), 8661–8684. https://doi.org/10.1021/acsaem.1c01624.

[3] Ji, S.; Chen, Y.; Wang, X.; Zhang, Z.; Wang, D.; Li, Y. Chemical Synthesis of Single Atomic Site Catalysts. Chemical Reviews 2020, 120 (21), 11900–11955. https://doi.org/10.1021/acs.chemrev.9b00818.