It is a significant advance for carbon dioxide capture and could bring more environmentally friendly fuel cells closer to market.
The research team, led by UD Professor Yushan Yan, reported their method in Nature Energy on Thursday, February 3.
Game-changing tech for fuel cell efficiency
Fuel cells work by converting fuel chemical energy directly into electricity. They can be used in transportation for things like hybrid or zero-emission vehicles.
Yan, Henry Belin du Pont Chair of Chemical and Biomolecular Engineering at UD, has been working for some time to improve hydroxide exchange membrane (HEM) fuel cells, an economical and environmentally friendly alternative to traditional acid-based fuel cells used today.
But HEM fuel cells have a shortcoming that has kept them off the road—they are extremely sensitive to carbon dioxide in the air. Essentially, the carbon dioxide makes it hard for a HEM fuel cell to breathe.
This defect quickly reduces the fuel cell’s performance and efficiency by up to 20%, rendering the fuel cell no better than a gasoline engine. Yan’s research group has been searching for a workaround for this carbon dioxide conundrum for over 15 years.
A few years back, the researchers realized this disadvantage might actually be a solution – for carbon dioxide removal.
“Once we dug into the mechanism, we realized the fuel cells were capturing just about every bit of carbon dioxide that came into them, and they were really good at separating it to the other side,” said Brian Setzler, assistant professor for research in chemical and biomolecular engineering and paper co-author.
While this isn’t good for the fuel cell, the team knew if they could leverage this built-in “self-purging” process in a separate device upstream from the fuel cell stack, they could turn it into a carbon dioxide separator.
“It turns out our approach is very effective. We can capture 99% of the carbon dioxide out of the air in one pass if we have the right design and right configuration,” said Yan.
So, how did they do it?
They found a way to embed the power source for the electrochemical technology inside the separation membrane. The approach involved internally short-circuiting the device.
“It’s risky, but we managed to control this short-circuited fuel cell by hydrogen. And by using this internal electrically shorted membrane, we were able to get rid of the bulky components, such as bipolar plates, current collectors or any electrical wires typically found in a fuel cell stack,” said Lin Shi, a doctoral candidate in the Yan group and the paper’s lead author.
Now, the research team had an electrochemical device that looked like a normal filtration membrane made for separating out gases, but with the capability to continuously pick up minute amounts of carbon dioxide from the air like a more complicated electrochemical system.
In effect, embedding the device’s wires inside the membrane created a short-cut that made it easier for the carbon dioxide particles to travel from one side to the other. It also enabled the team to construct a compact, spiral module with a large surface area in a small volume.
In other words, they now have a smaller package capable of filtering greater quantities of air at a time, making it both effective and cost-effective for fuel cell applications. Meanwhile, fewer components mean less cost, and more importantly, provide a way to easily scale up for the market.
The research team’s results showed that an electrochemical cell measuring 2 inches by 2 inches could continuously remove about 99% of the carbon dioxide found in air flowing at a rate of approximately two liters per minute. An early prototype spiral device about the size of a 12-ounce soda can is capable of filtering 10 liters of air per minute and scrubbing out 98% of the carbon dioxide, the researchers said.
Scaled for an automotive application, the device would be roughly the size of a gallon of milk, Setzler said, but the device could be used to remove carbon dioxide elsewhere, too. For example, the UD-patented technology could enable lighter, more efficient carbon dioxide removal devices in spacecraft or submarines, where ongoing filtration is critical.
“We have some ideas for a long-term roadmap that can really help us get there,” said Setzler.
According to Shi, since the electrochemical system is powered by hydrogen, as the hydrogen economy develops, this electrochemical device could also be used in airplanes and buildings where air recirculation is desired as an energy-saving measure. Later this month, following his dissertation defense, Shi will join Versogen, a UD spinoff company founded by Yan, to continue advancing research toward sustainable green hydrogen.
Co-authors on the paper from the Yan lab include Yun Zhao, co-first author and research associate, who performed experimental work essential for testing the device; Stephanie Matz, a doctoral student who contributed to the designing and fabrication of the spiral module, and Shimshon Gottesfeld, an adjunct professor of chemical and biomolecular engineering at UD. Gottesfeld was principal investigator on the 2019 project, funded by the Advanced Research Projects Agency-Energy (ARPA-E), that led to the findings.
As the global economy was affected by Covid-19, annual global fossil CO2-emissions declined from 2019 to 2020 by seven percent to approximately 33 Gt CO2.1 However, this decline is supposed to represent a temporary effect and immediate action aiming at reduction of emissions is required to limit the increase of global temperatures between a maximum of 1.5 °C and 2 °C as stated in the Paris Agreement.2 A variety of models has been developed to assess and determine future energy pathways and associated impacts on climate change.3,4 Integrated assessment models aim to model the future state of energy systems and technologies by generating energy scenarios.5–7
Based on integrated assessment model projections, the Intergovernmental Panel for Climate Change (IPCC) emphasized that the more delay in the peak of global CO2-emissions, the more the world will need to rely on Carbon Dioxide Removal (CDR) technologies (or Negative Emission Technologies (NETs)) to achieve climate goals.8 Most integrated assessment model scenarios rely on the large-scale deployment of CDR technologies to have a bigger chance than 50% to limit global temperature increases to less than 2 °C.9,10
Hence, it is expected that CDR technologies will have a crucial role to reach future climate goals.6,8,9,11–14 In this study, we define CDR technologies as intentional human efforts to remove Greenhouse Gas (GHG) emissions from the atmosphere (based on Minx et al.12).
However, there seems inconsistency in the scientific community on the definition and characteristics of negative emissions derived from CDR technologies. Based on the work of Tanzer and Ramírez,15 we emphasize that CDR technologies should meet the following requirements to result in negative GHG emissions.
First, a CDR technology permanently removes GHGs from the atmosphere. Second, all upstream and/or downstream GHG emissions are quantified and presented in the emission balance of a specific CDR technology. Third, the total removal of GHG emissions must be larger than the total GHG emissions emitted to the atmosphere, through processes required for GHG removal such as energy supply, transport, and/or land use changes.
The latter requirements demonstrate the complex characteristics of CDR technologies. Therefore, environmental assessment methodologies which exclude upstream and downstream environmental impacts are insufficient to assess CDR technology systems.15,23 Alternatively, Life Cycle Assessment (LCA) is the most widely used methodology to assess product systems (i.e. total supply chains, an example is provided in Fig. 2) on their entire life-cycle environmental performance.24–27 Further, LCA is a flexible methodology which offers various modelling choices, and as such can be used to quantify a variety of environmental impacts, such as acidification potential, ecotoxicity and water depletion.
Currently, the deployment of CDR technologies at the gigatonne scale is still debatable and real demonstration projects are scarce.8,12,28 Consequently, most CDR technologies are not sufficiently examined regarding their overall environmental performance. Relying on a gigatonne scale deployment of CDR technologies – without evaluating their performance from a full life-cycle perspective – could result in infeasible climate goals if the environmental benefits are less than expected.12,28 Further, relying on CDR technologies could result in a moral hazard, since policy-makers could use CDR technologies as a safeguard to postpone climate mitigation measures.12,29 Therefore, it is of great importance to evaluate the environmental performance of CDR technologies from a holistic point of view before a large-scale global implementation. To date, a wide body of literature reviews have been conducted on CDR technologies.
For example, Minx et al.12 and Fuss et al.13 presented an in-depth techno-economic review of a portfolio of CDR technologies. Their CDR technology portfolio included Afforestation and Reforestation (AR), biochar, Soil Carbon Sequestration (SCS), Enhanced Weathering (EW), Ocean Fertilisation (OF), Bioenergy with Carbon Capture and Storage (BECCS) and Direct Air Carbon Capture and Storage (DACCS). Technology potentials – in terms of CO2 removal capacity – were presented for 2050 with substantial uncertainties. Further, the National Academies of Sciences, Engineering, and Medicine30 reviewed the current status of different CDR technologies (i.e. AR, SCS, BECCS, DACCS, EW and other emerging CDR technologies) and concluded that a couple of land-based CDR technologies (i.e. BECCS, AR, SCS) are ready for a large scale deployment from a technical and economical point of view. However, the authors concluded that a large scale deployment of these CDR technologies does not remove sufficient CO2 to achieve the climate goals of the Paris Agreement. Moreover, Li and Wright31 presented a CDR technology review of the techno-economic and life-cycle performance of biomass production pathways used for the production of transportation fuels and power generation technologies. Besides, Goglio et al.23 presented a review of the current challenges in LCAs related to Greenhouse Gas Removal Technologies (GGRTs), and gave useful recommendations for future LCAs. The authors recommended to use a functional unit which captures the GHG removal potential of a CDR technology, to define multi-functional units in case of multiple product functions, to adopt multiple environmental impact categories, to apply consistent system boundaries, to utilize best available data, and to consider a method to include temporal aspects of carbon emissions and removals. Further, Smith et al.10 described potential environmental impacts and biophysical limits related to BECCS, DACCS, EW and AR. Their results showed that, to date, there is no CDR technology without any significant impact on land, albedo, energy, water, nutrients or cost. The authors argued to focus on emission reduction instead of relying on CDR technologies. Further, LCA literature reviews have been conducted on specific CDR technologies. For example, Goglio et al.26 focused on the integration of soil carbon changes in LCA, which is related to SCS systems. Additionally, a recent work of Matuštík et al.32 reviewed LCA studies for pyrolysis-based biochar systems with biochar as soil amendment function.
In general, above studies focused on the environmental and economic performance of CDR technologies, determined with different methodologies. The application of different methodologies and assumptions – often without a thorough discussion of their implications – resulted in a large variation of results on environmental and economic indicators per CDR technology. To our knowledge, an up-to-date and critical review on the environmental life-cycle performance and associated LCA modelling choices of a large portfolio of CDR technologies is missing. This study aims to close these research gaps and determines the current status of LCA literature on CDR technologies. We include the same CDR technology portfolio as proposed in Minx et al.12 and Fuss et al.,13 and use LCA as the most appropriate methodology to assess CDR technologies regarding their overall environmental performance. The contributions of this study can be summarized as follows:
• We include a wide variety of CDR technologies in our portfolio: AR, SCS, EW, OF, biochar, BECCS and DACCS. Additionally, we aim to capture LCAs of other promising CDR technologies.
• A comprehensive literature review is conducted to present the current status of LCA of these CDR technologies.
• A critical review is presented on the most important LCA aspects, such as the system boundaries, functional unit, multi-functionality and Life Cycle Impact Assessment (LCIA) categories applied.
• We synthesize the results, discuss current limitations and give guidelines for future (LCA) research on CDR technologies.
The scientific and social relevance of this work can be summarized as follows. First of all, our review should encourage the scientific community to assess the environmental performance of CDR technologies in a holistic and comprehensive way. Further, our recommendations represent guidelines on how to conduct LCAs of CDR technologies in a consistent way.
Table 1 gives an overview of CDR technologies and important definitions.
Table 1 Overview of key definitions and abbreviations used in this paper
|AR||Afforestation and reforestation||Planting of trees on places which have not been forested recently, while reforestation can be defined as the restocking of trees or forests on (recently depleted) land.13|
|Biochar||Biochar is a condensed carbon rich substance that can be produced at a large scale from biomass, for example with pyrolysis. Biochar can be used as either an energy product or as soil amendment.16|
|BECCS||Bioenergy with carbon capture and storage||Capture and permanent sequestration of biogenic CO2 during an energy conversion process from biomass (e.g. to produce energy within a power plant).17|
|CDR||Carbon dioxide removal||Permanent, or temporal, removal of CO2 or GHG emissions from the atmosphere.|
|DACCS||Direct air carbon capture and storage||Capturing of CO2 from the ambient air, due the binding of sorbents, and the subsequent storage of captured CO2 in a permanent way.18,19|
|EW||Enhanced weathering||Practice to stimulate the process of rock decomposition, while simultaneously increasing cation release to produce alkanity and geogenic nutrients to enhance atmospheric CO2-capture.13,20|
|NET||Negative emission technology||Technology which aims to capture GHG emissions from the atmosphere and which deployment results in negative GHG emissions, i.e. removal of GHGs from the atmosphere.|
|OF||Ocean fertilisation||Practice to enhance biological processes in oceans to stimulate the uptake of atmospheric CO2.21|
|SCS||Soil carbon sequestration||Removal of CO2 from the atmosphere due to increased carbon sequestration in soil organic matter, arising from improved management practices (e.g. due to a land management change or land use change).13,22|
reference link :https://pubs.rsc.org/en/content/articlehtml/2021/ee/d0ee03757e
More information: Lin Shi et al, A shorted membrane electrochemical cell powered by hydrogen to remove CO2 from the air feed of hydroxide exchange membrane fuel cells, Nature Energy (2022). DOI: 10.1038/s41560-021-00969-5