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Nanodesigned electrochemical converter of solar energy into hydrogen hosting natural enzymes or their mimics

Final Report Summary - SOLHYDROMICS (Nanodesigned electrochemical converter of solar energy into hydrogen hosting natural enzymes or their mimics)

Leaves can split water into oxygen and hydrogen at ambient conditions exploiting sun light. Prof. James Barber, one of the key players of SOLHYDROMICS, was the recipient of the international Italgas Prize in 2005 for his studies on Photosystem II (PSII), the enzyme that governs this process.

In photosynthesis, hydrogen (H2) is used to reduce carbon dioxide (CO2) and give rise to the various organic compounds needed by the organisms or even oily compounds which can be used as fuels. However, a specific enzyme, hydrogenase, may lead to non-negligible H2 formation even within natural systems under given operating conditions.

Building on this knowledge, and on the convergence of the work of the physics, materials scientists, biochemists and biologists involved in the project, an artificial device will be developed to convert sun energy into H2 with the potential of achieving 10 % efficiency by water splitting at ambient temperature, including:

- an electrode exposed to sunlight carrying PSII or a PSII-like chemical mimic deposited upon a suitable electrode;
- a membrane enabling transport of both electrons and protons via e.g. carbon nanotubes or TiO2 connecting the two electrodes and ion-exchange resins like e.g. Nafion, respectively;
- a cathode carrying the hydrogenase enzyme or an artificial hydrogenase catalyst in order to recombine protons and electrons into pure molecular hydrogen at the opposite side of the membrane.

The project involves a strong and partnership hosting highly ranked scientists (from the Imperial College London, the Politecnico di Torino and the HZG research centre on polymers in Geesthacht) who have a significant past cooperation record and four high-tech SMEs (Solaronix, Biodiversity, Nanocyl and Hysytech) to cover with expertise and no overlappings the key tasks of enzyme purification and enzyme mimics development, enzyme stabilisation on the electrodes, membrane development, design and manufacturing of the SOLHYDROMICS proof-of-concept prototype, market and technology implementation studies.

Within the project all project deliverables have been accomplished and studies have made progress on all aspects ranging from natural enzymes purification and immobilisation to mimics development, from testing of electro-catalysts to device modelling, from membrane development to system specifications setting.

The first fully operational Solhydromics prototype hosting natural enzymes has been built and operated by the end of the second year, deriving quite interesting results which were though regarded too far from target. Particularly, the duration of satisfactory performance is 30 min, and the efficiency of conversions of solar energy into hydrogen was orders of magnitude below target.

As a consequence, the last 1,5 years of the project have been dedicated to the development of water-splitting mimics and a second generation prototype whose final performance was much more satisfactory and close to the original targets:

- 1 % solar energy conversion into hydrogen;
- 1 day operation demonstrated with just a small deactivation.

These last regards results allow a moderate optimism on the exploitation chances of the technology. A final report on exploitation opportunities:

1. evolution of the Solhydromics cell into a tandem cell;
2. use of Co-MOF catalyst in a photo-activated alkali electrolyzer;
3. development of a photo-electrochemical reactor coupled with anaerobic digestion of organic wastes;
4. development of a photo-electrochemical reactor for CO2 reduction into methanol in a biorefinery;
5. development and commercialisation of a test rig for photo-electrochemical studies.) has been issued including a critical analysis and cost / performance targets for future research and development (R&D) efforts.

Project context and objectives:

The main technical and scientific objectives of the SOLHYDROMICS project are the following:

- Development of an innovative device capable of using sunlight to produce hydrogen from water splitting in a most cost effective way with routes based on photovoltaics coupled with electrochemically driven catalysis. An ambitious efficiency target is 10 % conversion of solar energy into pure hydrogen which is considered to be feasible based on preliminary calculations by the proponents.
- The device must be robust with long operational times. A target of one week continuous operation is envisaged for a first generation SOLHYDROMICS prototype based on natural enzymes, whilst a one month continuous operation is targeted for the second generation one based on stable enzyme mimics. Subsequent technology improvements, beyond the proposed project should lead to a lifetime of years.
- To disclose wide potential application opportunities, the above targets must be reached without using expensive noble metals or materials and via assembling techniques amenable for mass production.
- The potential of this artificial solar energy conversion route will also be assessed in comparison to intensive micro-algal growth systems aimed at producing hydrogen or vegetable oils as fuels.

More specifically, the following targets will be pursued while developing the various SOLHYDROMICS components according to an approach exploiting basic science and cross-cutting technologies:

- Development of cheap biochemical and molecular biological procedures to isolate appropriate enzymes (PSII, hydrogenases) at a sufficient quantity to assist the SOLHYDROMICS device development.
- Exploitation of carbon nanotubes (CNT) or Buckminster fullerene structures both as enzyme supports at the two electrode locations and as electron transfer materials through the membrane, by involving a specific high tech small and medium-sized enterprise (SME) (Nanocyl).
- Development of a TiO2 percolation interconnected structure as an alternative to CNT for the same objective; once again a specific high tech SME (Solaronix) will be the key player in this context.
- Immobilising of PSII and hydrogenase enzymes over the electrodes by means of anchoring promoters like Nafion and other functionalised polymers, His-tags, cystine-bridges. The specific expertise of a third high-tech SME (Biodiversity) will be exploited here.
- Nanoscopic tailoring of the enzyme-electrode-Nafion interface to allow the most rapid kinetics of the water splitting reaction and capture of electrons and protons by their respective transfer materials on the anode surface, and the recombination to H+ and electrons over the hydrogenase at the opposite side.
- Development of a suitable membrane based on Nafion or equivalent proton-transfer polymers hosting a percolation pattern of the electron transfer material (CNT, TiO2 etc). Techniques amenable for mass production for preserving a percolation structure for the electron conducting material will have to be em-ployed in this context (e.g. solution casting).
- Optimisation of the relative amount of hydrogen-transfer polymer and of the excited electrode conducting material so as to minimise the mass transfer resistance of the membrane thereby allowing the fastest possible hydrogen conversion while at the same time having an acceptable mechanical and chemical stability.
- Optimisation of the membrane structure to hamper as much as possible the permeation of oxygen derived from water splitting as it may affect the activity of the hydrogenase or the activity of an artificial 'hydrogenase-like' catalyst.
- Development of a first-generation SOLHYDROMICS prototype using immobilised natural enzymes proving effective water splitting to produce hydrogen at room temperature, by exploiting the expertise of a fourth high-tech SME (HySyTech) in the assembling of hydrogen and fuel cell systems.
- Design appropriate back-up technology for water feed systems and gas handling.
- Development of mimics of the natural enzymes having a higher stability (e.g. photochemical water splitting catalyst, oxygen resistant hydrogenase) and good energy conversion efficiencies.
- Development of a second generation prototype hosting these new synthetic water splitting and H2 generation catalysts.
- Assess the future potential impact of the SOLHYDROMICS system in the worldwide energy scenario.

Project results:

In the following summary, the main project results obtained are compared to the original project targets (taken from contract Annex 1), illustrating, when needed, plans for future R&D to close remaining gaps.

Objective 1
Development of an innovative device capable of using sunlight to produce hydrogen from water splitting in a most cost effective way with routes based on photovoltaics coupled with electrochemically driven catalysis. An ambitious efficiency target is 10 % conversion of solar energy into pure hydrogen which is considered to be feasible based on preliminary calculations by the proponents.

Set of results 1
Detailed modelling data are pointing at the way to go (D.6000.4) with the measured performances and show that 10 % conversion is quite compatible with thermodynamic calculations but requires the development of appropriate electrode micro- and nano-structure.

The best results with a Co-MOF74 electro-catalyst in the second generation Solhydromics prototype show a 1 % overall sunlight into hydrogen conversion efficiency, but a quantum yield close to the 10 % goal in the adsorption spectrum of the CoMOF74 material.

This improves significantly the performance of the first-generation prototype that was based on natural enzymes whose durability was just 30 minutes owing to PSII enzyme deactivation. This paves the way to full achievement of the ambitious goal of the project by:

- inserting further chromophores adsorbing light at >450 nm;
- nanostructuring the MOF layer.

As a whole the objective 1 can be regarded as partially achieved.

Objective 2
The device must be robust with long operational times. A target of one week continuous operation is envisaged for a first generation SOLHYDROMICS prototype based on natural enzymes, whilst a one month continuous operation is targeted for the second generation one based on stable enzyme mimics. Subsequent technology improvements, beyond the proposed project should lead to a lifetime of years.

Set of results 2

Over 90 % performance was retained by the best performing prototype based on mimics operated in alternated lightning-dark cycles for more than one day. This is much better that the few minutes achieved with the prototype based on natural enzymes, but still improvable.

Key measures pointed out to achieve this improvement are:

- better microstructure of the electrode;
- better bridging between MOF particles.

As a whole the objective 2 can be regarded as partially achieved.

Objective 3
To disclose wide potential application opportunities, the above targets must be reached without using expensive noble metals or materials and via assembling techniques amenable for mass production.

Set of results 3
Attention has been addressed mostly on the anode water-splitting side of the cell were noble metal catalysts are not present. The hydrothermal technique adopted for MOF synthesis is amenable for mass production but improvable from a LCA perspective if synthesis times would be lowered from days to hours.

As a whole the objective 3 can be regarded as achieved.

Objective 4
The potential of this artificial solar energy conversion route will also be assessed in comparison to intensive micro-algal growth systems aimed at producing hydrogen or vegetable oils as fuels.

Set of results 4
Comparisons were already proposed in D6000.1 even if the microalgal third generation biofuel production concept is not the most challenging competitor. A number of spin off applications in different application fields have been analysed from a techno-economic viewpoint in deliverable D6000.7 showing margins for profitable application of the technology should the efficiency and durability targets be achieved.

As a whole the objective 4 can be regarded as achieved.

Potential impact:

Exploitation

As reported before and in deliverables D5000.6/7 a final, second generation prototype capable of converting 1 % of the solar light into hydrogen and of a limited deactivation over a one day operation was developed. These results were defined as promising, especially if compared to those obtained with an original first-generation prototype based on natural enzymes.

However, the efficiency and durability targets were only partially achieved (10 000 h operation with 10 % solar energy conversion into hydrogen), and those targets are pre-requisites, as later explained, to have practical exploitation.

In deliverable D6000.7 rather than discussing the immediate application of a new technology in the market, the way was paved to future exploitation opportunities still requiring some additional research to be accomplished.

Five technology exploitation opportunities were conceived and analysed, namely:

1. evolution of the Solhydromics cell into a tandem cell;
2. use of Co-MOF catalyst in a photo-activated alkali electrolyzer;
3. development of a photo-electrochemical reactor coupled with anaerobic digestion of organic wastes;
4. development of a photo-electrochemical reactor for CO2 reduction into methanol in a biorefinery;
5. development and commercialisation of a test rig for photo-electrochemical studies.

Each of these technology spin-out opportunities of the Solhydromics project have been analyzed, related to the state-of-art technologies and analyzed for their potential market impact. In a later section of this report a brief description is provided for each of this application. However, the reader is addressed to deliverable D6000.7 for a deeper understanding and a good positioning of the new technologies in the current state of the art.

All things summed up we believe that all of those exploitation opportunities have potential even if options 3 and 4 have a significant amount of risk implied and require significant fundamental research to become practical.

Conversely, options 1, 2 and obviously, 5 seems to be closer to real application, despite some further R&D is needed.

The success of these exploitation opportunities may anticipate the advent of the so called hydrogen society.

The rather conservative International Energy Agency in its last report 'Energy technology perspectives: Scenarios and strategies to 2050' predicts, in the most advanced technological scenario, a 16 % share of biofuels in the mobility sector by 2050 against a 6 % of hydrogen. The success of the Solhydromics project may pave the way to offset these data and enable a higher share of hydrogen as a fuel at that time.

In this deliverable 6000.7 the cost upper boundaries for the practical exploitation of the Solhydromics cell were ranging between EUR 60 and 200/m2 including installation, depending on the exploitation opportunity considered.

The expected mass production cost of twin technologies like e.g. the PEM fuel cells for car application (EUR 30/m2) allow the Solhydromics partnership to regard the above cost constraints as possible to fulfill.

The Solhydromics partnership believes that achieving these techno-economic performance goals is a task for high-tech SMEs as those who have been actively participating in the project. This is perfectly in line with the FET spirit at the baseline of the Solhydromics project.

Dissemination

Owing to the fundamental research nature of the Solhydromics project a non-negligible dissemination tool was the publication of scientific articles. Nine articles were published related to the research carried out in Solhydromics, accompanied by one patent application. The records of these publications and patent are provided in the following, whereas they can be downloaded from the open repository at the web site of the project.

Among various congress presentations, four plenary lectures were delivered on the Solhydromics project R&D, two by Prof. Saracco and two by Prof. Garrone. Moreover, the Solhydromics project was briefly introduced in over 50 plenaries or lectures held by Prof. J. Barber during the project duration.

The dissemination activities included also one press release and two interviews on TV magazines, which can all be downloaded from http://www.solhydromics.com

Contact
details:
Guido Saracco, PhD
Professor of Chemistry
Head of Department
Chemistry Institute
Department of Applied Science and Technology
Politecnico di Torino
Corso Duca degli Abruzzi, 24
10129 Torino, Italy
Tel: +39-011-0904618
Fax: +39-011-0904699
Mobile: +39-335-8737127
E-mail: guido.saracco@polito.it