REDAEM: Anion-Exchange Membranes for Reverse Electrodialysis

Lead Research Organisation: University of Surrey
Department Name: Chemistry


The government commitment to reduce emissions (Climate Change Act 2008 and now the Clean Growth Strategy 2017) and the resulting ambitious targets for renewable energy production requires novel approaches towards efficient production of non-intermittent electricity from renewable sources that can compensate for the closure of fossil fuel power plants around the UK. Reverse electrodialysis (RED) is a "blue" non-intermittent energy technology involving salinity gradient energy, with importance to the UK's future renewable energy mix. RED has been relatively neglected to date, hence, a systematic evaluation of its potential based on innovative materials is urgently needed. Electricity is generated when waters of different salinities (saltiness) are mixed inside an electrochemical RED cell stack (can involve industrial waste streams). A recent conservative assessment of global salinity gradient power (SGP) potential indicates that 625 TWh per year of electricity is practically extractable from river mouths globally (3% of global electricity consumption).

RED cells contain multiple pairs of anion-exchange membranes (AEM) and cation-exchange membranes (CEM). The materials development aspect of this project will focus on the development of high performance AEMs and their application in RED cells (including those supplied with real-world, non-sterile waters). These will be compared to commercial benchmark AEMs. The project will focus on AEMs because CEMs (intended for RED application) were developed as part of a previous EPSRC grant [EP/I004882/1]; there is also less diversity of chemistries available for CEMs, compared to AEMs, which is why the latter requires a more dedicated research project. A wide range of AEMs will be synthesised using the electron-beam radiation-grafting technique. We will also explore the use of sonochemistry during the grafting stage, both in combination with and without the use of the electron-beam.

The RED cell performance data will also be compared to single ion-transport data (experimental and modelling) as well as data from modelling of RED cell engineering configurations. Accurate modelling of the RED stack is crucial in order to estimate the realistic potential of RED in a future UK energy mix. The modelling activities will be further extended to take into consideration the real scalability of the process in terms of potential contribution to the UK energy demand. The integration of data on the availability and locations of fresh water and saline waste streams (e.g. waste streams from industry) with the accurate model of the RED system will produce a precise map of the technology potential at different sites. This activity will then lead to the identification of potential integrations of the process according to the available streams: i.e. once you know where you have fresh water (and how much) you can calculate how much electricity you can actually produce. Furthermore, when an alternative (e.g. industrial) saline waste stream is located close to a fresh water body, this avoids the limitations when using seawater (in terms of coastal location and the magnitude of the salinity gradient).

For cost effectiveness, this project will fully utilise membrane characterisation and RED cell testing equipment that have been purchased/established using funds from prior related EPSRC and EU projects. For maximum transparency, all resulting open access publications (CC-BY) will include DOI locators to facilitate open access to the project's (non-IP-protected) raw data. The project will be used to establish new intra-UK and UK-Dutch research collaborations that should lead to additional links to other UK and EU networks.

Planned Impact

The successful development and implementation of reverse electrodialysis (RED) in the UK will have economic, environmental and societal benefits. The extension of the UK's ability to generate its own non-intermittent renewable electricity (base load) will have great impact on quality of life and public health for people in the UK by helping reduce emissions of carbon dioxide and other pollutants. There are energy security and economic advantages with increased UK self-reliance regarding its energy needs. Reduced dependence on fossil fuels can help improve worldwide socio-economic and political stability (lower costs for all).

There will be positive impacts for the people involved in the project who will benefit from: the knowledge and expertise developed, multidisciplinary training, and acquisition of transferrable skills. The Universities involved run a wide range of continued professional development courses for researchers (e.g. project and open data management for researchers, paper and grant writing skills, research ethics, presentation and science communication skills). The people in industry who we collaborate with will benefit from interaction with academics and the university environment, through exposure to alternative capabilities, thinking, and approaches.

The scientific and engineering base in general will benefit from advancements in a range of areas, including: materials synthesis and characterisation, RED and reaction engineering, and computational modelling methodology from individual membranes and RED cells right through to national-scale potential RED provisions. We will engage with a wide-range of commercial, policymaker, educational stakeholders to fully exploit potential impacts stemming from the research (both expected and unanticipated) and to widen awareness of RED technologies. Government and policy makers will benefit from expert input into the debates around options for the UK future renewable energy mix (the technology delivered will provide a new option for shaping our energy future). Related to the previous point, we will set up and host a "Blue Energy" network.

Materials-chemistry-based impact will be focused on identifying the cheapest materials that can be used to synthesise non-fluorinated ion-exchange membranes. Future scale-up/cost-reduction activities will involve efforts to obtain higher TRL funding once this project identifies the most suitable chemistry/substrate configurations. Ultimately, recyclable, ion-exchange membranes costing < £1 per square metre will need to be used for longer-term commercial viability and sustainability of RED. Our close links with the Dutch leaders in RED technology will be used to evaluate select materials and to validate our models in established scaled-up RED test systems. Once the politics have settled down, and future pathways to EU-UK collaborations are clarified, we will also explore options for obtaining cross-EU- funding for a major RED development project involving our Dutch partners along with other EU commercial concerns. Even before a major RED initiative in the UK, any IP that stems from this project will be commercially exploited to facilitate development of RED systems around the world (inward investment into UK): this could be from direct sales of materials or ethically licensing our IP to relevant parties. RED should be able to play an important role in official development assistance (ODA) countries where salinity gradients are available either naturally or due to production of industrial saline outflows: The Global Challenges Research Fund (GCRF) mechanism will be explored to port the project outcomes into positive benefits to relevant ODA partner countries.

Other efforts will involve an initial exploration of the integration of project-developed RED cells with desalination systems and engagement with the ultrasound processing industry if modification of polymers using ultrasound show promise.


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Description This project is focused on the identification of key anion-exchange membrane attributes for application in Reverse Electrodialysis (RED - a sustainable salinity gradient energy technology).

We have elucidated what polymer film types can be modified using the radiation-grafted route to produce anion-exchange membranes (AEM) with the best balance of low resistance and high permselectivity.

We have identified that cross-linking is essential. We have also identified the best way to introduce cross-linking. This was published in Journal of Materials Chemistry A in 2021.

We have established and validated new more accurate membrane resistance measuring cells. These will be used for our work in the final year of the project to accurately test the resistances of the planned series of new crosslinked anion-exchange membranes.

We are now identifying the cationic head-group type (non-aromatic, aromatic) that yields the best balance of ex situ RED-related characteristics.
Exploitation Route Cross-linking findings also being ported into EU SELECTCO2 Selective Electrochemical Reduction of CO2 to High Value Chemicals consortium grant (active until end 2022) and EPSRC grant EP/T009233/1.

The findings from this grant will help with the preparation of follow-up grant applications and activities, with a focus on the scaled-up fabrication of anion-exchange membrane with down-selected chemistries that look most promising in RED application. Anion-exchange membranes with the best characteristics are being synthesised for distribution to collaborators (after the grant ends in March 2022) to continue RED-related evaluations.
Sectors Chemicals,Energy,Environment

Description University of Surrey - University of Science and Technology of China (Hefei, PR China) 
Organisation University of Science and Technology of China USTC
Country China 
Sector Academic/University 
PI Contribution Developing new membrane chemistries for alkaline anion-exchange membrane fuel cells. Exchange of materials. Testing of USTC Hefei membranes in Surrey Fuel Cell Test Stations
Collaborator Contribution Supply of USTC Hefei membranes to test in Surrey Fuel Cell Test Stations
Impact NSFC joint grant awarded (NSFC grant 21720102003). Joint papers published: X. Liang, M. A. Shehzad, Y. Zhu, L. Wang, X. Ge, J. Zhang, Z. Yang, L. Wu, J. R. Varcoe, T. Xu, "Ionomer Cross-linking Immobilization of Catalyst Nanoparticles for High Performance Alkaline Membrane Fuel Cell", Chemistry of Materials, 31, 7812 (2019). L. Wu, Q. Pan, J. R. Varcoe, D. Zhou, J. Ran, Z. Yang, T. Xu, "Thermal Crosslinking of an Alkaline Anion Exchange Membrane Bearing Unsaturated Side Chains", J. Membr. Sci., 490, 1 (2015). Y. Zhu, L. Ding, X. Liang, M. A. Shehzad, L. Wang, X. Ge, Y. He, L. Wu, J. R. Varcoe, T. Xu, "Beneficial use of rotatable-spacer side-chains in alkaline anion exchange membrane fuel cells" Energy Environ. Sci., 11, 3472 (2018). X. Lin, X. Liang, S. D. Poynton, J. R. Varcoe, A. Ong, J. Ran, Y. Li, Q. Li, T. Xu, "Alkaline anion exchange membranes containing pendant benzimidazolium groups for alkaline fuel cells", J. Membr. Sci., 443, 193 (2013). X. Lin, J. R. Varcoe, S. D. Poynton, X. Liang, A. Ong, J. Ran, Y. Li, T. Xu, "Alkaline polymer electrolytes containing pendant dimethylimidazolium groups for alkaline membrane fuel cells", J. Mater. Chem. A, 1, 7262 (2013). X. Lin, Y. Liu, S. D. Poynton, A. Ong, J. R. Varcoe, L. Wu, Y. Li, X. Liang, Q. Li, T. Xu, "Cross-linked anion exchange membranes for alkaline fuel cells synthesized using a solvent free strategy", J. Power Sources, 233, 259 (2013). Z. Zhang, L. Wu, J. Varcoe, C. Li, A. Ong, S. Poynton, T. Xu, "Aromatic polyelectrolytes via polyacylation of pre-quaternized monomers for alkaline fuel cells.", J. Mater. Chem. A, 1, 2595 (2013). X. Lin, L. Wu, Y. Liu, A. L. Ong, S. D. Poynton, J. R. Varcoe, T. Xu, "Alkali resistant and conductive guanidinium-based anion-exchange membranes for alkaline polymer electrolyte fuel cells", J. Power Sources, 217, 373 (2012). J. Ran, L. Wu, J. R. Varcoe, A. L. Ong, S. D. Poynton, T. Xu, "Development of imidazolium-type alkaline anion exchange membranes for fuel cell application", J. Membr. Sci., 415-416, 242 (2012). Y. Wu, C. Wu, J. R. Varcoe, S. D. Poynton, T. Xu, Y. Fu, "Novel silica/poly(2,6-dimethyl-1,4-phenylene oxide) hybrid anion exchange membranes for alkaline fuel cells: effect of silica content and the single cell performance", J. Power Sources, 195, 3069 (2010).
Start Year 2010
Description Radiation-grafted anion-exchange polymer electrolytes for electrochemical applications (Invited Lecture EUPOC 2015) 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Type Of Presentation keynote/invited speaker
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact Talked sparked Q&amp;amp;A

I was invited by a participant to examine a PhD student in Sweden in Sept 2015
Year(s) Of Engagement Activity 2015