2020 BSJ Blog Spring 2020

Metal-Organic Frameworks show promise for a hydrogen-centric fuel economy

By Noah Bussell

With parts of California locked in a smoky haze for much of the fall and other regions of the world facing climate catastrophes of their own, the negative effects of fossil fuel dependence continue to reveal themselves in full force. As such, with the byproducts of fossil fuel-based processes leading to potentially irreversible environmental damage, scientists, activists, and politicians alike are looking to rethink the way we power our society.

While many ideas of how we can reimagine energy production have circled throughout scientific and political circles, widely adopted solutions such as lithium batteries often pose environmental issues of their own. Rather remarkably however, the simplest molecule, hydrogen (H2), possesses significant potential within the energy sector when produced in a renewable manner. By reacting hydrogen with oxygen, electricity can be generated with water as its sole byproduct, a shockingly simple yet clean process. While this reaction may appear rather elementary, there currently exist a multitude of issues with using hydrogen as a fuel source that need to be addressed and researched to facilitate usage at a large scale. Quite conveniently, a class of chemical compounds called metal-organic frameworks (MOFs), which consists of metal centers coordinated to organic groups (groups containing the elements associated with life) seem to be capable of tackling the issues of hydrogen production and storage. If improved, MOFs could ideally lead to hydrogen production with no fracking, no carbon dioxide, and no dirty money — just clean energy.

A recent paper published by the Lin Group at the University of Chicago has exhibited that MOFs are capable of synthesizing hydrogen molecules using solar energy while also eliminating the need for exotic, hazardous metals. By utilizing MOFs, the group was able to employ readily available metals, such as copper, whereas many previous attempts to harvest solar energy have required rare elements such as ruthenium that are also toxic and expensive. Furthermore, the Lin Group’s hydrogen evolution reaction (HER) circumvents the emission of greenhouse gases currently associated with the bulk of hydrogen production. By coupling these metal “photosensitizers”, or compounds able to take in solar energy and produce useful products, with organic frameworks and catalysts, the production of hydrogen can be done in a relatively safe, feasible, and green manner.

Inefficient hydrogen storage methods have also been hindering the development of a hydrogen-based economy, as hydrogen storage traditionally requires high pressures which can lead to high costs and safety concerns. However, MOFs have been applied to this issue as well, as shown in a recently published Nature article from the University of Michigan. By assembling a database of around 500,000 compounds using both computational and experimental approaches, the scientists behind the paper demonstrated the evolving ability of MOFs to store hydrogen without requiring high pressures. 

The study of MOFs started in the ‘80s and ‘90s, developed by chemists such as Professor Omar Yaghi at the University of California, Berkeley, but MOF research is in a relatively juvenile state compared with the general push for utilizing hydrogen as an energy source (which has been considered as early as the nineteenth century). However, concrete, real systems centered around this idea have only begun to emerge in recent years. Japan, for example, has set a precedent in allocating billions of dollars over the past twenty years towards fuel cell development and the implementation of hydrogen filling stations within the country. As such, Japan has begun to establish a grid under which a new and sustainable hydrogen economy can function. In Southern California, a program known as OCTA has developed a fleet of hydrogen powered buses and the largest “transit-operated hydrogen filling station” in the US. Even with all the impracticalities and issues currently associated with hydrogen fuel cells, they still are proving useful, and as such, institutions and governments are starting to set up the infrastructure for further adoption of these hydrogen-centric technologies. Thus, with the advent of MOFs in hydrogen power’s timeline, it is quite possible to picture a hydrogen-powered future not limited to small bus fleets, but rather inclusive of big-city metro systems and the likes. Ultimately, it would be quite lovely if our transit systems weren’t thought of as grimy polluters, but rather appreciated as machines that could take us from all the ‘A’s to any ‘B’ both comfortably and cleanly.

While the potential of these programs is tremendous, many of the current developments are still just projects with large potential but limited, tangible impact. Hydrogen power is currently responsible for only a smidge of the world’s energy production, and energy generation must substantially change if our planet is to be sustained. Mass developments in technologies such as MOFs must take place and the political will to adopt and fund these technologies must be mustered if this is to happen. The good news though is that with research groups across the world constantly turning out new MOF-related publications and collaborating with one another, this mission now seems just a little more possible.

 

References:

Ahmed, A., Seth, S., Purewal, J., Wong-Foy, A. G., Veenstra, M., Matzger, A. J., & Siegel, D. J. (2019). Exceptional hydrogen storage achieved by screening nearly half a million metal-organic frameworks. Nature Communications, 10(1), 1-9. https://doi.org/10.1038/s41467-019-09365-w

Behling, N., Williams, M. C., & Managi, S. (2015). Fuel cells and the hydrogen revolution: Analysis of a strategic plan in Japan. Economic Analysis and Policy, 48, 204-221. https://doi.org/10.1016/j.eap.2015.10.002

Cassia, R., Nocioni, M., Correa-Aragunde, N., & Lamattina, L. (2018). Climate change and the impact of greenhouse gasses: CO2 and NO, friends and foes of plant oxidative stress. Frontiers in Plant Science, 9, 273. https://doi.org/10.3389/fpls.2018.00273

Feng, X., Pi, Y., Song, Y., Brzezinski, C., Xu, Z., Li, Z., & Lin, W. (2020). Metal–Organic frameworks significantly enhance photocatalytic hydrogen evolution and CO2 reduction with earth-abundant copper photosensitizers. Journal of the American Chemical Society, 142(2), 690-695. https://doi.org/10.1021/jacs.9b12229

Hornyak, T. (2019, Feb 26). How Toyota is helping Japan with its multibillion-dollar push to create a hydrogen-fueled society. CNBC. https://www.cnbc.com/2019/02/26/how-toyota-is-helping-japan-create-a-hydrogen-fueled-society.html

Naterer, G. F., Jaber, O., & Dincer, I. (2010, July). Environmental impact comparison of steam methane reformation and thermochemical processes of hydrogen production. In 18th World Hydrogen Energy Conference (pp. 16-21). Retrieved December 6, 2020, from https://www.osti.gov/etdeweb/servlets/purl/21400908

Orange County Transportation Authority. Hydrogen fuel cell electric bus. OCTA. https://www.octa.net/About-OCTA/Environmental-Sustainability/Hydrogen-Fuel-Cell-Electric-Bus/

Ritchie, H., & Roser, M. (2018). Energy. Our world in data.

United Nations. Climate change. United Nations. https://www.un.org/en/sections/issues-depth/climate-change/

U.S. Energy Information Administration. (2020, January 21). Hydrogen explained production of hydrogen. Independent statistics & analysis. https://www.eia.gov/energyexplained/hydrogen/production-of-hydrogen.php

Zou, T. (2005, April 17). Introduction. Fuel cell technologies. http://web.ecs.baylor.edu/faculty/newberry/myweb/Ethics/Web%20Pages/Trent%20Zou%20-%20Fuel%20Cell/intro.html

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