Alternatives to fossil fuels as energy carriers are required to reach global climate targets. Hydrogen and ammonia are promising candidates that are carbon emission-free at point of combustion. Ammonia is critically important for fertiliser production and thus global food production. Additionally, low-carbon ammonia is a potentially valuable fuel for shipping, power generation, and industry. However, ammonia production today accounts for about 2% of total global carbon dioxide emissions. Conventional ammonia production based on methane reforming can be decarbonised by using carbon capture and storage, creating so-called blue ammonia. Alternatively, low-carbon electricity from additional clean energy sources can be used for electrolytic (green) hydrogen and ammonia production. Production tax credits (PTC) for clean hydrogen production via the 45V and carbon sequestration via the 45Q under the Inflation Reduction Act (IRA) in the United States have sparked interest in large-scale commercial low-carbon ammonia projects. In this work, we analyse different blue and electrolytic low-carbon ammonia production processes under economic and practical considerations. We propose and evaluate two novel designs: integrating a biomethane supply into the reformer; and combining blue and green ammonia production processes. Results show that all low-carbon ammonia plants can significantly reduce emissions compared to the conventional process. With the production tax credits, blue ammonia is likely to be the most economical production route in the near-term, being cheaper than conventional ammonia which is not eligible for any credits. The economics of electrolytic ammonia depend heavily on the price of reliable low-carbon electricity. A levelised cost of electricity of about 35 $/MWh and lower is required for electrolytic ammonia to be competitive with blue ammonia at average gas prices and upstream emissions. Of the two novel process designs, blending in biomethane shows promise as it can lead to carbon-neutral or even carbon-negative ammonia with a near-zero cost of production when supported by 45V. Blue-green ammonia on the other hand can improve economics if upstream emissions are small and low-carbon electricity is cheap. Overall, the IRA tax credits improve the economics of low-carbon ammonia production significantly and result in it being competitive with conventional ammonia production, enabling significant carbon emission reduction. Low-carbon ammonia competitive with conventional process with policy support. Novel hybrid processes and biomethane integration can offer additional benefits.

There is growing societal consensus that hydrogen is an absolutely necessary part of energy portfolio to reach the COP26 goal to secure global net-zero by mid-century. Hydrogen will play a major role in hard to decarbonize sectors such as industrial (production of steel, cement, and chemicals including ammonia) and heavy-duty, long-haul transportation. By different estimations, hydrogen production volume will be anywhere from 240 to 800 million metric tons per year (MMTY). More realistic predictions are in the range 500 – 600 MMTY that is 7 – 8.5 times more than current global hydrogen production, which predominantly uses fossil fuels and emits around 830 MMTY of carbon dioxide. It is assumed that hydrogen produced by water splitting became predominant by 2050. With less than 0.1% of current global hydrogen production delivered from water electrolysis, electrolytic hydrogen has tremendous potential for growth. Two commercial (alkaline and PEM) and two emerging (SOEC and AEM) will be compared based on current status and trends of technology (catalysts, membranes, system manufacturability, and capital cost). These technologies could benefit from the integration with energy sources (e.g., nuclear power) or downstream utilization (e.g., ammonia production). Suitability of these technologies for exemplary environments with different energy inputs, electricity prices, and capacity factors will be analyzed. In addition, the effect of different pathways for hydrogen delivery (pure and in the form of a hydrogen carrier) on the levelized cost of hydrogen will be considered. Development of advanced green hydrogen technologies including early stage research will be illustrated with projects funded by DOE Advanced Research Projects Agency (ARPA-E) and Hydrogen and Fuel Cell technologies Office (HFTO), and their role in DOE Hydrogen Program and Hydrogen Earthshot will be discussed.

Solid Oxide Fuel Cells (SOFCs) offer the potential for compelling value propositions in stationary and transportation applications through their high efficiency and fuel flexibility—two critical characteristics that will allow them to facilitate our transition to a carbon neutral economy. This paper describes the overall integration synergies that can be realized in hybrid systems comprised of an SOFC and an engine bottom-cycle. The development to date is reviewed, and application-specific value propositions are explored. Finally, the environmental impact of hybrid systems are discussed, and key challenges to overcome are examined for this highly efficient conversion technology to achieve commercial success.

Solid Oxide Fuel Cells (SOFCs) offer the potential for compelling thermo-economic value propositions in wide range of stationary and transportation applications through their potential for high conversion efficiency and their inherent fuel flexibility. Furthermore, many of the core SOFC materials, component, and system technologies have tremendous potential in electrolysis applications where fuels or chemicals could be produced using renewable electricity. However, to date, the wide-spread commercialization of SOFC/SOEC systems has been hampered by their high cost and durability challenges. Fortunately, high temperature solid oxide-based energy conversion systems are well suited for integration with thermal-mechanical energy conversion systems in configurations that offer the potential for significant cost and thermodynamic performance synergies. Specifically, their integration with gas turbines or internal combustion engines offers the potential for ultra-high (>70%) efficiency at an attractive manufacturing cost (<$1/W). In these hybrid systems, engines or turbines are used to convert stack waste exergy to additional useful work resulting in higher overall efficiency and lower power-specific cost (e.g., $/kW) compared to SOFC-only systems. Furthermore, in the case of SOFC and gas turbine hybrid systems, the SOFC stacks are typically located downstream of the gas turbine compressor and are at elevated pressure—enabling increased Nernst potential and decreased overpotentials and thereby higher power density at constant voltage. This benefit translates into a significant power-specific stack cost reduction. Additionally, the gas turbine compressor and recuperator may serve as the SOFC stack blower and recuperator—yielding further cost synergies via the elimination of duplicative balance of plant components. In 2017, ARPA-E launched the INTEGRATE program to develop hybrid system concepts and enabling component technologies that if realized would result in 100kW-scale distributed generation systems with >70% fuel to electricity conversion efficiencies and system manufacturing costs of <$1/W. In the initial two-year Phase I portion of the program, nine teams developed a suite of hybrid system concepts. Given these concepts, the teams then proceeded to develop 1) durable SOFC stacks that are capable of operating at high (~4 bar) pressure, 2) high temperature (>600 °C) and low-cost heat exchangers, and 3) innovative control system approaches. In 2019, three of the original nine teams were selected to design, build and demonstrate 100kW-scale systems by 2023. In the interest of focusing limited financial resources on foundational development risks, while avoiding the weight, volume, and fuel flexibility challenges associated with transportation applications and mitigating the financial risks associated with adopting new technologies at utility (e.g., >100MW) scale, natural gas fueled distributed generation (DG) systems were selected as the initial INTEGRATE application target. These DG systems would offer a fuel to electric power conversion efficiency that is roughly double that of the fossil fueled portion of the US electric grid. Furthermore, as renewable fuels such as hydrogen, ammonia, and bio- or electro- derived hydrocarbons (e.g., renewable natural gas or synthetic kerosene) become available, these systems would be capable of operating on them with relatively minor fuel processing system adjustments. Moving beyond stationary DG applications, SOFC hybrid systems can leverage their fuel flexibility in the pursuit of a decarbonized of long-distance transportation sector—if the systems can be made both light and small enough. To this end, ARPA-E recently launched three programs that have taken on the challenge of developing ultra-efficient, yet compact and light weight carbon-neutral electrified propulsion systems for commercial aviation. One of these programs is focused on carbon-neutral fuel to electric power conversion sub-systems—Range Extenders for Electric Aviation with Low Carbon and High Efficiency (REEACH). In the two-year Phase 1 of this program, six of nine selected teams will develop SOFC/gas turbine/battery hybrid systems that are fueled with renewable natural gas or synthetic kerosene. Phase 1 focuses on system conceptual design and fuel conversion component risk reduction, while full system design and prototype demonstration of a sub-scale fuel-to-electric power conversion device using a carbon-neutral liquid fuel is planned for Phase 2. If the REEACH-envisioned systems are successfully developed, they would enable economically attractive all-electric commercial aircraft up to a narrow body airframe with dramatically reduced (ideally zero) net carbon emissions. Furthermore, INTEGRATE/REEACH hybrid system technologies would also have attractive value propositions in maritime, rail, or heavy-duty vehicle applications.

The Advanced Research Projects Agency (ARPA-E) funds high risk, high reward transformational research to reduce energy related emissions, reduce imports of energy from foreign sources, improve energy efficiency across all economic sectors, and ensure US technological lead in advanced energy technologies, including electrochemical technologies for energy transformation and storage for distributed, grid scale and automotive applications. Ammonia is produced at a scale of about 180 million tons per year and is easily stored and transported, with excellent safety record. Currently it is mostly used as a fertilizer and a feedstock for production of various chemicals. However, its physical properties, high energy density, the absence of carbon emissions, availability of feedstock (air and water), and well developed synthesis and infrastructure make ammonia almost ideal energy vector. The most potentially efficient direct water and nitrogen electrolysis (electrochemical method) struggles with low faradaic efficiency and current density. Another, more practical approach, is to improve conventional Haber-Bosch process via reducing operational pressure and temperature. Produced using hydrogen from water electrolysis by renewable energy or from fossil fuels with carbon capture (reforming or methane pyrolysis), ammonia can be used for long duration energy storage and as a zero-emission transportation fuel as well as a hydrogen carrier. To address these technological challenges, ARPA-E launched the Renewable Electricity to Fuels through Utilization of Energy-dense Liquids (REFUEL) program. This program and, in part, OPEN program fund the development of transformational technologies for the conversion of intermittent renewable energy, water and air to energy-dense carbon neutral liquid fuels including ammonia and their conversion to hydrogen or back to electricity using fuel cells. Based on successes of REFUEL program, ARPA-E announced an integration and testing program (REFUEL+IT) that targets modular skid-mounted ammonia mini-plant combining technologies developed under REFEL program. The use of ammonia as fuel and hydrogen carrier will be discussed. Fuel cells provide the most efficient conversion of ammonia to electricity. Indirect fueling includes the intermediate ammonia cracking to hydrogen (Industrial process runs at 850oC but temperature could be substantially lower with advanced catalysts), which can be purified to PEM fuel cell grade. Direct fueling requires less capital expenses, and can be used with different types of fuel cells (SOFC, PCFC, AEMFC and molten carbonate fuel cells). Performance of direct ammonia fuel cells (DAFC) was demonstrated to be very close to the performance of the same cells fueled by hydrogen (with correction for the dilution). Issues of crossover (for polymer membranes), electrocatalyst stability (nitridation), cell architecture, and operation parameters will be discussed. Comparison of DAFCs with combustion engines fueled by ammonia for energy applications will be given. Different methods for hydrogen generation from ammonia will be also compared.

Commercial aviation enables the safe, low-cost and rapid movement of people and products but is also responsible for a significant and growing contribution to anthropogenic emissions associated with the burning of fossil fuels. In order to address this challenge, the Advanced Research Projects Agency-Energy (ARPA-E) is supporting the development of all-electric carbon neutral aircraft propulsion technologies. The critical element of such propulsion/power generation systems is the ultra-efficient conversion of the chemical energy in carbon neutral liquid fuels (CNLFs) to useful work. To tackle this part of the electrified propulsion system framework, ARPA-E initiated the Range Extenders for Electric Aviation with Low Carbon and High Efficiency (REEACH) program to develop ultra-efficient, yet light-weight, conversion technologies. If successfully developed, these systems would enable carbon-neutral commercial aircraft up to a narrow body frame size with payloads and missions that are commensurate with incumbent systems.

The Advanced Research Projects Agency (ARPA-E) funds high risk, high reward transformational research to reduce energy related emissions, reduce imports of energy from foreign sources, improve energy efficiency across all economic sectors, and ensure US technological lead in advanced energy technologies, including electrochemical technologies for energy transformation and storage for distributed, grid scale and automotive applications. Ammonia is produced at a scale of about 180 million tons per year and is easily stored and transported. Currently it is mostly used as a fertilizer and a feedstock for production of various chemicals. However, its physical properties, high energy density, the absence of carbon emissions, availability of feedstock (air and water), and well developed synthesis and infrastructure make ammonia almost ideal energy vector. Produced using renewable energy, it can be used for long duration energy storage and as a zero-emission transportation fuel as well as a hydrogen carrier. To address these technological challenges, ARPA-E launched the Renewable Electricity to Fuels through Utilization of Energy-dense Liquids (REFUEL) program. This program and, in part, OPEN program fund the development of transformational technologies for the conversion of intermittent renewable energy, water and air to energy-dense carbon neutral liquid fuels including ammonia and their conversion to hydrogen or back to electricity using fuel cells. All these directions will be covered in the presentation with emphasis on ammonia fuel cells. Fuel cells provide the most efficient conversion of ammonia to electricity. Indirect fueling includes the intermediate ammonia cracking to hydrogen (Industrial process runs at 850 o C but temperature could be substantially lower with advanced catalysts), which can be purified to PEM fuel cell grade. Direct fueling requires less capital expenses, and can be used with different types of fuel cells (SOFC, PCFC, AEMFC and molten carbonate fuel cells). Performance of direct ammonia fuel cells (DAFC) was demonstrated to be very close to the performance of the same cells fueled by hydrogen (with correction for the dilution). Issues of crossover (for polymer membranes), electrocatalyst stability (nitridation), cell architecture, and operation parameters will be discussed. Recent advances in the development of novel ammonia synthesis, its use for hydrogen generation, and DAFCs that is being funded by ARPA-E via REFUEL and OPEN 2018 programs will be presented. Comparison of DAFCs with combustion engines fueled by ammonia for energy applications will be given.

The DOE Hydrogen Program Plan provides a strategic view of how the Department conducts and coordinates hydrogen research, development, and demonstration (RD&D) activities under the DOE Hydrogen Program. With participation from the Offices of Energy Efficiency and Renewable Energy, Fossil Energy, Nuclear Energy, Electricity, Science, and ARPA-E, the DOE Hydrogen Program is a coordinated Departmental effort to advance the affordable production, transport, storage, and use of carbon-neutral hydrogen across different sectors of the economy. This version of the Plan updates and expands upon previous versions, including the Hydrogen Posture Plan and the DOE Hydrogen and Fuel Cells Program Plan, and provides a coordinated high-level summary of hydrogen-related activities across DOE.

Due to its high energy density, carbon-free character, and the convenience for storage and transportation, ammonia (NH3) is considered as an energy vector, capable of being used for energy storage and directly as a fuel. Increasing demands for ammonia have necessitated the development of alternative synthesis approaches as the backup technology to the energy-intensive Haber-Bosch process. Among others, the electrosynthesis of ammonia (ESA) technology offers a promising approach to produce NH3 via a cathodic nitrogen reduction reaction (NRR). However, current ESA technologies desperately suffer from insufficient production rates (<10(-6) mol h(-1) cm(-1)) and low Faradaic efficiency (<30%) due to the lack of highly active and selective NRR catalysts and favorable electrolytes to suppress competitive hydrogen evolution reaction. This review provides an insight into the ESA technology with an emphasis on the design of catalyst/electrolyte systems that optimizes the production of NH3 from N-2 and H2O under ambient conditions. Basic electrochemical principles and reaction mechanisms of the NRR are briefly analyzed in the first section, followed by the impacts of electrochemical components (e.g., catalysts and electrolytes) that define the effectiveness of EAS technologies. The challenges that limited the developments and the approaches that researchers have focused on the catalyst developments are discussed in detail with the main emphasis on the combined catalyst/electrolyte systems. Finally, NRR performance evaluation methods, along with economic analysis of the EAS, are critically examined.

Proton exchange membrane fuel cells have been regarded as the most promising candidate for fuel cell vehicles and tools. Their broader adaption, however, has been impeded by cost and lifetime. By integrating a thin layer of tungsten oxide within the anode, which serves as a rapid-response hydrogen reservoir, oxygen scavenger, sensor for power demand, and regulator for hydrogen-disassociation reaction, we herein report proton exchange membrane fuel cells with significantly enhanced power performance for transient operation and low humidified conditions, as well as improved durability against adverse operating conditions. Meanwhile, the enhanced power performance minimizes the use of auxiliary energy-storage systems and reduces costs. Scale fabrication of such devices can be readily achieved based on the current fabrication techniques with negligible extra expense. This work provides proton exchange membrane fuel cells with enhanced power performance, improved durability, prolonged lifetime, and reduced cost for automotive and other applications.

The Advanced Research Projects Agency (ARPA-E) funds high risk, high reward transformational research to reduce energy related emissions, reduce imports of energy from foreign sources, improve energy efficiency across all economic sectors, and ensure US technological lead in advanced energy technologies, including electrochemical technologies for energy transformation and storage for distributed, grid scale and automotive applications. Ammonia is produced at a scale of about 180 million tons per year and is easily stored and transported. Currently it is mostly used as a fertilizer and a feedstock for production of various chemicals. However, its physical properties, high energy density, the absence of carbon emissions, availability of feedstock (air and water), and well developed synthesis and infrastructure make ammonia almost ideal energy vector. Produced using renewable energy, it can be used for long duration energy storage and as a zero-emission transportation fuel as well as a hydrogen carrier. To address these technological challenges, ARPA-E launched the Renewable Electricity to Fuels through Utilization of Energy-dense Liquids (REFUEL) program. This program and, in part, OPEN program fund the development of transformational technologies for the conversion of intermittent renewable energy, water and air to energy-dense carbon neutral liquid fuels including ammonia and their conversion to hydrogen or back to electricity using fuel cells. All these directions will be covered in the presentation with emphasis on ammonia fuel cells. Fuel cells provide the most efficient conversion of ammonia to electricity. Indirect fueling includes the intermediate ammonia cracking to hydrogen (Industrial process runs at 850oC but temperature could be substantially lower with advanced catalysts), which can be purified to PEM fuel cell grade. Direct fueling requires less capital expenses, and can be used with different types of fuel cells (SOFC, PCFC, AEMFC and molten carbonate fuel cells). Performance of direct ammonia fuel cells (DAFC) was demonstrated to be very close to the performance of the same cells fueled by hydrogen (with correction for the dilution). Issues of crossover (for polymer membranes), electrocatalyst stability (nitridation), cell architecture, and operation parameters will be discussed. Recent advances in the development of novel DAFCs that is being funded by ARPA-E via REFUEL and OPEN 2018 programs will be presented. Comparison of DAFCs with combustion engines fueled by ammonia for energy applications will be given.

Conventional Li-ion batteries (LIBs) are close to practical limits in energy density and cost. The major disadvantage of LIBs is the presence of a flammable electrolyte and a porous separator, which makes them hazardous and restrict the choice of electroactive materials. Solid state batteries (SSBs) could be potentially safer and more energy dense if dendrite-free Li anode is used. The Advanced Research Projects Agency (ARPA-E), which funds high risk, high reward transformational research to reduce energy related emissions, reduce imports of energy from foreign sources, improve energy efficiency, and ensure US technological lead in advanced energy technologies, focuses on the development and scale up of membrane component for solid state batteries as well as full cells with high energy density. According the Integration and Optimization of Novel Ion-Conducting Solids (IONICS) program, a thin (≤20 μm) solid state (ceramic or polymer) electrolyte has to demonstrate ASR ≤5 Ohm-cm2 with high current density and movable areal capacity in Li metal cells. Several major risks for SSBs with Li metal anode have been identified: 1) low electrolyte conductivity, 2) incompatibility of solid membrane with Li metal, 3) anode volume change, 4) dendrite formation, and 5) non-uniform Li plating/segregation, and mitigation strategies will be examined. These issues are related mainly to cyclability, while the cell architecture (e.g. thickness, porosity, non-active materials) defines the energy density and affects its manufacturability, which remains mostly uncharted territory for solid state batteries. Recent advances and trends in the development of novel approaches to materials for solid state batteries, their design and manufacturing of large format full solid electrolyte cells with different cathodes that is being funded by ARPA-E via RANGE, IONICS and OPEN 2018 programs will be discussed.

The preeminent Haber–Bosch process has been feeding humankind for more than one hundred years. Are electrochemical pathways for ammonia synthesis able to compete with it in the future? Electrocatalysts, electrolytes and novel cell design may be key.

The Advanced Research Projects Agency (ARPA-E) funds high risk, high reward transformational research to reduce energy related emissions, reduce imports of energy from foreign sources, improve energy efficiency across all economic sectors, and ensure US technological lead in advanced energy technologies, including electrochemical technologies for energy transformation and storage for distributed, grid scale and automotive applications. Recently hydrogen PEM fuel cells (FC) made great progress in performance, durability and cost that reflected in the emerging of multiple commercial vehicles powered by FCs. However their market penetration is hampered mostly by the absence of hydrogen infrastructure including transportation and storage, and high cost of its implementation. On the other side, carbon-neutral liquid fuels (CNLFs) have energy density higher than of liquid hydrogen, better safety, low footprint and cost of transportation and storage. Easily liquefied ammonia and dimethyl ether as well as more traditional lower alcohols are the most promising CNLFs. They can be used with or without internal reforming in direct liquid fuel cells (DLFCs) or as a hydrogen carrier for PEM fuel cells thus allowing the use of existing liquid fuels infrastructure. History of DLFCs started in 1960s from first GE attempts to use diesel fuel in a FC and continued with development of direct methanol fuel cells (DMFCs). In spite intensive research, the latter found very limited application because of low efficiency and power density. As conventional low temperature PEMs and AEMs content a lot of water to support high H+ or OH- conductivity, high crossover rate of most CNLFs is inevitable and leads to low cell voltage and energy efficiency. In addition, traditional platinum group metal catalysts are easily poisoned by CNLFs or by intermediate oxidation products. Therefore, to realize high energy density of CNLFs and provide high FC power density, it is necessary to increase operation temperature of DLFCs, develop more active and less expensive electrocatalysts, develop selective ion conducting membranes and design electrodes and cells for using liquid fuels. Recent advances in the development of novel DLFCs that is being funded by ARPA-E via REFUEL and OPEN 2018 programs will be presented. Possible future ARPA-E program targeting the use of such fuel cells for transportation (in hybrids, range extenders, APUs for aviation and ground transportation) will be also discussed.

The use of water-soluble organic redox couples is a new and attractive pathway to a sustainable electrical energy storage system with the potential to be inexpensive and environmentally-friendly.[1][2][3] Further, several modifications of this type of redox flow battery arrangement using inorganic materials in combination with organic redox couples have also become the subject of research. [4][5] We have demonstrated the repeated cycling of a redox flow cell based on water-soluble organic redox couples (ORBAT) at high voltage efficiency, coulombic efficiency and power density. Recently, we presented for the first time the synthesis, characterization and properties of 3,6-dihydroxy-2,4-dimethylbenzenesulfonic acid (DHDMBS) as a new positive side electrolyte material for aqueous organic redox flow batteries (ORBAT). [6] DHDMBS overcame the major issue of the Michael reaction with water faced with previously reported positive electrolyte materials such as 4,5-dihydroxybenzene-1,3-disulfonic acid (BQDS) and other unsubstituted benzoquinones. The present study focuses on the crossover of DHDMBS from the positive side of the cell to the negative side. Specifically, we have explored various approaches to mitigate the effects of crossover. These approaches include low-permeability membranes, a new symmetric cell configuration using mixed electrolytes, and operating protocols that involve polarity switching. These approaches were found to reduce fade rates by 70% - 85%. We also uncover mechanistic pathways that lead to slow chemical modification that cause capacity to decrease under strongly acidic conditions during long-term cycling. The new understanding and methods presented here will contribute towards the development of ORBAT as an inexpensive and sustainable solution for large-scale electrical energy storage. Acknowledgement The Authors acknowledge the financial support for this research from ARPA-E Open-FOA program (DE-AR0000337), the University of Southern California, and the Loker Hydrocarbon Research [1] B. Yang, L. Hoober-Burkhardt, F. Wang, G. K. Surya Prakash, and S. R. Narayanan, “An Inexpensive Aqueous Flow Battery for Large-Scale Electrical Energy Storage Based on Water-Soluble Organic Redox Couples,” J. Electrochem. Soc., vol. 161, no. 9, pp. A1371–A1380, 2014. [2] B. Yang, L. Hoober-Burkhardt, S. Krishnamoorthy, A. Murali, G. K. S. Prakash, and S. R. Narayanan, “High-Performance Aqueous Organic Flow Battery with Quinone-Based Redox Couples at Both Electrodes,” J. Electrochem. Soc., vol. 163, no. 7, pp. A1442–A1449, 2016. [3] B. Huskinson, M. P. Marshak, C. Suh, S. Er, M. R. Gerhardt, C. J. Galvin, X. Chen, A. Aspuru-Guzik, R. G. Gordon, and M. J. Aziz, “A metal-free organic–inorganic aqueous flow battery,” Nature, vol. 505, no. 7482, pp. 195–198, 2014. [4] E. S. Beh, D. De Porcellinis, R. L. Gracia, K. T. Xia, R. G. Gordon, and M. J. Aziz, “A Neutral pH Aqueous Organic–Organometallic Redox Flow Battery with Extremely High Capacity Retention,” ACS Energy Lett., vol. 2, no. 3, pp. 639–644, 2017. [5] B. Hu, C. DeBruler, Z. Rhodes, and T. L. Liu, “Long-Cycling Aqueous Organic Redox Flow Battery (AORFB) toward Sustainable and Safe Energy Storage,” J. Am. Chem. Soc., vol. 139, no. 3, pp. 1207–1214, 2017. [6] L. Hoober-Burkhardt, S. Krishnamoorthy, B. Yang, A. Murali, A. Nirmalchandar, G. K. S. Prakash, and S. R. Narayanan, “A New Michael-Reaction-Resistant Benzoquinone for Aqueous Organic Redox Flow Batteries,” J. Electrochem. Soc., vol. 164, no. 4, pp. A600–A607, 2017. Figure 1

The Advanced Research Projects Agency (ARPA-E) funds high risk, high reward transformational research to reduce energy related emissions, reduce imports of energy from foreign sources, improve energy efficiency across all economic sectors, and ensure US technological lead in advanced energy technologies, including electrochemical technologies for energy transformation and storage for distributed, grid scale and automotive applications. Electrochemical technologies have a great potential for increasing efficiency of synthesis of sustainable fuels and their utilization for power generation for different applications. Switching from gaseous fuels (H2, CH4) as an energy vector to liquid fuels has numerous advantages including higher energy density, available infrastructure and increased safety. Low footprint and cost of storage and transportation of carbon-neutral liquid fuels (CNLFs) enables vehicle electrification (directly or as hydrogen carrier), long-time energy storage and effective long-distance energy transportation. Easily liquefied ammonia (4.25 kWh/L) is one of the most promising CNLFs. It can be used directly in fuel cells or as hydrogen carrier for PEM fuel cells thus enabling the infrastructure of hydrogen fueling stations for public transportation. The Renewable Electricity to Fuels through Utilization of Energy-dense Liquids (REFUEL) program funds the development of transformational technologies to reduce the barriers to widespread adoption of intermittent renewable energy sources by enabling the conversion of energy from these sources, water and air to energy-dense CNLFs, mostly ammonia, (Category 1) and their conversion back to electricity using fuel cells (Category 2). The program objective is to demonstrate delivery of source-to-use electricity (including production, transportation, storage, and conversion) at the cost below $0.30/kWh to be competitive with other carbon-free delivery methods. Development of novel synthetic methods for CNLFs and regenerative fuel cells for energy storage is also being funded via OPEN program. Possible future ARPA-E program targeting the use of CNLFs for transportation (in hybrids, range extenders, APUs) will be also discussed.

Replacement of conventional catalytic technologies for synthesis of sustainable, carbon-neutral fuels with direct electrochemical synthesis has a potential for big energy savings due to reduction of number of process steps and pressure/temperature. In addition, electrochemical technologies are easily scaled down to allow for low capital, modular plants that match the scale of renewable energy production. The use of these fuels in electrochemical devices opens a path to cost-effective long-term energy storage and distributed energy generation. Development of low cost, ion-selective membranes with low area specific resistance is, along with electrocatalyst development, critical for the success of such technologies. Not less important is development of membrane manufacturing methods at a practical scale. This presentation will review prospective technologies using ion-selective membranes for synthesis of carbon-neutral fuels for chemical energy storage and their use for generation of electricity (using fuel cells) and hydrogen. Advantages of electrochemical synthesis of ammonia from nitrogen and hydrogen or water compared to the conventional Haber-Bosch process will be discussed. Other processes include direct electrochemical synthesis of alcohols from CO2. The requirements to ion-selective membranes for these processes and fuel cells will be presented. The Advanced Research Projects Agency (ARPA-E) funds high risk, high reward transformational research to reduce energy related emissions, reduce imports of energy from foreign sources, improve energy efficiency across all economic sectors, and ensure US technological lead in advanced energy technologies, including electrochemical energy storage and transformation for grid scale and automotive applications. The Renewable Electricity to Fuels through Utilization of Energy-dense Liquids (REFUEL) program funds the development of transformational technologies to reduce the barriers to widespread adoption of intermittent renewable energy sources by enabling the conversion of energy from these sources, water and air to energy-dense zero-carbon liquid fuels and their use for electricity or hydrogen generation. REFUEL projects targeting various ion conducting membranes as well as related projects supported by ARPA-E through OPEN program will be highlighted.

The Advanced Research Projects Agency (ARPA-E) funds high risk, high reward transformational research to reduce energy related emissions, reduce imports of energy from foreign sources, improve energy efficiency across all economic sectors, and ensure US technological lead in advanced energy technologies, including electrochemical energy storage and transformation for grid scale and automotive applications. High temperature electrochemical technologies and supporting materials (membranes, current collectors, seals, etc.) play an important role in electrochemical (batteries with molten electrodes and molten salt electrolytes) and chemical (electrosynthesis of fuels) energy storage and energy conversion (intermediate and high temperature solid oxide and proton conducting fuel cells and electrolyzers). In addition, high temperature electrochemical technologies to process and recycle metals such as aluminum, titanium, and magnesium are important for advanced manufacturing. The use of high temperatures allows for utilization of ion conducting materials, electrolytes and electrocatalysts, which cannot be utilized at ambient conditions due to low conductivity or activity respectively. Current challenges in high temperature electrochemistry are increasing ionic conductivity of liquid and solid electrolytes to decrease working temperatures and expand material compatibility, improving activity and selectivity of electrocatalysts to decrease energy consumption and costs, increasing power density of stacks to decrease the capital costs, and optimizing the balance of system, which is extremely important for smaller scale devices. ARPA-E funded and currently funds multiple projects targeting high temperature electrochemical processes and development of materials compatible with these processes through OPEN, IDEAS and focused programs. The Modern Electro/Thermochemical Advances in Light Metals Systems (METALS) targets technologies that may provide inexpensive light metal materials for lightweight vehicles and aircraft. The Reliable Electricity Based on Electrochemical Systems (REBELS) program is focused at intermediate temperature fuel cells that operate between 200-500oC and includes cell capable to produce liquid fuels along with electricity to support the distributed energy generation for more reliable and flexible smart grid. The Renewable Electricity to Fuels through Utilization of Energy-dense Liquids (REFUEL) program seeks to fund the development of intermediate and high temperature electrosynthesis and fuel cells technologies to produce and utilize carbon-neutral fuels. This presentation will also highlight high temperature battery technologies using molten metal anodes funded by ARPA-E.

In 2014, the Advanced Research Projects Agency-Energy (ARPA-E) launched the Reliable Electricity Based on ELectrochemical Systems (REBELS) program with the goal of pursuing alternate fuel cell materials and operating conditions that could enable system cost reductions and new electrochemical functionality. This presentation will briefly revisit the original REBELS vision by elaborating the potential benefits of operation in an intermediate temperature range of 200-500 C. Trends in the U.S. electrical grid will be discussed, which reveal the benefits of enhanced fuel cell functionality such as in-situ charge storage and gas-to-liquids (GTL) capabilities. The most significant technical accomplishments from REBELS project teams will be highlighted, including several examples in which the program objective of a current density of 200 mA/cm2 at 0.78 V and 500 C on methane fuel was achieved. Furthermore, teams were able to demonstrate thousands of hours of operation on internally-reformed methane fuel at 500 C with no evidence of coke formation. Fuel cells with charge storage functionality in or near the anode showed a more rapid response to large changes in current density and a lower voltage decrease with high fuel utilization. The needs for further techno-economic assessment to evaluate this concept will be highlighted. Progress towards fuel cells that can also convert methane to liquid fuels will be summarized. Finally, overall lessons learned from the REBELS program will be discussed, such as the ability of ceramic proton conductors to deliver high current density at 500 C on non-hydrogen fuels with minimal degradation. The need for future work in this field will be stressed, especially a continued examination of whether stacks in this temperature range possess the appropriate combination of performance and cost to accelerate the commercialization of high efficiency fuel cells worldwide.