Results and Progress

Summary of the context and overall objectives of the project

To reduce dependency on fossil fuels and to contribute to growing efforts to decarbonise the transport sector, biofuels provide a way to shift to low-carbon, non-petroleum fuels, with minimal changes to vehicle stock and distribution infrastructure. Whilst improving vehicle efficiency is a key cost-effective way of reducing CO2 emissions in the transport sector, biofuels will play a significant role in replacing liquid fossil fuels (particularly for those modes of transport which cannot be electrified).

Production and use of biofuels can provide benefits such as increased energy security, reducing dependency on oil imports and reducing oil price volatility. Biofuels can also support economic development through creating new sources of income.

BAC-TO-FUEL will respond to the global challenge of finding new sustainable alternatives to fossil fuels by developing, integrating and validating a disruptive prototype system at TRL5 which is able to transform CO2/H2 into added-value products in a sustainable and cost-effective way which:

1) mimics the photosynthetic process of plants using novel inorganic photocatalysts which are capable of producing hydrogen in a renewable way from photocatalytic splitting of water in the presence of sunlight

2) uses enhanced bacterial media to convert CO2 and the renewable hydrogen into biofuels (i.e. ethanol and butanol both important fuels for transport) using a novel electro-biocatalytic cell which can handle fluctuations in hydrogen and power supply lending itself to coupling to renewable energy technologies

BAC-TO-FUEL is a multidisciplinary project which brings together leaders in the fields of materials chemistry, computational chemistry, chemical engineering, microbiology and bacterial engineering. BAC-TO-FUEL will validate a prototype system at TRL5 which is able to transform CO2/H2 into added-value products in a sustainable and cost effective way specifically for the European transport sector.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far 

WP1: In this WP we refined the system requirements for producing biofuels and reviewed the lab-scale process components and product targets, the integrated system specification, and the test protocols for the photocatalytic and electrobiocatalytic processes. 

(2021): System requirements for producing biofuels were refined. Lab-scale process components & product targets, the integrated system specification, & test protocols for photocatalytic & electrobiocatalytic processes were reviewed.

WP2: According to deliverable D1.1 (Review of materials specifications and specification for target outputs) -Point 4 of Section 1- we previously reported, the recently observed fact (M.P. de Lara-Castells, et al. J. Mat. Chem. A 7, 2019, 7489-7500) that Cu5 clusters can induce a huge increase in the optical response of TiO2 extending it into the visible region. This fact greatly simplifies the synthesis of clusters with absorption in the visible, the search for adequate substrates to support the clusters, and the construction of the photocatalyst. In this reporting period, we aimed to optimise and scale up the previously reported electrochemical synthesis of Cu5 clusters (S. Huseyinova et al. J. Phys.Chem.C, 120, 2016, 15902-15908). For this purpose, we have already increased the active surface area of the electrodes, as shown in the figure. We also investigated the deposition procedure (because the interaction of the clusters with the containers induces large inhomogeneities in the clusters which are deposited onto the TiO2 nanoparticles, and a large proportion of the clusters are lost) and the heating treatments needed to achieve the covalent bonding of clusters onto the TiO2.

2020: We use Cu5 and Ag5 clusters to induce a huge increase in the optical response of TiO2 extending it into the visible region. Therefore, instead of synthesizing larger clusters with absorption in the visible, we concentrate our efforts on the optimization of the synthesis of both type of clusters. By increasing the surface area of the electrodes, we could improve the synthesis production of Cu5 clusters (from microg/day to mg/day). Further increasing the surface area failed due to the large amount of unreduced ions in the solutions which negatively influence the photocatalytic activities. To resolve this issue a new electrochemical cell was designed and constructed, which helps to increase the concentration of clusters and to decrease the unreduced ions. For Ag5 clusters no increase in the production could be achieved through optimization of the electrochemical cell. Therefore, we used a new patented photochemical procedure allowing a high production of clusters (hundreds of milligrams/day). The main issue with these Ag5 samples in the photocatalytic experiments is the presence of ions in a ratio [Ag+]/[Ag5] ≈ 20:1. Several purification procedures to eliminate the metal ions and the excess salts were carried out, but large losses of clusters were observed. To avoid such losses a new strategy was developed, adding an inorganic group to capture and retain the clusters. 

(2021): Cu5 & Ag5 Atomic Quantum Clusters increase TiO2’s optical response into the visible region. Synthesis is being optimised. Cu5 AQCs made in mg/day by increasing the electrodes’ surface area, but further increases failed as unreduced ions in solution affected photocatalysis. A new cell design increased production to ~1g/day. This did not work for Ag5 AQCs; thus a new patented method was used (g/day). However, ions were present: [Ag+]/[Ag5] ≈ 20:1. Methods were studied to eliminate ions & excess salts, including adding an inorganic group to capture AQCs. Metal cation purification was improved (≈200 times): a lab scale automated process makes ≈ 100mg purified AQCs/day with a ≈0.1-0.3:1 cation to AQC ratio. A spectrophotometric technique was developed to rapidly calculate the number of AQCs in solution.

WP3: The work performed from the beginning of the project to the end of the reporting period included density functional theory calculations of the size and shape dependence of isolated Cu5, Ag5, and Au5 atomic quantum clusters (AQCs). 

2020: The work performed in this reporting period includes density functional theory calculations of the size and shape dependence of Cu5 atomic quantum clusters (AQCs) deposited on different semiconductors (rutile TiO2, anatase TiO2, CeO2) comprehensively. More specifically, new AQCs are obtained from new strategies to assess O2-adsorption, which complement the AQCs produced by month 12. The dissociation of adsorbed O2 dimer is investigated on Cu5 AQC and the corresponding electronic structures as well. The splitting barrier of H2O molecules on Cu5/TiO2 has been initiated and the effects of the corresponding molecular and dissociated water on the gap states is explored.

(2021): Density functional theory calculated the size & shape dependence of Cu5 AQCs deposited on TiO2 & CeO2 semiconductors. Both produce high-energy states to reduce protons to H2 split H2O spontaneously near the AQC/substrate composites interface. Defects on CeO2 reinforce the catalytic effect of Cu5 by creating high-energy polaron states & in turn, Cu5 is predicted to lower the O2 vacancy formation energy, thereby reducing the working temperature of TUB’s reactor. O2 adsorption on AQCs can lead to more gap states than on bare AQCs. The barrier to splitting H2O on Cu5/TiO2 was evaluated: H2 & O2 evolution occurs more easily at the interface, where H2O binds to Cu & Ti simultaneously.

WP4: TUB built a photoreactor with defined geometry for standardised photocatalyst testing. This is facilitating the comparison of the results between the groups of TUB and USC and this is leading to a better cooperation and feedback on the catalyst preparation. USC can measure the activity of the synthesized Copper-5 clusters with standardised conditions (due to the same photoreactor setup provided by TUB) before sending the Copper-5 clusters to TUB for detailed kinetic studies. The first qualitative trials of the Cu5@TiO2 photocatalysts (prepared using the method developed in WP2) using a solar simulator, gave a hydrogen evolution ≈ 5-8 times larger than the TiO2 alone. We will continue the optimisation of the photocatalyst, and the best one will be sent in approx. 1 month to TUB for the quantitative analysis of the efficiencies. 

2020: Different semiconductors were tested as a support material for AQCs. As the deposition method is crucial for the photocatalytic system’s performance in the overall water splitting reaction, different AQC deposition approaches were tested. The best results were achieved with Dry impregnation (incipient wetness impregnation). Modification of the semiconductors’ surface before the impregnation process will be investigated. Also a reverse reaction on the Cu AQCs and CuO has been observed. As a sacrificial agent/hole scavenger would be too expensive for the process, it was decided to focus on the overall water splitting reaction in the gas-phase. AQCs can also improve optical properties. We were able to produce H2 with a photon energy < 2.95 eV, which is lower than the bandgap of the semiconductor (TiO2 Anatase), by depositing AQCs on the surface. Overall water splitting in the gas phase is possible with TiO2 and P25 (Anatase) had the best performance regarding the turnover frequency. The photocatalytic efficiency is very low with STH = 10-6 %.

(2021): A light-induced renewable H2 evolution looping process was studied by varying the temperature, loading, cycle time & AQC type. By separating the HER from the OER, H2 & O2 separation was achieved. At a given temperature, semiconductors with O2 vacancies can split H2O to generate H2 without light. In theory, O2 vacancies can be generated by irradiation with light. These are then consumed by splitting H2O on the semiconductor’s surface. The catalysts can be regenerated via light to maintain a constant HER rate, but this process is very sensitive to operating conditions.

WP5: Six different microorganisms were selected with the best set of characteristics for the envisaged task of converting H2 and CO2 into fuels (Deliverable 5.1). These organisms have been analysed with respect to their physiology and genetic accessibility. In addition, the thermodynamic potential for the formation of different fuels was investigated and a metabolic model was constructed for predicting targets for engineering. Currently a smaller selection of three organisms is being targeted for the development of genome editing tools to expand the product spectrum of these organisms. Protocols for conjugation were optimized. A CRISPR-cas tool and a tool for controlled expression of the nuclease was developed. A first knockout was obtained, confirming that the engineering tool can be used successfully (Deliverable 5.3).

(2021): Organisms selected to convert H2 & CO2 into fuels. Their physiology & genetic accessibility was analysed. Their thermodynamic potential for forming fuels was studied & a metabolic model predicted engineering targets. Conjugation protocols were optimised. CRISPR-cas & tools to control nuclease expression were made. A knockout was obtained. Engineering options focus on C. autoethanogenum. Dedicated knockouts are being developed for improved ethanol production on H2/CO2.

WP6: An initial design of the reactor was prepared to improve the mass transfer of gases (hydrogen and carbon dioxide) and the patentability of the new design was explored. Three different reactor configurations were designed and the reactors were built. The first design is currently being operated and the other two are being set up for testing. Interactions were held with the WP5 leader, Wageningen University with regards to the selection of the bacterial strains. A major effort was undertaken during this period on the feasibility study of the Bac-To-Fuel concept with MI_DICE and the Tech2Market report. 

2020: The work on the bioreactor design and development continued together with hydrogen production and gas supply investigations. In year 1, after testing a small stainless reactor (100 mL volume) with wild type bacteria and showing increased ethanol production in pressurised conditions, this year, a lab-scale pilot reactor (1 L volume) was designed. The reactor was first designed using AutoCAD and has provision to integrate 4 capillary electrodes together with independent supply of CO2, N2 and H2. The reactor is now ready and will be tested with both wild type and genetically modified bacteria developed by WU in WP5. This reactor can operate under 10 bar pressure. Apart from the reactor, VITO also developed capillary electrodes for in situ production of hydrogen in the bioreactor. The developed electrodes were tested under different pressures to check the stability of the membrane which was intact up to 5 bars.

(2021): Tubular electrodes were up-scaled & tested in a pressurized reactor under real conditions. The reactor will soon be tested with bacteria to provide data for system design (WP7).

WP7: Initial evaluations were done for the life cycle assessment of the process. A functional unit and the research question were defined. 

2020: Collecting data and assumptions on the BAC-TO-FUEL process were made as the LCA is in processing. Additionally, a modular process model was done in ASPEN PLUS. The photocatalytic process was replaced by an electrocatalytic process combined with energy coming from photovoltaics. This combination is the benchmark, but at the same time an alternative solution for renewable H2 production. Therefore, an electrolyzer was bought for the integrated system.

2021: By doing a LCA, the basis for a TEA is set. A modular approach is followed for the TEA of the integrated BAC-TO-FUEL process. With more data on the processes’ units, a simulation can be made & the existing ASPEN PLUS model can be updated. The TEA & LCA will use the updated data.

WP8: The consortium has created a project website that has been regularly updated and google analytics analysis has shown that it contributes successfully towards improving dialogue within the consortium and with outside stakeholders. Contents for a first and second press release have been agreed among the members of the consortium. A twitter profile has been developed for the project that is distributing contents related to the project and the related technologies and markets. Consortium members participated in several events, workshops and conferences representing Bac-To-Fuel. 

2020: In relation to the dissemination activities, during 2020 our participation in webinars (16 attended), workshops (10), events (11) and our activity within social networks (mostly through LinkedIN) was increased according to the comments from the EC. We organised a series of webinars (specifically 6) where we could spread the work that the BAC-TO-FUEL project is doing. The website has been updated during the year with information obtained through MI-DICE project: CCUS technologies, biofuel production, series of webinars, scientific meetings, e-brochure; roadmap; green innovation forum; 3 publications about CO2, CCUS, and H2; Green Deal and RED II, among others. In relation to the exploitation activities, good progress was made on the exploitation and elaboration of the business case. The business case was defined during the last stage gate review. “The construction of a biofuel production plant” and it is supported by 9 technical annexes that improve the writing of the business case. One presentation was done at the GREEN INNOVATION FORUM event, where we could establish 3 one-to-one meetings to on board potential customers. Also, thanks to participation at several events, we could also present the project to potential customers (end users of the technology). In relation to the MI-DICE project, the second stage gate review entitled: Preliminary technoeconomic analysis” was accomplished. Good progress on the feasibility study, techtomarket plan, 9 technical annexes and stage gate reviews topics are updated and aligned with the status of the project. The consortium has already prepared the proposal for phase II that will be presented during the next Stage gate review.

2021: The dissemination, exploitation & communication strategy progressed. The business case was developed & updated with Duro Felguera. The planned technical assessment will support to the next phase of BAC-TO-FUEL. The last Network Patent Analysis is expected in February 2022.

Progress beyond the state of the art, expected results until the end of the project and potential impacts and use (including socio-economic impact and the wider societal implications of the project so far). 

WP1: As we explain in detail in the report, the specifications and requirements for producing biofuels in terms of: 1) cluster production, 2) photocatalytic and electrobiocatalytic processes involved, and 3) the final efficiencies of the integrated system are well beyond the state of the art. 

2021: Specifications & requirements for producing biofuels 1) AQC production, 2) photocatalytic & electrobiocatalytic processes, & 3) final efficiencies of the integrated system are beyond the state of the art.

WP2: According to the results obtained so far, we are close to achieving a novel production method for AQCs, which can be easily scaled up to produce ≈ 1 g/day of clusters. This is around 4 orders of magnitude larger than the current state of the art for the production of naked clusters by wet chemical methods. This will be a major breakthrough in the production of clusters, so we can foresee that in the near future, AQCs will be able to be produced and applied at an industrial scale. Therefore, their important properties can be exploited, not only in the photocatalysis field, but also in other important areas of socio-economic impact, such as therapeutics, catalysis, etc. 

2020: The newly developed synthetic methods (both electrochemical and photochemical) for the production of AQCs have progressed during this year well beyond the state of the art. New purification methods were established using inorganic capture groups to avoid excessive losses of clusters with standard purification methods. However, the purification of metal cations still needs to be further improved. New strategies were put in place so that the expected production of clusters with the appropriate purity for the photocatalytic experiments is expected.

2021: Electrochemical (Cu5) & photochemical (Ag5) AQC synthesis methods progressed & purification methods used inorganic capture groups to avoid excessive AQC losses (patent filed). Cation to AQC ratios of ≈< 0.3 are possible at lab scale or ≈0.7 when scaled to achieve ≈1g/day of purified AQCs. This is the first large scale example of AQC, of low atomicity without caping ligands, purification (patent pending). It will open up industrial scale applications for AQCs.

WP3: WP3 has progressed beyond the state of the art with its detailed simulations of the biding energies of oxygen molecules to the target Cu5 AQC, their interaction with a semiconductor substrate and the variations of the corresponding electronic structures.

2021: Progressed its simulations of the target Cu5 AQCs on rutile TiO2 & CeO2, that can enhance sunlight absorption by generating gap states, improve the catalytic properties of reducing protons in the dark by producing high-energy gap states, & create active sites to split H2O at the interface of the composite.

WP4: The photoreactor setup delivered by TUB is expected to improve the development of the photocatalyst as it will provide detailed feedback about their performance. It is expected to enhance the activity of the photocatalysts in the water splitting process with sunlight irradiation. Depending on the amount of hydrogen generated by the photocatalyst that has been developed, the optimised catalyst loading and reaction conditions will provide the basis for the design of the hydrogen generation unit within the demonstration unit. 

2020: WP4 has progressed beyond the state of the art as it was possible to achieve H2 production in a gas-phase with a photon energy below the bandgap of the semiconductor. By optimizing the loading and deposition of AQCs from a purified sample, a huge increase in the photocatalyst’s activity and the STH efficiency is expected.

2021: Gas-phase H2 production is possible with a photon energy < the bandgap of the semiconductor. By optimising loading & deposition of pure AQCs a huge increase in photocatalytic activity & STH efficiency is expected.

WP5: In addition to using established CRISPR-Cas9 tools, WP5 will develop new tools for genome editing in selected acetogenic microorganisms (dCas9, Cpf1, multiplexing), with the aim of improving biofuel production. The engineered micro-organisms will be used in electro-biocatalytic reactors (VITO) for the conversion of H2 and CO2 into fuels. We will overexpress the genes from C. kluyveri, which are involved in chain elongation to improve butanol and hexanol production.

2021: In addition to using established CRISPR-Cas tools we will develop tools for genome editing in selected acetogenic microorganisms (dCas9, Cas12a, multiplexing & Ribo-switches) to improve biofuel production. We developed a tool for controlled expression of CRISPR-Cas12 in Gram-positive bacteria.

WP6: Beyond the conventional microbial electrosynthesis system, which relies on the in situ generation of hydrogen at the electrode surface and which is most often limiting for the bacteria, a new approach to provide hydrogen (produced photocatalytically) along with carbon dioxide will be explored in Bac-To-Fuel. This will lead to a new reactor design with an improved gas liquid supply system that targets fuels like ethanol and butanol using bacteria modified with the CRISPR-Cas9 editing system in WP5 by Wageningen University. Initial calculations of the hydrogen required for the final target were also provided to WP4. WP6 developed a new electrode design based on the concept of ‘catalyst coated membrane’ which has the potential of being patented and this is being explored currently.

2021: A novel pressurized bioreactor able to go up to 10 bars & a new tubular electrode for H2 production were developed. Both these novel aspects go beyond the state of the art.

WP7: As stated before, initial evaluations were done for the life cycle assessment of the process. A functional unit and the research question were defined. 

2021: A life cycle assessment of the process was done. A functional unit & the research question were defined. Simulation of the integrated process will examine its feasibility & economic viability.

WP8: A fully-fledged feasibility study with a complete market analysis, competitor scenario and a description of the final end users will be developed in association with MI_DICE. This work is carried out by WP8, but all partners are contributing to it in several ways.

2020: In relation to MI-DICE project, during 2020, the second stage gate review entitled: “Preliminary technoeconomic analysis” was accomplished. Good progress on the feasibility study (already approved by INNOENERGY), tech-to-market plan (updated every week or month), 9 technical annexes (under development of the location annex) and stage gate review topics are updated and aligned with the status of the project. The consortium has already prepared the proposal for phase II that will be presented during the next Stage gate review. There have been trimestral meetings with Repsol, aligned with the objectives of the first Stage gate review. Finally, 3 potential customers might on board the project in 2021. 3 meetings where BAC-TO-FUEL was presented. They are keen to participate in the current project and elaborate phase II of the project.

2021: Location, design of equipment, mass & energy balance etc. will be reported on next to ensure that phase II will become reality.