Nanostructured Conductive Anion Exchange Composite Thin Films for Electrocatalytic Applications

da029a89-9d03-42c0-9f92-8a5ea51be22a

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EPSRC
EPSRC
EPSRC
EPSRC
EPSRC

£493,395

April 27, 2014

Oct. 27, 2015

Context: Fuel cells - why are they important?
Fuel cells are devices that are able to produce electricity for transport, industrial and residential applications directly from electrochemical reactions. Among fuel cells, proton-exchange membrane fuel cells (PEMFCs) are one of the most promising, since hydrogen is used to produce electricity that can be used to power an electric car, or a home. Fuel cells produce electricity very efficiently, and the use of hydrogen produces fewer greenhouse gases than does burning fossil fuels. This also helps to preserve energy resources, as well as to produce water as the only byproduct of the electrochemical reactions, which is a clear benefit for the environment. However, hydrogen is not found freely in nature and must be extracted from other sources. In addition, hydrogen is a gas and presents several issues in terms of safety (handling, transport and storage). Another important drawback of PEMFCs is the use of costly noble metals as catalysts, such as Pt and Pd. All these factors are an obstacle for full exploitation and implementation of PEMFCs.

What do novel hydroxide exchange membrane fuel cells (HEMFCs) have to offer?
The most significant advantage of HEMFCs is that under alkaline conditions, electrode reaction kinetics are much more facile, allowing the use of inexpensive, non-noble metal catalysts, such as NiO and CoO. Another key advantage is that while in acidic conditions as in PEMFCs corrosion is an important issue, instead in alkaline media as in HEMFCs, corrosion is substantially reduced. More importantly, alkaline media are favourable for the use of methanol or ethanol as a fuel. Methanol is very attracting in fuel cells because he has higher volumetric energy density compared to hydrogen and its storage and transportation is less problematic than hydrogen. Also, methanol crossover is reduced in HEMFCs compared to PEMFCs, due to the opposite direction of ion transport in the membrane, from the cathode to the anode. These characteristics make the HEMFC technology economically viable and competitive within internal combustion engines. The polymer utilised herein (TPQPOH) is very competitive in terms of costs (e.g. ~£1/m2 vs. ~£500/m2 for Nafion) and durable in an alkaline environment and additional advantages could be obtained when this polymer is used as a composite material along with carbon nanomaterials.

Impact
The biggest challenge in developing alkaline fuel cells is the anion exchange membrane. Typically, anion exchange membranes are composed of a polymer backbone with tethered cation exchange groups, in order to facilitate the transport of hydroxide ions. The role of the anionic exchange membranes is very similar to the role of Nafion membrane in PEMFCs, where a sulfonic (anion) group is covalently attached to the polymer backbone and protons travel from the anode to the cathode through the membrane. However, in HEMFCs , hydroxide ions travel through the membranes instead of protons, and the challenge is to fabricate membranes with high hydroxide conductivity, good mechanical stability and resistance to chemical deterioration at high temperatures. Another challenge is obtaining values of hydroxide conductivity comparable to proton conductivity observed in PEMFCs. The lack of effective hydroxide exchange membranes is one of the major obstacles to the development of HEMFCs.
Long-term development could generate impact through the development of novel composite materials including TPQPOH/carbon nanomaterial (single- and multi-walled carbon nanotubes and graphene) derivatives. More importantly, the use of doped graphene derivatives as catalyst will enable the development of metal-free fuel cells without the use of precious metal catalysts with an obvious beneficial impact in terms of costs. By switching from internal combustion engines to fuel cells, it is very clear how significant developments in fuel cells could have a dramatic positive impact to our society.

Potential Impact:
Fuel cells are devices that convert chemical energy into electricity through electrochemical reactions. However, improving the efficiency, durability and overall performances are still significant challenges for the full exploitation and commercialisation of these devices. Key components in fuel cell devices are the membranes that separate the anode from the cathode, and the metal catalysts that allow to speeding up the rate of the electrochemical reactions. Within this context, hydroxide exchange membrane fuel cells hold great potential to become novel, efficient, durable and more cost-effective class of membranes, provided that the charge transport and partitioning processes at the micro- and nano-scale are understood. Composite materials derived from hydroxide exchange membrane fuel cell are also very interesting because with proper insertion of metal nanoparticles and/or carbon nanomaterials, they may become materials displaying catalytic activity towards oxygen reduction (ORR) and hydrogen oxidation (HOR) reactions. Understanding the physico-chemical properties of thin film membranes that will be assembled in this project may pave the way for the development of more efficient and durable fuel cells, with an evident positive impact to the environment and use of the energy sources in a more efficient and more sustainable way. Accordingly, these composite membranes will have a dramatic impact across the academic and industrial sector, and in turn benefit society through greener and more efficient energy conversion devices.
A number of industries in the energy sector, ranging from membrane synthesis and assembly to car manufacturing companies could potentially directly benefit from the novel and more efficient composite material membranes developed from this proof-of-concept proposed research. The importance of these industries to the UK and wider society is recognised formally via EPSRC Priorities in Functional Materials, Catalysis, Hydrogen and Fuel Cells, and Materials Engineering-Composites. Impact for these sectors can originate directly from exploitable IP through supply of trained personnel.
This project will train a research staff in multidisciplinary skills essential for future career either in universities or in high added-value businesses. Increased focus in the fuel cells sector, has meant that post doctoral level scientists who are more and more familiar with advanced functional materials, catalysis and electrochemical methods are now needed. The impact of such scientists will therefore be very high, especially when considering that the current number of specialists trained across the necessary physical and engineering science backgrounds is still very low. The pathway to impact is accordingly well-defined for industry beneficiaries, since the work will enhance the pool of highly-trained scientists from which they can recruit.
Engagement with non-academic beneficiaries will be conducted via materials-focused conferences, publications, events, websites and, where appropriate, PDRA secondments. Further societal impact will come from active participation in public lectures and exhibitions (Royal Society, Swansea Science Cafe and others engagement/dissemination activities) and press/media interactions. Briefly, the impact of this research proposal can be summarised as follows:
-Contributing to increasing public awareness and understanding of science, economic and societal issues;
-Contributing toward wealth creation and economic prosperity, i.e. creation and growth of companies and jobs; enhancing business revenues and innovative capacity;
-Attracting R&D investment from global business;
-Contribution to regeneration and economic development;
-Commercialisation and exploitation of scientific knowledge, leading to spin-out companies, and the creation of new processes, product and services.