Team:Macquarie Australia/Practices/ImpPrototype
Prototype Design
Prototype – Deployment
Macquarie University 2015 is proud to present our prototype “The Hydrogen Hero - The H-Box”. Our modular self-sufficient energy solution that runs simply on water and sunlight.
Development of our H-Box prototype was arose from the expertise and feedback received from several key opinion leaders who interacted with our team over the course of the project. These expert leaders provided direction which allowed us to refine our design so as to be a commercially viable product, which is not only both novel and innovative, but can also compete with an ever diversifying energy market. The key points that drove our design of the H-box prototype were:
- Negating current challenges involved with using live organisms by instead using the isolated enzyme products themselves obtained from our modified E.coli.
- Exploring a deployment strategy for our prototype that negates the logistical and competitive challenges associated with transporting and marketing pure hydrogen.
- Finding a prospective commercial application for hydrogen use in a renewable energy market that lacks maturity.
- Offering a solution that is low maintenance, self-contained and costs little to run.
- Creating an environmentally friendly energy solution for remote communities that provides attractive prospects for ethical investors and sustainability funds.
The H-BOX PROTOTYPE – “The heart” of our Hydrogen Hero
To utilise the full benefit of recombinant expressed photosystem II, it must be coupled effectively with a suitable hydrogenase enzyme that is separated from molecular oxygen. Separation of these components in our prototype is essential as the hydrogenase cannot work in the presence of molecular oxygen as it will oxidise the iron centre. An effective system which can both (i) create hydrogen protons and (ii) move them across an osmotic gradient was devised. The heart of our H-BOX cell is a two part buffer system were the osmotic gradient can be maintained.
Figure 1: The “heart” of the H-BOX prototype consisting of: PSII and Hydrogenase connected via a graphite electrode (black) allowing the conduction of electrons. The semi-permeable membrane allows ONLY the diffusion of hydrogen protons and the resulting hydrogen accumulates in a reservoir.
Photosystem II is anchored on a conductive matrix where it uses solar energy to split water into hydrogen protons, electrons and molecular oxygen. This tether consists of a His-tag complex coupled to a Ni2+-NTA - thiosuccinamide ester bound to a conductive gold electrode as is consistent with the literature (2). This His-tag complex is an easy modification to be made to our BioBrick constructs. The photocurrent can be increased by introducing spacer molecules, such as BSA (bovine serum albumin) with PSII to increase the photocurrent of immobilised PSII, possibly up to 10 fold and higher. Furthermore, modified gold electrodes can facilitate a mediator-less electron transport through a conductive layer of poly-mercapto-p-benzpquinone to enhance current yield by a factor of ~100.
Figure 2: Tethering of PSII to the electrode using a His-tag.
Our hydrogenase enzymes can be immobilised between the two layers of montmorillonite clay mixed with poly(butylviologen) on glass carbon electrodes to retain conductivity (1). Immobilised mono and multilayer hydrogenase films yield up to 0.35nmol H2/min upon applying a suitable potential on a 40x5mm2. High rates of up to 103-104 turnovers per second for hydrogenases on graphite make them just as effective as platinum for proton reduction.
For the purpose of separating hydrogen protons from molecular oxygen, Nafion is a commercially available semipermeable membrane from DuPont. The fluorinated Teflon backbone of Nafion gives it high chemical stability and ionomer properties make it an ideal selective membrane for hydrogen protons which can migrate across sulfonate groups (see figure 3) (4). By using a two part phosphate buffer system of pH 8.0/pH 7.4, through microsphere marker experiments, the examination of osmotic gradients has been demonstrated. This minor gradient will be sufficient to pump protons across a Nafion membrane (5).
Figure 3: Nafion polymer backbone, showing sulphonyl group and stabile fluorinated backbone.
References
- Esper, B., Badura, A., and Rogner, M., (2006), Photosynthesis as a power supply for (bio-)hydrogen production, Trends in Plant Science, 11(11): 543-549
- Yehezkeli, O., Tel-Vered, R., Michaeli, D., Willner, I., & Nechushtai, R. (2014). Photosynthetic reaction center-functionalized electrodes for photo-bioelectrochemical cells. Photosynthesis research, 120(1-2), 71-85.
- An, N., Zhou, C. H., Zhuang, X. Y., Tong, D. S., & Yu, W. H. (2015). Immobilization of enzymes on clay minerals for biocatalysts and biosensors. Applied Clay Science, 114, 283-296.
- Heitner-Wirguin, C. (1996). "Recent advances in perfluorinated ionomer membranes: structure, properties and applications". Journal of Membrane Science 120: 1–33
- Q Zhao - (2009) Role of proton gradients in the mechanism of osmosis. J Phys Chem B. 6;113(31):10708-14