- Email: [email protected]
Pricing CO2 Direct Air Capture
developing thin and strong SPEs that are compatible for both anode and cathode with low interfacial resistance, more advanced high-energy-density energy storage and conversion devices can be expected for applications. 1. Manthiram, A., Fu, Y., Chung, S.H., Zu, C., and Su, Y.S. (2014). Rechargeable lithium-sulfur batteries. Chem. Rev. 114, 11751–11787. 2. Zhang, H., Oteo, U., Judez, X., Eshetu, G.G., Martinez-Iban˜ez, M., Carrasco, J., Li, C., and Armand, M. (2019). Designer Anion Enabling Solid-State Lithium-Sulfur Batteries. Joule 3, this issue, 1689–1702. 3. Pang, Q., Kwok, C.Y., Kundu, D., Liang, X., and Nazar, L.F. (2019). Lightweight Metallic
MgB2 Mediates Polysulfide Redox and Promises High-Energy-Density Lithium-Sulfur Batteries. Joule 3, 136–148. 4. Degott, P. (1986). Polymere Carbone-Soufre Synthese et Proprietes Electrochimiques. PhD thesis (l’Institut National Polytechnique de Grenoble). 5. https://www.bluecar.fr/sites/bluecar/files/ medias/PDF/2_bluecar_20_p.pdf. 6. Zhao, Q., Chen, P., Li, S., Liu, X., and Archer, L.A. (2019). Solid-state polymer electrolytes stabilized by task-specific salt additives. J. Mater. Chem. A Mater. Energy Sustain. 7, 7823–7830. 7. Ma, Q., Zhang, H., Zhou, C., Zheng, L., Cheng, P., Nie, J., Feng, W., Hu, Y.S., Li, H., Huang, X., et al. (2016). Single Lithium-Ion Conducting Polymer Electrolytes Based on a
Super-Delocalized Polyanion. Angew. Chem. Int. Ed. Engl. 55, 2521–2525. 8. Zhao, Q., Liu, X., Stalin, S., Khan, K., and Archer, L.A. (2019). Solid-state polymer electrolytes with in-built fast interfacial transport for secondary lithium batteries. Nat. Energy 4, 365–373. 9. Zhao, Q., Zheng, J., and Archer, L. (2018). Interphases in Lithium–Sulfur Batteries: Toward Deployable Devices with Competitive Energy Density and Stability. ACS Energy Lett. 3, 2104–2113. 10. Wan, J., Xie, J., Kong, X., Liu, Z., Liu, K., Shi, F., Pei, A., Chen, H., Chen, W., Chen, J., et al. (2019). Ultrathin, flexible, solid polymer composite electrolyte enabled with aligned nanoporous host for lithium batteries. Nat. Nanotechnol. Published online May 27, 2019. https://doi.org/10.1038/s41565-0190465-3.
Preview
Pricing CO2 Direct Air Capture Brandon R. Sutherland1,* Negative emissions technologies such as direct air capture systems are an important tool to impede climate change. Recently in Applied Energy, Azarabadi and Lackner reported a generalized cost model for direct air capture of CO2. Their findings emphasize the importance of sorbent cycle duration and stability in minimizing total system cost. The human-caused component of carbon dioxide emissions has grown exponentially starting from the early 1800s, doubling roughly every 30 years.1 This has resulted in an anthropogenic-driven climate change that has increased global average temperatures greater than 1 C beyond the pre-industrial level. To curtail adverse effects associated with a warmer Earth, the Paris Climate Change Agreement has set a target of reducing the temperature increase this century to well below 2 C of this level.2 Realizing this requires reducing all greenhouse gas (GHG) emissions to zero by mid21st century. The world’s ingrained dependence on fossil fuels to produce electricity, to control heating and cooling, and as a transportation fuel make a carbon-
free transition immensely challenging— especially considering the rapid timescales needed to meet climate targets. The energy infrastructure needs to shift toward renewable power sources and on-site capture, storage, and utilization of GHG exhaust streams. A lack of competitive economics for such technology to displace traditional fossil fuels has greatly impeded progress on this front. Still, society does have the tools to fight climate change through technology, government intervention, and public education. It is a complex problem shackled by economic influence that will require an open mind for new proposed solutions and long-term risk management. Beyond simply stopping the emission of GHGs, an idea that is only growing in
importance is taking CO2 out of the biosphere and putting it back in the geosphere using negative emissions technologies (NETs). While it is more cost-effective to reduce GHG emissions toward the zero limit, the further off track the world is from meeting climate goals the more NETs become necessary. Indeed, the Intergovernmental Panel on Climate Change predicts that a slow carbonneutral transition alone is insufficient and NETs are needed curb global average temperature rises.3 One category of NETs consists of CO2absorbing biomass. More trees can be planted (afforestation) or biomass can be farmed, combusted, or broken down through other means and then replanted. The carbon emissions from this process can be captured and sequestered or used. This is termed bioenergy with carbon capture and storage, BECCS. An alternative approach is to take atmospheric CO2 directly from the air and store it underground.4 A consistent problem with each of these methods
1Joule,
Cell Press, 50 Hampshire Street, 5th Floor, Cambridge, MA 02139, USA *Correspondence: [email protected] https://doi.org/10.1016/j.joule.2019.06.025
Joule 3, 1569–1577, July 17, 2019 ª 2019 Published by Elsevier Inc. 1571
DAC. The sorbent cycle life and stability were determined to be critical parameters that influence cost, something often neglected in design and testing at the research scale. This work sheds light on a common problem in materials research—neglecting that performance is coupled to cost, manufacturing complexity, and stability in real-world applications. Generalized cost models that factor in each of these components are therefore essential not only for companies looking to design DAC plants but for researchers working on the sorbent components in the lab.
Figure 1. A Direct Air Capture System with Sorbent Regeneration
is that the costs are high, often 1–2 orders of magnitude greater than the trading price of CO2. Direct air capture (DAC) is an emerging NET with recent pilot-scale cost estimates of $94 to $232 per ton CO2,5 predicted to drop below $60 by 2040.6 DAC uses water and energy as inputs and produces a pure, compressed stream of CO2 as an output. CO2 is captured directly from the air, where it flows through a separation element, often a liquid or solid sorbent. An example sorbent-based DAC process is shown in Figure 1. Ambient air is forced through a sorbent functionalized to bind CO2 either chemically or physically. Air with reduced CO2 partial pressures is returned to the atmosphere. Through heat, pressure, or humidity, the sorbent can be regenerated, releasing a pure CO2 stream and enabling re-use. The output pure CO2 stream in DAC systems can be stored underground, used to synthesize commodity chemicals, or re-synthesized into low-carbon fuels. Compared to approaches that utilize CO2-absorbing biomass, DAC
1572 Joule 3, 1569–1577, July 17, 2019
plants use 100–50,000+ times less land.7 Since CO2 is distributed homogenously throughout the atmosphere, DAC plants can be placed anywhere that is most economic, such as near a carbon sequestration site to minimize transport costs. Reducing the cost of DAC will be critical to expand its chance at having an impact, and there is a need for better, generalized models to estimate cost bounds. Recently in Applied Energy, Azarabadi and Lackner have developed a cost model for direct air capture systems that factors in market CO2 price as well as sorbent cycle time, loading capacity, degradation rate, and regeneration method.8 The model provides a value equation for DAC cost independent from system design, enabling easy comparison and unification of the multitude of sorbents and processes reported in literature. It was found that minimum costs considering sorbents under various conditions ranged from $29 to $91 per ton CO2. These estimates are part of a growing body of evidence for the falling costs of
At current rates of adoption for renewable power generation, humans will be unable to sufficiently limit global temperature rises. Even with a 100% renewable grid transition this century, younger generations will still have the burden of living in a post-climatechange world. It is human psychology to prioritize fixing an immediate problem over preventing future ones. However, new technology is rarely something that can immediately be applied at scale. Technology takes times to progress down the learning curve and reduce its cost. Without continued developments in NETs today, there will be one less weapon to combat climate change as its urgency accelerates in the future. 1. Hofmann, D.J., Butler, J.H., and Tans, P.P. (2009). A new look at atmospheric carbon dioxide. Atmos. Environ. 43, 2084–2086. 2. United Nations Framework Convention on Climate Change (2015). Adoption of the Paris Agreement. Proposal by the President. https:// unfccc.int/resource/docs/2015/cop21/eng/ l09.pdf. 3. V. Masson-Delmotte, P. Zhai, H.O. Po¨rtner, D. Roberts, J. Skea, P.R. Shukla, A. Pirani, W. Moufouma-Okia, C. Pe´an, and R. Pidcock, et al., eds. (2018). Global warming of 1.5 C. An IPCC Special Report on the impacts of global warming of 1.5 C above pre-industrial levels and related global greenhouse gas emission pathways, in the context of strengthening the global response to the threat of climate change, sustainable development, and efforts to eradicate poverty (World Meteorological Organization). 4. Sanz-Pe´rez, E.S., Murdock, C.R., Didas, S.A., and Jones, C.W. (2016). Direct Capture of
CO2 from Ambient Air. Chem. Rev. 116, 11840–11876. 5. Keith, D.W., Holmes, G., St. Angelo, D., and Heidel, K. (2018). A Process for Capturing CO2 from the Atmosphere. Joule 2, 1573– 1594.
6. Fasihi, M., Efimova, O., and Breyer, C. (2019). Techno-economic assessment of CO2 direct air capture plants. J. Clean. Prod. 224, 957–980. 7. Fajardy, M., and Mac Dowell, N. (2017). Can BECCS deliver sustainable and resource
efficient negative emissions? Energy Environ. Sci. 10, 1389–1426. 8. Azarabadi, H., and Lackner, K.S. (2019). A sorbent-focused techno-economic analysis of direct air capture. Appl. Energy 250, 959–975.
Preview
True or False in Electrochemical Nitrogen Reduction
bility and challenges of electrochemical NRR.
Cheng Tang1 and Shi-Zhang Qiao1,* Electrochemical nitrogen reduction to ammonia has recently gathered enormous interest as an attractive carbon-neutral alternative to the Haber-Bosch process. However, this novel process severely suffers from poor reproducibility and reliability. As reported recently in Nature, Chorkendorff and colleagues implemented a systematic benchmarking protocol to eliminate the false and retain the true in nitrogen electroreduction research. Ammonia, the second highest produced chemical in the world (170 Mt year–1), is the vital ingredient in most fertilizers used to sustain the evergrowing global population and is also being considered for use in renewable energy storage as an energy-dense carbon-neutral liquid fuel. Today, the preeminent Haber-Bosch process contributes 90% of annual ammonia production. However, this century-old process requires massive energy input and capital cost and creates significant CO2 emissions.1 Recently, the electrochemical nitrogen reduction reaction (NRR) using renewable electricity under ambient conditions was proposed in principle as a perfect alternative to the Haber-Bosch process.2 Ideally, this would make ammonia production less dependent on fossil fuels and decentralized for on-site and on-demand production.2,3 To date, various electrocatalysts and strategies to enhance electrochemical
NRR activity and selectivity have been reported. However, significant doubt and discussion has arisen as to whether these results should be ascribed to actual N2 electroreduction or false positives.4 Although many artifact sources have been recognized and a series of control experiments have been established since 2018,5–8 the reliability, accuracy, and reproducibility of recent literature still requires improvement. Therefore, a benchmarking protocol for electrochemical NRR research regarding contamination elimination, control experiments, and data reporting is urgently needed. In a landmark study recently published in Nature, Chorkendorff and colleagues highlighted this ‘‘true or false’’ issue in the electrochemical NRR research community.9 They put forward a rigorous protocol to correctly quantify N2 electroreduction activity and re-evaluated several catalysts and processes, revealing both the feasi-
Thorough identification and efficient elimination of all potential contaminant sources is the prerequisite to design and conduct meaningful NRR experiments. In addition to some gradually recognized contaminant sources, the authors especially emphasize artifacts originating from ion-conducting membranes and feed gas streams. Nafion membranes have been shown to allow significant accumulation, release, and crossover of ammonia, resulting in false negatives or positives. Alternatively, a microporous polypropylene membrane, Celgard 3401, was recommended for all aqueous experiments without the requirement of a cleaning procedure. However, commercial Celgard membranes are highly hydrophobic and designed for lithium batteries and thus require specific hydrophilic treatment while maintaining mechanical flexibility for aqueous NRR. Highpurity N2 gas or even isotope-labeled 15 N2 gas usually contains a tiny amount of impurities in the form of NH3 or NOx. The former contamination can be rationally excluded using control experiments with N2 at open-circuit potential (OCP), while the latter cannot be independently probed because NOx can readily be reduced electrochemically to NH3. The feed gas was thus
1Center
for Materials in Energy and Catalysis, School of Chemical Engineering and Advanced Materials, The University of Adelaide, Adelaide, SA 5005, Australia *Correspondence: [email protected] https://doi.org/10.1016/j.joule.2019.06.020
Joule 3, 1569–1577, July 17, 2019 ª 2019 Elsevier Inc. 1573
MgB2 Mediates Polysulfide Redox and Promises High-Energy-Density Lithium-Sulfur Batteries. Joule 3, 136–148. 4. Degott, P. (1986). Polymere Carbone-Soufre Synthese et Proprietes Electrochimiques. PhD thesis (l’Institut National Polytechnique de Grenoble). 5. https://www.bluecar.fr/sites/bluecar/files/ medias/PDF/2_bluecar_20_p.pdf. 6. Zhao, Q., Chen, P., Li, S., Liu, X., and Archer, L.A. (2019). Solid-state polymer electrolytes stabilized by task-specific salt additives. J. Mater. Chem. A Mater. Energy Sustain. 7, 7823–7830. 7. Ma, Q., Zhang, H., Zhou, C., Zheng, L., Cheng, P., Nie, J., Feng, W., Hu, Y.S., Li, H., Huang, X., et al. (2016). Single Lithium-Ion Conducting Polymer Electrolytes Based on a
Super-Delocalized Polyanion. Angew. Chem. Int. Ed. Engl. 55, 2521–2525. 8. Zhao, Q., Liu, X., Stalin, S., Khan, K., and Archer, L.A. (2019). Solid-state polymer electrolytes with in-built fast interfacial transport for secondary lithium batteries. Nat. Energy 4, 365–373. 9. Zhao, Q., Zheng, J., and Archer, L. (2018). Interphases in Lithium–Sulfur Batteries: Toward Deployable Devices with Competitive Energy Density and Stability. ACS Energy Lett. 3, 2104–2113. 10. Wan, J., Xie, J., Kong, X., Liu, Z., Liu, K., Shi, F., Pei, A., Chen, H., Chen, W., Chen, J., et al. (2019). Ultrathin, flexible, solid polymer composite electrolyte enabled with aligned nanoporous host for lithium batteries. Nat. Nanotechnol. Published online May 27, 2019. https://doi.org/10.1038/s41565-0190465-3.
Preview
Pricing CO2 Direct Air Capture Brandon R. Sutherland1,* Negative emissions technologies such as direct air capture systems are an important tool to impede climate change. Recently in Applied Energy, Azarabadi and Lackner reported a generalized cost model for direct air capture of CO2. Their findings emphasize the importance of sorbent cycle duration and stability in minimizing total system cost. The human-caused component of carbon dioxide emissions has grown exponentially starting from the early 1800s, doubling roughly every 30 years.1 This has resulted in an anthropogenic-driven climate change that has increased global average temperatures greater than 1 C beyond the pre-industrial level. To curtail adverse effects associated with a warmer Earth, the Paris Climate Change Agreement has set a target of reducing the temperature increase this century to well below 2 C of this level.2 Realizing this requires reducing all greenhouse gas (GHG) emissions to zero by mid21st century. The world’s ingrained dependence on fossil fuels to produce electricity, to control heating and cooling, and as a transportation fuel make a carbon-
free transition immensely challenging— especially considering the rapid timescales needed to meet climate targets. The energy infrastructure needs to shift toward renewable power sources and on-site capture, storage, and utilization of GHG exhaust streams. A lack of competitive economics for such technology to displace traditional fossil fuels has greatly impeded progress on this front. Still, society does have the tools to fight climate change through technology, government intervention, and public education. It is a complex problem shackled by economic influence that will require an open mind for new proposed solutions and long-term risk management. Beyond simply stopping the emission of GHGs, an idea that is only growing in
importance is taking CO2 out of the biosphere and putting it back in the geosphere using negative emissions technologies (NETs). While it is more cost-effective to reduce GHG emissions toward the zero limit, the further off track the world is from meeting climate goals the more NETs become necessary. Indeed, the Intergovernmental Panel on Climate Change predicts that a slow carbonneutral transition alone is insufficient and NETs are needed curb global average temperature rises.3 One category of NETs consists of CO2absorbing biomass. More trees can be planted (afforestation) or biomass can be farmed, combusted, or broken down through other means and then replanted. The carbon emissions from this process can be captured and sequestered or used. This is termed bioenergy with carbon capture and storage, BECCS. An alternative approach is to take atmospheric CO2 directly from the air and store it underground.4 A consistent problem with each of these methods
1Joule,
Cell Press, 50 Hampshire Street, 5th Floor, Cambridge, MA 02139, USA *Correspondence: [email protected] https://doi.org/10.1016/j.joule.2019.06.025
Joule 3, 1569–1577, July 17, 2019 ª 2019 Published by Elsevier Inc. 1571
DAC. The sorbent cycle life and stability were determined to be critical parameters that influence cost, something often neglected in design and testing at the research scale. This work sheds light on a common problem in materials research—neglecting that performance is coupled to cost, manufacturing complexity, and stability in real-world applications. Generalized cost models that factor in each of these components are therefore essential not only for companies looking to design DAC plants but for researchers working on the sorbent components in the lab.
Figure 1. A Direct Air Capture System with Sorbent Regeneration
is that the costs are high, often 1–2 orders of magnitude greater than the trading price of CO2. Direct air capture (DAC) is an emerging NET with recent pilot-scale cost estimates of $94 to $232 per ton CO2,5 predicted to drop below $60 by 2040.6 DAC uses water and energy as inputs and produces a pure, compressed stream of CO2 as an output. CO2 is captured directly from the air, where it flows through a separation element, often a liquid or solid sorbent. An example sorbent-based DAC process is shown in Figure 1. Ambient air is forced through a sorbent functionalized to bind CO2 either chemically or physically. Air with reduced CO2 partial pressures is returned to the atmosphere. Through heat, pressure, or humidity, the sorbent can be regenerated, releasing a pure CO2 stream and enabling re-use. The output pure CO2 stream in DAC systems can be stored underground, used to synthesize commodity chemicals, or re-synthesized into low-carbon fuels. Compared to approaches that utilize CO2-absorbing biomass, DAC
1572 Joule 3, 1569–1577, July 17, 2019
plants use 100–50,000+ times less land.7 Since CO2 is distributed homogenously throughout the atmosphere, DAC plants can be placed anywhere that is most economic, such as near a carbon sequestration site to minimize transport costs. Reducing the cost of DAC will be critical to expand its chance at having an impact, and there is a need for better, generalized models to estimate cost bounds. Recently in Applied Energy, Azarabadi and Lackner have developed a cost model for direct air capture systems that factors in market CO2 price as well as sorbent cycle time, loading capacity, degradation rate, and regeneration method.8 The model provides a value equation for DAC cost independent from system design, enabling easy comparison and unification of the multitude of sorbents and processes reported in literature. It was found that minimum costs considering sorbents under various conditions ranged from $29 to $91 per ton CO2. These estimates are part of a growing body of evidence for the falling costs of
At current rates of adoption for renewable power generation, humans will be unable to sufficiently limit global temperature rises. Even with a 100% renewable grid transition this century, younger generations will still have the burden of living in a post-climatechange world. It is human psychology to prioritize fixing an immediate problem over preventing future ones. However, new technology is rarely something that can immediately be applied at scale. Technology takes times to progress down the learning curve and reduce its cost. Without continued developments in NETs today, there will be one less weapon to combat climate change as its urgency accelerates in the future. 1. Hofmann, D.J., Butler, J.H., and Tans, P.P. (2009). A new look at atmospheric carbon dioxide. Atmos. Environ. 43, 2084–2086. 2. United Nations Framework Convention on Climate Change (2015). Adoption of the Paris Agreement. Proposal by the President. https:// unfccc.int/resource/docs/2015/cop21/eng/ l09.pdf. 3. V. Masson-Delmotte, P. Zhai, H.O. Po¨rtner, D. Roberts, J. Skea, P.R. Shukla, A. Pirani, W. Moufouma-Okia, C. Pe´an, and R. Pidcock, et al., eds. (2018). Global warming of 1.5 C. An IPCC Special Report on the impacts of global warming of 1.5 C above pre-industrial levels and related global greenhouse gas emission pathways, in the context of strengthening the global response to the threat of climate change, sustainable development, and efforts to eradicate poverty (World Meteorological Organization). 4. Sanz-Pe´rez, E.S., Murdock, C.R., Didas, S.A., and Jones, C.W. (2016). Direct Capture of
CO2 from Ambient Air. Chem. Rev. 116, 11840–11876. 5. Keith, D.W., Holmes, G., St. Angelo, D., and Heidel, K. (2018). A Process for Capturing CO2 from the Atmosphere. Joule 2, 1573– 1594.
6. Fasihi, M., Efimova, O., and Breyer, C. (2019). Techno-economic assessment of CO2 direct air capture plants. J. Clean. Prod. 224, 957–980. 7. Fajardy, M., and Mac Dowell, N. (2017). Can BECCS deliver sustainable and resource
efficient negative emissions? Energy Environ. Sci. 10, 1389–1426. 8. Azarabadi, H., and Lackner, K.S. (2019). A sorbent-focused techno-economic analysis of direct air capture. Appl. Energy 250, 959–975.
Preview
True or False in Electrochemical Nitrogen Reduction
bility and challenges of electrochemical NRR.
Cheng Tang1 and Shi-Zhang Qiao1,* Electrochemical nitrogen reduction to ammonia has recently gathered enormous interest as an attractive carbon-neutral alternative to the Haber-Bosch process. However, this novel process severely suffers from poor reproducibility and reliability. As reported recently in Nature, Chorkendorff and colleagues implemented a systematic benchmarking protocol to eliminate the false and retain the true in nitrogen electroreduction research. Ammonia, the second highest produced chemical in the world (170 Mt year–1), is the vital ingredient in most fertilizers used to sustain the evergrowing global population and is also being considered for use in renewable energy storage as an energy-dense carbon-neutral liquid fuel. Today, the preeminent Haber-Bosch process contributes 90% of annual ammonia production. However, this century-old process requires massive energy input and capital cost and creates significant CO2 emissions.1 Recently, the electrochemical nitrogen reduction reaction (NRR) using renewable electricity under ambient conditions was proposed in principle as a perfect alternative to the Haber-Bosch process.2 Ideally, this would make ammonia production less dependent on fossil fuels and decentralized for on-site and on-demand production.2,3 To date, various electrocatalysts and strategies to enhance electrochemical
NRR activity and selectivity have been reported. However, significant doubt and discussion has arisen as to whether these results should be ascribed to actual N2 electroreduction or false positives.4 Although many artifact sources have been recognized and a series of control experiments have been established since 2018,5–8 the reliability, accuracy, and reproducibility of recent literature still requires improvement. Therefore, a benchmarking protocol for electrochemical NRR research regarding contamination elimination, control experiments, and data reporting is urgently needed. In a landmark study recently published in Nature, Chorkendorff and colleagues highlighted this ‘‘true or false’’ issue in the electrochemical NRR research community.9 They put forward a rigorous protocol to correctly quantify N2 electroreduction activity and re-evaluated several catalysts and processes, revealing both the feasi-
Thorough identification and efficient elimination of all potential contaminant sources is the prerequisite to design and conduct meaningful NRR experiments. In addition to some gradually recognized contaminant sources, the authors especially emphasize artifacts originating from ion-conducting membranes and feed gas streams. Nafion membranes have been shown to allow significant accumulation, release, and crossover of ammonia, resulting in false negatives or positives. Alternatively, a microporous polypropylene membrane, Celgard 3401, was recommended for all aqueous experiments without the requirement of a cleaning procedure. However, commercial Celgard membranes are highly hydrophobic and designed for lithium batteries and thus require specific hydrophilic treatment while maintaining mechanical flexibility for aqueous NRR. Highpurity N2 gas or even isotope-labeled 15 N2 gas usually contains a tiny amount of impurities in the form of NH3 or NOx. The former contamination can be rationally excluded using control experiments with N2 at open-circuit potential (OCP), while the latter cannot be independently probed because NOx can readily be reduced electrochemically to NH3. The feed gas was thus
1Center
for Materials in Energy and Catalysis, School of Chemical Engineering and Advanced Materials, The University of Adelaide, Adelaide, SA 5005, Australia *Correspondence: [email protected] https://doi.org/10.1016/j.joule.2019.06.020
Joule 3, 1569–1577, July 17, 2019 ª 2019 Elsevier Inc. 1573