ELECTROCHEMICAL SYNTHESIS
There is no question that the global energy landscape is undergoing a metamorphosis towards energy carriers and energy conversion processes that possess a reduced anthropogenic carbon footprint. Because of its increased efficiency compared to internal combustion, the transportation sector is seeing the gradual electrification of passenger vehicles which is expected to dramatically grow in the next decade. In the electricity sector, coal is becoming less and less economically attractive and is being replaced largely by natural gas and an ever-increasing amount by solar and other renewable energy technologies that are becoming more and more cost competitive every day. On top of this, the threat of global climate change has brought considerable social, economic and political attention to the need for a significant reduction in CO2 emissions around the world. However, in the industrial sector, the least efficient sector in our economy after transportation, transformative innovations have lagged. The largest subset of the industrial sector from an energy perspective is the production of commodity chemicals – accounting for 5.5% of global energy consumption, which relies heavily on conventional natural gas and petrochemical processing. Our group aims to develop alternative chemical pathways that not only reduce CO2 emissions, or remove CO2 directly from the atmosphere, but to do it in a way that is economically viable.
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Direct CO2 Electrochemical Reduction
Reduction of carbon emissions from the petroleum and gas industry has proven challenging thus far in large part due to the current economic infeasibility of the capture and sale of carbon dioxide. As a result, the industry requires a process that can convert low-value carbon dioxide into high-value chemicals, allowing for monetarily incentivized reduction of greenhouse gas emissions. One such technology that has the potential to transform carbon dioxide into profitable chemicals is electrochemical carbon dioxide reduction (CO2RR) to form a variety of useful petroleum and natural gas substances including carbon monoxide, methane, methanol, ethylene, ethane, and ethanol. When coupled with renewable electricity and carbon capture systems, this technology has the capability to remove the carbon footprint from the production of various petroleum and gas compounds by consuming atmospheric carbon dioxide. In other words, the widespread, large-scale implementation of CO2RR could drastically reduce the emissions from the petroleum and gas industry by providing a carbon neutral alternative.
Our work investigates the synthesis and optimization of a promising class of catalysts known as single atom catalysts (SACs). SACs generally consist of a single transition metal cation stabilized in a functional contained within a conductive matrix or support (one example is shown in the HAADF-STEM image above). Because each of the active sites are identical, SACs have shown improved product selectivity and faradaic efficiency over many conventional bulk metal catalysts. Due to their unique structure, SACs also allow for tunability in how the catalyst interacts with carbon dioxide and subsequent reacting species, creating customizable product formation. In addition to controlling the coordination shell, we also aim to understand how the microenvironment during reaction changes the efficiency and selectivity of the catalyst. Lastly, we investigate how the stability of the catalyst is affected by the single atom coordination environment under industrially-relevant reaction conditions.
Methane and Acetate
As the main component of natural gas, methane is a well-established and widely available (at low cost with the recent discoveries of vast amounts of shale gas) feedstock for the production of chemicals, particularly small chain organics. Despite being widely deployed, its use has an intrinsic constraint that makes the process unavoidably expensive, energy consuming, and highly CO2 emitting. Therefore, many have called for the low temperature, direct transformation of methane to chemicals and fuels one of the “Holy Grails in Chemistry” – and advances in catalysis are central to achieving it. Our group investigates catalysts and reactors for electrochemical methane conversion to C1 and C2 products.
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Acetate is the major biofuel generated as a byproduct during biomass upgrading. Over the past few decades, acetate oxidation has been extensively studied using anaerobic digestion as well as photocatalytic and electrocatalytic methods. Electrochemical partial oxidation of acetate (AcOR) can generate fuels and value-added chemicals such as ethane, ethylene, ethanol, methanol, etc. Although many experimental investigations have been conducted, the mechanistic understanding of the electrolysis of acetic acid is limited. During AcOR, though the formation of CO2 is thermodynamically more favorable during acetate oxidation, other products are well-known to be formed through the Kolbe and Hofer-Moest mechanisms, highlighting the potential of tuning the products via partial oxidation. Due to the complexity of the reaction, a comprehensive evaluation of the role of reaction conditions on the product profile is essential. Our work has focuses on the influence of surface oxides over a wide range of operating conditions (including membrane choice, electrolyte concentration, and electrolysis technique) on the stability and selectivity of the oxidation products.
Techno-economic Analysis
Electrochemical technologies to create fuels are regarded as one of the most attractive options to improve greenhouse gas emissions while providing a pathway to produce the most important bulk industrial chemicals. In recent years, several reports demonstrated individual cells producing methanol and other C1 products from methane while proclaiming that these cells will inevitably lead to industrial adoption at small sites with flared, stranded natural gas. However, the practical realization of these systems relies on finding operating regimes that can lead to profitability, which has not been well studied in the literature to date. Our work focuses on performing detailed calculations of process profitability over 1000's cases while considering different reaction pathways, multiple production scales, a wide range of operating conditions (voltage, current density), and various electrical costs. Our analyses generally show, including methane to methanol (some outcomes pictured above), that modern technology requires substantial improvement before expecting profit. We also use the calculations to propose targets for future R&D.
CONTACT US
Professor William E. Mustain
Department of Chemical Engineering
Swearingen Engineering Center
University of South Carolina
301 Main St.
Columbia, SC 29208
803-576-6393