Electrochemical methane-to-methanol technologies are regarded as one of the most attractive options to improve greenhouse gas emissions while providing a pathway to produce one of the most important bulk industrial chemicals. In recent years, several reports demonstrated individual cells producing methanol and other C-1 products 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. Here we provide detailed calculations of process profitability over 4000 cases for electrochemical methane-to-methanol processes while considering two different overall reactions, multiple production scales, a wide range of operating conditions (voltage, current density), and various electrical costs. Finally, the analysis shows that the technology requires substantial improvement before expecting profit, and targets are determined for future performance, providing direction for R&D in this potentially transformational area.

Recent years has seen a tremendous growth in finding electrochemical pathways to produce chemicals and fuels because it is believed that pairing low-carbon electricity (solar, wind, nuclear) with renewable carbon sources and electrochemical processes will lead to a reduction in greenhouse gas emissions. One of the possible sources renewable carbon is biomass. During biomass upgrading, one of the byproducts is bio-oil, which contains a large amount of acetic acid. Acetic acid itself is a relatively low value product. Upgrading acetic acid (or its alkaline counterpart acetate) to a wider range of valuable products (e.g., methanol, ethylene) is extremely attractive. This can be done through thermochemical or electrochemical partial oxidation. Though acetic acid reactions have been studied for many years, details about its overall reaction mechanism still remain unknown. The most known and defended pathway in the literature is Kolbe electrolysis, where C-C bonds are formed from dimerization of methyl radicals as shown in Equation 1. 2CH3COOH → 2CO2 + C2H6 + 2H+ + 2e- (Equation 1) However, aqueous environments have shown deviations from this dimerization. It is often overlooked that these reactions occur at high potentials and the state and role of the formed surface oxide are not well described in the literature. It is even not known what water-oxide mechanism dominates for the formation of alcohol-based products. Although prior work has shown that a three-electrode batch cell can produce the typical Kolbe products (ethane and carbon dioxide) at high faradaic efficiencies and steady state when the electrolyte bath is held at the pKa (4.7) and high voltage (>3.0V vs. RHE) – our previous studies have shown that the reaction environment (e.g. concentration, addition of supporting electrolyte, pH) can vary the effluent composition and reaction rate considerably. Also, our recent work has shown that transitioning the same catalyst to a lower-water environment in a flow cell can yield a completely different product profile than in aqueous media. Therefore, the purpose of this study is to demonstrate how the catalyst and reacting environment affect the formation of various C1 and C2 products from acetate electrochemical oxidation. To do this, custom-made two-electrode (similar to an alkaline exchange membrane electrolyzer) and three-electrode cells are used. Another variable that is manipulated is the voltage profile, where both constant voltage and pulsed experiments are performed. In the flow cell, several anode electrocatalysts (e.g., Pt, PtRu, NiO, IrOx) were dispersed in inks and sprayed onto porous transport layers. The anode feed was 0.5M potassium acetate. No gases were fed to the cathode, but hydrogen was collected from the exhaust. The anode effluent (gas and liquid mixture) was separated downstream in a simple vessel with UHP helium flowing through the incoming effluent to carry the gas for GC/MS analysis. Liquid samples were analyzed by ex situ and NMR with D2O solvent. Two-electrode and three-electrode results will be combined to provide new insights into acetate oxidation and pathways for future research and development will be discussed.

Methane is the second-most emitted greenhouse gas (GHG) globally, and it has over 25x more potency toward the GHG effect than carbon dioxide. Methane emissions in the U.S. are equally distributed across the energy, agricultural, and industrial sectors – and occur in relatively small volumes at each site, though the total volume is sizable (e.g., 145 billion cubic meters of methane coextracted with U.S. oil alone per year). To avoid its direct emission, this “waste” methane is typically flared to produce CO2. Methane flaring sites contribute to approximately 2% of global CO2 emissions. These sites represent an opportunity to convert a waste stream into desirable products. Methane (natural gas)-to-chemicals conversion units are not implemented today because of economies of scale. Because each site is relatively small, the construction of a traditional stream-reforming based gas-to-liquid plant is not economically viable. It is also not profitable to build pipelines to these sites to take the natural gas to other locations. Recently, new concepts have been put forward for methanol production that are quoted as being more modular and possibly more profitable at smaller scales. Many of these concepts revolve around electrochemical and/or biochemical transformations. Proponents of electrochemical methane conversion have claimed that the technology will play a key role in eliminating these flare sites while opening up new business opportunities. Though this sounds very good, all of the research and development in this area remain on the bench scale as they have widely suffered from low current, high voltage losses and low faradaic efficiency. It should also be noted that there are very few studies in the literature that use economic analyses to understand the operational boundaries of a future electrochemical methane-to-methanol plant and to set realistic targets for its operation. Hence, research work is proceeding without clear operating targets in mind. In this presentation, we will present an economic analysis on an electrochemically driven methane-to-methanol plant. We investigate a wide range of possible production rates (from 2-2000 metric tons per day), operating current densities (10-1000 mA/cm2), operating voltages (Vthermo-2.0 V) and faradaic efficiencies. This analysis also takes into consideration the cost of the electrolyzer stacks, the balance-of-plant, building sizes/layouts, labor force, etc. Over this wide design space, we determine the possible operating space that will allow for profitable operation. While doing so, we test whether electrochemical processes can economically out-compete steam reforming plants at any scale. We also identify the operating modes where electrochemical processes emit fewer greenhouse gases that traditional plants.

The behavior of the anode electrode in the Anion Exchange Membrane Water Electrolyzer (AEMWE) – where the oxygen evolution reaction (OER) occurs – is complex and influenced by several factors. Very few studies have been performed to understand OER electrode performance by optimizing contributing individual factors that influence the performance. This study highlights the individual effects of: catalyst loading, catalyst selection, gas diffusion layer (GDL) type and conductive additive content. The influence of each factor is elucidated through a Design of Experiments (DoE) approach with a full statistical analysis. Electrochemical data, alongside Pareto charts, parametric trends and their mutual interactions will be presented. Such a DoE approach is also helpful in making useful predictions, allowing new combinations to be discovered and tested. The end result is very high performance with a current density of 1 A/cm2 at 1.64 V in 0.1 M KOH being achieved. Furthermore, we extend our understanding from this electrolyzer work, coupled with our previous electrode engineering for AEM fuel cells [1-3] to design electrodes for an AEM-based Unitized Regenerative Fuel Cell (URFC). Good baseline performance was achieved, including a round trip efficiency of 40.7 % at 500 mA/cm2. This study will serve as a guide for optimal electrode design with insights into design-performance compromises, which can be especially helpful when making design choices and performing techno-economic analyses. References [1]. Xiong Peng, Devashish Kulkarni, Ying Huang, Travis J Omasta, Benjamin Ng, Yiwei Zheng, Lianqin Wang, Jacob M LaManna, Daniel S Hussey, John R Varcoe, Iryna V Zenyuk, William E Mustain, “Using operando techniques to understand and design high performance and stable alkaline membrane fuel cells”, Nature Communications, Volume 1, Pages 1-10 2020. [2]. Noor Ul Hassan Mrinmay Mandal Garrett Huang Horie Adabi Firouzjaie Paul A. Kohl and William E. Mustain, “Achieving High‐Performance and 2000 h Stability in Anion Exchange Membrane Fuel Cells by Manipulating Ionomer Properties and Electrode Optimization”, Advanced Energy Materials, Volume 10, Issue 40 (2020). [3]. Garrett Huang, Mrinmay Mandal, Xiong Peng, Ami C Yang-Neyerlin, Bryan S Pivovar, William E Mustain, Paul A Kohl, “Composite poly (norbornene) anion conducting membranes for achieving durability, water management and high power (3.4 W/cm2) in hydrogen/oxygen alkaline fuel cells, Journal of the Electrochemical Society, Volume 166, Pages F637, 2020.

Over many decades, reliable pathways have been invented for heating and power, as well as facilitating the complex chemical transformations in standard industrial chemical plants that enable the goods around us. Unfortunately, essentially all these processes are higher greenhouse gas (GHG)-emitting, which has led to global climate change, which is a looming threat for our world. Therefore, there is a need to find alternative processes that are able to reduce, or possibly eliminate GHG emissions.Biofuels have been, and continue to be, researched as promising alternative fuels. However, the high carboxylic acids content of the resulting bio-oil is troublesome and requires further upgrading [1]. One possible process that is able to selectively upgrade these carboxylic acids are electrochemical reactors. Electrochemical upgrading of carboxylic acids proceeds through the Kolbe reaction. In this reaction, a pair of carboxylic acids decarboxylate to two radicals which can dimerize and form alkanes (Equation 1).2 RCOOH → R–R + 2 CO2 + 2 H+ + 2 e- (Equation 1)In bio-oil upgrading studies, Kolbe electrolysis of acetic acid is typically used as a model reaction. A large number of studies on Kolbe electrolysis have published, many that focus on gaining fundamental insight in the influence of reaction parameters, like potential, pH and reactor configuration on the product yield and selectivity of the reaction [2-4]. From these studies, it is known that the Kolbe reaction proceeds through a methyl-radical pathway. Interestingly, such observations also make this reaction a potential proxy reaction for methane activation, another reaction that has received increased interest in recent years [5-7]. However, despite the previous work in this area, the work has largely been descriptive and contradictory.Therefore, this work aims to provide experimental data and optimize the methyl-radical pathway by changing pH and potential to promote selectivity of ethane, the primary Kolbe product. To do that, several studies have been performed using dilute solutions of acetate on polycrystalline platinum. Two three-electrode electrochemical cells, one batch and one flow configuration, were used for this study. The cells were equipped with a platinum foil working electrode, a platinum counter electrode and an Ag/AgCl reference electrode. The formed gas products were analyzed using in situ GC-MS. Offline liquid analysis was performed using NMR. In addition, an attempt was made to study the surface reactions on a platinum electrode under various potentials using ATR-FTIR experiments.The potential window used in this work was 2.8 V to 3.5 V vs RHE. In this range, an array of products was observed in both the gas phase (e.g., methanol, ethanol, ethylene, methane, ethane, carbon dioxide, carbon monoxide, hydrogen) and the liquid phase (e.g., methanol). It was observed that under the applied potentials high faradaic efficiencies (~90-96%) to ethane can be obtained and that this is increased with more positive potentials. Furthermore, it was observe...