Exploiting membrane enzymes in biotechnology: Bioelectrocatalysis and fuel cells

It is increasingly clear that to tackle global warming and reduce our reliance on fossil fuels, a variety of approaches are required and a combination of new technologies needs to be put into practice. Many forms of renewable energy, like solar cells and windmills, provide intermittent power and hence it is important that this energy can be stored, either in batteries or by conversion into fuels. Such storage requires conversion from electrical to chemical energy and back again, which is performed by electrocatalysts. Many important reactions in energy conversion require expensive, rare metal catalysts. A case in point is hydrogen conversion. It has been estimated that the scarcity of platinum group metals will severely limit, if not prohibit, a conversion to a hydrogen economy.

Biology is very adept in energy conversion and many reactions in metabolism and respiration convert energy. These important reactions, like hydrogen or carbon dioxide conversions, are performed by biocatalysts (i.e., enzymes) that do not rely on expensive or rare metals. However, some of these enzymes reside in biological lipid membranes, which are hydrophobic (i.e. water repellent) and this makes it difficult to employ these types of biocatalysts in technologies for energy conversion.

In this project we aim to develop new types of electrocatalysts that use membrane enzymes. Our proposed technology is based on recent results, which show that membrane enzymes could be employed as electrocatalyst if deposited on conducting (metallic) surfaces. In this project, membrane enzymes will be mixed with specific types of polymers (plastic) as we previously demonstrated that these polymers can vastly extend the lifetime of membrane biocatalysts. Finally, isolating membranes enzymes from bacteria is very expensive. Thus, in this project we will not isolate these biocatalyst, but study how crude extracts from bacteria can be used as this will greatly reduce the cost of biocatalysis.

As a proof-of-principle, we will build a fuel cell that converts hydrogen and oxygen (oxygen from air) into electricity. Such hydrogen fuel cells might, in the future, recharge your laptop, phone or other mobile devices or even power your car.

Progress in biotechnology over the last two decades has greatly increased the use of biocatalyst in the industrial production of complex, pure chemicals. Advantages of biocatalysts over chemical catalyst are their (stereo)selectivity, higher turnover frequencies (TOF), 'green' as well as sustainable production and optimal activity under mild pH and temperature conditions. Fundamental reactions in energy conversion and storage are also catalysed by enzymes and many of these reside in biological lipid membranes, including enzymes active in hydrogen oxidation and evolution, carbon capture (e.g., CO2 to formate) and oxygen reduction. Membrane enzymes, however, are usually not considered for biocatalysis because of the high cost of purification and low stability in detergent environments.

This proposal aims to exploit membrane enzymes for applications in bioelectrocatalysis, in particular for bioenergy related applications such as (bio)fuel cells. A technology will be developed that builds on our recent results, which show that 'cheap-to-produce' crude membrane extracts are suitable catalyst systems and that amphiphilic polymers are able to induce an unprecedented improvement in biocatalyst stability. Our vision is that membrane enzymes exhibit properties that make them particularly suitable in electrocatalysis. The 2D nature of biomembranes and their ability to self-assemble in multilayer films naturally aligns with strategies to prepare electrocatalytic surfaces. Furthermore, the hydrophobic core of biomembranes provides an ideal environment to localise and trap hydrophobic redox mediators as many membrane enzymes have naturally evolved to exchange electrons with the quinone-pool in the membrane.

This project studies the fundamental properties of hybrid polymer-biomembrane multilayers on surfaces with respect to bioelectrocatalysis. It will thus impact the scientific communities working in bioelectrochemistry, membrane biology, soft matter biophysics, surfaces and biocatalysis. The development of novel bioelectrocatalytic surfaces will furthermore impact the biotechnological and biocatalytic industries. This project also aims to develop a proof-of-principle hydrogen fuel cell, which will impact on the energy industry. The development of 'green technology' will furthermore indirectly impact on society. Public engagement activities as part of this project will more directly impact general public.

Scientific communities working in membrane biology, soft matter biophysics, surfaces and biocatalysis:
The PDRA will be trained in the various interdisciplinary aspects of soft matter biophysics and bioelectrocatalysis. Our research results will be disseminated via presentations at conferences and publications in journals, as appropriate in this field. This project also includes two collaborates in Berlin and Bochum, Germany, which will impact these groups via sharing of methods, samples and data.

Biotechnological and biocatalysis industries:
This work will enhance our understanding of crude membrane extracts and hybrid polymer-biomembrane systems and the benefits these systems provide in terms of decreased cost and increased lifetimes of biocatalysts. The applicants, funded by a BBSRC pathfinder grant, are currently in contact with the biotechnology industry for the production of crude membrane extracts for the bioenergy community (industry and academia).

Hydrogen fuel cell industry:
This work will provide insight into the feasibility of using biocatalyst in the development of enzyme-based hydrogen fuel cells. In particular, it will enhance knowledge on whether hydrogenase could compete with platinum as catalyst for hydrogen conversion. Funded by a BBSRC pathfinder grant, market and cost analysis is currently being performed to test the commercialisation potential of this technology.

General public and society:
Impact to society and general public will be two fold. Direct impact will be achieved via public engagement activities, which includes participation in science-week and similar events and the commission and exhibition of an art work related to energy conversion by biocatalysis. Indirect impact to the society will be in form of research that could enhance the use of 'green' catalyst and enzyme-based hydrogen fuel cells, which subsequently could contribute to a greater use of renewable energy and a more sustainable future.