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Formic acid generated from CO2 has been proposed both as a key intermediate renewable chemical feedstock as well as a potential energy storage chemical media for hydrogen. In this paper, we describe a novel three compartment electrochemical cell configuration with the capability of directly producing a pure formic acid product in the concentration range of 5 – 20 wt% at high current densities and Faradaic yields. The electrochemical cell employs a Dioxide Materials Sustainion™ anion membrane, allowing for the improved CO2 electrochemical reduction performance. Stable electrochemical cell performance for more than 500 hours has been experimentally demonstrated.

This paper will describe the performance of alkaline water electrolyzers using newly developed Sustainion™-X5 membranes. Sustainion™ membranes have a styrene base, and mixtures of other components to produce a high conductivity in alkaline systems. The membranes are stable when soaked in 1 M KOH at room temperature for months. A CO2electrolyzer has run for over 4000 hours with no loss in performance. Initial tests also show stability in 1 M KOH at 60°C, See Figure 1, although no long term tests have yet been completed. The work here considers the performance of the membranes in model alkaline membrane electrolyzers. We manufactured a small MEA using platinum coated carbon paper as a cathode and a IrO2 coated carbon paper as an anode and a Sustainion™-X5 membrane. The MEA was mounted into Fuel Cell Technologies 5 cm² cell hardware with carbon flowfields. The cell was heated to 60 °C and 1 M KOH was fed into the anode and cathode. Figure 2 shows how the cell voltage varied with time at a fixed current of 0.8 A/cm² and 1 A/cm². The data were taken on a single cell, at a fixed current of 1 A/cm² during the day and 0.8 A/cm² at night. Initially the cell produced 0.8 A/cm² at 1.74 V and 1 A/cm² at 1.81 V, but the voltage rose to nearly 2V after 150 hours of operation. Disassembly of the cell showed that the carbon paper on the anode was corroding leading to a loss of anode catalyst. We have also started work on nickel catalysts. The initial results were modest, but additional results will be presented at the meeting. Acknowledgement Parts of this work were supported by ARPA-E under contract DE-AR0000684 and by 3M. The opinions here are those of the authors and may not reflect the opinions of ARPA-E or 3M. Figure 1

Electrochemical recycling of carbon dioxide back to fuels and chemicals could be a viable method for CO2 remediation if the efficiency of the process could be improved. One of the key challenges, though, is that the faradaic efficiency is low in the presence of water because water electrolysis is much easier than CO2 electrolysis on most transition metal catalysts. Previous investigators have found that one can eliminate water conversion, by eliminating water from the system, but this has not proven to be practical. Here we present an alternate route, where EMIM-BF4 is used to suppress water electrolysis. We observe that the addition of water to 1-ethyl-3-methyl imidazolium tetrafluoroborate (EMIM-BF4) actually increased the efficiency of CO2 conversion to CO. Indeed we find that little hydrogen is produced on silver in EMIM-Water solutions, provided the water concentration is no more than about 90% by mole. We observe an increase in rate of carbon monoxide (CO) production on silver and platinum as water is added to the electrolyte. We attribute this increase to the hydrolysis of tetrafluoroborate, which releases protons when mixed with water. Protons are shown to accelerate the reduction of CO2 until a critical mole fraction of water is reached.

Water electrolyzers are being developed as a way of storing renewable energy, as a way to produce hydrogen for fuel cell automobiles, and as a route to renewable fuels and chemicals. In this paper the effect of changes in the cathode catalyst on the performance of an anion exchange membrane water electrolyzer with Sustainion® membranes running at 60 °C in 1 M KOH. We choose commercial catalysts for study: Raney nickel from W.R. Grace, NiFeCo and Ni8Fe2 from US Nano, NiMoB, FeCoBSi, Ni80Mo20 from Fraunhofer Institute for Manufacturing Technology (IFAM), and NiMo/C from Pajarito Powder(PP). They are all supported on nickel fiber paper. Surprisingly, Raney nickel showed the best performance. At a fixed cell voltage of 2.0 volts in 1 M KOH at 60 °C, we observe 2.9 A/cm² cell current with the Raney Nickel catalyst, compared to 2.3 and 2.1 A/cm² with the US Nano catalysts, 1.7, 1.65 and 1.1 A/cm² with the IFAM catalysts, 1.5 A/cm² with the Pajarito Powder catalyst, and 0.95 A/cm² with the nickel fiber paper alone. These results demonstrate that catalysts that catalysts that show superior performance in a conventional alkaline water electrolyzer, may not show performance superior to Raney nickel in an anion exchange membrane water electrolyzer. Figure 1

Anion exchange membrane fuel cells are of interest since they allow to use non-precious metal catalyst for both anode and cathode reaction. More than 2000 articles have been published on alkaline membrane fuel cells(1). There is one previous report indicating initial power densities of 1W/cm² but with no long term data(2). The best long term data shows a cell voltage decrease by about 25% over 800hr at a current density of 400mA/cm2 and 60°C. Presently, Sustainion® 37 anion exchange membranes have demonstrate excellent stability in anion exchange membrane carbon dioxide (CO2) and water electrolyzer(3-6). Carbon dioxide electrolyzer runs at pH 6-8 with 10mM KHCO3 in anode(3), while water electrolyzer runs at pH close to 14 with circulating 1M KOH at both anode and cathode at 60C(4-6). Both alkaline CO2 and water electrolyzers have demonstrated 4000hr runs with only 1-6µV/hr increase in the cell voltage(3, 5). Here we report our preliminary results for fuel cells with Sustainion® 43 anion exchange membranes as shown in Figure 1. In this data, Pt/C catalysts were used as both cathode and anode, and humidified H2 and O2 were fed to anode and cathode, respectively. The cell operated at 60 °C with back pressure of 1 atm. The maximum power density was 0.44W/cm² and the maximum current density was 2A/cm². These initial results suggest that Sustainion® 43 membranes could be useful for alkaline membrane fuel cells. Figure 1 Cell voltage and power density as function of current density of the fuel cell with Sustanion anion exchange membrane and Pt/C for both anode and cathode. Back pressure: 1 atm; cell temperature at 60°C. D. R. Dekel, Journal of Power Sources, 375, 158 (2018). L. Wang, E. Magliocca, E. L. Cunningham, W. E. Mustain, S. D. Poynton, R. Escudero-Cid, M. M. Nasef, J. Ponce-Gonzalez, R. Bance-Souahli, R. C. T. Slade, D. K. Whelligan and J. R. Varcoe, Green Chemistry, 19, 831 (2017). R. B. Kutz, Q. Chen, H. Yang, S. D. Sajjad, Z. Liu and I. R. Masel, Energy Technology, 5, 929 (2017). Z. Liu, S. D. Sajjad, Y. Gao, J. Kaczur and R. Masel, ECS Transactions, 77, 71 (2017). Z. C. Liu, S. D. Sajjad, Y. Gao, H. Z. Yang, J. J. Kaczur and R. I. Masel, International Journal of Hydrogen Energy, 42, 29661 (2017). R. I. Masel, Z. Liu and S. Sajjad, ECS Transactions, 75, 1143 (2016). Figure 1

Fuel cells are envisioned as a next generation power source to supply clean power for a variety of applications. Currently, water management remains a challenge for proton exchange membrane fuel cells, particular at low temperatures or during power transients. Water formed during oxygen reduction impacts the fuel cell in many ways. In this study, the cathode flow fields are examined using Magnetic Resonance Imaging (MRI). High resolution images are gathered, illustrating the effects of fuel cell flow field geometry and surface energy on water distribution. It is also found that irregularities in the surface of the flow channel can contribution to water stagnation inside the fuel cell, even at significant gas flow rates which would be expected to expel any water build up.

The purpose of this research was to develop a liquid medium in which the oxime would remain stable, while still being able to function as intented in the microsensor. Oxime solutions in pure organic solvents show no noticeable degradation and on average, had ~450 times greater solubility than the original aqueous buffer. However, the reaction between oxime and organo-phosphate requires hydroxide ions. As a result, pure organic solvents will not be compatible with the microsensor electrochemistry. To avoid the oxime degradation a concentrated organic oxime solution will be combined with the basic aqueous buffer just prior to being used in the detection process. Ethanol was chosen as the best organic solvent due to its stabilizing effect on the oxime and minimal interference with the aqueous electrochemistry. The sensor response utilizing the integrated micromixer was nearly identical to the response when the solutions were premixed and fed at the same rate.

Water management remains a significant challenge for the commercialization of PEM fuel cells. Many mathematical models have been created to gain insight into the effects of water distribution on cell performance. However, model verification remains difficult due to the challenging nature of acquiring relevant experimental data about water generation and movement inside an operating fuel cell. In this work, magnetic resonance imaging (MRI) is demonstrated as a strong diagnostic tool to gather information about water generation and transport inside an operating PEM fuel cell. The MRI technique is used to gather quantitative water distribution data in three dimensions. Acquisition times are as fast as 8 seconds, allowing observation of dynamic processes within the flow channels. Flow channel depth, geometry and hydrophobicity are varied, and the effect on water distribution and overall cell performance measured.

Carbon dioxide (CO2) electrolysis provides a pathway to turn waste CO2 into valuable fuels and chemicals but most previous efforts demonstrate low selectivity, high overpotential and low rates for the targeted products. In recent work Dioxide Materials has been using Sustainion™ imidazolium functionalized membranes and ionomers to improve the performance. Runs at a fixed current density of 200 mA/cm2 showed that one can maintain 98% selectivity for six months at about 3 V applied potential, with a voltage increase of only 5 µV/hour. Other runs showed stable performance at 400 and 600 mA/cm². Present areas for improvement of the technology include a better understanding of the processes that are occurring on the cathode catalysts, improving response to process upsets, developing cell designs that can be scaled to the m2 size and alternates to iridium as an anode catalyst. Initial work on these issues will be discussed.

Water electrolyzers are being developed as a way of storing renewable energy, as a way to produce hydrogen for fuel cell automobiles, and as a route to renewable fuels and chemicals. In this paper, we demonstrate alkaline water electrolyzers at 60 °C with iron/nickel/cobalt catalysts that show 1 A/cm² at a 1.9 V cell potential The performance is stable for 2000 hours, showing only 3-5 µV/hr degradation. Key to the findings is the development of new Sustainion™ alkaline exchange membranes that show high conductivity and stability in 1 M KOH. The paper will discuss new developments that improve the response of the electrolyzers to process upsets, and to improve the on-off performance of the devices.

This paper will consider the effects of catalyst composition on alkaline membrane electrolyzers with Sustainion™ membranes. In previous work1, 2we have demonstrated that Sustainion™ membranes are stable at 60 °C for at least 1500 hours in 1 M KOH. Here we compare a number of base metal catalysts on the performance of an alkaline water electrolyzer. Figure 1 shows the voltage needed to maintain 1 A/cm2 in an alkaline water electrolyzer running at 60 °C in 1 M KOH. The blue circles in Figure 1 were taken with nickel nanoparticles on carbon paper on both anode and cathode. Initially we observed good performance, with a cell voltage of 2.1 V but the voltage increased by about 110 µV/hr over the 2000 hour run. The voltage needed to maintain 1 A/cm2 decreased to 2.05 V when NiFeCo was substituted for Ni on the cathode, but we still observed a voltage rise of 44 µV/hr. We stopped the runs after 2000 hours and found that the membrane was still fine, but the carbon paper on the anode was degrading. So we replaced the carbon paper with metal cloth. We also substituted NiFeOx for Ni on the anode. The voltage needed to maintain 1 A/cm2 dropped to 1.9 V, and was stable for 500 hours. The run is continuing. It is useful to compare our results to those from the recent literature. The best previous alkaline water electrolyzers with base metal catalysts ran at currents below 0.25 A/cm² at 2 V3, 4 and even precious metal catalysts have had trouble maintaining 1 A/cm2 at under 2 V5, 6. These results show that alkaline water electrolyzers with Sustainion™ membranes and base metal catalysts show near precious metal performance. [1]. Kutz, R., Q. Chen, H. Yang, S.D. Sajjad, Z. Liu, and R.I. Masel, Sustainion™ Imidazolium Functionalized Polymers for CO2 Electrolysis.Energy Technology, 2017to appear. [2]. Masel, R.I., Z. Liu, and S. Sajjad, Anion Exchange Membrane Electrolyzers Showing 1 A/cm2 at Less Than 2 V. ECS Transactions, 2016. 75: p. 1143-1146. [3]. Zeng, K. and D. Zhang, Recent progress in alkaline water electrolysis for hydrogen production and applications. Progress in Energy and Combustion Science, 2010. 36: p. 307-326. [4]. Bodner, M., A. Hofer, and V. Hacker, H2 generation from alkaline electrolyzer. Wiley Interdisciplinary Reviews: Energy and Environment, 2015. 4: p. 365-381. [5]. Ahn, S.H., S.J. Yoo, H.-J. Kim, D. Henkensmeier, S.W. Nam, S.-K. Kim, and J.H. Jang, Anion exchange membrane water electrolyzer with an ultra-low loading of Pt-decorated Ni electrocatalyst. Applied Catalysis B: Environmental, 2016. 180: p. 674-679. [6]. Leng, Y., G. Chen, A.J. Mendoza, T.B. Tighe, M.A. Hickner, and C.-Y. Wang, Solid-State Water Electrolysis with an Alkaline Membrane. Journal of the American Chemical Society, 2012. 134: p. 9054-9057. Figure 1

This paper will describe the development and applications of Dioxide Materials’ new brand of novel Sustanion™ polymer Anion Exchange Membranes (AEMs). The styrene backbone of these membranes is functionalized in various degrees by the imidazolium functional group and includes other additives to yield several compositions for tailoring the properties and performance of these membranes. The advantage of using the Sustanion™ membranes over any commercially available AEM technologies is demonstrated in terms of their significantly higher anionic conductivities in Figure 1. Furthermore, the membranes are stable and maintain these conductivities when exposed to 1M KOH at 60 oC for up to a period of at least 1500 hours. We have corroborated these finding by testing these membranes in-situ CO2 and water electrolyzers. Our results speak for themselves. The CO2 electrolyzers have run under 3V at 200 mA/cm² with a voltage rise of only between 4 and 6 µV/hr for 3700 hours. Keep in mind, these currents are more than a factor of 4 higher than our closest competitor. For water electrolyzers, our Sustainion™ membranes have helped us embark on the Holy Grail of base metal catalysts using NiFe on stainless steel anodes and NiFeCo cathodes. We can maintain 1 A/cm² at 1.9V at 60oC in 1M KOH for 200 hours with less than 5 mV voltage variation. This is unprecedented since under the same conditions, we have failed to find a single instance in literature of values surpassing the above results by including even high loadings of precious metal catalysts. The cell is still running. As such, we are expecting to offer these membranes for beta-testing by various academic and industry groups. Based on our current findings, we envision the Sustainion™ membranes making similar breakthroughs in applications of alkaline anion exchange based fuel cells, flow batteries and even electrodiyalsis among other untapped electrochemical applications. Acknowledgement Parts of this work were supported by ARPA-E under contracts DE-AR0000345 and DE-AR0000684 and by 3M. The opinions here are those of the authors and may not reflect the opinions of ARPA-E or 3M. Assistance from colleagues, collaborators and friends from 3M are gratefully acknowledged. Figure 1

Formic acid generated from CO2 has been proposed both as a key intermediate renewable chemical feedstock as well as a potential energy storage chemical media for hydrogen. In this paper, we describe a novel three compartment electrochemical cell configuration with the capability of directly producing a pure formic acid product in the concentration range of 5 – 20 wt% at high current densities and Faradaic yields. The electrochemical cell employs a Dioxide Materials Sustainion™ anion membrane, allowing for the improved CO2 electrochemical reduction performance. Stable electrochemical cell performance for more than 500 hours has been experimentally demonstrated. Figure 1 shows the current produced as a function of the cell voltage in a cell with a tin cathode, and IrO2 anode, and deionized water in the middle compartment with no electrolyte added to the water. Notice that one can obtain up to 200 mA/cm² at reasonable cell voltages. Figure 2 shows how the exit concentration and Faradaic efficiency varies with flowrate. Experimentally, as the Faradaic efficiency decreases as the formic acid concentration rises. Physically, the some of the formic acid is transported to the anode, where it is oxidized leading to formic acid loss. The use of thicker and/or higher MW PSA cation membranes significantly reduces these formate losses. Figure 3 shows a steady state run. In this case, we are able to maintain an output concentration of 15% formic acid for 500 hours, with no significant change in cell voltage. Figure 1

Economic production of syngas from CO2 and H2O could produce new routes to synthetic fuels. In this paper we will describe recent work on the electrolysis of CO2 in a 5 cm² alkaline electrolyzer using standard Fuel Cell Technologies fuel cell hardware. Previous work had demonstrated CO2 conversion with steady state currents of 50 mA/cm² or less at 3 V. In this paper we find that by optimizing the composition of the membrane and ionomer we can raise the current to 280 mA/cm² at 3V and 600 mA/cm² at 3.25-3.35 V. Table 1 shows how the performance of the electrolyzer varies with membrane composition for several different membranes using bare silver cathode catalysts, ruthenium anode catalysts and a variety of membranes. In all cases the measurements were done by sandwiching the membrane between two pieces of carbon cloth that were coated with membrane, mounting the resultant MEA in 5 cm² fuel cell hardware, supplying humidified CO2 to the cathode, applying 3 V, waiting 20 minutes to 1 hr for the current to stabilize and recording the current. Notice that the faradaic efficiency for the conversion of CO2 to CO varies from 0 to 95%. While the current varies from 5 to 80 mA/cm². Sustainion™ membranes give higher currents and faradaic efficiency than the others. These results demonstrate that the membrane composition makes a significant difference to the electrolyzer performance. Figure 1 shows how the polarization curve of the cell varies as we add different amounts of Sustainion™-X5 to the cathode layer in a cell with a Sustainion™-X4 membrane. Notice that one can obtain currents of 1.4 amps (280 mA/cm²) at 3 volts with a Sustainion™-X4 membrane and and Sustainion™-X5 ionomer. Figure 2 shows a steady state run at 600 mA/cm² using an optimal amount of Sustainion™-X6 in the catalyst layer. Notice that we can maintain 600 mA/cm² at between 3.25 and 3.35 V. By comparison, the closest competitor needed almost 7 V to obtain the same current. Figure 3 shows a steady state run at 200 mA/cm² using a Sustainion™-X1 membrane and an optimal amount of Sustainion™-X5 in the catalyst layer. Notice that we were able to maintain constant current for over 600 hours. Unfortunately, these runs ended abruptly when the power went off and then surged as it went on. But in runs without Sustainion™-X5 in the catalyst layer and no power surges, stable performance was observed for over 4000 hours. These results show that the ionomer and membrane can make a substantial difference to the performance of a CO2 electrolyzer. Acknowledgement Parts of this work were supported by ARPA-E under contract DE-AR0000345 and by 3M. The opinion are those of the authors and may not reflect the opinions of ARPA-E or 3M. Figure 1

The electrochemical production of syngas would enable production of transportation fuels from carbon dioxide (CO2), water and renewable energy, but a suitable process does not exist. CO2 reduction to carbon monoxide (CO) has been a particular problem, in that high overpotentials are often needed to drive the CO2 reduction process, so the cost of the process was too high to be economic. Recently, we discovered a helper catalyst, an imidazolium-based ionic liquid (IL), by which CO2 can be reduced to CO at an overpotential as low as 0.17 V on silver (Ag) particle catalysts [1]. The IL suppresses hydrogen evolution on the Ag electrode to a degree tunable by modifying, for instance, the pH and water content of the IL electrolyte. In previous work, the currents were too low to be practical. In the present paper, we present results using a newly developed DX4-13 membrane. We find that the new membranes allow us to obtain 300 mA/cm2 of CO current at room temperature and atmospheric pressure. We also find that by changing the membrane composition, or varying the pH, we can produce syngas from a single electrolyzer. We have observed syngas production from a single cell running at room temperature at 100 mA/cm2 total current, however H2production is reduced at higher currents due to CO poisoning of the hydrogen production process. These and other results will be discussed. [1] Rosen, B. A.; Salehi-Khojin, A.; Thorson, M. A.; Zhu, W.; Whipple, D. T.; Kenis, P. J. A.; Masel, R. I. Science, 2011 , 334, 643.

The impact of climate change on our society is both real and immediate. With rising sea levels, ocean acidification, loss of arctic ice cover, record high temperatures, and severe and lengthening droughts, ignoring CO2 emissions is a risk that we simply cannot afford to take. To combat climate change, we seek ways to both reduce and remediate anthropogenic greenhouse gas emissions. For example, one method of reducing atmospheric CO2 emissions is utilizing clean, renewable energy to electrochemically convert the effluent from carbon-intensive processes such as steel mills and cement factories into a more reactive form of carbon. The resulting reactive form of carbon can then be used as a feedstock to existing industrial hydrocarbon syntheses, preventing the CO2 from otherwise venting into the environment and providing a source of valuable raw materials. Traditionally, the electrochemical reduction of CO2 has required an overpotential on the order of 1.0 V to run efficiently owing to a very high-energy barrier intermediate. In 2011, Dioxide Materials developed an ionic liquid-based helper catalyst that greatly lowered the overpotential required for electrochemical reduction of CO2 to CO with high selectivity1. 3M subsequently partnered with Dioxide Materials in a joint effort, largely funded by ARPA-e, to further develop this nascent technology into an industrial-scale process with the ultimate goal of finding less expensive routes of producing carbon-based fuels from CO2. This collaboration so far has yielded three different electrolyzer cell designs: an all liquid-based cell; an all solid-state (gas phase products and reactants) cell; and a hybrid liquid/solid design. The solid state cell provides a number of advantages over the liquid cell, primarily owing to the reduced device complexity and thus lower overall operating costs; however, liquid-phase CO2 reduction products (such as formic acid) are more difficult to isolate in such a system. Each cell design has been tested in a number of configurations, including constant-current and constant-voltage, using a variety of ionic liquids and operating conditions, including liquid and gas flow rates, temperature, and electrolyte pH. It was found that the product selectivity of the output gas stream depends upon all of these conditions. Initially, our liquid-based cell gave us the best overall performance in terms of both selectivity and current density, achieving >99% CO selectivity (with H2 being the dominant side product) at a current density of 50 mA/cm2. However, performance degradation was a serious drawback owing to a number of design challenges. A follow-up study to the initial report on ionic liquid helper catalysts from Rosen et al. found that the ionic liquid anion (tetrafluoroborate in this case) played an important role in the overall product selectivity and faradaic conversion efficiency of the device2. While 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIM-BF4) showed excellent results at suppressing water electrolysis, we found that BF4 - readily hydrolyzed under standard operating conditions yielding HF acid which severely corroded the current collectors in the liquid cell design. Utilizing an alternative ionic liquid such as EMIM-Cl exhibited similar results at water electrolysis suppression, giving high selectivity; however, the Cl- anion was easily oxidized at the anode, yielding Cl2 gas, resulting in a sharp pH gradient across the cell and a steady loss of selectivity over time. More recently, we have made substantial progress on our solid-state design and have achieved >90% CO selectivity for more than 23 hours of continuous operation which represented a major breakthrough for the project (see Figure 1). The realization of this design required the fabrication of new materials which will be discussed in greater detail in our presentation. Our report will focus on our efforts at optimizing cell design and operating conditions in order to maximize CO production at a high selectivity and low cell voltage. Included will be a discussion of studies into ionic liquid anion effect, pH dependence, and catholyte and anolyte flow conditions on device performance. Acknowledgement. The information, data, or work presented herein was funded in part by the Advanced Research Projects Agency-Energy (ARPA-e), U.S. Department of Energy, under Award Number DE-AR000345. References (1) Rosen, B. A.; Salehi-Khojin, A.; Thorson, M. A.; Zhu, W.; Whipple, D. T.; Kenis, P. J. A.; Masel, R. I. Science., 2011 , 334, 643. (2) Rosen, B. A.; Zhu, W.; Kaul, G.; Salehi-Khojin, A.; Masel, R. I. J. Electrochem. Soc. 2013, 160(2), H138. Figure 1

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