Up-scaling solar hydrogen production
Lead Research Organisation:
Imperial College London
Department Name: Chemical Engineering
Abstract
'Solar fuels' are synthetic, storable, high energy density chemicals, produced using sunlight as the sole energy source. Solar fuels include hydrogen (termed "golden hydrogen"), which is generated by solar-driven water reduction, and various carbon-based fuels produced through the reduction of carbon dioxide. Fuels synthesised in this way can contribute towards reaching net zero greenhouse gas emissions.
The projected increase in global power demand necessitates urgent decarbonisation of power sources and fuels to limit the release of CO2 into the atmosphere. One major pathway to achieving this goal is to harness and utilise renewable energies. These, however, are intermittent and so require management, for example via energy storage in chemical bonds.
Photoelectrochemical reactors present a potential technological solution for producing solar fuels at scale. Such reactors combine - in a single device - the functions of photovoltaic (PV) panels and electrolysers; the former convert solar energy to electrical energy, while the latter convert electrical energy to chemical energy. In photoelectrochemical reactors, photoabsorbing components are immersed in liquid media. This approach was conceived to lower the capital cost of solar fuel production compared with commercially available PV + electrolyser systems.
The overarching aim of this research is to answer the question 'What might an industrial scale photoelectrochemical reactor system ultimately look like?'. Development of up-scaled reactors is a multidisciplinary challenge, involving material science, (photo)electrochemistry, electrochemical engineering and optics, supplemented by numerical modelling of the complete system to guide its design and optimisation. These many considerations need to be addressed simultaneously. By answering some of these critical questions and developing large-scale prototype reactors, this project will accelerate the development of sustainable hydrogen production using photoelectrochemical devices and bring us closer to the decarbonisation of our energy systems that we urgently need.
The projected increase in global power demand necessitates urgent decarbonisation of power sources and fuels to limit the release of CO2 into the atmosphere. One major pathway to achieving this goal is to harness and utilise renewable energies. These, however, are intermittent and so require management, for example via energy storage in chemical bonds.
Photoelectrochemical reactors present a potential technological solution for producing solar fuels at scale. Such reactors combine - in a single device - the functions of photovoltaic (PV) panels and electrolysers; the former convert solar energy to electrical energy, while the latter convert electrical energy to chemical energy. In photoelectrochemical reactors, photoabsorbing components are immersed in liquid media. This approach was conceived to lower the capital cost of solar fuel production compared with commercially available PV + electrolyser systems.
The overarching aim of this research is to answer the question 'What might an industrial scale photoelectrochemical reactor system ultimately look like?'. Development of up-scaled reactors is a multidisciplinary challenge, involving material science, (photo)electrochemistry, electrochemical engineering and optics, supplemented by numerical modelling of the complete system to guide its design and optimisation. These many considerations need to be addressed simultaneously. By answering some of these critical questions and developing large-scale prototype reactors, this project will accelerate the development of sustainable hydrogen production using photoelectrochemical devices and bring us closer to the decarbonisation of our energy systems that we urgently need.
| Description | This project is currently just past the ½ way mark and research is ongoing. The three foci of this project photoelectrochemical reactor development were on: (i) up-scaling the size of photoelectroactive materials, (ii) implementing these materials within a large-scale (> 100 cm2) photoelectrochemical reactor prototype and (iii) designing the optics to guide light into the PEC, with the overall aim of answering the question 'What might an industrial scale photoelectrochemical reactor system ultimately look like?'. The success of the project is being ensured by meeting the following objectives: 1. Simulation of the PEC device and overall system performance using a multi-scale, Multiphysics model, followed by design optimisation; 2. Fabrication of inexpensive and chemically robust oxide-based photoelectrode materials which, when coupled in the PEC reactor, would generate an internal bias that is sufficient to drive spontaneous H2 and O2 evolution. 3. Design of optical components that will support reactor operation under (i) predominantly direct solar irradiance and (ii) predominantly diffuse solar irradiance. 4. Experimental characterisation of the PEC reactor to determine the preperformance, quantified in terms of: (i) rate of hydrogen production, (ii) solar-to-hydrogen conversion efficiency, (iii) temporal chemical stability of the photoelectrodes and (iv) net energy output of the system, when balanced against the power consumption of auxiliary components such as pumps through which electrolyte is recirculated. Thus far, objectives 2 and 3 have been met. We are currently fulfilling objective 4, after which we will focus on objective 1. The project is being carried out in collaboration with Stellenbosch University, who are assisting us with the development of optical components - we will shortly be visiting them on a field trip for carrying our outdoor testing and characterisation of our newly built reactor. The key findings thus far are that light can be effectively guided into a photoelectrochemical reactor from two directions, for irradiating two photoactive components (photoanode and photocathode OR photoanode and an externally-mounted PV panel). This light can be directed using reflective mirrors, or using a combination of linear Fresnel lenses and stepped waveguides. This strategy increases the H2 production rate in the photoelectrochemical reactor. Another key finding is that when attempting to identify compatible photoanode and photocathode materials, it is far better to find materials that can be irradiated through the back contact, as this ensures a uniform electric field distribution between the electroactive components and hence ensures a uniform reaction rate. |
| Exploitation Route | The outcomes will be valuable to the research community working on alternative fuel production, through the system design guidelines we are generating through our device demonstrator. |
| Sectors | Energy |
| Description | Up-scaling solar hydrogen production |
| Organisation | University of Stellenbosch |
| Country | South Africa |
| Sector | Academic/University |
| PI Contribution | My research group at Imperial contributes capabilities in: (i) synthesis of photoactive materials, (ii) PEC reactor engineering and (iii) Multiphysics modelling of photoelectrochemical systems. This expertise is valuable to my collaborator at Stellenbosch University, Prof McGregor, who wishes to develop expertise in the design of solar hydrogen production systems, whilst I would like to develop expertise in optics. I have already contributed to our partnership by hosting a PhD student from Stellenbosch in my laboratory at Imperial for 8 weeks; during this time the student received intensive training in photoactive material synthesis for photoelectrochemical systems, as well as reactor engineering and Multiphysics modelling. This has enabled our two teams to develop a deep understanding of the photoelectrochemical reactor requirements towards which we now work independently. I funder the researcher visit through an internal £9k 'Imperial Global Seeds' fund. Together with my team, I have now developed a photoelectrochemical reactor system which we will shortly travel to test in Stellenbosch. |
| Collaborator Contribution | My research group currently lacks expertise in the design and modelling of optical components, which are essential for photoelectrochemical reactor scale-up, as well as facilities for testing them. This expertise is brought by my collaborator at Stellenbosch University, Professor Craig McGregor, who specialises in solar collector technologies and has both indoor and outdoor facilities for the design, characterisation and testing of optical equipment. Prof McGregor's team focuses on the research and development of optical components of concentrating solar thermal energy plants, and the study of their application within the larger energy system. His team extensively researches heliostats, the dual-axis tracking mirrors that focus the solar insolation at a single focal point to capture thermal energy at high temperatures. The team also has experience with other optical systems including parabolic through, parabolic dish, linear Fresnel reflector and compound parabolic collectors, that could be coupled with PEC reactors. Prof Mc Gregor's team has designed, built and modelled an optical system for delivering light into the photoelectrochemical reactor that my team designed and built at Imperial. We will shortly be travelling to Stellenbosch with our reactor and will test it, together with the optical system, using the facilities at Stellenbosch. The expected outcome of this work is a minimum of 3 high-impact research papers. |
| Impact | p |
| Start Year | 2022 |
| Description | Future Energy Festival 2023 |
| Form Of Engagement Activity | Participation in an activity, workshop or similar |
| Part Of Official Scheme? | No |
| Geographic Reach | National |
| Primary Audience | Professional Practitioners |
| Results and Impact | The annual Future Energy Festival is a major showcase of energy research at Imperial College London. This event is open to the public and is an opportunity to learn about the work the Imperial community is doing to address global and local energy challenges. The 2023 festival will included exhibits hosted by research groups from the Faculties of Engineering and Natural Sciences and the Imperial College Business School. The Festival covered a diverse range of research areas, and included everything from demonstrations of photocatalytic technologies to displays of work on electric vehicles. We showcased out work on solar energy conversion to hydrogen. |
| Year(s) Of Engagement Activity | 2023 |
| URL | https://www.imperial.ac.uk/events/164378/save-the-date-energy-futures-lab-future-energy-festival-202... |
| Description | Great Exhibition Road Festival 2023 |
| Form Of Engagement Activity | Participation in an activity, workshop or similar |
| Part Of Official Scheme? | No |
| Geographic Reach | Regional |
| Primary Audience | Public/other audiences |
| Results and Impact | The Great Exhibition Road Festival (GERF) is weekend of free events for all ages celebrating science and the arts, led by Imperial College London in collaboration with partners. I contributed a stall that exhibited out photoelectrochemical reactor prototypes and explained the benefit of hydrogen as a fuel, when it is made from water. |
| Year(s) Of Engagement Activity | 2023 |
| URL | https://www.greatexhibitionroadfestival.co.uk/ |
| Description | International Women's Day event - 'ITSHER' |
| Form Of Engagement Activity | A formal working group, expert panel or dialogue |
| Part Of Official Scheme? | No |
| Geographic Reach | International |
| Primary Audience | Professional Practitioners |
| Results and Impact | The event was a 'Women in STEM Summit' - the first summit of its kind, with universities and businesses in the UK and Ireland coming together to celebrate science, research and innovations by women across all disciplines in STEMM. I delivered a talk about my work on solar hydrogen production. |
| Year(s) Of Engagement Activity | 2024 |
| URL | https://itsher.today/summit-2024/#is |
| Description | MAT-SUS nanoGe Fall 2023 |
| Form Of Engagement Activity | A talk or presentation |
| Part Of Official Scheme? | No |
| Geographic Reach | International |
| Primary Audience | Professional Practitioners |
| Results and Impact | I was invited to organise a symposium on solar fuel production at a high-profile international conference. I was also invited to give a talk there. |
| Year(s) Of Engagement Activity | 2023 |
| URL | https://www.nanoge.org/MATSUSFall23/home |
| Description | Solar2Chem workshop - EPFL |
| Form Of Engagement Activity | Participation in an activity, workshop or similar |
| Part Of Official Scheme? | No |
| Geographic Reach | International |
| Primary Audience | Postgraduate students |
| Results and Impact | I delivered training in photoelectrochemical reactor engineering to a group of PhD students on EU-funded studentships under the umbrella of the 'Solar2Chem' program - the purpose of this program is to train 15 early stage researchers to fill the existing gap in the European industrial landscape in the area of solar chemicals production and usage in technical, economic and policy aspects. |
| Year(s) Of Engagement Activity | 2023 |
| URL | https://www.solar2chem.eu/newsandevents/solar2chem-6th-training-workshop-epfl-switzerland/ |