Skip to main content

Thank you for visiting nature.com. You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

  • Analysis
  • Published:

Cost and potential of metal–organic frameworks for hydrogen back-up power supply

Nature Energy volume 7, pages 448–458 (2022)Cite this article

Subjects

Abstract

Hydrogen offers a route to storing renewable electricity and lowering greenhouse gas emissions. Metal–organic framework (MOF) adsorbents are promising candidates for hydrogen storage, but a deep understanding of their potential for large-scale, stationary back-up power applications has been lacking. Here we utilize techno-economic analysis and process modelling, which leverage molecular simulation and experimental results, to evaluate the future opportunities of MOF-stored hydrogen for back-up power applications and set critical targets for future material development. We show that with carefully designed charging–discharging patterns, MOFs coupled with electrolysers and fuel cells are economically comparable with contemporary incumbent energy-storage technologies in back-up power applications. Future research should target developing MOFs with 15 g kg−1 of recoverable hydrogen adsorbed (excess uptake) and could be manufactured for under US$10 kg−1 to make the on-site storage system a leading option for back-up power applications.

This is a preview of subscription content, access via your institution

Access options

Buy this article

  • Purchase on Springer Link
  • Instant access to full article PDF
Buy now

Prices may be subject to local taxes which are calculated during checkout

Fig. 1: Process flow for the base-case scenario using hydrogen stored by MOF adsorbents as back-up power system.
Fig. 2: Performance of promising MOFs compared with conventional physical storage methods.
Fig. 3: Cost breakdowns of MOFs and comparison with physical hydrogen-storage methods.
Fig. 4: System costs of MOF H2 storage system and incumbent technologies.
Fig. 5: Current performance and material targets for H2 back-up power systems via MOF storage.

Similar content being viewed by others

Data availability

The data that support the results of this study are provided in the main text and Supplementary Notes 1–11. Source data are provided with this paper.

Code availability

The current study uses Microsoft Excel tool ‘Tankinator’ and open-source Python software (RASPA and Coolprop); source codes are available from https://www.hymarc.org/models.html, https://github.com/iRASPA/RASPA2 and http://www.coolprop.org, respectively. All steps in the analysis are described in equations (1)–(40) and Supplementary Notes 1–11. Scripts automating the analysis are available from the corresponding author on reasonable request.

References

  1. Stone, B. et al. Compound climate and infrastructure events: how electrical grid failure alters heat wave risk. Environ. Sci. Technol. 55, 6957–6964 (2021).

    Article  Google Scholar 

  2. Masanet, E., Shehabi, A., Lei, N., Smith, S. & Koomey, J. Recalibrating global data center energy-use estimates. Science 367, 984–986 (2020).

    Article  Google Scholar 

  3. Bawaneh, K., Ghazi Nezami, F., Rasheduzzaman, M. & Deken, B. Energy consumption analysis and characterization of healthcare facilities in the United States. Energies 12, 3775 (2019).

    Article  Google Scholar 

  4. Shehabi, A. et al. United States Data Center Energy Usage Report (Lawrence Berkeley National Laboratory, 2016).

  5. Mytton, D. Hiding greenhouse gas emissions in the cloud. Nat. Clim. Change 10, 701–701 (2020).

    Article  Google Scholar 

  6. Benton, K., Yang, X. & Wang, Z. Life cycle energy assessment of a standby diesel generator set. J. Clean. Prod. 149, 265–274 (2017).

    Article  Google Scholar 

  7. Chen, H., He, J. & Zhong, X. Engine combustion and emission fuelled with natural gas: a review. J. Energy Inst. 92, 1123–1136 (2019).

    Article  Google Scholar 

  8. Chalise, S. et al. Data center energy systems: current technology and future direction. In 2015 IEEE Power & Energy Society General Meeting 1–5 (2015).

  9. Kontorinis, V. et al. Battery Provisioning and Associated Costs for Data Center Power Capping. (Univ. of California San Diego, 2012).

  10. Mongird, K. et al. 2020 Grid Energy Storage Technology Cost and Performance Assessment (Pacific Northwest National Laboratory, 2020).

  11. Pivovar, B., Rustagi, N. & Satyapal, S. Hydrogen at scale (H2@scale): key to a clean, economic, and sustainable energy system. Electrochem. Soc. Interface 27, 47–52 (2018).

    Article  Google Scholar 

  12. Stetson, N. & Wieliczko, M. Hydrogen technologies for energy storage: a perspective. MRS Energy Sustain. 7, E41 (2020).

    Article  Google Scholar 

  13. Curtin, S., Gangi, J. & Skukowski, R. State of the States. Fuel Cells in America 2017 (US Department of Energy, Office of Energy Efficiency and Renewable Energy, 2018).

  14. Kurtz, J., Saur, G. & Sprik, S. Hydrogen Fuel Cell Performance as Telecommunications Backup Power in the United States (National Renewable Energy Laboratory, 2015).

  15. Wei, M. et al. Improving Energy System Resilience at Berkeley Lab and Beyond (Lawrence Berkeley National Laboratory, 2020).

  16. Thomas, J. M., Edwards, P. P., Dobson, P. J. & Owen, G. P. Decarbonising energy: the developing international activity in hydrogen technologies and fuel cells. J. Energy Chem. 51, 405–415 (2020).

    Article  Google Scholar 

  17. Ruth, M. F. et al. The Technical and Economic Potential of the H2@Scale Hydrogen Concept within the United States (National Renewable Energy Laboratory, 2020).

  18. Marocco, P. et al. A study of the techno-economic feasibility of H2-based energy storage systems in remote areas. Energy Convers. Manag. 211, 112768 (2020).

    Article  Google Scholar 

  19. Shet, S. P., Priya, S. S., Sudhakar, K. & Tahir, M. A review on current trends in potential use of metal–organic framework for hydrogen storage. Int. J. Hydrog. Energy 46, 11782–11803 (2021).

    Article  Google Scholar 

  20. Zhang, X. et al. Optimization of the pore structures of MOFs for record high hydrogen volumetric working capacity. Adv. Mater. 32, 1907995 (2020).

    Article  Google Scholar 

  21. Suresh, K. et al. Optimizing hydrogen storage in MOFs through engineering of crystal morphology and control of crystal size. J. Am. Chem. Soc. 143, 10727–10734 (2021).

    Article  Google Scholar 

  22. Ahmed, A. et al. Exceptional hydrogen storage achieved by screening nearly half a million metal–organic frameworks. Nat. Commun. 10, 1568 (2019).

    Article  Google Scholar 

  23. Gómez-Gualdrón, D. A. et al. Evaluating topologically diverse metal–organic frameworks for cryo-adsorbed hydrogen storage. Energy Environ. Sci. 9, 3279–3289 (2016).

    Article  Google Scholar 

  24. Lin, L. et al. Techno-economic analysis and comprehensive optimization of an on-site hydrogen refuelling station system using ammonia: hybrid hydrogen purification with both high H2 purity and high recovery. Sustain. Energy Fuels 4, 3006–3017 (2020).

    Article  Google Scholar 

  25. Niermann, M., Drünert, S., Kaltschmitt, M. & Bonhoff, K. Liquid organic hydrogen carriers (LOHCs)–techno-economic analysis of LOHCs in a defined process chain. Energy Environ. Sci. 12, 290–307 (2019).

    Article  Google Scholar 

  26. Anastasopoulou, A. et al. Technoeconomic analysis of metal–organic frameworks for bulk hydrogen transportation. Energy Environ. Sci. 14, 1083–1094 (2021).

    Article  Google Scholar 

  27. Giraldez Miner, J. I., Flores-Espino, F., MacAlpine, S. & Asmus, P. Phase I Microgrid Cost Study: Data Collection and Analysis of Microgrid Costs in the United States (National Renewable Energy Laboratory, 2018).

  28. Distributed Generation Renewable Energy Estimate of Costs (National Renewable Energy Laboratory, 2016).

  29. Sharma, P. et al. Design and operational analysis of a green data center. IEEE Internet Comput. 21, 16–24 (2017).

    Article  Google Scholar 

  30. Standard for Emergency and Standby Power Systems (National Fire Protection Association, 2022); https://www.nfpa.org/codes-and-standards/all-codes-and-standards/list-of-codes-and-standards/detail?code=110

  31. Annual Electric Power Industry Report. US Energy Information Administration https://www.eia.gov/electricity/data/eia861/ (2021).

  32. Bobbitt, N. S., Chen, J. & Snurr, R. Q. High-throughput screening of metal–organic frameworks for hydrogen storage at cryogenic temperature. J. Phys. Chem. C 120, 27328–27341 (2016).

    Article  Google Scholar 

  33. Goldsmith, J., Wong-Foy, A. G., Cafarella, M. J. & Siegel, D. J. Theoretical limits of hydrogen storage in metal–organic frameworks: opportunities and trade-offs. Chem. Mater. 25, 3373–3382 (2013).

    Article  Google Scholar 

  34. García-Holley, P. et al. Benchmark study of hydrogen storage in metal–organic frameworks under temperature and pressure swing conditions. ACS Energy Lett. 3, 748–754 (2018).

    Article  Google Scholar 

  35. Ahluwalia, R. K., Peng, J. K. & Hua, T. Q. in Compendium of Hydrogen Energy (eds Gupta, R. et al.) 119–145 (Woodhead Publishing, 2016).

  36. Aziz, M., Oda, T. & Kashiwagi, T. Comparison of liquid hydrogen, methylcyclohexane and ammonia on energy efficiency and economy. Energy Proc. 158, 4086–4091 (2019).

    Article  Google Scholar 

  37. Hydrogen and Fuel Cell Technologies Office Multi-Year Research, Development, and Demonstration Plan (US Department of Energy, 2015); https://www.energy.gov/eere/fuelcells/articles/hydrogen-and-fuel-cell-technologies-office-multi-year-research-development

  38. Liu, X.-M., Xie, L.-H. & Wu, Y. Recent advances in the shaping of metal–organic frameworks. Inorg. Chem. Front. 7, 2840–2866 (2020).

    Article  Google Scholar 

  39. Rubio-Martinez, M. et al. New synthetic routes towards MOF production at scale. Chem. Soc. Rev. 46, 3453–3480 (2017).

    Article  Google Scholar 

  40. Kapelewski, M. T. et al. Record high hydrogen storage capacity in the metal–organic framework Ni2 (m-dobdc) at near-ambient temperatures. Chem. Mater. 30, 8179–8189 (2018).

    Article  Google Scholar 

  41. Jaramillo, D. E. et al. Ambient-temperature hydrogen storage via vanadium(II)-dihydrogen complexation in a metal–organic framework. J. Am. Chem. Soc. 143, 6248–6256 (2021).

    Article  Google Scholar 

  42. Ericson, S. J. & Olis, D. R. A Comparison of Fuel Choice for Backup Generators (National Renewable Energy Laboratory, 2019).

  43. Busby, J. W. & et al. Cascading risks: Understanding the 2021 winter blackout in Texas. Energy Res. Soc. Sci. 77, 102106 (2021).

    Article  Google Scholar 

  44. Ma, Z., Eichman, J. & Kurtz, J. Fuel cell backup power system for grid service and microgrid in telecommunication applications. J. Energy Res. Technol. 141, 062002 (2019).

    Article  Google Scholar 

  45. Li, Y. et al. Dynamic modelling and techno-economic analysis of adiabatic compressed air energy storage for emergency back-up power in supporting microgrid. Appl. Energy 261, 114448 (2020).

    Article  Google Scholar 

  46. Farquharson, D., Jaramillo, P. & Samaras, C. Sustainability implications of electricity outages in sub-Saharan Africa. Nat. Sustain. 1, 589–597 (2018).

    Article  Google Scholar 

  47. Müller, M., Kimiaie, N. & Glüsen, A. Direct methanol fuel cell systems for backup power—influence of the standby procedure on the lifetime. Int. J. Hydrog. Energy 39, 21739–21745 (2014).

    Article  Google Scholar 

  48. Golmohamadi, H. Demand-side management in industrial sector: a review of heavy industries. Renew. Sustain. Energy Rev. 156, 111963 (2022).

    Article  Google Scholar 

  49. Yin, Y. et al. COPA: highly cost-effective power back-up for green datacenters. IEEE Trans. Parallel Distrib. Syst. 31, 967–980 (2020).

    Article  Google Scholar 

  50. El-Sayed, E.-S. M. & Yuan, D. Waste to MOFs: sustainable linker, metal, and solvent sources for value-added MOF synthesis and applications. Green Chem. 22, 4082–4104 (2020).

    Article  Google Scholar 

  51. DeSantis, D. et al. Techno-economic analysis of metal–organic frameworks for hydrogen and natural gas storage. Energy Fuels 31, 2024–2032 (2017).

    Article  Google Scholar 

  52. Xiao, J. et al. Effect of hydrogen refueling parameters on final state of charge. Energies 12, 645 (2019).

    Article  Google Scholar 

  53. Study of Equipment Prices in the Power Sector (World Bank Group, 2009); http://hdl.handle.net/10986/17531

  54. Kapelewski, M. T. et al. M2 (m-dobdc)(M = Mg, Mn, Fe, Co, Ni) metal–organic frameworks exhibiting increased charge density and enhanced H2 binding at the open metal sites. J. Am. Chem. Soc. 136, 12119–12129 (2014).

    Article  Google Scholar 

  55. Wieme, J. et al. Thermal engineering of metal–organic frameworks for adsorption applications: a molecular simulation perspective. ACS Appl. Mater. Interfaces 11, 38697–38707 (2019).

    Article  Google Scholar 

  56. Neves, M. I. S., Gkaniatsou, E., Nouar, F., Pinto, M. L. & Serre, C. MOF industrialization: a complete assessment of production costs. Faraday Discuss. 231, 236–341 (2021).

    Google Scholar 

  57. Bhatia, S. K. & Myers, A. L. Optimum conditions for adsorptive storage. Langmuir 22, 1688–1700 (2006).

    Article  Google Scholar 

  58. Albertus, P., Manser, J. S. & Litzelman, S. Long-duration electricity storage applications, economics, and technologies. Joule 4, 21–32 (2020).

    Article  Google Scholar 

  59. Lenzen, D. et al. A metal–organic framework for efficient water-based ultra-low-temperature-driven cooling. Nat. Commun. 10, 3025 (2019).

    Article  Google Scholar 

  60. Heptonstall, P. J. & Gross, R. J. K. A systematic review of the costs and impacts of integrating variable renewables into power grids. Nat. Energy 6, 72–83 (2021).

    Article  Google Scholar 

  61. Aakko-Saksa, P. T., Cook, C., Kiviaho, J. & Repo, T. Liquid organic hydrogen carriers for transportation and storing of renewable energy—review and discussion. J. Power Sources 396, 803–823 (2018).

    Article  Google Scholar 

  62. Semelsberger, T. A. & Brooks, K. P. Chemical hydrogen storage material property guidelines for automotive applications. J. Power Sources 279, 593–609 (2015).

    Article  Google Scholar 

  63. Dalebrook, A. F., Gan, W., Grasemann, M., Moret, S. & Laurenczy, G. Hydrogen storage: beyond conventional methods. Chem. Commun. 49, 8735–8751 (2013).

    Article  Google Scholar 

  64. Allendorf, M. D. et al. An assessment of strategies for the development of solid-state adsorbents for vehicular hydrogen storage. Energy Environ. Sci. 11, 2784–2812 (2018).

    Article  Google Scholar 

  65. Luyben, W. L. Estimating refrigeration costs at cryogenic temperatures. Comput. Chem. Eng. 103, 144–150 (2017).

    Article  Google Scholar 

  66. Ladner, D. R. Performance and mass vs. operating temperature for pulse tube and stirling cryocoolers. In International Cryocooler Conference Inc. (eds Miller, S. D. & Ross, R. G. Jr.) 633–644 (2011).

  67. Turton, R., Bailie, R. C., Whiting, W. B. & Shaeiwitz, J. A. Analysis, Synthesis and Design of Chemical Processes 5th edn (Pearson Education, 2018).

  68. Andersson, J. & Grönkvist, S. Large-scale storage of hydrogen. Int. J. Hydrog. Energy 44, 11901–11919 (2019).

    Article  Google Scholar 

  69. Rivard, E., Trudeau, M. & Zaghib, K. Hydrogen storage for mobility: a review. Materials 12, 1973 (2019).

    Article  Google Scholar 

  70. Wang, H., Leung, D. Y., Leung, M. & Ni, M. A review on hydrogen production using aluminum and aluminum alloys. Renew. Sustain. Energy Rev. 13, 845–853 (2009).

    Article  Google Scholar 

  71. Barthélémy, H., Weber, M. & Barbier, F. Hydrogen storage: recent improvements and industrial perspectives. Int. J. Hydrog. Energy 42, 7254–7262 (2017).

    Article  Google Scholar 

  72. Dubbeldam, D., Calero, S., Ellis, D. E. & Snurr, R. Q. RASPA: molecular simulation software for adsorption and diffusion in flexible nanoporous materials. Mol. Simul. 42, 81–101 (2016).

    Article  Google Scholar 

  73. Groom, C. R., Bruno, I. J., Lightfoot, M. P. & Ward, S. C. The Cambridge structural database. Acta Crystallogr. B 72, 171–179 (2016).

    Article  Google Scholar 

  74. Brooks, K. P. et al. PNNL Development and Analysis of Material-Based Hydrogen Storage Systems for the Hydrogen Storage Engineering Center of Excellence (Pacific Northwest National Laboratory, 2016).

  75. Thornton, M. J. & Simpson, L. J. System Design, Analysis, and Modeling Activities Supporting the DOE Hydrogen Storage Engineering Center of Excellence (HSECoE): Final Project Report (National Renewable Energy Laboratory, 2019).

  76. Tamburello, D. et al. Compact cryo-adsorbent hydrogen storage systems for fuel cell vehicles. In Proc. of the ASME 2018 Power Conference POWER2018-7474 (ASME, 2018).

  77. Yates, J. et al. Techno-economic analysis of hydrogen electrolysis from off-grid stand-alone photovoltaics incorporating uncertainty analysis. Cell Rep. Phys. Sci. 1, 100209 (2020).

    Article  Google Scholar 

  78. Wei, M. et al. A Total Cost of Ownership Model for Low Temperature PEM Fuel Cells in Combined Heat and Power and Backup Power Applications (Lawrence Berkeley National Laboratory, 2014).

  79. Barbir, F. in PEM Fuel Cells 33–72 (Academic Press, 2005).

  80. Barbir, F. in Encyclopedia of Electrochemical Power Sources 224–237 (Elsevier, 2009).

  81. Muthukumar, P., Maiya, M. P. & Murthy, S. S. Performance tests on a thermally operated hydrogen compressor. Int. J. Hydrog. Energy 33, 463–469 (2008).

    Article  Google Scholar 

  82. Sdanghi, G., Maranzana, G., Celzard, A. & Fierro, V. Review of the current technologies and performances of hydrogen compression for stationary and automotive applications. Renew. Sustain. Energy Rev. 102, 150–170 (2019).

    Article  Google Scholar 

  83. Geankoplis, C. J. Transport Processes and Separation Process Principles (Includes Unit Operations) (Prentice Hall Professional Technical Reference, 2003).

  84. Haug, P., Kreitz, B., Koj, M. & Turek, T. Process modelling of an alkaline water electrolyzer. Int. J. Hydrog. Energy 42, 15689–15707 (2017).

    Article  Google Scholar 

  85. Brauns, J. & Turek, T. Alkaline water electrolysis powered by renewable energy: a review. Processes 8, 248 (2020).

    Article  Google Scholar 

  86. Wong, C. et al. Additives in proton exchange membranes for low- and high-temperature fuel cell applications: a review. Int. J. Hydrog. Energy 44, 6116–6135 (2019).

    Article  Google Scholar 

  87. Özgür, T. & Yakaryilmaz, A. C. Thermodynamic analysis of a proton exchange membrane fuel cell. Int. J. Hydrog. Energy 43, 18007–18013 (2018).

    Article  Google Scholar 

Download references

Acknowledgements

The authors gratefully acknowledge support from the Hydrogen Materials—Advanced Research Consortium (HyMARC) established as part of the Energy Materials Network under the US DOE Office of Energy Efficiency and Renewable Energy (EERE), Hydrogen and Fuel Cell Technologies Office, under contract number DE-AC02-05CH11231 with Lawrence Berkeley National Laboratory (P.P., A.A., H.F., J.R.L. and H.B.) and DE-AC05-76RL01830 with Pacific Northwest National Laboratory (K.B., M.E.B. and T.A.). We thank M. Monroe of Microsoft for his insight.

Author information

Authors and Affiliations

  1. Energy Analysis and Environmental Impacts Division, Lawrence Berkeley National Laboratory, Berkeley, CA, USA

    Peng Peng, Aikaterini Anastasopoulou & Hanna Breunig

  2. Department of Chemical and Biomolecular Engineering, University of Delaware, Newark, DE, USA

    Aikaterini Anastasopoulou

  3. Energy and Environment Directorate, Pacific Northwest National Laboratory, Richland, WA, USA

    Kriston Brooks

  4. Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA, USA

    Hiroyasu Furukawa & Jeffrey R. Long

  5. Department of Chemistry, University of California, Berkeley, CA, USA

    Hiroyasu Furukawa & Jeffrey R. Long

  6. Physical and Computational Sciences Directorate, Pacific Northwest National Laboratory, Richland, WA, USA

    Mark E. Bowden & Tom Autrey

  7. Department of Chemical and Biomolecular Engineering, University of California, Berkeley, CA, USA

    Jeffrey R. Long

Authors
  1. Peng Peng
    View author publications

    You can also search for this author in PubMed Google Scholar

  2. Aikaterini Anastasopoulou
    View author publications

    You can also search for this author in PubMed Google Scholar

  3. Kriston Brooks
    View author publications

    You can also search for this author in PubMed Google Scholar

  4. Hiroyasu Furukawa
    View author publications

    You can also search for this author in PubMed Google Scholar

  5. Mark E. Bowden
    View author publications

    You can also search for this author in PubMed Google Scholar

  6. Jeffrey R. Long
    View author publications

    You can also search for this author in PubMed Google Scholar

  7. Tom Autrey
    View author publications

    You can also search for this author in PubMed Google Scholar

  8. Hanna Breunig
    View author publications

    You can also search for this author in PubMed Google Scholar

Contributions

H.B., J.R.L., T.A., K.B. and M.E.B. conceptualized and conceived the analysis. H.B., P.P. and A.A. developed the methodology. H.B. and P.P. conducted the investigation. H.F. and J.R.L. provided the experimental resources. P.P. and H.F. curated the data. P.P. and H.B. wrote the original draft. H.B., P.P., A.A., K.B., H.F., M.E.B., J.R.L. and T.A. reviewed and edited the paper. P.P. and H.B. visualized the results. J.R.L., T.A. and H.B. supervised and obtained funding and resources for the project.

Corresponding author

Correspondence to Hanna Breunig.

Ethics declarations

Competing interests

The authors declare the following competing interests: J.R.L. has a financial interest in Mosaic Materials Inc., a start-up company working to commercialize metal−organic frameworks for gas adsorption applications. The University of California, Berkeley, has been issued a patent relating to the use of Ni2(m-dobdc) on which J.R.L. is listed as a co-inventor and has applied for a patent relating to the use of V-btdd on which J.R.L. is listed as a co-inventor. The remaining authors declare no competing interests.

Peer review

Peer review information

Nature Energy thanks Dimitri Mignard, Genevieve Saur and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

Additional information

Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Supplementary information

Supplementary Information

Supplementary Notes 1-11, Supplementary Figures 1-13, Supplementary Tables 1-7

Source data

Source Data Fig. 2

Statistical Source Data

Source Data Fig. 3

Statistical Source Data

Source Data Fig. 4

Statistical Source Data

Source Data Fig. 5

Statistical Source Data

Rights and permissions

Reprints and permissions

About this article

Check for updates. Verify currency and authenticity via CrossMark

Cite this article

Peng, P., Anastasopoulou, A., Brooks, K. et al. Cost and potential of metal–organic frameworks for hydrogen back-up power supply. Nat Energy 7, 448–458 (2022). https://doi.org/10.1038/s41560-022-01013-w

Download citation

  • Received:

  • Accepted:

  • Published:

  • Issue Date:

  • DOI: https://doi.org/10.1038/s41560-022-01013-w

Search

Advanced search

Quick links

Nature Briefing

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing